Skip to main content

Full text of "On the origin of species by means of natural selection; or, The preservation of favoured races in the struggle for life"

See other formats 


<<7^ 


^ 


H.  E.  BARKER 

tLincolniana 

1714  Westmoreland  Boulevard 

Los  Angeles,  California 

•■fiFrnff-T— nrn!^  — -^ 


SB  tRITII^rS  OF  CflAHLr:S  DARWIH, 
H—»«*— «—    ■      II     ■!  I         I    I    I       II      I  II    I     I      II       I      «       I      IIIIM— — W»» 

This  writer  n^s  bom  Fob.    12^    13^9, 
the  same  birUx-dat©  as  that  of  Abraham 
Lincoln*  His  first  book  has  entitled 
''Journal  of  He  searches  into  Geology  and 
Natural  History,"  published  in  I659f  - 
a  second  edition  of  the  sazae  appearing 
in   1  "yh^  It  is  likely  this  is  the  work 
referred  to  by  Willian  H.  Tlemdon  as  be- 
ing at  Lincoln's  Imnd  to  be  dipped  into 
as  the  Eiood  mi^t  incline  him;  othor 
works  appeared  from  ti>30  to  tiae,  but 
none  with  titles  to  attract  Lincoln  until 
the  "Origin  of  Species*',  tJhich  ^?as  first 
published  in  book  fom  in   1660.  TliiD,   too, 
may  be  included  in  the  ^rorks  referred  to 
by  Hemdon  v*ien  he  says:   "I  purclmsed  the 
vorks  of  Spencer,  Darwin,  and  the  utter- 
enoes  of  other  FYiglish  scientists,  etc." 
Lincoln  wDuld  ''snatch  one  up  and  peruse 
it  for  a  little  vdiile,  but  soon  throw  it 
down  with  the  suggestion  that  it  ^jsas  en- 
tirely too  heavy  for  an  ordinary  iiind  to 
digest. " 

(See  Hemdon' 3  Lincoln,  ivage  ^^56) 


Digitized  by  the  Internet  Arclnive 

in  2010  with  funding  from 

The  Institute  of  Museum  and  Library  Services  through  an  Indiana  State  Library  LSTA  Grant 


http://www.archive.org/details/onoriginofspecieOOindarw 


/- 


^^/ 


ON 

THE  ORIGIN  OF  SPECIES. 


"  But  with  regard  to  the  material  world,  we  can  at  least  go  so  far  as 
this — we  can  perceive  that  events  are  brought  about  not  by  insulated  in- 
terpositions of  Divine  power,  exerted  in  each  particular  case,  but  by  the 
eetabUshment  of  general  laws." 

W.  Whewell  :  Bridgewater  Treatise. 


"  To  conclude,  therefore,  let  no  man  out  of  a  weak  conceit  of  sobriety, 
or  an  ill-applied  moderation,  think  or  maintain,  that  a  man  can  search  too 
far  or  be  too  well  studied  in  the  book  of  God's  word,  or  in  the  book  of  God's 
works;  divinity  or  philosophy;  but  rather  let  men  endeavour  an  endless 
progress  or  proficience  in  both." 

Bacon:  Advancement  of  Learning. 

"  The  only  distinct  meaning  of  the  word  '  natural '  is  stated,  fixed,  or 
gettled;  since  what  is  natural  as  much  requires  and  presupposes  an  intelli- 
gent agent  to  render  it  so,  i.  e.  to  effect  it  continually  or  at  stated  times,  sm 
what  is  supernatural  or  miraculous  does  to  effect  it  for  once." 

Butler  :  Analogy  of  Revealed  Religion. 


Down,  Bromley,  Kent, 

October  \st,  1859. 


ON 


THE  ORIGIN  OF  SPECIES 


BY 


MEANS  OF  NATURAL  SELECTION, 


OR   THE 


PRESERVATION"  OF  FAVOURED  RACES  IN  THE  STRUGGLE 

FOR  LIFE. 


BY 

CHARLES  DARWIN,  M.A., 

FELLOW    OF    THE    KOYAL,    GEOLOGICAL,    LINN^AN,    ETC.,    SOCIETIES  ; 

ATTTHOR    OF    "JOURNAL    OF     RESEARCHES    DURING    H.     M.    S.    BEAGLB'S    VOVAGB     BOUND 

IHE   WORLD." 


A  NEW  EDITION,  REVISED  AND  AUGMENTED  BY  THE  AUTHOR, 


NEW  YORK: 
D.    APPLETON    AND    COM  PAN  \^ 

443    &    445    BROADWAY. 

M.DCCC.LX. 


PREFACE. 

CONTRIBUTED  BY  THE  AUTHOR  TO  THIS  AMERICAN  EDITION. 

I  WILL  here  attempt  to  give  a  brief,  but  I  fear  imper- 
fect, sketch  of  the  progress  of  opinion  on  the  Origin  of 
Species.  The  great  majority  of  naturalists  have  beheved 
that  species  were  immutable  productions  and  liave  been 
separately  created  :  this  view  has  been  ably  maintained 
by  many  authors.  A  few  naturalists,  and  several  who 
have  not  particularly  studied  natural  history,  believe,  on 
the  other  hand,  that  species  undergo  modification,  and 
that  the  existing  forms  of  life  have  descended  by  true  gen- 
eration from  pre-existing  forms.  Passing  over  authors  of 
the  classical  period,  and  likewise  Demaillet  and  Bufibn, 
with  whose  writings  I  am  not  familiar,  Lamarck  was  the 
first  man,  whose  view  that  species  undergo  change  ex- 
cited much  attention.  This  justly  celebrated  naturalist 
published  his  Philosophic  Zoologique  in  1809,  and  his  In- 
troduction to  his  Hist.  Kat.  des  animaux  sans  Yert^bres 
in  1815,  in  which  works  he  upholds  the  doctrine  that  spe- 
cies are  descended  from  each  other.  He  seems  to  have 
been  chiefly  led  to  this  conclusion  by  the  difficulty  of  dis- 
tinguishing species  and  varieties, — by  tlie  almost  perfect 
gradation  of  the  forms  in  certain  groups,  and  by  the  anal- 
ogy of  domestic  productions.  With  respect  to  the  means 
of  modification,  he  attributed  something  to  the  action  of 


VI  PREFACE. 

external  conditions,  something  to  the  crossing  of  already- 
existing  forms,  and  mncli  to  use  and  disuse  or  the  effects 
of  habit.  To  this  latter  agency  he  seems  to  attribute  all 
the  beautiful  adaptations  in  nature, — such  as  the  long 
neck  of  the  giraffe  for  browsing  on  the  branches  of  trees.* 
Eut  he  likewise  believed  in  a  law  of  progressive  develop- 
ment ;  and  as  all  the  forms  of  life  thus  tended  to  progress, 
in  order  to  account  for  the  presence  of  very  simple  pro- 
ductions at  the  present  day,  he  maintained  that  such  forms 
were  now  spontaneously  generated. 

Geoffroy  Saint  Hilaire,  as  is  stated  in  his  Life  by  his 
Son,  as  early  as  1795,  suspected  that  what  we  call  species 
are  various  degenerations  of  the  same  type.  It  was  not 
until  1828  that  he  published  his  conviction  that  the  same 
forms  have  not  been  perpetuated  since  the  origin  of  all 
things.  Geoffroy  seems  to  have  relied  chiefly  on  the  con- 
ditions of  life,  or  the  "  monde  ambiant,"  as  the  cause  of 
change  ;  but  he  was  cautious,  and,  as  his  son  says,  "  C'est 
done  un  probl^me  k  reserver  enti^rement  a  I'avenir,  sup- 
pose meme  que  I'avenir  doive  avoir  prise  sur  lui." 

In  England,  the  Hon.  and  Eev.  W.  Herbert,  after- 
wards Dean  of  Manchester,  in  his  work  on  the  Amarylli- 
dacese  (1837,  p.  19,  339),  declares  that  "horticultural 
experiments  have  established,  beyond  the  possibility  of 
refutation,  that  botanical  species  are  only  a  higher  and 
more  permanent  class  of  varieties."  He  extends  the  same 
view  to  animals.  The  Dean  believes  that  single  species 
of  each  genus  w^ere  created  in  an  originally  highly  plastic 
condition,  and  that  these  by  intercrossing  and  by  varia- 
tion have  produced  all  our  existing  species. 

*  It  is  curious  how  completely  my  grandfather,  Dr.  Erasmus  Darwin, 
anticipated  these  erroneous  views  in  his  Zoonoraia  (vol.  i.  pp.  500-510),  pub- 
lished in  1'794. 


PREFACE.  Vll 

In  1843-44,  Prof.  Haldeman  (in  the  Boston  (U.  S.) 
Journal  of  Nat.  Hist.,  vol.  iv.,  p.  468)  has  ably  given  the 
arguments  for  and  against  the  hypothesis  of  the  develop- 
ment and  modification  of  species :  he  seems  to  me  to  lean 
towards  the  side  of  change. 

The  Yestiges  of  Creation  appeared  in  1844.  In  the 
last  or  tenth  and  much  improved  edition  (1853,  p.  155), 
the  anonymous  author  says :  ^'  The  proposition  determined 
on  after  much  consideration  is,  that  the  several  series  of 
animated  beings,  from  the  simplest  and  oldest  up  to  the 
highest  and  most  recent,  are,  under  the  providence  of  God, 
the  results,  Jirst,  of  an  impulse  which  has  been  imparted 
to  the  forms  of  life,  advancing  them,  in  definite  times,  by 
generation,  through  grades  of  organisation  terminating  in 
the  highest  dicotyledons  and  vertebrata,  these  grades  be- 
ing few  in  number,  and  generally  marked  by  intervals  of 
organic  character  which  we  find  to  be  a  practical  diflSculty 
in  ascertaining  affinities;  second,  of  another  impulse  con- 
nected with  the  vital  forces,  tending  in  the  course  of  gen- 
erations to  modify  organic  structures  in  accordance  with 
external  circumstances,  as  food,  the  nature  of  the  habitat 
and  the  meteoric  agencies,  these  being  the  '  adaptations ' 
of  the  natural  theologian."  The  author  apparently  be- 
lieves that  organisation  progresses  by  sudden  leaps  ;  but 
that  the  effects  produced  by  the  conditions  of  life  are 
gradual.  The  author  argues  with  much  force  on  general 
grounds  that  species  are  not  immutable  productions.  But, 
I  cannot  see  how  the  two  supposed  "  impulses "  account 
in  a  scientific  sense  for  the  numerous  and  beautiful  co- 
adaptations,  which  we  see  throughout  nature ; — I  cannot 
see  that  we  thus  gain  any  insight  how,  for  instance,  a 
woodpecker  has  become  adapted  to  its  peculiar  habits  of 
life.     The  work,  from   its   powerful   and  brilliant  style, 


Vlll  PREFACE. 

though  displaying  in  the  earlier  editions  little  accurate 
knowledge  and  a  great  want  of  scientific  caution,  immedi- 
ately had  a  very  wide  circulation.  In  my  opinion,  it  has 
done  excellent  service  in  calling  in  this  country  attention 
to  the  subject,  and  in  removing  prejudices. 

In  1846,  the  veteran  geologist,  M.  J.  d'Omalius  d'Hal- 
loz,  published  in  an  excellent,  though  short,  paper  (Bulle- 
tins de  I'Acad.  Roy.  Bruxelles,  tom.  xiii.,  p.  581),  his  opin- 
ion that  it  is  more  probable  that  new  species  have  been 
produced  by  descent  with  modification,  than  that  they 
have  been  separately  created :  the  author  first  promul- 
gated this  opinion  in  1831. 

M.  Isidore  Geoffroy  Saint  Hilaire,  in  his  Lectures  de- 
livered in  1850  (of  which  a  Resume  appeared  in  the  Re- 
vue et  Mag.  de  Zoolog.,  Jan.  1851),  briefly  gives  his 
reasons  for  believing  that  specific  characters  "  sont  fixes, 
pour  chaque  espece,  tant  qu'elle  se  perpetue  au  milieu  des 
memes  circonstances,  ils  se  modifient,  si  les  circonstances 
ambiantes  viennent  a  changer."  "  En  resume,  V observa- 
tion des  animaux  sauvages  demontre  deja  la  variability 
limitee  des  especes.  Les  exphiences  sur  les  animaux  sau- 
vages devenus  domestiques,  et  sur  les  animaux  domes- 
tiques  redevenus  sauvages,  la  demontrent  plus  clairement 
encore.  Ces  memes  experiences  prouvent,  de  plus,  que 
les  difi'erences  produites  peuvent  etre  de  valeur  gme- 
TiqueP 

Mr.  Herbert  Spencer,  in  an  Essay  (originally  pub- 
lished in  the  Leader,  March,  1852,  and  republished  in  his 
Essays,  1858),  has  contrasted  the  theories  of  the  creation 
and  development  of  organic  beings  with  remarkable  skill 
and  force.  He  argues  from  the  analogy  of  domestic  pro- 
ductions, from  the  changes  which  the  embryos  of  many 
species  undergo,  from  the  difficulty  of  distinguishing  spe- 


PEEFACE.  iX 

cies  and  varieties,  and  from  the  principle  of  general  gra- 
dation, that  species  have  been  modified ;  and  he  attributes 
the  modification  to  the  change  of  circumstances.  The 
author  (1855)  has  treated  Psychology  on  the  principle  of 
the  necessary  acquirement  of  each  mental  power  and  ca- 
pacity by  gradation. 

In  1852  (Revue  Horticole,  p.  102),  M.  ISTaudin,  a  dis- 
tinguished botanist,*  has  expressly  stated  his  belief  that 
species  are  formed  in  an  analogous  manner  as  varieties  are 
under  cultivation ;  and  the  latter  process  he  attributes  to 
man's  power  of  selection.  But  he  does  not  show  how  se- 
lection can  act  under  nature.  He  believes,  like  Dean 
Herbert,  that  species  when  nascent  were  more  plastic. 
He  lays  weight  on  what  he  calls  the  principle  of  finality, 
^•puissance  myst^-ieuse,  indeterminee  ;  fatalite  pour  les 
nns  ;  pour  les  autres,  volonte  providentielle,  dont  Faction 
incessante  sur  les  etres  vivants  determine,  k  toutes  les 
epoques  de  I'existence  du  monde,  la  forme,  le  volume  et 
la  duree  de  chacun  d'eux,  en  raison  de  sa  destinee  dans 
I'ordre  de  choses  dont  il  fait  partie.  C'est  cette  puissance 
qui  harmonise  chaque  membre  a  I'ensemble  en  I'appropri- 
ant  a  la  fonction  qu'il  doit  remphr  dans  I'organisme  gene- 
ral de  la  nature,  fonction  qui  est  pour  lui  sa  raison  d'etre." 

In  1853,  a  celebrated  geologist,  Count  Keyserling  (Bul- 
letin de  la  Soc.  Geolog.,  2d  ser.,  torn,  x.,  p.  357)  suggested 
that  as  new  diseases,  supposed  to  JUave  been  caused  by 
some  miasma,  have  arisen  and  spread  over  the  world,  so 
at  certain  periods  the  germs  of  existing  species  may  have 
been  chemically  afifected  by  circumambient  molecules  of 
a  particular  nature,  and  thus  have  given  rise  to  new 
forms. 

*  M.  Lecoq,  another  French  botanist,  entertains,  I  believe,  analogous 
viewa  on  the  modification  and  descent  of  species. 
1* 


X  PREFACE. 

The  "  Philosophy  of  Creation  "  has  been  treated  in  an 
admirable  manner  by  the  Rev.  Baden  Powell,  in  his  Es- 
says on  the  Unity  of  Worlds,  1855.  ITothing  can  be  more 
striking  than  the  manner  in  which  he  shows  that  the  in- 
troduction of  new  species  is  "a  regular,  not  a  casual, 
phenomenon,"  or,  as  Sir  John  Herschel  expresses  it,  "a 
natural  in  contradistinction  to  a  miraculous  process."  I 
think  this  work  can  hardly  have  failed  to  have  produced 
a  great  effect  in  every  philosophical  mind. 

The  third  volume  of  the  Journal  of  the  Linnean  So- 
ciety (August,  1858)  contains  papers  by  Mr.  Wallace  and 
myself,  in  which,  as  stated  in  the  introductory  remarks  to 
this  volume,  the  theory  of  ITatural  Selection  is  promul- 
gated. 

In  June,  1859,  Professor  Huxley  gave  a  lecture  be- 
fore the  Royal  Institution  on  the  Persistent  Types  of  Ani- 
mal Life.  Referring  to  such  cases,  he  remarks :  "  It  is 
difficult  to  comprehend  the  meaning  of  such  facts  as  these, 
if  we  suppose  that  each  species  of  animal  and  plant,  or 
each  great  type  of  organisation,  was  formed  and  placed 
upon  the  surface  of  the  globe,  at  long  intervals,  by  a  dis- 
tinct act  of  creative  power ;  and  it  is  well  to  recollect  that 
such  an  assumption  is  as  unsupported  by  tradition  or  reve- 
lation as  it  is  opposed  to  the  general  analogy  of  nature. 
If,  on  the  other  hand,  we  view  '  Persistent  Types '  in  rela- 
tion to  that  hypothesis  which  supposes  the  species  living 
at  anytime  to  be  the  result  of  the  gradual  modification  of 
pre-existing  species, — a  hypothesis  which,  though  un- 
proven,  and  sadly  damaged  by  some  of  its  supporters,  is 
yet  the  only  one  to  which  physiology  lends  any  counte- 
nance—  their  existence  would  seem  to  show  that  the 
amount  of  modification  which  living  beings  have  under- 
gone during  geological  time  is  but  very  small  in  relation 


PREFACE.  XI 

to  the  whole  series   of  changes  which  they  have  suf- 
fered." 

In  November,  1859,  the  first  edition  of  this  work  was 
published.  In  December,  1859,  Dr.  Hooker  published 
his  Introduction  to  the  Tasmanian  Flora :  in  the  first  part 
of  this  admirable  essay  he  admit-s  the  truth  of  the  descent 
and  modification  of  species ;  and  supports  this  doctrine 
by  many  original  and  valuable  observations. 

Chaeles  Daewin 
Down,  Bromley,  Kent,  Feb.  1860. 


CONTENTS. 


INTBODV0TIOI7,        .........  Page  9 

CHAPTER  I. 

VARIATION   tJNDEE  DOMESTICATION. 

Causes  of  Variability— Effects  of  Habit— Correlation  of  Growtb— Inheritance— Char- 
acter of  Domestic  Varieties — Difficulty  of  distinguishing  between  Varieties 
and  Species — Origin  of  Domestic  Varieties  from  one  or  more  Species — Domestic 
Pigeons,  their  Differences  and  Origin — Principle  of  Selection  anciently  followed,  its 
Effects — Methodical  and  Unconscious  Selection — Unknown  Origin  of  our  Domes- 
tic Productions — Circumstances  favourable  to  Man's  power  of  Selection,  .    14 

CHAPTER   II. 

VARIATION  UNDER  NATURE. 

Variability — Individual  differences — Doubtful  species — Wide  ranging,  much  diffused, 
and  common  species  vary  most — Species  of  the  larger  genera  in  any  country  vary 
more  than  the  species  of  the  smaller  genera — Many  of  the  species  of  the  larger 
genera  resemble  varieties  in  being  very  closely,  but  unequally,  related  to  each 
other,  and  in  having  restricted  ranges,  .  .  .  .  ,  .46 

CHAPTER   III. 

STRUGGLE     FOR    EXISTENCE. 

Bears  on  natural  selection — The  term  used  in  a  wide  sense — Geometrical  powers  of 
increase — Rapid  increase  of  naturalised  animals  and  plants — Nature  of  the  checlis 
to  increase — Competition  universal — Effects  of  climate — Protection  from  the  num- 
ber of  individuals — Complex  relations  of  all  animals  and  plants  throughout  nature 
— Struggle  for  life  most  severe  between  individuals  and  varieties  of  the  same  spe- 
cies ;  often  severe  between  species  of  the  same  genus — The  relation  of  organism 
to  organism  the  most  important  of  all  relations,        .  .  .  .  .60 

CHAPTER    IV. 

NATURAL     SELECTION. 

Natural  Selection— its  power  compared  with  man's  selection— its  power  on  characters 
of  trifling  importance— its  power  at  all  ages  and  on  both  sexes— Sexual  Selection— 


^ 


CONTENTS. 

On  the  generality  of  intercrosses  between  individuals  of  the  same  species — Cir- 
cumstances favourable  and  unfavourable  to  Natural  Selection,  namely,  intercross- 
ing, isolation,  number  of  individuals — Slow  action — Extinction  caused  by  Natural 
Selection — Divergence  of  Cliaracter,  related  to  the  diversity  of  inhabitants  of  any 
small  area,  and  to  naturalisation — Action  of  Natural  Selection,  through  Divergence 
of  Character  and  Extinction,  on  the  descendants  from  a  common  parent — Explains 
the  Grouping  of  all  organic  beings,     .......      77 


CHAPTER    V. 

LAWS     OP     VARIATION. 

Effects  of  external  conditions— Use  and  disuse,  combined  with  natural  selection  ; 
organs  of  flight  and  of  vision — Acclimatisation— Correlation  of  growth— Compen- 
sation and  economy  of  growth — False  correlations— Multiple,  rudimentary,  and 
lowly  organised  structures  variable — Parts  developed  in  an  unusual  manner  are 
highly  variable  :  specific  characters  more  variable  than  generic  :  secondary  sexual 
characters  variable— Species  of  the  same  genus  vaiy  in  an  analogous  manner— Re- 
versions to  long  lost  characters — Summary,  .....    120 


CHAPTER    VI. 

DIFFICULTIES    ON    THEORY. 

Difliculties  on  the  theory  of  descent  with  modification — Transitions — Absence  or 
rarity  of  transitional  varieties — Transitions  in  habits  of  life — Diversified  habits  in 
the  same  species— Species  with  habits  widely  different  from  those  of  their  allies — 
Organs  of  extreme  perfection — Means  of  transition — Cases  of  difficulty — Natura 
non  facit  saltum — Organs  of  small  importance — Organs  not  in  all  cases  absolutely 
perfect— The  law  of  Unity  of  Type  and  of  the  Conditions  of  Existence  embraced 
by  the  theory  of  Natural  Selection,    ......  154 


CHAPTER    VII. 

INSTINCT. 

Instincts  comparable  with  habits,  but  different  in  their  origin— Instincts  graduated— 
Aphides  and  ants— Instincts  variable— Domestic  instincts,  their  origin— Natural 
instincts  of  the  cuckoo,  ostrich,  and  parasitic  bees— Slave-making  ants— Hive-bee, 
its  cell-making  instinct— Difficulties  on  the  theory  of  the  Natural  Selection  of 
instincts — Neuter  or  sterile  insects— Summary,       .....    185 


CHAPTER   VIII. 

HYBRIDISM. 

Distinction  between  the  sterility  of  first  crosses  and  of  hybrids— Sterility  various  in 
degree,  not  universal,  affected  by  close  interbreeding,  removed  by  domestication- 
Laws  governing  the  sterility  of  hybrids— Sterility  not  a  special  endowment,  but 
incidental  on  other  diflerences— Causes  of  the  sterility  of  first  crosses  and  of 
hybrids— Parallelism  between  the  eflects  of  changed  conditions  of  life  and  crosa- 


CONTENTS.  rj 

ing— Fertility  of  varieties  -when  crossed  and  of  their  mongrel  offspring  not  uni- 
versal—Hybrids and  mongrels  compared  independently  of  their  fertility— Sum- 
mary,   217 

CHAPTER    IX. 

ON  THE  IMPERFECTION  OF  THE  GEOLOGICAL  RECORD. 

On  the  absence  of  intermediate  varieties  at  the  present  day — On  the  nature  of  extinct 
intermediate  varieties  ;  on  their  number — On  the  vast  lapse  of  time,  as  inferred 
from  the  rate  of  deposition  and  of  denudation — On  the  poorness  of  our  palasonto- 
logical  collections— On  the  intermittence  of  geological  formations— On  the  absence 
of  intermediate  varieties  in  any  one  formation — On  the  sudden  appearance  of 
groups  of  species — On  their  sudden  appearance  in  the  lowest  known  fossiliferous 
strata,        ...........    245 

CHAPTER    X. 

ON   THE   GEOLOGICAL   SUCCESSION  OF  ORGANIC  BEINGS. 

On  the  slow  and  successive  appearance  of  new  species — On  their  different  rates  of 
change — Species  once  lost  do  not  reappear — Groups  of  species  follow  the  same  gen- 
eral rules  in  their  appearance  and  disappearance  as  do  single  species — On  Extinc- 
tion— On  simultaneous  changes  in  the  forms  of  life  throughout  the  world — On  the 
affinities  of  extinct  species  to  each  other  and  to  living  species — On  the  state  of  de- 
velopment of  ancient  foi-ms — On  the  succession  of  the  same  types  within  the  same 
areas— Summary  of  preceding  and  present  chapters,         ....    273 

CHAPTER    XI. 

GEOGRAPHICAL   DISTRIBUTION. 

Present  distribution  cannot  be  accounted  for  by  differences  in  physical  conditions — Im- 
portance of  barriers — Affinity  of  the  productions  of  the  same  continent — Centres 
of  creation — Means  of  dispersal,  by  changes  of  climate  and  of  the  level  of  the 
land,  and  by  occasional  means — Dispersal  during  the  Glacial  period  co-extensive 
with  the  world,     ..........    302 

CHAPTER   XII. 

GEOGRAPHICAL  DISTRIBUTION — Continued. 

Distribution  of  fresh-water  'productions— On  the  inhabitants  of  oceanic  islands — Ab- 
sence of  Batrachians  and  of  terrestrial  mammals — On  the  relation  of  the  inhabit- 
ants of  islands  to  those  of  the  nearest  mainland — On  colonisation  from  the  nearest 
source  with  subsequent  modification — Summary  of  the  last  and  present  chap- 
ters, ...........     334 

CHAPTER    XIII. 

MUTUAL    AFFINITIES     OF     ORGANIC     BEINGS  :     MORPHOLOGY  :     EMBRYOLOGY  :     RUDI- 
MENTARY  ORGANS. 

Classification,  groups  subordinate  to  groups— Natural  system— Rules  and  difficul- 
ties in  classification,  explained  on  the  theory  of  descent  with  modification— Classi- 


g  CONTENTS. 

fication  of  varieties— Descent  always  used  in  classification — Analogical  or  adaptive 
characters — Affinities,  general,  complex  and  radiating — Extinction  separates  and 
defines  groups — Morphology,  between  members  of  the  same  class,  between  parts 
of  the  same  individual — Embryology,  laws  of,  explained  by  variations  not  super- 
vening at  an  early  age,  and  being  inherited  at  a  corresponding  age — Rudimentary 
organs  •,  their  origin  explained — Summary,  .....    358 

CHAPTER    XIV. 

EECAPITULATION  AND   CONCLUSION. 

Recapitulation  of  the  difficulties  on  the  theory  of  Natural  Selection — Recapitulation 
of  the  general  and  special  circumstances  in  its  favour — Causes  of  the  general 
heUef  in  the  immutability  of  species — How  far  the  theory  of  natural  selection  may 
be  extended— Effects  of  its  adoption  on  the  study  of  Natural  History — Concluding 
remarks,  ..........    S9S 

Ljdex, 425 


tnttruction  to  Bindcr.~l!ho  Diagram  to  front  pago  133. 


01^  THE  ORIGIN  OF  SPECIES. 


INTEODUOTION. 

"When  on  board  H.  M.  S.  '  Beagle '  as  naturalist,  I  was 
mucli  struck  with  certain  facts  in  the  distribution  of  the 
inhabitants  of  South  America,  and  in  the  geological  rela- 
tions of  the  present  to  the  past  inhabitants  of  that  con- 
tinent. These  facts  seemed  to  me  to  throw  some  light 
on  the  origin  of  species — that  mystery  of  mysteries,  as  it 
has  been  called  by  one  of  our  greatest  philosophers.  On 
my  return  home,  it  occurred  to  me,  in  1837,  that  some- 
thing might  perhaps  be  made  out  on  this  question  by 
patiently  accumulating  and  reflecting  on  all  sorts  of  facts 
which  could  possibly  have  any  bearing  on  it.  After  five 
years'  work  I  allowed  myself  to  speculate  on  the  subject, 
and  drew  up  some  short  notes  ;  these  I  enlarged  in  1844: 
into  a  sketch  of  the  conclusions,  which  then  seemed  to  me 
probable :  from  that  period  to  the  present  day  I  have  stead- 
ily pursued  the  same  object.  I  hope  that  I  may  be  ex- 
cused for  entering  on  these  personal  details,  as  I  give 
them  to  show  that  I  have  not  been  hasty  in  coming  to  a 
decision. 

My  work  is  now  nearly  finished  ;  but  as  it  will  take 
me  two  or  three  more  years  to  complete  it,  and  as  my 
health  is  far  from  strong,  I  have  been  urged  to  publish 
this  Abstract.  I  have  more  especially  been  induced  to 
do  this,  as  Mr.  Wallace,  who  is  now  studying  the  natural 
history  of  the  Malay  archipelago,  has  arrived  at  almost 
exactly  the  same  general  conclusions  that  I  have  on  the 
origin  of  species.  Last  year  he  sent  to  me  a  memoir  on 
this  subject,  with  a  request  that  I  would  forward  it  to  Sir 


-^Q  INTRODUCTIOK 

Charles  Lyell,  who  sent  it  to  the  Linnean  Society,  aud  it 
is  published  in  the  third  Tolume  of  the  Journal  of  that 
Society.  Sir  C.  Lyell  and  Dr.  Hookei*,  who  both  knew 
of  my  work — the  latter  having  read  my  sketch  of  1844 
— ^liononred  me  by  thinking  it  advisable  to  publish, 
with  Mr.  Wallace's  excellent  memoir,  some  brief  extracts 
from  my  manuscripts. 

This  Abstract,  which  I  now  publish,  must  necessarily 
be  imperfect.  I  cannot  here  give  references  and  author- 
ities for  my  several  statements ;  and  I  must  trust  to  the 
reader  rej)Osing  some  confidence  in  my  accuracy.  Ko 
doubt  errors  will  have  crept  in,  though  I  hope  I  have 
always  been  cautious  in  trusting  to  good  authorities  alone. 
I  can  here  give  only  the  general  conclusions  at  which  I 
have  arrived,  with  a  few  facts  in  illustration,  but  which, 
I  hope,  in  most  cases  will  suffice.  I^o  one  can  feel  more 
sensible  than  I  do  of  the  necessity  of  hereafter  publishing 
in  detail  all  the  facts,  with  references,  on  which  my  con- 
clusions have  been  grounded  ;  and  I  hope  in  a  future  work 
to  do  this.  For  I  am  well  aware  that  scarcely  a  single 
point  is  discussed  in  this  volume  on  which  facts  cannot 
be  adduced,  often  a]3parently  leading  to  conclusions  di- 
rectly opposite  to  those  at  which  I  have  arrived.  A  fair 
result  can  be  obtained  only  by  fully  stating  and  balancing 
the  facts  and  arguments  on  both  sides  of  each  question ; 
and  this  cannot  possibly  be  here  done. 

I  much  regret  that  want  of  space  prevents  my  having 
the  satisfaction  of  acknowledging  the  generous  assistance 
which  I  have  received  from  very  many  naturalists,  some 
of  them  personally  unknown  to  me.  I  cannot,  however, 
let  this  opportunity  pass  without  expressing  my  deep 
obligations  to  Dr.  Hooker,  who  for  the  last  fifteen  years 
has  aided  me  in  every  possible  way  by  his  large  stores  of 
knowledge  and  his  excellent  judgment. 

In  considering  the  Origin  of  Species,  it  is  quite  con- 
ceivable that  a  naturalist,  reflecting  on  the  mutual  affini- 
ties of  organic  beings,  on  their  embryological  relations, 
their  geographical  distribution,  geological  succession,  and 
other  such  facts,  might  come  to  the  conclusion  that  each 
species  had  not  been  independently  created,  but  had  de- 


INTRODUCTION. 


11 


scended,  like  varieties,  from  other  species.  JSTevertheless 
such  a  conclusion,  even  if  well  founded,  would  be  unsat- 
isfactory, until  it  could  be  shown  how  the  innumerable 
species  inhabiting  this  world  have  been  modified,  so  as  to 
acquire  that  perfection  of  structure  and  coadaptation 
which  most  justly  excites  our  admiration.  Naturalists 
continually  refer  to  external  conditions,  such  as  climate, 
food,  &c.,  as  the  only  possible  cause  of  variation.  In  one 
very  limited  sense,  as  we  shall  hereafter  see,  this  may  be 
true  ;  but  it  is  preposterous  to  attribute  to  mere  external 
conditions,  the  structure,  for  instance,  of  the  woodpecker, 
with  its  feet,  tail,  beak,  and  tongue,  so  admirably  adapted 
to  catch  insects  under  the  bark  of  trees.  In  the  case  of 
the  misseltoe,  which  draws  its  nourishment  from  certain 
trees,  which  has  seeds  that  must  be  transported  by  certain 
birds,  and  which  has  flowers  with  separate  sexes  abso- 
lutely requiring  the  agency  of  certain  insects  to  bring  pol- 
len from  one  flower  to  the  other,  it  is  equally  preposterous 
to  account  for  the  structure  of  this  parasite,  with  its  rela- 
tions to  several  distinct  organic  beings,  by  the  effects  of 
external  conditions,  or  of  habit,  or  of  the  volition  of  the 
plant  itself. 

It  is,  therefore,  of  the  highest  importance  to  gain  a 
clear  insight  into  the  means  of  modification  and  coadapta- 
tion. At  the  commencement  of  my  observations  it  seemed 
to  me  probable  that  a  careful  study  of  domesticated  ani- 
mals and  of  cultivated  plants  would  offer  the  best  chance 
of  making  out  this  obscure  problem.  ISTor  have  I  been 
disappointed ;  in  this  and  in  all  other  perplexing  cases  I 
have  invariably  found  that  our  knowledge,  imperfect 
though  it  be,  of  variation  under  domestication,  afforded 
the  best  and  safest  clue.  I  may  venture  to  express  my 
conviction  of  the  high  value  of  such  studies,  although  they 
have  been  very  commonly  neglected  by  naturalists. 

From  these  considerations,  I  shall  devote  the  first 
chapter  of  this  Abstract  to  Yariation  under  Domestica- 
tion. We  shall  thus  see  that  a  large  amount  of  hereditary 
modification  is  at  least  possible ;  and,  what  is  equally  or 
more  important,  we  shall  see  how  great  is  the  power  of 
man  in  accumulating  by  his  Selection  successive  slight 


12 


INTRODUCTION. 


variations.  I  will  then  pass  on  to  the  variability  of 
species  in  a  state  of  nature ;  bnt  I  stall,  unfortunately, 
be  compelled  to  treat  tliis  subject  far  too  briefly,  as  it  can 
be  treated  properly  only  by  giving  long  catalogues  of 
facts.  We  shall,  however,  be  enabled  to  discuss  what 
circumstances  are  most  favourable  to  variation.  In  the 
next  chapter  the  Struggle  for  Existence  amongst  all  or- 
ganic beings  throughout  the  world,  which  inevitably  fol- 
lows from  their  high  geometrical  powers  of  increase,  will 
be  treated  of.  This  is  the  doctrine  of  Malthus,  applied  to 
the  whole  animal  and  vegetable  kingdoms.  As  many 
more  individuals  of  each  species  are  born  than  can  pos- 
sibly survive ;  and  as,  consequently,  there  is  a  frequently 
recurring  struggle  for  existence,  it  follows  that  any  being, 
if  it  vary  however  slightly  in  any  manner  profitable  to 
itself,  under  the  complex  and  sometimes  varying  con 
ditions  of  life,  will  have  a  better  chance  of  surviving,  ano 
thus  be  naturally  selected.  From  the  strong  principle  of 
inheritance,  any  selected  variety  will  tend  to  propagatf 
its  new  and  modified  form. 

This  fundamental  subject  of  Natural  Selection  will  be 
treated  at  some  length  in  the  fourth  chapter ;  and  wc 
shall  then  see  how  Natural  Selection  almost  inevitably 
causes  much  Extinction  of  the  less  improved  forms  of  life, 
and  induces  what  I  have  called  Divergence  of  Character. 
In  the  next  chapter  I  shall  discuss  the  complex  and  little 
known  laws  of  variation  and  of  correlation  of  growth.  In 
the  four  succeeding  chapters,  the  most  apparent  and 
gravest  difiiculties  on  the  theory  will  be  given  :  namely, 
first,  the  difficulties  of  transitions,  or  in  understanding 
how  a  simple  being  or  a  simple  organ  can  be  changed  and 
perfected  into  a  highly  developed  being  or  elaborately  con- 
structed organ ;  secondly,  the  subject  of  Instinct,  or  the 
mental  powers  of  animals  ;  thirdly.  Hybridism,  or  the  in- 
fertility of  species  and  the  fertility  of  varieties  when  inter- 
crossed ;  and  fourthly,  the  imperfection  of  the  Geological 
Record.  In  the  next  chapter  I  shall  consider  the  geolog- 
ical succession  of  organic  beings  throughout  time ;  in  the 
eleventh  and  twelfth,  their  geographical  distribution 
throughout  space ;    in  the  thirteenth,  their  classification 


INTRODUCTIOIT.  13 

or  mutual  affinities,  both  when  mature  and  in  an  em- 
bryonic condition.  In  the  last  chapter  I  shall  give  a 
brief  recapitulation  of  the  whole  work,  and  a  few  con- 
cluding remarks. 

No  one  ought  to  feel  surprise  at  much  remaining  as 
yet  unexplained  in  regard  to  the  origin  of  species  and 
varieties,  if  he  makes  due  allowance  for  our  profound 
ignorance  in  regard  to  the  mutual  relations  of  all  the 
beings  which  live  around  us.  Who  can  explain  why  one 
species  ranges  widely  and  is  very  numerous,  and  why 
another  allied  species  has  a  narrow  range  and  is  rare? 
Yet  these  relations  are  of  the  highest  importance,  for  they 
determine  the  present  welfare,  and,  as  I  believe,  the  future 
success  and  modification  of  every  inhabitant  of  this  world. 
Still  less  do  we  know  of  the  mutual  relations  of  the  in- 
numerable inhabitants  of  the  world  during  the  many  past 
geological  epochs  in  its  history.  Although  much  remains 
obscure,  and  will  long  remain  obscure,  I  can  entertain  no 
doubt,  after  the  most  deliberate  study  and  dispassionate 
judgment  of  which  I  am  capable,  that  the  view  which 
most  naturalists  entertain,  and  which  I  formerly  enter- 
tained— namely,  that  each  species  has  been  independently 
created — is  erroneous.  I  am  fully  convinced  that  species 
are  not  immutable ;  but  that  those  belonging  to  what  are 
called  the  same  genera  are  lineal  descendants  of  some 
other  and  generally  extinct  species,  in  the  same  manner 
as  the  acknowledged  varieties  of  any  one  species  are  the 
descendants  of  that  species.  Furthermore,  I  am  convinced 
that  [N'atural  Selection  has  been  the  main  but  not  exclu- 
give  means  of  modification. 


14  VARIATION  UNDER  DOMESTICATION.  IChap.  I. 


CHAPTER    I 


VARIATION    UNDER    DOMESTICATION. 

Causes  of  Variability — Effects  of  Habit — Correlation  of  Growth — Inheritance — Char- 
acter of  Domestic  Varieties — Difficulty  of  distinguishing  between  Varieties 
and  Species — Origin  of  Domestic  Varieties  from"one  or  more  Species — Domestio 
Pigeons,  their  Dfferences  and  Origin — Principle  of  Selection  anciently  followed,  its 
Effects — Methodical  and  Unconscious  Selection — Unknown  Origin  of  our  Domes- 
tio Productions — Circumstances  favourable  to  Man's  power  of  Selection. 

When  we  look  to  tlie  individuals  of  the  same  variety  or 
sub-variety  of  our  older  cultivated  plants  and  animals, 
one  of  the  first  points  which  strikes  us,  is,  that  they  gen- 
erally differ  much  more  from  each  other,  than  do  the  in- 
dividuals of  any  one  species  or  variety  in  a  state  of  nature. 
"When  we  reflect  on  the  vast  diversity  of  the  plants  and 
animals  which  have  been  cultivated,  and  which  have 
varied  during  all  ages  under  the  most  different  climates 
and  treatment,  I  think  we  are  driven  to  conclude  that  this 
greater  variability  is  simply  due  to  our  domestic  produc- 
tions having  been  raised  under  conditions  of  life  not  so. 
uniform  as,  and  somewhat  different  from,  those  to  which 
the  parent-species  have  been  exposed  under  nature. 
There  is,  also,  I  think,  some  probability  in  the  view  pro- 
pounded by  Andrew  Knight,  that  this  variability  may  be 
partly  connected  with  excess  of  food.  It  seems  pretty 
clear  that  organic  beings  must  be  exposed  during  sev^eral 
generations  to  the  new  conditions  of  life  to  cause  any  ap- 
preciable amount  of  variation  ;  and  that  when  the  organ- 
isation has  once  begun  to  vary ,  it  generally  continues  to 
vary  for  many  generations.  No  case  is  on  record  of  a 
variable  being  ceasing  to  be  variable  under  cultivation. 
Our  oldest  cultivated  plants,  such  as  wheat,  still  often 
yield  new  varieties :  our  oldest  domesticated  animals  are 
still  capable  of  rapid  improvement  or  modification. 


Chap.  I.J  UNDER  DOMESTICATION.  J^g 

It  has  been  disputed  at  what  period  of  life,  the  causes 
of  variability,  whatever  they  may  be,  generally  act ; 
whether  during  the  early  or  late  period  of  development 
of  the  embryo,  or  at  the  instant  of  conception.  Geoifroy 
St.  Hilaire's  experiments  show  that  unnatural  treatment 
of  the  embryo  causes  monstrosities ;  and  monstrosities 
cannot  be  separated  by  any  clear  line  of  distinction  from 
mere  variations.  But  I  am  strongly  inclined  to  suspect 
that  the  most  frequent  cause  of  variability  may  be  attrib- 
uted to  the  male  and  female  reproductive  elements  having 
been  affected  prior  to  the  act  of  conception.  Several 
reasons  make  me  believe  in  this ;  but  the  chief  one  is  the 
remarkable  effect  which  confinement  or  cultivation  has 
on  the  functions  of  the  reproductive  system  ;  this  system 
appearing  to  be  far  more  susceptible  than  any  other  part 
of  the  organisation,  to  the  action  of  any  change  in  the 
conditions  of  life.  i^Tothing  is  more  easy  than  to  tame  an 
animal,  and  few  things  more  difficult  than  to  get  it  to 
breed  freely  under  confinement,  even  in  the  many  cases 
when  the  male  and  female  unite.  How  many  animals 
there  are  which  will  not  breed,  though  living  long  under 
not  very  close  confinement  in  their  native  country  !  This 
is  generally  attributed  to  vitiated  instincts ;  but  how 
many  cultivated  plants  display  the  utmost  vigour,  and 
yet  rarely  or  never  seed  !  In  some  few  such  cases  it  has 
been  found  out  that  very  trifiing  changes,  such  as  a  little 
more  or  less  water  at  some  particular  period  of  growth, 
will  determine  whether  or  not  the  plant  sets  a  seed.  I 
cannot  here  enter  on  the  copious  details  which  I  have  col- 
lected on  this  curious  subject ;  but  to  show  how  singular 
the  laws  are  which  determine  the  reproduction  of  animals 
under  confinement,  I  may  just  mention  that  carnivorous 
animals,  even  from  the  tropics,  breed  in  this  country  pretty 
freely  under  cofinement,  with  the  exception  of  the  planti- 
grades or  bear  family  ;  whereas,  carnivorous  birds,  with 
the  rarest  exceptions,  hardly  ever  lay  fertile  eggs.  Many 
exotic  plants  have  pollen  utterly  worthless,  in  the  same 
exact  condition  as  in  the  most  sterile  hybrids.  When,  on 
the  one  hand,  we  see  domesticated  animals  and  plants, 
though  often  weak  and  sickly,  yet  breeding  quite  freely 


\ 


IQ  VARIATION  [Chap.  1 

under  confinement ;  and  when,  on  tlie  other  hand,  we  see 
individuals,  though  taken  youn^  from  a  state  of  nature, 
perfectly  tamed,  long-lived,  and  healthy  (of  which  I  could 
give  numerous  instances),  yet  having  their  reproductive 
system  so  seriously  affected  by  unperceiyed  causes  as  to 
fail  in  acting,  we  need  not  be  surprised  at  this  system, 
when  it  does  act  under  confinement,  acting  not  quite  reg- 
ularly, and  producing  offspring  not  perfectly  like  their 
parents  or  variable. 

Sterility  has  been  said  to  be  the  bane  of  horticulture ; 
but  on  this  view  we  owe  variability  to  the  same  cause 
which  produces  sterility  ;  and  variability  is  the  source  of 
all  the  choicest  productions  of  the  garden.  I  may  add, 
that  as  some  organisms  will  breed  most  freely  under  the 
most  nnnatural  conditions  (for  instance,  the  rabbit  and 
ferret  kept  in  hutches),  showing  that  their  reproductive 
system  has  not  been  thus  affected  ;  so  will  some  animals 
and  plants  withstand  domestication  or  cultivation,  and 
vary  very  slightly — perhaps  hardly  more  than  in  a  state 
of  nature. 

A  long  list  could  easily  be  given  of  "  sporting  plants ; " 
by  this  term  gardeners  mean  a  single  bud  or  ofl'set,  which 
suddenly  assumes  a  new  and  sometimes  very  different 
character  from  that  of  the  rest  of  the  plant.  Such  buds 
can  be  propagated  by  grafting,  &c.,  and  sometimes  by 
seed.  These  "  sports"are  extremely  rare  under  nature, 
but  far  from  rare  under  cultivation ;  and  in  this  case  we 
see  that  the  treatment  of  the  parent  has  affected  a  bud  or 
offset,  and  not  the  ovules  or  pollen.  But  it  is  the  opinion 
of  most  physiologists  that  there  is  no  essential  difference 
between  a  bud  and  an  ovule  in  their  earliest  stages  of  for- 
mation ;  so  that,  in  fact,  "  sports  "  support  my  view,  that 
variability  may  be  largely  attributed  to  the  ovules  or  pol- 
len, or  to  both,  having  been  affected  by  the  treatment  of 
the  parent  prior  to  the  act  of  conception.  These  cases 
anyhow  show  that  variation  is  not  necessarily  connected, 
as  some  authors  have  supposed,  with  the  act  of  gen- 
eration. 

Seedlings  from  the  same  fruit,  and  the  young  of  the 
same  litter,  sometimes  differ  considerably  from  each  other. 


Chap.  I.]  UNDER  DOMESTICATION.  ^fj 

tliough  both  the  young  and  the  parents,  as  Miiller  has  re- 
marked, have  apparently  been  exposed  to  exactly  the 
same  conditions  of  life ;  and  this  shows  how  unimportant 
the  direct  effects  of  the  conditions  of  life  are  in  comparison 
with  the  law^s  of  reproduction,  and  of  growth,  and  of  in- 
heritance ;  for  had  the  action  of  the  conditions  been  di- 
rect, if  any  of  the  young  had  varied,  all  would  probably 
have  varied  in  the  same  manner.  To  judge  how  much, 
in  the  case  of  any  variation,  we  should  attribute  to  the 
direct  action  of  heat,  moisture,  light,  food,  &c.,  is  most 
difficult :  my  impression  is,  that  with  animals  such  agen- 
cies have  produced  very  little  direct  effect,  though  ap- 
parently more  in  the  case  of  plants.  Under  this  point  of 
view,  Mr.  Buckman's  recent  experiments  on  j^lants  seem 
extremely  valuable.  When  all  or  nearly  all  the  individ- 
uals exposed  to  certain  conditions  are  affected  in  the  same 
way,  the  change  at  first  appeal's  to  be  directly  due  to 
such  conditions ;  but  in  some  cases  it  can  be  shown  that 
quite  opposite  conditions  produce  similar  changes  of  struc- 
ture. ISTevertheless  some  slight  amount  of  change  may, 
I  think,  be  attributed  to  the  direct  action  of  the  conditions 
of  life — as,  in  some  cases,  increased  size  from  amount  of 
food,  colour  from  particular  kinds  of  food  and  from  light, 
and  perhaps  the  thickness  of  fur  from  climate. 

Habit  also  has  a  decided  influence,  as  in  the  period  of 
flowering  with  plants  when  transported  from  one  climate 
to  another.  In  animals  it  has  a  more  marked  eftect ;  for 
instance,  I  find  in  the  domestic  duck  that  the  bones  of  the 
w4ng  weigh  less  and  the  bones  of  the  leg  more,  in  propor- 
tion to  the  whole  skeleton,  than  do  the  same  bones  in  the 
wild  duck ;  and  I  presume  that  this  change  may  be  safely 
attributed  to  the  domestic  duck  flying  much  less,  and 
walking  more,  than  its  wild  parent.  The  great  and  in- 
herited development  of  the  udders  in  cows  and  goats  in 
countries  where  they  are  habitually  milked,  in  comparison 
with  the  state  of  these  organs  in  other  countries,  is  another 
instance  of  the  eftect  of  \ise.  Xot  a  single  domestic  ani- 
mal can  be  named  wdiich  has  not  in  some  country  droop- 
ing ears  ;  and  the  view  suggested  by  some  authors,  that 
the  drooping  is  due  to  the  disuse  of  the  muscles  of  the 
2^ 


■£g  VARIATION  [Chap.  L 

ear,  from  the  animals  not  being  mucli  alarmed  by  danger, 
seems  probable. 

There  are  many  laws  regulating  variation,  some  few 
of  which  can  be  dimly  seen,  and  will  be  hereafter  briefly 
mentioned.  I  will  here  only  allude  to  what  may  be  called 
correlation  of  growth.  Any  change  in  the  embryo  or 
larva  will  almost  certainly  entail  changes  in  the  mature 
animal.  In  monstrosities,  the  correlations  between  quite 
distinct  parts  are  very  curious  ;  and  many  instances  are 
given  in  Isidore  Geoffroy  St.  Hilaire's  great  work  on  this 
subject.  Breeders  believe  that  long  limbs  are  almost 
always  accompanied  by  an  elongated  head.  Some  in- 
stances of  correlation  are  quite  whimsical :  thus  cats  with 
blue  eyes  are  invariably  deaf;  colour  and  constitutional 
peculiarities  go  together,  of  which  many  remarkable  cases 
could  be  given  amongst  animals  and  plants.  From  the 
facts  collected  by  Heusinger,  it  appears  that  white  sheep- 
and  pigs  are  differently  affected  from  coloured  individuals 
by  certain  vegetable  poisons.  Hairless  dogs  haA^e  imper- 
fect teeth  ;  long-haired  and  coarse-haired  animals  are  aj)t 
to  have,  as  is  asserted,  long  or  many  horns  ;  pigeons  with 
feathered  feet  have  skin  between  their  outer  toes ;  pigeons 
with  short  beaks  have  small  feet,  and  those  with  long 
beaks  large  feet.  Hence,  if  man  goes  on  selecting,  and 
thus  augmenting,  any  peculiarity,  he  will  almost  certainly 
unconsciously  modify  other  parts  of  the  structure,  owing 
to  the  mysterious  laws  of  the  correlation  of  growth. 

The  result  of  the  various,  quite  unknown,  or  dimly 
seen  laws  of  variation  is  infinitely  complex  and  diversi- 
fied. It  is  well  worth  while  carefully  to  study  the  several 
treatises  published  on  some  of  our  old  cultivated  plants, 
as  on  the  hyacinth,  potato,  even  the  dahlia,  (fee.  ;  and  it 
is  really  surprising  to  note  the  endless  points  in  structure 
and  constitution  in  which  the  varieties  and  subvarieties 
differ  slightly  from  each  other.  Tlie  whole  organisation 
seems  to  have  become  plastic,  and  tends  to  depart  in  some 
small  degree  from  that  of  the  parental  type. 

Any  variation  which  is  not  inheritable  is  unimportant 
for  us.  But  the  number  and  diversity  of  inheritable  de- 
viations of  structure,  both  those  of  slight  and  those  of 


Chap.  I.]  UNDER  DOMESTICATION".  -^g 

considerable  physiological  importance,  is  endless.  Dr. 
Prosper  Lucas's  treatise,  in  two  large  volumes,  is  the  full- 
est and  the  best  on  this  subject.  'No  breeder  doubts  how 
strong  is  the  tendency  to  inheritance  :  like  j^roduces  like  is 
his  fundamental  belief:  doubts  have  been  thrown  on  this 
principle  by  theoretical  writers  alone.  When  any  devia- 
tion of  structure  often  appears,  and  we  see  it  in  the  father 
and  child,  we  cannot  tell  whether  it  may  not  be  due  to 
the  same  cause  having  acted  on  both  ;  but  when  amongst 
individuals,  apparently  exposed  to  the  same  conditions, 
any  very  rare  deviation,  due  to  some  extraordinary  com- 
bination of  circumstances,  appears  in  the  parent— say, 
once  amongst  several  million  individuals — and  it  reappears 
in  the  child,  the  mere  doctrine  of  chances  almost  compels 
us  to  attribute  its  reappearance  to  inheritance.  Every  one 
must  have  heard  of  cases  of  albinism,  prickly  skin,  hairy 
bodies,  &c.,  appearing  in  several  members  of  the  same  fami- 
ly. If  strange  and  rare  deviations  of  structure  are  truly 
inherited,  less  strange  and  commoner  deviations  may  be 
freely  admitted  to  be  inheritable.  Perhaps  the  correct 
way  of  viewing  the  whole  subject,  would  be,  to  look  at 
the  inheritance  of  every  character  whatever  as  the  rule, 
and  non-inheritance  as  the  anomaly. 

The  laws  governing  inheritance  are  quite  unknown ;  no 
one  can  say  why  the  same  peculiarity  in  diflerent  indi- 
viduals of  the  same  species,  and  in  individuals  of  different 
species,  is  sometimes  inherited  and  sometimes  not  so  ; 
why  the  child  often  reverts  in  certain  characters  to  its 
grandfather  or  grandmother  or  other  much  more  remote 
ancestor  ;  why  a  peculiarity  is  often  transmitted  from  one 
sex  to  both  sexes,  or  to  one  sex  alone,  more  commonly  but 
not  exclusively  to  the  like  sex.  It  is  a  fact  of  some  little 
importance  to  us,  that  peculiarities  appearing  in  the  males 
of  our  domestic  breeds  are  often  transmitted  either  ex- 
clusively, or  in  a  much  greater  degree,  to  males  alone. 
A  much  more  important  rule,  which  I  think  may  be 
trusted,  is  that,  at  whatever  period  of  life  peculiarity  first 
appears,  it  tends  to  appear  in  the  offspring  at  a  correspond- 
hig  age,  though  sometimes  earlier.  Li  many  cases  this 
could  not  be  otherwise  :  thus  the  inherited  peculiarities  in 


20  VARIATION  [Chap.  L 

the  horns  of  cattle  conld  appear  only  in  the  ofi'spring  when 
nearly  mature  ;  j)ecnliarities  in  the  silkworm  are  known 
to  appear  at  the  corresponding  caterpillar  or  cocoon  stage. 
Bnt  hereditary  diseases  and  some  other  facts  make  me 
believe  that  the  rnle  has  a  wider  extension,  and  that  when 
there  is  no  apparent  reason  why  a  peculiarity  should  appear 
at  any  particular  age,  yet  that  it  does  tend  to  appear  in 
the  offspring  at  the  same  period  at  which  it  first  appeared 
in  the  parent.  I  believe  this  rule  to  be  of  the  highest 
importance  in  explaining  the  laws  of  embryology.  These 
remarks  are  of  course  confined  to  the  firs*:  appearance  of 
the  j)eculiarity,  and  not  to  its  primary  cause,  which  may 
have  acted  on  the  ovules  or  male  element ;  in  nearly  the 
same  manner  as  in  the  crossed  ofl'spring  from  a  short- 
horned  cow  by  a  long-horned  bull,  the  greater  length  of 
horn,  though  appearing  late  in  life,  is  clearly  due  to  the 
male  element. 

Having  alluded  to  the  subject  of  reversion,  I  may  here 
refer  to  a  statement  often  made  by  naturalists — namely, 
that  our  domestic  varieties,  when  run  wild,  gradually  but 
certainly  revert  in  character  to  their  aboriginal  stocks. 
Hence  it  has  been  argued  that  no  deductions  can  be  drawn 
from  domestic  races  to  species  in  a  state  of  nature.  I 
have  in  vain  endeavoured  to  discover  on  what  decisive  facts 
the  above  statement  has  so  often  and  so  boldly  been  made. 
There  would  be  great  difiiculty  in  proving  its  truth  :  we 
may  safely  conclude  that  very  many  of  the  most  strongly- 
marked  domestic  varieties  could  not  possibly  live  in  a 
wild  state.  In  many  cases  we  do  not  know  Avhat  the  ab- 
original stock  was,  and  so  could  not  tell  whether  or  not 
nearly  perfect  reversion  had  ensued.  It  would  be  quite 
necessary,  in  order  to  prevent  the  efiects  of  intercrossing, 
that  only  a  single  variety  should  be  turned  loose  in  its 
new  home.  Nevertheless,  as  our  varieties  certainly  do 
occasionally  revert  in  some  of  their  characters  to  ancestral 
forms,  it  seems  to  me  not  improbable,  that  if  we  could 
succeed  in  naturalising,  or  were  to  cultivate,  during  many 
■  generations,  the  several  races,  for  instance,  of  the  cabbage, 
in  very  poor  soil  (in  which  case,  however,  some  efiect 
would  have  to  be  attributed  to  the  direct  action  of  the 


Ohap.  I.]  UNDER  DOMESTICATION.  21 

poor  soil),  that  tliey  wonld  to  a  large  extent,  or  even 
wholly,  revert  to  the  wild  aboriginal  stock.  Whether  or 
not  the  experiment  would  succeed,  is  not  of  great  impor- 
tance for  our  line  of  argument ;  for  by  the  experiment 
itself  the  conditions  of  life  are  changed.  If  it  could  be 
shown  that  our  domestic  varieties  manifested  a  strong 
tendency  to  reversion, — that  is,  to  lose  their'  acquired 
characters,  whilst  kept  under  unchanged  conditions,  and 
whilst  kept  in  a  considerable  body,  so  that  free  intercross- 
ing might  check,  by  blending  together,  any  slight  devia- 
tions of  structure,  in  such  case,  I  grant  that  we  could 
deduce  nothing  from  domestic  varieties  in  regard  to 
species.  But  there  is  not  a  shadow  of  evidence  in  favour 
of  this  view  :  to  assert  that  we  could  not  breed  our  cart 
and  race-horses,  long  and  short-horned  cattle,  and  poultry 
of  various  breeds,  and  esculent  vegetables,  for  an  almost 
infinite  number  of  generations,  would  be  opposed  to  all 
experience.  I  may  add,  that  when  under  nature  the  con- 
ditions of  life  do  change,  variations  and  reversions  of  char- 
acter probably  do  occur;  but  natural  selection,  as  will 
hereafter  be  explained,  will  determine  how  far  the  new 
characters  thus  arising  shall  be  preserved. 

When  we  look  to  the  hereditary  varieties  or  races  of 
our  domestic  animals  and  plants,  and  compare  them  with 
species  closely  allied  together,  we  generally  perceive  in 
each  domestic  race,  as  already  remarked,  less  uniformity 
of  character  than  in  true  species.  Domestic  races  of  the 
same  species,  also,  often  have  a  somewhat  monstrous  char- 
acter ;  by  which  I  mean,  that,  although  difiering  from 
each  other,  and  from  the  other  species  of  the  same  genus, 
in  several  trifling  respects,  they  often  differ  in  an  extreme 
degree  in  some  one  part,  both  when  compared  one  with 
another,  and  more  especially  when  com]3ared  with  all  the 
species  in  nature  to  which  they  are  nearest  allied.  Wil-h 
these  exceptions  (and  Avith  that  of  the  perfect  fertility  of 
varieties  when  crossed, — a  subject  hereafter  to  be  dis- 
cussed), domestic  races  of  the  same  sj)ecies  differ  from 
each  other  in  the  same  manner  as,  only  in  most  cases  in  a 
lesser  degree  than,  do  closely-allied  species  of  the  same 
genus  in  a  state  of  nature.     I  think  this  must  be  admitted, 


22  VARIATION  [Chap.  I. 

wlien  we  find  that  there  are  hardly  any  domestic  races, 
either  amongst  animals  or  plants,  which  have  not  been 
ranked  by  some  competent  judges  as  mere  varieties,  and 
by  other  competent  judges  as  the  descendants  of  aborigi- 
nally distinct  species.  If  any  marked  distinction  existed 
between  domestic  races  and  species,  this  source  of  doubt 
could  not  so  perpetually  recur.  It  has  often  been  stated 
that  domestic  races  do  not  differ  from  each  other  in  char- 
acters of  generic  value.  I  think  it  could  be  shown  that 
this  statement  is  hardly  correct ;  but  naturalists  difler 
most  widely  in  determining  what  characters  are  of  generic 
value ;  all  such  valuations  being  at  present  empirical. 
Moreover,  on  the  view  of  the  origin  of  genera  which  I  shall 
presently  give,  we  have  no  right  to  expect  often  to  meet 
with  generic  differences  in  our  domesticated  productions. 

When  we  attempt  to  estimate  the  amount  of  structural 
difference  between  the  domestic  races  of  the  same  species, 
we  are  soon  involved  in  doubt,  from  not  knowing  whether 
they  have  descended  from  one  or  several  parent-species. 
This  point,  if  it  could  be  cleared  up,  would  be  interesting ; 
if,  for  instance,  it  could  be  shown  that  the  greyhound, 
bloodhound,  terrier,  spaniel,  and  bull- dog,  which  we  all 
know  propagate  their  kind  so  truly,  were  the  offspring  of 
any  single  species,  then  such  facts  would  have  great  weight 
in  making  us  doubt  about  the  immutability  of  the  many 
very  closely  allied  natural  species — for  instance,  of  the  many, 
foxes — inhabiting  different  quarters  of  the  world.  I  do  not 
believe,  as  we  shall  presently  see,  that  the  whole  amount  of 
difference  between  the  several  breeds  of  the  dog  has  been 
produced  under  domestication ;  I  believe  that  some  small 
part  of  the  difference  is  due  to  their  being  descended  from 
distinct  species.  In  the  case  of  some  other  domesticated 
species,  there  is  presumptive,  or  even  strong  evidence,  that 
all  the  breeds  have  descended  from  a  single  wild  stock. 

It  has  often  been  assumed  tJiat  man  has  chosen  for 
domestication  animals  and  plants  having  an  extraordi- 
nary inherent  tendency  to  vary,  and  likewise  to  withstand 
diverse  climates.  I  do  not  dispute  that  these  capacities 
have  added  largely  to  the  value  of  most  of  our  domesti- 
cated productions ;  but  how  could  a  savage  possibly 
know,  when  he  first  tamed  an  animal,  whether  it  would 


Chap.  I.]  UNDER  DOMESTICATION.  23 

vary  in  succeeding  generations,  and  whether  it  would 
endure  other  climates  ?  Has  the  little  variability  of  the 
ass  or  guinea-fowl,  or  the  small  power  of  endurance  of 
warmth  by  the  rein-deer,  or  of  cold  by  the  common  camel, 
prevented  their  domestication  ?  I  cannot  doubt  that  if 
other  animals  and  plants,  equal  in  number  to  our  domes- 
ticated productions,  and  belonging  to  equally  diverse 
classes  and  countries,  were  taken  from  a  state  of  nature, 
and  could  be  made  to  breed  for  an  equal  number  of  gen- 
erations under  domestication,  they  would  vary  on  an 
average  as  largely  as  the  parent  species  of  our  existing 
domesticated  productions  have  varied. 

In  the  case  of  most  of  our  anciently  domesticated  ani- 
mals and  plants,  I  do  not  think  it  is  possible  to  come  to 
any  definite  conclusion,  whether  they  have  descended 
from  one  or  several  species.  The  argument  mainly  relied 
on  by  those  who  believe  in  the  multiple  origin  of  our  do- 
mesticated animals  is,  that  we  find  in  the  most  ancient 
records,  more  especially  on  the  monuments  of  Egypt, 
much  diversity  in  the  breeds  ;  and  that  some  of  the  breeds 
closely  resemble,  perhaps  are  identical  with,  those  still 
existing.  Even  if  this  latter  fact  were  found  more  strictly 
and  generally  true  than  seems  to  me  to  be  the  case,  what 
does  it  show,  but  that  some  of  our  breeds  originated  there 
four  or  five  thousand  years  ago  ?  After  the  recent  discov- 
eries of  flint  tools  or  celts  in  the  superficial  deposits  of 
France  and  England,  few  geologists  will  doubt  that  man, 
in  a  sufiiciently  civilized  state  to  have  manufactured 
weapons,  existed  at  a  period  extremely  remote  as  measured 
by  years ;  and  we  know  that  at  the  present  day  there  is 
hardly  any  tribe  so  barbarian  as  not  to  have  domesticated 
at  least  the  dog. 

The  whole  subject  must,  I  think,  remain  vague;  nev- 
ertheless, I  may,  without  here  entering  on  any  details, 
state  that,  from  geographical  and  other  considerations,  I 
think  it  highl}'-  probable  that  our  domestic  dogs  have 
descended  from  several  wild  species.  Knowing,  as  we 
do,  that  savages  are  very  fond  of  taming  animals,  it 
seems  to  me  unlikely,  in  the  case  of  the  dog-genus,  which 
is  distributed  in  a  wild  state  throughout  the  world, 
that  since  man  first  appeared  one  single  species  alone 


24  VARIATION  [Chap.  1. 

sliould  have  been  domesticated.  In  regard  to  sheep 
and  goats  I  can  form  no  opinion.  I  should  think,  from 
facts  communicated  to  me  by  Mr.  Blyth,  on  the  habits, 
voice,  and  constitution,  (fee,  of  the  humped  Indian  cattle, 
that  these  had  descended  from  a  different  aboriginal  stock 
from  our  European  cattle  ;  and  several  competent  judges 
believe  that  these  latter  have  had  more  than  one  wild 
parent.  With  respect  to  horses,  from  reasons  which  I 
cannot  give  here,  I  am  doubtfully  inclined  to  believe,  in 
opposition  to  several  authors,  that  all  the  races  have  de- 
scended from  one  wild  stock.  Mr.  Blyth,  whose  opinion, 
from  his  large  and  varied  stores  of  knowledge,  I  should 
value  more  than  that  of  almost  any  one,  thinks  that  all 
the  breeds  of  poultry  have  proceeded  from  the  common 
wild  Indian  fowl  (Gallus  bankiva).  In  regard  to  ducks 
and  rabbits,  the  breeds  of  which  differ  considerably  from 
each  other  in  structure,  I  do  not  doubt  that  they  all  have 
descended  from  the  common  wild  duck  and  rabbit. 

The  doctrine  of  the  origin  of  our  several  domestic  races 
from  several  aboriginal  stocks,  has-  been  carried  to  an 
absurd  extreme  by  some  authors.  They  believe  that 
every  race  which  breeds  true,  let  the  distinctive  characters 
be  ever  so  slight,  has  had  its  wild  prototype.  At  this 
rate  there  must  have  existed  at  least  a  score  of  species  of 
wild  cattle,  as  many  sheep,  and  several  goats  in  Euroj)e 
alone,  and  several  even  within  Great  Britain.  One 
author  believes  that  there  formerly  existed  in  Great  Britain 
eleven  wild  species  of  sheej)  peculiar  to  it !  When  we 
bear  in  mind '  that  Britain  has  now  hardly  one  peculiar 
mammal,  and  France  but  few  distinct  from  those  of  Ger- 
many and  conversely,  and  so  with  Hungary,  Spain,  (fee, 
but  that  each  of  these  kingdoms  possesses  several  pecu- 
liar breeds  of  cattle,  sheep,  (fee,  we  must  admit  that  many 
domestic  breeds  have  originated  in  Europe  ;  for  whence 
could  they  have  been  derived,  as  these  several  countries 
do  not  possess  a  number  of  peculiar  species  as  distinct 
parent-stocks  ?  So  it  is  in  India.  Even  in  the  case  of  the 
domestic  dogs  of  the  whole  world,  which  I  fully  admit 
have  probably  descended  from  several  wild  species,  I  can- 
not doubt  that  there  has  been  an  immense  amount  of  in- 
herited variation.     Who  can  believe  that  animals  closely 


Chap.  I.]  UNDER  DOMESTICATION.  25 

resembling  the  Italian  greylionnd,  the  bloodhound,  the 
bnll-dog,  or  Blenheim  spaniel,  &c. — so  nnlike  all  wild 
Canidse — ever  existed  freely  in  a  state  of  nature  ?  It  has 
often  been  loosely  said  that  all  oiir  races  of  dogs  have  been 
produced  by  the  crossing  of  a  few  aboriginal  species  ;  but 
by  crossing  we  can  get  only  forms  in  some  degree  inter- 
mediate between  their  parents;  and  if  we  account  for  our 
several  domestic  races  by  this  process,  we  must  admit 
the  former  existence  of  the  most  extreme  forms,  as  the 
Italian  greyhound,  bloodhound,  bull-dog,  &c.,  in  the  wild 
state.  Moreover,  the  possibility  of  making  distinct  races 
by  crossing  has  been  greatly  exaggerated.  Tliere  can  be 
no  doubt  that  a  race  may  be  modified  by  occasional 
crosses,  if  aided  by  the  careful  selection  of  those  individual 
mongrels,  which  present  any  desired  character ;  but  that 
a  race  could  be  obtained  nearly  intermediate  between  two 
extremely  different  races  or  species,  I  can  hardly  believe. 
Sir  J.  Sebright  expressly  experimentised  for  this  object, 
and  failed.  The  offsj)ring  from  the  first  .cross  between 
two  pure  breeds  is  tolerably  and  sometimes  (as  I  have 
found  with  pigeons)  extremely  uniform,  and  everything 
seems  simple  enough  ;  but  when  these  mongrels  are  cross- 
ed one  with  another  for  several  s^enerations,  hardly  two  of 
them  will  be  alike,  and  then  the  extreme  difiiculty,  or 
rather  utter  hoj)elessness,  of  the  task  becomes  apparent. 
Certainly,  a  breed  intermediate  between  tioo  very  distinct 
breeds  could  not  be  got  without  extreme  care  and  long- 
continued  selection;  nor  can  I  find  a  single  case  on  record 
of  a  permanent  race  having  been  thus  formed. 

On  the  Breeds  of  the  Domestic  Pigeon.  —Believing 
that  it  is  always  best  to  study  some  special  group,  I  have, 
after  deliberation,  taken  up  domestic  pigeons.  I  have 
kept  every  breed  which  I  could  purchase  or  obtain,  and 
have  been  most  kindly  favoured  with  skins  from  several 
quarters  of  the  world,  more  especially  by  the  Hon.  W. 
Elliot  from  India,  and  by  the  Hon.  C.  Muri'ay  from  Per- 
sia. Many  treatises  in  different  languages  have  been 
published  on  pigeons,  and  some  of  them  are  very  impor- 
tant, as  being  of  considerable  antiquity.  I  have  associated 
with  several  eminent  fanciers,  and  have  been  permitted  to 
j  oi  n  two  of  the  London  Pigeon  Clubs.  The  diversity  of  the 
2* 


2g  DOMESTIC  PIGEON'S.  [Chap.  L 

breeds  is  something  astonishing.  Compare  the  English 
carrier  and  the  short-faced  tumbler,  and  see  the  wonderful 
difference  in  their  beaks,  entailing  corresponding  differ- 
ences in  their  skulls.  The  carrier,  more  especially  the 
male  bird,  is  also  remarkable  from  the  wonderful  develoj)- 
ment  of  the  carunculated  skin  above  the  head,  and  this  is 
accompanied  by  greatly  elongated  eyelids,  very  large  ex- 
ternal orifices  to  the  nostrils,  and  a  wide  gape  of  mouth. 
The  short-faced  tumbler  has  a  beak  in  outline  almost  like 
that  of  a  finch  ;  and  the  common  tumbler  has  the  singular 
and  strictly  inherited  habit  of  fiying'  at  a  great  height  in 
a  compact  fiock,  and  tumbling  in  the  air  head  over  heels. 
The  runt  is  a  bird  of  great  size,  with  long,  massive  beak 
and  large  feet ;  some  of  the  sub-breeds  of  runts  have  very 
long  necks,  others  very  long  wings  and  tails,  others  singu- 
larly short  tails.  The  barb  is  allied  to  the  carrier,  but, 
instead  of  a  very  long  beak,  has  a  very  short  and  very 
broad  one.  The  pouter  has  a  much  elongated  body, 
wings,  and  legs ;  and  its  enormously  developed  crop, 
which  it  glories  in  inflating,  may  well  excite  astonishment 
and  even  laughter.  The  turbit  has  a  very  short  and 
conical  beak,  with  a  line  of  reversed  feathers  down  the 
breast ;  and  it  has  the  habit  of  continually  expanding 
slightly  the  upper  part  of  the  oesophagus.  Tlie  Jacobin 
has  the  feathers  so  much  reversed  along  the  back  of  the 
neck  that  they  form  a  hood,  and  it  has,  proportionally  to 
its  size,  much  elongated  wing  and  tailfeathers.  The 
trumpeter  and  laugher,  as  their  names  express,  utter  a 
Tcry  different  coo  from  the  other  breeds.  The  fantail  has 
thirty  or  even  forty  tailfeathers,  instead  of  twelve  or  four- 
teen, the  normal  number  in  all  members  of  the  great 
pigeon  family  ;  and  these  feathers  are  kept  expanded,  and 
are  carried  so  erect  that  in  good  birds  the  head  and  tail 
touch;  the  oil-gland  is  quite  aborted.  Several  other  less 
distinct  breeds  might  have  been  specified. 

In  the  skeletons  of  the  several  breeds,  the  develop- 
ment of  the  bones  of  the  face  in  length  and  breadth  and 
curvature  differs  enormously.  The  shape,  as  well  as  the 
breadth  and  length  of  the  ramus  of  the  lower  jaw,  varies 
ill  a  highly  remarkable  manner.  The  number  of  the  cau- 
dal and  sacral  vertebra3  vary  ;  as  does  the  number  of  the 


Chap.  I.)  DOMESTIC  PIGEONS.  27 

ribs,  together  with  their  relative  breadth  and  the  presence 
of  processes.  The  size  and  shape  of  the  apertures  in  the 
sternum  are  highly  variable ;  so  is  the  degree  of  divergence 
and  relative  size  of  the  two  arms  of  the  furcula.  The  j)ro- 
portional  width  of  the  gape  of  mouth,  the  proportional 
length  of  the  eyelids,  of  the  orifice  of  the  nostrils,  of  the 
tongue  (not  always  in  strict  correlation  with  the  length  of 
beak),  the  size  of  the  croj)  and  of  the  upper  part  of  the 
oesophagus;  the  development  and  abortion  of  the  oil- 
gland  ;  the  number  of  the  primary  wing  and  caudal 
feathers ;  the  relative  length  of  wing  and  tail  to  each 
other  and  to  the  body;  the  relative  length  of  leg  and  of 
the  feet ;  the  number  of  scutellse  on  the  toes,  the  develop- 
ment of  skin  between  the  toes,  are  all  points  of  structure 
which  are  variable.  The  period  at  which  the  perfect  plu- 
mage is  acquired  varies,  as  does  the  state  of  the  down 
with  which  the  nestling  birds  are  clothed  when  hatched. 
The  shape  and  size  of  the  eggs  vary.  The  manner  of 
flight  differs  remarkably ;  as  does  in  some  breeds  the 
voice  and  disposition.  Lastly,  in  certain  breeds,  the 
males  and  females  have  come  to  difl^er  to  a  slight  degree 
from  each  other. 

Altogether  at  least  a  score  of  pigeons  might  be 
chosen,  which  if  shown  to  an  ornithologist,  and  he  were 
told  that  they  were  wild  birds,  would  certainly,  I  think, 
be  ranked  by  him  as  well-defined  species.  Moreover,  I 
do  not  believe  that  any  ornithologist  would  place  the 
English  carrier,  the  short-faced  tumbler,  the  runt,  the 
barb,  pouter,  and  fantail  in  the  same  genus  ;  more  espe- 
cially as  in  each  of  these  breeds  several  truly-inherited 
sub-breeds,  or  species  as  he  might  have  called  them, 
could  be  shown  him. 

Great  as  the  diflerences  are  between  the  breeds  of 
pigeons,  I  am  fully  convinced  that  the  common  opinion 
of  naturalists  is  correct,  namely,  that  all  have  descended 
from  the  rock-pigeon  (Columba  livia),  including  under 
this  term  several  geographical  races  or  sub-species,  which 
differ  from  each  other  in  the  most  trifiing  respects.  As 
several  of  the  reasons  which  have  led  me  to  this  belief  are 
in  some  degree  applicable  in  other  cases,  I  will  here  briefly 
give  them.     If  the  several  breeds  are  not  varieties,  and 


2g  DOMESTIC  PIGEONS.  [Chap.  I. 

have  not  proceeded  from  the  rock-pigeon,  they  must  have 
descended  from  at  least  seven  or  eight  aboriginal  stocks  ; 
for  it  is  impossible  to  make  the  present  domestic  breeds 
by  the  crossing  of  any  lesser  number :  how,  for  instance, 
could  a  pouter  be  produced  by  crossing  two  breeds  unless 
one  of  the  parent-stocks  possessed  the  characteristic  enor- 
mous crop  ?  The  supposed  aboriginal  stocks  must  all 
have  been  rock-pigeons,  that  is,  not  breeding  or  willingly 
perching  on  trees.  But  besides  C.  livia,  with  its  geo- 
graphical sub-species,  only  two  or  three  of  the  species  of 
rock-pigeons  are  known ;  and  these  have  not  any  of  the 
characters  of  the  domestic  breeds.  Hence  the  supposed 
aboriginal  stocks  must  either  still  exist  in  the  countries 
where  they  were  originally  domesticated,  and  yet  be  un- 
known to  ornithologists ;  and  this,  considering  their  size, 
habits,  and  remarkable  characters,  seems  very  improba- 
ble ;  or  they  must  have  become  extinct  in  the  wild  state. 
But  birds  breeding  on  precipices,  and  good  fliers,  are  un- 
likely to  be  exterminated ;  and  the  common  rock-pigeon, 
which  has  the  same  habits  with  the  domestic  breeds,  has 
not  been  exterminated  even  on  several  of  the  smaller 
British  islets,  or  on  the  shores  of  the  Mediterranean. 
Hence  the  supposed  extermination  of  so  many  species 
having  similar  habits  with  the  rock-pigeon  seems  to  me  a 
very  rash  assumption.  Moreover,  the  several  above- 
named  domesticated  breeds  have  been  transported  to  all 
parts  of  the  world,  and,  therefore,  some  of  them  must 
have  been  carried  back  again  into  their  native  country  ; 
but  not  one  has  ever  become  wild  or  feral,  though  the 
dovecot-pigeon,  which  is  the  rock-pigeon  in  a  very  slightly 
altered  state,  has  become  feral  in  several  places.  Again, 
all  recent  experience  shows  that  it  is  most  difficult  to  get 
any  wild  animal  to  breed  freely  under  domestication ; 
yet  on  the  hypothesis  of  the  multiple  origin  of  our  pigeons, 
it  must  be  assumed  that  at  least  seven  or  eight  species 
were  so  thoroughly  domesticated  in  ancient  times  by  half- 
civilized  man,  as  to  be  quite  prolific  under  confinement. 

An  argument,  as  it  seems  to  me,  of  great  weight,  and 
applicable  in  several  other  cases,  is,  that  the  above-speci- 
fied breeds,  though  agreeing  generally  in  constitution, 
habits,  voice,  colouring,  and  in  most  parts  of  their  struo* 


Chap.  I.]  DOMESTIC  PIGEONS. 


29 


ture,  with  the  wild  rock-pigeon,  yet  are  certainly  highly 
abnormal  in  other  parts  of  their  structure :  we  may  look 
in  vain  throughout  tJie  whole  great  family  of  Columbidse 
for  a  beak  like  that  of  the  English  carrier,  or  that  of  the 
short-faced  tumbler,  or  barb ;  for  reversed  feathers  like 
those  of  the  jacobin  ;  for  a  crop  like  that  of  the  pouter: 
for  tail-feathers  like  those  of  the  fantail.  Hence  it  must 
be  assumed  not  only  that  half-civilized  man  succeeded  in 
thoroughly  domesticating  several  species,  but  that  he  in- 
tentionally or  by  chance  picked  out  extraordinarily  ab- 
normal species ;  and  further,  that  these  very  species  have 
since  all  become  extinct  or  unknown.  So  many  strange 
contingencies  seem  to  me  improbable  in  the  highest  de- 
gree. 

Some  facts  in  regard  to  the  colouring  of  pigeons  well 
deserve  consideration.  The  rock-pigeon  is  of  a  slaty-blue, 
and  has  a  white  rump  (the  Indian  sub-species,  C.  inter- 
media of  Strickland,  having  it  bluish) ;  the  tail  has  a  ter- 
minal dark  bar,  with  the  bases  of  the  outer  feathers  ex- 
ternally edged  with  white ;  the  Vv^ings  have  two  black 
bars;  some  semi-domestic  breeds  and  some  apparently 
truly  wild  breeds  have,  besides  the  two  black  bars,  the 
wings  chequered  with  black.  These  several  marks  do  not 
occur  together  in  any  other  species  of  the  whole  family. 
ISTow,  in  every  one  of  the  domestic  breeds,  taking 
thoroughly  well-bred  birds,  all  the  above  marks,  even  to 
the  white  edging  of  the  outer  tail-feathers,  sometimes  con- 
cur perfectly  developed.  Moreover,  when  two  birds  be- 
longing to  two  distinct  breeds  are  crossed,  neither  of 
which  is  blue  or  has  any  of  the  above-specified  marks,  the 
mongrel  offspring  are  very  apt  suddenly  to  acquire  these 
characters ;  for  instance,  I  crossed  some  uniformly  white 
fantails  with  some  uniformly  black  barbs,  and  they  pro- 
duced mottled  brown  and  black  birds ;  these  I  again 
crossed  together,  and  one  grandchild  of  the  pure  white 
fantail  and  pure  black  barb  was  of  as  beautiful  a  blue 
colour,  with  the  white  rump,  double  black  wing-bar,  and 
barred  and  white-edged  tail-feathers,  as  any  wild  rock- 
pigeon.  We  can  understand  these  facts,  on  the  well- 
known  principle  of  reversion  to  ancestral  characters,  if  all 


30  DOMESTIC  PIGEONS.  [Chap.  1. 

the  domestic  breeds  have  descended  from  the  rock-pigeon. 
But  if  we  deny  this,  we  mnst  make  one  of  the  two  follow- 
ing highly  improbable  suppositions.  Either,  firstly,  that 
all  the  several  imagined  aboriginal  stocks  were  coloured, 
and  marked  like  the  rock-pigeon,  although  no  other  ex- 
isting species  is  thus  coloured  and  marked,  so  that  in  each 
separate  breed  there  might  be  a  tendency  to  revert  to  the 
very  same  colours  and  markiogs.  Or,  secondly,  that  each 
breed,  even  the  purest,  has  within  a  dozen  or,  at  most, 
within  a  score  of  generations,  been  crossed  by  the  rock- 
pigeon  :  I  say  within  a  dozen  or  twenty  generations,  for 
we  know  of  no  fact  countenancing  the  belief  that  the 
child  ever  reverts  to  some  one  ancestor,  removed  by  a 
greater  number  of  generations.  In  a  breed  which  has 
been  crossed  only  once  with  some  distinct  breed,  the  ten- 
dency to  reversion  to  any  character  derived  from  such 
cross  will  naturally  become  less  and  less,  as  in  each  suc- 
ceeding generation  there  will  be  less  of  the  foreign  blood ; 
but  when  there  has  been  no  cross  with  a  distinct  breed, 
and  there  is  a  tendency  in  both  parents  to  revert  to  a 
character,  which  has  been  lost  during  some  former  gener- 
ation, this  tendency,  for  all  that  we  can  see  to  the  con- 
trary, may  be  transmitted  undiminished  for  an  indefinite 
number  of  generations.  These  two  distinct  cases  are  often 
confounded  in  treatises  on  inheritance. 

Lastly,  the  hybrids  or  mongrels  from  between  all  the 
domestic  breeds  of  pigeons  are  perfectly  fertile.  I  can 
state  this  from  my  own  observations,  purposely  made  on 
the  most  distinct  breeds.  ]N"ow,  it  is  difficult,  2:)erhaps  im- 
possible, to  bring  forward  one  case  of  the  hybrid  offspring 
of  two  animals  clearly  distinct  being  themselves  perfectly 
fertile.  Some  authors  believe  that  long-continued  domes- 
tication eliminates  this  strong  tendency  to  sterility  :  from 
the  history  of  the  dog  I  think  there  is  some  probability  in 
this  hypothesis  if  applied  to  species  closely  related  to- 
gether, though  it  is  unsupported  by  a  single  experiment. 
But  to  extend  the  hypothesis  so  far  as  to  suppose  that 
species,  aboriginally  as  distinct  as  carriers,  tumblers, 
pouters,  and  fantails  now  are,  should  yield  offspring  per- 
fectly fertile,  inter  se,  seems  to  me  rash  in  the  extreme. 


Chap.  I.]  DOMESTIC  PIGEONS.  •  3-J^ 

From  these  several  reasons,  namely,  the  improbability 
of  man  having  formerly  got  seven  or  eight  supposed  spe- 
cies of  pigeons  to  breed  freely  nnder  domestication  ;  these 
supposed  species  being  quite  unknown  in  a  wild  state, 
and  their  becoming  nowhere  feral ;  these  species  having 
very  abnormal  characters  in  certain  respects,  as  compared 
with  all  other  Columbidse,  though  so  like  in  most  other 
respects  to  the  rock-pigeon ;  the  blue  colour  and  various 
marks  occasionally  appearing  in  all  the  breeds,  both  when 
kept  pure  and  when  crossed ;  the  mongrel  offspring  being 
perfectly  fertile  ; — from  these  several  reasons,  taken  to- 
gether, I  can  feel  no  doubt  that  all  our  domestic  breeds 
have  descended  from  the  Columba  livia  with  its  geograph- 
ical sub-species. 

In  favour  of  this  view,  I  may  add,  firstly,  that  C.  livia, 
or  the  rock-pigeon,  has  been  found  capable  of  domestica- 
tion in  Europe  and  in  India  ;  and  that  it  agrees  in  habits 
and  in  a  great  number  of  points  of  structure  with  all  the 
domestic  breeds.  Secondly,  although  an  English  carrier 
or  short-faced  tumbler  differs  immensely  in  certain  char- 
acters from  the  rock-pigeon,  yet  by  comparing  the  several 
sub-breeds  of  these  breeds,  more  especially  those  brought 
from  distant  countries,  we  can  make  an  almost  perfect 
series  between  the  extremes  of  structure.  Thirdly,  those 
characters  which  are  mainly  distinctive  of  each  breed,  for 
instance  the  wattle  and  length  of  beak  of  the  carrier,  the 
shortness  of  that  of  the  tumbler,  and  the  number  of  tail- 
feathers  in  the  fantail,  are  in  each  breed  eminently  vari- 
able ;  and  the  explanation  of  this  fact  will  be  obvious 
when  we  come  to  treat  of  selection.  Fourthly,  pigeons 
have  been  watched,  and  tended  with  the  utmost  care,  and 
loved  by  many  people.  They  have  been  domesticated  for 
thousands  of  years  in  several  quarters  of  the  world  ;  the 
earliest  known  record  of  pigeons  is  in  the  fifth  Egyptian 
dynasty,  about  3000  b.  c,  as  was  pointed  out  to  me  by 
Professor  Lepsius  ;  but  Mr.  Birch  informs  me  that  pigeons 
are  given  in  a  bill  of  fare  in  the  previous  dynasty.  In  the 
time  of  the  Romans,  as  we  hear  from  Pliny,  immense 
prices  were  given  for  pigeons  ;  "  nay,  they  are  come  to 
this  pass,  that  they  can  reckon   up    their  pedigree  and 


32  •  DOMESTIC  PIGEONS.  [Chap.  1. 

race."  Pigeons  were  much  yahied  by  Akber  Khan  in 
Liclia,  about  the  year  1600  ;  never  less  than  20,000  pigeons 
were  taken  with  the  court.  "  The  nionarchs  of  Iran  and 
Turan  sent  him  some  very  rare  birds  ;  "  and,  continues 
the  courtly  historian,  "  His  Majesty  by  crossing  the  breeds, 
whicli  method  was  never  practised  before,  has  improved 
them  astonishingly."  About  this  same  period  the  Dutch 
were  as  eager  about  pigeons  as  were  the  old  Eomans. 
The  paramount  importance  of  these  considerations  in  ex- 
plaining the  immense  amount  of  variation  which  pigeons 
have  undergone,  will  be  obvious  when  we  treat  of  Selec- 
tion. We  shall  then,  also,  see  how  it  is  that  the  breeds 
so  often  have  a  somewhat  monstrous  character.  It  is  also 
a  most  favourable  circumstance  for  the  production  of  dis- 
tinct breeds,  that  male  and  female  pigeons  can  be  easily 
mated  for  life ;  and  thus  different  breeds  can  be  kept  to- 
gether in  the  same  aviary. 

I  have  discussed  the  probable  origin  of  domestic 
pigeons  at  some,  yet  quite  insufficient,  length  ;  because 
when  I  first  kept  pigeons  and  watched  the  several  kinds, 
knowing  well  how  true  they  bred,  I  felt  fully  as  much 
difficulty  in  believing  that  they  could  ever  have  descended 
from  a  common  parent,  as  any  naturalist  could  in  coming 
to  a  similar  conclusion  in  regard  to  the  many  species  of 
finches,  or  other  large  groups  of  birds,  in  nature.  One 
circumstance  has  struck  me  much  ;  namely,  that  all  the 
breeders  of  the  various  domestic  animals  and  the  culti- 
vators of  plants,  with  whom  I  have  ever  conversed,  or 
whose  treatises  I  have  read,  are  firmly  convinced  that  the 
several  breeds  to  which  each  has  attended,  are  descended 
from  so  many  aboriginally  distinct  species.  Ask,  as  I 
have  asked,  a  celebrated  raiser  of  Hereford  cattle,  whether 
his  cattle  might  not  have  descended  from  long-liorns,  and 
he  will  laugh  you  to  scorn.  I  have  never  met  a  pigeon, 
or  poultry,  or  duck,  or  rabbit  fancier,  who  was  not  full}'- 
(;onvinced  that  each  main  breed  was  descended  from  a 
distinct  species.  Yan  Mons,  in  liis  treatise  on  pears  and 
apples,  sliows  how  utterly  he  disbelieves  that  the  several 
sorts,  for  instance  a  Kibston-pippin  or  Codlin-apple,  could 
ever  have  proceeded  from  the  seeds  of  the  same  tree.     In- 


Chap.  I.]  BELEOTION  BY  MAN.  33 

nnmerable  otlier  examples  conld  be  given.  The  explana- 
tion, I  think,  is  simple :  from  long-continued  stndj  they 
are  strongly  impressed  with  the  dilFerences  between  the 
several  races  ;  and  though  they  well  know  that  each  race 
varies  slightly,  for  they  win  their  prizes  by  selecting  snch 
slight  differences,  yet  Ihey  ignore  all  general  arguments, 
and  refuse  to  sum  up  in  their  minds  slight  differences  ac- 
cumulated during  many  successive  generations.  May  not 
those  naturalists  who,  knowing  far  less  of  the  laws  of  in- 
heritance than  does  the  breeder,  and  knowing  no  more 
than  he  does  of  the  intermediate  links  in  the  long  lines  of 
descent,  yet  admit  that  many  of  our  domestic  races  have 
descended  from  the  same  parents — may  they  not  learn  a 
lesson  of  caution,  when  they  deride  the  idea  of  species  in 
a  state  of  nature  being  lineal  descendants  of  other  species  ? 
Selection. — Let  us  now  briefly  consider  the  stej)S  by 
which  domestic  races  have  been  produced,  either  from 
one  or  from  several  allied  species.  Some  little  effect  may, 
perhaps,  be  attributed  to  the  direct  action  of  the  external 
conditions  of  life,  and  some  little  to  habit ;  but  he  would 
be  a  bold  man  who  would  account  by  such  agencies  for 
the  differences  of  a  dray  and  race  horse,  a  greyhound  and 
bloodhound,  a  carrier  and  tumbler  pigeon.  One  of  the 
most  remarkable  features  in  our  domesticated  races  is 
that  we  see  in  them  adaptation,  not  indeed  to  the  animal's 
or  plant's  own  good,  but  to  man's  use  or  fancy.  Some 
variations  useful  to  him  have  probably  arisen  suddenly, 
or  by  one  step  ;  many  botanists,  for  instance,  believe  that 
the  fuller's  teazle,  with  its  hooks,  which  cannot  be  rivalled 
by  any  mechanical  contrivance,  is  only  a  variety  of  the 
wild  Dipsacus  ;  and  this  amount  of  change  may  have  sud- 
denly arisen  in  a  seedling.  So  it  has  probably  been  with 
the  turnspit  dog  ;  and  this  is  known  to  have  been  the  case 
with  the  ancon  sheep.  But  when  we  compare  the  dray- 
horse  and  race-horse,  the  dromedary  and  camel,  the  va- 
rious breeds  of  sheep  fitted  either  for  cultivated  land  or 
mountain  pasture,  with  the  wool  of  one  breed  good  for 
one  purpose,  and  that  of  another  breed  for  another  pur- 
pose ;  when  we  compare  the  many  breeds  of  dogs,  each 
good  for  man  in  very  different  ways  ;  when  we  compare 


34  SELECTION  BY  MAN.  [Chap.  I. 

the  game-cock,  so  pertinacious  in  battle,  with  other  breeds 
so  little  quarrelsome,  with  "  everlasting  layers "  which 
never  desire  to  sit,  and  with  the  bantam  so  small  and 
elegant ;  when  we  compare  the  host  of  agricultural,  cnli- 
nary,  orchard,  and  flower-garden  races  of  plants,  most  nse- 
ful  to  man  at  difi:erent  seasons  and  for  different  pui-poses, 
or  so  beautiful  in  his  eyes,  we  must,  I  think,  look  fui'ther 
than  to  mere  variability.  "We  cannot  suppose  that  all  the 
breeds  were  suddenly  produced  as  perfect  and  as  nseful 
as  we  now  see  them ;  indeed,  in  several  cases,  we  know 
that  this  has  not  been  their  history.  The  key  is  man's 
power  of  accumulative  selection  :  nature  gives  successive 
variations ;  man  adds  them  up  in  certain  directions  useful 
to  him.  In  this  sense  he  may  be  said  to  make  for  himself 
useful  breeds. 

The  great  power  of  this  principle  of  selection  is  not 
hypothetical.  It  is  certain  that  several  of  our  eminent 
breeders  have,  even  within  a  single  lifetime,  modified  to 
a  large  extent  some  breeds  of  cattle  and  sheep.  In  order 
fully  to  realise  what  they  have  done,  it  is  almost  necessary 
to  read  several  of  the  many  treatises  devoted  to  this  sub- 
ject, and  to  inspect  the  animals.  Breeders  habitually 
speak  of  an  animal's  organisation  as  something  quite 
plastic  which  they  can  model '  almost  as  they  please.  If 
I  had  space  I  could  quote  numerous  passages  to  this  effect 
from  highly  competent  authorities.  Youatt,  who  was 
probably  better  acquainted  with  the  works  of  agricultur- 
ists than  almost  any  other  individual,  and  who  was  him- 
self a  very  good  judge  of  an  animal,  speaks  of  the  prin- 
ciple of  selection  as  "  that  which  enables  the  agricultur- 
ist, not  only  to  modify  the  character  of  his  flock,  but  to 
change  it  altogether.  It  is  the  magician's  wand,  by 
means  of  which  he  may  summon  into  life  whatever  form 
and  mould  he  pleases."  Lord  Somerville,  speaking  of 
what  breeders  have  done  for  sheep,  says: — "It  would 
seem  as  if  they  liad  chalked  out  upon  a  wall  a  form  per- 
fect in  itself,  and  then  had  given  it  existence."  That 
most  skilful  breeder,  Sir  John  Sebright,  used  to  say,  with 
respect  to  pigeons,  that  "  he  would  produce  any  given 
"^ather  in  three  years,  but  it  would  take  him  six  years  to 


Chap.  I.]  SELECTION  BY  MAN.  35 

obtain  head  and  beak."  In  Saxony  the  importance  of 
the  principle  of  selection  in  regard  to  merino  sheep  is  so 
fully  recognised,  that  men  follow  it  as  a  trade  :  the  sheep 
are  placed  on  a  table  and  are  studied,  like  a  picture  by 
a  connoisseur ;  this  is  done  three  times  at  intervals  of 
months,  and  the  sheep  are  each  time  marked  and  classed, 
so  that  the  very  best  may  ultimately  be  selected  for 
breeding. 

What  English  breeders  have  actually  effected  is  proved 
by  the  enormous  prices  given  for  animals  with  a  good  ped- 
igree ;  and  these  have  now  been  exported  to  almost  every 
quarter  of  the  world.  The  improvement  is  by  no  means 
generally  due  to  crossing  different  breeds  ;  all  the  best 
breeders  are  strongly  opposed  to  this  practice,  except 
sometimes  amongst  closely  allied  sub-breeds.  And  when 
a  cross  has  been  made,  the  closest  selection  is  far  more 
indispensable  even  than  in  ordinary  cases.  K  selection 
consisted  merely  in  separating  some  very  distinct  variety, 
and  breeding  from  it,  the  principle  would  be  so  obvious 
as  hardly  to  be  worth  notice ;  but  its  importance  con- 
sists in  the  great  effect  produced  by  the  accumulation  in. 
one  direction,  during  successive  generations,  of  differences 
absolutely  inappreciable  by  an  uneducated  eye — differ- 
ences which  I  for  one  have  vainly  attempted  to  appre- 
ciate. ISTot  one  man  in  a  thousand  has  accuracy  of  eye 
and  judgment  sufficient  to  become  an  eminent  breeder. 
If  gifted  with  these  qualities,  and  he  studies  his  subject 
for  years,  and  devotes  his  lifetime  to  it  with  indomitable 
perseverance,  he  will  succeed,  and  may  make  great  im- 
provements ;  if  he  wants  any  of  these  qualities,  he  will  as- 
suredly fail.  Few  would  readily  believe  in  the  natural 
capacity  and  years  of  practice  requisite  to  become  even  a 
skilful  pigeon-fancier. 

The  same  principles  are  followed  by  horticulturists  ; 
but  the  variations  are  here  often  more  abrupt,  l^o  one 
supposes  that  our  choicest  productions  have  been  pro- 
duced by  a  single  variation  from  the  aboriginal  stock. 
We  have  proofs  that  this  is  not  so  in  some  cases,  in  which 
exact  records  have  been  kept ;  thus,  to  give  a  very  trifling 
instance,  the  steadily  increasing  size  of  the  common  goose- 


QQ  METHODICAL  SELECTION.  [Chap,  L 

berry  may  be  quoted.  We  see  an  astonisbing  improve- 
ment in  many  florists'  flowers,  wben  tbe  flowers  of  tbe 
present  day  are  compared  witb  drawings  made  only 
twenty  or  thirty  years  ago.  When  a  race  of  plants  is 
once  pretty  well  established,  the  seed-raisers  do  not  pick 
out  the  best  plants,  but  merely  go  over  their  seed-beds, 
and  pull  up  the  "  rogues,"  as  they  call  the  plants  that 
deviate  from  the  proper  standard.  With  animals  this 
kind  of  selection  is,  in  fact,  also  followed  ;  for  hardly  any 
one  is  so  careless  as  to  allow  his  worst  animals  to  breed. 

In  regard  to  plants,  there  is  another  means  of  observing 
the  accumulated  efi'ects  of  selection — namely,  by  compar- 
ing the  diversity  of  flowers  in  the  difi'erent  varieties  of 
the  same  species  in  the  flower-garden ;  the  diversity  of 
leaves,  pods,  or  tubers,  or  whatever  part  is  valued,  in  the 
kitchen-garden,  in  comparison  with  the  flowers  of  the 
same  varieties  ;  and  the  diversity  of  fruit  of  the  same 
species  in  the  orchard,  in  comparison  with  the  leaves  and 
flowers  of  the  same  set  of  varieties.  See  how  different 
the  leaves  of  the  cabbage  are,  and  how  extremely  alike 
the  flowers ;  how  unlike  the  flowers  of  the  heartsease  are, 
and  how  alike  the  leaves  ;  how  much  the  fruit  of  the 
difi'erent  kinds  of  gooseberries  difi'er  in  size,  colour,  shape, 
and  hairiness,  and  yet  the  flowers  present  very  slight 
difterences.  It  is  not  that  the  varieties  which  difi'er 
largely  in  some  one  point  do  not  difi'er  at  all  in  other 
points  ;  this  is  hardly  ever,  perhaps  never,  the  case. 
The  laAvs  of  correlation  of  growth,  the  importance  of 
which  should  never  be  overlooked,  will  ensure  some  dif- 
ferences ;  but,  as  a  general  rule,  I  cannot  doubt  that  the 
continued  selection  of  slight  variations,  cither  in  the 
leaves,  the  flowers,  or  the  fruit,  will  produce  races  difier- 
ing  from  each  other  chiefly  in  these  characters. 

It  may  be  objected  that  the  principle  of  selection  has 
been  reduced  to  methodical  practice  for  scarcely  more 
than  three-quarters  of  a  century  ;  it  has  certainly  been 
more  attended  to  of  late  years,  and  many  treatises  have 
been  published  on  the  subject ;  and  the  result,  I  may  add, 
has  been,  in  a  corresponding  degree,  rapid  and  important. 
But  it  is  very  far  from  true  that  the  principle  is  a  modern 


Chap.   I.]  METHODICAL  SELECTION".  g/Jr 

discovery.  I  could  give  several  references  to  tlie  full 
acknowledgment  of  the  importance  of  tlie  principle  in 
works  of  liigli  antiquity.  In  rude  and  barbarous  periods 
of  English  history  choice  animals  were  often  imported, 
and  laws  were  passed  to  prevent  their  exportation  :  the 
destruction  of  horses  under  a  certain  size  was  ordered, 
and  this  may  be  compared  to  the  "  roguing  "  of  plants 
by  nurserymen.  The  ])rinciple  of  selection  I  find  dis- 
tinctly given  in  an  ancient  Chinese  encyclopaedia.  Ex- 
plicit rules  are  laid  down  by  some  of  the  Roman  classical 
writers.  From  ^^assages  in  Genesis,  it  is  clear  that  the 
colour  of  domestic  animals  was  at  that  early  period  at- 
tended to.  Savages  now  sometimes  cross  their  dogs  with 
wild  canine  animals,  to  improve  the  breed,  and  they 
formerly  did  so,  as  is  attested  by  j^assages  in  Pliny.  The 
savages  in  South  Africa  match  their  draught  cattle  by 
colour,  as  do  some  of  the  Esquimaux  their  teams  of  dogs. 
Livingstone  shows  how  much  good  domestic  breeds  are 
valued,  by  the  negroes  of  the  interior  of  Africa  who  have 
not  associated  ivitli  Europeans.  Some  of  these  facts  do 
not  show  actual  selection,  but  they  show  that  the  breeding 
of  domestic  animals  was  carefully  attended  to  in  ancient 
times,  and  is  now  attended  to  by  the  lowest  savages.  It 
would,  indeed,  have  been  a  strange  fact,  had  attention  not 
been  paid  to  breeding,  for  the  inheritance  of  good  and 
bad  qualities  is  so  obvious. 

At  the  present  time,  eminent  breeders  try  by  methodi- 
cal selection,  with  a  distinct  object  in  view,  to  make  a  new 
strain  or  sub-breed,  superior  to  any  thing  existing  in  the 
country.  But,  for  our  purpose,  a  kind  of  Selection,  which 
may  be  called  Unconscious,  and  which  results  from  every 
one  trying  to  possess  and  breed  from  the  best  individua'. 
animals,  is  more  important.  Thus,  a  man  who  intends 
keeping  pointers  naturally  tries  to  get  as  good  dogs  as  he 
can,  and  afterwards  breeds  from  his  own  best  dogs,  but  he 
has  no  wish  or  expectation  of  permanently  altering  the 
breed.  I^evertheless  I  cannot  doubt  that  this  process, 
continued  during  centuries,  w^ould  improve  and  modify 
any  breed,  in  the  same  way  as  Bakewell,  Collins,  &c.,  by 
this  very  same  process,  only  carried  on  more  methodically. 


38  UNCONSCIOUS  SELECTION.  [Chap.  I. 

did  greatly  modify,  even  during  their  own  lifetimes,  the 
forms  and  qualities  of  their  cattle.  Slow  and  insensible 
changes  of  this  kind  could  never  be  recognised  unless 
actual  measurements  or  careful  drawings  of  the  breeds  in 
question  had  been  made  long  ago,  which  might  serve  for 
comparison.  In  some  cases,  however,  unchanged  or  but 
little  changed  individuals  of  the  same  breed  may  be  found 
in  less  civilized  districts,  where  the  breed  has  been  less 
improved.  There  is  reason  to  believe  that  King  Charles's 
spaniel  has  been  unconsciously  modified  to  a  large  extent 
since  the  time  of  that  monarch.  Some  highly  competent 
authorities  are  convinced  that  the  setter  is  directly  derived 
from  the  spaniel,  and  has  probably  been  slowly  altered  from 
it.  It  is  known  that  the  English  pointer  has  been  greatly 
changed  within  the  last  century,  and  in  this  case  the 
change  has,  it  is  believed,  been  chiefly  effected  by  crosses 
with  the  fox-hound  ;  but  what  concerns  us  is,  that  the 
change  has  been  effected  unconsciously  and  gradually, 
and  yet  so  effectually,  that,  though  the  old  Spanish 
pointer  certainly  came  from  Spain,  Mr.  Borrow  has  not 
seen,  as  I  am  informed  by  him,  any  native  dog  in  Spain 
like  our  pointer. 

By  a  similar  process  of  selection,  and  by  careful  train- 
ing, the  whole  body  of  English  race-horses  have  come  to 
surpass  in  fleetness '  and  size  the  parent  Arab  stock,  so 
that  the  latter,  by  the  regulations  for  the  Goodwood 
Races,  are  favoured  in  the  weights  they  carry.  Lord 
Spencer  and  others  have  shown  how  the  cattle  of  England 
have  increased  in  weight  and  in  early  maturity,  compared 
with  the  stock  formerly  kept  in  this  country.  By  com- 
paring the  accounts  given  in  old  pigeon  treatises  of  car- 
riers and  tumblers  with  these  breeds  as  now  existing  in 
Britain,  India,  and  Persia,  we  can,  I  think,  clearly  trace 
the  stages  through  which  they  have  insensibly  passed,  and 
come  to  differ  so  greatly  from  the  rock-pigeon. 

Youatt  gives  an  excellent  illustration  of  the  effects  of 
a  course  of  selection,  which  may  be  considered  as  uncon- 
sciously followed,  in  so  far  that  the  breeders  could  never 
iiave  expected  or  even  have  wished  to  have  produced  the 
result  which  ensued — namely,  the  production  of  two  dis- 


Chap.  I.]  UNCONStJIOUS  SELECTION.  39 

tinct  strains.  The  two  flocks  of  Leicester  sheep  kept  by 
Mr.  Buckley  and  Mr.  Burgess,  as  Mr.  Youatt  remarks, 
"  have  been  purely  bred  from  the  original  stock  of  Mr. 
Bakewell  for  upwards  of  fifty  years.  There  is  not  a  sus- 
picion existing  in  the  mind  of  any  one  at  all  acquainted 
with  the  subject  that  the  owner  of  either  of  them  has 
deviated  in  any  one  instance  from  the  pure  blood  of 
Mr.  Bakewell's  flock,  and  yet  the  difi'erence  between  the 
sheep  possessed  by  these  two  gentlemen  is  so  great  that 
they  have  the  appearance  of  being  quite  diflerent  va- 
rieties." 

If  there  exist  savages  so  barbarous  as  never  to  think 
of  the  inherited  character  of  the  oflspring  of  their  domestic 
animals,  yet  any  one  animal  particularly  useful  to  them, 
for  any  special  purpose,  would  be  carefully  preserved  dur- 
ing famines  and  other  accidents,  to  which  savages  are  so 
liable,  and  such  choice  animals  would  tlius  generally  leave 
more  off'spring  than  the  inferior  ones  ;  so  that  in  this  case 
there  would  be  a  kind  of  unconscious  selection  going  on. 
We  see  the  value  set  on  animals  even  by  the  barbarians  of 
Tierra  del  Fuego,  by  their  killing  and  devouring  their  old 
women  in  times  of  dearth,  as  of  less  value  than  their  dogs. 

In  plants  the  same  gradual  process  of  improvement, 
through  the  occasional  preservation  of  the  best  individuals, 
whether  or  not  sufliciently  distinct  to  be  ranked  at  their  first 
apj)earance  as  distinct  varieties,  and  whether  or  not  tvfo 
or  more  species  or  races  have  become  blended  together  by 
crossing,  may  plainly  be  recognised  in  the  increased  size 
and  beauty  which  we  now  see  in  the  varieties  of  the 
heartsease,  rose,  pelargonium,  dahlia,  and  other  plants, 
when  compared  with  the  older  varieties  or  with  their 
parent-stocks.  'No  one  would  ever  expect  to  get  a  first- 
rate  heartsease  or  dahlia  from  the  seed  of  a  wild  plant 
No  one  would  expect  to  raise  a  first-rate  melting  pear 
from  the  seed  of  the  wild  pear,  though  he  might  succeed 
from  a  poor  seedling  growing  wild,  if  it  had  come  from  a 
garden-stock.  The  pear,  though  cultivated  in  classical 
times,  appears,  from  Pliny's  description,  to  have  been  a 
fruit  of  very  inferior  quality.  I  have  seen  great  surprise 
expressed  in  horticultural  works  at  the  wonderful  skill  of 


4-0  UNCONSCIOUS  SELECTION.  [Chap.  L 

gardeners,  in  having  produced  such  splendid  results  from 
such  poor  materials  ;  but  the  art,  I  canot  doubt,  has  been 
simple,  and,  as  far  as  the  final  result  is  concerned,  has 
been  followed  almost  unconsciously.  It  has  consisted  in 
.always  cultivating  the  best  known  variety,  sowing  its 
seeds,  and,  when  a  slightly  better  variety  has  chanced  to 
appear,  selecting  it,  and  so  onwards.  But  the  gardeners 
of  the  classical  period,  who  cultivated  the  best  j)ear  they 
could  procure,  never  thought  what  splendid  fruit  we 
should  eat ;  though  we  owe  our  excellent  fruit,  in  some 
small  degree,  to  their  having  naturally  chosen  and  pre- 
served the  best  varieties  they  could  anywhere  find. 

A  large  amount  of  change  in  our  cultivated  plants, 
thus  slowly  and  unconsciously  accumulated,  explains,  as  I 
believe,  the  well-hnown  fact,  that  in  a  vast  number  of 
cases  we  cannot  recognise,  and  therefore  do  not  know,  the 
wild  parent-stocks  of  the  plants  which  have  been  longest 
cultivated  in  our  flower  and  kitchen  gardens.  If  it  has 
taken  centuries  or  thousands  of  years  to  improve  or 
modify  most  of  our  plants  up  to  their  present  standard 
of  usefulness  to  man,  we  can  understand  how  it  is  that 
neither  Australia,  the  Cape  of  Good  Hope,  nor  any  other 
region  inhabited  by  quite  uncivilised  man,  has  aflbrded  us 
a  single  plant  worth  culture.  It  is  not  that  these  countries, 
so  rich  in  species,  do  not  by  a  strange  chance  possess  the 
aboriginal  stocks  of  any  useful  plants,  but  that  the  native 
plants  have  not  been  improved  by  continued  selection  up 
to  a  standard  of  j)erfection  comparable  with  that  given  to 
the  plants  in  countries  anciently  civilised. 

In  regard  to  the  domestic  animals  kept  by  uncivilised 
man,  it  should  not  be  overlooked  that  they  almost  always 
have  to  struggle  for  their  own  food,  at  least  during  certain 
seasons.  And  in  two  countries  very  difi'erently  circum- 
stanced, individuals  of  the  same  species,  having  slightly 
different  constitutions  or  structure,  would  often  succeed 
better  in  the  one  country  than  in  the  other,  and  thus  by  a 
process  of  "  natural  selection,"  as  will  hereafter  be  more 
fully  explained,  two  sub-breeds  might  be  formed.  This, 
perhaps,  j)artly  explains  what  has  been  remarked  by  some 
authors,  namely,  that  the  varieties  kept  by  savages  have 


Chap  I.]  SELECTION  BY  MAN.  ^^ 

more  of  the  character  of  species  than  the  varieties  kept  in 
civilised  countries. 

On  the  view  here  given  of  the  all-important  part  which 
selection  by  man  has  played,  it  becomes  at  once  obvious, 
how  it  is  that  onr  domestic  races  show  adaptation  in  their 
structure  or  in  their  habits  to  man's  wants  or  fancies. 
We  can,  I  think,  further  understand  the  frequently  ab- 
normal character  of  our  domestic  races,  and  likewise  their 
differences  being  so  great  in  external  characters  and  rela- 
tively so  slight  in  internal  parts  or  organs.  Man  can 
hardly  select,  or  only  with  much  difficulty,  any  deviation 
of  structure  excepting  such  as  is  externally  visible  ;  and 
indeed  he  rarely  cares  for  what  is  internal.  He  can  never 
act  by  selection,  excepting  on  variations  which  are  first 
given  to  him  in  some  slight  degree  by  nature.  JSTo  man 
would  ever  try  to  make  a  fantail,  till  he  saw  a  pigeon  with 
a  tail  developed  in  some  slight  degree  in  an  unusual  man- 
ner, or  a  pouter  till  he  saw  a  pigeon  with  a  crop  of  some- 
what unusual  size  ;  and  the  more  abnormal  or  unusual 
any  character  was  when  it  first  appeared,  the  more  likely 
it  would  be  to  catch  his  attention.  But  to  use  such  an 
expression  as  trying  to  make  a  fantail,  is,  I  have  no  doubt, 
in  most  cases,  utterly  incorrect.  The  man  who  first  select- 
ed a  pigeon  with  a  slightly  larger  tail,  never  dreamed 
what  the  descendants  of  that  pigeon  would  become  through 
long-continued,  partly  unconscious  and  partly  methodical 
selection.  Perhaps  the  parent  bird  of  all  fantails  had 
only  fourteen  tail-feathers  somewhat  expanded,  like  the 
present  Java  fantail,  or  like  individuals  of  other  and  dis- 
tinct breeds,  in  which  as  many  as  seventeen  tail-feathers 
have  been  counted.  Perhaps  the  first  pouter-pigeon  did 
not  inflate  its  crop  much  more  than  the  turbit  now  does 
the  upper  part  of  its  oesophagus, — a  habit  which  is  dis- 
regarded by  all  fanciers,  as  it  is  not  one  of  the  points  of 
the  breed. 

Nor  let  it  be  thought  that  some  great  deviation  of 
structure  would  be  necessary  to  catch  the  fancier's  eye : 
he  perceives  extremely  small  differences,  and  it  is  in 
human  nature  to  value  any  novelty,  however  slight,  in 
one's  own  possession.  ISTor  must  the  value  which  would 
3 


^2  SELECTIOiN'  BY  MAN.  [Chap.  1. 

formerly  be  set  on  any  sliglit  differences  in  the  individnals 
of  tlie  same  species,  be  judged  of  by  the  value  which 
would  now  be  set  on  them,  after  several  breeds  have  once 
fairly  been  established.  Many  slight  differences  might, 
and  indeed  do  now,  arise  amongst  pigeons,  which  are 
rejected  as  faults  or  deviations  from  the  standard  of  per- 
fection of  each  breed.  The  common  goose  has  not  given 
rise  to  any  marked  varieties  ;  hence  the  Thoulouse  and 
the  common  breed,  which  differ  only  in  colour,  that  most 
fleetins:  of  characters,  have  latelv  been  exhibited  as  dis- 
tinct  at  our  poultry-shows. 

I  thmk  these  views  further  explain  ivhat  has  sometimes 
been  noticed — namely,  that  we  know  nothing  about  the 
origin  or  history  of  any  of  our  domestic  breeds.  But,  in 
fact,  a  breed,  like  the  dialect  of  a  language,  can  hardly 
be  said  to  have  had  a  definite  origin.  A  man  preserves 
and  breeds  from  an  individual  with  some  slight  deviation 
of  structure,  or  takes  more  care  than  usual  in  matching 
his  best  animals,  and  thus  improves  them,  and  the  im- 
proved individuals  slowly  spread  in  the  immediate  neigh- 
bourhood. But  as  yet  they  wdll  hardly  have  a  distinct 
name,  and  from  being  only  slightly  valued,  their  history 
will  be  disregarded.  When  further  improved  by  the 
same  slow  and  gradual  process,  they  will  spread  more 
widely,  and  will  get  recognised  as  something  distmct  and 
valuable,  and  will  then  probably  first  receive  a  provincial 
name.  In  semi-civilised  countries,  with  little  free  com- 
munication, the  spreading  and  knowledge  of  any  new  sub- 
breed  will  be  a  slow  process.  As  soon  as  the  points  of 
value  of  the  new  sub-breed  are  once  fullv  acknowledo-ed, 
the  principle,  as  I  have  called  it,  of  unconscious  selection 
will  always  tend, — perhaps  more  at  one  period  than  at 
another,  as  the  breed  rises  or  falls  in  fashion, — perhaps 
more  in  one  district  than  in  another,  according  to  the  state 
of  civilisation  of  the  inhabitants, — slowly  to  add  to  the 
characteristic  features  of  the  breed,  whatever  they  may 
be.  But  the  chance  will  be  infinitely  small  of  any  record 
having  been  preserved  of  such  slow,  varying,  and  insensi- 
ble changes. 

I  m.ust  now  say  a  few  words  on  the  circumstances, 


Chap.  I.J       ClilCUMSTANCES  FAVOURABLE  TO  SELECTION.  ^3 

favourable,  or  the  reverse,  to  man's  power  of  selection. 
A  higli  degree  of  variability  is  obviously  favourable,  as 
freely  giving  tlie  materials  for  selection  to  work  on  ;  not 
that  mere  individual  differences  are  not  amply  sufficient, 
with  extreme  care,  to  allow  of  the  accumulation  of  a  large 
amount  of  modification  in  almost  any  desired  direction. 
But  as  variations  manifestly  useful  or  pleasing  to  man 
appear  only  occasionally,  the  chance  of  their  appearance 
will  be  much  increased  by  a  large  number  of  individuals 
being  kejDt ;  and  hence  this  comes  to  be  of  the  highest 
importance  to  success.  On  this  principle  Marshall  has 
remarked,  with  respect  to  sheep  of  parts  of  Yorkshire, 
that  "  as  they  generally  belong  to  poor  people,  and  are 
niostlj  171  S7nall  lots,  thej  neyer  can  be  improved."  On 
the  other  hand,  nurserymen,  from  raising  large  stocks 
of  the  same  plants,  are  generally  far  more  successful  than 
amateurs  in  getting  new  and  valuable  varieties.  The  keep- 
ing of  a  large  number  of  individuals  of  a  species  in  any 
country  requires  that  the  species  should  be  placed  under 
favourable  conditions  of  life,  so  as  to  breed  freely  in  that 
country.  When  the  individuals  of  any  species  are  scanty, 
all  the  individuals,  whateyer  their  quality  may  be,  will  gen- 
erally be  allowed  to  breed,  and  this  will  efi'ectually  prevent 
selection.  But  probably  the  most  important  point  of  all 
is,  that  the  animal  or  plant  should  be  so  highly  useful  to 
man,  or  so  much  valued  by  him,  that  the  closest  attention 
should  be  paid  to  even  the  slightest  deviation  in  the  qual- 
ities or  structure  of  each  individual.  Unless  such  attention 
be  paid  nothing  can  be  eflected.  I  have  seen  it  graveH 
remarked,  that  it  was  most  fortunate  that  the  strawberry 
began  to  vary  just  when  gardeners  began  to  attend  closely 
to  this  plant.  'No  doubt  the  strawberry  had  always  varied 
since  it  was  cultivated,  but  the  slight  varieties  had  been 
neglected.  As  soon,  however,  as  gardeners  picked  out 
individual  plants  with  slightly  larger,  earlier,  or  better 
fruit,  and  raised  seedlings  from  them,  and  again  picked 
out  tlie  best  seedlings  and  bred  from  them,  then,  there 
appeared  (aided  by  some  crossing  witJi  distinct  s]3ecies) 
those  many  admirable  varieties  of  the  strawberry  which 
have  been  raised  during  the  last  thirty  or  forty  years. 


^  SUMMARY  ON  VARIATION  [Chap.  I. 

In  the  case  of  animals  with  separate  sexes,  facility 
in  preventing  crosses  is  an  important  element  of  success 
in  the  formation  of  new  races, — at  least  in  a  country 
which  is  already  stocked  with  other  races.  Li  this  respect 
enclosure  of  the  land  plays  a  part.  Wandering  savages 
or  the  inhabitants  of  open  plains  rarely  possess  more  than 
one  breed  of  the  same  species.  Pigeons  can  be  mated  for 
life,  and  this  is  a  great  convenience  to  the  fancier,  for  thus 
many  races  may  be  kept  true,  though  mingled  in  the 
same  aviary  ;  and  this  circumstance  must  have  largely 
favoured  the  improvement  and  formation  of  new  breeds. 
Pigeons,  I  may  add,  can  be  propagated  in  great  numbers 
and  at  a  very  quick  rate,  and  inferior  birds  may  be  freely 
rejected,  as  when  killed  they  serve  for  food.  On  the 
other  hand,  cats,  from  their  nocturnal  rambling  habits, 
cannot  be  matched,  and,  although  so  much  valued  by 
women  and  children,  we  hardly  ever  see  a  distinct  breed 
kept  up  ;  such  breeds  as  we  do  sometimes  see  are  almost 
always  imported  from  some  other  country,  often  from 
islands.  Although  I  do  not  doubt  that  some  domestic 
animals  vary  less  than  others,  yet  the  rarity  or  absence  of 
distinct  breeds  of  the  cat,  the  donkey,  peacock,  goose, 
&c.,  may  be  attributed  in  main  part  to  selection  not  hav- 
ing been  brought  into  play  :  in  cats,  from  the  difficulty  in 
pairing  them  ;  in  donkeys,  from  only  a  few  being  kept 
by  poor  people,  and  little  attention  paid  to  their  breed- 
ing ;  in  peacocks,  from  not  being  very  easily  reared, 
and  a  large  stock  not  kept ;  in  geese,  from  being  valuable 
only  for  two  purposes,  food  and  feathers,  and  more  es- 
pecially from  no  pleasure  having  been  felt  in  the  display 
of  distinct  breeds. 

To  sum  up  on  the  origin  of  our  Domestic  Paces  of  ani- 
mals and  plants.  I  believe  that  the  conditions  of  life, 
from  their  action  on  the  reproductive  system,  are  so  far 
of  the  highest  importanc'e  as  causing  variability.  I  do 
not  believe  that  variability  is  an  inherent  and  necessary 
contingency,  under  all  circumstances,  with  all  organic 
beings,  as  some  authors  have  thought.  The  effects  of 
variability  are  modified  by  various  degrees  of  inheritance 
and  of  reversion.     Yariability  is  governed  by  many  un- 


Chap.  1.]  UNDER  DOMESTICATION.  45 

known  laws,  more  especially  by  that  of  correlation  of 
growth.  Something  may  be  attributed  to  the  direct  action 
of  the  conditions  of  life.  Something  must  be  attributed 
to  use  and  disuse.  The  final  result  is  thus  rendered  in- 
finitely complex.  In  some  cases  I  do  not  doubt  that  the 
intercrossing  of  species,  aboriginally  distinct,  has  played 
an  important  part  in  the  origin  of  our  domestic  produc- 
tions. When  in  any  country  several  domestic  breeds  have 
once  been  established,  their  occasional  intercrossing,  with 
the  aid  of  selection,  has,  no  doubt,  largely  aided  in  the 
formation  of  new  sub-breeds ;  but  the  importance  of  the 
crossing  of  varieties,  has,  I  believe,  been  greatly  exagge- 
rated, both  in  regard  to  animals  and  to  those  plants  which 
are  propagated  by  seed.  In  plants  which  are  temporarily 
propagated  by  cuttings,  buds,  &c.,  the  importance  of  the 
crossing  both  of  distinct  species  and  of  varieties  is  im- 
mense ;  for  the  cultivator  here  quite  disregards  the  ex- 
treme variability  both  of  hybrids  and  mongrels,  and  the 
frequent  sterility  of  hybrids  ;  but  the  cases  of  plants  not 
propagated  by  seed  are  of  little  importance  to  us,  for 
their  endurance  is  only  temporary.  Over  all  these  causes 
of  Change  I  am  convinced  that  the  accumulative  action 
of  Selection,  whether  applied  methodically  and  more 
quickly,  or  unconsciously  and  more  slowly,  but  more 
efficiently,  is  by  far  the  predominant  Power. 


4.g  VARIATION  UNDER  NATURE.  [Chap.  11. 


CHAPTEK   II. 

VARIATION  UNDER  NATURE. 

Variability— Individual  differences— Doubtful  species— "Wide  ranging^  mucli  diffused, 
and  common  species  vary  most— Species  of  the  larger  genera  in  any  country  vary 
more  than  the  species  of  the  smaller  genera — Many  of  the  species  of  the  larger 
genera" resemble  varieties  in  being  very  closely,  but  unequally,  related  to  each 
other,  and  in  having  restricted  ranges 

Before  applying  tlie  principles  arrived  at  in  tlie  last 
chapter  to  organic  beings  in  a  state  of  nature,  we  must 
briefly  discuss  wliether  these  latter  are  subject  to  any 
variation.  To  treat  this  subject  at  all  properly,  a  long 
catalogue  of  dry  facts  should  be  given  ;  but  these  I  shall 
reserve  for  my  future  work.  Nor  shall  I  here  discuss  the 
various  definitions  which  have  been  given  of  the  term 
species.  ISTo  one  definition  has  as  yet  satisfied  all  natural- 
ists ;  yet  every  naturalist  knows  vaguely  what  he  means 
when  he  speaks  of  a  species.  Generally  the  term  includes 
the  unknown  element  of  a  distinct  act  of  creation.  The 
term  "  variety  "  is  almost  equally  difficult  to  define  ;  but 
here  community  of  descent  is  almost  universally  implied, 
though  it  can  rarely  be  proved.  We  have  also  what  are 
called  monstrosities  ;  but  they  graduate  into  varieties. 
By  a  monstrosity  I  presume  is  meant  some  considerable 
deviation  of  structure  in  one  part,  either  injurious  to  or  not 
useful  to  the  species,  and  not  generally  propagated.  Some 
authors  use  the  term  "  variation"  in  a  technical  sense,  as 
implying  a  modification  directly  due  to  the  physical  con- 
ditions of  life  ;  and  "  variations  "  in  this  sense,  are  sup- 
posed not  to  be  inherited  :  but  who  can  say  that  the 
dwarfed  condition  of  shells  in  the  brackish  waters  of  the 
Baltic,  or  dwarfed  plants  on  Alpine  summits,  or  the 
thicker  fur  of  an  animal  from  far  northwards,  would  not 


OuAi-.  11.]  VARIATION  UNIjER  NATURE.  AfT 

ill  some  cases  be  inherited  for  at  least  some  few  geneia- 
tions  ?  and  in  tliis  case  I  presume  tliat  the  form  would  be 
called  a  variety. 

Again,  we  have  many  slight  differences  which  may 
be  called  individual  differences,  such  as  are  known  fre- 
quently to  appear  in  the  offspring  from  the  same  parents, 
or  which  may  be  presumed  to  have  thus  arisen,  from  be- 
ing frequently  observed  in  the  individuals  of  the  same 
species  inhabiting  the  same  confined  locality.  ISTo  one 
supposes  that  all  the  individuals  of  the  same  species  are 
cast  in  the  very  same  mould.  These  individual  differences 
are  highly  important  for  us,  as  they  afford  materials  for 
natural  selection  to  accumulate,  in  the  same  manner  as 
man  can  accumulate  in  any  given  direction  individual 
differences  in  his  domesticated  productions.  These  indi- 
vidual differences  generally  affect  what  naturalists  con- 
sider unimportant  parts  ;  but  I  could  show  by  a  long  cat- 
alogue of  facts,  that  parts  which  must  be  called  important, 
whether  viewed  under  a  physiological  or  classificatory 
point  of  view,  sometimes  vary  in  the  individuals  of  the 
same  species.  I  am  convinced  that  the  most  experienced 
naturalist  would  be  surprised  at  the  number  of  the  cases 
of  variability,  even  in  important  parts  of  structure,  which 
he  could  collect  on  good  authority,  as  I  have  collected, 
dm-ing  a  course  of  years.  It  should  be  remembered  that 
systematists  are  far  from  pleased  at  finding  variability  in 
important  characters,  and  that  there  are  not  many  men 
who  will  laboriously  examine  internal  and  important  or- 
gans, and  compare  them  in  many  specimens  of  the  same 
species.  I  should  never  have  expected  that  the  branch- 
ing of  the  main  nerves  close  to  the  great  central  ganglion 
of  an  insect  would  have  been  variable  in  the  same  species ; 
I  should  have  expected  that  changes  of  this  nature  could 
have  been  effected  only  by  slow  degrees  :  yet  quite  re- 
cently Mr.  Lubbock  has  shown  a  degree  of  variability  in 
these  main  nerves  in  Coccus,  which  may  almost  be  com- 
pared to  the  irregular  branching  of  the  stem  of  a  tree. 
This  philosophical  naturalist,  I  may  add,  has  also  quite 
recently  shown  that  the  muscles  in  the  larvge  of  certain 
insects  are  very  far  from  uniform.     Authors  sometimes 


43  VARIATION  UNDER  NATURE.  [Chap.  II. 

argue  in  a  circle  when  tliey  state  that  important  organs 
never  vary  ;  for  these  same  authors  practically  rank  that 
character  as  important  (as  some  few  naturalists  have  hon- 
estly confessed)  vdiich  does  not  vary  ;  and,  under  this 
point  of  viev^,  no  instance  of  an  important  part  varying 
will  ever  be  found  :  but  under  any  other  point  of  view 
many  instances  assuredly  can  be  given. 

There  is  one  point  connected  with  individual  differ- 
ences, which  seems  to  me  extremely  perplexing :  I  refer 
to  those  genera  which  have  sometimes  been  called  "  pro- 
tean "  or  "  polymorphic,"  in  which  the  species  present  an 
inordinate  amount  of  variation  ;  and  hardly  two  natural- 
ists can  agree  which  forms  to  rank  as  species,  and  which 
as  varieties.  We  may  instance  Kubus,  Rosa,  and  Hiera- 
cium  amongst  plants,  several  genera  of  insects,  and  sev- 
eral genera  of  Erachiopod  shells.  In  most  polymorphic 
genera  some  of  the  species  have  fixed  and  definite  char- 
acters. Genera  which  are  polymorphic  in  one  country 
seem  to  be,  with  some  few  exceptions,  polymorphic  in 
other  countries,  and  likewise,  judging  from  Brachiopod 
shells,  at  former  periods  of  time.  These  facts  seem  to  be 
very  perplexing,  for  they  seem  to  show  that  this  kind  of 
variability  is  independent  of  the  conditions  of  life.  I  am 
inclined  to  suspect  that  we  see  in  these  polymorphic  gen- 
era variations  in  points  of  structure  which  are  of  no 
service  or  disservice  to  the  species,  and  which  conse- 
quently have  not  been  seized  on  and  rendered  definite  by 
natural  selection,  as  hereafter  will  be  explained. 

Those  forms  which  possess  in  some  considerable  de- 
gree the  character  of  species,  but  which  are  so  closely 
similar  to  some  other  forms,  or  are  so  closely  linked  to 
them  by  intermediate  gradations,  that  naturalists  do  not 
like  to  rank  them  as  distinct  species,  are  in  several  re- 
spects the  most  impoj-tant  for  us.  We  have  every  reason 
to  believe  that  many  of  these  doubtful  and  closely-allied 
forms  have  permanently  retained  their  characters  in  their 
own  country  for  a  long  time ;  for  as  long,  as  far  as  we 
know,  as  have  good  and  true  species.  Practically,  when 
a  naturalist  can  unite  two  forms  together  by  others  hav- 
ing intermediate  characters,  he  treats  the  one  as  a  variety 


Chap.  II.]  DOUBTFUL  SPECIES. 


49 


of  the  other,  ranking  the  most  common,  but  sometimes 
the  one  first  described,  as  the  species,  and  the  other  as 
the  variety.  But  cases  of  great  difiiculty,  which  I  will 
not  here  enumerate,  sometimes  occur  in  deciding  whether 
or  not  to  rank  one  form  as  a  variety  of  another,  even 
when  they  are  closely  connected  by  intermediate  links ; 
nor  will  the  commonly-assumed  hybrid  nature  of  the  in- 
termediate links  always  remove  the  difficulty.  In  very 
many  cases,  however,  one  form  is  ranked  as  a  variety  of 
another,  not  because  the  intermediate  links  have  actually 
been  found,  but  because  analogy  leads  the  observer  to 
suppose  either  that  they  do  now  somewhere  exist,  or  may 
formerly  have  existed ;  and  here  a  wide  door  for  the 
entry  of  doubt  and  conjecture  is  opened. 

Hence,  in  determining  whether  a  form  should  be  rank- 
ed as  a  species  or  a  variety,  the  opinion  of  naturalists  hav- 
ing sound  judgment  and  wide  experience  seems  the  only 
guide  to  follow.  We  must,  however,  in  many  cases,  de- 
cide by  a  majority  of  naturalists,  for  few  well-marked  and 
well-known  varieties  can  be  named  which  have  not  been 
ranked  as  species  by  at  least  some  competent  judges. 

That  varieties  of  this  doubtful  nature  are  far  from  un- 
common cannot  be  disputed.  Compare  the  several  floras 
of  Great  Britain,  of  France  or  of  the  United  States,  drawn 
up  by  diflerent  botanists,  and  see  what  a  surprising  num- 
ber of  forms  have  been  ranked  by  one  botanist  as  good 
species,  and  by  another  as  mere  varieties.  Mr.  H.  C. 
AVatson,  to  whom  I  lie  under  deep  obligation  for  assist- 
ance of  all  kinds,  has  marked  for  me  182  British  plants, 
which  are  generally  considered  as  varieties,  but  which 
have  all  been  ranked  by  botanists  as  species  ;  and  in 
making  this  list  he  has  omitted  many  trifling  varieties, 
but  which  nevertheless  have  been  ranked  by  some  bota- 
nists as  species,  and  he  has  entirely  omitted  several  highly 
polymorphic  genera.  Under  genera,  including  the  most 
polymorphic  forms,  Mr.  Babington  gives  251  species, 
whereas  Mr.  Bentham  gives  only  112, — a  difl'erence  of 
139  doubtful  forms  !  Amongst  animals  which  unite  for 
each  birth,  and  which  are  highly  locomotive,  doubtful 
forms,  ranked  by  one  zoologist  as  a  species  and  by  another 
3* 


50  DOUBTFUL  SPECIES.  [Chap,  t' 

as  a  variety,  can  rarely  be  found  witHn  the  same  conn 
try,  but  are  common  in  separate  areas.  How  many  of 
those  birds  and  insects  in  North  America  and  Europe, 
which  differ  very  slightly  from  each  other,  have  been 
ranked  by  one  eminent  naturalist  as  undoubted  species, 
and  by  another  as  varieties,  or,  as  they  are  often  called, 
as  geographical  races !  Many  years  ago,  when  compar- 
ing, and  seeing  others  compare,  the  birds  from  the  sepa- 
rate islands  of  the  Galapagos  ArchijDclago,  both  one  with 
another,  and  with  those  from  the  American  mainland,  I 
was  much  struck  how  entirely  vague  and  arbitrary  is  the 
distinction  between  species  and  varieties.  On  the  islets 
of  the  little  Madeira  group  there  are  many  insects  which 
are  characterised  as  varieties  in  Mr.  AVollaston's  admirable 
work,  but  which  it  cannot  be  doubted  would  be  ranked 
as  distinct  species  by  many  entomologists.  Even  Ireland 
has  a  few  animals,  now  generally  regarded  as  varieties, 
but  which  have  been  ranked  as  species  by  some  zoologists. 
Several  most  experienced  ornithologists  consider  our  Brit- 
ish red  grouse  as  only  a  strongly-marked  race  of  a  Nor- 
wegian species,  whereas  the  greater  number  rank  it  as  an 
undoubted  species  peculiar  to  Great  Britain.  A  wide 
distance  between  the  homes  of  two  doubtful  forms  leads 
many  naturalists  to  rank  both  as  distinct  species;  but 
what  distance,  it  has  been  well  asked,  will  suffice  ?  if  that 
between  America  and  Europe  is  ample,  will  that  between 
the  Continent  and  the  Azores,  or  Madeira,  or  the  Cana- 
ries, or  Ireland,  be  sufficient  ?  It  must  be  admitted  that 
many  forms,  considered  by  highly  competent  judges  as 
varieties,  have  so  perfectly  the  character  of  species  that 
they  are  ranked  by  other  highly  competent  judges  as  good 
and  true  species.  But  to  discuss  whether  they  are  rightly 
called  species  or  varieties,  before  any  definition  of  these 
terms  has  been  generally  accepted,  is  vainly  to  beat  the 
air. 

Many  of  the  cases  of  strongly-marked  varieties  or 
doubtful  s]Decies  well  deserve  consideration ;  for  several 
interesting  lines  of  argument,  from  geographical  distribu- 
tion, analogical  variation,  hybridism,  (fee,  have  been 
brought  to  bear  on  the  attempt  to  determine  their  rank. 


Chap.  II.]  DOUBTFUL  SPECIES.  g-j^ 

I  will  here  give  only  a  single  instance, — the  well-known 
one  of  the  primrose  and  cowslip,  or  Primula  vulgaris 
and  veris.  These  plants  differ  considerably  in  appearance ; 
they  have  a  different  flavour  and  emit  a  different  odour ; 
they  flower  at  slightly  different  periods  ;  they  grow  in 
somewhat  different  stations ;  they  ascend  mountains  to 
different  heights  ;  they  have  different  geographical  ranges  ; 
and  lastly,  according  to  very  numerous  experiments  made 
during  several  years  by  that  most  careful  observer  Gart- 
ner, they  can  be  crossed  only  with  much  difficulty.  We 
could  hardly  wish  for  better  evidence  of  the  two  forms 
being  specifically  distinct.  On  the  other  hand,  they  are 
united  by  many  intermediate  links,  and  it  is  very  doubt- 
ful whether  these  links  arc  hybrids ;  and  there  is,  as  it 
seems  to  me,  an  overwhelming  amount  of  experimental 
evidence,  showing  that  they  descend  from  common 
parents,  and  consequently  must  be  ranked  as  varieties. 

Close  investigation,  in  most  cases,  will  bring  natural- 
ists to  an  agreement  how  to  rank  doubtful  forms.  Yet  it 
must  be  confessed,  that  it  is  in  the  best-known  countries 
that  we  find  the  greatest  number  of  forms  of  doubtful 
value.  I  have  been  struck  with  the  fact,  that  if /any 
animal  or  plant  in  a  state  of  nature  be  highly  useful  to 
man,  or  from  any  cause  closely  attract  his  attention,  va- 
rieties of  it  will  almost  universally  be  found  recorded. 
These  varieties,  moreover,  will  be  often  ranked  by  some 
authors  as  species.  Look  at  the  common  oak,  how  closely 
it  has  been  studied ;  yet  a  German  author  makes  more 
than  a  dozen  species  out  of  forms,  w^hich  are  very  gener- 
ally considered  as  varieties  ;  and  in  this  country  the  high- 
est botanical  authorities  and  practical  men  can  be  quoted 
to  show  that  the  sessile  and  pedunculated  oaks  are  either 
good  and  distinct  species  or  mere  varieties. 

When  a  young  naturalist  commences  the  study  of  a 
group  of  organisms  quite  unknown  to  him,  he  is  at  first 
much  perplexed  to  determine  what  differences  to  consider 
as  specific,  and  what  as  varieties ;  for  he  knows  nothing 
of  the  amount  and  kind  of  variation  to  which  the  group 
is  subject;  and  this  shows,  at  least,  how  very  generally 
there  is  some  variation.     But  if  he  confine  his  attention 


52  DOUBTFUL  SPECIES.  [Chap.  II. 

to  one  class  within  one  country,  lie  will  soon  make  up  his 
mind  how  to  rank  most  of  the  doubtful  forms.  His  gen- 
eral tendency  will  be  to  make  many  species,  for  he  will  be- 
come impressed,  just  like  the  pigeon  or  poultry  fancier  be- 
fore alluded  to,  with  the  amount  of  difference  in  the  forms 
which  he  is  continually  studying ;  and  he  has  little  gen- 
eral knowledge  of  analogical  variation  in  other  groups 
and  in  other  countries,  by  which  to  correct  his  first  im- 
pressions. As  he  extends  the  range  of  his  observations, 
he  will  meet  with  more  cases  of  difficulty  ;  for  he  will  en- 
counter a  greater  number  of  closely-allied  forms.  But  if  his 
observations  be  widely  extended,  he  will  in  the  end  gen- 
erally be  enabled  to  make  up  his  own  mind  which  to  call 
varieties  and  which  species  ;  but  he  will  succeed  in  this 
at  the  expense  of  admitting  much  variation, — and  the 
truth  of  this  admission  will  often  be  disputed  by  other 
naturalists.  "When,  moreover,  he  comes  to  study  allied 
forms  brought  from  countries  not  now  continuous,  in 
which  case  he  can  hardly  hope  to  find  the  intermediate 
links  between  his  doubtful  forms,  he  will  have  to  trust 
almost  entii'ely  to  analogy,  and  his  difficulties  will  rise  to 
a  climax. 

Certainly  no  clear  line  of  demarcation  has  as  yet  been 
drawn  between  species  and  sub-species — that  is,  the  forms 
which  in  the  opinion  of  some  naturalists  come  very  near 
to,  but  do  not  quite  arrive  at  the  rank  of  species  ;  or, 
again,  between  sub-species  and  well-marked  varieties,  or 
between  lesser  varieties  and  individual  differences.  These 
differences  blend  into  each  other  in  an  insensible  series ; 
and  a  series  impresses  the  mind  with  the  idea  of  an  actual 
passage. 

Hence  I  look  at  individual  differences,  though  of  small 
interest  to  the  systematist,  as  of  high  importance  for  us, 
as  being  the  first  step  towards  such  slight  varieties  as  are 
barely  thought  worth  recording  in  works  on  natural  liis- 
tory.  And  I  look  at  varieties  which  are  in  any  degree 
more  distinct  and  permanent,  as  steps  leading  to  more 
strongly  marked  and  more  permanent  varieties ;  and  at 
these  latter,  as  leading  to  sub-species,  and  to  species.  The 
passage  from  one  stage  of  difference  to  another  and  higher 


Chap.  II.l  VARIETIES  GRADUATE  INTO  SPECIES.  53 

stage  may  be,  in  some  cases,  due  merely  to  the  long-con- 
tinued action  of  different  physical  conditions  in  two  dif- 
ferent regions ;  but  I  have  not  much  faith  in  this  view ; 
and  I  attribute  the  passage  of  a  variety,  from  a  state  in 
which  it  differs  very  slightly  from  its  parent  to  one  in 
which  it  differs  more,  to  the  action  of  natural  selection  in 
accumulating  (as  will  hereafter  be  more  fully  explained) 
differences  of  structure  in  certain  definite  directions. 
Hence  I  believe  a  w^ell-marked  variety  may  be  justly 
called  an  incipient  species ;  but  whether  this  belief  be 
justifiable  must  be  judged  of  by  the  general  weight  of 
the  several  facts  and  views  given  throughout  this  work. 

It  need  not  be  supposed  that  all  varieties  or  incipient 
species  necessarily  attain  the  rank  of  species.  They  may 
whilst  in  this  incipient  state  become  extinct,  or  they  may 
endure  as  varieties  for  very  long  periods,  as  has  been 
shown  to  be  the  case  by  Mr.  Wollaston  with  the  varieties 
of  certain  fossil  land-shells  in  Madeira.  If  a  variety  were 
to  flourish  so  as  to  exceed  in  numbers  the  parent  species, 
it  would  then  rank  as  the  species,  and  the  species  as  the 
variety  ;  or  it  might  come  to  supplant  and  exterminate 
the  parent  species  ;  or  both  might  co-exist,  and  both  rank 
as  independent  species.  But  we  shall  hereafter  have  to 
return  to  this  subject. 

From  these  remarks  it  will  be  seen  that  I  look  at  the 
terai  species,  as  one  arbitrarily  given  for  the  sake  of  con- 
venience to  a  set  of  individuals  closely  resembling  each 
other,  and  that  it  does  not  essentially  differ  from  the  term 
variety,  which  is  given  to  less  distinct  and  more  fluctuat- 
ing forms.  The  term  variety,  again,  in  comparison  with 
mere  individual  diA'crences,  is  also  applied  arbitrarily, 
and  for  mere  convenience  sake. 

Guided  by  theoretical  considerations,  I  thought  that 
some  interesting  results  might  be  obtained  in  regard  to 
the  nature  and  relations  of  the  species  which  vary  most, 
by  tabulating  all  the  varieties  in  several  well-worked 
floras.  At  first  this  seemed  a  simple  task ;  but  Mr.  H. 
C.  Watson,  to  whom  I  am  much  indebted  for  valuable 
advice  and  assistance  on  this  subject,  soon  convinced  me 
that  there  were  many  difficulties,  as  did  subsequently  Dr. 


54  DOMINANT  SPECIES  VARY  MOST.  [Chap.  II. 

Hooker,  even  in  stronger  terms.  I  shall  reserve  for  my 
future  work  tlie  discussion  of  these  difficulties,  and  the 
tables  themselves  of  the  proportional  numbers  of  the  vary- 
ing species.  Dr.  Hooker  permits  me  to  add,  that  after 
having  carefully  read  my  manuscript,  and  examined  the 
tables,  he  thinks  that  the  following  statements  are  fairly 
well  established.  The  whole  subject,  however,  treated  as 
it  necessarily  here  is  with  much  brevity,  is  rather  per- 
plexing, and  allusions  cannot  be  avoided  to  the  "  struggle 
for  existence,"  "  divergence  of  character,"  and  other  ques- 
tions, hereafter  to  be  discussed. 

Al23h.  De  CandoUe  and  others  have  shov/n  that  plants 
which  have  very  wide  ranges  generally  present  varieties ; 
and  this  might  have  been  expected,  as  they  become  ex- 
posed to  diverse  physical  conditions,  and  as  they  come 
into  competition  (which,  as  we  shall  hereafter  see,  is  a  far 
more  important  cii'cumstance)  with  different  sets  of  or- 
ganic beings.  But  my  tables  further  show  that,  in  any 
limited  country,  the  species  which  are  most  common,  that 
is,  abound  most  in  individuals,  and  the  species  which  are 
most  widely  diffused  within  their  own  country  (and  this 
is  a  different  consideration  from  wide  range,  and  to  a  cer- 
tain extent  from  commonness),  often  give  rise  to  varieties 
sufficiently  well-marked  to  have  been  recorded  in  botani- 
cal works.  Hence  it  is  the  most  flourishing,  or,  as  they 
may  be  called,  the  dominant  species, — those  which  range 
widely  over  the  world,  are  the  most  diffused  in  their  own 
country,  and  are  the  most  numerous  in  individuals, — 
whicli  oftenest  produce  well-marked  varieties,  or,  as  I  con- 
sider them,  incipient  species.  And  this,  perhaps,  might 
have  been  anticij^ated  ;  for,  as  varieties,  in  order  to  be- 
come in  any  degree  permanent,  necessarily  have  to  strug- 
gle with  the  other  inhabitants  of  the  country,  tlie  species 
which  are  already  dominant  will  be  the  most  likely  to 
yield  offspring  which,  though  in  some  slight  degree  modi- 
fied, will  still  inherit  those  advantages  that  enabled  their 
parents  to  become  dominant  over  their  compatriots. 

If  the  plants  inhabiting  a  country  and  described  in 
any  Flora  be  divided  into  two  equal  masses,  all  those  in 
the  larger  genera  being  placed  on  one  side,  and  all  those 


Chap    II.]  SPECIES  OF  LARGE  GENERA  VARIABLE.  55 

in  the  smaller  genera  on  tlie  other  side,  a  somewhat  larger 
number  of  the  very  common  and  mnch  diffused  or  domi- 
nant species  will  be  found  on  the  side  of  the  larger  genera. 
This,  again,  might  have  been  anticipated  ;  for  the  mere 
fact  of  many  species  of  the  same  genus  inhabiting  any 
country,  shows  that  there  is  something  in  the  organic  or 
inorganic  conditions  of  that  country  favourable  to  the 
genus  ;  and,  consequently,  we  might  have  expected  to 
have  found  in  the  larger  genera,  or  those  including  many 
species,  a  large  proportional  number  of  dominant  species. 
But  so  many  causes  tend  to  obscure  this  result,  that  I  am 
surprised  that  my  tables  show  even  a  small  majority  on 
the  side  of  the  larger  genera.  I  will  here  allude  to  only 
two  causes  of  obscurity.  Fresh-water  and  salt-loving 
plants  have  generally  very  wide  ranges  and  are  much 
diffused,  but  this  seems  to  he  connected  with  the  nature 
of  the  stations  inhabited  by  them,  and  has  little  or  no  re- 
lation to  the  size  of  the  genera  to  which  the  species 
belong.  Again,  plants  low  in  the  scale  of  organisation 
are  generally  much  more  widely  diffused  than  plants 
higher  in  the  scale ;  and  here  again  there  is  no  close  rela- 
tion to  the  size  of  the  genera.  The  cause  of  lowly-organ- 
ised plants  ranging  widely  will  be  discussed  in  our  chap- 
ter on  geographical  distribution. 

From  looking  at  species  as  only  strongly-marked  and 
well-defined  varieties,  I  was  led  to  anticipate  that  the 
species  of  the  larger  genera  in  each  country  would  oftener 
present  varieties,  than  the  species  of  the  smaller  genera  ; 
for  wherever  many  closely  related  species  {i.  e.  species  of 
the  same  genus)  have  been  formed,  many  varieties  or  in- 
cipient species  ought,  as  a  general  rule,  to  be  now  form- 
ing. Where  many  large  trees  grow,  we  expect  to  find 
saplings.  Where  many  species  of  a  genus  have  been 
formed  through  variation,  circumstances  have  been  favour- 
able for  variation ;  and  hence  we  might  expect  that  the 
circumstances  would  generally  be  still  favourable  to  vari- 
ation. On  the  other  hand,  if  we  look  at  each  species  as 
a  special  act  of  creation,  there  is  no  apparent  reason  why 
more  varieties  should  occur  in  a  group  having  many  spe- 
cies, than  in  one  having  few. 


56  SPECIES  OF  LARGE  GENERA  [Chap.  II. 

To  test  the  truth  of  this  anticipation  I  have  arranged 
the  plants  of  twelve  countries,  and  the  coleopterous  in 
sects  of  two  districts,  into  two  nearly  equal  masses,  the 
species  of  the  larger  genera  on  one  side,  and  those  of  the 
smaller  genera  on  the  other  side,  and  it  has  invariably 
proved  to  be  the  case  that  a  large  projDortion  of  the  spe- 
cies on  the  side  of  the  larger  genera  present  varieties, 
than  on  the  side  of  the  smaller  genera.  Moreover,  the 
species  of  the  large  genera  which  present  any  varieties, 
invariably  present  a  larger  average  number  of  varieties 
than  do  the  species  of  the  small  genera.  Both  these  re- 
sults follow  when  another  division  is  made,  and  when  all 
the  smallest  genera,  with  from  only  one  to  four  species, 
are  absolutely  excluded  from  the  tables.  Tliese  facts  are 
of  plain  signification  on  the  view  that  species  are  only 
strongly  marked  and  permanent  varieties  ;  for  wherever 
many  species  of  the  same  genus  have  been  formed,  or 
w^here,  if  we  may  use  the  expression,  the  manufactory  of 
species  has  been  active,  we  ought  generally  to  find  the 
manufactory  still  in  action,  more  especially  as  we  have 
every  reason  to  believe  the  process  of  manufacturing  new 
species  to  be  a  slow  one.  And  this  certainly  is  the  case, 
if  varieties  be  looked  at  as  incipient  species  ;  for  my  tables 
clearly  show  as  a  general  rule  that,  wherever  many  spe- 
cies of  a  genus  have  been  formed,  the  species  of  that 
genus  present  a  number  of  varieties,  that  is,  of  incipient 
species,  beyond  the  average.  It  is  not  that  all  large 
genera  are  now  varying  much,  and  are  thus  increasing 
in  the  number  of  their  species,  or  that  no  small  genera 
are  now  varying  and  increasing ;  for  if  this  had  been  so, 
it  would  have  been  fatal  to  my  theory ;  inasmuch  as 
geology  plainly  tells  us  that  small  genera  have  in  the 
lapse  of  time  often  increased  greatly  in  size ;  and  that 
large  genera  have  often  come  to  their  maxima,  declined, 
and  disappeared.  All  that  we  want  to  show  is,  that  where 
many  species  of  a  genus  have  been  formed,  on  an  average 
many  are  still  forming  ;  and  this  holds  good. 

There  are  other  relations  between  the  species  of  large 
genera  and  their  recorded  varieties  which  deserve  notice. 
\Ye  have  seen  that  there  is  no  infallible  criterion  by  which 


Chap    II.l  RESEMBLE  VARIETIES.  5';^ 

to  distinguish  species  and  well-marked  varieties ;  and  in 
those  cases  in  which  intermediate  links  have  not  been 
found  between  doubtful  forms,  naturalists  are  compelled 
to  come  to  a  determination  by  the  amount  of  difference 
between  them,  judging  by  analogy  whether  or  not  the 
amount  suffices  to  raise  one  or  both  to  the  rank  of  species. 
Hence  the  amount  of  difference  is  one  very  important 
criterion  in  settling  whether  two  forms  should  be  ranked 
as  species  or  varieties.  Now  Fries  has  remarked  in  re- 
gard to  plants,  and  Westwood  in  regard  to  insects,  that 
in  large  genera  the  amount  of  difference  between  the  spe- 
cies is  often  exceedingly  small.  I  have  endeavoured  to 
test  this  numerically  by  averages,  and,  as  far  as  my  im- 
perfect results  go,  they  always  confirm  the  view.  I  have 
also  consulted  some  sagacious  and  most  experienced  ob- 
servers, and,  after  deliberation,  they  concur  in  this  view. 
In  this  respect,  therefore,  the  species  of  the  larger  genera 
resemble  varieties,  more  than  do  the  species  of  the  smaller 
genera.  Or  the  case  may  be  put  in  another  way,  and  it 
may  be  said,  that  in  the  larger  genera,  in  which  a  num- 
ber of  varieties  or  incipient  species  greater  than  the  aver- 
age are  now  manufacturing,  many  of  the  species  already 
manufactured  still  to  a  certain  extent  resemble  varieties, 
for  they  differ  from  each  other  by  a  less  than  usual 
amount  of  difference. 

Moreover,  the  species  of  the  larger  genera  are  related 
to  each  other,  in  the  same  manner  as  the  varieties  of  any 
one  species  are  related  to  each  other.  No  naturalist  pre- 
tends that  all  the  species  of  a  genus  are  equally  distinct 
from  each  other ;  they  may  generally  be  divided  into  sub- 
genera, or  sections,  or  lesser  groups.  As  Fries  has  well 
remarked,  little  groups  of  species  are  generally  clustered 
like  satellites  around  certain  other  species.  And  what  are 
varieties  but  groups  of  forms,  unequally  related  to  each 
other,  and  clustered  round  certain  forms  ? — -that  is,  round 
their  parent-species  ?  Undoubtedly  there  is  one  most  im- 
portant point  of  difference  between  varieties  and  species  ; 
namely,  that  the  amount  of  difference  between  varieties, 
when  compared  with  each  other  or  with  their  parent- 
species,  is  much  less  than  that  between  the  species  of  the 


gg  SPECIES  OF  LARGE  GENERA  [Chap.  II. 

same  genus.  But  when  we  come  to  discuss  the  principle, 
as  I  call  it,  of  Divergence  of  Character,  we  shall  see  how 
this  may  be  explained,  and  how  the  lesser  differences 
between  varieties  will  tend  to  increase  into  the  greater 
differences  between  species. 

There  is  one  other  point  which  seems  to  me  worth 
notice.  Yarieties  generally  have  much  restricted  ranges  : 
this  statement  is  indeed  scarcely  more  than  a  truism,  for 
if  a  variety  were  found  to  have  a  wider  range  than  that 
of  its  supposed  parent-species,  their  denominations  ought 
to  be  reverssd.  But  there  is  also  reason  to  believe,  that 
those  sj^ecies  which  are  very  closely  allied  to  other  species, 
and  in  so  far  resemble  varieties,  often  have  much  restrict- 
ed ranges.  For  instance,  Mr.  H.  C.  Watson  has  marked 
for  me  in  the  well-sifted  London  Catalogue  of  plants  (4th 
edition)  63  plants  which  are  therein  ranked  as  species, 
but  which  he  considers  as  so  closely  allied  to  other  species 
as  to  be  of  doubtful  valne  :  these  63  reputed  species  range 
on  an  average  over  6.9  of  the  provinces  into  which  Mr. 
Watson  has  divided  Great  Britain.  ITow,  in  this  same 
catalogue,  53  acknowledged  varieties  are  recorded,  and 
these  range  over  Y.7  provinces ;  whereas,  the  species  to 
which  these  varieties  belong  range  over  14.3  provinces. 
So  that  the  acknowledged  varieties  have  very  nearly  the 
same  restricted  average  range,  as  have  those  very  closely 
allied  forms,  marked  for  me  by  Mr.  Watson  as  doubtful 
species,  but  which  are  almost  universally  ranked  by  Brit- 
ish botanists  as  good  and  true  species. 


Finally,  then,  varieties  have  the  same  general  charac- 
ters as  species,  for  they  cannot  be  distinguished  from 
species, — except,  firstly,  by  the  discovery  of  intermediate 
linking  forms,  and  the  occurrence  of  such  links  cannot 
affect  the  actual  characters  of  the  forms  which  they  con- 
nect ;  and  except,  secondly,  by  a  certain  amount  of  differ- 
ence, for  two  forms,  if  differing  very  little,  are  generally 
ranked  as  varieties,  notwithstanding  that  intermediate  link- 
insT  forms  have  not  been  discovered  ;  but  the  amount  of 
di&erence  considered  necessary  to  give  to  two  forms  the 


Ohap.  II.  1  RESEMBLE  VARIETIES.  59 

rank  of  species  is  quite  indefinite.  In  genera  having 
more  than  the  average  number  of  species  in  any  country, 
the  species  of  these  genera  have  more  than  the  average 
number  of  varieties.  In  large  genera  the  species  are  apt 
to  be  closely,  but  unequally  allied  together,  forming  little 
clusters  round  certain  species.  Species  very  closely  allied 
to  other  species  apparently  have  restricted  ranges.  In  all 
these  several  respects  the  species  of  large  genera  present 
a  strong  analogy  with  varieties.  And  we  can  clearly  un- 
derstand these  analogies,  if  species  have  once  existed  as 
varieties,  and  have  thus  originated  :  whereas,  these  analo- 
gies are  utterly  inexplicable  if  each  species  has  been  in- 
dependently created. 

We  have,  also,  seen  that  it  is  the  most  flourishing  and 
dominant  species  of  the  larger  genera  which  on  an  aver- 
age vary  most ;  and  varieties,  as  we  shall  hereafter  see, 
tend  to  become  converted  into  new  and  distinct  species. 
The  larger  genera  thus  tend  to  become  larger ;  and 
throughout  nature  the  forms  of  life  which  are  now  domi- 
nant tend  to  become  still  more  dominant  by  leaving  many 
modified  and  dominant  descendants.  But  by  steps  here- 
after to  be  explained,  the  larger  genera  also  tend  to  break 
up  into  smaller  genera.  And  thus,  the  forms  of  life 
throughout  the  universe  become  divided  into  groups  sub- 
ordinate to  groups. 


gQ  STRUGGLE   FOR   EXISTENCE.  [Chap.  in. 


CHAPTER    III. 

STRUGGLE     FOR     EXISTENCE. 

Bears  on  natural  selection — The  term  used  in  a  wide  sense — Geometrical  powers  of 
increase — Rapid  increase  of  naturalised  animals  and  plants — Nature  of  the  checks 
to  increase — Competition  universal— Eflects  of  climate — Protection  from  the  num- 
ber of  individuals— Complex  relations  of  all  animals  and  plants  throughout  nature 
— Struggle  for  life  most  severe  between  individuals  and  varieties  of  the  same  spe- 
cies ;  often  severe  between  species  of  the  same  genus — The  relation  of  organism 
to  organism  the  most  important  of  all  relations. 

Before  entering  on  tlie  subject  of  this  chapter,  I  must 
make  a  few  preliminary  remarks,  to  show  how  the  strug- 
gle for  existence  bears  on  ISTatural  Selection.  It  has  been 
seen  in  the  last  chapter  that  amongst  organic  beings  in  a 
state  of  nature  there  is  some  individual  variability ;  in- 
deed I  am  not  aware  that  this  has  ever  been  disputed. 
It  is  immaterial  for  us  whether  a  multitude  of  doubtful 
forms  be  called  species  or  sub-species  or  varieties ;  what 
rank,  for  instance,  the  two  or  three  hundred  doubtful 
forms  of  British  plants  are  entitled  to  hold,  if  the  exist- 
ence of  any  well-marked  varieties  be  admitted.  But  the 
mere  existence  of  individual  variability  and  of  some  few 
well-marked  varieties,  though  necessary  as  the  foundation 
for  the  work,  helps  us  but  little  in  understanding  how 
species  arise  in  nature.  How  have  all  those  exquisite 
adaptations  of  one  part  of  the  organisation  to  another 
part,  and  to  the  conditions  of  life,  and  of  one  distinct  or- 
ganic being  to  another  being,  been  perfected  ?  We  see 
these  beautiful  co-adaptations  most  plainly  in  the  wood- 
pecker and  misseltoe ;  and  only  a  little  less  plainly  in  the 
humblest  parasite  which  clings  to  the  hairs  of  a  quadruped 
or  feathers  of  a  bird  ;  in  the  structure  of  the  beetle  which 
dives  through  the  water ;  in  the  plumed  seed  which  is 
wafted  by  the  gentlest  breeze ;  in  short,  we  see  beautiful 


Chap.  III.]  STRUGGLE    FOR    EXISTENCE. 


61 


adaptations  everywhere  and  in  every  part  of  the  organic 
world. 

Again,  it  may  be  asked,  how  is  it  that  varieties,  which 
I  have  called  incipient  species,  become  ultimately  con- 
verted into  good  and  distinct  species,  which  in  most  cases 
obviously  differ  from  each  other  far  more  than  do  the 
varieties  of  the  same  species  ?  How  do  those  groups  of 
species,  which  constitute  what  are  called  distinct  genera, 
and  which  differ  from  each  other  more  than  do  the  species 
of  the  same  genus,  arise  ?  All  these  results,  as  we  shall 
more  fully  see  in  the  next  chapter,  follow  inevitably  from 
the  struggle  for  life.  Owing  to  this  struggle  for  life,  any 
variation,  however  slight  and  from  whatever  cause  pro- 
ceeding, if  it  be  in  any  degree  profitable  to  an  individual 
of  any  species,  in  its  infinitely  complex  relations  to  other 
organic  beings  and  to  -  external  nature,  will  tend  to  the 
preservation  of  that  individual,  and  will  generally  be  in- 
herited by  its  offspring.  The  offspring,  also,  will  thus  have 
a  better  chance  of  surviving,  for,  of  the  many  individuals 
of  any  species  which  are  periodically  born,  but  a  small 
number  can  survive.  I  have  called  this  principle,  by 
which  each  slight  variation,  if  useful,  is  preserved,  by 
the  term  of  IN'atural  Selection,  in  order  to  mark  its  relation 
to  man's  power  of  selection.  We  have  seen  that  man  by 
selection  can  certainly  produce  great  results,  and  can 
adapt  organic  beings  to  his  own  uses,  through  the  accumu- 
lation of  slight  but  useful  variations,  given  to  him  by  the 
hand  of  ISTature.  But  ISTatural  Selection,  as  we  shall  here- 
after see,  is  a  power  incessantly  ready  for  action,  and  is  as 
immeasurably  superior  to  man's  feeble  eftbrts,  as  the  works 
of  JSTature  are  to  those  of  Art. 

AYe  will  now  discuss  a  little  more  in  detail  the  struggle 
for  existence.  In  my  future  work  this  subject  shall  be 
treated,  as  it  well  deserves,  at  much  greater  length.  The 
elder  De  Candolle  and  Lyelle  have  largely  and  philosophi- 
cally shown  that  all  organic  beings  are  exposed  to  severe 
competition.  In  regard  to  plants,  no  one  has  treated  this 
subject  with  more  spirit  and  ability  than  ^Y.  Herbert, 
Dean  of  Manchester,  evidently  the  result  of  his  great 
horticultural  knowledge.     Nothing  is  easier  than  to  admit 


Q2  STRUGGLE   FOR   EXISTENCE.  [Chap.  Ill 

in  words  the  truth  of  the  universal  struggle  for  life,  or 
more  difficult — at  least  I  have  found  it  so — than  constantly 
to  bear  this  conclusion  in  mind.  Yet  unless  it  be  thorough- 
ly engrained  in  the  mind,  I  am  convinced  that  the  whole 
economy  of  nature,  with  every  fact  on  distribution,  rarity, 
abundance,  extinction,  and  variation,  will  be  dimly  seen 
or  quite  misunderstood.  We  behold  the  face  of  nature 
l)right  with  gladness,  we  often  see  superabundance  of 
food ;  we  do  not  see,  or  we  forget,  that  the  birds  which 
are  idly  singing  round  us  mostly  live  on  insects  or  seeds, 
and  are  thus  constantly  destroying  life  ;  or  we  forget  how 
largely  these  songsters,  or  their  eggs,  or  their  nestlings,  are 
destroyed  by  birds  and  beasts  of  prey ;  we  do  not  always 
bear  in  mind,  that  though  food  may  be  now  superabun- 
dant, it  is  not  so  at  all  seasons  of  each  recurring  year. 

I  should  premise  that  I  use  the  term  Struggle  for 
Existence  in  a  large  and  metaphorical  sense,  including 
dependence  of  one  being  on  another,  and  including  (which 
is  more  important)  not  only  the  life  of  the  individual,  but 
success  in  leaving  progeny.  Two  canine  animals  in  a  time 
of  dearth,  may  be  truly  said  to  struggle  with  each  other 
which  shall  get  food  and  live.  But  a  plant  on  the  edge 
of  a  desert  is  said  to  struggle  for  life  against  the  drought, 
though  more  properly  it  should  be  said  to  be  dependent  on 
the  moisture.  A  plant  which  annually  produces  a  thou- 
sand seeds,  of  which  on  an  average  only  one  comes  to 
maturity,  may  be  more  truly  said  to  struggle  with  the 
plants  of  the  same  and  other  kinds  which  already  clothe 
the  ground.  The  misseltoe  is  dependent  en  the  apple  and 
a  few  other  trees,  but  can  only  in  a  far-fetched  sense  be 
said  to  struggle  with  these  trees,  for  if  too  many  of  these 
parasites  grow  on  the  same  tree,  it  will  languish  and  die. 
But  several  seedling  misseltoes,  growing  close  together  on 
the  same  branch,  may  more  truly  be  said  to  struggle  with 
each  other.  As  the  misseltoe  is  disseminated  by  birds, 
its  existence  depends  on  birds ;  and  it  may  metaphor- 
ically be  said  to  struggle  with  other  fruit-bearing  plants, 
in  order  to  tempt  birds  to  devour  and  thus  disseminate  its 
seeds  rather  than  those  of  other  plants.  In  these  several 
senses,  which  pass  into  each  other,  I  use  for  convenience 
sake  the  general  term  of  struggle  for  existence. 


Chap.  III.]  HIGH    RATE    OF   INCREASE.  g3 

A  struggle  for  existence  inevitably  follows  from  the 
high  rate  at  which  all  organic  beings  tend  to  increase. 
Every  being,  which  during  its  natural  lifetime  produces 
several  eggs  or  seeds,  must  suffer  destruction  during  some 
period  of  its  life,  and  during  some  season  or  occasional  year, 
otherwise,  on  the  principle  of  geometrical  increase,  its  num- 
bers would  quickly  become  so  inordinately  great  that  no 
country  could  support  the  product.  Hence  as  more  indi- 
viduals are  produced  than  can  possibly  survive,  there  must 
in  every  case  be  a  struggle  for  existence,  either  one  indi- 
vidual with  another  of  the  same  species,  or  with  the  indi- 
viduals of  distinct  species,  or  with  the  physical  conditions 
of  life.  It  is  the  doctrine  of  Malthus  applied  with  manifold 
force  to  the  whole  animal  and  vegetable  kingdoms ;  for  in 
this  case  there  can  be  no  artificial  increase  of  food,  and  no 
prudential  restraint  from  marriage.  Although  some  species 
may  be  now  increasing,  more  or  less  rapidly,  in  numbers, 
all  caimot  do  so,  for  the  world  would  not  hold  them. 

There  is  no  exception  to  the  rule  that  every  organic 
being  naturally  increases  at  so  high  a  rate,  that  if  not 
destroyed,  the  earth  would  soon  be  covered  by  the  progeny 
of  a  single  pair.  Even  slow-breeding  man  has  doubled  in 
twenty-live  years,  and  at  this  rate,  in  a  few  thousand  years, 
there  would  literally  not  be  standing  room  for  his  progeny. 
Linnaeus  has  calculated  that  if  an  annual  plant  produced 
only  two  seeds — and  there  is  no  plant  so  unproductive  as 
this — and  their  seedlings  next  year  produced  two,  and  so 
on,  then  in  twenty  years  there  would  be  a  million  plants. 
The  elephant  is  reckoned  to  be  the  slowest  breeder  of  all 
known  animals,  and  I  have  taken  some  pains  to  estimate 
its  probable  minimum  rate  of  natural  increase  :  it  will  be 
under  the  mark  to  assume  that  it  breeds  when  thirty  years 
old,  and  goes  on  breeding  till  ninety  years  old,  bringing 
forth  three  pair  of  young  in  this  interval ;  if  this  be  so,  at 
the  end  of  the  fifth  century  there  would  be  alive  fifteen 
million  elephants,  descended  from  the  first  pair. 

But  we  have  better  evidence  on  this  subject  than  mere 
theoretical  calculations,  namely,  the  numerous  recorded 
cases  of  the  astonishingly  rapid  increase  of  various  animals 
in   a   state   of    nature,   when   circumstances   have    been 


g^  HIGH   RATE    OF    INCREASE.  [Chap.  IH 

favourable  to  tliem  during  two  or  three  following  seasons. 
Still  more  striking  is  the  evidence  from  our  domestic  ani- 
mals of  many  kinds  which  have  run  wild  in  several  parts 
of  the  world  :  if  the  statements  of  the  rate  of  increase 
of  slow-breeding  cattle  and  horses  in  South  America,  and 
latterly  in  Australia,  had  not  been  well  authenticated, 
they  would  have  been  quite  incredible.  So  it  is  with 
plants  :  cases  could  be  given  of  introduced  plants  which 
have  become  common  throughout  whole  islands  in  a 
period  of  less  than  ten  years.  Several  of  the  plants  now 
most  numerous  over  the  wide  plains  of  La  Plata,  clothing 
square  leagues  of  surface  almost  to  the  exclusion  of  all 
other  plants,  have  been  introduced  from  Europe  ;  and 
there  are  plants  which  now  range  in  India,  as  I  hear  from 
Dr.  Falconer,  from  Cape  Comorin  to  the  Himalaya,  which 
have  been  imported  from  America  since  its  discovery. 
In  such  cases,  and  endless  instances  could  be  given,  no  one 
supposes  that  the  fertility  of  these  animals  or  plants  has 
been  suddenly  and  temporarily  increased  in  any  sensible 
degree.  The  obvious  explanation  is  that  the  conditions  of 
life  have  been  very  favourable,  and  that  there  has  conse- 
quently been  less  destruction  of  the  old  and  young,  and 
that  nearly  all  the  young  have  been  enabled  to  breed.  In 
such  cases  the  geometrical  ratio  of  increase,  the  result  of 
which  never  fails  to  be  surprising,  simply  explains  the 
extraordinarily  rapid  increase  and  wide  diffusion  of  natu- 
ralised productions  in  their  new  homes. 

In  a  state  of  nature  almost  every  plant  produces  seed, 
and  amongst  animals  there  are  very  few  which  do  not  annu- 
ally pair.  Hence  we  may  confidently  assert,  that  all  plants 
and  animals  are  tending  to  increase  at  a  geometrical  ratio, 
that  all  would  most  rapidly  stock  every  station  in  which 
they  could  anyhow  exist,  and  that  the  geometrical  tendency 
to  increase  must  be  checked  by  destruction  at  some  period 
of  life.  Our  familiarity  with  the  larger  domestic  animals 
tends,  I  think,  to  mislead  us  :  we  see  no  great  destruction 
falling  on  them,  and  we  forget  that  thousands  are  annually 
slaughtered  for  food,  and  that  in  a  state  of  nature  an  equal 
number  would  have  somehow  to  be  disposed  of 

The  only  difference  between  organisms  wdiich  annually 


Chap.  III.]  HIGH   RATE    OF   INCREASE. 


65 


produce  eggs  or  seeds  by  the  ttiousand,  and  those  which 
produce  extremely  few,  is,  that  the  slow-breeders  would 
require  a  few  more  years  to  people,  under  favourable 
conditions,  a  whole  district,  let  it  be  ever  so  large.  The 
condor  lays  a  couple  of  eggs  and  the  ostrich  a  score,  and 
yet  in  the  same  country  the  condor  may  be  the  more 
numerous  of  the  two  :  the  Fulmar  petrel  lays  but  one 
egg,  yet  it  is  believed  to  be  the  most  numerous  bird  in  the 
world.  One  fly  deposits  hundreds  of  eggs,  and  another, 
like  the  hippobosca,  a  single  one  ;  but  this  difference  does 
not  determine  how  many  individuals  of  the  two  species 
can  be  supported  in  a  district.  A  large  number  of  eggs 
is  of  some  importance  to  those  species,  which  depend  on  a 
rapidly  fluctuating  amount  of  food,  for  it  allows  them 
rapidly  to  increase  in  number.  But  the  real  importance 
of  a  large  number  of  eggs  or  seeds  is  to  make  up  for 
much  destruction  at  some  period  of  life  ;  and  this  period 
in  the  great  majority  of  cases  is  an  early  one.  If  an 
animal  can  in  any  way  protect  its  own  eggs  or  young,  a 
small  number  may  be  produced,  and  yet  the  average  stock 
be  fully  kept  up  ;  but  it'  many  eggs  or  young  are  destroyed, 
many  must  be  produced,  or  the  species  will  become  ex- 
tinct. It  would  suflice  to  keep  up  the  full  number  of  a 
tree,  which  lived  on  an  average  for  a  thousand  years,  if  a 
single  seed  were  produced  once  in  a  thousand  years,  sup- 
posing that  this  seed  were  never  destroyed,  and  could  be 
ensured  to  germinate  in  a  fitting  place.  So  that  in  all 
cases,  the  average  number  of  any  animal  depends  only 
indirectly  on  the  number  of  its  eggs  or  seeds. 

In  looking  at  ligature,  it  is  most  necessary  to  keep 
the  foregoing  considerations  always  in  mind — never  to 
forget  that  every  single  organic  being  around  us  may  be 
said  to  be  striving  to  the  utmost  to  increase  in  numbers  ; 
that  each  lives  by  a  struggle  at  some  period  of  its  life ; 
that  heavy  destruction  inevitably  falls  either  on  the  young 
or  old,  during  each  generation  or  at  recurrent  intervals. 
Lighten  any  check,  mitigate  the  destruction  ever  so  little, 
and  the  number  of  the  species  will  almost  instantaneously 
increase  to  any  amount.  The  face  of  Nature  may  be 
compared  to  a  yielding  surface,  with  ten  thousand  sharp 
4 


QQ  CHECKS   TO    INCREASE.  [Chap.  IIL 

wedges  packed  close  together  and  driven  inwards  by 
incessant  blows,  sometimes  one  wedge  being  struck,  and 
tben  another  with  greater  force. 

What  checks  the  natural  tendency  of  each  species  to 
increase  in  number  is  most  obscure.  Look  at  the  most 
vigorous  species  ;  by  as  much  as  it  swarms  in  numbers, 
by  so  much  will  its  tendency  to  increase  be  still  further 
increased.  We  know  not  exactly  what  the  checks  are  in 
even  one  single  instance.  Nor  will  this  surprise  any  one 
who  reflects  how  ignorant  we  are  on  this  head,  even  in 
regard  to  mankind,  so  incomparably  better  known  than 
any  other  animal.  This  subject  has  been  ably  treated  by 
several  authors,  and  I  shall,  in  my  future  work,  discuss 
some  of  the  checks  at  considerable  length,  more  especially 
in  regard  to  the  feral  animals  of  South  America.  Here 
I  will  make  only  a  few  remarks,  just  to  recall  to  the 
reader's  mind  some  of  the  chief  points.  Eggs  or  very 
young  animals  seem  generally  to  suffer  most,  but  this  is 
not  invariably  the  case.  With  plants  there  is  a  vast 
destruction  of  seeds,  but,  from  some  observations  which  I 
have  made,  I  believe  that  it  is  the  seedlings  which  suffer 
most  from  germinating  in  ground  already  thickly  stocked 
with  other  plants.  Seedlings,  also,  are  destroyed  in  vast 
numbers  by  various  enemies  ;  for  instance,  on  a  piece  of 
ground  three  feet  long  and  two  wide,  dug  and  cleared, 
and  where  there  could  be  no  choking  from  other  plants,  I 
marked  all  the  seedlings  of  our  native  weeds  as  they  came 
up,  and  out  of  the  357,  no  less  than  295  were  destroyed, 
chiefly  by  slugs  and  insects.  If  turf  which  has  long  been 
mown,  and  the  case  would  be  the  same  with  turf  closely 
browsed  by  quadrupeds,  be  let  to  grow,  the  more  vigorous 
plants  gradually  kill  the  less  vigorous,  though  fully  grown, 
plants  :  thus  out  of  twenty  species  growing  on  a  little 
spot  of  turf  (three  feet  by  four)  nine  species  perished  from 
the  other  species  being  allowed  to  grow  up  freely. 

The  amount  of  food  for  each  species  of  course  gives 
the  extreme  limit  to  which  each  can  increase  ;  but  very 
frequently  it  is  not  the  obtaining  food,  but  the  serving  as 
prey  to  other  animals,  which  determines  the  average  num- 
bers of  a  species.    Thus,  there  seems  to  be  little  doubt  that 


Chap.  III.]  CHECKS   TO    INCREASE.  Q^ 

the  stock  of  partridges,  grouse,  and  hares,  on  any  large 
estate,  depends  chiefly  on  the  destruction  of  vermin.  If 
not  one  head  of  game  were  shot  during  the  next  twenty 
years  in  England,  and,  at  the  same  time,  if  no  vermin 
were  destroyed,  there  would,  in  all  probability,  be  less 
game  than  at  present,  although  hundreds  of  thousands  of 
game  animals  are  now  annually  killed.  On  the  other 
hand,  in  some  cases,  as  with  the  elephant  and  rhinoceros, 
none  are  destroyed  by  beasts  of  prey  :  even  the  tiger  in 
India  most  rarely  dares  to  attack  a  young  elephant  pro- 
tected by  its  dam. 

Climate  plays  an  important  part  in  determining  the 
average  numbers  of  a  species,  and  periodical  seasons  of 
extreme  cold  or  drought,  I  believe  to  be  the  most  effective 
of  all  checks.  I  estimated  that  the  winter  of  1854:-55 
destroyed  four-fifths  of  the  birds  in  my  own  grounds ; 
and  this  is  a  tremendous  destruction,  when  we  remember 
that  ten  per  cent,  is  an  extraordinarily  severe  mortality 
from  epidemics  with  man.  The  action  of  climate  seems 
at  first  sight  to  be  quite  independent  of  the  struggle  for 
existence  ;  but  in  so  far  as  climate  chiefly  acts  in  reducing 
food,  it  brings  on  the  most  severe  struggle  between  the 
individuals,  whether  of  the  same  or  of  distinct  species, 
which  subsist  on  the  same  kind  of  food.  Even  when  cli- 
mate, for  instance  extreme  cold,  acts  directly,  it  will  be 
the  least  vigorous,  or  those  which  have  got  least  food 
through  the  advancing  winter,  which  will  suffer  most. 
When  we  travel  from  south  to  north,  or  from  a  damp 
region  to  a  dry,  we  invariably  see  some  species  gradually 
getting  rarer  and  rarer,  and  finally  disappearing  ;  and  the 
change  of  climate  being  conspicuous,  we  are  tempted  to 
attribute  the  whole  efi'ect  to  its  direct  action.  But  this  is 
a  very  false  view :  we  forget  that  each  species,  even 
where  it  most  abounds,  is  constantly  suffering  enormous 
destruction  at  some  period  of  its  life,  from  enemies  or 
from  competitors  for  the  same  place  and  food  ;  and  if 
these  enemies  or  competitors  be  in  the  least  degree  fa- 
voured by  any  slight  change  of  climate,  they  will  increase 
in  numbers,  and,  as  each  area  is  already  fully  stocked 
with  inhabitants,  the  other  species  will  decrease.     When 


^§  CHECKS   TO    INCREASE.  [Cuap.  Ill, 

we  travel  soutliward  and  see  a  species  decreasing  in 
numbers,  we  may  feel  sure  that  the  cause  lies  quite  as 
much  in  other  species  being  favoured,  as  in  this  one  being 
hurt.  So  it  is  when  we  travel  northward,  but  in  a  some- 
what lesser  degree,  for  the  number  of  species  of  all  kinds, 
and  therefore  of  competitors,  decreases  northwards ;  hence 
in  going  northward,  or  in  ascending  a  mountain,  we  far 
oftener  meet  with  stunted  forms,  due  to  the  directly  inju- 
rious action  of  climate,  than  we  do  in  proceeding  south- 
wards or  in  descending  a  mountain.  "When  we  reach  the 
Arctic  regions,  or  snow-capped  summits,  or  absolute  des- 
erts, the  struggle  for  life  is  almost  exclusively  with  the 
elements. 

That  climate  acts  in  main  part  indirectly  by  favouring 
other  species,  we  may  clearly  see  in  the  prodigious  num- 
ber of  plants  in  our  gardens  which  can  perfectly  well 
endure  our  climate,  but  which  never  become  naturalised, 
for  they  cannot  compete  with  our  native  plants,  nor  resist 
destruction  by  our  native  animals. 

When  a  species,  owing  Xo  highly  favourable  circum- 
stances, increases  inordinately  in  numbers  in  a  small  tract, 
epidemics — at  least,  this  seems  generally  to  occur  with 
our  game  animals — often  ensue  :  and  here  we  have  a  lim- 
iting check  independent  of  the  struggle  for  life.  But 
even  some  of  these  so-called  epidemics  appear  to  be  due 
to  parasitic  worms,  which  have  from  some  cause,  possibly 
in  part  through  facility  of  diifusion  amongst  the  crowded 
animals,  been  disproportionably  favoured  :  and  here  comes 
in  a  sort  of  struggle  between  the  parasite  and  its  prey. 

On  the  other  liand,  in  many  cases,  a  large  stock  of 
individuals  of  the  same  species  relatively  to  the  numbers 
of  its  enemies,  is  absolutely  necessary  for  its  preservation. 
Thus  we  can  easily  raise  plenty  of  corn  and  rape-seed, 
&c.,  in  our  fields,  because  the  seeds  are  in  great  excess 
compared  with  the  number  of  birds  which  feed  on  them  ; 
nor  can  the  bird,  though  having  a  super-abundance  of 
food  at  this  one  season,  increase  in  number  proportionally 
to  the  supply  of  seed,  as  their  numbers  are  checked  during 
winter :  but  any  one  who  has  tried,  knows  how  trouble- 
some it  is  to  get  seed  from  a  few  wheat  or  other  such 


Chap.  III.]  MUTUAL    CHECKS   TO    INCREASE.  g9 

plants  in  a  garden  ;  I  have  in  this  case  lost  every  single 
seed.  This  view  of  the  necessity  of  a  large  stock  of  the 
same  species  for  its  preservation,  explains,  I  believe,  some 
singular  facts  in  nature,  such  as  that  of  very  rare  plants 
being  sometimes  extremely  abundant  in  the  few  spots 
where  they  do  occur ;  and  that  of  some  social  plants  being 
social,  that  is,  abounding  in  individuals,  even  on  the  ex- 
treme confines  of  their  range.  For  in  such  cases,  we  may 
believe,  that  a  plant  could  exist  only  where  the  conditions 
of  its  life  were  so  favourable  that  many  could  exist  to- 
gether, and  thus  save  each  other  from  utter  destruction. 
I  should  add  that  the  good  effects  of  frequent  intercrossing, 
and  the  ill  effects  of  close  interbreeding,  probably  come 
into  play  in  some  of  these  cases  ;  but  on  this  intricate 
subject  I  will  not  here  enlarge. 

Many  cases  are  on  record  showing  how  complex  and 
unexpected  are  the  checks  and  relations  between  organic 
beings,  which  have  to  struggle  together  in  the  same 
country.  I  will  give  only  a  single  instance,  which, 
though  a  simple  one,  has  interested  me.  In  Staffordshire, 
on  the  estate  of  a  relation  where  I  had  ample  means  of 
investigation,  there  was  a  large  and  extremely  barren 
heath,  which  had  never  been  touched  by  the  hand  of 
man ;  but  several  hundred  acres  of  exactly  the  same 
nature  had  been  enclosed  twenty-five  years  previously 
and  planted  with  Scotch  fir.  The  change  in  the  native 
vegetation  of  the  planted  part  of  the  heath  was  most 
remarkable,  more  than  is  generally  seen  in  passing  from 
one  quite  different  soil  to  another :  not  only  the  proper 
tional  numbers  of  the  heath  plants  were  wholly  changed, 
but  twelve  species  of  plants  (not  counting  grasses  and 
carices)  flourished  in  the  plantations,  which  could  not  be 
found  on  the  heath.  The  effect  on  the  insects  must 
have  been  still  greater,  for  six  insectivorous  birds  were 
very  common  in  the  plantations,  which  were  not  to  be  seen 
on  the  heath  ;  and  the  heath  was  frequented  by  two  or 
three  distinct  insectivorous  birds.  Here  we  see  how 
potent  has  been  the  eflect  of  the  introduction  of  a  single 
tree,  nothing  whatever  else  having  been  done,  with  the 
exception  that  the  land  had  been  enclosed,  so  that  cattle 


f^Q  MUTUAL    CHECKS    TO    INCREASE,  [Chap.  111. 

could  not  enter.  But  liow  important  an  element  enclosure 
is,  I  plainly  saw  near  Fariiham,  in  Surrey.  Here  there 
are  extensive  heaths,  with  a  few  clumps  of  old  Scotch  hrs 
on  the  distant  hill-tops  :  within  the  last  ten  years  large 
spaces  have  been  enclosed,  and  self-sown  firs  are  now 
springing  up  in  multitudes,  so  close  together  that  all  can- 
not live.  When  I  ascertained  that  these  young  trees  had 
not  been  sown  or  planted,  I  was  so  much  surprised  at  their 
numbers  that  I  went  to  several  points  of  view,  whence  I 
could  examine  hundreds  of  acres  of  the  unenclosed  heath, 
and  literally  I  could  not  see  a  single  Scotch  fir,  except  the 
old  planted  clumps.  But  on  looking  closely  between  the 
stems  of  the  heath,  I  found  a  multitude  of  seedlings  and 
little  trees,  which  had  been  perpetually  browsed  down  by 
the  cattle.  In  one  square  yard,  at  a  point  some  hundred 
yards  distant  from  one  of  the  old  clumps,  I  counted  thirty- 
two  little  trees  ;  and  one  of  them,  with  twenty-six  rings 
of  growth,  had  during  many  years  tried  to  raise  its  head 
above  the  stems  of  the  heath,  and  had  failed.  'No 
wonder  that,  as  soon  as  the  land  was  enclosed,  it  became 
thickly  clothed  with  vigorously  growing  young  firs.  Yet 
the  heath  was  so  extremely  barren  and  so  extensive  that 
no  one  would  ever  have  imagined  that  cattle  would  have 
so  closely  and  elfectually  searched  it  for  food. 

Here  we  see  that  cattle  absolutely  determine  the  exist- 
ence of  the  Scotch  fir  ;  but  in  several  parts  of  the  world 
insects  determine  the  existence  of  cattle.  Perhaps  Para- 
guay ofiers  the  most  curious  instance  of  this ;  for  here 
neither  cattle  nor  horses  nor  dogs  have  ever  run  Avild, 
though  they  swarm  southward  and  northward  in  a  feral 
state ;  and  Azara  and  Pengger  have  shown  that  this  is 
caused  by  the  greater  number  in  Paraguay  of  a  certain 
fly,  which  lays  its  eggs  in  the  navels  of  these  animals 
when  first  born.  Tlie  increase  of  these  flies,  numerous  as 
they  are,  must  be  habitually  checked  by  some  means, 
probably  by  birds.  Hence,  if  certain  insectivorous  birds 
(whose  numbers  are  probably  regulated  by  hawks  or 
beasts  of  prey)  were  to  increase  in  Paraguay,  the  flies 
would  decrease — then  cattle  and  horses  would  become 
feral,  and  this  would  certainly  greatly  alter  (as  indeed  I 


Chap.  III.]  MtJTUAL    CHECKS    TO    INCREASE.  f^^ 

have  observed  in  parts  of  Sontli  America)  the  vegetation  : 
this  again  Tvoiild  largely  affect  the  insects  ;  and  this,  as  we 
just  have  seen  in  Staffordshire,  the  insectivorous  birds, 
and  so  onwards  in  ever-increasing  circles  of  complexity. 
We  began  this  series  by  insectivorous  birds,  and  we  have 
ended  with  them.  ISTot  that  in  nature  the  relations  can 
eter  be  as  simj)le  as  this.  Battle  within  battle  must  ever 
be  recurring  with  varying  success  ;  and  yet  in  the  long- 
iTin  the  forces  are  so  nicely  balanced,  that  the  face  of 
nature  remains  uniform  for  long  periods  of  time,  though 
assuredly  the  merest  trifle  would  often  give  the  victory  to 
one  organic  being  over  another.  ^Nevertheless  so  pro- 
found is  our  ignorance,  and  so  high  our  presumption,  that 
we  marvel  when  we  hear  of  the  extinction  of  an  organic 
being ;  and  as  we  do  not  see  the  cause,  we  invoke  cata- 
clysms to  desolate  the  world,  or  invent  laws  on  the  dura- 
tion of  the  forms  of  life  ! 

I  am  tempted  to  give  one  more  instance  showing  how 
plants  and  animals,  most  remote  in  the  scale  of  nature, 
are  bound  together  by  a  web  of  complex  relations.  I  shall 
hereafter  have  occasion  to  show  that  the  exotic  Lobelia 
fulgens,  in  this  part  of  England,  is  never  visited  by  in- 
sects, and  consequently,  from  its  peculiar  structure,  nevei 
can  set  a  seed.  Many  of  our  orchidaceous  plants  abso- 
lutely require  the  visits  of  moths  to  remove  their  pollen- 
masses  and  thus  to  fertilise  them.  I  have,  also,  reason  to 
believe  that  humble-bees  are  indispensable  to  the  fertilisa- 
tion of  the  heartsease  (Yiola  tricolor),  for  other  bees  do 
not  visit  this  flower.  From  experiments  which  I  have 
lately  tried,  I  have  found  that  the  visits  of  bees  are  neces- 
sary for  the  fertilisation  of  some  kinds  of  clover ;  for  in- 
stance, 20  heads  of  Dutch  clover  (Trifolium  repens)  yielded 
2290  seeds,  but  20  other  heads  protected  from  bees  pro- 
duced not  one  ;  again,  100  heads  of  red  clover  (T.  pratense) 
produced  2700  seeds,  but  the  same  number  of  protected 
heads  produced  not  a  single  seed.  Humble-bees  alone 
visit  red  clover,  as  other  bees  cannot  reach  the  nec- 
tar. Hence  I  have  very  little  doubt,  that  if  the  v/hole 
genus  of  humble-bees  became  extinct  or  very  rare  in 
England,  the  heartsease   and  red  clover  would  become 


72 


MUTUAL   CHECKS    TO    INCREASE.  [Chap.  Ill 


very  rare,  or  wholly  disappear.  The  number  of  humble 
bees  in  any  district  depends  in  a  great  degree  on  the 
number  of  field-mice,  which  destroy  their  combs  and 
nests  ;  and  Mr.  H.  Ilewman,  who  has  long  attended  to 
the  habits  of  humble-bees,  believes  that  "  more  than  two- 
thirds  of  them  are  thus  destroyed  all  over  England." 
Now  the  number  of  mice  is  largely  dependent,  as  every 
one  kaows,  on  the  number  of  cats ;  and  Mr.  ITewman 
says,  "  ]N"ear  villages  and  small  towns  I  have  found  the 
nests  of  humble-bees  more  numerous  than  elsewhere,  which 
I  attribute  to  the  number  of  cats  that  destroy  the  mice." 
Hence  it  is  quite  creditable  that  the  presence  of  a  feline 
animal  in  large  numbers  in  a  district  might  determine, 
through  the  intervention  first  of  mice  and  then  of  bees, 
the  frequency  of  certain  flow^ers  in  that  district ! 

In  the  case  of  every  species,  many  different  checks, 
acting  at  different  periods  of  life,  and  during  different 
seasons  or  years,  probably  come  into  play  ;  some  one 
check  or  some  few  being  generally  the  most  potent,  but 
all  concurring  in  determining  the  average  number  or  even 
the  existence  of  the  species.  In  some  cases  it  can  be 
shown  that  widely-different  checks  act  on  the  same  species 
in  different  districts.  When  we  look  at  the  plants  and 
bushes  clothing  an  entangled  bank,  we  are  temj^ted  to 
attribute  their  proportional  numbers  and  kinds  to  what 
we  call  chance.  But  how  false  a  view  is  this !  Every 
one  has  heard  that  when  an  American  forest  is  cut  down, 
a  very  different  vegetation  springs  up  ;  but  it  has  been 
observed  that  the  trees  now  growing  on  the  ancient  Indian 
mounds,  in  the  Southern  United  States,  display  the  same 
beautiful  diversity  and  proportion  of  kinds  as  in  the  sur- 
rounding virgin  forests.  AVliat  a  struggle  between  the 
several  kinds  of  trees  must  here  have  gone  on  during  long 
centuries,  each  annually  scattering  its  seeds  by  the  thou- 
sand ;  what  war  between  insect  and  insect — between  in- 
sects, snails,  and  other  animals  with  birds  and  beasts  of 
prey — all  striving  to  increase,  and  all  feeding  on  each 
other  or  on  the  trees  or  their  seeds  and  seedlings,  or  on 
the  plants  which  first  clothed  the  ground  and  thus  checked 
the  growth  of  the  trees  !     Throw  up  a  handful  of  feathers, 


Chap.  III.]  MUTUAL   CHECKS   TO    INCREASE.  7*3 

and  all  must  fall  to  the  ground  according  to  definite  laws ; 
but  liow  simple  is  this  problem  compared  to  the  action 
and  reaction  of  the  innumerable  plants  and  animals  which 
have  determined,  in  the  course  of  centuries,  the  propor- 
tional numbers  and  kinds  of  trees  now  growing  on  the  old 
Indian  ruins  ! 

The  dependency  of  one  organic  being  on  another,  as 
of  a  parasite  on  its  prey,  lies  generally  between  beings 
remote  in  the  scale  of  nature.  This  is  often  the  case  with 
those  which  may  strictly  be  said  to  struggle  with  each 
other  for  existence,  as  in  the  case  of  locusts  and  grass- 
feeding  quadrupeds.  But  the  struggle  almost  invariably 
will  be  most  severe  between  the  individuals  of  the  same 
species,  for  they  frequent  the  same  districts,  require  the 
same  food,  and  are  exposed  to  the  same  dangers.  In  the 
case  of  varieties  of  the  same  species,  the  struggle  will 
generally  be  almost  equally  severe,  and  we  sometimes  see 
the  contest  soon  decided  :  for  instance,  if  several  varieties 
of  wheat  be  sown  together,  and  the  mixed  seeds  be  re- 
sown,  some  of  the  varieties  which  best  suit  the  soil  or 
climate,  or  are  naturally  the  most  fertile,  will  beat  the 
others  and  so  yield  more  seed,  and  will  consequently  in  a 
few  years  quite  supplant  the  other  varieties.  To  keep  up 
a  mixed  stock  of  even  such  extremely  close  varieties  as 
the  variously  coloured  sweet-peas,  they  must  be  each  year 
harvested  separately,  and  the  seed  then  mixed  iu  due  pro- 
portion, otherwise  the  weaker  kinds  will  steadily  decrease 
in  numbers  and  disappear.  So  again  with  the  varieties 
of  sheep  :  it  has  been  asserted  that  certain  mountain- 
varieties  will  starve  out  other  mountain-varieties,  so  that 
they  cannot  be  kept  together.  Tlie  same  result  has  fol- 
lowed from  keeping  together  different  varieties  of 
the  medicinal  leech.  It  may  even  be  doubted  whether" 
the  varieties  of  any  one  of  our  domestic  plants  or  animals 
have  so  exactly  the  same  strength,  habits,  and  constitu- 
tion, that  the  original  proportions  of  a  mixed  stock  could 
be  kept  up  for  half  a  dozen  generations,  if  they  were 
allowed  to  struggle  together,  like  beings  in  a  state  of 
nature,  and  if  the  seed  or  young  were  not  annually  sorted. 
As  species  of  the  same  genus  have  usually,  though  by 
4* 


^4:  STRUGGLE    FOR   EXISTEKCE.  [OnAP.  in 

no  means  invariably,  some  similarity  in  habits  and  consti- 
tution, and  always  in  structure,  the  struggle  "will  generally 
be  more  severe  between  species  of  the  same  genus,  when 
they  come  into  competition  with  each  other,  than  between 
species  of  distinct  genera.  We  see  this  in  the  recent  ex- 
tension over  parts  of  the  United  States  of  one  species  of 
swallow  having  caused  the  decrease  of  another  species. 
The  recent  increase  of  the  missel-thrush  in  parts  of  Scot- 
land has  caused  the  decrease  of  the  song-thrush.  How 
frequently  we  hear  of  one  species  of  rat  taking  the  place 
of  another  species  under  the  most  different  climates  !  In 
Russia  the  small  Asiatic  cockroach  has  everywhere  driven 
before  it  its  great  congener.  One  species  of  charlock  will 
supplant  another,  and  so  in  other  cases.  We  can  dimly 
see  why  the  competition  should  be  most  severe  between 
allied  forms,  which  fill  nearly  the  same  place  in  the  econo- 
my of  nature ;  but  probably  in  no  one  case  could  we 
precisely  say  why  one  species  has  been  victorious  over 
another  in  the  great  battle  of  life. 

A  corollary  of  the  highest  importance  may  be  deduced 
from  the  foregoing  remarks,  namely,  that  the  structure 
of  every  organic  being  is  related,  in  the  most  essential 
yet  often  hidden  manner,  to  that  of  all  other  organic  be- 
ings, with  which  it  comes  into  competition  for  food  or  resi- 
dence, or  from  which  it  has  to  escape,  or  on  which  it 
preys.  This  is  obvious  in  the  structure  of  the  teeth  and 
talons  of  the  tiger ;  and  in  that  of  the  legs  and  claws  of 
the  parasite  which  clings  to  the  hair  on  the  tiger's  body. 
But  in  the  beautifully  plumed  seed  of  the  dandelion,  and 
in  the  flattened  and  fringed  legs  of  the  water-beetle,  the 
relation  seems  at  first  confined  to  the  elements  of  aii"  and 
water.  Yet  the  advantage  of  plumed  seeds  no  doubt 
'stands  in  the  closest  relation  to  the  land  being  already 
thickly  clothed  by  other  plants  ;  so  that  the  seeds  may  be 
w^idely  distributed  and  fall  on  unoccupied  ground.  In  the 
water-beetle,  the  structure  of  its  legs,  so  well  adapted  for 
diving,  allows  it  to  compete  with  other  aquatic  insects,  to 
hunt  for  its  own  prey,  and  to  escape  serving  as  prey  to 
other  animals. 

The  store  of  nutriment  laid  up  within  the  seeds  of 


Chap.  III.]  STRUGGLE    FOR   EXISTENCE.  ^^ 

many  plants  seems  at  first  sight  to  have  no  sort  of  relation 
to  other  plants.  But  from  the  strong  growth  of  young 
plants  produced  from  such  seeds  (as  peas  and  beans),  when 
sown  in  the  midst  of  long  grass,  I  suspect  that  the  chief 
use  of  the  nutriment  in  the  seed  is  to  favour  the  growth 
of  the  young  seedling,  whilst  struggling  with  other  plants 
growing  vigorously  all  around. 

Look  at  a  plant  in  the  midst  of  its  range,  why  does  it 
not  double  or  quadruple  its  numbers  ?  We  know  that  it 
can  perfectly  well  withstand  a  little  more  heat  or  cold, 
dampness  or  dryness,  for  elsewhere  it  ranges  into  slightly 
hotter,  or  colder,  damper  or  drier  districts.  In  this  case 
we  can  clearly  see  that  if  we  wished  in  imagination  to 
give  the  plant  the  power  of  increasing  in  number,  we 
should  have  to  give  it  some  advantage  over  its  competi- 
tors, or  over  the  animals  which  preyed  on  it.  On  the 
confines  of  its  geographical  range,  a  change  of  constitu- 
tion with  respect  to  climate  would  clearly  be  an  advantage 
to  our  plant ;  but  we  have  reason  to  believe  that  only  a 
few  plants  or  animals  range  so  far,  that  they  are  destroyed 
by  the  rigour  of  the  climate  alone.  IS'ot  until  we  reach 
the  extreme  confines  of  life,  in  the  arctic  regions  or  on 
the  borders  of  an  utter  desert,  will  competition  cease. 
The  land  may  be  extremely  cold  or  dry,  yet  there  will  be 
competition  between  some  few  species,  or  between  the 
individuals  of  the  same  species,  for  the  warmest  or  damp- 
est spots. 

Hence,  also,  we  can  see  that  when  a  plant  or  animal  is 
placed  in  a  new  country  amongst  new  competitors,  though 
the  climate  may  be  exactly  the  same  as  in  its  former  home, 
yet  the  conditions  of  its  life  will  generally  be  changed  in 
an  essential  manner.  If  we  wished  to  increase  its  average 
numbers  in  its  new  home,  we  should  have  to  modify  it  in 
a  difi*erent  way  to  what  we  should  have  done  in  its  native 
country  ;  for  we  should  have  to  give  it  some  advantage 
over  a  difi'erent  set  of  competitors  or  enemies. 

It  is  good  thus  to  try  in  our  imagination  to  give  any 
form  some  advantage  over  another.  Probably  in  no  smgle 
instance  should  we  know  what  to  do,  so  as  to  succeed.  It 
will  convince  us  of  our  ignorance  on  the  mutual  relations 


'JQ  BTRTJGGLE   FOR   EXISTENCE.  [Chap.  Ill, 

of  all  organic  beings  ;  a  conviction  as  necessary,  as  it 
seems  to  be  difficult  to  acquire.  All  that  we  can  do,  is  to 
keep  steadily  in  mind  that  each  organic  being  is  striving 
to  increase  at  a  geometrical  ratio ;  that  each  at  some 
period  of  its  life,  during  some  season  of  the  year,  during 
each  generation  or  at  intervals,  has  to  struggle  for  life, 
and  to  suffer  great  destruction.  When  we  reflect  on  this 
struggle,  we  may  console  ourselves  with  the  full  belief, 
that  the  war  of  nature  is  not  incessant,  that  no  fear  is  felt, 
that  death  is  generally  prompt,  and  that  the  vigorous,  the 
healthy,  and  the  happy  survive  and  multiply. 


Chap.  IV.]  NATURAL   SELECTION. 


77 


CHAPTER   IT. 

NATURAL     SELECTION. 

Natural  Selection^its  power  compared  with  man's  selection — its  power  on  chafactera 
of  trifling  importance — its  power  at  all  ages  and  on  toth  sexes — Sexual  Selection — 
On  the  generality  of  intercrosses  between  individuals  of  the  same  species — Cir* 
cumstances  favourable  and  unfavourable  to  Natural  Selection,  namely,  intercross- 
ing, isolation,  number  of  individuals— Slow  action— Extinction  caused  by  Natural 
Selection — Divergence  of  Character,  related  to  the  diversity  of  inhabitants  of  any 
email  area,  and  to  naturalisation — Action  of  Natural  Selection,  through  Divergence 
of  Character  and  Extinction,  on  the  descendants  from  a  common  parent — Explains 
the  Grouping  of  all  organic  beings* 

How  will  tlie  struggle  for  existence,  discussed  too  briefly 
in  the  last  chapter,  act  in  regard  to  variation  ?  Can  the 
principle  of  selection,  which  we  have  seen  is  so  potent  in 
the  hands  of  man,  apply  in  nature  ?  I  think  we  shall  see 
that  it  can  act  most  eftectually.  Let  it  be  borne  in  mind 
in  what  an  endless  number  of  strange  peculiarities  our 
domestic  productions,  and,  in  a  lesser  degree,  those  under 
nature,  vary  ;  and  how  strong  the  hereditary  tendency  is. 
Under  domestication,  it  may  be  truly  said  that  the  whole 
organisation  becomes  in  some  degree  plastic.  Let  it  be 
borne  in  mind  how  infinitely  complex  and  close-fitting 
are  the  mutual  relations  of  all  organic  beings  to  each 
other  and  to  their  physical  conditions  of  life.  Can  it, 
then,  be  thought  improbable,  seeing  that  variations  useful 
to  man  have  undoubtedly  occurred,  that  other  variations 
useful  in  some  way  to  each  being  in  the  great  and  com- 
plex battle  of  life,  should  sometimes  occur  in  the  course 
of  thousands  of  generations?  K  such  do  occur,  can  we 
doubt  (remembering  that  many  more  individuals  are  bom 
than  can  possibly  survive)  that  individuals  having  any 
advantage,  however  slight,  over  others,  would  have  the 
best  chance  of  surviving  and  of  procreating  their  kind? 


«rg  NATURAL    SELECTI02T.  [Chap.  IV. 

On  tlie  otlier  hand,  we  may  feel  sure  that  any  variation 
in  the  least  degree  injurious  would  be  rigidly  destroyed. 
This  preservation  of  favourable  variations  and  the  rejec- 
tion of  injurious  variations,  I  call  ISTatural  Selection. 
Yariations  neither  useful  nor  injurious  would  not  be  affect- 
ed by  natural  selection,  and  would  be  left  a  fluctuating 
element,  as  perhaps  we  see  in  the  species  called  polymor- 
phic. 

We  shall  best  understand  the  probable  course  of  na- 
tural selection  by  taking  the  case  of  a  country  undergo- 
ing some  physical  change,  for  instance,  of  climate.  The 
proportional  numbers  of  its  inhabitants  would  almost  im- 
mediately undergo  a  change,  and  some  species  might  be- 
come extinct.  We  may  conclude,  from  what  we  have 
seen  of  the  intimate  and  complex  manner  in  which  the  in- 
habitants of  each  country  are  bound  together,  that  any 
change  in  the  numerical  proportions  of  some  of  the  in- 
habitants, independently  of  the  change  of  climate  itself, 
would  most  seriously  affect  many  of  the  others.  If  the 
country  were  open  on  its  borders,  new  forms  would  cer- 
tainly immigrate,  and  this  also  would  seriously  disturb 
the  relations  of  some  of  the  former  inhabitants.  Let  it  be 
remembered  how  powerful  the  influence  of  a  single  intro- 
duced tree  or  mammal  has  been  shown  to  be.  But  in  the 
case  of  an  island,  or  of  a  country  partly  surrounded  by 
barriers,  into  which  new  and  better  adapted  forms  could 
not  freely  enter,  we  should  then  have  places  in  the  econo- 
my of  nature  which  would  assuredly  be  better  filled  up, 
if  some  of  the  original  inhabitants  were  in  some  manner 
modified  ;  for,  had  the  area  been  open  to  immigration, 
these  same  places  would  have  been  seized  on  by  intruders. 
In  such  case,  every  slight  modification,  which  in  the  course 
of  ages  chanced  to  arise,  and  which  in  any  way  favoured 
the  individuals  of  any  of  the  species,  by  better  adapting 
them  to  their  altered  conditions,  would  tend  to  be  pre- 
served ;  and  natural  selection  would  thus  have  free  scope 
for  the  work  of  improvement. 

We  have  reason  to  believe,  as  stated  in  the  first  chap- 
ter, that  a  change  in  the  conditions  of  life,  by  specially 
acting  on  the  reproductive  system,  causes   or  increases 


Chap.  IV.]  NATURAL  'SELECTION.  Y9 

variability ;  and  in  the  foregoing  case  the  conditions  of 
life  are  supposed  to  have  undergone  a  change,  and  this 
would  manifestly  be  favourable  to  natural  selection,  by 
giving  a  better  chance  of  profitable  variations  occurring ; 
and  unless  profitable  variations  do  occur,  natural  selection 
can  do  nothing.  Kot  that,  as  I  believe,  any  extreme 
amount  of  variability  is  necessary  ;  as  man  can  certainly 
produce  great  results  by  adding  up  in  any  given  direction 
mere  individual  differences,  so  could  IS^ature,  but  far  more 
easily,  from  having  incomparably  longer  time  at  her  dis- 
posal. JN^or  do  I  believe  that  any  great  physical  change, 
as  of  climate,  or  any  unusual  degree  of  isolation  to  check 
immigration,  is  actually  necessary  to  produce  new  and 
unoccupied  places  for  natural  selection  to  fill  up  by  modi- 
fying and  improving  some  of  the  varying  inhabitants. 
For  as  all  the  inhabitants  of  each  country  are  struggling 
together  with  nicely  balanced  forces,  extremely  slight 
modifications  in  the  structure  or  habits  of  one  inhabitant 
would  often  give  it  an  advantage  over  others ;  and  still 
further  modifications  of  the  same  kind  would  often  still 
further  increase  the  advantage.  'No  country  can  be 
named  in  which  all  the  native  inhabitants  are  now  so  per- 
fectly adapted  to  each  other  and  to  the  physical  conditions 
under  which  they  live,  that  none  of  them  could  anyhow 
be  improved  ;  for  in  all  countries,  the  natives  have  been 
so  far  conquered  by  naturalised  productions,  that  they 
have  allowed  foreigners  to  take  firm  possession  of  the  land. 
And  as  foreigners  have  thus  everywhere  beaten  some  of 
the  natives,  we  may  safely  conclude  that  the  natives 
might  have  been  modified  with  advantage,  so  as  to  have 
better  resisted  such  intruders. 

As  man  can  produce  and  certainly  has  produced  a 
great  result  by  his  methodical  and  unconscious  means  of 
selection,  what  may  not  nature  effect  ?  Man  can  act  only 
on  external  and  visible  characters :  nature  cares  nothing 
for  appearances,  except  in  so  far  as  they  may  be  useful 
to  any  being.  She  can  act  on  every  internal  organ,  on 
every  shade  of  constitutional  difference,  on  the  whole 
machinery  of  life.  Man  selects  only  for  his  own  good ; 
!N"ature  only  for  that  of  the  being  which  she  tends.     Every 


go  NATURAL   SELECTION.  [Chap.  IV. 

selected  character  is  fullj  exercised  by  lier ;  and  the  being 
is  placed  under  well-suited  conditions  of  life.  Man  keeps 
the  natives  of  many  climates  in  the  same  country  ;  he  sel- 
dom exercises  each  selected  character  in  some  peculiar 
and  fitting  mamier ;  he  feeds  a  long  and  a  short-beaked 
pigeon  on  the  same  food ;  he  does  not  exercise  a  long- 
backed  or  long-legged  quadruped  in  any  peculiar  manner ; 
he  exposes  sheep  with  long  and  short  wool  to  the  same 
climate.  He  does  not  allow  the  most  vigorous  males  to 
struggle  for  the  females.  He  does  not  rigidly  destroy  all 
inferior  animals,  but  protects  during  each  varying  season, 
as  far  as  lies  in  his  power,  all  his  productions.  He  often 
begins  his  selection  by  some  half-monstrous  form ;  *or  at 
least  by  some  modification  prominent  enough  to  catch  his 
eye,  or  to  be  plainly  useful  to  him.  Under  nature,  the 
slightest  difi'erence  of  structure  or  constitution  may  well 
turn  the  nicely-balanced  scale  in  the  struggle  for  life,  and 
so  be  preserved.  How  fleeting  are  the  wishes  and  eflbrts 
of  man !  how  short  his  time  !  and  consequently  how  poor 
will  his  products  be,  compared  with  those  accumulated  by 
nature  during  whole  geological  periods.  Can  we  won- 
der, then,  that  nature's  productions  should  be  far  "  truer  " 
in  character  than  man's  productions  ;  that  they  should  be 
infinitely  better  adapted  to  the  most  complex  conditions 
of  life,  and  should  plainly  bear  the  stamp  of  far  higher 
workmanship  ? 

It  may  be  said  that  natural  selection  is  daily  and 
hourly  scrutinising,  throughout  the  world,  every  varia- 
tion, even  the  slightest ;  rejecting  that  which  is  bad,  pre- 
serving and  adding  up  all  that  is  good ;  silently  and  in- 
sensibly working,  whenever  and  wherever  opportunity 
ofi*ers,  at  the  improvement  of  each  organic  being  in  rela- 
tion to  its  organic  and  inorganic  conditions  of  life.  We 
see  nothing  of  these  slow  changes  in  progress,  until  the 
hand  of  time  has  marked  the  long  lapse  of  ages,  and  then 
so  imperfect  is  our  view  into  long  past  geological  ages, 
that  we  only  see  that  the  forms  of  life  are  now  difi'erent 
from  what  they  formerly  were. 

Although  natural  selection  can  act  only  through  and 
for  the  good  of  each  being,  yet  characters  and  structures, 


Chap,  IV.]  NATURAL   SELECTION.  81 

which  we  are  apt  to  consider  as  of  very  trifling  impor- 
tance, may  thus  be  acted  on.  When  we  see  leaf-eating  in- 
sects green,  and  bark-feeders  mottled-grey;  the  alpine 
ptarmigan  white  in  winter,  the  red-grouse  the  colour  of 
heather,  and  the  black-grouse  that  of  peaty  earth,  we  must 
believe  that  these  tints  are  of  service  to  these  birds  and 
insects  in  preserving  them  from  danger.  Grouse,  if  not 
destroyed  at  some  period  of  their  lives,  would  increase  in 
countless  numbers ;  they  are  known  to  suffer  largely  from 
birds  of  prey  ;  and  hawks  are  guided  by  eyesight  to  their 
prey, — so  much  so,  that  on  parts  of  the  Continent  persons 
are  warned  not  to  keep  white  pigeons,  as  being  the  most 
liable  to  destruction.  Hence  I  can  see  no  reason  to  doubt 
that  natural  selection  might  be  most  effective  in  giving 
the  proper  column  to  each  kind  of  grouse,  and  in  keeping 
that  colour,  when  once  acquired,  true  and  constant. 
'Nor  ought  we  to  think  that  the  occasional  destruction  of 
an  animal  of  any  particular  colour  would  produce  little 
effect :  we  should  remember  how  essential  it  is  in  a  flock 
of  white  sheep  to  destroy  every  laAb  with  the  faintest 
trace  of  black.  In  plants  the  down  on  the  fruit  and  the 
colour  of  the  flesh  are  considered  by  botanists  as  charac- 
ters of  the  most  trifling  importance  :  yet  we  hear  from  an 
excellent  horticulturist.  Downing,  that  in  the  United 
States  smooth-skinned  fruits  suffer  far  more  from  a  beetle, 
a  curculio,  than  those  with  down ;  that  purple  plums 
suffer  far  more  from  a  certain  disease  than  yellow  plums ; 
whereas  another  disease  attacks  yellow-fleshed  peaches  far 
more  than  those  with  other  coloured  flesh.  If,  with  all 
the  aids  of  art,  these  slight  differences  make  a  great  differ- 
ence in  cultivating  the  several  varieties,  assuredly,  in  a 
state  of  nature,  where  the  trees  would  have  to  struggle  with 
other  trees,  and  with  a  host  of  enemies,  such  differences 
would  effectually  settle  which  variety,  whether  a  smooth 
or  downy,  a  yello^v  or  purple  fleshed  fruit,  should  succeed. 
In  looking  at  many  small  points  of  difference  between 
species,  which,  as  far  as  our  ignorance  permits  us  to  judge, 
seem  to  be  quite  unimportant,  we  must  not  forget  that 
climate,  food,  &c.,  probably  produce  some  slight  and  di- 
rect effect.     It  is,  however,  far  more  necessary  to  bear  in 


g2  NATURAL   SELECTION.  [Chap.  IV. 

mind  that  there  are  many  unknown  laws  of  correlation  of 
growth,  which,  when  one  part  of  the  organisation  is  modi- 
fied through  variation,  and  the  modifications  are  accumu- 
lated by  natural  selection  for  the  good  of  the  being,  will 
cause  other  modifications,  often  of  the  most  unexpected 
nature. 

As  we  see  that  those  variations  which  under  domesti- 
cation appear  at  any  particular  period  of  life,  tend  to  re- 
appear in  the  offspring  at  the  same  period  ; — for  instance, 
in  the  seeds  of  the  many  varieties  of  our  culinary  and 
agricultural  plants  ;  in  the  caterpillar  and  cocoon  stages 
of  the  varieties  of  the  silkworm  ;  in  the  eggs  of  poultry, 
and  in  the  colour  of  the  down  of  their  chickens ;  in  the 
horns  of  our  sheep  and  cattle  when  nearly  adult ; — so  in  a 
state  of  nature,  natural  selection  will  be  enabled  to  act  on 
and  modify  organic  beings  at  any  age,  by  the  accumula- 
tion of  profitable  variations  at  that  age,  and  by  their  inher- 
itance at  a  corresjDonding  age.  If  it  profit  a  plant  to  have 
its  seeds  more  and  more  widely  disseminated  by  the  wind, 
I  can  see  no  greater  difficulty  in  this  being  effected  through 
natural  selection,  than  in  the  cotton-planter  increasing  and 
improving  by  selection  the  down  in  the  pods  on  his  cot- 
ton-trees. Natural  selection  may  modify  and  adapt  the 
larva  of  an  insect  to  a  score  of  contingencies,  wholly  dif- 
ferent from  those  which  concern  the  mature  insect.  These 
modifications  will  no  doubt  affect,  through  the  laws  of 
correlation,  the  structure  of  the  adult ;  and  probably  in 
the  case  of  those  insects  which  live  only  for  a  few  hours, 
and  which  never  feed,  a  large  part  of  their  structure  is 
merely  the  correlated  result  of  successive  changes  in  the 
structure  of  their  larvae.  So,  conversely,  modifications  in 
the  adult  will  probably  often  affect  the  structure  of  the 
larva ;  but  in  all  cases  natural  selection  will  ensure  that 
modifications  consequent  on  other  modifications  at  a  dif- 
ferent period  of  life,  shall  not  be  in  the  least  degree  inju- 
rious :  for  if  they  became  so,  they  would  cause  the  extinc- 
tion of  the  species. 

ISTatural  selection  will  modify  the  structure  of  the 
young  in  relation  to  the  parent,  and  of  the  parent  in  rela- 
tion to  the  young.     In  social  animals  it  will  adapt  the 


Chap.  IV.]  BEXUAL    SELECTION.  §3 

structure  of  eacli  individual  for  the  benefit  of  tlie  commu- 
nity ;  if  each  in  consequence  profits  by  the  selected 
change.  What  natural  selection  cannot  do,  is  to  modify 
the  structure  of  one  species,  without  giving  it  any  advan- 
tage, for  the  good  of  another  species  ;  and  though  state- 
ments to  this  eflect  may  be  found  in  works  of  natural  his- 
tory, I  cannot  find  one  case  which  will  bear  investigation. 
A  structure  used  only  once  in  an  animal's  whole  life,  if 
of  high  importance  to  it,  might  be  modified  to  any  extent 
by  natural  selection ;  for  instance,  the  great  jaws  possessed 
by  certain  insects,  and  used  exclusively  for  opening  the 
cocoon — or  the  hard  tip  to  the  beak  of  nestling  birds, 
used  for  breaking  the  egg.  It  has  been  asserted,  that  of 
the  best  short-beaked  tumbler-pigeons  more  perish  in  the 
egg  than  are  able  to  get  out  of  it ;  so  that  fanciers  assist 
in  the  act  of  hatching.  'Now,  if  nature  had  to  make  the 
beak  of  a  full-grown  pigeon  very  short  for  the  bird's  own 
advantage,  the  process  of  modification  would  be  very 
slow,  and  there  would  be  simultaneously  the  most  rigor- 
ous selection  of  the  young  birds  within  the  egg,  which 
had  the  most  powerful  and  hardest  beaks,  for  all  with  weak 
beaks  would  inevitably  perish :  or,  more  delicate  and  more 
easily  broken  shells  might  be  selected,  the  thickness  of  the 
shell  being  known  to  vary  like  every  other  structure. 

Sexual  Selection. — Inasmuch  as  peculiarities  often  ap- 
pear under  domestication  in  one  sex  and  become  heredi- 
tarily attached  to  that  sex,  the  same  fact  probably  occurs 
under  nature,  and  if  so,  natural  selection  will  be  able  to 
modify  one  sex  in  its  functional  relations  to  the  other  sex, 
or  in  relation  to  wholly  difi'erent  habits  of  life  in  the  two 
sexes,  as  is  sometimes  the  case  with  insects.  And  this 
leads  me  to  say  a  few  words  on  what  I  call  Sexual  Selec- 
tion. This  depends,  not  on  a  struggle  for  existence,  but 
on  a  struggle  between  the  males  for  possession  of  the 
females  ;  the  result  is  not  death  to  the  unsuccessful  com- 
petitor, but  few  or  no  ofi'spring.  Sexual  selection  is,  there- 
fore, less  rigorous  than  natural  selection.  Generally,  the 
most  vigorous  males,  those  which  are  best  fitted  for  their 
places  in  nature,  will  leave  most  progeny.     But  in  many 


34-  SEXUAL   SELECTION.  [Chip.  IV. 

cases,  victory  will  depend  not  on  general  vigour,  bnt  on 
having  special  weapons,  confined  to  the  male  sex.  A 
hornless  stag,  or  spnrless  cock  would  have  a  poor  chance 
of  leaving  offspring.  Sexual  selection  hj  always  allowing 
the  victor  to  breed  might  surely  give  indomitable  cour- 
age, length  to  the  spur,  and  strength  to  the  wing  to  strike 
in  the  spurred  leg,  as  well  as  the  brutal  cock-fighter,  who 
knows  well  that  he  can  improve  his  breed  by  careful 
selection  of  the  best  cocks.  How  low  in  the  scale  of 
nature  this  law  of  battle  descends,  I  know  not ;  male  alli- 
gators have  been  described  as  fighting,  bellowing,  and 
whirling  round,  like  Indians  in  a  war-dance,  for  the  pos- 
session of  the  females  ;  male  salmons  have  been  seen 
fighting  all  day  long ;  male  stag-beetles  often  bear  wounds 
from  the  huge  mandibles  of  other  males.  The  war  is, 
perhaps,  severest  between  the  males  of  polygamous  ani- 
mals, and  these  seem  oftenest  provided  with  special 
weapons.  The  males  of  carnivorous  animals  are  already 
well  armed  ;  though  to  them  and  to  others,  special  means 
of  defence  may  be  given  tln-ough  means  of  sexual  selec- 
tion, as  the  mane  to  the  lion,  the  shoulder-pad  to  the  boar, 
and  the  hooked  jaw  to  the  male  salmon ;  for  the  shield 
may  be  as  important  for  victory,  as  the  sword  or  spear. 

Amongst  birds,  the  contest  is  often  of  a  more  peaceful 
character.  All  those  who  have  attended  to  the  subject, 
believe  that  there  is  the  severest  rivalry  between  the 
males  of  many  species  to  attract  by  singing  the  females. 
The  rock-thrush  of  Guiana,  birds  of  Paradise,  and  some 
others,  congregate  ;  and  successive  males  display  their 
gorgeous  plumage  and  perform  strange  antics  before  the 
females,  which  standing  by  as  spectators,  at  last  choose 
the  most  attractive  partner.  Those  who  have  closely 
attended  to  birds  in  confinement  well  know  that  they 
often  take  individual  preferences  and  dislikes :  thus  Sir 
R.  Heron  has  described  how  one  pied  peacock  was  emi- 
nently attractive  to  all  his  hen  birds.  It  may  appear 
childish  to  attribute  any  effect  to  such  apparently  weak 
mjeans :  I  cannot  here  enter  on  the  details  necessary  to 
support  this  view ;  but  if  man  can  in  a  short  time  give 
elegant  carriage  and  beauty  to  his  bantams,  according  to 


Chap.  IV.]  NATURAL   SELECTION.  §5 

his  standard  of  beauty,  I  can  see  no  good  reason  to  doubt 
that  female  birds,  by  selecting,  during  thousands  of  gen- 
erations, the  most  melodious  or  beautiful  males,  according 
to  their  standard  of  beauty,  might  produce  a  marked 
effect.  I  strongly  suspect  that  some  well-known  laws  with 
respect  to  the  plumage  of  male  and  female  birds,  in  com- 
parison with  the  plumage  of  the  young,  can  be  explained 
on  the  view  of  plumage  having  been  chiefly  modified  by 
sexual  selection,  acting  when  the  birds  have  come  to  the 
breeding  age  or  during  the  breeding  season ;  the  modi- 
fications thus  produced  being  inherited  at  corresponding 
ages  or  seasons,  either  by  the  males  alone,  or  by  the 
males  and  females  ;  but  I  have  not  space  here  to  enter  on 
this  subject. 

Thus  it  is,  as  I  believe,  that  w^hen  the  males  and 
females  of  any  animal  have  the  same  general  habits  of  life, 
but  differ  in  structure,  colour,  or  ornament,  such  differ- 
ences have  been  mainly  caused  by  sexual  selection  ;  that 
is,  individual  males  have  had,  in  successive  generations, 
some  slight  advantage  over  other  males,  in  their  weapons, 
means  of  defence,  or  charms  ;  and  have  transmitted  these 
advantages  to  their  male  offspring.  Yet,  I  would  not 
wish  to  attribute  all  such  sexual  differences  to  this  agen- 
cy :  for  we  see  peculiarities  arising  and  becoming  attached 
to  the  male  sex  in-  our  domestic  animals  (as  the  wattle  in 
male  carriers,  horn-like  protuberances  in  the  cocks  of 
certain  fowls,  &c.),  which  we  cannot  believe  to  be  either 
useful  to  the  males  in  battle,  or  attractive  to  the  females. 
"We  see  analogous  cases  under  nature,  for  instance,  the 
tuft  of  hair  on  the  breast  of  the  turkey-cock,  which  can 
hardly  be  either  useful  or  ornamental  to  this  bird  ; — in- 
deed, had  the  tuft  appeared  under  domestication,  it  would 
have  been  called  a  monstrosity. 

Illustrations  of  the  action  of  Natiiral  Selection. — ^In 
order  to  make  it  clear  how,  as  I  believe,  natural  selection 
acts,  I  must  be^  permission  to  give  one  or  two  imaginary 
illustrations.  Let  us  take  the  case  of  a  wolf,  which  preys 
on  various  animals,  securing  some  by  craft,  some  by 
strength,  and  some  by  fleetness  ;  and  let  us  suppose  that 


QQ  NATURAL   SELECTION.  -  [Chap.  IV. 

the  fleetest  prey,  a  deer  for  instance,  had  from  any  change 
in  the  country  increased  in  numbers,  or  that  other  pre;y 
had  decreased  in  numbers,  during  that  season  of  the  year 
when  the  wolf  is  hardest  pressed  for  food.  I  can  under 
such  circumstances  see  no  reason  to  doubt  that  the  swift- 
est and  slimmest  wolves  would  have  the  best  chance  of 
surviving,  and  so  be  preserved  or  selected, — provided 
always  that  they  retained  strength  to  master  their  prey 
at  this  or  at  some  other  period  of  the  year,  when  they 
might  be  compelled  to  prey  on  other  animals.  I  can  see 
no  more  reason  to  doubt  this,  than  that  man  can  improve 
the  fleetness  of  his  greyhounds  by  careful  and  methodical 
selection,  or  by  that  unconscious  selection  which  results 
from  each  man  trying  to  keep  the  best  dogs  without  any 
thought  of  modifying  the  breed. 

Even  without  any  change  in  the  proportional  numbers 
of  the  animals  on  wdiich  our  wolf  preyed,  a  cub  might 
be  born  with  an  innate  tendency  to  pursue  certain  kinds 
of  prey.     Nor  can  this  be  thought  very  improbable  ;  for 
we  often  observe  great  differences  in  the  natural  tenden- 
cies of  our  domestic  animals  ;  one  cat,  for  instance,  taking 
to  catch  rats,  another  mice  ;  one  cat,  according  to  Mr.  St. 
John,  bringing  home  winged  game,  another  hares  or  rab- 
bits, and  another  hunting  on  marshy  ground  and  almost 
nightly  catching  woodcocks  or  snipes.     The  tendency  to 
catch  rats  rather  than  mice  is  known  to  be  inherited. 
Now,  if  any  slight  innate  change  of  habit  or  of  structure 
benefited    an    individual  wolf,  it  would  have  the    best 
chance  of  surviving  and  of  leaving  offspring.     Some  of 
its   young  would   probably  inherit  the   same  habits  or 
structure,  and  by  the  repetition  of  this  process,  a  new 
variety  might  be  fonned  which  would  either  supplant  or 
coexist  with  the  parent  form  of  wolf.      Or,  again,  the 
wolves  inhabiting  a  mountainous  district,  and  those  fre- 
quenting the  lowlands,  would  naturally  be  forced  to  hunt 
different  prey  ;  and  from  the  continued  preservation  of 
the  individuals  best  fitted  for  the  two  sites,  two  varieties 
might  slowly  be  formed.      These  varieties  would  cross 
and  blend  where  they  met ;  but  to  this  subject  of  inter- 
crossing we  shall  soon  have  to  return.     I  may  add,  that, 


Chap.  IV.  1  NATURAL   SELECTION.  gY 

according  to  Mr.  Pierce,  there  are  two  varieties  of  the 
wolf  inhabiting  the  Catskill  Mountains  in  the  United 
States,  one  with  a  light  grevhound-like  form,  which  j)nr- 
sues  deer,  and  the  other  more  bulky,  with  shorter  legs, 
which  more  frequently  attacks  the  shepherd's  flocks. 

Let  us  now  take  a  more  complex  case.  Certain  plants 
excrete  a  sweet  juice,  apparently  for  the  sake  of  elimina- 
ting something  injurious  from  their  sap  :  this  is  effected 
by  glands  at  the  base  of  the  stipules  in  some  Leguminosse, 
and  at  the  beak  of  the  leaf  of  the  common  laurel.  This 
juice,  though  small  in  quantity,  is  greedily  sought  by 
insects.  Let  us  now  suppose  a  little  sweet  juice  or  nectar 
to  be  excreted  by  the  inner  bases  of  the  petals  of  a  flower. 
In  this  case,  insects  in  seeking  the  nectar  would  get  dusted 
with  pollen,  and  would  certainly  often  transport  the  pollen 
from  one  flower  to  the  stigma  of  another  flower.  The 
flowers  of  two  distinct  individuals  of  the  same  species 
would  thus  get  crossed ;  and  the  act  of  crossing,  we  have 
good  reason  to  believe  (as  will  hereafter  be  more  fully 
alluded  to),  would  produce  very  vigorous  seedlings,  which 
consequently  would  have  the  best  chance  of  flourishing 
and  surviving.  Some  of  these  seedlings  would  probably 
inherit  the  nectar-excreting  power.  Those  individual 
flowers  which  had  the  largest  glands  or  nectaries,  and 
which  excreted  most  nectar,  would  be  oftenest  visited  by 
insects,  and  would  be  oftenest  crossed  ;  and  so  m  the  long 
run  would  gain  the  upper  hand.  Those  flowers,  also, 
which  had  their  stamens  and  pistils  placed,  in  relation 
to  the  size  and  habits  of  the  particular  insects  which  vis- 
ited them,  so  as  to  favour  in  any  degree  the  transportal 
of  their  pollen  from  flower  to  flower,  would  likewise  be 
favoured  or  selected.  "We  might  have  taken  the  case  of 
insects  visiting  flowers  for  the  sake  of  collecting  pollen 
instead  of  nectar ;  and  as  pollen  is  formed  for  the  sole 
object  of  fertilisation,  its  destruction  appears  a  simple  loss 
to  the  plant ;  yet  if  a  little  pollen  were  carried,  at  first 
occasionally  and  then  habitually,  by  the  pollen-devouring 
insects  from  flower  to  flower,  and  a  cross  thus  eftected, 
although  nine-tenths  of  the  pollen  were  destroyed,  it  might 
still  be  a  great  gain  to  the  plant ;  and  those  individuals 


gg  NATURAL  SELECTION.  [Chap.  rV. 

wliicli  produced  more  and  more  pollen,  and  had  larger 
and  larger  anthers,  wonld  be  selected. 

"When  our  plant,  bj  this  process  of  the  continued  pre- 
servation or  natural  selection  of  more  and  more  attractive 
flowers,  had  been  rendered  highly  attractive  to  insects, 
they  would,  unintentionlly  on  their  part,  regularly  carry 
pollen  from  flower  to  flcs^er ;  and  that  they  can  most 
effectually  do  this,  I  could  easily  show  by  many  striking 
instances.  I  will  give  only  one — not  as  a  very  striking 
case,  but  as  likewise  illustrating  one  step  in  the  separation 
of  the  sexes  of  plants,  presently  to  be  alluded  to.  Some 
holly-trees  bear  only  male  flowers,  which  have  four  sta- 
mens producing  rather  a  small  quantity  of  pollen,  and  a 
rudimentary  pistil ;  other  holly-trees  bear  only  female 
flowers ;  these  have  a  full-sized  pistil,  and  four  stamens 
with  shrivelled  anthers,  in  which  not  a  grain  of  pollen 
can  be  detected.  Having  found  a  female  tree  exactly 
sixty  yards  from  a  male  tree,  I  put  the  stigmas  of  twenty 
flowers,  taken  from  difierent  branches,  under  the  micro- 
scope, and  on  all,  without  exception,  there  were  pollen- 
grains,  and  on  some  a  profusion  of  pollen.  As  the  wind 
had  set  for  several  days  from  the  female  to  the  male  tree, 
the  j)ollen  could  not  thus  have  been  carried.  The  weather 
had  been  cold  and  boisterous,  and  therefore  not  favourable 
to  bees,  nevertheless  every  female  flower  which  I  examined 
had  been  efi'ectually  fertilised  by  the  bees,  accidentally 
dusted  with  pollen,  having  flown  from  tree  to  tree  in  search 
of  nectar.  But  to  return  to  our  imaginary  case :  as  soon 
as  the  plant  had  been  rendered  so  highly  attractive  to 
insects  that  pollen  was  regularly  carried  from  flower  to 
flower,  another  process  might  commence.  IS^o  naturalist 
doubts  the  advantage  of  what  has  been  called  the  "  phy- 
siological division  of  labour ; "  hence  we  may  believe  that 
it  would  be  advantageous  to  a  plant  to  produce  stamens 
alone  in  one  flower  or  on  one  whole  plant,  and  pistils  alone 
in  another  flower  or  on  another  plant.  In  plants  under 
culture  and  placed  under  new  conditions  of  life,  sometimes 
the  ntale  organs  and  sometimes  the  female  organs  become 
more  or  less  impotent ;  now  if  we  suppose  this  to  occur 
in  ever  so  slight  a  degree  under  nature,  then  as  pollen  is 


Chap.  IV.l  NATURAL    SELECTION.  g9 

already  carried  regularly  from  flower  to  flower,  and  as  a 
more  complete  separation  of  the  sexes  of  our  plant  would 
be  advantageous  on  the  principle  of  the  division  of  labour, 
individuals  with  this  tendency  more  and  more  increased, 
would  be  continually  favoured  or  selected,  until  at  last  a 
complete  separation  of  the  sexes  would  be  efi'ected. 

Let  us  now  turn  to  the  nectar-feeding  insects  in  our 
imaginary  case :  we  may  suppose  the  plant  of  which  we 
have  been  slowly  increasing  the  nectar  by  continued  selec- 
tion, to  be  a  common  plant ;  and  that  certain  insects  de- 
pended in  main  part  on  its  nectar  for  food.  I  could  give 
many  facts,  showing  how  anxious  bees  are  to  save  time ; 
for  instance,  their  habit  of  cutting  holes  and  sucking  the 
nectar  at  the  bases  of  certain  flowers,  which  they  can, 
with  a  very  little  more  trouble,  enter  by  the  mouth. 
Bearing  such  facts  in  mind,  I  can  see  no  reason  to  doubt 
that  an  accidental  deviation  in  the  size  and  form  of  the 
body,  or  in  the  curvature  and  length  of  the  proboscis, 
&c.,  far  too  slight  to  be  appreciated  by  us,  might  profit  a 
bee  or  other  insects,  so  that  an  individual  so  characterised 
would  be  able  to  obtain  its  food  more  quickly,  and  so 
have  a  better  chance  of  living  and  leaving  descendants. 
Its  descendants  would  probably  inherit  a  tendency  to  a 
similar  slight  deviation  of  structure.  The  tubes  of  the 
corollas  of  the  common  red  and  incarnate  clovers  (Trifo- 
lium  pratense  and  incarnatum)  do  not  on  a  hasty  glance 
appear  to  difi'er  in  length ;  yet  the  hive-bee  can  easily 
suck  the  nectar  out  of  the  incarnate  clover,  but  not  out 
of  the  common  red  clover,  which  is  visited  by  humble- 
bees  alone  ;  so  that  whole  fields  of  the  red  clover  ofi'er  in 
vain  an  abundant  supply  of  precious  nectar  to  the  hive- 
bee.  Thus  it  might  be  a  great  advantage  to  the  hive-bee 
to  have  a  slightly  longer  or  difi'erently  constructed  pro- 
boscis. On  the  other  hand,  I  have  found  by  experiment 
that  the  fertility  of  clover  greatly  depends  on  bees  visiting 
and  moving  parts  of  the  corolla,  so  as  to  push  the  pollen 
on  to  the  stigmatic  surface.  Hence,  again,  if  humble-bees 
were  to  become  rare  in  any  country,  it  might  be  a  great 
advantage  to  the  red  clover  to  have  a  shorter  or  more 
deeply  divided  tube  to  its  corolla,  so  that  the  hive-bee 
6 


90  OIT   THE    ADVANTAGE  [Chap.  IV. 

could  visit  its  flowers.  Thus  I  can  understand  how  a 
flower  and  a  bee  might  slowly  become,  either  simulta- 
neously or  one  after  the  other,  modified  and  adapted  in 
the  most  perfect  manner  to  each  other,  by  the  continued 
preservation  of  individuals  presenting  mutual  and  slightly 
favourable  deviations  of  structure. 

I  am  well  aware  that  this  doctrine  of  natural  selection, 
exemplified  in  the  above  imaginary  instances,  is  open  to 
the  same  objections  which  were  at  first  urged  against  Sir 
Charles  Ly ell's  noble  views  on  "  the  modern  changes  of 
the  earth,  as  illustrative  of  geology  ;  "  but  we  now  very 
seldom  hear  the  action,  for  instance,  of  the  coast-waves, 
called  a  trifling  and  insignificant  cause,  when  applied  to 
the  excavation  of  gigantic  valleys  or  to  the  formation  of 
the  longest  lines  of  inland  clifis.  I^atural  selection  can 
act  only  by  the  preservation  and  accumulation  of  infini- 
tesimally  small  inherited  modifications,  each  profitable  to 
the  preserved  being ;  and  as  modern  geology  has  almost 
banished  such  views  as  the  excavation  of  a  great  valley 
by  a  single  diluvial  wave,  so  will  natural  selection,  if  it  be 
a  true  principle,  banish  the  belief  of  the  continued  crea- 
tion of  new  organic  beings,  or  of  any  great  and  sudden 
modification  in  their  structure. 

On  the  Intercrossing  of  Individuals. — I  must  here  in- 
troduce a  short  diOT'ession.  In  the  case  of  animals  and 
plants  with  separated  sexes,  it  is  of  course  obvious  that  two 
individuals  must  always  (with  the  exception  of  the  curious 
and  not  well-understood  cases  of  parthenogenesis)  unite  for 
each  birth  ;  but  in  the  case  of  hermaphrodites  this  is  far 
from  obvious.  JSTevertheless  I  am  strongly  inclined  to  be- 
lieve that  with  all  hermaphrodites  two  individuals,  either 
occasionally  or  habitually,  concur  for  the  reproduction  of 
their  kind.  This  view  was  first  suggested  by  Andrew 
Knight.  We  shall  j^resently  see  its  importance ;  but  I 
must  here  treat  the  subject  with  extreme  brevity,  though 
I  have  the  materials  prepared  for  an  ample  discussion. 
All  vertebrate  animals,  all  insects,  and  some  other  large 
groups  of  animals,  pair  for  each  birth.  Modern  research 
has  much  diminished  the  number  of  supposed  hermaphro- 
dites, and  of  real  hermaphrodites  a  large  number  pair ; 


Chap.  IV.]  OF   INTERCROSSING.  g^ 

tliat  is,  two  individuals  regularly  unite  for  reproduction, 
which  is  all  that  concerns  us.  But  still  there  are  many- 
hermaphrodite  animals  which  certainly  do  not  habitually 
pair,  and  a  vast  majority  of  plants  are  hermaphrodites. 
What  reason,  it  may  be  asked,  is  there  for  supposing  in 
these  cases  that  two  individuals  ever  concur  in  reproduc- 
tion ?  As  it  is  impossible  here  to  enter  on  details,  I  must 
trust  to  some  general  considerations  alone. 

In  the  first  place  I  have  collected  so  large  a  body  of 
facts  showing,  in  accordance  with  the  almost  universal 
belief  of  breeders,  that  with  animals  and  plants  a  cross 
between  diflerent  varieties,  or  between  individuals  of  the 
same  variety  but  of  another  strain,  gives  vigour  and  fer- 
tility to  the  ofi'spring ;  and  on  the  other  hand,  that  close 
interbreeding  diminishes  vigour  and  fertility  ;  that  these 
facts  alone  incline  me  to  believe  that  it  is  a  general  law 
of  nature  (utterly  ignorant  though  we  be  of  the  meaning 
of  the  law)  that  no  organic  being  fertilizes  itself  for  an 
eternity  of  generations  ;  but  that  a  cross  with  another  in- 
dividual is  occasionally — perhaps  at  very  long  intervals — 
indispensable. 

On  the  belief  that  this  is  a  law  of  nature,  we  can,  1 
think,  understand  several  large  classes  of  facts,  such  as 
the  following,  which  on  any  other  view  are  inexplicable. 
Every  hybridizer  knows  how  unfavourable  exposure  to 
Avet  is  to  the  fertilisation  of  a  flower,  yet  what  a  multi- 
tude of  flowers  have  their  anthers  and  stigmas  fully  ex- 
posed to  the  weather  !  but  if  an  occasional  cross  be  indis- 
pensable, the  fullest  freedom  for  the  entrance  of  pollen 
from  another  individual  will  explain  this  state  of  expo- 
sure, more  especially  as  the  plant's  own  anthers  and  pistil 
generally  stand  so  close  together  that  self-fertilisation 
seems  almost  inevitable.  Many  flowers,  on  the  other 
hand,  have  their  organs  of  fructification  closely  enclosed, 
as  in  the  great  papilionaceous  or  pea-family  ;  but  in  sev- 
eral, perhaps  in  all,  such  fiowers,  there  is  a  very  curious 
adaptation  between  the  structure  of  the  flower  and  the 
manner  in  which  bees  suck  the  nectar  ;  for,  in  doing  this, 
they  either  push  the  flower's  own  pollen  on  the  stigma, 
or  bring  pollen  from  another  flower.     So  necessary  are 


92  ON   THE   ADVANTAGE  [Chap.  IV. 

the  visits  of  bees  to  papilionaceous  flowers,  that  I  have 
found,  by  experiments  published  elsewhere,  that  their 
fertility  is  greatly  diminished  if  these  visits  be  prevented. 
Kow,  it  is  scarcely  possible  that  bees  should  fly  from 
flower  to  flower,  and  not  carry  pollen  from  one  to  the 
other,  to  the  great  good,  as  I  believe,  of  the  plant.  Bees 
will  act  like  a  camel-hair  pencil,  and  it  is  quite  sufficient 
just  to  touch  the  anthers  of  one  flower  and  then  the  stig- 
ma of  another  with  the  same  brush  to  ensure  fertilisation ; 
but  it  must  not  be  supposed  that  bees  would  thus  pro- 
duce a  multitude  of  hybrids  between  distinct  species ; 
for  if  you  bring  on  the  same  brush  a  plant's  own  pollen 
and  pollen  from  another  species,  the  former  will  have 
such  a  prepotent  efi'ect,  that  it  will  invariably  and  com- 
pletely destroy,  as  has  been  shown  by  Gartner,  any  in- 
fluence from  the  foreign  pollen. 

"When  the  stamens  of  a  flower  suddenly  spring  towards 
the  pistil,  or  slowly  move  one  after  the  other  towards  it, 
the  contrivance  seems  adapted  solely  to  ensure  self-fertili- 
sation ;  and  no  doubt  it  is  useful  for  this  end  :  but,  the 
agency  of  insects  is  often  required  to  cause  the  stamens 
to  spring  forward,  as  Kolreuter  has  shown  to  be  the  case 
with  the  barberry  ;  and  curiously  in  this  very  genus,  which 
seems  to  have  a  special  contrivance  for  self-fertilisation, 
it  is  Avell  known  that  if  very  closely-allied  forms  or  varie- 
ties are  planted  near  each  other,  it  is  hardly  possible  to 
raise  pure  seedlings,  so  largely  do  they  naturally  cross. 
In  many  other  cases,  far  from  there  being  any  aids  for 
self-fertilisation,  there  are  special  contrivances,  as  I  could 
show  from  the  writings  of  C.  C.  Sprengel  and  from  my 
own  observations,  which  eflectually  prevent  the  stigma 
receiving  pollen  from  its  own  flower:  for  instance,  in 
Lobelia  fulgens,  there  is  a  really  beautiful  and  elaborate 
contrivance  by  which  every  one  of  the  infinitely  numer- 
ous pollen-granules  are  swept  out  of  the  conjoined  anthers 
of  each  flower,  before  the  stigma  of  that  individual  flower 
is  ready  to  receive  them  ;  and  as  this  flower  is  never 
visited,  at  least  in  my  garden,  by  insects,  it  never  sets  a 
seed,  though  by  placing  pollen  from  one  flower  on  tlie 
stigma  of  another,  I  raised  plenty  of  seedlings ;  and  whilst 


Chap.  IVJ  OF   INTERCROSSING.  93 

another  species  of  Lobelia  growing  close  by,  which,  is 
visited  by  bees,  seeds  freely.  In  very  many  other  cases, 
though  there  be  no  special  mechanical  contrivance  to  pre- 
vent the  stigma  of  a  flower  receiving  its  own  j^ollen,  yet, 
as  C.  C.  Sprengel  has  shown,  and  as  I  can  confirm,  either 
the  anthers  burst  before  the  stigma  is  ready  for  fertilisation, 
or  the  stigma  is  ready  before  the  pollen  of  that  flower  is 
ready,  so  that  these  plants  have  in  fact  separated  sexes, 
and  must  habitually  be  crossed.  How  strange  are  these 
facts  !  How  strange  that  the  pollen  and  stigmatic  surface 
of  the  same  flower,  though  placed  so  close  together,  as  if 
for  the  very  purpose  of  self-fertilisation,  should  in  so  many 
cases  be  mutually  useless  to  each  other  !  How  simply 
are  these  facts  explained  on  the  view  of  an  occasional 
cross  with  a  distinct  individual  being  advantageous  or  in- 
dispensable ! 

K  several  varieties  of  the  cabbage,  radish,  onion,  and 
of  some  other  plants,  be  allowed  to  seed  near  each  other, 
a  large  majority,  as  I  have  found,  of  the  seedlings  thus 
raised  will  turn  out  mongrels :  for  instance,  I  raised  233 
seedling  cabbages  from  some  plants  of  difi'erent  varieties 
growing  near  each  other,  and  of  these  only  Y8  were  true 
to  their  kind,  and  some  even  of  these  were  not  perfectly 
true.  Yet  the  pistil  of  each  cabbage-flower  is  surrounded 
not  only  by  its  own  six  stamens,  but  by  those  of  the  many 
other  flowers  on  the  same  plant.  How,  then,  comes  it 
that  such  a  vast  number  of  the  seedlings  are  mongrelized? 
I  suspect  that  it  must  arise  from  the  pollen  of  a  distinct 
"variety  having  a  prepotent  efi'ect  over  a  flower's  own 
pollen ;  and  that  this  is  part  of  the  general  law  of  good 
being  derived  from  the  intercrossing  of  distinct  individuals 
of  the  same  species.  When  distinct  species  are  crossed 
the  case  is  directly  the  reverse,  for  a  plant's  own  pollen  is 
always  prepotent  over  foreign  pollen ;  but  to  this  subject 
we  shall  return  in  a  future  chapter. 

Li  the  case  of  a  gigantic  tree  covered  with  innumera- 
ble flowers,  it  may  be  objected  that  pollen  could  seldom 
be  carried  from  tree  to  tree,  and  at  most  only  from  flower 
to  flower  on  the  same  tree,  and  that  flowers  on  the  same 
tree  can  be  considered  as  distinct  individuals  only  in  a 


9^  ON   THE   ADVANTAGE  [Chap.  IV, 

limited  sense.  I  believe  this  objection  to  be  valid,  but 
that  nature  lias  largely  provided  against  it  bv  giving  to 
trees  a  strong  tendency  to  bear  flowers  with  separated 
sexes.  "When  the  sexes  are  separated,  although  the  male 
and  female  flowers  may  be  produced  on  the  same  tree,  we 
can  see  that  pollen  must  be  regularly  carried  from  flower 
to  flower ;  and  this  will  give  a  better  chance  of  pollen 
being  occasionally  carried  from  tree  to  tree.  That  trees 
belonging  to  all  Orders  have  their  sexes  more  often  sepa- 
rated than  other  plants,  I  find  to  be  the  case  in  this  coun- 
try ;  and  at  my  request  Dr.  Hooker  tabulated  the  trees 
of  l^ew  Zealand,  and  Dr.  Asa  Gray  those  of  the  United 
States,  and  the  result  was  as  I  anticipated.  On  the  other 
hand,  Dr.  Hooker  has  recently  informed  me  that  he  finds 
that  the  rule  does  not  hold  in  Australia  ;  and  I  have  made 
these  few  remarks  on  the  sexes  of  trees  simply  to  call  at- 
tention to  the  subject. 

Turning  for  a  very  brief  space  to  animals  :  on  the  land 
there  are  some  hermaphrodites,  as  land-mollusca  and 
earth-worms ;  but  these  all  pair.  As  yet  I  have  not  found 
a  single  case  of  a  terrestrial  animal  which  fertilises  itself. 
We  can  understand  this  remarkable  fact,  which  oflers  so 
strong  a  contrast  with  terrestrial  plants,  on  the  view  of 
an  occasional  cross  being  indispensable,  by  considering 
the  medium  in  which  terrestrial  animals  live,  and  the  na- 
ture of  the  fertilising  element ;  for  we  know  of  no  meanSj 
analogous  to  the  action  of  insects  and  of  the  wind  in  tlie 
case  of  plants,  by  which  an  occasional  cross  could  be 
efi*ected  with  terrestrial  animals  without  the  concurrence 
of  two  individuals.  Of  aquatic  animals,  there  are  many 
self-fertilising  hermaphrodites ;  but  here  currents  in  the 
water  ofi'er  an  obvious  means  for  an  occasional  cross. 
And,  as  in  the  case  of  flowers,  I  have  as  yet  failed,  after 
consultation  with  one  of  the  highest  authorities,  namely, 
Professor  Huxley,  to  discover  a  single  case  of  an  hermaph- 
rodite animal  with  the  organs  of  reproduction  so  per- 
fectly enclosed  within  the  body,  that  access  from  without 
and  the  occasional  influence  of  a  distinct  individual  can 
be  shown  to  be  physically  impossible.  Cirripedcs  long 
appeared  to  me  to  present  a  case  of  very  great  difficulty 


CHAP.  IV.]  OF    INTERCROSSING.  95 

under  tins  point  of  view  ;  bnt  I  liave  been  enabled,  by  a 
fortunate  cliance,  elsewhere  to  prove  that  two  individuals, 
though  both  are  self-fertilising  hermaphrodites,  do  some- 
times  cross. 

It  must  have  struck  most  naturalists  as  a  strange  anom- 
aly that,  ill  the  case  of  both  animals  and  plants,  species 
of  the  same  family  and  even  of  the  same  genus,  though 
agreeing  closely  with  each  other  in  almost  their  whole 
organisation,  yet  are  not  rarely,  some  of  them  hermaphro- 
dites, and  some  of  them  unisexual.  But  if,  in  fact,  all 
hermaphrodites  do  occasionally  intercross  with  other  in- 
dividuals, the  difference  between  hermaphrodites  and  uni- 
sexual species,  as  far  as  function  is  concerned,  becomes 
very  small. 

From  these  several  considerations  and  from  the  many 
special  facts  which  I  have  collected,  but  which  I  am  not 
here  able  to  give,  I  am  strongly  inclined  to  suspect  that, 
both  in  the  vegetable  and  animal  kingdoms,  an  occasional 
intercross  with  a  distinct  individual  is  a  law  of  nature. 
I  am  well  aware  that  there  are,  on  this  view,  many  cases 
of  difficulty,  some  of  which  I  am  trying  to  investigate. 
Finally  then,  we  may  conclude  that  in  many  organic  be- 
ings, a  cross  between  two  individuals  is  an  obvious  neces- 
sity for  each  birth ;  in  many  others  it  occurs  perhaps  only 
at  long  intervals  ;  but  in  none,  as  I  suspect,  can  self-ferti- 
lisation go  on  for  perpetuity. 

Circumstances  favourable  to  Natural  Selection. — Tliis 
is  an  extremely  intricate  subject.  A  large  amount  of 
inheritable  and  diversified  variability  is  favourable,  but  I 
believe  mere  individual  differences  suffice  for  the  work. 
A  large  number  of  individuals,  by  giving  a  better  chance 
for  the  appearance  within  any  given  period  of  profitable 
variations,  will  compensate  for  a  lesser  amount  of  varia- 
bility in  each  individual,  and  is,  I  believe,  an  extremely 
important  element  of  success.  Though  nature  grants  vast 
periods  of  time  for  the  work  of  natural  selection,  she  does 
not  grant  an  indefinite  period ;  for  as  all  organic  beings 
are  striving,  it  may  be  said,  to  seize  on  each  place  in  the 
economy  of  nature,  if  any  one  species  does  not  become 


9 (J  CIRCUMSTAIirCES   FAVOURABLE  [Chap,  IV. 

modified  and  improved  in  a  corresponding  degree  with 
its  competitors,  it  will  soon  be  exterminated. 

In  man's  methodical  selection,  a  breeder  selects  for 
some  definite  object,  and  free  intercrossing  will  wholly 
stop  his  work.  But  when  many  men,  without  intending 
to  alter  the  breed,  have  a  nearly  common  standard  of 
perfection,  and  all  try  to  get  and  breed  from  the  best  ani- 
mals, much  improvement  and  modification  surely  but 
slowly  follows  from  this  unconscious  process  of  selection, 
notwithstanding  a  large  amount  of  crossing  with  inferior 
animals.  Thus  it  will  be  in  nature ;  for  within  a  confined 
area,  with  some  place  in  its  polity  not  so  perfectly  occu- 
pied as  might  be,  natural  selection  will  always  tend  to 
preserve  all  the  individuals  varying  in  the  right  direction, 
though  in  different  degrees,  so  as  better  to  fill  up  the 
unoccupied  place.  But  if  the  area  be  large,  its  several 
districts  will  almost  certainly  present  difi'erent  conditions 
of  life ;  and  then  if  natural  selection  be  modifying  and 
improving  a  species  in  the  several  districts,  there  will  be 
intercrossing  with  the  other  individuals  of  the  same  species 
on  the  confines  of  each.  And  in  this  case  the  eflects  of 
intercrossing  can  hardly  be  counterbalanced  by  natural 
selection  always  tending  to  modify  all  the  individuals  in 
each  district  in  exactly  the  same  manner  to  the  conditions 
of  each  ;  for  in  a  continuous  area,  the  conditions  will 
generally  graduate  away  insensibly  from  one  district  to. 
another.  The  intercrossing  will  most  aflJ'ect  those  animals 
which  unite  for  each  birth,  which  wander  much,  and  which 
do  not  breed  at  a  very  quick  rate.  Plence  in  animals  of 
this  nature,  for  instance  in  birds,  varieties  will  generally 
be  confined  to  separated  countries  ;  and  this  I  believe  to 
be  the  case.  In  hermaphrodite  organisms  which  cross 
only  occasionally,  and  likewise  in  animals  which  unite  for 
each  birth,  but  which  wander  little  and  which  can  increase 
at  a  very  rapid  rate,  a  new  and  improved  variety  might 
be  quickly  formed  on  any  one  spot,  and  might  there  main- 
tain itself  in  a  body,  so  that  whatever  intercrossing  took 
place  would  be  chiefly  between  the  individuals  of  the  same 
new  variety.  A  local  variety  when  once  thus  formed 
might  subsequently  slowly  spread  to  other  districts.     On 


Chap.  IV.]  TO   NATURAL   SELECTION.  Q^ 

tlie  above  principle,  nurserymen  always  prefer  getting  seed 
from  a  large  body  of  plants  of  tlie  same  variety,  as  the 
cbance  of  intercrossing  with  other  varieties  is  thus  les- 
sened. 

Even  in  the  case  of  slow-breeding  animals,  which  unite 
for  each  birth,  we  must  not  overrate  the  ejffects  of  inter- 
crosses in  retarding  natural  selection ;  for  I  can  bring  a 
considerable  catalogue  of  facts,  showing  that  within  the 
same  area,  varieties  of  the  same  animal  can  long  remain 
distinct,  from  haunting  different  stations,  from  breeding  at 
slightly  different  seasons,  or  from  varieties  of  the  same 
kind  preferring  to  pair  together. 

Intercrossing  plays  a  very  important  part  in  nature  in 
keeping  the  individuals  of  the  same  species,  or  of  the 
same  variety,  true  and  uniform  in  character.  It  will 
obviously  thus  act  far  more  efficiently  with  those  animals 
which  unite  for  each  birth ;  but  I  have  already  attempted 
to  show  that  we  have  reason  to  believe  that  occasional 
intercrosses  take  place  with  all  animals  and  with  all  plants. 
Even  if  these  take  place  only  at  long  intervals,  I  am  con- 
vinced that  the  young  thus  produced  will  gain  so  much 
in  vigour  and  fertility  over  the  offspring  from  long- 
continued  self-fertilisation,  that  they  will  have  a  better 
chance  of  surviving  and  propagating  their  kind  ;  and 
thus,  in  the  long  run,  the  influence  of  intercrosses,  even 
at  rare  intervals,  will  be  great.  If  there  exist  organic 
beings  which  never  intercross,  uniformity  of  character 
can  be  retained  amongst  them,  as  long  as  their  conditions 
of  life  remain  the  same,  only  through  the  principle  of 
inheritance,  and  through  natural  selection  destroying  any 
which  depart  from  the  proper  type ;  but  if  their  conditions 
of  life  change  and  they  undergo  modilication,  uniformity 
of  character  can  be  given  to  their  modified  offspring, 
solely  by  natural  selection  preserving  the  same  favourable 
variations. 

Isolation,  also,  is  an  important  element  in  the  process 
of  natural  selection.  In  a  confined  or  isolated  area,  if  not 
very  large,  the  organic  and  inorganic  conditions  of  life 
will  generally  be  in  a  great  degree  uniform ;  so  that  natu- 
ral selection  will  tend  to  modify  all  the  individuals  of  a 
5* 


98  CIRCUMSTANCES   FAVOURABLE  [Chap.  IV. 

varying  species  tlirouglioiit  the  area  in  the  same  manner 
in  relation  to  the  same  conditions.  Intercrosses,  also, 
with  the  individuals  of  the  same  species,  which  otherwise 
would  have  inhabited  the  surrounding  and  differently 
circumstanced  districts,  will  be  prevented.  But  isolation 
probably  acts  more  efficiently  in  checking  the  immigration 
of  better  adapted  organisms,  after  any  physical  change, 
such  as  of  climate  or  elevation  of  the  land,  &c. ;  and  thus 
new  places  in  the  natural  economy  of  the  country  are 
left  open  for  the  old  inhabitants  to  struggle  for,  and  be- 
come adaj)ted  to,  through  modifications  in  their  structure 
and  constitution.  Lastly,  isolation,  by  checking  immigra- 
tion and  consequently  competition,  T^'ill  give  time  for  any 
new  variety  to  be  slowly  improved  ;  and  this  may  some- 
times be  of  importance  in  the  production  of  new  species. 
If,  however,  an  isolated  area  be  very  small,  either  from 
being  surrounded  by  barriers,  or  from  having  very  peculiar 
physical  conditions,  the  total  number  of  the  individuals 
supported  on  it  will  necessarily  be  very  small ;  and  few- 
ness of  individuals  will  greatly  retard  the  production  of 
new  species  through  natural  selection,  by  decreasing  the 
chance  of  the  appeai-ance  of  favourable  variations. 

If  we  turn  to  nature  to  test  the  truth  of  these  remarks, 
and  look  at  any  small  isolated  area,  such  as  an  oceanic 
island,  although  the  total  number  of  the  species  inhabit- 
ing it,  will  be  found  to  be  small,  as  we  shall  see  in  our. 
chapter  on  geographical  distribution  ;  yet  of  these  species 
a  very  large  proportion  are  endemic, — that  is,  have  been 
produced  there,  and  nowhere  else.  Hence  an  oceanic  isl- 
and at  first  sight  seems  to  have  been  highly  favourable 
for  the  production  of  new  species.  But  we  may  thus 
greatly  deceive  ourselves,  for  to  ascertain  whether  a  small 
isolated  area,  or  a  large  open  area  like  a  continent,  has 
been  most  favourable  for  the  production  of  new  organic 
forms,  we  ought  to  make  the  comparison  within  equal 
times  ;  and  this  we  are  incapable  of  doing. 

Although  I  do  not  doubt  that  isolation  is  of  considera- 
ble importance  in  the  production  of  new  species,  on  the 
whole  I  am  inclined  to  believe  tliat  largeness  of  area  is 
of  more  importance,  more  especially  in  the  production  of 


Chap.  IV.]  TO    NATURAL   SELECTION.  99 

species,  wliicli  will  prove  capable  of  enduring  for  a  long 
period,  and  of  spreading  widely.  Tlirongliout  a  great  and 
open  area,  not  only  will  tliere  be  a  better  chance  of 
favourable  visitations  arising  from  the  large  number  of 
individuals  of  the  same  species  there  supported,  but  the 
conditions  of  life  are  infinitely  complex  from  the  large  num- 
ber of  already  existing  species  ;  and  if  some  of  these  many 
species  become  modified  and  improved,  others  will  have 
to  be  improved  in  a  corresponding  degree  or  they  will  be 
exterminated.  Each  new  form,  also,  as  soon  as  it  has 
been  much  improved,  will  be  able  to  spread  over  the 
open  and  continuous  area,  and  will  thus  come  into  com- 
petition with  many  others.  Hence,  more  new  places  will 
be  formed,  and  the  competition  to  fill  them  will  be  more 
severe,  on  a  large  than  on  a  small  and  isolated  area. 
Moreover,  great  areas,  though  now  continuous,  owing  to 
oscillations  of  level,  will  often  have  recently  existed  in  a 
broken  condition,  so  that  the  good  efi'ects  of  isolation  will 
generally,  to  a  certain  extent,  have  concurred.  Finally, 
I  conclude  that,  although  small  isolated  areas  probably 
have  been  in  some  respects  highly  favourable  for  the  pro- 
duction of  new  species,  yet  that  the  course  of  modification 
will  generally  have  been  more  rapid  on  large  areas  ;  and 
what  is  more  important,  that  the  new  forms  produced  on 
large  areas,  which  already  have  been  victorious  over 
many  competitors,  will  be  those  that  will  spread  most 
widely,  will  give  rise  to  most  new  varieties  and  species, 
and  will  thus  play  an  important  part  in  the  changing  his- 
tory of  the  organic  world. 

We  can,  perhaps,  on  these  views,  understand  some 
facts  which  will  be  again  alluded  to  in  our  chapter  on 
geographical  distribution ;  for  instance,  that  the  produc- 
tions of  the  smaller  continent  of  Australia  have  formerly 
yielded,  and  apparently  are  now  yielding,  before  those  of 
the  larger  Europaso-Asiatic  area.  Thus,  also,  it  is  that 
continental  productions  have  everywhere  become  so  largely 
naturalised  on  islands.  On  a  small  island,  the  race  foV 
life  will  have  been  less  severe,  and  there  will  have  been 
less  modification  and  less  extermination.  Hence,  perhaps,  • 
it  comes  that  the  flora  of  Madeira,  according  to  Oswald 


■j^QQ  CIRCUMSTANCES   FAVOURABLE  [Chap.  IV, 

Heer,  resembles  the  extinct  flora  of  Europe.  All  fresh- 
water basins,  taken  together,  make  a  small  area  compared 
with  that  of  the  sea  or  of  the  land  ;  and,  consequently, 
the  competition  between  fresh-water  productions  will  have 
been  less  severe  than  elsewhere  ;  new  forms  will  have 
been  more  slowly  formed,  and  old  forms  more  slowly  ex- 
terminated. And  it  is  in  fresh  water  that  we  find  seven 
genera  of  Ganoid  fishes,  remnants  of  a  once  preponderant 
order :  and  in  fresh  water  we  find  some  of  the  most 
anomalous  forms  now  known  in  the  world,  as  the  Ornitho- 
rhynchus  and  Lepidosiren,  which,  like  fossils,  connect  to 
a  certain  extent  orders  now  widely  separated  in  the  natural 
scale.  These  anomalous  forms  may  almost  be  called  living 
fossils  ;  they  have  endured  to  the  present  day,  from  hav- 
ing inhabited  a  confined  area,  and  from  having  thus  been 
exposed  to  less  severe  competition. 

To  sum  up  the  circumstances  favourable  and  unfavour- 
able to  natural  selection,  as  far  as  the  extreme  intricacy 
of  the  subject  permits.  I  conclude,  looking  to  the  future, 
that  for  terrestrial  productions  a  large  continental  area, 
which  will  probably  undergo  many  oscillations  of  level, 
and  which  consequently  will  exist  for  long  periods  in  a 
broken  condition,  will  be  the  most  favourable  for  the  pro- 
duction of  many  new  forms  of  life,  likely  to  endure  long 
and  to  spread  widely.  For  the  area  will  first  have  existed 
as  a  continent,  and  the  inhabitants,  at  this  period  nu- 
merous in  individuals  and  kinds,  will  have  been  subjected 
to  very  severe  competition.  When  converted  by  subsi- 
dence into  large  separate  islands,  there  will  still  exist 
many  individuals  of  the  same  species  on  each  island  :  in- 
tercrossing on  the  confines  of  the  range  of  each  species 
will  thus  be  checked  :  after  physical  changes  of  any  kind, 
immigration  will  be  prevented,  so  that  new  places  in  the 
polity  of  each  island  will  have  to  be  filled  up  by  modifi- 
cations of  the  old  inhabitants  ;  and  time  will  be  allowed 
for  the  varieties  in  each  to  become  well  modified  and  per- 
fected. When,  by  renewed  elevation,  the  islands  shall 
be  reconverted  into  a  continental  area,  there  will  again  be 
severe  competition  :  the  most  favoured  or  improved  vari- 
eties will  be  enabled  to  spread :  there  will  be  much  ex- 


Chap.  IV.]  TO    NATURAL   SELECTION.  JQl 

tinction  of  the  less  improved  forms,  and  the  relative 
proportional  numbers  of  the  various  inhabitants  of  the 
renewed  continent  will  again  be  changed ;  and  again 
there  will  be  a  fair  field  for  natural  selection  to  improve 
still  further  the  inhabitants,  and  thus  produce  new 
species. 

That  natural  selection  will  always  act  with  extreme 
slowness,  I  fully  admit.  Its  action  depends  on  there  being 
places  in  the  polity  of  nature,  which  can  be  better  occupied 
by  some  of  the  inhabitants  of  the  country  undergoing  mod- 
ification of  some  kind.  The  existence  of  such  places  will 
often  depend  on  physical  changes,  which  are  generally 
very  slow,  and  on  the  immigration  of  better  adapted 
forms  having  been  checked.  But  the  action  of  natural 
selection  will  probably  still  oftener  depend  on  some  of 
the  inhabitants  becoming  slowly  modified  ;  the  mutual 
relations  of  many  of  the  other  inhabitants  being  thus  dis- 
turbed. Nothing  can  be  effected,  imless  favourable  vari- 
ations occur,  and  variation  itself  is  apparently  always  a 
very  slow  process.  The  process  will  often  be  greatly 
retarded  by  free  intercrossing.  Many  will  exclaim  that 
these  several  causes  are  amply  sufiicient  wholly  to  stop 
the  action  of  natural  selection.  I  do  not  believe  so.  On 
the  other  hand,  I  do  believe  that  natural  selection  will 
always  act  very  slowly,  often  only  at  long  intervals  of 
time,  and  generally  on  only  a  very  few  of  the  inhabitants 
of  the  same  region  at  the  same  time.  I  further  believe, 
that  this  very  slow,  intermittent  action  of  natural  selec- 
tion accords  perfectly  well  with  what  geology  tells  us  of 
the  rate  and  maimer  at  which  the  inhabitants  of  this 
world  have  changed. 

Slow  though  the  process  of  selection  may  be,  if  feeble 
man  can  do  much  by  his  powers  of  artificial  selection,  1 
can  see  no  limit  to  the  amount  of  change,  to  the  beauty 
and  infinite  complexity  of  the  coadaptations  between  all 
organic  beings,  one  with  another  and  with  their  physical 
conditions  of  life,  which  may  be  effected  in  the  long 
course  of  time  by  nature's  power  of  selection. 

Extinction. — ^This  subject  will  be  more  fully  discussed 


^Q2  EXTINCTION,  [Chap.  IV. 

in  our  chapter  on  Geology ;  but  it  must  be  liere  alluded 
to  from  being  intimately  connected  with  natural  selection. 
ISTatural  selection  acts  solely  through  the  preservation  of 
variations  in  some  way  advantageous,  which  consequently 
endure.  But  as  from  the  high  geometrical  powers  of  in- 
crease of  all  organic  beings,  each  area  is  already  fully 
stocked  with  inhabitants,  it  follows  that  as  each  selected 
and  favoured  form  increases  in  number,  so  will  the  less 
favoured  forms  decrease  and  become  rare.  Rarity,  as 
geology  tells  us,  is  the  precursor  to  extinction.  ~We  can, 
also,  see  that  any  form  represented  by  few  individuals 
will,  during  fluctuations  in  the  seasons  or  in  the  number 
of  its  enemies,  run  a  good  chance  of  utter  extinction.  But 
we  may  go  further  than  this  J  for  as  new  forms  are  con- 
tinually and  slowly  being  produced,  unless  we  believe 
that  the  number  of  specific  forms  goes  on  perpetually  and 
almost  indefinitely  increasing,  numbers  inevitably  must 
become  extinct.  That  the  number  of  specific  forms  has 
not  indefinitely  increased,  geology  shows  us  plainly  ;  and 
indeed  we  can  see  reason  why  they  should  not  have  thus 
increased,  for  the  number  of  places  in  the  polity  of  nature 
is  not  indefinitely  great, — ^not  that  we  have  any  means 
of  knowing  that  any  one  region  has  as  yet  got  its  maxi- 
mum of  species.  Probably  no  region  is  as  yet  fully 
stocked,  for  at  the  Cape  of  Good  Hope,  where  more 
species  of  plants  are  crowded  together  than  in  any  other 
quarter  of  the  world,  some  foreign  plants  have  become 
naturalised,  without  causing,  as  far  as  we  know,  the  ex- 
tinction of  any  natives. 

Furthermore,  the  species  which  are  most  numerous  in 
individuals  will  have  the  best  chance  of  producing  within 
any  given  period  favourable  variations.  We  have  evi- 
dence of  this,  in  the  facts  given  in  the  second  chapter, 
showing  that  it  is  the  common  species  which  afford  the 
greatest  number  of  recorded  varieties,  or  incipient  species. 
Hence,  rare  species  will  be  less  quickly  modified  or  im- 
proved within  any  given  period,  and  they  will  consequent- 
ly be  beaten  in  the  race  for  life  by  the  modified  descend- 
ants of  the  commoner  species. 

From  these  several  considerations  I  think  it  inevitably 


Chap.  IV.]  DIVERGENCE   OF    CHARACTER.  j[Q3 

follows,  that  as  new  species  in  the  course  of  time  are 
formed  through  natural  selection,  others  will  become  rarer 
and  rarer,  and  finally  extinct.  The  forms  whicli  stand  in 
closest  competition  with  those  undergoing  modification 
and  improvement,  will  naturally  sufler  most.  And  we 
have  seen  in  the  chapter  on  the  Struggle  for  Existence 
that  it  is  the  most  closely-allied  forms, — varieties  of  the 
same  species,  and  species  of  the  same  genus  or  of  related 
genera, — which,  from  having  nearly  the  same  structure, 
constitution,  and  habits,  generally  come  into  the  severest 
competition  with  each  other.  Consequently,  each  new 
variety  or  species,  during  the  progress  of  its  formation, 
will  generally  press  hardest  on  its  nearest  kindred,  and 
tend  to  extermmate  them.  We  see  the  same  process  of 
extermination  amongst  our  domesticated  productions, 
through  the  selection  of  improved  forms  by  man.  Many 
curious  instances  could  be  given  showing  how  quickly 
new  breeds  of  cattle,  sheep,  and  other  animals,  and  varie- 
ties of  flowers,  take  the  place  of  older  and  inferior  kinds. 
In  Yorkshire,  it  is  historically  known  that  the  ancient 
black  cattle  were  displaced  by  the  long-horns,  and  that 
these  "  were  swept  away  by  the  short-horns  "  (I  quote  the 
words  of  an  agricultural  writer),  "  as  if  by  some  murder- 
ous pestilence." 

Divergence  of  Character. — The  principle,  which  I 
have  designated  by  this  term,  is  of  high  importance  on 
my  theory,  and  explains,  as  I  believe,  several  important 
facts.  In  the  first  place,  varieties,  even  strongly-marked 
ones,  though  having  somewhat  of  the  character  of  species 
— as  is  shown  by  the  hopeless  doubts  in  many  cases  how 
to  rank  them — yet  certainly  difi'er  from  each  other  far  less 
than  do  good  and  distinct  species.  Nevertheless,  accord- 
ing to  my  view^,  varieties  are  species  in  the  process  of  for- 
mation, or  are,  as  I  have  called  them,  incipient  species. 
How,  then,  does  the  lesser  difl'erence  between  varieties 
become  augmented  into  the  greater  difi'erence  between 
species  ?  That  this  does  habitually  happen,  we  must  in- 
fer from  most  of  the  innumerable  species  throughout  na- 
ture presenting  well-marked  difterences;  whereas  varie- 


JQ^  NATURAL   SELECTION.  [Chap.  IV, 

ties,  the  supposed  protot^q^es  and  parents  of  future  well- 
marked  species,  present  slight  and  ill-defined  differences. 
Mere  cliance,  as  we  may  call  it,  might  cause  one  variety 
to  differ  in  some  character  from  its  parents,  and  the  off- 
spring of  this  variety  again  to  differ  from  its  parent  in  the 
very  same  character  and  in  a  greater  degree ;  but  this 
alone  would  never  account  for  so  habitual  and  large  an 
amount  of  difference  as  that  between  varieties  of  the  same 
species  and  species  of  the  same  genus. 

As  has  always  been  my  practice,  let  us  seek  light  on 
this  head  from  our  domestic  productions.  "We  shall  here 
find  something  analogous.  A  fancier  is  struck  by  a 
pigeon  having  a  slightly  shorter  beak ;  another  fancier 
is  struck  by  a  pigeon  having  a  rather  longer  beak ; 
and  on  the  acknowledged  principle  that  "  fanciers  do  not 
and  will  not  admire  a  medium  standard,  but  like  ex- 
tremes," they  both  go  on  (as  has  actually  occurred  with 
tumbler  pigeons)  choosing  and  breeding  from  birds  with 
longer  and  longer  beaks,  or  with  shorter  and  shorter  beaks. 
Again,  we  may  supj)ose  that  at  an  early  period  one  man 
preferred  swifter  horses  ;  another  stronger  and  more  bulky 
horses.  The  early  differences  would  be  very  slight ;  in 
the  course  of  time,  from  the  continual  selection  of  swifter 
horses  by  some  breeders,  and  of  stronger  ones  by  others, 
the  differences  would  become  greater,  and  would  be  noted 
as  forming  two  sub-breeds  ;  finally,  after  the  lapse  of  cen- 
turies, the  sub-breeds  would  become  converted  into  two 
well-established  and  distinct  breeds.  As  the  difterences 
slowly  become  greater,  the  inferior  animals  with  interme- 
diate characters,  being  neither  very  swift  nor  very  strong, 
will  have  been  neglected,  and  will  have  tended  to  disap- 
pear. Here,  then,  we  see  in  man's  j)roductions  the  action 
of  what  may  be  called  the  principle  of  divergence,  causing 
differences,  at  first  barely  appreciable,  steadily  to  in- 
crease, and  the  breeds  to  diverge  in  character  l)oth  from 
each  other  and  from  their  common  parent. 

But  how,  it  may  be  asked,  can  any  analogous  princi- 
ple apply  in  nature?  I  believe  it  can  and  doc^s  apply 
most  efiiciently,  from  the  simj)le  circumstance  that  the 
more  diversified  the  descendants  from  any  one  species 


Chap.  IV.]  DIVERGENCE    OF    CHARACTER.  IQ^ 

become  in  structure,  constitution,  and  habits,  by  so  mucb 
will  they  be  better  enabled  to  seize  on  many  and  widely 
diversified  places  in  tlie  polity  of  nature,  and  so  be  enabled 
to  increase  in  numbers. 

We  can  clearly  see  this  in  the  case  of  animals  with 
simple  habits.  Take  the  case  of  a  carnivorous  quadruped, 
of  which  the  number  that  can  be  supported  in  any  coun- 
try has  long  ago  arrived  at  its  full  average.  If  its  natu- 
ral powers  of  increase  be  allowed  to  act,  it  can  succeed  in 
increasing  (the  country  not  undergoing  any  change  in  its 
conditions)  only  by  its  varying  descendants  seizing  on 
places  at  present  occupied  by  other  animals  :  some  of 
them,  for  instance,  being  enabled  to  feed  on  new  kinds 
of  prey,  either  dead  or  alive ;  some  inhabiting  new  sta- 
tions, climbing  trees,  frequenting  water,  and  some  per- 
haps becoming  less  carnivorous.  The  more  diversified  in 
habits  and  structure  the  descendants  of  our  carnivorous 
animal  became,  the  more  places  they  would  be  enabled  to 
occupy.  What  applies  to  one  animal  will  apply  through- 
out all  time  to  all  animals — that  is,  if  they  vary — for 
otherwise  natural  selection  can  do  nothing.  So  it  will  be 
with  plants.  It  has  been  experimentally  proved,  that  if 
a  plot  of  ground  be  sown  with  one  species  of  grass,  and 
a  similar  plot  be  sown  with  several  distinct  genera  of 
grasses,  a  greater  number  of  plants  and  a  greater  weight 
of  dry  herbage  can  thus  be  raised.  The  same  has  been 
found  to  hold  good  when  first  one  variety  and  then  sever- 
al mixed  varieties  of  wheat  have  been  sown  on  equal 
spaces  of  ground.  Hence,  if  any  one  species  of  grass  were 
to  go  on  varying,  and  those  varieties  were  continually 
selected  which  differed  from  each  other  in  at  all  the  same 
manner  as  distinct  species  and  genera  of  grasses  differ 
from  each  other,  a'greater  number  of  individual  plants  of 
this  species  of  grass,  includiDg  its  modified  descendants, 
would  succeed  in  living  on  the  same  piece  of  ground.  And 
we  well  know  that  each  species  and  each  variety  of  grass 
is  aimually  sowing  almost  countless  seeds ;  and  thus,  as  it 
may  be  said,  is  striving  its  utmost  to  increase  its  numbers. 
Consequently,  I  cannot  doubt  that  in  the  course  of  many 
thousands  of  generations,  the  most  distinct  varieties  of  any 


•J[Qg  NATURAL   SELECTION".  [Chap.  IV. 

one  species  of  grass  would  always  have  the  best  chance 
of  succeeding  and  of  increasing  in  numbers,  and  thus  of 
suj)planting  the  less  distinct  varieties ;  and  varieties,  when 
rendered  very  distinct  from  each  other,  take  the  rank  of 
species. 

The  truth  of  the  principle,  that  the  greatest  amount  of 
life  can  be  supported  by  great  diversification  of  structure, 
is  seen  under  many  natural  circumstances.  In  an  ex- 
tremely small  area,  especially  if  freely  open  to  immigra- 
tion, and  where  the  contest  between  individual  and  indi- 
vidual must  be  severe,  we  always  find  great  diversity  iti 
its  inhabitants.  For  instance,  I  found  that  a  piece  of  turf, 
three  feet  by  four  in  size,  which  had  been  exposed  for 
many  years  to  exactly  the  same  conditions,  supported 
twenty  species  of  plants,  and  these  belonged  to  eighteen 
genera  and  to  eight  orders,  which  shows  how  much  these 
plants  differ  from  each  other.  So  it  is  with  the  plants 
and  insects  on  small  and  uniform  islets ;  and  so  in  small 
ponds  of  fresh  water.  Farmers  find  that  they  can  raise 
most  food  by  a  rotation  of  plants  belonging  to  the  most 
different  orders :  nature  follows  what  may  be  called  a 
simultaneous  rotation.  Most  of  the  animals  and  plants 
which  live  close  round  any  small  piece  of  groimd,  could 
live  on  it  (supposing  it  not  to  be  in  any  way  peculiar  in 
its  nature),  and  may  be  said  to  be  striving  to  the  utmost 
to  live  there ;  but,  it  is  seen,  that  where  they  come  into 
the  closest  competition  with  each  other,  the  advantages 
of  diversification  of  structure,  with  the  accompanying 
differences  of  habit  and  constitution,  determine  that  the 
inhabitants,  which  thus  jostle  each  other  most  closely, 
shall,  as  a  general  rule,  belong  to  what  we  call  different 
genera  and  orders. 

The  same  principle  is  seen  in  the  naturalisation  of 
plants  through  man's  agency  in  foreign  lands.  It  might 
have  been  expected  that  the  plants  which  have  succeeded 
in  becoming  naturalised  in  any  land  would  generally  have 
been  closely  allied  to  the  indigenes ;  for  these  are  com- 
monly looked  at  as  sj)ecially  created  and  adapted  for  their 
own  country.  It  might,  also,  perhaps  have  been  expect- 
ed that  naturalised  plants  would  have  belonged  to  a  few 


Chap.  IV.]  DIVERGENCE   OF   CHARACTER.  j^Q^ 

groups  more  especially  adapted  to  certain  stations  in  their 
new  homes.  But  the  case  is  very  different ;  and  Alph. 
De  Candolle  has  well  remarked  in  his  great  and  admira- 
ble work,  that  floras  gain  by  naturalisation,  proportionally 
with  the  number  of  tlie  native  genera  and  SjDecies,  far 
more  in  new  genera  than  in  new  species.  To  give  a  single 
instance :  in  the  last  edition  of  Dr.  Asa  Gray's  '  Manual 
of  the  Flora  of  the  ISTorthern  United  States,'  260  natural- 
ised plants  are  enumerated,  and  these  belong  to  162  genera. 
We  thus  see  that  these  naturalised  plants  are  of  a  highly 
diversified  nature.  They  differ,  moreover,  to  a  large  ex- 
tent from  the  indigenes,  for  out  of  the  162  genera,  no  less 
than  100  genera  are  not  there  indigenous,  and  thus  a 
large  proportional  addition  is  made  to  the  genera  of  these 
States. 

By  considering  the  nature  of  the  plants  or  animals 
which  have  struggled  successfully  with  the  indigenes  of 
any  country,  and  have  there  become  naturalised,  wx  can 
gain  some  crude  idea  in  what  manner  some  of  the  natives 
would  have  had  to  be  modified,  in  order  to  have  gained 
an  advantage  over  the  other  natives  ;  and  we  may,  I 
think,  at  least  safely  infer  that  diversification  of  structure, 
amounting  to  new  generic  differences,  would  have  been 
profitable  to  them. 

The  advantao;e  of  diversification  in  the  inhabitants  of 
the  same  region  is,  in  fact,  the  same  as  that  of  the  physi- 
ological division  of  labour  in  the  organs  of  the  same 
individual  bodies — a  subject  so  well  elucidated  by  Milne 
Edwards.  ISTo  physiologist  doubts  that  a  stomach  by 
being  adapted  to  digest  vegetable  matter  alone,  or  flesh 
alone,  draws  most  nutriment  from  these  substances.  So 
in  the  general  economy  of  any  land,  the  more  widely  and 
perfectly  the  animals  and  plants  are  diversified  for  different 
habits  of  life,  so  will  a  greater  number  of  individuals  be 
capable  of  there  supporting  themselves.  A  set  of  ani- 
mals, with  their  organisation  but  little  diversified,  could 
hardly  compete  with  a  set  more  perfectly  diversified  in 
structure.  It  may  be  doubted,  for  instance,  whether  the 
Australian  marsupials,  which  are  divided  into  groups 
differing  but  little  from  each  other,  and  feebly  represent- 


J^Qg  NATURAL    SELECTION.  [Chap.  IV. 

ing,  as  Mr.  Waterhouse  and  others  have  remarked,  our 
carnivorous,  ruminant,  and  rodent  mammals,  could  suc- 
cessfully compete  with  these  well-pronounced  orders.  In 
the  Australian  mammals,  we  see  the  process  of  diversifi- 
cation in  an  early  and  incomplete  stage  of  development. 

After  the  foregoing  discussion,  which  ought  to  have 
been  much  amplified,  we  may,  I  think,  assume  that  the 
modified  descendants  of  any  one  species  will  succeed  by 
so  much  the  better  as  they  become  more  diversified  in 
structure,  and  are  thus  enabled  to  encroach  on  places  oc- 
cupied by  other  beings.  'Now  let  us  see  how  this  princi- 
ple of  great  benefit  being  derived  from  divergence  of 
character,  combined  with  the  principles  of  natural  selec- 
tion and  of  extinction,  will  tend  to  act. 

The  accompanying  diagram  will  aid  us  in  understand- 
ing this  rather  perplexing  subject.  Let  A  to  L  represent 
the  species  of  a  genus  large  in  its  own  country  ;  these 
species  are  supposed  to  resemble  each  other  in  unequal  de- 
grees, as  is  so  generally  the  case  in  nature,  and  as  is  repre- 
sented in  the  diagram  by  the  letters  standing  at  unequal 
distances.  I  have  said  a  large  genus,  because  we  have 
seen  in  the  second  chapter,  that  on  an  average  more  of 
the  species  of  Itirge  genera  vary  than  of  small  genera  ; 
and  the  varying  species  of  the  large  genera  j)i*esent  a 
greater  number  of  varieties.  We  have,  also,  seen  that 
the  species,  which  are  the  commonest  and  the  most  widely- 
diffused,  vary  more  than  rare  species  with  restricted 
ranges.  Let  (A)  be  a  common,  widely-diffused,  and  vary- 
ing species,  belonging  to  a  genus  large  in  its  own  country. 
The  little  fan  of  diverging  dotted  lines  of  unequal  length 
proceeding  from  (A),  may  represent  its  varying  off'spring. 
The  variations  are  supposed  to  be  extremely  slight,  but 
of  the  most  diversified  nature ;  they  are  not  supposed  all  to 
appear  simultaneously,  but  often  after  long  intervals  of 
time  ;  nor  are  they  all  supposed  to  endure  for  equal  peri- 
ods. Only  those  variations  which  are  in  some  way 
profitable  will  be  preserved  or  naturally  selected.  And 
here  the  importance  of  the  principle  of  benefit  being 
derived  from  divergence  of  character  comes  in  ;  for  this 
will  generally  lead  to  the  most  different  or  divergent  vari- 


14  ,  .  '/ 


I  ' 


>  I 


\  I  / 

>  I         / 

\  I       / 


// 


xiu 

XII 
XI 


I       K      L 


X 


IX 


^r'--::-l 


T:.    \  ■  . 


■'■■'     7 


-V 


Zidt.ct'SarvTU/.Ma/cr)^  I^inpp. 
^4Q Prraduai/ .1/  K 


'  /  / 


IV 


III 


1-ii 


■•.■■..'  7: 


3[Q3  NATURAL   SELECTION.  [Chap.  IV. 

ing,  as  Mr.  Watertioiise  and  others  liave  remarked,  our 
carniYoroiis,  rurainant,  and  rodent  mammals,  could  suc- 
cessfully compete  with  these  well-pronounced  orders.  In 
the  Australian  mammals,  we  see  the  process  of  diversifi- 
cation in  an  early  and  incomplete  stage  of  development. 

After  the  foregoing  discussion,  which  ought  to  have 
been  much  amplified,  we  may,  I  think,  assume  that  the 
modified  descendants  of  any  one  species  will  succeed  by 
so  much  the  better  as  they  become  more  diversified  in 
structure,  and  are  thus  enabled  to  encroach  on  places  oc- 
cupied by  other  beings.  Now  let  us  see  how  this  princi- 
ple of  great  benefit  being  derived  from  divergence  of 
character,  combined  with  the  principles  of  natural  selec- 
tion and  of  extinction,  will  tend  to  act. 

The  accompanying  diagram  will  aid  us  in  understand- 
ing this  rather  perplexing  subject.  Let  A  to  L  represent 
the  species  of  a  genus  large  in  its  own  country  ;  these 
species  are  supposed  to  resemble  each  other  in  unequal  de- 
grees, as  is  so  generally  the  case  in  nature,  and  as  is  repre- 
sented in  the  diagram  by  the  letters  standing  at  unequal 
distances.  I  have  said  a  large  genus,  because  we  have 
seen  in  the  second  chapter,  that  on  an  average  more  of 
the  species  of  Targe  genera  vary  than  of  small  genera ; 
and  the  varying  species  of  the  large  genera  present  a 
greater  number  of  varieties.  "We  have,  also,  seen  that 
the  species,  which  are  the  commonest  and  the  most  widely- 
diffused,  vary  more  than  rare  species  with  restricted 
ranges.  Let  (A)  be  a  common,  widely-diffused,  and  vary- 
ing species,  belonging  to  a  genus  large  in  its  own  country. 
The  little  fan  of  diverging  dotted  lines  of  unequal  length 
proceeding  from  (A),  may  represent  its  varying  ofl'spring. 
The  variations  are  supposed  to  be  extremely  slight,  but 
of  the  most  diversified  nature ;  they  are  not  supposed  all  to 
appear  simultaneously,  but  often  after  long  intervals  of 
time  ;  nor  are  they  all  supposed  to  endure  for  equal  peri- 
ods. Only  those  variations  which  are  in  some  way 
profitable  Avill  be  preserved  or  naturally  selected.  And 
here  the  importance  of  the  principle  of  benefit  being 
derived  from  divergence  of  character  comes  in  ;  for  this 
will  generally  lead  to  the  most  different  or  divergent  vari- 


in        E  F 


Vf 


ilr" 


h '         / ' 


:\h" 


-LL '■'4'" 


\]    XIV 

7    XIII 

XII 

XI 

X 

IX 

VIII 

VII 

VI 

V 
,1V 

III 

II 

I 


A      B       r         D  E      F  (;      H        I 


D.Aliplrldii  S.:  C"  Neil- York 


K       L 

/ 


Ufh.of'.'iaTVfU/Mt'JC'^  f('iir/>/K 


Chap.  IV.]  DIVERGENCE    OF    CHARACTER.  ][()9 

ations  (represented  by  the  outer  dotted  lines)  being  pre- 
served and  accumnlated  bj  natural  selection.  When  a 
dotted  line  reaches  one  of  the  horizontal  lines,  and  is  there 
marked  by  a  small  numbered  letter,  a  sufficient  amount 
of  variation  is  supposed  to  have  been  accumulated  to 
have  formed  a  fairly  well-marked  variety,  such  as  would 
be  thought  worthy  of  record  in  a  systematic  work. 

The  intervals  between  the  horizontal  lines  in  the  dia- 
gram, may  represent  each  a  thousand  generations  ;  but 
it  would  have  been  better  if  each  had  represented  ten 
thousand  generations.  After  a  thousand  generations, 
species  (A)  is  supposed  to  have  produced  two  fairly  well- 
marked  varieties,  namely  «^  and  7??/\  These  two  varieties 
will  generally  continue  to  be  exposed  to  the  same  condi- 
tions which  made  their  parents  variable,  and  the  tendency 
to  variability  is  in  itself  hereditary,  consequently  they 
will  tend  to  vary,  and  generally  to  vary  in  nearly  the 
same  manner  as  their  parents  varied.  Moreover,  these 
two  varieties,  being  only  slightly  modified  forms,  will 
tend  to  inherit  those  advantages  which  made  their  common 
parent  (A)  more  numerous  than  most  of  the  other  inhabi- 
tants of  the  same  country  ;  they  will  likewise  partake  of 
those  more  general  advantages  which  made  the  genus  to 
which  the  parent-species  belonged,  a  large  genus  in  its 
own  country.  And  these  circumstances  we  know  to  be 
favourable  to  the  production  of  new  varieties. 

If,  then,  these  two  varieties  be  variable,  the  most 
divergent  of  their  variations  will  generally  be  preserved 
during  the  next  thousand  generations.  And  after  this 
interval,  variety  cC'  is  supposed  in  the  diagram  to  have 
produced  variety  «^,  which  will,  owing  to  the  principle  of 
divergence,  differ  more  from  (A)  than  did  variety  a}. 
Variety  m^  is  supposed  to  have  produced  two  varieties, 
namely  m",  and  s^^  difi'ering  from  each  other,  and  more 
considerably  from  their  common  parent  (A).  We  may 
continue  the  process  by  similar  steps  for  any  length  of 
time ;  some  of  the  varieties,  after  each  thousand  genera- 
tions, producing  only  a  single  variety,  but  in  a  more  and 
more  modified  condition,  some  producing  two  or  three 
varieties,  and  some  failing  to  produce  any.     Thus  the 


IIQ  NATURAL   SELECTION.  [Chap.  IV. 

varieties  or  modified  descendants,  proceeding  from  tlie 
common  parent  (A),  will  generally  go  on  increasing  in 
number,  and  diverging  in  character.  In  tlie  diagram  the 
process  is  rej)resented  np  to  the  ten  thousandth  genera- 
tion, and  under  a  condensed  and  simplified  form  up  to  the 
fourteen-thousandth  generation. 

But  I  must  here  remark  that  I  do  not  suppose  that  the 
process  ever  goes  on  so  regularly  as  is  represented  in  the 
diagram,  though  in  itself  made  somewhat  irregular.  I 
am  far  from  thinking  that  the  most  divergent  varieties 
will  invariably  prevail  and  multiply  :  a  medium  form 
may  often  long  endure,  and  may  or  may  not  produce 
more  than  one  modified  descendant ;  for  natural  selection 
will  always  act  according  to  the  nature  of  the  places 
which  are  either  unoccupied  or  not  perfectly  occupied  by 
other  beings  ;  and  this  will  depend  on  infinitely  complex 
relations.  But  as  a  general  rule,  the  more  diversified  in 
structure  the  descendants  from  any  one  species  can  be 
rendered,  the  more  places  they  will  be  enabled  to  seize 
on,  and  the  more  their  modified  progeny  will  be  in- 
creased. In  our  diagram  the  line  of  succession  is  broken 
at  regular  intervals  by  small  numbered  letters  marking 
the  successive  forms  which  have  become  sufiiciently  dis- 
tinct to  be  recorded  as  varieties.  But  these  breaks  are 
imaginary,  and  might  have  been  inserted  anywhere,  aftei 
intervals  long  enough  to  have  allowed  the  accumulation 
of  a  considerable  amount  of  divergent  variation. 

As  all  the  modified  descendants  from  a  common  and 
widely-difiused  species,  belonging  to  a  large  genus,  will 
tend  to  partake  of  the  same  advantages  which  made  their 
parent  successful  in  life,  they  will  generally  go  on  multi- 
plying in  number  as  well  as  diverging  in  character  :  this 
is  represented  in  the  diagram  by  the  several  divergent 
branches  proceeding  from  (A).  The  modified  offspring 
from  the  latter  and  more  highly  improved  branches  in  the 
lines  of  descent,  will,  it  is  probable,  often  take  the  place 
of,  and  so  destroy,  the  earlier  and  less  improved  branches : 
this  is  represented  in  the  diagram  by  some  of  the  lower 
branches  not  reaching  to  the  upper  horizontal  lines.  In 
some  cases  I  do  not  doubt  that  the  process  of  modification 


Chap.  IV.]  DIVERGENCE  OF  CHARACTER.  ][j[;J^ 

will  be  confined  to  a  single  line  of  descent,  and  tlie  num- 
ber of  tlie  descendants  will  not  be  increased ;  altbough. 
the  amount  of  divergent  modification  may  bave  been  in- 
creased in  the  successive  generations.  Tbis  case  would  be 
represented  in  tbe  diagram,  if  all  the  lines  proceeding 
from  (A)  were  removed,  excepting  tbat  from  a''  to  a)'\  In 
tbe  same  way,  for  instance,  tbe  Englisb  race-borse  and 
Englisb  pointer  bave  apparently  botb  gone  on  slowly 
diverging  in  cbaracter  from  tbeir  original  stocks,  witbout 
eitber  baving  given  off  any  fresb  brancbes  or  races. 

After  ten  tbousand  generations,  species  (A)  is  supposed 
to  bave  produced  tbree  forms,  a'",  /*'",  and  m'",  wbicb, 
from  baving  diverged  in  cbaracter  during  tbe  successive 
generations,  will  bave  come  to  differ  largely,  but  perbaps 
unequally,  from  eacb  otber  and  from  tbeir  common  parent. 
If  we  suppose  tbe  amount  of  cbange  between  eacb  bori- 
zontal  line  in  our  diagram  to  be  excessively  small,  tbese 
tbree  forms  may  only  still  be  well-marked  varieties ;  or 
tbey  may  bave  arrived  at  tbe  doubtful  category  of  sub- 
species ;  but  we  bave  only  to  suppose  tbe  steps  in  tbe 
process  of  modification  to  be  more  numerous  or  greater 
in  amount,  to  convert  tbese  tbree  forms  into  well-defined 
species  :  tbus  tbe  diagram  illustrates  tbe  steps  by  wbicb 
tbe  small  differences  distinguisbing  varieties  are  increased 
into  tbe  larger  differences  distinguisbing  species.  By  con- 
tinuing tbe  same  process  for  a  greater  number  of  genera- 
tions (as  sbown  in  tbe  diagram  in  a  condensed  and  sim- 
plified manner),  we  get  eigbt  species  marked  by  tbe  let- 
ters between  cC'^  and  m",  all  descended  from  (A).  Tbus, 
as  I  believe,  species  are  multiplied  and  genera  are  formed. 

Li  a  large  genus  it  is  probable  tbat  more  tban  one 
species  would  vary.  In  tbe  diagram  I  bave  assumed  tbat 
a  second  species  (I)  bas  produced,  by  analogous  steps, 
after  ten  tbousand  generations,  eitber  two  well-marked 
varieties  {w^"  and  s")  or  two  species,  according  to  tbe 
amount  of  cbange  supposed  to  be  represented  between  tbe 
borizontal  lines.  After  fourteen  tbousand  generations,  six 
new  species,  marked  by  tbe  letters  n^"^  to  s'*,  are  sup]30sed 
to  bave  been  produced.  In  eacb  genus,  tbe  species,  wbicb 
are  already  extremely  different  in  cbaracter,  will  generally 


H2  NATURAL   SELECTION.  [Chap.  IV. 

tend  to  produce  the  greatest  number  of  modified  descend- 
ants ;  'for  these  will  have  the  best  chance  of  filling  new 
and  widely  difi'erent  places  in  the  polity  of  nature : 
hence  in  the  diagram  I  have  chosen  the  extreme  species 
(A),  and  the  nearly  extreme  species  (I),  as  those  which 
have  largely  varied,  and  have  given  rise  to  new  varieties 
and  species.  The  other  nine  species  (marked  by  capital 
letters)  of  our  original  genus,  may  for  a  long  period  con- 
tinue transmitting  unaltered  descendants ;  and  this  is 
shown  in  the  diagram  by  the  dotted  lines  not  prolonged 
far  upwards  from  want  of  space. 

But  during  the  process  of  modification,  represented  in 
the  diagram,  another  of  our  principles,  namely  that  of 
extinction,  will  have  played  an  important  part.  As  in 
each  fully  stocked  country,  natural  selection  necessarily 
acts  by  the  selected  form  having  some  advantage  in  the 
struggle  for  life  over  other  forms,  there  will  be  a  constant 
tendency  in  the  improved  descendants  of  any  one  species 
to  supplant  and  exterminate  in  each  stage  of  descent  their 
predecessors  and  their  original  parent.  For  it  should  be 
remembered  that  the  competition  will  generally  be  most 
severe  between  those  forms  which  are  most  nearly  related 
to  each  other  in  habits,  constitution,  and  structure.  Hence 
all  the  intermediate  forms  between  the  earlier  and  later 
states,  that  is  between  the  less  and  more  improved  state 
of  a  species,  as  well  as  the  original  parent-species  itself, 
will  generally  tend  to  become  extinct.  So  it  probably 
will  be  with  many  whole  collateral  lines  of  descent,  which 
will  be  conquered  by  later  and  improved  lines  of  descent. 
If,  however,  the  modified  ofi"spring  of  a  species  get  into 
some  distinct  country,  or  become  quickly  adapted  to  some 
quite  new  station,  in  which  child  and  parent  do  not  come 
into  competition,  both  may  continue  to  exist. 

If  then  our  diagram  be  assumed  to  represent  a  consid- 
erable amount  of  modification,  species  (A)  and  all  the 
earlier  varieties  will  have  become  extinct,  having  been 
replaced  by  eight  new  species  {a^'^  to  oii''^) ;  and  (I)  will 
have  been  replaced  by  six  (ti"  to  z"^)  new  species. 

But  we  may  go  further  than  this.  The  original  speciea 
of  our  genus  were  supposed  to  resemble  each  other  in 


€hap.  IV.]  DIVERGENCE   OF   CHARACTER.  ;[j^3 

unequal  degrees,  as  is  so  generally  the  case  in  nature; 
species  (A)  being  more  nearly  related  to  B,  C,  and  D, 
than  to  the  other  species  ;  and  sj)ecies  (I)  more  to  G,  H, 
K,  L,  than  to  tlie  others.  These  two  species  (A)  and  (I), 
were  also  supposed  to  be  very  common  and  widely  dif- 
fused species,  so  that  they  must  originally  have  Iiad  some 
advantage  over  most  of  the  other  species  of  the  genus, 
Their  modified  descendants,  fourteen  in  number  at  the 
fourteen-thousandth  generation,  will  probably  have  inher- 
ited some  of  the  same  advantages  :  they  have  also  been 
modified  and  improved  in  a  diversified  manner  at  each 
stage  of  descent,  so  as  to  have  become  adapted  to  many 
related  places  in  the  natural  economy  of  their  country. 
It  seems,  therefore,  to  me  extremely  probable  that  they 
will  have  taken  the  places  of,  and  thus  exterminated,  not 
only  their  parents  (A)  and  (I),  but  likewise  some  of  the 
original  species  which  were  most  nearly  related  to  their 
parents.  Hence  very  few  of  the  original  species  will  have 
transmitted  oft'spring  to  the  fourteen-thousandth  genera- 
tion. We  may  suppose  that  only  one  (F),  of  the  two 
species  which  were  least  closely  related  to  the  other  nine 
original  species,  has  transmitted  descendants  to  this  late 
stage  of  descent. 

The  new  species  in  our  diagram  descended  from  the 
original  eleven  species,  will  now.  be  fifteen  in  number. 
Owing  to  the  divergent  tendency  of  natural  selection,  the 
extreme  amount  of  diflerence  in  character  between  species 
«^*  and  z^*  will  be  much  greater  than  that  between  the 
most  difi'erent  of  the  original  eleven  species.  The  new 
species,  moreover,  will  be  allied  to  each  other  in  a  widely 
difi'erent  manner.  Of  the  eight  descendants  from  (A)  the 
three  marked  a^\  q'\  p'%  will  be  nearly  related  from  hav- 
ing recently  branched  off  from  «"  ;  h^*  and/"'*,  from  bar- 
ing diverged  at  an  earlier  period  from  a%  will  be  in  some 
degree  distinct  from  the  three  first-named  species  ;  and 
lastly,  o'\  e'\  and  m'\  will  be  nearly  related  one  to  the 
other,  but  from  haviiig  diverged  at  the  first  commence- 
ment of  the  process  of  modifecation,  will  be  widely  dif- 
ferent from  the  other  five  species,  and  may  constitute  a 
sub-genus  or  even  a  distinct  genus. 
6 


j[2^  NATURAL   SELECTION.  [Chap.  IV. 

The  six  descendants  from  (I)  will  form  two  sii"b-genera 
or  even  genera.  But  as  the  original  species  (I)  differed 
largely  from  (A),  standing  nearly  at  the  extreme  points 
of  the  original  genus,  the  six  descendants  from  (I)  will, 
owing  to  inheritance,  differ  considerably  from  the  eight 
descendants  from  (A)  ;  the  two  groups,  moreover,  are 
supposed  to  have  gone  on  diverging  in  different  directions. 
The  intermediate  species,  also  (and  this  is  a  very  impor- 
tant consideration),  which  connected  the  original  species 
(A)  and  (I),  have  all  become,  excepting  (F),  extinct,  and 
have  left  no  descendants.  Hence  the  six  new  species 
descended  from  (I),  and  the  eight  descended  from  (A),  will 
have  to  be  ranked  as  very  distinct  genera,  or  even  as  dis- 
tinct sub-families. 

Thus  it  is,  as  I  believe,  that  two  or  more  genera  are 
produced  by  descent,  with  modification,  from  two  or  more 
species  of  the  same  genus.  And  the  two  or  more  parent- 
species  are  supposed  to  have  descended  from  some  one 
species  of  an  earlier  genus.  In  our  diagram,  this  is  indi- 
cated by  the  broken  lines,  beneath  the  capital  letters,  con- 
verging in  sub-branches  downwards  towards  a  single  point ; 
this  point  representing  a  single  species,  the  supposed  single 
parent  of  our  several  new  sub-genera  and  genera. 

It  is  worth  while  to  reflect  for  a  moment  on  the  char- 
acter of  the  new  species  r'",  which  is  supposed  not  to  have 
diverged  much  in  character,  but  to  have  retained  the  form 
of  (F),  either  unaltered  oi»  altered  only  in  a  slight  degree. 
In  this  case,  its  afiinities  to  the  other  fourteen  new  sj^ecies 
will  be  of  a  curious  and  circuitous  nature.  Having  de- 
scended from  a  form  which  stood  between  the  two  parent- 
species  (A)  and  (I),  now  supposed  to  be  distinct  and  un- 
known, it  will  be  in  some  degree  intermediate  in  character 
between  the  two  groups  descended  from  these  species. 
But  as  these  two  groups  have  gone  on  diverging  in  char- 
acter from  the  type  of  their  parents,  the  new  species  (r^*) 
will  not  be  directly  intermediate  between  them,  but  rather 
between  types  of  the  two  groups  ;  *  and  every  naturalist 
will  be  able  to  bring  some  such  case  before  his  mind. 

In  the  diagram,  each  horizontal  line  has  hitherto  been 
supposed  to  represent  a  thousand  generations,  but  each 


Chap.  IV. j  DIVERGENCE    OF    CHARACTER.  215 

may  represent  a  million  or  hundred  million  generations, 
and  likewise  a  section  of  the  snccessive  strata  of  the 
earth's  crust  including  extinct  remains.  We  shall,  when 
we  come  to  our  chapter  on  Geology,  have  to  refer 
again  to  this  subject,  and  I  think  we  shall  then  see  that 
the  diagram  throws  light  on  the  affinities  of  extinct 
beings,  which,  though  generally  belonging  to  the  same 
orders,  or  families,  or  genera,  with  those  now  living,  yet 
are  often,  in  some  degree,  intermediate  in  character  between 
existing  groups  ;  and  we  can  understand  this  fact,  for  the 
extinct  species  lived  at  very  ancient  epochs  when  the 
branching  lines  of  descent  had  diverged  less. 

I  see  no  reason  to  limit  the  process  of  modification,  as 
now  explained,  to  the  formation  of  genera  alone.  If,  in 
our  diagram,  we  suppose  the  amount  of  change  represented 
by  each  successive  group  of  diverging  dotted  lines  to  be 
very  great,  the  forms  marked  cC'^  to  j?'*,  those  marked  If^ 
and  y ^*,  and  those  marked  d"^  to  ^?i'\  will  form  three  very 
distinct  genera.  We  shall  also  have  two  very  distinct 
genera  descended  from  (I) ;  and  as  these  latter  two  genera, 
both  from  continued  divergence  of  character  and  from 
inheritance  from  a  different  parent,  will  difi'er  widely 
from  the  three  genera  descended  from  (A),  the  two  little 
groups  of  genera  will  form  two  distinct  families,  or  even 
orders,  according  to  the  amount  of  divergent  modification 
supposed  to  be  represented  in  the  diagram.  And  the  two 
new  families,  or  orders,  will  have  descended  from  two  spe- 
cies of  the  original  genus  ;  and  these  two  species  are  sup- 
posed to  have  descended  from  one  sj)ecies  of  a  still  more 
ancient  and  unknown  genus. 

We  have  seen  that  in  each  country  it  is  the  species  of 
the  larger  genera  which  oftenest  present  varieties  or  inci- 
j)ient  species.  This,  indeed,  might  have  been  expected  ; 
for  as  natural  selection  acts  through  one  form  having  some 
advantage  over  other  forms  in  the  struggle  for  existence, 
it  will  chiefly  act  on  those  which  already  have  some  ad- 
vantage ;  and  the  largeness  of  any  group  shows  that  its 
species  have  inherited  from  a  common  ancestor  some  ad- 
vantage in  common.  Hence,  the  struggle  for  the  pro- 
duction of  new  and  modified  descendants,  will  mainly  lie 


1\Q  NATURAL   SELECTI027.  [Chap.  IV. 

between  the  larger  groups,  wliicli  are  all  trying  to  increase 
in  number.  One  large  group  will  slowly  conquer  another 
large  group,  reduce  its  numbers,  and  thus  lessen  its  chance 
for  further  variation  and  improvement.  "Within  the  same 
large  group,  the  later  and  more  highly  j)erfected  sub- 
groups, from  branching  out  and  seizing  on  many  new 
places  in  the  polity  of  ISTature,  will  constantly  tend  to 
supplant  and  destroy  the  earlier  and  less  improved  sub- 
groups. Small  and  broken  groups  and  sub-groups  will 
hnally  tend  to  disa]3pear.  Looking  to  the  future,  we  can 
predict  that  the  groups  of  organic  beings  which  are  now 
large  and  triumphant,  and  which  are  least  broken  up, 
that  is,  which  as  yet  have  suffered  least  extinction,  will 
for  a  long  period  continue  to  increase.  But  which  groups 
will  ultimately  prevail,  no  man  can  predict ;  for  we  well, 
know  that  many  groups,  formerly  most  extensively  devel- 
oped, have  now  become  extinct.  Looking  still  more 
remotely  to  the  future,  we  may  predict  that,  owing  to  the 
continued  and  steady  increase  of  the  larger  groups,  a 
multitude  of  smaller  groups  will  become  utterly  extinct, 
and  leave  no  modified  descendants  ;  and  consequently 
that  of  the  species  living  at  any  one  period,  extremely 
few  will  transmit  descendants  to  a  remote  futurity.  I 
shall  have  to  return  to  this  subject  in  the  chapter  on 
Classification,  but  I  may  add  that  on  this  view  of  ex- 
tremely few  of  the  more  ancient  species  having  transmitted 
descendants,  and  on  the  view  of  all  the  descendants  of 
the  same  species  making  a  class,  we  can  understand  how 
it  is  that  there  exist  but  very  few  classes  in  each  main 
division  of  the  animal  and  vegetable  kingdoms.  Although 
extremely  few  of  the  most  ancient  species  may  now  have 
living  and  modified  descendants,  yet  at  the  most  remote 
geological  period,  the  earth  may  have  been  as  well  peopled 
wdth  many  species  of  many  genera,  families,  orders,  and 
classes,  as  at  the  present  day. 

A  distinguished  naturalist  has  objected  that  the  con- 
tinued action  of  natural  selection  and  divergence  will  tend 
to  make  an  indefinite  number  of  specific  forms.  As  lar 
as  mere  inorganic  conditions  are  concerned,  it  seems  proba- 
ble that  a  sufficient  number  of  species  would  soon  become 


Chap.  IV.]  DIVERGENCE  OF  CHARACTER.  116* 

adapted  to  all  considerable  diversities  of  heat,  moisture, 
(fee. ;  but  I  fully  admit  that  the  mutual  relations  of  or- 
ganic beings  are  the  most  important,  and  as  the  number 
of  species  in  any  country  goes  on  increasing,  the  organic 
conditions  of  life  will  become  more  and  more  complex. 
Consequentl}^,  there  seems  at  first  to  be  no  limit  to  the 
amount  of  profitable  diversification  of  structure,  and  there- 
fore no  limit  to  the  number  of  species  which  might  be 
produced.  "We  do  not  know  that  even  the  most  prolific 
area  is  fully  stocked  with  specific  forms  ;  at  the  Cape  of 
Good  Hope,  which  supports  such  an  astonishing  number 
of  species,  many  European  plants  have  become  naturalised. 
But  geology  shows  us,  at  least  within  the  whole  immense 
Tertiary  period,  that  the  number  of  species  of  shells,  and 
probably  of  mammals,  has  not  increased.  What,  then, 
checks  an  indefinite  increase  in  the  number  of  species  ? 
Firstly,  the  amount  of  life  (I  do  not  mean  the  number  of 
specific  forms)  supported  on  any  area  must  have  a  limit, 
depending  so  largely  as  it  does  on  physical  conditions : 
therefore  where  very  many  species  are  supported,  each, 
or  nearly  each,  will  be  few  in  individuals ;  and  any  species 
with  scanty  numbers  would  be  liable  to  extermination 
from  accidental  fluctuations  in  the  nature  of  seasons  and 
in  the  number  of  its  enemies.  The  process  of  extermina- 
tion would  in  such  cases  be  rapid,  whereas  the  process  of 
the  production  of  new  species  would  always  be  slow.  Im- 
agine the  extreme  case  of  as  many  species  as  individuals 
in  England,  and  the  first  severe  winter  or  very  dry  sum- 
mer would  exterminate  thousands  on  thousands  of  species ; 
and  individuals  of  other  species  would  take  their  places. 
Secondly,  I  suspect  that  when  any  species  becomes  very 
rare,  close  interbreeding  will  tend  to  exterminate  it ;  at 
least  authors  have  thought  that  this  comes  into  play  in  ac- 
counting for  the  deterioration  of  aurochs  in  Lithuania,  of 
red  deer  in  Scotland,  and  of  bears  in  Norway,  &c. 
Thirdly,  as  far  as  animals  are  concerned,  some  species  are 
closely  adapted  to  prey  on  some  one  other  being ;  but  if 
this  other  being  had  been  rare,  it  would  not  have  been 
any  advantage  to  the  animal  to  have  been  produced  in 
close  relation  to  its  prey ;  therefore  it  would  not  have 


11^^  '   NATURAL  SELECTION.  [Chap.  IV. 

been  produced  by  natural  selection.  Fourthly,  when  any 
species  becomes  few  in  number,  the  process  of  modifica- 
tion will  be  slower,  for  the  chance  of  favourable  variations 
arising  will  be  lessened ;  therefore  if  we  suppose  an  area 
to  be  inhabited  by  very  many  species,  each,  or  nearly 
each,  species  will  be  poor  in  individuals,  and  consequently 
the  process  of  modification  and  of  giving  birth  to  new 
forms  will  be  retarded.  Fifthly,  and  this  I  am  inclined  to 
think  is  the  most  important  element,  a  dominant  species 
which  has  already  beaten  many  competitors  in  its  own 
home,  will  tend  to  spread  and  supplant  many  others. 
Alph.  de  Candolle  has  shown  that  those  species  which 
spread  widely,  tend  generally  to  spread  veri/  widely ;  and 
consequently  they  will  tend  to  exterminate  several  species 
in  several  areas,  and  thus  check  the  inordinate  increase 
of  specific  forms  throughout  the  world.  Hooker  has  re- 
cently shown  that  in  the  S.  E.  corner  of  Australia,  where 
aj)parently  there  are  many  invaders  from  different  quar- 
ters of  the  world,  the  endemic  Australian  species  have 
apparently  been  greatly  reduced  in  number.  How  much 
weight  to  attribute  to  these  several  causes,  I  do  not  pre- 
tend to  assign ;  but  conjointly  I  think  they  must  limit  in 
each  country  the  tendency  to  an  indefinite  augmentation 
of  specific  forms. 

Natural  Selection  acts,  as  we  have  seen,  exclusively 
by  the  preservation  and  accumulation  of  variations,  which 
are  beneficial  under  the  oi'ganic  and  inorganic  conditions 
of  life  to  which  each  creature  is  at  each  successive  period 
exposed.  The  ultimate  result  will  be  that  each  creature 
will  tend  to  become  more  and  more  improved  in  relation 
to  its  conditions  of  life.  This  improvement  will,  I  think, 
inevitably  lead  to  the  gradual  advancement  of  the  organi- 
sation of  the  greater  number  of  living  beings  tbrougliout 
the  world.  But  here  we  enter  on  a  very  intricate  sub- 
ject, for  naturalists  have  not  defined  to  each  other's  satis- 
faction what  is  meant  by  an  advance  in  organisation. 
Amongst  the  Yertebrata,  the  degree  of  intellect  and  an 
approach  in  structure  to  man  clearly  come  into  play.  It 
might  be  thought  that  the  amount  of  change  which  the 
various  parts  and  organs  undergo  in  their  development 


Chap.  IV.]  DIVERGENCE  OF    CHARACTER.  118* 

from  the  embryo  to  matmity  would  suffice  as  a  standard 
of  comparison ;  but  there  are  cases,  as  with  certain  para- 
sitic crustaceans,  in  which  several  parts  of  the  structure 
become  less  j^erfect  and  even  monstrous,  so  that  the  ma- 
ture animal  cannot  be  called  higher  than  its  larva.  Yon 
Baer's  standard  seems  the  most  widely  applicable  and  the 
best ;  namely,  the  amount  of  differentiation  of  the  differ- 
ent parts  (in  the  adult  state,  as  I  should  be  inclined  to 
add),  and  their  specialisation  for  different  functions ;  or 
as  Milne  Edwards  would  express  it,  the  completeness  of 
the  division  of  physiological  labour.  But  we  shall  see 
how  obscure  a  subject  this  is,  if  we  look,  for  instance,  to 
Fish,  amongst  which  some  naturalists  rank  those  as  high- 
est which,  like  the  sharks,  approach  nearest  to  reptiles ; 
whilst  other  naturalists  rank  the  common  bony  or  teleos- 
tean  fishes  as  the  highest,  inasmuch  as  they  are  most 
strictly  fish-like,  and  differ  most  from  the  other  vertebrate 
orders.  Still  more  plainly  we  see  the  obscurity  of  the 
subject,  by  turning  to  plants,  where  the  standard  of  intel- 
lect is  of  course  quite  excluded ;  and  here  some  botanists 
rank  those  plants  as  highest  which  have  every  organ,  as 
sepals,  petals,  stamens  and  pistils,  fully  developed  in  each 
flower;  whereas  other  botanists,  probably  with  more 
truth,  look  at  the  plants  which  have  their  several  organs 
much  modified  and  somewhat  reduced  in  number  as  being 
of  the  highest  rank. 

If  we  look  at  the  differentiation  and  specialisation  of 
the  several  organs  of  each  being,  when  adult  (and  this 
will  include  the  advancement  of  the  brain  for  intellectual 
purposes),  as  the  best  standard  of  highness  of  organisa- 
tion, natural  selection  will  clearly  lead  towards  highness  ; 
for  all  physiologists  admit  that  the  specialisation  of  organs, 
inasmuch  as  they  perform  in  this  state  their  functions  bet- 
ter, is  an  advantage  to  each  being ;  and  hence  the  accu- 
mulation of  variations  tending  towards  specialisation  is 
within  the  scope  of  natural  selection.  On  the  other  hand, 
we  can  see,  bearing  in  mind  that  all  organic  beings  are 
striving  to  increase  at  a  high  ratio  and  to  seize  on  every 
ill-occupied  place  in  the  economy  of  nature,  that  it  is 
quite  possible  for  natural  selection  gradually  to  fit  an  or- 


Iig^  NATURAL  SELECTION  (Chap  IV. 

ganic  being  to  a  situation  in  which  several  organs  -vvonld 
be  superflu-ons  and  useless  ;  and  in  such  cases  there  might 
be  retrogression  in  the  scale  of  organisation.  Whether 
organisation  on  the  whole  has  actuallj^  advanced  from  the 
remotest  geological  periods  to  the  present  day  will  be 
more  conveniently  discussed  in  our  chapter  on  geological 
succession. 

But  it  may  be  objected,  that  if  all  organic  beings  thus 
tend  to  rise  in  the  scale,  how  is  it  that  throughout  the 
world  a  multitude  of  the  lowest  forms  still  exist,  and  how 
is  it  that  in  each  great  class  some  forms  are  far  more 
highly-developed  than  others  ?  Why  have  not  the  more 
higldy-developed  forms  everywhere  supplanted  and  exter- 
minated the  lower?  Lamarck,  who  believed  in  an  innate 
and  inevitable  tendency  towards  peifection  in  all  organic 
beings,  seems  to  have  felt  this  difficulty  so  strongly,  that 
he  was  led  to  suppose  that  new  and  simple  forms  were 
continually  being  produced  by  spontaneous  generation. 
I  need  hardly  say  that  science  in  her  progress  has  forbid 
den  us  to  believe  that  living  creatures  are  now  ever  pro- 
duced from  inorganic  matter.  On  my  theory  the  present 
existence  of  lowly  organized  ^productions  offers  no  diffi- 
culty ;  for  natural  selection  includes  no  necessary  and 
universal  law  of  advancement  or  development ;  it  only 
takes  advantage  of  such  variations  as  arise  and  are  bene- 
iicial  to  each  creature  under  its  complex  relations  of  life. 
And  it  may  be  asked,  what  advantage,  as  far  as  we  can 
see,  would  it  be  to  an  infusorian  animalcule — to  an  intes- 
tinal worm — or  even  to  an  earth-worm,  to  be  highly  or- 
ganized ?  If  it  were  no  advantage,  these  forms  would  be 
left  by  natural  selection  unimproved  or  but  little  im- 
proved ;  and  might  remain  for  indefinite  ages  in  their 
present  little  advanced  condition.  And  geology  tells  us 
that  some  of  the  lowest  forms,  as  the  infusoria  and  rhizo- 
pods,  have  remained  for  an  enormous  jDcriod  in  neai-ly 
their  present  state.  But  to  suppose  that  most  of  the  many 
now-existing  low  forms  have  not  in  the  least  advanced 
since  the  first  dawn  of  life,  would  be  rash ;  for  every 
naturalist  who  has  dissected  some  of  the  beings  now  ranked 
as  very  low  in  the  scale,  must  often  have  been  struck  with 
their  really  wondrous  and  beautiful  organisation. 


Chap.  IV.]  DIVERGENCE  OP  CHARACTER.  120* 

iN'early  the  same  remarks  are  applicable,  if  we  look  to 
the  great  existing  differences  in  the  grades  of  organisation 
■svitliin  almost  every  clasSj  excepting  birds ;  for  instance, 
to  the  coexistence  of  mammals  and  lisli  in  the  vertebrata, 
— or  to  the  coexistence  of  man  and  the  ornithorhynchus 
amongst  mammalia, — or  amongst  fish,  of  the  shark  and 
Amphioxus,  which  latter  fish  in  the  extreme  simplicity  of 
its  structure  closely  approaches  the  invertebrate  classes. 
But  mammals  and  fish  hardly  come  into  competition  with 
each  other ;  the  advancement  of  certain  mammals  or  of 
the  whole  class  to  the  highest  grade  of  organisation  would 
not  lead  to' their  taking  the  place  of  and  thus  exterminat- 
ing fishes.  Physiologists  believe  that  the  brain  must  be 
bathed  by  warm  blood  to  be  highl}^  active,  and  this  re- 
quires aerial  respiration  ;  so  that  warm-blooded  mammals, 
when  inhabiting  the  water,  live  under  some  disadvantages 
compared  with  fishes.  In  this  latter  cUiss  members  of  the 
shark  family  would  not,  it  is  probable,  tend  to  supplant 
the  Amphioxus ;  the  struggle  for  existence  in  the  case  of 
the  Amphioxus  must  lie  with  members  of  the  invertebrate 
classes.  The  three  lowest  orders  of  mammals — namely, 
marsupials,  edentata  and  rodents  —  coexist  in  South 
America  in  the  same  region  with  numerous  monkeys. 
Although  organisation,  on  the  whole,  may  advance 
throughout  the  world,  yet  the  scale  of  perfection  will  still 
present  all  degrees  for  the  high  advancement  of  certain 
v/hole  classes,  or  of  certain  members  of  each  class,  does 
not  at  all  necessarily  lead  to  the  extinction  of  those  groups 
with  which  they  do  not  enter  into  close  competition.  In 
some  cases,  as  we  shall  hereafter  see,  lowly-organized 
forms  seem  to  have  been  preserved  to  the  present  day, 
from  having  inhabited  peculiar  or  isolated  stations  where 
they  have  been  subjected  to  less  severe  competition ;  and 
where  they  have  not  advanced  in  organization  owing  to 
their  scanty  individual  numbers,  which,  as  already  ex- 
plained, retards  the  chance  of  favourable  variations 
arising. 

Finally,  I   believe   that   lowly-organised   forms   now 
exist   in    numbers  throughout  the  world  and  in  nearly 
every  class,  from  various  causes.     In  some  cases  favoura- 
6* 


121'^  NATURAL  SELECTION".  [Chap.  IV. 

ble  variations  may  never  have  arisen  for  natural  selection 
to  act  on  and  accumulate.  In  no  case,  perhaps,  has  time 
sufficed  for  ttie  utmost  possible  maximum  of  development. 
In  some  few  cases  there  may  have  been  what  we  must 
call  retrogression  of  organisation.  But  the  main  cause 
lies  in  the  circumstance,  that  under  very  simple  condi- 
tions of  life,  a  high  organisation  would  be  of  no  service — 
possibly  would  be  of  actual  disservice,  as  being  of  a  more 
delicate  nature,  and  more  liable  to  be  put  out  of  order 
and  thus  injured. 

A  difficulty,  diametrically  opposite  to  this  which  we 
have  just  been  considering,  might  be  advanced  ;  namely, 
looking  to  the  dawn  of  life,  when  all  organic  beings,  as 
we  may  imagine,  presented  the  simplest  structure,  how 
could  the  first  steps  in  advancement  or  in  the  differentia- 
tion and  specialization  of  parts  arise?  I  can  make  no 
sufficient  answer,  and  can  only  say  that  we  have  no  facts 
to  guide  us,  and  therefore  that  all  speculations  on  this 
subject  would  be  baseless  and  useless. 

Buimnary  of  Chapter. — If  during  the  long  course  of 
ages  and  under  varying  conditions  of  life,  organic  beings 
vary  at  all  in  the  several  parts  of  their  organisation,  and 
I  think  this  cannot  be  disputed ;  if  there  be,  owing  to  the 
high  geometrical  powers  of  increase  of  each  species,  at 
some  age,  season,  or  year,  a  severe  struggle  for  life,  and , 
this  certainly  cannot  be  disputed  ;  then,  considering  the 
infinite  complexity  of  the  relations  of  all  organic  beings 
to  each  other  and  to  their  conditions  of  existence,  causing 
an  infinite  diversity  in  structure,  constitution,  and  habits, 
to  be  advantageous  to  them,  I  think  it  would  be  a  most 
extraordinary  fact  if  no  variation  ever  had  occurred  useful 
to  each  being's  own  welfare,  in  the  same  way  as  so  many 
variations  have  occurred  useful  to  man.  But  if  variations 
useful  to  any  organic  being  do  occur,  assuredly  individuals 
thus  characterized  will  have  the  best  chance  of  being  pre- 
served in  the  struggle  for  life ;  and  from  the  strong  prin- 
ciple of  inheritance  they  will  tend  to  produce  offspring 
similarly  characteriired.  This  principle  of  preservation, 
I  have  called,  for  the  sake  of  brevity,  Natural  Selection. 


Chap.  IV. 3  SUMMARY.  l^^ 

Natural  selection,  on  the  principle  of  qualities  being  in- 
herited at  corresponding  ages,  can  modify  the  egg^  seed, 
or  young,  as  easily  as  the  adult.  Amongst  many  animals, 
sexual  selection  will  give  its  aid  to  ordinary  selection,  by 
assuring  to  the  most  vigorous  and  best  adapted  males  the 
greatest  number  of  offsj^ring.  Sexual  selection  will  also 
give  characters  useful  to  the  males  alone,  in  their  struggles 
with  other  males. 

"Whether  natural  selection  has  really  thus  acted  in  na- 
ture, in  modifying  and  adapting  the  various  forms  of  life 
to  their  several  conditions  and  stations,  must  be  judged 
of  by  the  general  tenour  and  balance  of  evidence  given  in 
the  following  chapters.  But  we  already  see  how  it  entails 
extinction ;  and  how  largely  extinction  has  acted  in  the 
world's  history,  geology  plainly  declares.  Natural  selec- 
tion, also,  leads  to  divergence  of  character  ;  for  more  living 
beings  can  be  supported  on  the  same  area  the  more  they 
diverge  in  structure,  habits,  and  constitution,  of  which  we 
see  proof  by  looking  at  the  inhabitants  of  any  small  spot 
or  at  naturalised  productions.  Therefore  during  the  modi- 
fication of  the  descendants  of  any  one  species,  and  during 
the  incessant  struggle  of  all  species  to  increase  in  numbers, 
the  more  diversified  these  descendants  become,  the  better 
will  be  their  chance  of  succeeding  in  the  battle  of  life. 
Thus  the  small  differences  distinguishing  varieties  of  the 
same  species,  will  steadily  tend  to  increase  till  they  come 
to  equal  the  greater  difi'erences  between  species  of  the 
same  genus,  or  even  of  distinct  genera. 

We  have  seen  that  it  is  the  common,  the  widely-difi*used, 
and  widely-ranging  species,  belonging  to  the  larger  genera, 
which  vary  most ;  and  these  will  tend  to  transmit  to  their 
modified  offspring  that  superiority  Avhich  now  makes  them 
dominant  in  their  own  countries.  Natural  selection,  as  has 
just  been  remarked,  leads  to  divergence  of  character  and  to 
much  extinction  of  the  less  improved  and  intermediate  forms 
of  life.  On  these  principles,  I  believe  that  the  differences 
in  rank  of  the  innumerable  organic  beings  in  each  class 
thi-oughout  the  world,  as  well  as  the  nature  of  their  affini- 
ties, may  be  explained.  It  is  a  truly  wonderful  fact — the 
wonder  of  which  we  are  apt  to  overlook  from  familiarity 


Ilg  NATURAL   8ELECTI0X.  [Chap.  IV. 

— that  all  animals  and  all  plants  thronghout  all  time  and 
space  should  be  related  to  each  other  in  group  subordinate 
to  group,  in  the  manner  which  we  everywhere  behold — • 
namely,  varieties  of  the  same  species  most  closely  related 
together,  species  of  the  same  genus  less  closely  and  un- 
equally related  together,  forming  sections  and  sub-genera, 
species  of  distinct  genera  much  less  closely  related,  and 
genera  related  in  different  degrees,  forming  sub-families, 
families,  orders,  sub-classes,  and  classes.  The  several 
subordinate  groups  in  any  class  cannot  be  ranked  in  a 
siDgle  tile,  but  seem  rather  to  be  clustered  round  points, 
and  these  round  other  points,  and  so  on  in  almost  endless 
cycles.  On  the  view  that  each  species  has  been  inde- 
pendently created,  I  can  see  no  explanation  of  this  great 
fact  in  the  classification  of  all  organic  beings  ;  but,  to  the 
best  of  my  judgment,  it  is  explained  through  inheritance 
and  the  complex  action  of  natural  selection,  entailing 
extinction  and  divergence  of  character,  as  we  have  seen 
illustrated  in  the  diagram. 

The  affinities  of  all  the  beings  of  the  same  class  have 
sometimes  been  represented  by  a  great  tree.  I  believe 
this  simile  largely  speaks  the  truth.  The  green  and  bud- 
ding twigs  may  represent  existing  species  ;  and  those  pro- 
duced during  each  former  year  may  represent  the  long 
succession  of  extinct  species.  At  each  period  of  growth 
all  the  gi'owing  twigs  have  tried  to  branch  out  on  all  sides, . 
and  to  overtop  and  kill  the  surrounding  twigs  and  branch- 
es, in  the  same  manner  as  species  and  groups  of  species 
have  tried  to  overmaster  other  species  in  the  great  battle 
for  life.  The  limbs  divided  into  great  branches,  and  these 
into  lesser  and  lesser  branches,  were  themselves  once, 
when  the  tree  was  small,  budding  twigs ;  and  tliis  con- 
nection of  the  former  and  present  buds  by  ramifying 
branches  may  well  represent  the  classification  of  all  extinct 
and  living  species  in  groups  subordinate  to  groups.  Of 
the  many  twigs  which  flourished  when  the  tree  was  a 
mere  bush,  only  two  or  three,  now  grown  into  great 
branches,  yet  survive  and  bear  all  the  other  branches  ;  so 
with  the  species  which  lived  during  long-past  geological 
periods,  very  few  now  have  living  and  modified  descend- 


Chap.  IV.]  SUMMARY.  119 

ants.  From  the  first  growth  of  the  tree,  many  a  limb  and 
branch  has  decayed  and  dropped  off;  and  these  lost 
branches  of  various  sizes  may  represent  those  whole 
orders,  families,  and  genera  which  have  now  no  living 
representatives,  and  which  are  known  to  ns  only  from 
having  been  found  in  a  fossil  state.  As  we  here  and  there 
see  a  thin  straggling  branch  springing  from  a  fork  low 
down  in  a  tree,  and  which  by  some  chance  has  been 
favoured  and  is  still  alive  on  its  summit,  so  we  occasionally 
see  an  animal  like  the  Ornithorhynchns  or  Lepidosiren, 
which  in  some  small  degree  connects  by  its  affinities  two 
large  branches  of  life,  and  which  has  apparently  been 
saved  from  fatal  competition  by  having  inhabited  a  pro- 
tected station.  As  buds  give  rise  by  growth  to  fresh  buds, 
and  these,  if  vigorous,  branch  out  and  overtop  on  all  sides 
many  a  feebler  branch,  so  by  generation  I  believe  it  has 
been  with  the  great  Tree  of  Lue,  which  fills  with  its  dead 
and  broken  branches  the  crust  of  the  earth,  and  covers 
the  surface  with  its  ever  branching  and  beautiful  ramifi- 
cations. 


120 


LAWS    OF    VARIATION.  (Chap.  V. 


CHAPTER    y. 

LAWS      OF      VARIATION. 

Effects  of  external  conditions — Use  and  disuse,  combined  with  natural  selection  ; 
organs  of  flight  and  of  vision— Acclimatisation— Correlation  of  growth— Compen- 
sation and  economy  of  growth — False  correlations — Multiple,  rudimentary,  and 
lowly  organised  structures  variable — Parts  developed  in  an  unusual  manner  are 
highly  variable  :  specific  characters  more  variable  than  generic  :  secondary  sexual 
characters  variable — Species  of  the  same  genus  vary  in  an  analogous  manner — Re- 
versions to  long  lost  characters — Summary. 

I  HAVE  liitlierto  sometimes  spoken  as  if  the  yariations — so 
common  and  multiform  in  organic  beings  nncler  domes- 
tication,  and  in  a  lesser  degree  in  those  in  a  state  of  nature 
— ^had  been  due  to  chance.  This,  of  course,  is  a  wholly  in- 
correct expression,  but  it  serves  to  acknowledge  j)lainlj 
our  ignorance  of  the  cause  of  each  particular  variation. 
Some  authors  believe  it  to  be  as  much  the  function  of  the 
rej^roductive  system  to  produce  individual  differences,  or 
very  slight  deviations  of  structure,  as  to  make  the  child 
like  its  parents.  But  the  much  greater  variability,  as 
well  as  the  greater  frequency  of  monstrosities  under  do- 
mestication or  cultivation,  than  under  nature,  leads  me  to 
believe  that  deviations  of  structure  are  in  some  way  due 
to  the  nature  of  tlie  conditions  of  life  to  which  the  parents 
and  tlieir  more  remote  ancestors  have  been  exposed  during 
several  generations.  I  have  remarked  in  the  first  chapter 
— ^but  a  long  catalogue  of  facts  which  cannot  be  here 
given,  would  be  necessary  to  show  the  truth  of  the  remark 
— that  the  reproductive  system  is  eminently  susceptible 
to  changes  in  the  conditions  of  life;  and  to  this  system 
being  functionally  disturbed  in  the  parents,  I  chiefly  at- 
tribute the  varying  or  plastic  condition  of  the  offspring. 
The  male  and  female  sexual  elements  seem  to  be  affected 


Chap.  V.]  LAWS   OF   VARIATION.  |21 

before  that  union  takes  place  wliicli  is  to  form  a  new  be- 
ing. In  the  case  of  "  sporting  "  plants,  the  bnd,  which  in 
its  earliest  condition  does  not  apparently  differ  essentially 
from  an  ovule,  is  alone  affected.  But  why,  because  the 
reproductive  system  is  disturbed,  this  or  that  part  should 
vary  more  or  less,  we  are  profoundly  ignorant.  ISTeverthe- 
less,  we  can  here  and  there  dimly  catch  a  faint  ray  of 
light,  and  we  may  feel  sure  tliat  there  must  be  some  cause 
for  each  deviation  of  structure,  however  slight. 

How  much  direct  effect  difference  of  climate,  food, 
&c.,  produces  on  any  being  is  extremely  doubtful.  My 
impression  is,  that  the  effect  is  extremely  small  in  the  case 
of  animals,  but  perhaps  rather  more  in  that  of  plants. 
We  may,  at  least,  safely  conclude  that  such  influences  can- 
not have  produced  the  many  striking  and  complex  co- 
adaptations  of  structure  between  one  organic  being  and 
another,  which  we  see  everywhere  throughout  nature. 
Some  little  influence  may  be  attributed  to  climate,  food, 
&c. :  thus,  E.  Forbes  spealvs  confidently  that  shells  at  their 
southern  limit,  and  when  living  in  shallow  water,  are  more 
brightly  coloured  than  those  of  the  same  species  further 
north  or  from  greater  depths.  Gould  believes  that  birds 
of  the  same  species  are  more  brightly  coloured  under  a 
clear  atmosphere,  than  when  living  on  islands  or  near  the 
coast.  So  with  insects,  Wollaston  is  convinced  that  res- 
idence near  the  sea  affects  their  colours.  Moquin-Tandon 
gives  a  list  of  plants  which  when  growing  near  the  sea- 
shore have  their  leaves  in  some  degree  fleshy,  though  not 
elsewhere  flesliy.  Several  other  such  cases  could  be 
given. 

The  fact  of  varieties  of  one  species,  when  they  range 
into  the  zone  of  habitation-  of  other  species,  often  acquir- 
ing in  a  very  sliglit  degree  some  of  the  characters  of  such 
sjDccies,  accords  with  our  view  that  species  of  all  kinds  are 
only  well-marked  and  permanent  varieties.  Thus  the  spe- 
cies of  shells  which  are  confined  to  tropical  and  shallow 
seas  are  generally  brighter-coloured  than  those  confined 
to  cold  and  deeper  seas.  The  birds  which  are  confined  to 
continents  are,  according-  to  Mr.  Gould,  brighter-coloured 
than  those  of  islands.     The  insect-species  confined  to  sea- 


j^22  LAWS   OF   VARIATION.  [Chap.  \. 

coasts,  as  every  collector  knows,  are  often  brassy  or  lurid- 
Plants  which  live  exclusively  on  the  sea-side  are  very  apt 
to  have  fleshy  leaves.  He  who  believes  in  the  creation  of 
each  species,  will  have  to  say  that  this  shell,  for  instance, 
was  created  with  bright  colours  for  a  Avarm  sea  ;  but  that 
this  other  shell  became  bright-coloured  by  variation  when 
it  ranged  into  warmer  or  shallower  waters. 

When  a  variation  is  of  the  slightest  use  to  a  being,  we 
cannot  tell  how  much  of  it  to  attribute  to  the  accumulative 
action  of  natural  selection,  and  how  much  to  the  con- 
ditions of  life.  Thus,  it  is  well  known  to  furriers  that  an- 
imals of  the  same  species  have  thicker  and  better  fur  tlie 
more  severe  the  climate  is  under  which  they  have  lived  ; 
but  who  can  tell  how  much  of  this  difference  may  be  due 
to  the  warmest-clad  individuals  having  been  favoured  and 
preserved  during  many  generations,  and  how  much  to  the 
direct  action  of  the  severe  climate  ?  for  it  would  appear 
that  climate  has  some  direct  action  on  the  hair  of  our  do- 
mestic quadrupeds. 

Instances  could  be  given  of  the  same  variety  being 
produced  under  conditions  of  life  as  difi'erent  as  can  well 
be  conceived  ;  and,  on  the  other  hand,  of  different  varie- 
ties being  produced  from  the  same  species  under  the  same 
conditions.  Such  facts  show  how  indirectly  the  conditions 
of  life  must  act.  Again,  innumerable  instances  are  known 
to  every  naturalist  of  species  keeping  true,  or  not  varying, 
at  all,  although  living  under  the  most  oj)posite  climates. 
Such  considerations  as  these  incline  me  to  lay  very  little 
weight  on  the  direct  action  of  the  conditions  of  life.  In- 
directly, as  already  remarked,  they  seem  to  play  an  im- 
portant part  in  affecting  the  reproductive  system,  and  in 
thus  inducing  variability  ;  and  natural  selection  will  then 
accumulate  all  profitable  variations,  however  slight,  until 
they  become  plainly  developed  and  appreciable  by  us. 

Effects  of  Use  mid  Disuse. — From  the  facts  alluded  to 
in  the  first  chapter,  I  think  there  can  be  little  doubt  that 
use  in  our  domestic  animals  strengthens  and  enlarges  cer- 
tain parts,  and  disuse  diminishes  them  ;  and  that  such 
modincations  are  inherited.     Under  free  nature,  we  can 


Chap,  V.]  USE   AND   DISUSE.  ][23 

have  no  standard  of  comparison,  by  wMcli  to  judge  of  the 
effects  of  long-contmued  nse  or  disuse,  for  we  know  not 
the  parent-forms  ;  but  many  animals  have  structures  which 
can  be  explained  by  the  effects  of  disuse.  As  Professor 
Owen  has  remarked,  there  is  no  greater  anomaly  in 
nature  than  a  bird  that  cannot  fly ;  yet  there  arc  several 
in  this  state.  The  loggerheaded  duck  of  South  America 
can  only  flap  along  the  surface  of  the  water,  and  has  its 
wings  in  nearly  the  same  condition  as  the  domestic  Ayles- 
bury duck.  As  the  larger  ground-feeding  birds  seldom 
take  flight  except  to  escape  danger,  I  believe  that  the 
nearl}"  wingless  condition  of  several  birds,  which  now  in- 
habit or  have  lately  inhabited  several  oceanic  islands, 
tenanted  by  no  beast  of  prey,  has  been  caused  by  disuse. 
The  ostrich  indeed  inhabits  continents,  and  is  exposed  to 
danger  from  which  it  cannot  escape  by  flight,  but  by 
kicking  it  can  defend  itself  from  enemies,  as  well  as  any 
of  the  smaller  quadrupeds.  We  may  imagine  that  the 
early  progenitor  of  the  ostrich  had  habits  like  those  of  a 
bustard,  and  that  as  natural  selection  increased  in  succes- 
sive generations  the  size  and  weight  of  its  body,  its  legs 
were  used  more,  and  its  wings  less,  until  they  became  in- 
capable of  flight. 

Ivirby  has  remarked  (and  I  have  observed  the  same 
fiict)  that  the  anterior  tarsi,  or  feet,  of  many  male  dung- 
feeding  beetles  are  very  often  broken  oft";  he  examined 
seventeen  specimens  in  his  own  collection,  and  not  one  had 
even  a  relic  left.  In  the  Onites  apelles  the  tarsi  are  so 
habitually  lost,  that  the  insect  has  been  described  as  not 
having  them.  In  some  other  genera  they  are  present,  but 
in  a  rudimentary  condition.  In  the  Ateuchus  or  sacred 
beetle  of  the  Egyptians,  they  are  totally  deficient.  There 
is  not  suflicient  evidence  to  induce  us  to  believe  that  mu- 
tilations are  ever  inherited  ;  and  I  should  prefer  explain- 
ing the  entire  absence  of  the  anterior  tarsi  in  Ateuchus, 
and  their  rudimentary  condition  m  some  other  genera,  by 
the  long-continued  effects  of  disuse  in  their  progenitors  ; 
for  as  the  tarsi  are  almost  always  lost  in  many  dung-feed- 
ing beetles,  they  must  be  lost  early  in  life,  and  therefore 
cannot  be  much  used  by  these  insects. 


j[24:  LAWS    OF   VARIATION.  [Chap.  V. 

Ill  some  cases  we  miglit  easily  i^iit  down  to  disuse  mod- 
ifications of  structure  which  are  wholly,  or  mainly,  due  to 
natural  selection.  Mr.  Wollaston  has  discovered  the  re- 
markable fact  that  200  beetles,  out  of  the  550  species 
inhabiting  Madeira,  are  so  far  deficient  in  wings  that 
they  cannot  fly  ;  and  that  of  the  twenty-nine  endemic 
genera,  no  less  than  twenty-three  genera  have  all  their 
species  in  this  condition!  Several  facts,  namely,  that 
beetles  in  many  parts  of  the  world  are  very  frequently 
blown  to  sea  and  perish  ;  that  the  beetles  in  Madeira,  as 
observed  by  Mr.  Wollaston,  lie  much  concealed,  until  the 
wind  lulls  and  the  sun  shines ;  that  the  proportion  of  wing- 
less beetles  is  larger  on  the  exposed  Dezertas  than  in  Ma- 
deira itself;  and  especially  the  extraordinary  -fact,  so 
strongly  insisted  on  by  Mr.  "Wollaston,  of  the  almost  entire 
absence  of  certain  large  groups  of  beetles,  elsewhere  ex- 
cessively numerous,  and  which  groups  have  habits  of  life 
almost  necessitating  frequent  flight ; — these  several  con- 
siderations have  made  me  believe  that  the  wingless  con- 
dition of  so  many  Madeira  beetles  is  mainly  due  to  the 
action-  of  natural  selection,  but  combined  probably  with 
disuse.  For  during  thousands  of  successive  generations 
each  individual  beetle  which  flew  least,  either  from  its 
wings  having  been  ever  so  little  less  perfectly  developed 
or  from  indolent  habit,  will  have  had  the  best  chance 
of  surviving  from  not  being  blown  out  to  sea ;  and,  on 
the  other  hand,  those  beetles  which  most  readily  took 
to  flight  will  oftenest  have  been  blown  to  sea  and  thus 
have  been  destroyed. 

The  insects  in  Madeira  which  are  not  ground-feeders, 
and  which,  as  the  flower-feeding  coleoj^tera  and  lepidop- 
tera,  must  habitually  use  their  wings  to  gain  their  subsist- 
ence, have,  as  Mr.  AYollaston  suspects,  their  wings  not  at 
all  reduced,  but  even  enlarged.  This  is  quite  compatible 
with  the  action  of  natural  selection.  For  when  a  new  in- 
sect first  arrived  on  the  island,  the  tendency  of  natural 
selection  to  enlarge  or  to  reduce  the  wings,  would  depend 
on  whether  a  greater  number  of  individuals  were  saved  by 
successfully  battling  with  the  winds,  or  by  giving  up  the 
attempt  and  rarely  or  never  flying.     As  with  mariners 


Chap.  V.J  USE   AND   DISUSE.  ]^25 

shipwrecked  near  a  coast,  it  would  have  been  better  for 
the  good  swimmers,  if  they  had  been  able  to  swim  still 
further,  whereas  it  would  have  been  better  for  the  bad 
swimmers  if  they  had  not  been  able  to  swim  at  all  and  had 
stuck  to  the  wreck. 

The  eyes  of  moles  and  of  some  burrowing  rodents  are 
rudimentary  in  size,  and  in  some  cases  are  quite  covered 
up  by  skin  and  fur.  This  state  of  the  eyes  is  probably  due 
to  gradual  reduction  from  disuse,  but  aided  perhaps  by 
natural  selection.  In  South  America,  a  burrowing  rodent, 
the  tuco-tuco,  or  Ctenomys,  is  even  more  subterranean  in 
its  habits  than  the  mole ;  and  I  was  assured  by  a  Spaniard, 
who  had  often  caught  them,  that  they  were  frequently 
blind ;  one  which  I  kept  alive  was  certainly  in  this  con- 
dition, the  cause,  as  appeared  on  dissection,  having  been 
inflammation  of  the  nictitating  membrane.  As  frequent 
inflammation  of  the  eyes  must  be  injurious  to  any  animal, 
and  as  eyes  are  certainly  not  indispensable  to  animals  with 
subterranean  habits,  a  reduction  in  their  size  with  the  ad- 
hesion of  the  eyelids  and  growth  of  fur  over  them,  might 
in  such  case  be  an  advantage  ;  and,  if  so,  natural  selection 
would  constantly  aid  the  elfects  of  disuse. 

It  is  well  known  that  several  animals,  belonging  to  the 
most  diff'erent  classes,  which  inhabit  the  caves  of  Styria 
and  of  Kentucky,  are  blind.  In  some  of  the  crabs 
the  foot-stalk  for  the  eye  remains,  though  the  eye  is  gone  ; 
the  stand  for  the  telescope  is  there,  though  the  telescope 
with  its  glasses  has  been  lost.  As  it  is  difficult  to  imagine 
that  eyes,  though  useless,  could  be  in  any  way  injurious 
to  animals  living  in  darkness,  I  attribute  their  loss  wholly 
to  disuse.  In  one  of  the  blind  animals,  namely,  the  cave- 
rat,  the  eyes  are  of  immense  size ;  and  Professor  Silliman 
thought  that  it  regained,  after  living  some  days  in  the 
light,  some  slight  power  of  vision.  In  the  same  manner 
as  in  Madeira  the  wings  of  some  of  the  insects  have  been 
enlarged,  and  the  wings  of  others  have  been  reduced  by 
natural  selection  aided  by  use  and  disuse,  so  in  the  case  of 
the  cave-rat  natural  selection  seems  to  have  struggled  with 
the  loss  of  light  and  to  have  increased  the  size  of  the  eyes ; 
whereas  with  all  the  other  inhabitants  of  the  caves,  disuse 
by  itself  seems  to  have  done  its  work. 


12Q  LAWS    OF   VARIATION.  [Chap.  V. 

It  is  difficult  to  imagine  conditions  of  life  more  similar 
than  deep  limestone  caverns  under  a  nearly  similar 
climate  ;  so  that  on  tlie  common  view  of  the  blind  animals 
having  been  separately  created  for  the  American  and 
European  caverns,  close  similarity  in  their  organisation 
and  affinities  might  have  been  expected ;  but,  as  Schicidte 
and  others  have  remarked,  this  is  not  the  case,  and  the 
caVe-insects  of  the  two  continents  are  not  more  closely 
allied  than  might  have  been  anticipated  from  the  general 
resemblance  of  the  other  inhabitants  of  I^orth  America 
and  Europe.  On  my  view  we  must  suppose  that  Amer- 
ican animals,  having  ordinary  powers  of  vision,  slowly 
migrated  by  successive  generations  from  the  outer  world 
into  the  deeper  and  deeper  recesses  of  the  Kentucky  caves, 
as  did  European  animals  into  the  caves  of  Euroj)e.  We 
have  some  evidence  of  this  gradation  of  habit ;  for,  as 
Schiodte  remarks :  "  We  accordingly  look  upon  the  subter- 
ranean Faunas  as  small  ramifications  which  have  penetra- 
ted into  the  earth  from  the  geographically-limited  Faunas 
of  the  adjacent  tracts,  and  which  as  they  extended  them- 
selves into  darkness,  have  been  accommodated  to  surround- 
ing circumstances.  Animals  not  far  remote  from  ordinary 
forms,  prepare  the  transition  from  light  to  darkness. 
'Next  follow  those  that  are  constructed  for  twilight ;  and, 
last  of  all,  those  destined  for  total  darkness."  By  the 
time  that  an  animal  had  reached,  after  numberless  gener- 
ations, the  deepest  recesses,  disuse  will  on  this  view  have 
more  or  less  j)erfectly  obliterated  its  eyes,  and  natural  se- 
lection, will  often  have  effected  other  changes,  such  as  an 
increase  in  the  length  of  the  antennse  or  palpi,  as  a  com- 
pensation for  blindness.  ^Notwithstanding  such  modifica- 
tions, we  might  expect  still  to  see  in  the  cave-animals  of 
America,  affinities  to  the  other  inhabitants  of  that  con- 
tinent, and  in  those  of  Europe,  to  the  inhabitants  of  the 
European  continent.  And  this  is  the  case  with  some  of 
the  American  cave-animals,  as  I  hear  from  Professor 
Dana ;  and  some  of  the  European  cave-insects  are  very 
closely  allied  to  those  of  the  surrounding  country.  It 
would  be  most  difficult  to  give  any  rational  exj^lanation 
of  the  affinities  of  the  blind  cave-animals  to  the  other  in- 
habitants of  the  two  continents  on  the  ordinary  view  of 


Chap.  V.]  ACCLIMATISATION.  ^27 

their  independent  creation.  That  several  of  the  inhabi- 
tants of  the  caves  of  the  Old  and  ]^ew  Worlds  should  be 
closely  related,  we  might  expect  from  the  well-known  re- 
lationship of  most  of  their  other  productions.  Some,  in- 
deed, of  the  cave-insects  common  to  both  hemispheres, 
belong  to  genera  existing  nowhere  except  in  the  caves ; 
but  the  progenitors  of  these  insects  may  formerly  have 
ranged  widely  over  the  whole  area.  Blind  species  of  the 
genus  Adelops  now  inhabit  caves,  and  are  likewise  found 
in  dark  places  under  moss.  Far  from  feeling  any  sur- 
prise that  some  of  the  cave-animals  should  be  very  anoma- 
lous, as  Agassiz  has  remarked  in  regard  to  the  blind  fish,  the 
Amblyopsis,  and  as  is  the  case  with  the  blind  Proteus  with 
reference  to  the  reptiles  of  Europe,  I  am  only  surprised 
that  more  wrecks  of  ancient  life  have  not  been  preserved, 
owing  to  the  less  severe  competition  to  which  the  inhabi- 
tants of  these  dark  abodes  will  probably  have  been  exposed. 

AcclwiatisaUon. — Habit  is  hereditary  with  plants,  as 
in  the  period  of  flowering,  in  the  amount  of  rain  requisite 
for  seeds  to  germinate,  in  the  time  of  sleep,  &c.,  and  this 
leads  me  to  say  a  few  words  on  acclimatisation.  As  it  is 
extremely  common  for  species  of  the  same  genns  to  in- 
habit very  hot  and  very  cold  countries,  and  as  I  believe 
that  all  the  species  of  the  same  genus  have  descended 
from  a  single  parent,  if  this  view  be  correct,  acclimatisa- 
tion must  be  readily  eflected  during  long-continued 
descent.  It  is  notorious  that  each  sj)ecies  is  adapted  to 
the  climate  of  its  own  home :  species  from  an  arctic  or 
even  from  a  temperate  region  cannot  endure  a  tropical 
climate,  or  conversely.  So  again,  many  succulent  j)lants 
cannot  endure  a  damp  climate.  But  the  degree  of  adap- 
tation of  species  to  the  climates  nnder  which  they  live  is 
often  overrated.  AYe  may  infer  this  from  our  frequent  in- 
ability to  predict  whether  or  not  an  imported  plant  will 
endure  our  climate,  and  from  the  number  of  plants  and 
animals  brought  from  warmer  countries  which  here  enjoy 
good  health.  We  have  reason  to  believe  that  species  in  a 
state  of  nature  are  limited  in  their  ranges  by  the  compe- 
tition of  other  organic  beings  quite  as  much  as,  or  more 
than,  by  adaptation  to  particular  climates.     But  whether 


128  LAWS    OF    VARIATIUN.  [Chap.  V. 

or  not  the  adaptation  Le  generally  very  close,  we  liave 
evidence,  in  the  case  of  some  few  plants,  of  their  becom- 
ing, to  a  certain  extent,  naturally  habituated  to  different 
temperatures,  or  becoming  acclimatised :  thus  the  pines  and 
rliododendrons,  raised  from  seed  collected  by  Dr.  Hooker 
from  trees  growing  at  different  heights  on  the  Himalaya, 
were  found  in  this  country  to  possess  different  constitu- 
tional ]30wers  of  resisting  cold.  Mr.  Thwaites  informs  me 
that  he  has  observed  similar  facts  in  Ceylon,  and  analo- 
gous observations  have  been  made  by  Mr.  H,  C.  Watson 
on  European  species  of  j)lants  brought  from  the  Azores 
to  England.  In  regard  to  animals,  several  authentic  cases 
could  be  given  of  species  within  historical  times  having 
largely  extended  their  range  from  warmer  to  cooler  lati- 
tudes, and  conversely  ;  but  we  do  not  positively  know 
that  these  animals  were  strictly  adapted  to  their  native 
climate,  but  in  all  ordinary  cases  we  assume  such  to  be 
the  case ;  nor  do  we  know  that  they  have  subsequently 
become  acclimatised  to  their  new  homes. 

As  I  believe  that  our  domestic  animals  were  originally 
chosen  by  uncivilised  man  because  they  were  useful  and 
bred  readily  under  confinement,  and  not  because  they 
were  subsequently  found  capable  of  far-extended  trans- 
portation, 1  think  the  common  and  extraordinary  capacity 
in  our  domestic  animals  of  not  only  Avith standing  the 
most  difierent  climates  but  of  being  perfectly  fertile  (a  far 
severer  test)  under  them,  may  be  used  as  an  argument 
that  a  large  proportion  of  other  animals,  now  in  a  state 
of  nature,  could  easily  be  brought  to  bear  widely  different 
climates.  We  must  not,  however,  push  the  foregoing  ar- 
gument too  far,  o]i  account  of  the  probable  origin  of  some 
of  our  domestic  animals  from  several  wild  stocks  :  the 
blood,  for  instance,  of  a  tropical  and  arctic  wolf  or  wild 
dog  may  perhaps  be  mingled  in  our  domestic  breeds.  Tlie 
rat  and  mouse  cannot  be  considered  as  domestic  animals, 
but  they  have  been  transported  by  man  to  many  parts  of 
the  world,  and  now  have  a  far  wider  range  than  any  other 
rodent,  living  free  under  the  cold  climate  of  Faroe  in  the 
north  and  of  the  Falklands  in  the  south,  and  on  many 
islands  in  the  torrid  zone.  Hence  I  am  inclined  to  look 
at  adaptation  to  any  special  climate  a^  a  quality  readily 


Chap.  V.]  ACCLIMATISATION.  -j^29 

grafted  on  an  innate  wide  flexibility  of  constitution,  which 
is  common  to  most  animals.  On  this  view,  the  capacity 
of  enduring  the  most  different  climates  by  man  himself 
and  by  his  domestic  animals,  and  such  facts  as  that  for- 
mer species  of  the  elephant  and  rhinoceros  were  capable 
of  enduring  a  glacial  climate,  whereas  the  living  species 
are  now  all  tropical  or  sub-tropical  in  their  habits,  ought 
not  to  be  looked  at  as  anomalies,  but  merely  as  examples 
of  a  very  common  flexibility  of  constitution,  brought, 
under  peculiar  circumstances,  into  play. 

How  much  of  the  acclimatisation  of  species  to  any 
peculiar  climate  is  due  to  mere  habit,  and  how  much  to 
the  natural  selection  of  varieties  having  different  innate 
constitutions,  and  how  much  to  both  means  combined,  is 
a  very  obscure  question.  That  habit  or  custom  has  some 
influence  I  must  believe,  both  from  analogy,  and  from  the 
incessant  advice  given  in  agricultural  works,  even  in  the 
ancient  Encyclopaedias  of  China,  to  be  very  cautious  in 
transposing  animals  from  one  district  to  another ;  for  it 
is  not  likely  that  man  should  have  succeeded  in  selecting 
so  many  breeds  and  sub-breeds  with  constitutions  spe- 
cially fitted  for  their  own  districts  :  the  result  must,  I 
think,  be  due  to  habit.  On  the  other  hand,  I  can  see  no 
reason  to  doubt  that  natural  selection  will  continually 
tend  to  i)i'eserve  those  individuals  which  are  born  with 
constitutions  best  adapted  to  their  native  countries.  In 
treatises  on  many  kinds  of  cultivated  plants,  certain  vari- 
eties are  said  to  withstand  certain  climates  better  than 
others  :  this  is  very  strikingly  shown  in  works  on  fruit 
trees  published  in  the  United  States,  in  which  certain 
varieties  are  habitually  recommended  for  the  northern, 
and  others  for  the  southern  States  ;  and  as  most  of  these 
varieties  are  of  recent  origin,  they  cannot  owe  their  con- 
stitutional difterences  to  habit.  The  case  of  the  Jerusalem 
artichoke,  which  is  never  propagated  by  seed,  and  of 
which  consequently  new  varieties  have  not  been  pro- 
duced, has  even  been  advanced — for  it  is  now  as  tender 
as  ever  it  was — as  proving  that  acclimatisation  cannot  be 
eftected !  The  case,  also,  of  the  kidney-bean  has  been 
often  cited  for  a  similar  purpose,  and  with  much  greater 
weight ;  but  until  some  one  will  sow,  during  a  score  of 


130  LAWS   OF   VARIATION.  [Chap,  "V. 

generations,  his  kidney-beans  so  early  that  a  very  large 
proportion  are  destroyed  by  frost,  and  then  collect  seed 
from  the  few  survivors,  with  care  to  prevent  accidental 
crosses,  and  then  again  get  seed  from  these  seedlings,  with 
the  same  precautions,  the  experiment  cannot  be  said  to 
have  been  even  tried.  'Nov  let  it  be  supposed  that  no 
differences  in  the  constitution  of  seedling  kidney-beans 
ever  appear,  for  an  account  has  been  published  how  much 
more  hardy  some  seedlings  appeared  to  be  than  others. 

On  the  whole,  I  think  we  may  conclude  that  habit, 
use,  and  disuse,  have,  in  some  cases,  played  a  considerable 
part  in  the  modification  of  the  constitution,  and  of  the 
structure  of  various  organs  ;  but  that  the  effects  of  use 
and  disuse  have  often  been  largely  combined  with,  and 
sometimes  overmastered  by,  the  natural  selection  of  innate 
differences. 

Correlation  of  Groivth. — I  mean  by  this  expression 
that  the  whole  organisation  is  so  tied  together  during  its 
growth  and  development,  that  when  slight  variations  in 
any  one  part  occur,  and  are  accumulated  through  natural 
selection,  other  parts  become  modified.  This  is  a  very 
important  subject,  most  imperfectly  understood.  Tlie 
most  obvious  case  is,  that  modifications  accumulated 
solely  for  the  good  of  the  young  or  larva,  will,  it  may 
safely  be  concluded,  affect  the  structure  of  the  adult ;  in 
the  same  manner  as  any  malconformation  afi'ecting  the 
early  embryo,  seriously  affects  the  whole  organisation  of 
the  adult.  The  several  parts  of  the  body  which  are  homo- 
logous, and  which,  at  an  early  embryonic  period,  are 
alike,  seem  liable  to  vary  in  an  allied  manner :  we  see 
this  in  the  right  and  left  sides  of  the  body  varying  in  the 
same  manner  ;  in  the  front  and  hind  legs,  and  even  in 
the  jaws  and  limbs,  varying  together,  for  the  lower  jaw 
is  believed  to  be  homologous  with  the  limbs.  These  ten- 
dencies, I  do  not  doubt,  may  be  mastered  more  or  less 
completely  by  natural  selection  :  thus  a  family  of  stags 
once  existed  with  an  antler  only  on  one  side  ;  and  if  this 
had  been  of  any  great  use  to  the  breed  it  might  probably 
have  been  rendered  pennanent  by  natural  selection. 

Homologous  parts,  as  has  been  remarked  by  some 


Chap,  v.]  C0RRELA.TION    OF    GHOWTII.  |3( 

authors,  tend  to  cohere ;  this  is  often  seen  in  monstrous 
plants  ;  and  nothing  is  more  common  than  the  nnion  of 
homologous  parts  in  normal  structures,  as  the  union  of 
the  petals  of  the  corolla  into  a  tube.  Hard  parts  seem  to 
aftect  the  form  of  adjoining  soft  parts  ;  it  is  believed  by 
some  authors  that  the  diversity  in  the  shape  of  the  pelvis 
in  birds  causes  the  remarkable  diversity  in  the  shape  of 
their  kidneys.  Others  believe  that  the  shape  of  the  pel- 
vis in  the  human  mother  influences  by  pressure  the  shape 
of  the  head  of  the  child.  In  snakes,  according  to  Schle- 
gel,  the  shape  of  the  body  and  the  manner  of  swallowing 
determine  the  position  of  several  of  the  most  important 
viscera. 

The  nature  of  the  bond  of  correlation  is  very  frequently 
quite  obscure.  M.  Is.  Geoffroy  St.  Hilaire  has  forcibly 
remarked,  that  certain  malconformations  very  frequently, 
and  that  others  rarely  coexist,  without  our  being  able  to 
assign  any  reason.  What  can  be  more  singular  than  the 
relation  between  blue  eyes  and  deafness  in  cats,  and  the 
tortoise-shell  colour  with  the  female  sex  ;  the  feathered 
feet  and  skin  between  the  outer  toes  in  pigeons,  and  the 
presence  of  more  or  less  down  on  the  young  birds  when 
nrst  hatched,  with  the  future  colour  of  their  plumage  ;  or, 
again,  the  relation  between  the  hair  and  teeth  in  the 
naked  Turkish  dog,  though  here  proba^  ^y  homology 
comes  into  play  ?  With  respect  to  this  latte^-  case  of  cor- 
relation, I  think  it  can  hardly  be  accidental,  that  if  we 
pick  out  the  two  orders  of  mammalia  which  are  most  ab- 
normal in  their  dermal  covering,  viz.  Cetacea  (whales) 
and  Edentata  (armadilloes,  scaly  ant-eaters,  &c.),  that  these 
are  likewise  the  most  abnormal  in  their  teeth. 

I  know  of  no  case  better  adapted  to  show  the  impor- 
tance of  the  laws  of  correlation  in  modifying  important 
structures,  independently  of  utility  and,  therefore,  of  nat- 
ural selection,  than  that  of  the  difference  between  the 
outer  and  inner  flowers  in  some  Compositous  and  Umbel- 
liferous plants.  Every  one  knows  the  difference  in  the 
ray  and  central  florets  of,  for  instance,  the  daisy,  and  this 
difference  is  often  accompanied  with  the  abortion  of  parts 
of  the  flower.  But,  in  some  Compositous  plants,  the  seeds 
also  dift'er  in  shape  and  sculpture  ;  and  even  the  ovary 


J32  LAWS    OF    VAUIATION.  [Chap.  "V, 

itself,  witli  its  accessory  parts,  differs,  as  has  been  de- 
scribed by  Cassini.  These  diff'erences  have  been  attrib- 
uted by  some  authors  to  i^ressnre,  and  the  shape  of  the 
seeds  in  the  ray-florets  in  some  Compositse  countenances 
this  idea  ;  bnt,  in  the  case  of  the  corolla  of  the  TJmbel- 
liferse,  it  is  by  no  means,  as  Dr.  Hooker  informs  me,  in 
species  with  the  densest  heads  that  the  inner  and  outer 
flowers  most  frequently  differ.  It  might  have  been  thought 
that  the  development  of  the  ray-petals  by  drawing  nour- 
ishment from  certain  other  parts  of  the  flower  had  caused 
their  abortion  ;  but  in  some  Compositse  there  is  a  differ- 
ence in  the  seeds  of  the  outer  and  inner  florets  without 
any  difference  in  the  corolla.  Possibly,  these  several  dif- 
ferences may  be  connected  with  some  difference  in  the 
flow  of  nutriment  towards  the  central  and  external  flowers : 
we  know,  at  least,  that  in  irregular  flowers,  those  nearest 
to  the  axis  are  oftenest  subject  to  peloria,  and  become 
regular.  I  may  add,  as  an  instance  of  this,  and  of  a  strik- 
ing case  of  correlation,  that  I  have  recently  observed  in 
some  garden  pelargoniums,  that  the  central  flower  of  the 
truss  often  loses  the  patches  of  darker  colour  in  the  two 
upper  petals  ;  and  that  when  this  occurs,  the  adherent 
nectary  is  quite  aborted  ;  when  the  colour  is  absent  from 
only  one  of  the  two  uj^per  petals,  the  nectary  is  only 
much  shortened. 

"With  respect  to  the  difference  in  the  corolla  of  the 
central  and  exterior  flowers  of  a  head  or  umbel,  I  do  not 
feel  at  all  sure  that  C.  C.  Sprengel's  idea  that  the  ray- 
florets  serve  to  attract  insects,  whose  agency  is  highly  ad- 
vantageous in  the  fertilisation  of  plants  of  these  two 
ordei'.^,  is  so  far-fetched,  as  it  may  at  first  appear :  and  if 
it  be  advantageous,  natural  selection  may  have  come  into 
play.  -But  in  regard  to  the  differences  both  in  the  internal 
and  external  structure  of  the  seeds,  which  are  not  always 
correlated  with  any  differences  in  the  flowers,  it  seems  im- 
possible that  they  can  be  in  any  way  advantageous  to  the 
plant :  yet  in  the  Umbelliferse  these  differences  are  of  such 
apparent  importance — the  seeds  being  in  some  cases,  ac- 
cording to  Tausch,  orthospermous  in  the  exterior  flowers, 
and  coelospermous  in  the  central  flowers, — that  the  elder 
De  Candolle  founded  his  main  divisions  of  the  order  on 


CsAr.  v.]  CORRELATION    OF    GROWTH.  ;{;];> 

analogous  differences.  Hence  we  see  that  modifications 
of  structure,  viewed  by  systematists  as  of  high  value,  may 
be  wholly  due  to  unknown  laws  of  correlated  growth,  and 
without  being,  as  far  as  we  can  see,  of  the  slightest  service 
to  the  species. 

We  may  often  falsely  attribute  to  correlation  of  growth, 
structures  which  are  common  to  whole  groups  of  species, 
and  which  in  truth  are  simply  due  to  inheritance  ;  for  an 
ancient  progenitor  may  have  acquired  through  natural 
selection  some  one  modification  in  structure,  and,  after 
thousands  of  generations,  some  other  and  independent 
modification ;  and  these  two  modifications,  having  been 
transmitted  to  a  whole  group  of  descendants  with  diverse 
habits,  would  naturally  be  thought  to  be  correlated  in 
some  necessary  manner.  So,  again,  I  do  not  doubt  that 
some  apparent  correlations,  occurring  throughout  whole 
orders,  are  entirely  due  to  the  manner  alone  in  which  nat- 
ural selection  can  act.  For  instance,  Alph.  De  Candolle 
has  remarked  that  winged  seeds  are  never  found  in  fruits 
which  do  not  open  :  I  should  explain  the  rule  by  the  fact 
that  seeds  could  not  gradually  become  winged  through 
natural  selection,  except  in  fruits  which  opened ;  so  that 
the  individual  plants  producing  seeds  which  were  a  little 
better  fitted  to  be  wafted  further,  miffht  2:et  an  advantag^e 
over  those  producing  seeds  less  fitted  for  dispersal ;  and 
this  process  could  not  possibly  go  on  in  fruit  which  did 
not  open. 

The  elder  Geofi'roy  and  Goethe  propounded,  at  about 
the  same  period,  their  law  of  compensation,  or  balance- 
ment  of  growth ;  or,  as  Goethe  expressed  it,  "  in  order  to 
spend  on  one  side,  nature  is  forced  to  economise  on  the 
other  side."  I  think  this  holds  true  to  a  certain  extent 
with  our  domestic  productions  :  if  nourishment  flows  to 
one  part  or  organ  in  excess,  it  rarely  flows,  at  least  in 
excess,  to  another  part ;  thus  it  is  difiicult  to  get  a  cow  to 
give  much  milk  and  to  fatten  readily.  The  same  variety 
of  the  cabbage  do  not  yield  abundant  and  nutritious  foli- 
age and  a  copious  supply  of  oil-bearing  seeds.  "When 
the  seeds  in  our  fruits  become  atrophied,  the  fruit  itself 
gains  largely  in  size  and  cpality.  In  our  poultry,  a  large 
tuft  of  feathers  on  the  head  is  generally  accompanied  by 


][34:  LAWS  OF  VARIATION.  [Chap.  V 

a  diminished  comb,  and  a  large  beard  by  diminished  wat- 
tles. With  species  in  a  state  of  nature  it  can  hardly  be 
maintained  that  the  law  is  of  nniversal  application  ;  but 
many  good  observers,  more  especially  botanists,  believe  in 
its  truth.  I  will  not,  however,  here  give  any  instances, 
for  I  see  hardly  any  way  of  distinguishing  between  the 
effects,  on  the  one  hand,  of  a  part  being  largely  developed 
through  natural  selection  and  another  and  adjoining  part 
being  reduced  by  this  same  process  or  by  disuse,  and,  on 
the  other  hand,  the  actual  withdrawal  of  nutriment  from 
one  part  owing  to  the  excess  of  growth  in  another  and 
adjoining  part. 

I  suspect,  also,  that  some  of  the  cases  of  compensation 
which  have  been  advanced,  and  likewise  some  other  facts, 
may  be  merged  under  a  more  general  principle,  namely, 
that  natural  selection  is  continually  trying  to  economise 
in  every  part  of  the  organisation.  If  under  changed  con- 
ditions of  life  a  structure  before  useful  becomes  less  useful, 
any  diminution,  however  slight  in  its  development,  will 
be  seized  on  by  natural  selection,  for  it  will  profit  the  in- 
dividual not  to  have  its  nutriment  wasted  in  building  up 
an  useless  structure.  I  can  thus  only  understand  a  fact 
with  which  I  was  much  struck  when  examining  cirrij^edes, 
and  of  which  many  other  instances  could  be  given: 
namely,  that  when  a  cirripede  is  parasitic  within  another 
and  is  thus  protected,  it  loses  more  or  less  completely  its 
own  shell  or  carapace.  This  is  the  case  with  the  male 
Ibla,  and  in  a  truly  extraordinary  manner  with  the  Pro- 
teolepas  :  for  the  carripace  in  all  other  cirripedes  consist 
of  the  three  highly-important  anterior  segments  of  the 
head-  enormously  developed,  and  furnished  with  great 
nerves  and  muscles  ;  but  in  the  parasitic  and  protected 
Proteolepas,  the  whole  anterior  part  of  the  head  is  reduced 
to  the  merest  rudiment  attached  to  the  bases  of  the  pre- 
hensile antennae.  ]N'ow  the  saving  of  a  large  and  complex 
structure,  when  rendered  superfluous  by  the  parasitic  hab- 
it.s  of  the  Proteolepas,  though  effected  by  slow  steps,  would 
t/e  a  decided  advantage  to  each  successive  individual  of 
the  species  ;  for  in  the  struggle  for  life  to  which  every  ani- 
mal is  exposed,  each  individual  Proteolepas  would  have  a 
better  chance  of  supporting  itself,  by  less  nutriment  being- 
wasted  in  developing  a  structure  now  become  useless. 


Chap.  V.]  CORRELATIOJT   O?   GROWTH.  ^^35 

ThuSj  as  I  believe,  natural  selection  will  always  succeed 
in  the  long  run  in  reducing  and  saving  every  part  of  the 
organisation,  as  soon  as  it  is  rendered  superfluous,  without 
by  any  means  causing  some  otJier  part  to  be  largely  de- 
veloped in  a  corresponding  degree.  And,  conversely, 
that  natural  selection  may  perfectly  well  succeed  in 
largely  de^'eloping  any  organ,  without  requiring  as  a 
necessary. comj^ensation  the  reduction  of  some  adjoining- 
part. 

It  seems  to  be  a  rule,  as  remarked  by  Is.  Geoffroy  St. 
Hilaire,  both  in  varieties  and  in  species,  that  when  any 
part  or  organ  is  repeated  many  times  in  the  structure  of 
the  same  individual  (as  the  vertebrge  in  snakes,  and  the 
stamens  in  polyandrous  flowers)  the  number  is  variable  ; 
whereas  the  number  of  the  same  part  or  organ,  when  it 
occurs  in  lesser  numbers,  is  constant.  The  same  author 
and  some  botanists  have  further  remarked  that  multiple 
parts  are  also  very  liable  to  variation  in  structure.  Inas- 
much as  this  "  vegetative  repetition,"  to  use  Prof.  Owen's 
expression,  seems  to  be  a  sign  of  low  organisation  ;  the 
foregoing  remark  seems  connected  with  the  very  general 
opinion  of  naturalists,  that  beings  low  in  the  scale  of 
nature  are  more  variable  than  those  which  are  higher.  I 
presume  that  lowiiess  in  this  case  means  that  the  several 
parts  of  the  organisation  have  been  but  little  specialised 
for  particular  functions ;  and  as  long  as  the  same  part  has 
to  perform  diversified  work,  we  can  perhaps  see  why  it 
should  remain  variable,  that  is,  why  natural  selection 
should  have  preserved  or  rejected  each  little  deviation  of 
form  less  carefully  than  when  the  part  has  to  serve  for 
one  special  purpose  alone.  In  the  same  way  that  a  knife 
which  has  to  cut  all  sorts  of  things  may  be  of  almost  any 
shape  ;  whilst  a  tool  for  some  particular  object  had  better 
be  of  some  particular  shape.  JSTatural  selection,  it  should 
never  be  forgotten,  can  act  on  each  part  of  each  being, 
solely  throug-h  and  for  its  advantage. 

Eudimentary  parts,  it  has  been  stated  by  some  authors, 
and  I  believe  with  truth,  are  apt  to  be  highly  variable. 
We  shall  have  to  recur  to  the  general  subject  of  rudimen- 
tary and  aborted  organs ;  and  I  will  here  only  add  that 


I^Q  LAWS   OF   VARIATION.  [Chap.  V. 

their  variability  seems  to  be  owing  to  tbeir  uselessness, 
and  therefore  to  natural  selection  having  no  power  to 
check  deviations  in  their  structure.  Thus  rudimentary 
parts  are  left  to  the  free  play  of  the  various  laws  of 
growth,  to  the  effects  of  long-continued  disuse,  and  to  the 
tendency  to  reversion. 

A  jpart  developed  in  any  species  in  an  extraordinary 
degree  or  manner^  in  co7nparison  vnth  the  same  part  in 
allied  species^  tends  to  he  highly  varial>le. — Several  years 
ago  I  was  much  struck  with  a  remark,  nearly  to  the  above 
effect,  published  by  Mr.  Waterhouse.  I  infer  also  from 
an  observation  made  by  Professor  Owen,  with  respect  to 
the  length  of  the  arms  of  tiie  ourang-outang,  that  he  has 
come  to  a  nearly  similar  conclusion.  It  is  hopeless  to 
attempt  to  convince  any  one  of  the  truth  of  this  proposi- 
tion without  giving  the  long  array  of  facts  which  I  have 
collected,  and  which  cannot  possibly  be  here  introduced. 
I  can  only  state  my  conviction  that  it  is  a  rule  of  high 
generality.  I  am  aware  of  several  causes  of  error,  but  I 
hope  that  I  have  made  due  allowance  for  them.  It  should 
be  understood  that  the  rule  by  no  means  applies  to  any 
part,  however  unusually  developed,  unless  it  be  unusually 
developed  in  comparison,  with  the  same  part  in  closely 
allied  species.  Thus,  the  bat's  wing  is  a  most  abnormal 
structure  in  the  class  mammalia ;  but  the  rule  would 
not  here  apply,  because  there  is  a  whole  group  of  bats 
having  wings  ;  it  would  apply  only  if  some  one  species 
of  bat  had  its  wings  developed  in  some  remarkable  man- 
ner in  comparison  with  the  other  sj^ecies  of  the  same 
genus.  The  rule  applies  very  strongly  in  the  case  of 
secondary  sexual  characters,  when  displayed  in  any  un- 
usual manner.  The  term,  secondary  sexual  characters, 
used  by  Ilimter,  applies  to  characters  which  are  attached 
to  one  sex,  but  are  not  directly  connected  with  the  act  of 
rej^roduction.  The  rule  applies  to  males  and  females  ; 
but  as  females  more  rarely  offer  remarkable  secondary 
sexual  characters,  it  aj^plies  more  rarely  to  them.  The 
rule  being  so  plainly  applicable  in  the  case  of  secondary 
Bexnal  characters,  may  be  due  to  the  great  variability  of 


Chap.  V.]  LAWS    OF   VARIATION.  jj^g^ 

these  cliaracters,  whether  or  not  displayed  in  any  iimisnal 
manner — of  which  fact  I  think  there  can  be  little  doubt. 
But  that  our  rule  is  not  confined  to  secondary  sexual  char- 
acters is  clearly  shown  in  the  case  of  hermaphrodite  cirri- 
pedes  ;  and  I  may  here  add,  that  I  particularly  attended 
to  Mr.  AVaterhouse's  remark,  whilst  investigating  this 
Order,  and  I  am  fully  convinced  that  the  rule  almost 
invariably  holds  good  with  cirripedes.  I  shall,  in  my 
future  work,  give  a  list  of  the  more  remarkable  cases  ;  I 
will  here  only  briefly  give  one,  as  it  illustrates  the  rule  in 
its  largest  application.  The  opercular  valves  of  sessile 
cirripedes  (rock  barnacles)  are,  in  every  sense  of  the 
word,  very  important  structures,  and  they  differ  extreme- 
ly little  even  in  different  genera  ;  but  in  the  several  spe- 
cies of  one  genus,  Pyrgoma,  these  valves  present  a  mar- 
vellous amount  of  diversification  :  the  homologous  valves 
in  the  different  species  being  sometimes  wholly  unlike  in 
shape  ;  and  the  amount  of  variation  in  the  individuals  of 
several  of  the  species  is  so  great,  that  it  is  no  exaggeration 
to  state  that  the  varieties  differ  more  from  each  other  in 
the  chai'acters  of  these  important  valves  than  do  other 
species  of  distinct  genera. 

As  birds  within  the  same  country  vary  in  a  remark- 
ably small  degree,  I  have  particularly  attended  to  them, 
and  the  rule  seems  to  me  certainly  to  hold  good  in  this 
class.  I  cannot  make  out  that  it  applies  to  plants,  and 
this  would  seriously  have  shaken  my  belief  in  its  truth, 
had  not  the  great  variability  in  plants  made  it  particularly 
difficult  to  comjDare  their  relative  degrees  of  variability. 

When  we  see  any  part  or  organ  developed  in  a  re- 
markable degree  or  manner  in  any  species,  the  fair  pre- 
sumption is  that  it  is  of  high  importance  to  that  species  ; 
nevertheless  the  part  in  this  case  is  eminently  liable  tc 
variation.  Why  should  this  be  so  ?  On  the  view  that 
each  species  has  been  independently  created,  with  all  its 
parts  as  we  now  see  them,  I  can  see  no  explanation.  But 
on  the  view  that  groups  of  sgecies  have  descended  from 
other  species,  and  have  been  modified  through  natural 
selection,  I  think  we  can  obtain  some  light.  In  our  do- 
mestic animals,  if  any  part,  or  the  whole  animal,  be  neg- 


[38  LAWS    OF    VARIATION.  [Uhap.  ^ 

lected  and  no  selection  be  applied,  that  part  (for  instance, 
tlie  comb  in  the  Dorking  fowl)  or  the  whole  breed  will 
cease  to  have  a  nearly  uniform  character.  The  breed  will 
then  be  said  to  have  degenerated.  Li  rudimentary  or- 
gans, and  in  those  which  have  been  but  little  specialised 
for  any  particular  purpose,  and  perhaps  in  polymorphic 
groups,  we  see  a  nearly  parallel  natural  case ;  for  in  such 
cases  natural  selection  either  has  not  or  cannot  come  into 
full  play,  and  thus  the  organisation  is  left  in  a  fluctuating 
condition.  But  what  here  more  especially  concerns  us  is, 
that  in  our  domestic  animals  those  points,  which  at  the 
present  time  are  undergoing  rapid  change  by  continued 
selection,  are  also  eminently  liable  to  variation.  Look  at 
the  breeds  of  the  pigeon  ;  see  what  a  prodigious  amount 
of  difference  tlicre  is  in  the  beak  of  the  different  tumblers, 
in  the  beak  and  wattle  of  the  different  carriers,  in  the 
carriage  and  tail  of  our  fantails,  &c.,  these  being  the 
points  now  mainly  attended  to  by  English  fanciers.  Even 
in  the  sub-breeds,  as  in  the  short-faced  tumbler,  it  is  no- 
toriously difficult  to  breed  them  nearly  to  perfection,  and 
frequently  individuals  are  born  which  depart  widely  from 
the  standard.  There  may  be  truly  said  to  be  a  constant 
struggle  going  on  between,  on  the  one  hand,  the  tendency 
to  reversion  to  a  less  modiiied  state,  as  well  as  an  innate 
tendency  to  further  variability  of  all  kinds,  and.  on  tlie 
other  hand,  the  power  of  steady  selection  to  keep  the 
breed  true.  In  the  long  run  selection  gains  the  day,  and 
we  do  not  expect  to  fail  so  far  as  to  breed  a  bird  as  coarse 
as  a  common  tumbler  from  a  good  short-faced  strain.  But 
as  long  as  selection  is  rapidly  going  on,  there  may  always 
be  expected  to  be  much  variability  in  the  structure  under- 
going modification.  It  further  deserves  notice  that  these 
variable  characters,  produced  by  man's  selection,  some- 
times become  attached,  from  causes  quite  unknown  to  us, 
more  to  one  sex  than  to  the  other,  generally  to  the  male 
sex,  as  with  the  wattle  of  carriers  and  the  enlarged  crop 
of  pouters. 

Now  let  us  turn  to  nature.  When  a  part  has  been  de- 
veloped in  an  extraordinary  manner  in  any  one  species, 
compared  with  the  other  species  of  the  same  genus,  we 


Chap.  V.]  LAWS   OF   VARIATION.  ^^g 

may  conclude  that  this  part  has  undergone  an  extraordi- 
nary amount  of  modification,  since  the  period  when  the 
species  branched  ofli"  from  the  common  progenitor  of  the 
genus.  This  period  will  seldom  be  remote  in  any  extreme 
degree,  as  species  very  rarely  endure  for  more  than  one 
geological  period.  An  extraordinary  amount  of  modifica- 
tion implies  an  unusually  large  and  long-continued  amount 
of  variability,  which  has  continually  been  accumulated  by 
natural  selection  for  the  benefit  of  the  species.  But  as 
the  variability  of  the  extraordinarily-developed  part  or 
organ  has  been  so  great  and  long-continued  within  a 
period  not  excessively  remote,  we  might,  as  a  general 
rule,  expect  still  to  find  more  variability  in  such  parts 
than  in  other  parts  of  the  organisation,  which  have  re- 
maiaied  for  a  much  longer  period  nearly  constant.  And 
this,  I  am  convinced,  is  the  case.  That  the  struggle  be- 
tween natural  selection  on  the  one  hand,  and  the  tendency 
to  reversion  and  variability  on  the  other  hand,  will  in  the 
course  of  time  cease ;  and  that  the  most  abnormally  de- 
veloped organs  may  be  made  constant,  I  can  see  no  reason 
to  doubt.  Hence  when  an  organ,  however  abnormal  it 
may  be,  has  been  transmitted  in  approximately  the  same 
condition  to  many  modified  descendants,  as  in  the  case  of 
the  wing  of  the  bat,  it  must  have  existed,  according  to  my 
theory,  for  an  immense  period  in  nearly  the  same  state ; 
and  thus  it  comes  to  be  no  more  variable  than  any  other 
structure.  It  is  only  in  those  cases  in  which  the  modifi- 
cation has  been  comparatively  recent  and  extraordinarily 
great  that  we  ought  to  find  the  generative  variability^  as 
it  may  be  called,  still  present  in  a  high  degree.  For  in 
this  case  the  variability  will  seldom  as  yet  have  been  fixed 
by  the  continued  selection  of  the  individuals  varying  in 
the  required  manner  and  degree,  and  by  the  continued 
rejection  of  those  tending  to  revert  to  a  former  and  less 
modified  condition. 

The  principle  included  in  these  remarks  may  be  ex- 
tended. It  is  notorious  that  specific  characters  are  more 
variable  than  generic.  To  explain  by  a  simple  example 
what  is  meant.  If  some  species  in  a  large  genus  of  plants 
had  blue  flowers  and  some  had  red,  the  colour  would  be 


^J^Q  LAWS   OF    VARIATION".  [Chap.  V. 

only  a  specific  character,  and  no  one  would  he  surprised 
at  one  of  the  blue  species  varying  into  red,  or  conversely  ; 
but  if  all  the  species  had  blue  flowers,  the  colour  would 
become  a  generic  character,  and  its  variation  would  be  a 
more  unusual  circumstance.  I  have  chosen  this  example 
^because  an  explanation  is  not  in  this  case  applicable, 
which  most  naturalists  would  advance,  namely,  that  spe- 
cific characters  are  more  variable  than  generic,  because 
they  are  taken  from  parts  of  less  physiological  importance 
than  those  commonly  used  for  classing  genera.  I  believe 
this  explanation  is  partly,  yet  only  indii-ectly,  true;  I 
shall,  however,  have  to  return  to  this  subject  in  our  chap- 
ter on  Classification.  It  would  be  almost  superfluous  to 
adduce  evidence  in  support  of  the  above  statement,  that 
specific  characters  are  more  variable  than  generic  ;  but  I 
have  repeatedly  noticed  in  works  on  natural  history,  that 
when  an  author  lias  remarked  with  surprise  that  some 
important  organ  or  part,  which  is  generally  very  constant 
throughout  large  groups  of  species,  has  differed  consider- 
ably in  closely-allied  species,  that  it  has,  also,  been  vari- 
able in  the  individuals  of  some  of  the  species.  And  this 
fact  shows  that  a  character,  which  is  generally  of  generic 
value,  when  it  sinks  in  value  and  becomes  only  of  specific 
value,  often  becomes  variable,  though  its  physiological 
importance  may  remain  the  same.  Something  of  the 
same  kind  applies  to  monstrosities  :  at  least  Is.  Geofiroy 
St.  Hilaire  seems  to  entertain  no  doubt,  that  the  more  an 
organ  normally  diff'ers  in  the  difi'erent  species  of  the  same 
group,  the  more  subject  it  is  to  individual  anomalies. 

On  the  ordinary  view  of  each  species  having  been  in- 
dependently created,  why  should  that  part  of  the  struc- 
ture, which  difters  from  the  same  part  in  other  independ- 
ently-created species  of  the  same  genus,  be  more  variable 
than  those  parts  which  are  closely  alike  in  the  several 
species  ?  I  do  not  see  that  any  explanation  can  be  given. 
But  on  the  view  of  species  being  only  strongly  marked 
and  fixed  vai-icties,  we  might  surely  expect  to  find  them 
still  often  continuing  to  vary  in  those  parts  of  their  struc- 
ture which  have  varied  within  a  moderately  recent  period, 
and  which  have  thus  come  to  diff*er.     Or  to  state  the  case 


Chap.  V.]  LAWS    OS''  VARIATION.  ^^^l 

ill  another  manner : — tlie  points  in  which,  all  tne  species 
of  a  genus  resemble  each  other,  and  in  which  they  differ 
from  the  species  of  some  other  genus,  are  called  generic 
characters  ;  and  these  characters  in  common  I  attribute 
to  inheritance  from  a  common  progenitor,  for  it  can  rarely 
have  hapi^ened  that  natural  selection  will  have  modified 
several  sjDecies,  fitted  to  more  or  less  widely-diftercnt 
habits,  in  exactly  the  same  manner :  and  as  tliese  so-called 
generic  characters  have  been  inherited  from  a  remote 
period,  since  that  period  when  the  species  first  branched 
off  from  their  common  progenitor,  and  subsequently  have 
not  varied  or  come  to  differ  in  any  degree,  or  only  in  a 
slight  degree,  it  is  not  probable  that  they  should  vary  at 
the  present  day.  On  the  other  hand,  the  points  in  which 
species  differ  from  other  species  of  the  same  genus,  are 
called  specific  characters  ;  and  as  these  specific  characters 
have  varied  and  come  to  differ  within  the  period  of  the 
branching  off  of  the  species  from  a  common  progenitor,  it 
is  probable  that  they  should  still  often  be  in  some  degree 
variable, — at  least  more  variable  than  those  parts  of  the 
organisation  which  have  for  a  very  long  period  remained 
constant. 

In  connexion  with  the  present  subject,  I  will  make 
only  two  other  remarks.  I  think  it  will  be  admitted, 
without  my  entering  on  details,  that  secondary  sexual 
characters  are  very  variable ;  I  think  it  also  will  be  ad- 
mitted that  sj^ecies  of  the  same  group  differ  from  each 
other  more  widely  in  their  secondary  sexual  characters, 
than  in  other  parts  of  their  organisation ;  compare,  for 
instance,  the  amount  of  difierence  between  the  males  of 
gallinaceous  birds,  in  which  secondary  sexual  characters 
are  strongly  displayed,  with  the  amount  of  difference  be- 
tween their  females  ;  and  the  truth  of  this  proposition 
will  be  granted.  The  cause  of  the  original  variability  of 
secondary  sexual  characters  is  not  manifest ;  but  we  can 
see  why  these  characters  should  not  have  been  rendered 
a5  constant  and  uniform  as  other  parts  of  the  organisation ; 
for  secondary  sexual  characters  have  been  accumulated 
by  sexual  selection,  which  is  less  rigid  in  its  action  than 
ordinary  selection,  as  it  does  not  entail  death,  but  only 


j^2  LAWS   05'   VALUATION.  [Cha?.  ^. 

gives  fewer  offspring  to  the  less  favoured  males.  What- 
ever the  cause  may  be  of  the  variability  of  secondary  sex- 
ual characters,  as  they  are  highly  variable,  sexual  selection 
will  have  had  a  wide  scope  for  action,  and  may  thns 
readily  have  succeeded  in  giving  to  the  species  of  the 
same  group  a  greater  amount  of  difference  in  their  sexual 
characters,  than  in  other  parts  of  their  structure. 

It  is  a  remarkable  fact,  that  the  secondary  sexual  dif- 
ferences between  the  two  sexes  of  the  same  species  are 
generally  displayed  in  the  very  same  parts  of  the  organi- 
sation in  which  the  different  species  of  the  same  genus 
differ  from  each  other.  Of  this  fact  I  will  give  in  illus- 
tration two  instances,  the  first  which  happen  to  stand  on 
my  list ;  and  as  the  differences  in  these  cases  are  of  a  very 
unusual  nature,  the  relation  can  hardly  be  accidentaL 
The  same  number  of  joints  in  the  tarsi  is  a  character  gen- 
erally common  to  very  large  groups  of  beetles,  but  in  the 
Engidse,  as  "Westwood  has  remarked,  the  number  varies 
greatly  ;  and  the  number  likewise  differs  in  the  two  sexes 
of  the  same  species  :  again  in  a  fossorial  hymenoptera,  the 
manner  of  neuration  of  the  wings  is  a  character  of  the 
highest  importance,  because  common  to  large  groups  ;  but 
in  certain  genera  the  neuration  differs  in  the  different 
species,  and  likewise  in  the  two  sexes  of  the  same  species. 
This  relation  has  a  clear  meaning  on  my  view  of  the  sub- 
ject :  I  look  at  all  the  species  of  the  same  genus  as  having 
as  certainly  descended  from  the  same  progenitor,  as  have 
the  two  sexes  of  any  one  of  the  species.  Consequently, 
whatever  part  of  the  structure  of  the  common  progenitor, 
or  of  its  early  descendants,  became  variable  ;  variations 
of  this  part  would,  it  is  highly  probable,  be  taken  advan- 
tage of  by  natural  and  sexual  selection,  in  order  to  fit  the 
several  species  to  their  several  places  in  the  economy  of 
nature,  and  likewise  to  fit  the  two  sexes  of  the  same  spe- 
cies to  each  otJier,  or  to  fit  the  males  and  females  to  dif- 
ferent habits  of  life,  or  the  males  to  struggle  with  other 
males  for  tlie  possession  of  the  females. 

Finally,  then,  I  conclude  that  the  greater  variability  of 
specific  characters,  or  those  which  distinguish  species  from 
species,  than  of  generic  characters,  or  those  which  the 


Chap,  v.]  laws   OF   VARIATION.  ^^q 

species  possess  in  common ; — that  the  frequent  extreme 
variability  of  any  part  which  is  developed  in  a  species  in 
an  extraordinary  manner  in  comparison  with  the  same 
part  in  its  congeners  ;  and  the  not  great  degree  of  varia- 
bility in  a  part,  however  extraordinarily  it  may  be  devel- 
oped, if  it  be  common  to  a  whole  gi-onp  of  species  ; — that 
the  great  variability  of  secondary  sexual  characters,  and 
the  great  amount  of  diflerence  in  these  same  characters 
between  closely  allied  species ; — that  secondary  sexual  and 
ordinarily  specific  difi'erences  are  generally  displayed  in 
the  same  parts  of  the  organisation, — are  all  principles 
closely  connected  together.  All  being  mainly  due  to  the 
species  of  the  same  group  having  descended  Irom  a  com- 
mon progenitor,  from  whom  they  have  inherited  much  in 
common, —  to  parts  which  have  recently  and  largely 
varied  being  more  likely  still  to  go  on  varying  tlian  parts 
which  have  long  been  inherited  and  have  not  varied, — to 
natural  selection  having  more  or  less  completely,  accord- 
ing to  the  lapse  of  time,  overmastered  the  tendency  to  re- 
version and  to  further  variability, — to  sexual  selection 
being  less  rigid  than  ordinary  selection, — and  to  variations 
in  the  same  parts  having  been  accumulated  by  natural 
and  sexual  selection,  and  thus  adapted  for  secondary 
sexual,  and  for  ordinary  specific  purposes. 

Distinct  species  present  analogous  variations  /  and  a 
variety  of  one  species  often  assumes  some  of  the  characters 
of  an  allied  species,  or  reverts  to  some  of  the  characters  of 
an  early  progenitor. — These  propositions  will  be  most 
readily  understood  by  looking  to  our  domestic  races. 
The  most  distinct  breeds  of  pigeons,  in  countries  most 
widely  apart,  present  sub-varieties  with  reversed  feathers 
on  the  head  and  feathers  on  the  feet, — characters  not  pos- 
sessed by  the  aboriginal  rock-pigeon ;  these  then  are  an- 
alogous variations  in  two  or  more  distinct  races.  The  fre- 
quent presence  of  fourteen  or  even  sixteen  tailfeathers  in 
the  pouter,  may  be  considered  as  a  variation  representing 
the  normal  structure  of  another  race,  the  fantail.  I  pre- 
sume that  no  one  will  doubt  that  all  such  analogous  varia- 
tions are  due  to  the  several  races  of  the  pigeon  having 


1^j_  LAWS   OF   VARIATIO^r.  [Chap.  V. 

inherited  from  a  common  parent  the  same  constitution  and 
tendency  to  variation,  when  acted  on  by  similar  miknown 
influences.  In  the  vegetable  kingdom  we  have  a  case  of 
analogous  variation,  in  the  enlarged  stems,  or  roots  as  com- 
monly called,  of  the  Swedish  turnip  and  Ruta  baga,  plants 
which  several  botanists  rank  as  varieties  produced  by  cul- 
tivation from  a  common  parent :  if  this  be  not  so,  the  case 
will  then  be  one  of  analogous  variation  in  two  so-called 
distinct  species;  and  to  these  a  third  may  be  added, 
namely,  the  commn  turnip.  According  to  the  ordinary 
view  of  each  species  having  been  independently  created, 
we  should  have  to  attribute  this  similarity  in  the  enlarged 
stems  of  these  three  plants,  not  to  the  vera  causa  of  com- 
munity of  descent,  and  a  consequent  tendency  to  vary  in 
a  like  manner,  but  to  three  separate  yet  closely  related 
acts  of  creation. 

"With  pigeons,  however,  we  have  another  case,  namely, 
the  occasional  appearance  in  all  the  breeds,  of  slaty-blue 
birds  with  two  black  bars  on  the  wings,  a  white  rump,  a 
bar  at  the  end  of  the  tail,  with  the  other  feathers  external^ 
ly  edged  near  their  bases  with  white.  As  all  these  re- 
marks are  characteristic  of  the  parent  rock-pigeon,  I  pre- 
sume that  no  one  will  doubt  that  this  is  a  case  of  rever- 
sion, and  not  of  a  new  yet  analogous  variation  aj^pearing 
in  the  several  breeds.  We  may  I  think  confidently  come 
to  this  conclusion,  because,  as  we  have  seen,  these 
coloured  marks  are  eminently  liable  to  appear  in  the 
crossed  oflfspring  of  two  distinct  and  differently  coloured 
breeds  ;  and  in  this  case  there  is  nothing  in  the  external 
conditions  of  life  to  cause  the  reappearance  of  the  slaty- 
blue,  with  the  several  marks,  beyond  the  influence  of  the 
mere  act  of  crossing  on  the  laws  of  inheritance. 

No  doubt  it  is  a  very  surprising  fact  that  characters 
should  reappear  after  having  been  lost  for  many,  perhaps 
for  hundreds  of  generations.  But  when  a  breed  has  been 
crossed  only  once  by  some  other  breed,  the  offspring  oc- 
casionally show  a  tendency  to  revert  in  character  to  the 
foreign  breed  for  many  generations — some  say,  for  a  dozen 
or  even  a  score  of  generations.  After  twelve  generations, 
the  proportion  of  blood,  to  use  a  common  expression,  of 


Chap.  V.l  LAWS    OF   VARIATION.  ^^^ 

any  one  ancestor,  is  only  1  in  2048  ;  and  yet,  as  we  see,  it 
is  generally  believed  that  a  tendency  to  reversion  is  re- 
tained by  this  very  small  proportion  of  foreign  blood.  In 
a  breed  which  has  not  been  crossed,  but  in  which  both 
parents  have  lost  some  character  which  their  progenitor 
possessed,  the  tendency,  whether  strong  or  weak,  to  repro- 
duce the  lost  character  might  be,  as  was  formerly  remark- 
ed, for  all  that  we  can  see  to  the  contrary,  transmitted  for 
almost  any  number  of  generations.  When  a  character 
which  has  been  lost  in  a  breed,  reappears  after  a  great 
number  of  generations,  the  most  probable  hypothesis  is, 
not  that  the  offspring  suddenly  takes  after  an  ancestor 
some  hundred  generations  distant,  but  that  in  each  succes- 
sive generation  there  has  been  a  tendency  to  reproduce 
the  character  in  question,  which  at  last,  under  unknown 
favourable  conditions,  gains  an  ascendancy.  For  instance, 
it  is  probable  that  in  each  generation  of  the  barb-pigeon, 
which  produces  most  rarely  a  blue  and  black-barred  bird, 
there  has  been  a  tendency  in  each  generation  in  the  plu- 
mage to  assume  this  colour.  This  view  is  hypothetical, 
but  could  be  supported  by  some  facts  ;  and  I  can  see  no 
more  abstract  improbability  in  a  tendency  to  produce  any 
character  being  inherited  for  an  endless  number  of  gener- 
ations, than  in  quite  useless  or  rudimentary  organs  being,  as 
we  all  know  them  to  be,  thus  inherited.  Indeed,  we  may 
sometimes  observe  a  mere  tendency  to  produce  a  rudi- 
ment inherited :  for  instance,  in  the  common  snap-dragon 
(Antirrhinum)  a  rudiment  of  a  fifth  stamen  so  often  ap- 
pears, that  this  plant  must  have  an  inherited  tendency  to 
produce  it. 

As  all  the  species  of  the  same  genus  are  supposed,  on 
my  theory,  to  have  descended  from  a  common  parent,  it 
might  be  expected  that  they  would  occasionally  vary  in 
an  analogous  manner ;  so  that  a  variety  of  one  species 
would  resemble  in  some  of  its  characters  another  species  ; 
this  other  species  being  on  my  view  only  a  well-marked 
and  permanent  variety.  But  characters  thus  gained 
would  probably  be  of  an  unimportant  nature,  for  the 
presence  of  all  important  characters  will  be  governed  by 
natural  selection,  in  accordance  with  the  diverse  habits  of 


j^^g  LAWS   OF  VARIATION.  [Chap.  V. 

the  species,  and  will  not  be  left  to  the  mutual  actions  of 
the  condition  of  life  and  of  a  similar  inherited  constitu- 
tion. It  might  further  be  expected  that  the  species  of  the 
same  genus  would  occasionally  exhibit  reversions  to  lost 
ancestral  characters.  As,  however,  we  never  know  the 
exact  character  of  the  common  ancestor  of  a  group,  we 
could  not  distinguish  these  two  cases :  if,  for  instance,  we 
did  not  know  that  the  rock-pigeon  was  not  feather-footed 
or  turn-crowned,  we  could  not  have  told,  whether  these 
characters  in  our  domestic  breeds  were  reversions  or  only 
analogous  variations;  but  we  might  have  inferred  that  the 
blueness  was  a  case  of  reversion,  from  the  number  of  the 
markings,  which  are  correlated  with  the  blue  tint,  and 
which  it  does  not  appear  probable  would  all  appear  to- 
gether from  simple  variation.  More  especially  we  might 
have  inferred  this,  from  the  blue  colour  and  marks  often 
appearing  when  distinct  breeds  of  diverse  colours  are 
crossed.  Hence,  though  under  nature  it  must  generally 
be  left  doubtful,  what  cases  are  reversions  to  an  anciently 
existing  character,  and  what  are  new  but  analogous  varia- 
tions, yet  we  ought,  on  my  theory,  sometimes  to  find  the 
varying  offspring  of  a  species  assuming  characters  (either 
from  reversion  or  from  analogous  variation)  which  already 
occur  in  some  other  members  of  the  same  group.  And 
this  undoubtedly  is  the  case  in  nature. 

A  considerable  part  of  the  difficulty  in  recognising  a 
variable  species  in  our  systematic  works,  is  due  to  its 
varieties  mocking,  as  it  were,  some  of  the  other  species  of 
the  same  genus.  A  considerable  catalogue,  also,  could  be 
given  of  forms  intermediate  between  two  other  forms, 
which  themselves  must  be  doubtfully  ranked  as  either 
varieties  or  species  ;  and  this  shows,  unless  all  these  forms 
be  considered  as  independently  created  species,  that  the 
one  in  varying  has  assumed  some  of  the  characters  of  the 
other,  so  as  to  produce  the  intermediate  form.  But  the 
best  evidence  is  afforded  by  parts  or  organs  of  an  impor- 
tant and  uniform  nature  occasionally  varying  so  as  to  ac- 
quire, in  some  degree,  the  character  of  the  same  part  or 
organ  in  an  allied  species.  I  have  collected  a  long  list  of 
Buch  cases ;  but  here,  as  before,  I  lie  under  a  great  disad- 


Chap.  V.]  LAWS   OF   VARIATION.  -[^^^ 

vantage  in  not  being  able  to  give  them.  I  can  only  repeat 
that  sucli  cases  certainly  do  occur,  and  seem  to  me  very 
remarkable. 

I  will,  however,  give  one  cnrions  and  complex  case, 
not  indeed  as  affecting  any  important  character,  but  from 
occurring  in  several  sj^ecies  of  the  same  genus,  partly 
under  domestication  and  partly  under  nature.  It  is  a 
case  apparently  of  reversion.  The  ass  not  rarely  has  very 
distinct  transverse  bars  on  its  legs,  like  those  on  the  legs  of 
the  zebra :  it  has  been  asserted  that  these  are  plainest  in 
the  foal,  and  from  inquiries  which  I  have  made,  I  believe 
this  to  be  true.  It  has  also  been  asserted  that  the  stripe 
on  each  shoulder  is  sometimes  double.  The  shoulder- 
stripe  is  certainly  very  variable  in  length  and  outline. 
A  white  ass,  but  not  an  albino,  has  been  described  with- 
out either  spinal  or  shoulder  stripe ;  and  these  stripes  are 
sometimes  very  obscure,  or  actually  quite  lost,  in  dark- 
coloured  asses.  The  koulan  of  Pallas  is  said  to  have  been 
seen  with  a  double  shoulder-stripe.  The  hemionus  has 
no  shoulder-stripe ;  but  traces  of  it,  as  stated  by  Mr.  Blyth 
and  others,  occasionally  appear :  and  I  have  been  informed 
by  Colonel  Poole  that  the  foals  of  this  sj)ecies  are  generally 
striped  on  the  legs,  and  faintly  on  the  shoulder.  The 
quagga,  though  so  plainly  barred  like  a  zebra  over  the 
body,  is  without  bars  on  the  legs ;  but  Dr.  Gray  has 
figured  one  specimen  with  very  distinct  zebra-like  bars 
on  the  hocks. 

AVith  respect  to  the  horse  I  have  collected  cases  in 
England  of  the  spinal  stripe  in  horses  of  the  most  distinct 
breeds,  and  of  all  colours ;  transverse  bars  on  the  legs  are 
not  rare  in  duns,  mouse-duns,  and  in  one  instance  in  a 
chestnut :  a  faint  shoulder-stripe  may  sometimes  be  seen 
in  duns,  and  I  have  seen  a  trace  in  a  bay  horse.  My  son 
made  a  careful  examination  and  sketch  for  me  of  a  dun 
Belgian  cart-horse  with  a  double  stripe  on  each  shoulder 
and  with  leg-stripes ;  and  a  man,  whom  I  can  implicitly 
trust,  has  examined  for  me  a  small  dun  Welch  pony  with 
three  short  parallel  stripes  on  each  shoulder. 

In  the  north-west  part  of  India  the  Kattywar  breed  of 
horses  is  so  generally  striped,  that,  as  I  hear  from  Colonel 


248  LAWa   OF   VARIATION.  [Chap.  V. 

Poole,  wlio  examined  the  breed  for  tlie  Indian  Groyern- 
ment,  a  horse  without  stripes  is  not  considered  as  pnrelj- 
bred.  The  spine  is  always  striped ;  the  legs  are  generally 
barred;  and  the  shonlder-stripe,  which  is  sometimes 
double  and  sometimes  treble,  is  common ;  the  side  of  the 
face,  moreover,  is  sometimes  striped.  The  stripes  are 
plainest  in  the  foal ;  and  sometimes  quite  disappear  in 
old  horses.  Colonel  Poole  has  seen  both  gray  and  bay 
Kattywar  horses  striped  when  first  foaled.  I  have,  also, 
reason  to  suspect,  from  information  given  me  by  Mi\  W. 
W.  Edwards,  that  with  the  English  race-horse  the  spinal 
stripe  is  much  commoner  in  the  foal  than  in  the  full-grown 
animal.  Without  here  entering  on  further  details,  I  may 
state  that  I  have  collected  cases  of  leg  and  shoulder 
stripes  in  horses  of  very  difi*erent  breeds,  in  various  coun- 
tries from  Britain  to  Eastern  China  ;  and  from  Norway  in 
the  north  to  the  Malay  Archipelago  in  the  south.  In  all 
parts  of  the  world  these  stripes  occur  far  oftenest  in  duns 
and  mouse-duns  ;  by  the  term  dun  a  large  range  of  colour 
is  included,  from  one  between  brown  and  black  to  a  close 
approach  to  cream-colour. 

I  am  aware  that  Colonel  Hamilton  Smith,  who  has 
written  on  this  subject,  believes  that  the  several  breeds  of 
the  horse  have  descended  from  several  aboriginal  species — 
one  of  which,  the  dun,  was  striped ;  and  that  the  above- 
described  appearances  are  all  due  to  ancient  crosses  with 
the  dun  stock.  But  I  am  not  at  all  satisfied  with  this 
theory,  and  should  be  loth  to  apply  it  to  breeds  so  distinct 
as  the  heavy  Belgian  cart-horse,  AVelch  ponies,  cobs,  the 
lanky  Kattywar  race,  &c.,  inhabiting  the  most  distant 
parts  of  the  world. 

JS'ow  let  us  tm-n  to  the  efi'ects  of  crossing  the  several 
species  of  the  horse-genus.  Rollin  asserts,  that  the  com- 
mon mule  from  the  ass  and  horse  is  particularly  apt  to 
have  bars  on  its  legs  :  according  to  Mr.  Gosse,  in  certain 
parts  of  the  United  States  about  nine  out  of  ten  mules 
have  striped  legs.  I  once  saw  a  mule  with  its  legs  so 
much  sti-iped  that  any  one  would  at  first  have  thought 
that  it  must  have  been  the  product  of  a  zebra ;  and  Mr. 
W.  C.  Martin,  in  his  excellent  treatise  on  the  horse,  has 
ffiven  a  figure  of  a  similar  mule.     In  four  coloured  draw- 


CuAP.  v.]  LAWS   OF   VAllIATIOX.  -j^^q 

ings,  which  I  have  seen,  of  hybrids  between  the  ass  and 
zebra,  the  legs  were  much  more  plainly  barred  than  the 
rest  of  the  body ;  and  in  one  of  them  there  was  a  double 
shoulder-stripe.  In  Lord  JMoreton's  famous  hybrid  from 
a  chestnut  mare  and  male  quagga,  the  liybrid,  and  even 
the  pure  offspring  subsequently  produced  from  the  mare 
by  a  black  Arabian  sire,  were  much  more  plainly  barred 
across  the  legs  than  is  even  the  pure  quagga.  Lastly,  and 
this  is  another  most  remarkable  case,  a  hybrid  has  been 
figured  by  Dr.  Gray  (and  he  informs  me  that  he  knows 
of  a  second  case)  from  the  ass  and  the  hemionus  ;  and  this 
hybrid,  though  the  ass  seldom  has  stripes  on  its  legs  and 
the  hemionus  has  none  and  has  not  even  a  shoulder-stripe, 
nevertheless  had  all  four  legs  barred,  and  had  three  short 
shoulder-stripes,  like  those  on  the  dun  "Welch  pony,  and 
even  had  some  zebra-like  stripes  on  the  sides  of  its  face. 
With  respect  to  this  last  fact,  I  was  so  convinced  that  not 
even  a  stripe  of  colour  appears  from  what  would  com- 
monly be  called  an  accident,  that  I  was  led  solely  from  the 
occurrence  of  the  face-stripes  on  this  hybrid  from  the  ass 
and  hemionus,  to  ask  Colonel  Poole  whether  such  face- 
stripes  ever  occur  in  the  eminently  striped  Kattywar 
breed  of  horses,  and  w^as,  as  we  have  seen,  answered  in 
the  aflimiative. 

What  now  are  we  to  say  to  these  several  facts  ?  We 
see  several  very  distinct  species  of  the  horse-genus  becom- 
ing, by  simple  variation,  striped  on  the  legs  like  a  zebra, 
or  striped  on  the  shoulders  like  an  ass.  In  the  horse  we 
see  this  tendency  strong  whenever  a  dun  tint  appears — a 
tint  which  approaches  to  that  of  the  general  colouring  of 
the  other  species  of  the  genus.  The  appearance  of  the 
stripes  is  not  accompanied  by  any  change  of  form  or  by 
any  other  new  character.  We  see  this  tendency  to  be- 
come striped  most  strongly  displayed  in  hybrids  from  be- 
tween several  of  the  most  distinct  species.  IS^ow  observe 
the  case  of  the  several  breeds  of  j^igeons  :  they  are  de- 
scended from  a  pigeon  (includng  two  or  three  sub-si^ecies, 
or  geographical  races)  of  a  bluish  colour,  with  certain 
bars  and  other  marks ;  and  when  any  breed  assumes  by 
simple  variation  a  bluish  tint,  these  bars  and  other  marks 
invariably  reappear;  but  without  any  other  change  of 


JL5Q  LAWS   OF   VARIATION.  [Chap.  V. 

form  or  character.  "WTien  tlie  oldest  and  truest  breeds  of 
various  colours  are  crossed,  we  see  a  strong  tendency  for 
ttie  blue  tint  and  bars  and  marks  to  reappear  in  the  mon- 
grels. I  have  stated  that  tlie  most  probable  hypothesis  to 
account  for  the  reappearance  of  very  ancient  characters, 
is — that  there  is  a  tendency  in  the  young  of  each  succes- 
sive generation  to  produce  the  long-lost  character,  and 
that  this  tendency,  from  unknown  causes,  sometimes  pre- 
vails. And  we  have  just  seen  that  in  several  species  of 
the  horse-genus  the  stripes  are  either  plainer  or  appear 
more  commonly  in  the  young  than  in  the  old.  Call  the 
breeds  of  pigeons,  some  of  which  have  bred  true  for  cen- 
turies, species ;  and  how  exactly  parallel  is  the  case  with 
that  of  the  species  of  the  horse-genus  !  For  myself,  I  ven- 
ture confidently  to  look  back  thousands  on  thousands  of 
generations,  and  I  see  an  animal  striped  like  a  zebra,  but 
perhaps  otherwise  very  differently  constructed,  the  com- 
mon parent  of  our  domestic  horse,  whether  or  not  it  be 
descended  from  one  or  more  wild  stocks,  of  the  ass,  the 
hemionus,  quagga,  and  zebra. 

He  who  believes  that  each  equine  species  was  inde- 
j)endently  created,  will,  I  presume,  assert  that  each  spe- 
cies has  been  created  with  a  tendency  to  vary,  both  under 
nature  and  under  domestication,  in  this  particular  manner, 
so  as  often  to  become  striped  like  other  species  of  the 
genns ;  and  that  each  has  been  created  with  a  strong 
tendency,  when  crossed  with  species  inhabiting  distant 
quarters  of  the  world,  to  produce  hybrids  resembling  in 
their  stripes,  not  their  own  parents,  but  other  sj)ecies  of 
the  genus.  To  admit  this  view  is,  as  it  seems  to  me,  to 
reject  a  real  for  an  unreal,  or  at  least  for  an  unknown, 
cause.  It  makes  the  works  of  God  a  mere  mockery  and 
deception ;  I  would  almost  as  soon  believe  with  the  old 
and  ignorant  cosmogonists,  that  fossil  shells  had  never 
lived,  but  had  been  created  in  stone  so  as  to  mock  the 
shells  now  living  on  the  sea-shore. 

Summary. — Our  ignorance  of  the  laws  of  variation 
is  profound,     l^ot  in  one  case  out  of  a  hundred  can  we 


Ohap,  v.]  summary.  1^^ 

pretend  to  assign  any  reason  why  this  or  that  part 
differs,  more  or  less,  from  the  same  part  in  the  parents. 
But  whenever  we  have  the  means  of  instituting  a  com- 
parison, the  same  laws  appear  to  have  acted  in  producing 
the  lesser  diflerences  between  varieties  of  the  same  spe- 
cies, and  the  greater  differences  between  species  of  the 
same  genus.  The  external  conditions  of  life,  as  climate 
and  food,  &c.,  seem  to  have  induced  some  slight  modifica- 
tions. Habit  in  producing  constitutional  differences,  and 
use  in  strengthening,  and  disuse  in  weakening  and  dimin- 
ishing organs,  seem  to  have  been  more  potent  in  their 
effects.  Homologous  parts  tend  to  vary  in  the  same  way, 
and  homologous  parts  tend  to  cohere.  Modifications  in 
hard  parts  and  in  external  parts  sometimes  affect  softer 
and  internal  parts.  When  one  part  is  largely  developed, 
perhaps  it  tends  to  draw  nourishment  from  the  adjoining 
parts ;  and  every  part  of  the  structure  which  can  be  saved 
without  detriment  to  the  individual,  will  be  saved. 
Changes  of  structure  at  an  early  age  will  generally  affect 
parts  subsequently  developed  ;  and  there  are  very  many 
other  correlations  of  growth,  the  nature  of  which  we  are 
utterly  unable  to  understand.  Multiple  parts  are  variable 
in  number  and  in  structure,  perhaps  arising  from  such 
parts  not  having  been  closely  specialised  to  any  particular 
function,  so  that  their  modifications  have  not  been  closely 
cliecked  by  natural  selection.  It  is  probably  from  this 
same  cause  that  organic  beings  low  in  the  scale  of  nature 
are  more  variable  than  those  v/liich  have  their  whole 
organisation  more  specialised,  and  are  higher  in  the  scale. 
Rudimentary  organs,  from  being  useless,  will  be  dis- 
regarded by  natural  selection,  and  hence  probably  are 
variable.  Specific  characters — that  is,  the  characters  which 
have  come  to  differ  since  the  several  species  of  the  same 
genus  branched  off  from  a  common  parent — are  more 
variable  than  generic  characters,  or  those  which  have 
long  been  inherited,  and  have  not  differed  within  this 
same  period.  In  these  remarks  we  have  referred  to  special 
parts  or  organs  being  still  variable,  because  they  have 
recently  varied  and  thus  come  to  difi'er ;  but  we  have  also 
seen  in  the  second  Chapter  that  the  same  principle  applies 


1^2  LAWS    OF    VARIATION.  [Chap.  V. 

to  the  whole  individual ;  for  in  a  district  where  many 
species  of  any  genns  are  found — that  is,  where  there  has 
been  much  former  variation  and  differentiation,  or  where 
the  manufactory  of  new  specific  forms  has  been  actively 
at  work — there,  on  an  average,  we  now  find  most  varieties 
or  incipient  species.  Secondary  sexual  characters  are 
highly  variable,  and  such  characters  differ  much  in  the 
sj)ecies  of  the  same  group.  Variability  in  the  same  parts 
of  the  organisation  has  generally  been  taken  advantage 
of  in  giving  secondary  sexual  differences  to  the  sexes  of 
the  same  species,  and  specific  differences  to  the  several 
species  of  the  same  genus.  Any  part  or  organ  developed 
to  an  extraordinary  size  or  in  an  extraordinary  manner, 
in  comparison  with  the  same  part  or  organ  in  the  allied 
species,  must  have  gone  through  an  extraordinary  amount 
of  modification  since  the  genus  arose ;  and  thus  we  can 
understand  why  it  should  often  still  be  variable  in  a  much 
higher  degree  than  other  parts  ;  for  variation  is  a  long- 
continued  and  slow  process,  and  natural  selection  will  in 
such  cases  not  as  yet  have,  had  time  to  overcome  the 
tendency  to  further  variability  and  to  reversion  to  a  less 
modified  state.  But  when  a  species  with  any  extra- 
ordinarily-developed organ  has  become  the  parent  of  many 
modified  descendants — which  on  my  view  must  be  a  very 
slow  process,  requiring  a  long  lapse  of  time — in  this  case, 
natural  selection  may  readily  have  succeeded  in  giving  a 
fixed  character  to  the  organ,  in  however  extraordinary  a 
manner  it  may  be  developed.  Species  inheriting  nearly 
tlie  same  constitution  from  a  common  parent  and  exposed 
to  similar  influences  will  naturally  tend  to  present  ana- 
logous variations,  and  these  same  species  may  occasionally 
revert  to  some  of  the  characters  of  their  ancient  progen- 
itors. Although  new  and  important  modifications  may 
not  arise  from  reversion  and  analogous  variation,  such 
modifications  will  add  to  the  beautiful  and  harmonious 
diversities  of  nature. 

Whatever  the  cause  may  be  of  each  slight  difference 
in  the  offspring  from  their  parents — and  a  cause  for  each 
must  exist — ^it  is  the  steady  accumulation,  through  natural 


Chap,  V.]  '  SUMMARY, 


153 


selection,  of  such  diiferences,  when  beneficial  to  the  indi- 
vidual, that  gives  rise  to  all  the  more  important  modifica- 
tions of  structure,  by  which  the  innumerable  beings  on 
the  face  of  this  earth  are  enabled  to  struggle  with  each 
other,  and  the  best  adapted  to  survive. 


|/54  DIFFICULTIES   ON   THEORY.  [Chap.  Vl, 


CHAPTER    YI. 

DIFFICULTIES      ON      THEORY. 

Difficulties  on  the  theory  of  descent  with  modification — Transitions — Absence  or 
rarity  of  transitional  varieties— Transitions  in  habits  of  life— Diversified  habits  in 
the  same  species— Species  with  habits  widely  different  from  those  of  their  alUes— 
Organs  of  extreme  perfection — Means  of  transition— Cases  of  difficulty — Natura 
non  facit  saltum— Organs  of  small  importance— Organs  not  in  all  cases  absolutely 
perfect— The  law  of  Unity  of  Type  and  of  the  Conditions  of  Existence  embraced 
by  the  theory  of  Natural  Selection.  ^ 

Long  "before  having  arrived  at  this  part  of  my  work,  a 
crowd  of  difficulties  will  have  occurred  to  the  reader. 
Some  of  them  are  so  grave  that  to  this  daj  I  can  never 
reflect  on  them  without  being  staggered  ;  but,  to  the  best 
of  my  judgment,  the  greater  number  are  only  apparent, 
and  those  that  are  real  are  not,  I  think,  fatal  to  my 
theory. 

These  difficulties  and  objections  may  be  classed  under 
the  following  heads : — Firstly,  why,  if  species  have  de- 
scended from  other  species  by  insensibly  fine  gradations, 
do  we  not  everywhere  see  innumerable  transitional  forms  ? 
Why  is  not  all  nature  in  confusion  instead  of  the  species 
being,  as  we  see  them,  well  defined  ? 

Secondly,  is  it  possible  that  an  animal  having,  for 
instance,  the  structure  and  habits  of  a  bat,  could  have 
been  formed  by  the  modification  of  some  animal  with 
wholly  diflerent  liabits  ?  Can  we  believe  that  natural 
selection  could  produce,  on  the  one  hand,  organs  of  trifling 
importance,  such  as  the  tail  of  a  girafte,  which  serves  as 
a  fiy-flapper,  and,  on  the  other  hand,  organs  of  such 
wonderful  structure,  as  the  eye,  of  which  we  hardly  as 
yet  fully  understand  the  inimitable  perfection  ? 

Thirdly,  can  instincts  be  acquired  and  modified  through 
natural  selection  ?     AVhat  shall  we  say  to  so  marvellous 


Chap.  VI.]  TRANSITIONAL   VARIETIES.  255 

an  instinct  as  that  wliicli  leads  the  bee  to  make  cells, 
which  have  practically  anticipated  the  discoveries  of  pro- 
found mathematicians  ? 

Fourthly,  how  can  we  account  for  species,  when  crossed, 
being  sterile  and  producing  sterile  offspring,  whereas, 
when  varieties  are  crossed,  their  fertility  is  unimpaired  ? 

The  two  first  heads  shall  be  here  discussed — Instinct 
and  Hybridism  in  separate  chapters. 

On  tJie  absence  or  rarity  of  transitional  varieties. — As 
natural  selection  acts  solely  by  the  preservation  of  profit- 
able modifications,  each  new  form  will  tend  in  a  fully- 
stocked  country  to  take  the  place  of,  and  finally  to  exter- 
minate, its  own  less  improved  parent  or  other  less-favoured 
forms  with  which  it  comes  into  competition.  Thus  ex- 
tinction and  natural  selection  will,  as  we  have  seen,  go 
hand  in  hand.  Hence,  if  we  look  at  each  species  as 
descended  from  some  other  unknown  form,  both  the  parent 
and  all  the  transitional  varieties  will  generally  have  been 
exterminated  by  the  very  process  of  formation  and  per- 
fection of  the  new  form. 

But,  as  by  this  theory  innumerable  transitional  forms 
must  have  existed,  why  do  we  not  find  them  embedded 
in  countless  numbers  in  the  crust  of  the  earth  ?  It  will 
be  much  more  convenient  to  discuss  this  question  in  the 
chapter  on  the  Imperfection  of  the  geological  record  ; 
and  I  will  here  only  state  that  I  believe  tlie  answer  mainly 
lies  in  the  record  being  incomparably  less  perfect  than  is 
generally  supposed  ;  the  imperfection  of  the  record  being 
chiefly  due  to  organic  beings  not  inhabiting  profound 
depths  of  the  sea,  and  to  their  remains  being  embedded 
and  preserved  to  a  future  age  only  in  masses  of  sediment 
suflficiently  thick  and  extensive  to  withstand  an  enormous 
amount  of  future  degradation ;  and  such  fossiliferous 
masses  can  be  accumulated  only  where  much  sediment  is 
deposited  on  the  shallow  bed  of  the  sea,  whilst  it  slowly 
subsides.  These  contingencies  will  concur  only  rarely, 
and  after  enormously  long  intervals.  Whilst  the  bed  of 
the  sea  is  stationary  or  is  rising,  or  when  very  little  sedi- 
ment is  being  deposited,  there  will  be  blanks  in  our  geo- 
8 


256  DIFFICULTIES    OX   THEORY.  [Chap.  VL 

logical  history.  The  crust  of  tlie  earth  is  a  vast  museum ; 
but  the  natural  collections  have  been  made  only  at  inter- 
vals of  time  immensely  remote. 

But  it  may  be  urged  tliat  when  several  closely-allied 
species  inhabit  the  same  territory  we  surely  ought  to  find 
at  the  j^resent  time  many  transitional  forms.  Let  us  take 
a  simple  case  :  in  travelling  from  north  to  south  over  a 
continent,  we  generally  meet  at  successive  intervals  with 
closely  allied  or  representative  sj)ecies,  evidently  filling 
nearly  the  same  place  in  the  natural  economy  of  the  land. 
These  representative  species  often  meet  and  interlock ; 
and  as  the  one  becomes  rarer  and  rarer,  the  other  becomes 
more  and  more  frequent,  till  the  one  replaces  the  other. 
But  if  we  compare  these  species  where  they  intermingle, 
they  are  generally  as  absolutely  distinct  from  each  other. 
in  every  detail  of  structure  as  are  specimens  taken  from 
the  metropolis  inhabited  by  each.  By  my  theory  these 
allied  species  have  descended  from  a  common  parent ; 
and  during  the  process  of  modification,  each  has  become 
adapted  to  the  conditions  of  life  of  its  own  region,  and 
has  supplanted  and  exterminated  its  original  parent  and 
all  the  transitional  varieties  between  its  past  and  present 
states.  Hence  we  ought  not  to  expect  at  the  present  time 
to  meet  with  numerous  transitional  varieties  in  each 
region,  though  they  must  have  existed  there,  and  may  be 
embedded  there  in  a  fossil  condition.  But  in  the  inter- 
mediate region,  having  intermediate  conditions  of  life,  why 
do  we  not  now  find  closely-linking  intermediate  varieties  ? 
This  difiiculty  for  a  long  time  quite  confounded  me.  But 
I  think  it  can  be  in  large  part  explained. 

In  the  first  place  we  should  be  extremely  cautious  in 
inferring,  because  an  area  is  now  continuous,  that  it  has 
been  continuous  during  a  long  period.  Geology  would 
lead  us  to  believe  that  almost  every  continent  has  been 
broken  up  into  islands  even  during  the  later  tertiary 
periods  ;  and  in  such  islands  distinct  species  might  have 
been  separately  formed  without  the  possibility  of  inter- 
mediate varieties  existing  in  the  intermediate  zones.  By 
changes  in  the  form  of  the  land  and  of  climate,  marine 
areas   now  continuous   must   often  have  existed  within 


Chap.  VI.]  TRANSITIONAL   VARIETIES.  ^^5^ 

recent  times  in  a  far  less  continuous  and  uniform  condition 
than  at  present.  But  I  will  pass  over  tins  way  of  escap- 
ing from  the  difficulty  ;  for  I  believe  that  many  perfectly 
delined  species  have  been  formed  on  strictly  continuous 
areas  ;  though  I  do  not  doubt  that  the  formerly  broken 
condition  of  areas  now  continuous  has  played  an  impor- 
tant part  in  the  formation  of  new  species,  more  especially 
with  freely-crossing  and  wandering  animals. 

In  looking  at  species  as  they  are  now  distributed  over 
a  wide  area,  we  generally  find  them  tolerably  numerous 
over  a  large  territory,  then  becoming  somewhat  abruptly 
rarer  and  rarer  on  the  confines,  and  finally  disappearing. 
Hence  the  neutral  territory  between  two  representative 
species  is  generally  narrow  in  comparison  with  the  terri- 
tory proper  to  each.  We  see  the  same  fact  in  ascending 
mountains,  and  sometimes  it  is  quite  remarkable  how 
abruptly,  as  Alph.  De  Candolle  has  observed,  a  common 
alpine  species  disappears.  The  same  fact  has  been  noticed 
by  Forbes  in  sounding  the  depths  of  the  sea  with  the 
dredge.  To  those  who  look  at  climate  and  the  ^^hysical 
conditions  of  life  as  the  all-important  elements  of  distri- 
bution, these  facts  ought  to  cause  surprise,  as  climate  and 
height  or  depth  graduate  away  insensibly.  But  when  we 
bear  in  mind  that  almost  every  species,  even  in  its  metro- 
polis, would  increase  immensely  in  numbers,  were  it  not 
for  other  competing  species  ;  that  nearly  all  either  prey 
on  or  serve  as  prey  for  others ;  in  short,  that  each  organic 
being  is  either  directly  or  indirectly  related  in  the  most 
important  manner  to  other  organic  beings,  we  must  see 
that  the  range  of  the  inhabitants  of  any  country  by  no 
means  exclusively  depends  on  insensibly  changing  physical 
conditions,  but  in  large  part  on  the  presence  of  other  spe- 
cies, on  which  it  depends,  or  by  which  it  is  destroyed,  or 
with  which  it  comes  into  competition  ;  and  as  these  spe- 
cies are  already  defined  objects  (however  they  may  have 
become  so),  not  blending  one  into  another  by  insensible 
gradations,  the  range  of  any  one  species,  depending  as  it 
does  on  the  range  of  others,  will  tend  to  be  sharply  de- 
fined. Moreover,  each  species  on  the  confines  of  its 
range,  where  it  exists  in  lessened  numbers,  will,  during 


-J^gg  DIFFICULTIES    ON   THEORY.  [Chap.  VI. 

fluctuations  in  tlie  nnmber  of  its  enemies  or  of  its  prey, 
or  in  the  seasons,  be  extremely  liable  to  utter  extermina- 
tion ;  and  thus  its  geographical  range  will  come  to  be 
still  more  sharply  denned. 

If  I  am  right  in  believing  that  allied  or  representative 
species,  when  inhabiting  a  continuous  area,  are  generally 
so  distributed  that  each  has  a  wide  range,  with  a  com- 
paratively narrow  neutral  territory  between  them,  in 
which  they  become  rather  suddenly  rarer  and  rarer ;  then, 
as  varieties  do  not  essentially  differ  from  species,  the  same 
rule  will  probably  aj)ply  to  both  ;  and  if  we  in  imagina- 
tion adapt  a  varying  species  to  a  very  large  area,  we  shall 
have  to  adapt  two  varieties  to  two  large  areas,  and  a  third 
variety  to  a  narrow  intermediate  zone.  The  intermediate 
variety,  consequently,  will  exist  in  lesser  numbers  from 
inhabiting  a  narrow  and  lesser  area ;  and  practically,  as 
far  as  I  can  make  out,  this  rule  holds  good  with  varieties 
in  a  state  of  nature.  I  have  met  with  striking  instances 
of  the  rule  in  the  case  of  varieties  intermediate  between 
well-marked  varieties  in  the  genus  Balanus.  And  it  would 
appear  from  information  given  me  by  Mr.  Watson,  Dr. 
Asa  Gray,  and  Mr.  Wollaston,  that  generally  when  varie- 
ties intermediate  between  two  other  forms  occur,  they 
are  much  rarer  numerically  than  the  forms  which  they 
connect.  ISTow,  if  we  may  trust  these  facts  and  inferences, 
and  therefore  conclude  that  varieties  linking  two  other 
varieties  together  have  generally  existed  in  lesser  numbers 
than  the  forms  which  they  connect,  then,  I  think,  we  can 
understand  why  intermediate  varieties  should  not  endure 
for  very  long  periods ; — why  as  a  general  rule  they  should 
be  exterminated  and  disappear,  sooner  than  the  forms 
which  they  originally  linked  together. 

For  any  form  existing  in  lesser  numbers  would,  as 
already  remarked,  run  a  greater  chance  of  being  exter- 
minated than  one  existing  in  large  numbers  ;  and  in  tliis 
particular  case  the  intermediate  form  would  be  eminently 
liable  to  the  inroads  of  closely  allied  forms  existing  on 
both  sides  of  it.  But  a  far  more  important  consideration, 
as  I  believe,  is  that,  during  the  process  of  further  modifi- 
cation, by  which  two  varieties  are  supposed  on  my  theory 


Chap.  VI.]  TRANSITIONAL   VARlETIEa  J^gg 

to  be  converted  and  perfected  into  two  distinct  species, 
the  two  wliicli  exist  in  larger  numbers  from  inhabiting 
larger  areas,  will  have  a  great  advantage  over  the  inter- 
mediate variety,  which  exists  in  smaller  numbers  in  a 
narrow  and  intermediate  zone.  For  forms  existing  in 
larger  numbers  will  always  have  a  better  chance,  within 
any  given  period,  of  presenting  further  favourable  varia- 
tions for  natural  selection  to  seize  on,  than  will  the  rarer 
forms  which  exist  in  lesser  numbers.  Hence,  the  more 
common  forms,  in  the  race  for  life,  will  tend  to  beat  and 
supplant  the  less  common  forms,  for  these  will  be  more 
slowly  modified  and  improved.  It  is  the  same  principle 
which,  as  I  believe,  accounts  for  the  common  species  in 
each  country,  as  shown  in  the  second  chapter,  presenting 
on  an  average  a  greater  number  of  well-marked  varieties 
than  do  the  rarer  s]3ecies.  I  may  illustrate  what  I  mean 
by  supposing  three  varieties  of  sheep  to  be  kept,  one 
adapted  to  an  extensive  mountainous  region  ;  a  second  to 
a  comparatively  narrow,  hilly  tract ;  and  a  third  to  wide 
plains  at  the  base  ;  and  that  the  inhabitants  are  all  trying 
with  equal  steadiness  and  skill  to  improve  their  stocks  by 
selection;  the  chances  in  this  case  will  be  strongly  in 
favour  of  the  great  holders  on  the  mountains  or  on  the 
plains  improving  their  breeds  more  quickly  than  the  small 
holders  on  the  intermediate  narrow,  hilly  tract ;  and  conse- 
quently the  improved  mountain  or  plain  breed  will  soon 
take  the  place  of  the  less  improved  hill  breed  ;  and  thus 
the  two  breeds,  which  originally  existed  in  gi-eater  num- 
bers, will  come  into  close  contact  with  each  other,  with- 
out the  interposition  of  the  supplanted,  intermediate  hill- 
variety. 

To  sum  up,  I  believe  that  species  come  to  be  tolerably 
well-defined  objects,  and  do  not  at  any  one  period  present 
an  inextricable  chaos  of  varying  and  intermediate  links : 
firstly,  because  new  varieties  are  very  slowly  formed,  for 
variation  is  a  very  slow  process,  and  natural  selection  can 
do  nothing  until  favourable  variations  chance  to  occur, 
and  imtil  a  place  in  the  natural  polity  of  the  country  can 
be  better  filled  by  some  modification  of  some  one  or  more 
of  its  inhabitants.     And  such  new  places  will  depend  on 


■^QQ  DIFFICULTIES   ON   THEORY.  [Chap.  VI. 

slow  clianges  of  climate,  or  on  the  occasional  immigration 
of  new  inhabitants,  and,  probably,  in  a  still  more  impor- 
tant degree,  on  some  of  the  old  inhabitants  becoming 
slowly  modified,  with  the  new  forms  thus  produced  and 
the  old  ones  acting  and  reacting  on  each  other.  So  that, 
in  any  one  region  and  at  any  one  time,  we  ought  only  to 
see  a  few  species  presenting  slight  modifications  of  struc- 
ture in  some  degree  permanent;  and  this  assm'edly  we 
see. 

Secondly,  areas  now  continuous  must  often  have  ex- 
isted within  the  recent  period  in  isolated  portions,  in 
which  many  forms,  more  especially  amongst  the  classes 
which  unite  for  each  birth  and  wander  much,  may  have 
separately  been  rendered  sufficiently  distinct  to  rank  as 
representative  species.  In  this  case,  intermediate  varieties 
between  the  several  representative  species  and  their  com- 
mon parent,  must  formerly  have  existed  in  each  broken 
portion  of  the  land,  but  these  links  will  have  been  sup- 
planted and  exterminated  during  the  process  of  natural 
selection,  so  that  they  will  no  longer  exist  in  a  living 
state. 

Thirdly,  when  two  or  more  varieties  have  been  formed 
in  difi'erent  portions  of  a  strictly  continuous  area,  inter- 
mediate varieties  will,  it  is  probable,  at  first  have  been 
formed  in  the  intermediate  zones,  but  they  will  generally 
have  ha,d  a  short  duration.  For  these  intermediate  vari- 
eties will,  from  reasons  already  assigned  (namely  from 
what  we  know  of  the  actual  distribution  of  closely  allied 
or  representative  species,  and  likewise  of  acknowledged 
varieties),  exist  in  the  intermediate  zones  in  lesser  num- 
bers than  the  varieties  which  they  tend  to  connect.  From 
this  cause  alone  the  intermediate  varieties  will  be  liable 
to  accidental  extermination;  and  during  the  process  of  fur- 
ther modification  through  natural  selection,  they  will 
almost  certainly  be  beaten  and  supplanted  by  the  forms 
which  they  connect ;  for  these  from  existing  in  greater 
numbers  will,  in  the  aggregate,  present  more  variation, 
and  thus  be  further  improved  through  natural  selection 
and  gain  further  advantages. 

Lastly,  looking  not  to  any  one  time,  but  to  all  time,  if 


Chap.  VLl  TRANSITIONAL   HABITS.  ^61 

my  theory  be  true,  numberless  intermediate  varieties,  link- 
ing most  closely  all  the  sjDecies  of  the  same  grouj)  together^ 
must  assuredly  have  existed  ;  but  the  very  process  of 
natural  selection  constantly  tends,  as  has  been  so  often  re- 
marked, to  exterminate  the  parent-forms  and  the  inter- 
mediate links.  Consequently  evidence  of  their  fomer  ex- 
istence could  be  found  only  amongst  fossil  remains,  which 
are  preserved,  as  we  shall  in  a  future  chapter  attempt  to 
show,  in  an  extremely  imperfect  and  intermittent  record. 

On  the  origin  and  i/ransitions  of  organic  teings  with 
peculiar  habits  and  structure.- — It  has  been  asked  by  the 
opponents  of  such  views  as  I  hold,  how,  for  instance,  a 
land  carnivorous  animal  could  have  been  converted  into 
one  with  aquatic  habits  ;  for  how  could  the  animal  in  its 
transitional  state  have  subsisted  ?  It  would  be  easy  to 
show  that  within  the  same  group  carnivorous  animals  ex- 
ist having  every  intermediate  grade  between  truly  aquatic 
and  strictly  terrestrial  habits  ;  and  as  each  exists  by  a 
struggle  for  life,  it  is  clear  that  each  is  well  adapted  in 
its  habits  to  its  place  in  nature.  Look  at  the  Mustela 
vison  of  N^orth  America,  which  has  webbed  feet  and 
which  resembles  an  otter  in  its  fur,  short  legs,  and  form 
of  tail ;  during  summer  this  animal  dives  for  and  preys 
on  fish,  but  during  the  long  winter  it  leaves  the  frozen 
waters,  and  preys  like  other  pole-cats  on  mice  and  land 
animals.  If  a  different  case  had  been  taken,  and  it  had 
been  asked  how  an  insectivorous  quadruped  could  pos- 
sibly have  been  converted  into  a  flying  bat,  the  question 
would  have  been  far  more  difficult,  and  I  could  have  given 
no  answer.  Yet  I  think  such  difficulties  have  very  little 
weight. 

Here,  as  on  other  occasions,  I  lie  under  a  heavy  dis- 
advantage, for  out  of  the  many  striking  cases  wh'icli  I 
have  collected,  I  can  give  only  one  or  two  instauccs  of 
transitional  habits  and  structures  in  closely  allied  species 
of  the  same  genus;  and  of  diversified  habits,  eitlicr  con- 
stant or  occasional,  in  the  same  species.  And  it  eoems  to 
me  that  nothing  less  than  a  long  list  of  such  cases  is  suf- 
ficient to  lessen  the  difficulty  in  any  particular  case  like 
that  of  t]ie  bat. 


\Q2  DIFFICULTIES    O^-   THEORY.  [Chap.  VI. 

Look  at  the  family  of  squirrels ;  here  we  have  the 
finest  gradation  from  animals  with  their  tails  only  slightly 
flattened,  and  from  others,  as  Sir  J.  Richardson  has  re- 
marked, with  the  posterior  part  of  their  bodies  rather 
wide  and  with  the  skin  on  their  flanks  rather  full,  to  the 
so-called  flying  squirrels ;  and  flying  squirrels  have  their 
limbs  and  even  the  base  of  the  tail  united  by  a  broad  ex- 
panse of  skin,  which  serves  as  a  parachute  and  allows 
them  to  glide  through  the  air  to  an  astonishing  distance 
from  tree  to  tree.  vVe  cannot  doubt  that  each  structure 
is  of  use  to  each  kind  of  squirrel  in  its  own  country,  by 
enabling  it  to  escape  birds  or  beasts  of  prey,  or  to  collect 
food  more  quickly,  or,  as  there  is  reason  to  believe,  by 
lessening  the  danger  from  occasional  falls.  But  it  does 
not  follow  from  this  fact  that  the  structure  of  each 
squirrel  is  the  best  that  it  is  possible  to  conceive  under 
all  natural  conditions.  Let  the  climate  and  vegetation 
change,  let  other  competing  rodents  or  new  beasts  of  prey 
immigrate,  or  old  ones  become  modified,  and  all  analogy 
would  lead  us  to  believe  that  some  at  least  of  the  squirrels 
would  decrease  in  numbers  or  become  exterminated,  un- 
less they  also  became  modified  and  improved  in  stnicture 
in  a  corresponding  manner.  Tlierefore,  I  can  see  no  dif- 
ficulty, more  especially  under  changing  conditions  of  life, 
in  the  continued  preservation  of  individuals  with  fuller 
and  fuller  flank-membranes,  each  modification  being  use- 
ful, each  being  propagated,  until  by  the  accumulated 
effects  of  this  process  of  natural  selection,  a  perfect  so- 
called  flying  squirrel  was  produced. 

ITow  look  at  the  Galeopithecus  or  flying  lemur,  which 
formerly  was  falsely  ranked  amongst  bats.  It  has  an  ex- 
tremely wide  flank-membrane,  stretching  from  the  corners 
of  the  jaw  to  the  tail,  and  including  the  limbs  and  the 
elongated  fingers  :  the  flank-membrane  is,  also,  furnished 
with  an  extensor  muscle.  Although  no  graduated  links 
of  structure,  fitted  for  gliding  through  the  air,  now  con- 
nect the  Galeopithecus  with  the  other  Lemuridte,  yet  I 
can  see  no  difficulty  in  supposing  that  such  links  formerly 
existed,  and  that  each  had  been  formed  by  the  same  steps 
as  in  the  case  of  the  less  perfectly  gliding  squirrels ;  and 


Chap.  VL]  TRANSITIONAL  HABITS. 


163 


that  eacii  grade  of  structure  had  been  useful  to  its  pos- 
sessor. Nor  can  I  see  any  insuperable  difficulty  in  fur- 
ther believing  it  possible  that  the  membrane-connected 
lingers  and  fore-arm  of  the  Galeopithecus  might  be 
greatly  lengthened  by  natural  selection  ;  and  this,  as  far 
as  the  organs  of  flight  are  concerned,  would  convert  it 
into  a  bat.  In  bats  which  have  the  wing-membrane  ex- 
tended from  the  top  of  the  shoulder  to  the  tail,  including 
the  hind-legs,  we  perhaps  see  traces  of  an  apparatus  orig- 
inally constructed  for  gliding  through  the  air  rather  than 
for  flight. 

If  about  a  dozen  genera  of  birds  had  become  extinct 
or  were  unknown,  who  would  have  ventured  to  have  sur- 
mised that  birds  might  have  existed  which  used  their 
wings  solely  as  flappers,  like  the  logger-headed  duck 
(Micropterus  of  Ey  ion) ;  as  fins  in  the  water  and  front 
legs  on  the  land,  like  the  penguin  ;  as  sails,  like  the 
ostrich  ;  and  functionally  for  no  purpose,  like  the  Apteryx. 
Yet  the  structure  of  each  of  these  birds  is  good  for  it, 
under  the  conditions  of  life  to  which  it  is  exposed,  for 
each  has  to  live  by.  a  struggle  ;  but  it  is  not  necessarily 
the  best  possible  under  all  possible  conditions.  It  must 
not  be  inferred  from  these  remarks  that  any  of  the  grades 
of  wing-structure  here  alluded  to,  which  perhaps  may  all 
have  resulted  from  disuse,  indicate  the  natural  steps  by 
which  birds  have  acquired  their  perfect  power  of  flight ; 
but  they  serve,  at  least,  to  show  what  diversifled  means 
of  transition  are  possible. 

Seeing  that  a  few  members  of  such  water-breathing 
classes  as  the  Crustacea  and  Mollusca  are  adapted  to  live 
on  the  land,  and  seeing  that  we  have  flying  birds  and 
mammals,  flying  insects  of  the  most  diversified  types,  and 
formerly  had  flying  reptiles,  it  is  conceivable  that  flyiug- 
fish,  which  now  glide  far  through  the  air,  slightly  rising 
and  turning  by  the  aid  of  their  fluttering  flns,  mic^ht  have 
been  modified  into  perfectly  winged  animals.  If'this  1  ad 
been  cftected,  who  would  have  ever  imagined  that  in  an 
early  transitional  state  they  had  been  inhabitants  of  the 
open  ocean,  and  had  used  their  incipient  organs  of  flight 
exclusivclv,  as  far  as  we  know,  to  escape  being  devoured 
by  other  fish  ? 


IQ4:  DIFFICULTIES   ON   THEORY.  [Chap.  Y1. 

When  we  see  any  structure  Mglily  perfected  for  any 
particular  habit,  as  the  wings  of  a  bird  for  flight,  we 
should  bear  in  mind  that  animals  displaying  early  tran- 
sitional grades  of  the  structure  will  seldom  continue  to 
exist  to  the  present  day,  for  they  will  have  been  supplant- 
ed by  the  very  process  of  perfection  through  natural  se- 
lection. Furthermore,  we  may  conclude  that  transitional 
grades  between  stiaictures  fitted  for  very  difi'erent  habits 
of  life  will  rarely  have  been  develoj)ed  at  an  early  period 
in  great  numbers  and  under  many  subordinate  forms. 
Thus,  to  return  to  our  imaginary  illustration  of  the  flying- 
fish,  it  does  not  seem  probable  that  fishes  capable  of  true 
flight  would  have  been  developed  under  many  subordi 
nate  forms,  for  taking  prey  of  many  kinds  in  many  ways, 
on  the  land  and  in  the  water,  until  their  organs  of  flight 
had  come  to  a  high  stage  of  perfection,  so  as  to  have 
given  them  a  decided  advantage  over  other  animals  in  the 
battle  for  life.  Hence  the  chance  of  discovering  species 
with  transitional  grades  of  structure  in  a  fossil  condition 
will  always  be  less,  from  their  having  existed  in  lesser 
numbers,  than  in  the  case  of  species  with  fully  developed 
structures. 

I  will  now  give  two  or  three  instances  of  diversified 
and  of  changed  habits  in  the  individuals  of  the  same  spe- 
cies. When  either  case  occurs,  it  would  be  easy  for  na- 
tural selection  to  fit  the  animal,  by  some  modification  of 
its  structure,  for  its  changed  habits,  or  exclusively  for  one 
of  its  several  diflPerent  habits.  But  it  is  difficult  to  tell, 
and  immaterial  for  us,  whether  habits  generally  change 
first  and  structure  afterwards  ;  or  whether  slight  modifica- 
tions of  structure  lead  to  changed  habits  ;  both  probably 
often  change  almost  simultaneously.  Of  cases  of  changed 
habits  it  will  suffice  merely  to  allude  to  that  of  the  many 
British  insects  which  now  feed  on  exotic  plants,  or  exclu- 
sively on  artificial  substances.  Of  diversified  habits  innu- 
merable instances  could  be  given  :  I  have  often  watched 
a  tyrant  flycatcher  (Saurophagus  sulphuratus)  in  South- 
America,  hovering  over  one  spot  and  then  proceeding  to 
another,  like  a  kestrel,  and  at  other  times  standing  station- 
ary on  the  margin  of  water,  and  then  dashing  like  a  king- 


Chap.  VI.]  TRANSITIONAL  HABITS.  105 

fisher  at  a  fish.  In  our  own  country  the  large  titmouse 
(Parus  major)  may  be  seen  climbing  branches,  almost  like 
a  creeper';  it  often,  like  a  shrike,  kills  small  birds,  by 
blows  on  the  head  ;  and  I  have  many  times  seen  and 
heard  it  hammering  the  seeds  of  the  yew  on  a  branch,  and 
thus  breaking  them  like  a  nuthatch.  In  E'orth  America 
the  black  bear  was  seen  by  Plearne  swimming  for  hours 
with  widely  open  mouth,  thus  catching,  like  a  whale,  in- 
sects in  the  water.  Even  in  so  extreme  a  case  as  this,  if 
the  supply  of  insects  were  constant,  and  if  better  adapted 
competitors  did  not  already  exist  in  the  country,  I  can  see 
no  difficulty  in  a  race  of  bears  being  rendered,  by  natural 
selection,  more  and  more  aquatic  in  their  structure  and 
habits,  with  larger  and  larger  mouths,  till  a  creature  was 
produced  as  monstrous  as  a  whale. 

As  w^e  sometimes  see  individuals  of  a  species  following 
habits  widely  different  from  those  both  of  their  own  species 
and  of  the  other  species  of  the  same  genus,  w^e  might  ex- 
pect, on  my  theory,  that  such  individuals  would  occasion- 
ally have  given  rise  to  new  species,  having  anomalous 
habits,  and  with  their  structure  either  slightly  or  consid- 
erably modified  from  that  of  their  projDcr  type.  And  such 
instances  do  occur  in  nature.  Can  a  more  striking  in- 
stance of  adaptation  be  given  than  that  of  a  woodpecker 
for  climbing  trees  and  for  seizing  insects  in  the  chinks  of 
the  bark  ?  Yet  in  ]N"orth  America  there  are  woodpeckers 
which  feed  largely  on  fruit,  and  others  with  elongated 
wings  which  chase  insects  on  the  wing  ;  and  on  the  plains 
of  La  Plata,  where  not  a  tree  grows,  there  is  a  woodpeck- 
er, which  in  every  essential  part  of  its  organisation,  even 
in  its  colouring,  in  the  harsh  tone  of  its  voice,  and  undu- 
latory  flight,  told  me  plainly  of  its  close  blood-relationship 
to  our  common  species  ;  yet  it  is  a  woodpecker  which 
never  climbs  a  tree  ! 

Petrels  are  the  most  aerial  and  oceanic  of  birds,  yet 
in  the  quiet  Sounds  of  Tierra  del  Fuego,  the  Puffinuria 
berardi,  in  its  general  habits,  in  its  astonishing  power  of 
diving,  its  manner  of  swimming,  and  of  flying  when  un- 
willingly it  takes  flight,  would  be  mistaken  by  any  one 
for   an  auk  or  grebe;    nevertheless,  it  is   essentially  a 


ji  (Jg  DIFFICULTIES    027   THEORY.  [Chip   VI, 

petrel,  but  witli  many  parts  of  its  organisation  profoundly 
modified.  On  the  other  hand,  the  acutest  observer  by 
examhiing  the  dead  body  of  the  water-ouzel  would  never 
have  suspected  its  sub-aquatic  habits  ;  yet  this  anomalous 
member  of  the  strictly  terrestrial  thrush  family  wholly 
subsists  by  diving, — grasping  the  stones  with  its  feet  and 
using  its  wings  under  water. 

He  who  believes  that  each  being  has  been  created  as 
we  now  see  it,  must  occasionally  have  felt  surprised  when 
he  has  met  with  an  animal  having  habits  and  structure 
not  at  all  in  agreement.  What  can  be  plainer  than  that 
the  webbed  feet  of  ducks  and  geese  are  formed  for  swim- 
ming? yet  there  are  upland  geese  with  webbed  feet  which 
rarely  or  never  go  near  the  water ;  and  no  one  except 
Audubon  has  seen  the  frigate  bird,  which  has  all  its  four 
toes  webbed,  alight  on  the  surface  of  the  sea.  On  the 
other  hand,  grebes  and  coots  are  eminently  aquatic,  al- 
though their  toes  are  only  bordered  by  membrane.  What 
seems  plainer  than  that  the  long  toes  of  grallatores  are 
formed  for  walking  over  swamps  and  floating  plants,  yet 
the  water-hen  is  nearly  as  aquatic  as  the  coot ;  and  the 
landrail  nearly  as  terrestrial  as  the  quail  or  partridge.  In 
such  cases,  and  many  others  could  be  given,  habits  have 
changed  without  a  corresponding  change  of  structure. 
The  webbed  feet  of  the  upland  goose  may  be  said  to  have 
been  rudimentary  in  function,  though  not  in  structure. 
In  the  frigate-bird,  the  deeply  scooped  membrane  between 
the  toes  shows  that  structure  has  begun  to  change. 

He  who  believes  in  separate  and  innumerable  acts  of 
creation  will  say,  that  in  these  cases  it  has  pleased  the 
Creator  to  cause  a  being  of  one  type  to  take  the  place  of 
one  of  another  type  ;  but  this  seems  to  me  only  restating 
the  fact  in  dignified  language.  He  who  believes  in  the 
struggle  for  existence  and  in  the  principle  of  natural  se- 
lection, will  acknowledge  that  every  organic  being  is  con- 
stantly endeavouring  to  increase  in  numbers  ;  and  that  if 
any  one  being  vary  ever  so  little,  either  in  habits  or  struc- 
ture, and  thus  gain  an  advantage  over  some  other  inhab- 
itant of  the  country,  it  will  seize  on  the  place  of  that  in- 
habitant, however  difi'erent  it  may  be  from  its  own  place. 


Chap.  VL]     ORGANS  OF  EXTREME  PERFECTION 


167 


Hence  it  will  cause  him  no  surprise  that  there  should  be 
geese  and  frigate-birds  with  webbed  feet,  either  living  on 
the  dry  land  or  most  rarely  alighting  on  the  water  ;  that 
there  should  be  long-toed  corncrakes  living  in  meadows 
instead  of  in  swamps  ;  that  there  should  be  woodpeckers 
where  not  a  tree  grows;  that  there  should  be  diving 
thrushes,  and  petrels  with  the  habits  of  auks. 

Organs  of  extreme  perfection  and  complication. — To 
suppose  that  the  eye,  with  all  its  inimitable  contrivances 
for  adjusting  the  focus  to  different  distances,  for  admit- 
ing  different  amounts  of  light,  and  for  the  correction  of 
spherical  and  chromatic  aberration,  could  have  been 
formed  by  natural  selection,  seems,  I  freely  confess,  absurd 
in  the  highest  possible  degree.  Yet  reason  tells  me,  that 
if  numerous  gradations  from  a  perfect  and  complex  eye 
to  one  very  imperfect  and  simple,  each  grade  being  use- 
ful to  its  possessor,  can  be  shown  to  exist ;  if,  further,  the 
eye  does  vary  ever  so  slightly,  and  the  variations  be  in- 
herited, which  is  certainly  the  case  ;  and  if  any  variation 
or  modification  in  the  organ  be  ever  useful  to  an  animal 
under  clianging  conditions  of  life,  then  the  difficulty  of 
believing  that  a  perfect  and  complex  eye  could  be  formed 
by  natural  selection,  though  insuperable  by  our  imagina- 
tion, can  hardly  be  considered  real.  How  a  nerve  comes 
to  be  sensitive  to  light,  hardly  concerns  us  more  than  how 
life  itself  first  originated  ;  but  I  may  remark  that  several 
facts  make  me  suspect  that  any  sensitive  nerve  may  be 
rendered  sensitive  to  light,  and  likewise  to  those  coarser 
vibrations  of  the  air  which  produce  sound. 

In  looking  for  the  gradations  by  which  an  organ  in 
any  species  has  been  perfected,  we  ought  to  look  exclu- 
sively to  its  lineal  ancestors  ;  but  this  is  scarcely  ever 
possible,  and  we  are  forced  in  each  case  to  look  to  species 
of  the  same  group,  that  is  to  the  collateral  descendants 
from  the  same  original  parent-form,  in  order  to  see  what 
gradations  are  possible,  and  for  the  chance  of  some  gra- 
dations having  been  transmitted  from  the  earlier  stages 
of  descent,  in  an  unaltered  or  little  altered  condition. 
Amongst  existing  Yertebrata,  we  find  but  a  small  amount 


;[gg  DIFFICULTIES    ON    THEORY.  [Chap.  VI. 

of  gradation  in  tlie  structure  of  the  eye,  and  from  fossil 
species  we  can  learn  nothing  on  this  head.  In  this  great 
class  we  should  jjrobably  have  to  descend  far  beneath  the 
lowest  known  fossiliferons  stratum  to  discover  the  earlier 
stages,  bj  which  the  eye  has  been  perfected. 

In  the  Articulata  we  can  commence  a  series  with  an 
optic  nerve  merely  coated  with  pigment,  and  without  any 
other  mechanism ;  and  from  this  low  stage  numerous  gra- 
dations of  structure,  branchino;  off  in  two  fundamentally 
different  lines,  can  be  shown  to  exist,  until  we  reach  a 
moderately  high  stage  of  perfection.  In  certain  crusta- 
ceans, for  instance,  there  is  a  double  cornea,  the  inner  one 
divided  into  facets,  within  each  of  w^hich  there  is  a  lens- 
shaped  swelling.  In  other  crustaceans  the  transparent 
cones  which  are  coated  by  pigment,  and  which  properly 
act  only  by  excluding  lateral  pencils  of  light,  are  convex  at 
their  upper  ends  and  must  act  by  convergence ;  and  at 
their  lower  ends  there  seems  to  be  an  imperfect  vitreous 
substance.  With  these  facts,  here  far  too  briefly  and  im- 
perfectly given,  which  show  that  there  is  much  graduated 
diversity  in  the  eyes  of  living  crustaceans,  and  bearing  in 
mind  how  small  the  number  of  living  animals  is  in  pro- 
portion to  those  which  have  become  extinct,  I  can  see  no 
very  great  difficulty  (not  more  than  in  the  case  of  many 
other  structures)  in  believing  that  natural  selection  has 
converted  the  simple  aj)paratus  of  an  optic  nerve  merely 
coated  with  pigment  and  invested  by  transparent  mem- 
brane, into  an  optical  instrument  as  perfect  as  is  ]30ssessed 
by  any  member  of  the  great  Articulate  class. 

He  who  will  go  thus  far,  if  lie  finds  on  finishing  this 
treatise  that  large  bodies  of  facts,  otherwise  inexplicable, 
can  be  explained  by  the  theory  of  descent,  ought  not  to 
hesitate  to  go  further,  and  to  admit  that  a  structure  even 
as  perfect  as  the  eye  of  an  eagle  might  be  formed  by  na- 
tural selection,  although  in  this  case  he  does  not  know  any 
of  the  transitional  grades.  His  reason  ought  to  conquer 
his  imagination ;  though  I  have  felt  the  difficulty  far  too 
keenly  to  be  surprised  at  any  degree  of  hesitation  in  ex- 
tending the  principle  of  natural  selection  to  such  startling 
lengths. 


Chap.  VI.]     ORGANS  OF  EXTREME  PERFECTION".         IQQ 

It  is  scarcely  possible  to  avoid  comparing  the  eye  to 
a  telescope.  Ave  know  that  this  instrument  has  been 
perfected  by  the  long-continued  efforts  of  the  highest  hu- 
man intellects ;  and  we  naturally  infer  that  the  eye  has 
been  formed  by  a  somewhat  analogous  process.  But  may 
not  this  inferejice  be  presumptuous  ?  Have  we  any  right 
to  assume  that  the  Creator  works  by  intellectual  powers 
like  those  of  man  ?  K  we  must  compare  the  eye  to  an 
optical  instrument,  we  ought  in  imagination  to  take  a 
thick  layer  of  transparent  tissue,  with  a  nerve  sensitive  to 
light  beneath,  and  then  suppose  every  part  of  this  layer 
to  be  continually  changing  slowly  in  density,  so  as  to 
separate  into  layers  of  different  densities  and  thicknesses, 
placed  at  diflerent  distances  from  each  other,  and  with  the 
surfaces  of  each  layer  slowly  changing  in  form.  Further 
we  must  suppose  tHat  there  is  a  power  always  intently 
watching  each  slight  accidental  alteration  in  the  trans- 
parent layers ;  and  carefully  selecting  each  alteration 
which,  under  varied  circumstances,  may  in  any  way,  or 
in  any  degree,  tend  to  produce  a  distincter  image.  We 
must  suppose  each  new  state  of  the  instrument  to  be  mul- 
tiplied by  the  million ;  and  each  to  be  preserved  till  a 
better  be  produced,  and  then  the  old  ones  to  be  destroyed. 
In  livmg  bodies,  variation  will  cause  the  slight  alterations, 
generation  will  multiply  them  almost  infinitely,  and  na- 
tural selection  will  pick  out  with  unerring  skill  each  im- 
provement. Let  this  process  go  on  for  millions  on  mil- 
lions of  years  ;  and  during  each  year  on  millions  of  indi- 
viduals of  many  kinds ;  and  may  we  not  believe  that  a 
living  optical  instrument  might  thus  be  formed  as  superior 
to  one  of  glass,  as  the  works  of  the  Creator  are  to  those  of 
man  ? 

^  If  it  could  be  demonstrated  that  any  complex  organ 
existed,  which  could  not  possibly  have  been  formed  by 
numerous,  successive,  slight  modifications,  my  theory 
would  absolutely  break  down.  But  I  can  find  out  no 
such  case.  JN'o  doubt  many  organs  exist  of  which  we  do 
not  know  the  transitional  grades,  more  especially  if  we 
look  to  much-isolated  species,  round  which,  according  to 
ray  theory,  there  has  been  much  extinction.     Or  again,  if 


^>JQ  DIFFICULTIES    ON   THEORY.  [Chap.  VI. 

we  look  to  an  organ  common  to  all  tlie  members  of  a 
large  class,  for  in  this  latter  case  the  organ  mnst  have 
been  first  formed  at  an  extremely  remote  period,  since 
which  all  the  many  members  of  the  class  have  been  de- 
veloped ;  and  in  order  to  discover  the  early  transitional 
grades  through  which  the  organ  has  passed,  we  should 
have  to  look  to  very  ancient  ancestral  forms,  long  since 
become  extinct. 

We  should  be  extremely  cautious  in  concluding  that  an 
organ  could  not  have  been  formed  by  transitional  grada- 
tions of  some  kind.  ISTumerous  cases  could  be  given 
amongst  the  lower  animals  of  the  same  organ  perform- 
ing at  the  same  time  wholly  distinct  functions  ;  thus  the 
alimentary  canal  respires,  digests,  and  excretes  in  the 
larva  of  the  dragon-fly  and  in  the  fish  Cobites.  In  the 
Hydra,  the  animal  may  be  turned  in^de  out,  and  the  ex- 
terior surface  will  then  digest  and  the  stomach  respire. 
In  such  cases  natural  selection  might  easily  specialise,  if 
any  advantage  were  thus  gained,  a  part  or  organ,  which 
had  performed  two  functions,  for  one  function  alone,  and 
thus  wholly  change  its  nature  by  insensible  steps.  Two 
distinct  organs  sometimes  perform  simultaneously  the 
same  function  in  the  same  individual ;  to  give  one  in- 
stance, there  are  fish  with  gills  or  branchiae  that  breathe 
the  air  dissolved  in  the  water,  at  the  same  time  that  they 
breathe  free  air  in  their  swimbladders,  this  latter  organ 
having  a  ductus  pneumaticus  for  its  supply,  and  being 
divided  by  highly  vascular  partitions.  In  these  cases,  one 
of  the  two  organs  might  with  ease  be  modified  and  per- 
fected so  as  to  perform  all  the  work  by  itself,  being  aided 
during  the  process  of  modification  by  the  other  organ ; 
and  then  this  other  organ  might  be  modified  for  some 
other  and  quite  distinct  purpose,  or  be  quite  obliterated. 

The  illustration  of  the  swimbladder  in  fishes  is  a  good 
one,  because  it  shows  us  clearly  the  highly  important  fact 
that  an  organ  originally  constructed  for  one  purpose, 
namely  flotation,  may  be  converted  into  one  for  a  wholly 
diflerent  purpose,  namely,  respiration.  The  swimbladder 
has,  also,  been  worked  in  as  an  accessory  to  the  auditory 
organs  of  certain  fish,  or,  for  I  do  not  know  which  view 


Chap.  VI.]  TRANSITIONS    OF    ORGANS.  2Y1 

is  now  generally  held,  a  part  of  the  auditory  apparatus 
has  been  worked  in  as  a  complement  to  the  swiinbladder. 
All  physiologists  admit  that  the  swimbladder  is  homolo- 
gons,  or  "  ideally  similar,"  in  position  and  structure  with 
the  lungs  of  the  higher  vertebrate  animals  :  hence  there 
seems  to  me  to  be  no  great  difficulty  in  believing  that 
natural  selection  has  actually  converted  a  swimbladdei 
into  a  lung,  or  organ  used  exclusively  for  respiration. 

I  can,  indeed,  hardly  doubt  that  all  vertebrate  ani- 
mals having  true  lungs  have  descended  by  ordinary  gen- 
eration from  an  ancient  prototype,  of  which  we  know 
nothing,  furnished  with  a  floating  apparatus  or  swim- 
bladder.  We  can  thus,  as  I  infer  from  Professor  Owen's 
interesting  description  of  these  parts,  understand  the 
strange  fact  that  every  particle  of  food  and  drink  which 
we  swallow  has  to  pass  over  the  orifice  of  the  trachea, 
with  some  risk  of  falling  into  the  lungs,  notwithstanding 
the  beautiful  contrivance  by  which  the  glottis  is  closeo. 
In  the  higher  Yertebrata  the  branchiae  have  Avholly  disap- 
peared— the  slits  on  the  sides  of  the  neck  and  the  loop-like 
course  of  the  arteries  still  marking  in  the  embryo  their 
former  position.  But  it  is  conceivable  that  the  now  ut- 
terly lost  branchise  might  have  been  gradually  worked  in 
by  natural  selection  for  some  quite  distinct  purpose :  in 
the  same  manner  as,  on  the  view  entertained  by  some 
naturalists  that  the  branchiae  and  dorsal  scales  of  Annelids 
are  homologous  with  the  wings  and  wing-covers  of  insects, 
it  is  ^^robable  that  organs  which  at  a  very  ancient  period 
served  for  respiration  have  been  actually  converted  into 
organs  of  flight. 

In  considering  transitions  of  organs,  it  is  so  important 
to  bear  in  mind  the  probability  of  conversion  from  one 
function  to  another,  that  I  will  give  one  more  instance. 
Pedunculated  cirripedes  have  two  minute  folds  of  skin, 
called  by  me  the  ovigerous  frena,  which  serve,  through 
the  means  of  a  sticky  secretion,  to  retain  the  eggs  until 
they  are  hatched  within  the  sack.  These  cirripedes  have 
no  branchiae,  the  whole  surface  of  the  body  and  sack,  in- 
cluding the  small  frena,  serving  for  respiration.  The 
Balanidge  or  sessile  cirripedes,  on  the  other  hand,  have  no 


j['^2  DIFFICULTIES    ON   THEORY.  [Chap.  VI. 

ovigeroiis  frena,  the  eggs  lying  loose  at  the  bottom  of  the 
sack,  in  the  well-enclosed  shell ;  but  they  have  large 
folded  branchiae.  IS^ow  I  think  no  one  will  dispute  that 
the  ovigerous  frena  in  the  one  family  are  strictly  homolo- 
gous with  the  branchiae  of  the  other  family ;  •  indeed,  they 
graduate  into  each  other.  Therefore  I  do  not  doubt  that 
little  folds  of  skin,  which  originally  served  as  ovigerous 
frena,  but  which,  likewise,  very  slightly  aided  the  act  of 
respiration,  have  been  gradually  converted  by  natural  se- 
lection into  branchiae,  simply  through  an  increase  in  their 
size  and  the  obliteration  of  their  adhesive  glands.  If  all 
pedunculated  cirripedes  had  become  extinct,  and  they 
have  already  suffered  far  more  extinction  than  have  sessile 
cirripedes,  who  would  ever  have  imagined  that  the  branchiae 
in  this  latter  family  had  originally  existed  as  organs  for 
preventing  the  ova  from  being  washed  out  of  the  sack  ? 

Although  we  must  be  extremely  cautious  in  con- 
cluding that  any  organ  could  not  possibly  have  been  pro- 
duced by  successive  transitional  gradations,  yet,  un- 
doubtedly, grave  cases  of  difficulty  occur,  some  of  which 
will  be  discussed  in  my  future  work. 

One  of  the  gravest  is  that  of  neuter  insects,  which  are 
often  very  differently  constructed  from  either  the  males 
or  fertile  females ;  but  this  case  will  be  treated  of  in  the 
next  chapter.  The  electric  organs  of  fishes  offer  another 
case  of  special  difficulty  ;  it  is  impossible  to  conceive  by 
what  steps  these  wondrous  organs  have  been  produced ; 
but  as  Owen  and  others  have  remarked,  their  intimate 
structure  closely  resembles  that  of  common  muscle ;  and 
as  it  has  lately  been  shown  that  Kays  have  an  organ 
closely  analogous  to  the  electric  apparatus,  and  yet  do 
not,  as  Matteucci  asserts,  discharge  any  electricity,  we 
must  own  that  we  are  far  too  ignorant  to  argue  that  no 
transition  of  any  kind  is  possible. 

The  electric  organs  offer  another  and  even  more  serious 
difficulty  ;  for  they  occur  in  only  about  a  dozen  fishes, 
of  which  several  are  widely  remote  in  their  affinities. 
Generally  when  the  same  organ  appears  in  several  mem- 
bers of  the  same  class,  especially  if  in  members  having 
very  different  habits  of  life,  we  may  attribute  its  presence 


Chap.  VI.]  TRANSITIONS   OF   ORGANS.  J^>^3 

to  inheritance  from  a  common  ancestor ;  and  its  absence 
in  some  of  the  members  to  its  loss  through  disuse  or  natu- 
ral selection.  But  if  the  electric  organs  had  been  inherited 
from  one  ancient  progenitor  thus  j)rovided,  we  might  have 
expected  that  all  electric  fishes  would  have  been  specially 
related  to  each  other.  Nor  does  geology  at  all  lead  to  the 
belief  that  formerly  most  fishes  had  electric  organs,  which 
most  of  their  modified  descendants  have  lost.  The  pres- 
ence of  luminous  organs  in  a  few  insects,  belonging  to 
difierent  families  and  orders,  ofi!*ers  a  parallel  case  of 
difiiculty.  Other  cases  could  be  given ;  for  instance  in 
plants,  the  very  curious  contrivance  of  a  mass  of  pollen- 
grains,  borne  on  a  foot-stalk  with  a  sticky  gland  at  the 
end,  is  the  same  in  Orchis  and  Asclepias, — genera  almost 
as  remote  as  possible  amongst  flowering  plants.  Li  all 
these  cases  of  two  very  distinct  species  furnished  with 
apparently  the  same  anomalous  organ,  it  should  be  ob- 
served that,  although  the  general  appearance  and  function 
of  the  organ  may  be  the  same,  yet  some  fundamental 
diflerence  can  generally  be  detected.  I  am  inclined  to 
believe  that  in  nearly  the  same  way  as  two  men  have 
sometimes  indei^endently  hit  on  the  very  same  invention, 
so  natural  selection,  working  for  the  good  of  each  being 
and  taking  advantage  of  analogous  variations,  has  some- 
times modified  in  very  nearly  the  same  manner  two  parts 
in  two  organic  beings,  which  owe  but  little  of  their  struc- 
tm*e  in  common  to  inheritance  from  the  same  ancestor. 

Although  in  many  cases  it  is  most  difficult  to  conjecture 
by  what  transitions  an  organ  could  have  arrived  at  its 
present  state  ;  yet,  considering  that  the  proportion  of  liv- 
ing and  known  forms  to  the  extinct  and  unknown  is  very 
small,  I  have  been  astonished  how  rarely  an  organ  can  be 
named,  towards  which  no  transitional  grade  is  known  to 
lead.  The  truth  of  this  remark  is  indeed  shown  by  that 
old  canon  in  natural  history  of  "  l^atura  non  facit  saltum." 
We  meet  with  tliis  admission  in  the  writings  of  almost 
every  experienced  naturalist ;  or,  as  Milne  Edwards  has 
well  expressed  it,  nature  is  prodigal  in  variety,  but  niggard 
in  innovation.  Why,  on  the  theory  of  Creation,  should 
this  be  so  ?     Why  should  all  the  parts  and  organs  of  many 


][Y4:  DIFFICULTIES   OK   THEORY.  [Chap.  Vt 

independent  beings,  each,  supposed  to  have  been  separate- 
ly created  for  its  proper  place  in  nature,  be  so  invariably 
linked  together  by  graduated  steps?  Why  should  not 
ISTature  have  taken  a  leap  from  structure  to  structure  ? 
On  the  theory  of  natural  selection,  Tve  can  clearly  under- 
stand why  she  should  not ;  for  natural  selection  can  act 
only  by  taking  advantage  of  slight  successive  variations  ; 
she  can  never  take  a  leap,  but  must  advance  by  the  short- 
est and  slowest  steps. 

Organs  of  little  wpparent  importance. — As  natural  se- 
lection acts  by  life  and  death, — by  the  preservation  of 
individuals  with  any  favorable  variation,  and  by  the  de- 
struction of  those  with  any  unfavorable  deviation  of 
structure, — I  have  sometimes  felt  much  difficulty  in  un- 
derstanding the  origin  of  simple  parts,  of  which  the  im- 
portance does  not  seem  sufficient  to  cause  the  preservation 
of  successively  varying  individuals.  I  have  sometimes 
felt  as  much  difficulty,  though  of  a  very  different  kind,  on 
this  head,  as  in  the  case  of  an  organ  as  perfect  and  com- 
plex as  the  eye. 

In  the  first  place,  we  are  much  too  ignorant  in  regard 
to  the  wliole  economy  of  any  one  organic  being,  to  say 
what  slight  modifications  would  be  of  importance  or  not. 
In  a  former  chapter  I  have  given  instances  of  most  trifling 
characters,  such  as  the  down  on  fruit  and  the  colour  of  the , 
flesh,  which,  from  determining  the  attacks  of  insects  or 
from  being  correlated  with  constitutional  differences,  might 
assuredly  be  acted  on  by  natural  selection.  The  tail  of 
the  giraffe  looks  like  an  artificially  constructed  fly-flapper ; 
and  it  seems  at  first  incredible  that  this  could  have  been 
adapted  for  its  present  purpose  by  successive  slight  modi- 
fications, each  better  and  better,  for  so  trifiing  an  object 
as  driving  away  flies  ;  yet  we  should  pause  before  being 
too  positive  even  in  this  case,  for  we  know  that  the  distri- 
bution and  existence  of  cattle  and  other  animals  in  South 
America  absolutely  depends  on  their  power  of  resisting 
the  attacks  of  insects :  so  that  individuals  which  could  by 
any  means  defend  tliemselves  from  these  small  enemies, 
would  be  able  to  range  into  new  pastures  and  thus  gain  a 


Chap.  VI.  1  ORGANS   OF   LITTLE    IMPORTANCE. 


175 


great  advantage.  It  is  not  tliat  tlie  larger  quadrupeds  are 
actually  destroyed  (except  in  some  rare  cases)  by  the  flies, 
but  they  are  incessantly  harassed  and  their  strength  re- 
duced, so  that  they  are  more  subject  to  disease,  or  not  so 
well  enabled  in  a  coming  dearth  to  search  for  food,  or  to 
escape  from  beasts  of  prey. 

Organs  now  of  trifling  importance  have  probably  in 
some  cases  been  of  high  importance  to  an  early  progenitor, 
and,  after  having  been  slowly  perfected  at  a  former  period, 
have  been  transmitted  in  nearly  the  same  state,  although 
now  become  of  very  slight  use ;  and  any  actually  inju- 
rious deviations  in  their  structures  will  always  have  been 
checked  by  natural  selection.  Seeing  how  important  an 
organ  of  locomotion  the  tail  is  in  most  aquatic  animals, 
its  general  presence  and  use  for  many  purposes  in  so 
many  land  animals,  which  in  their  lungs  or  modified 
swimbladders  betray  their  aquatic  origin,  may  perhaps  be 
thus  accounted  for,  A  well-developed  tail  having  been 
formed  in  an  aquatic  animal,  it  might  subsequently  come 
to  be  worked  in  for  all  sorts  of  purposes,  as  a  fl^^-flapper, 
an  organ  of  prehension,  or  as  an  aid  in  turning,  as  with 
the  dog,  though  the  aid  must  be  slight,  for  the  hare,  with 
hardly  any  tail,  can  double  quickly  enough. 

In  the  second  place,  we  may  sometimes  attribute  im- 
portance to  characters  which  are  really  of  very  little  im- 
portance, and  which  have  originated  from  quite  secondary 
causes,  independently  of  natural  selection.  We  should 
remember  that  climate,  food,  &c.,  probably  have  some 
little  direct  influence  on  the  organisation ;  that  characters 
reappear  from  the  law  of  reversion  ;  tliat  correlation  of 
growth  will  have  had  a  most  important  influence  in  mod- 
ifying various  structures ;  and,  finally,  tliat  sexual  selection 
will  often  have  largely  modified  the  external  characters 
of  animals  having  a  will,  to  give  one  male  an  advantage 
in  fighting  with  another  or  in  charming  the  females. 
Moreover  when  a  modification  of  structure  has  primarily 
arisen  from  the  above  or  other  unknown  causes,  it  may  at 
first  have  been  of  no  advantage  to  the  species,  but  may 
subsequently  have  been  taken  advantage  of  by  the  de- 
scendants of  the  species  under  new  conditions  of  life  and 
with  newly  acquired  habits. 


l^^Q  DIFFICULTIES    ON    THEORY.  [Chap.  VI. 

To  give  a  few  instances  to  illustrate  these  latter  re- 
marks. If  green  woodpeckers  alone  had  existed,  and  we 
did  not  know  that  there  were  many  black  and  pied  kinds^ 
I  dare  say  that  we  should  have  thought  that  the  green 
colour  was  a  beautiful  adaptation  to  hide  this  tree-frequent- 
ing bird  from  its  enemies  ;  and  consequently  that  it  was 
a  character  of  importance  and  might  have  been  acquired 
through  natural  selection  ;  as  it  is,  I  have  no  doubt  that 
the  colour  is  due  to  some  quite  distinct  cause,  probably  to 
sexual  selection.  A  trailing  bamboo  in  the  Malay  Ar- 
chipelago climbs  the  loftiest  trees  by  the  aid  of  exquisitely 
constructed  hooks  clustered  around  the  ends  of  the  branch- 
es, and  this  contrivance,  no  doubt,  is  of  the  highest  service 
to  the  plant ;  but  as  we  see  nearly  similar  hooks  on  many 
trees  which  are  not  climbers,  the  hooks  on  the  bamboo 
may  have  arisen  from  unknown  laws  of  growth,  and  have 
been  subsequently  taken  advantage  of  by  the  plant  under- 
going further  modification  and  becoming  a  climber.  The 
naked  skin  on  the  head  of  a  vulture  is  generally  looked 
at  as  a  direct  adaptation  for  wallowing  in  putridity  ;  and 
so  it  may  be,  or  it  may  possibly  be  due  to  the  direct  action 
of  putrid  matter ;  but  we  should  be  very  cautious  in  draw- 
ing any  such  inference,  when  we  see  that  the  skin  on  the 
head  of  the  clean-feeding  male  turkey  is  likewise  naked. 
The  sutures  in  the  skulls  of  young  mammals  have  been 
advanced  as  a  beautiful  adaptation  for  aiding  parturition, 
and  no  doubt  they  facilitate,  or  may  be  indispensable  for 
this  act ;  but  as  sutures  occur  in  the  skulls  of  young  birds 
and  reptiles,  which  have  only  to  escape  from  a  broken 
egg,  we  may  infer  that  this  structure  has  arisen  from  the 
laws  of  growth,  and  has  been  taken  advantage  of  in  the 
parturition  of  the  higher  animals. 

We  are  profoundly  ignorant  of  the  causes  producing 
slight  and  unimportant  variations  ;  and  we  are  imme- 
diately made  conscious  of  this  by  reflecting  on  the  diifer- 
ence  in  the  breeds  of  our  domesticated  animals  in  diflerent 
countries, — more  especially  in  the  less  civilized  comitries 
where  there  has  been  but  little  artificial  selection.  Care- 
ful observers  are  convinced  that  a  damp  climate  aflects 
the  growth  of  the  hair,  and  that  with  the  hair  the  horns 


Chap.  VI.]  ORGANS   OF   LITTLE   IMPORTANCE.  ]_Y7 

are  correlated.  Mountain  breeds  always  differ  from  low- 
land breeds  ;  and  a  mountainous  country  would  probably 
affect  the  hind  limbs  from  exercising  them  more,  and 
possibly  even  the  form  of  the  pelvis ;  and  then  by  the 
law  of  homologous  variation,  the  front  limbs  and  even  the 
head  would  probably  be  affected.  The  shape,  also,  of  the 
pelvis  might  affect  by  pressure  the  shape  of  the  head  of 
the  young  in  the  womb.  The  laborious  breathing  neces- 
sary in  high  regions  would,  we  have  some  reason  to  be- 
lieve, increase  the  size  of  the  chest ;  and  again  correlation 
would  come  into  play.  Animals  kept  by  savages  in  dif- 
ferent countries  often  have  to  struggle  for  their  own  sub- 
sistence, and  would  be  exposed  to  a  certain  extent  to 
natural  selection,  and  individuals  with  slightly  different 
constitutions  would  succeed  best  under  different  climates ' 
and  there  is  reason  to  believe  that  constitution  and  coloui 
are  correlated.  A  good  observer,  also,  states  that  in 
cattle  susceptibility  to  the  attacks  of  flies  is  correlated 
with  colour,  as  is  the  liability  to  be  poisoned  by  certain 
plants;  so  that  colour  would  be  thus  subjected  to  the 
action  of  natural  selection.  But  we  are  far  too  ignorant 
to  speculate  on  the  relative  importance  of  the  several 
known  and  unknown  laws  of  variation  ;  and  I  have  here 
alluded  to  them  only  to  show  that,  if  we  are  unable  to 
account  for  the  characteristic  differences  of  our  domestic 
breeds,  which  nevertheless  we  generally  admit  to  have 
arisen  through  ordinary  generation,  we  ought  not  to  lay 
too  much  stress  on  our  ignorance  of  the  precise  cause  of 
the  slight  analogous  differences  between  species.  I  might 
have  adduced  for  this  same  purpose  the  differences  be- 
tween the  races  of  man,  which  are  so  strongly  marked  ;  I 
may  add  that  some  little  light  can  apparently  be  thrown 
on  the  origin  of  these  differences,  chiefly  through  sexual 
selection  of  a  particular  kind,  but  without  here  entering 
on  copious  details  my  reasoning  would  appear  frivolous. 

The  foregoing  remarks  lead  me  to  say  a  few  words  on 
the  protest  lately  made  by  some  naturalists,  against  the 
utilitarian  doctrine  that  every  detail  of  structure  has  been 
produced  for  the  good  of  its  possessor.  They  believe  that 
very  many  structures  have  been  created  for  beauty  in  the 


j^Y8  DIFFICULTIES   ON   THEORY  [CnAP.  VL 

eyes  of  man,  or  for  mere  variety.  This  doctrine,  if  true, 
would  be  absolutely  fatal  to  my  tbeory.  Yet  I  fully  ad- 
mit that  many  structures  are  of  no  direct  use  to  their  j)os- 
sessors.  Physical  conditions  probably  have  had  some 
little  effect  on  structure,  quite  independently  of  any  good 
thus  gained.  Correlation  of  growth  has  no  doubt  played 
a  most  important  part,  and  a  useful  modification  of  one 
part  will  often  have  entailed  on  other  parts  diversified 
changes  of  no  direct  use.  So  again  characters  which  for- 
merly were  useful,  or  which  formerly  had  arisen  from 
correlation  of  growth,  or  from  other  unknown  cause,  may 
reappear  from  the  law  of  reversion,  though  now  of  no 
du-ect  use.  The  effects  of  sexual  selection,  when  displayed 
in  beauty  to  charm  the  females,  can  be  called  useful  only 
in  rather  a  forced  sense.  But  by  far  the  most  important 
consideration  is  that  the  chief  part  of  the  organisation  of 
every  being  is  simply  due  to  inheritance ;  and  conse- 
quently, though  each  being  assuredly  is  well  fitted  for  its 
place  in  nature,  many  structures  now  have  no  direct  rela- 
tion to  the  habits  of  life  of  each  species.  Thus,  we  can 
hardly  believe  that  the  webbed  feet  of  the  upland  goose 
or  of  the  frigate-bird  are  of  special  use  to  these  birds  ;  we 
cannot  believe  that  the  same  bones  in  the  arm  of  the 
monkey,  in  the  fore  leg  of  the  horse,  in  the  wing  of  the 
bat,  and  in  the  flipper  of  the  seal,  are  of  special  use  to 
these  animals.  We  may  safely  attribute  these  structures 
to  inheritance.  But  to  the  progenitor  of  the  upland  goose 
and  of  the  frigate-bird,  webbed  feet  no  doubt  were  as  use- 
ful as  they  now  are  to  the  most  aquatic  of  existing  birds. 
So  we  may  believe  that  the  progenitor  of  the  seal  had  not 
a  flipper,  but  a  foot  with  five  toes  fitted  for  walking  or 
grasping ;  and  we  may  further  venture  to  believe  that  the 
several  bones  in  the  limbs  of  the  monkey,  horse,  and  bat, 
which  have  been  inherited  from  a  common  progenitor, 
were  formerly  of  more  special  use  to  that  progenitor,  or 
its  progenitors,  than  they  now  are  to  these  animals  having 
such  widely  diversified  habits.  Therefore  we  may  infer 
that  these  several  bones  might  have  been  acquired  through 
natural  selection,  subjected  formerly,  as  now,  to  the  sev- 
eral laws  of  inheritance,  reversion,  correlation  of  growth, 


Ohap.  VI.]  "WHAT   NATURAL   SELECTION    CAN   DO.  ^f^^ 

&c.  Hence  every  detail  of  structure  in  every  living 
creature  (making  some  little  allowance  for  the  direct 
action  of  physical  conditions)  may  be  viewed,  either  as 
having  been  of  special  nse  to  some  ancestral  form,  or  as 
being  now  of  special  use  to  the  descendants  of  this  foi'm 
— either  directly  or  indirectly  through  the  complex  laws 
of  growth, 

Natural  selection  cannot  possibly  produce  any  modifi- 
cation in  any  one  species  exclusively  for  the  good  of 
another  species ;  though  throughout  nature  one  species 
incessantly  takes  advantage  of,  and  profits  by,  the  struc- 
ture of  another.  But  natural  selection  can  and  does  often 
produce  structures  for  the  direct  injury  of  other  species, 
as  we  see  in  the  fang  of  the  adder,  and  in  the  ovipositor 
of  the  ichneumon,  by  which  its  eggs  are  deposited  in  the 
living  bodies  of  other  insects.  If  it  could  be  proved  that 
any  part  of  the  structure  of  any  one  species  had  been 
formed  for  the  exclusive  good  of  another  species,  it  would 
annihilate  my  theory,  for  such  could  not  have  been  pro- 
duced through  natural  selection.  Although  many  state- 
ments may  be  found  in  works  on  natural  history  to  this 
eifect,  I  cannot  find  even  one  which  seems  to  me  of  any 
weight.  It  is  admitted  that  the  rattlesnake  has  a  poison- 
fang  for  its  own  defence  and  for  the  destruction  of  its 
prey  ;  but  some  authors  suppose  that  at  the  same  time 
this  snake  is  furnished  with  a  rattle  for  its  own  injur}", 
namely,  to  warn  its  prey  to  escape.  I  would  almost  as 
60on  believe  that  the  cat  curls  the  end  of  its  tail  when 
preparing  to  spring,  in  order  to  warn  the  doomed  mouse. 
But  I  have  not  space  here  to  enter  on  this  and  other  such 
cases. 

Natural  selection  will  never  produce  in  a  being  any- 
thing injurious  to  itself,  for  natural  selection  acts  solely 
by  and  for  the  good  of  each.  No  organ  will  be  formed, 
as  Paley  has  remarked,  for  the  purpose  of  causing  pain  or 
for  doing  an  injury  to  its  possessor.  If  a  fair  balance  be 
struck  between  the  good  and  evil  caused  by  each  part, 
each  will  be  found  on  the  whole  advantageous.  After 
the  lapse  of  time,  under  changing  conditions  of  life,  if  any 
part  comes  to  be  injurious,  it  will  be  modified ;  or  if  it  be 
9 


j^gQ  DIFFICULTIES   ON    THEORY.  [Chap.  VI. 

not  SO,  the  being  will  become  extinct,  as  myi'iads  have  be- 
come extinct. 

E'atural  selection  tends  only  to  make  each  organic 
being  as  perfect  as,  or  slightly  more  perfect  than,  the 
other  inhabitants  of  the  same  country  with  which  it  has 
to  struggle  for  existence.  And  we  see  that  this  is  the 
degree  of  perfection  attained  nnder  nature.  The  endemic 
productions  of  I^ew  Zealand,  for  instance,  are  perfect  one 
compared  with  another  ;  but  they  are  now  rapidly  yield- 
ing before  the  advancing  legions  of  plants  and  animals 
introduced  from  Europe.  Natural  selection  will  not  pro- 
duce absolute  perfection,  nor  do  we  always  meet,  as  far 
as  we  can  judge,  with  this  high  standard  under  nature. 
The  correction  for  the  aberration  of  light  is  said,  on  high 
authority,  not  to  be  perfect  even  in  that  most  perfect 
organ,  the  eye.  If  our  reason  leads  us  to  admire  with 
enthusiasm  a  multitude  of  inimitable  contrivances  in 
nature,  this,  same  reason  tells  us,  though  we  may  easily 
err  on  both  sides,  that  some  other  contrivances  are  less 
perfect.  Can  we  consider  the  sting  of  the  wasp  or  of  the 
bee  as  perfect,  which,  when  used  against  many  attacking 
animals,  cannot  be  withdrawn,  owing  to  the  backward 
serratures,  and  so  inevitably  causes  the  death  of  the  insect 
by  tearing  out  its  viscera  ? 

If  we  look  at  the  sting  of  the  bee,  as  having  originally 
existed  in  a  remote  progenitor  as  a  boring  and  serrated 
instrument,  like  that  in  so.  many  members  of  the  same 
great  order,  and  which  has  been  modified  but  not  perfected 
for  its  present  purpose,  with  the  poison  originally  adapted 
to  cause  galls  subsequently  intensified,  we  can  perhaps 
understand  how  it  is  that  the  use  of  the  sting  should  so 
often  cause  the  insect's  own  death  :  for  if  on  the  whole  the 
power  of  stinging  be  useful  to  the  community,  it  will 
fulfil  all  the  requirements  of  natural  selection,  though  it 
may  cause  the  death  of  some  few  members.  K  we  admire 
the  truly  wonderful  power  of  scent  by  which  the  males 
of  many  insects  find  their  females,  can  we  admire  the 
production  for  this  single  purpose  of  thousands  of  drones, 
which  are  utterly  useless  to  the  community  for  any  other 
end,  and  which  are  ultimately  slaughtered  by  their  indus- 


Chap.  VI,]  .  SUMMARY.  JgJ_ 

trious  and  sterile  sisters?  It  may  be  difficult,  but  we 
ought  to  admire  the  savage  instinctive  hatred  of  the 
queen-bee,  which  urges  her  instantly  to  destroy  the  young 
queens  her  daughters  as  soon  as  born,  or  to  perish  herself 
in  the  combat ;  for  undoubtedly  this  is  for  the  good  of 
the  community  ;  and  maternal  love  or  maternal  hatred, 
though  the  latter  fortunately  is  most  rare,  is  all  the  same 
to  the  inexorable  principle  of  natural  selection.  If  we 
admire  the  several  ingenious  contrivances,  by  which  the 
flowers  of  the  orchis  and  of  many  other  plants  are  fertil- 
ised through  insect  agency,  can  we  consider  as  equally 
perfect  the  elaboration  by  our  fir-trees  of  dense  clouds  of 
pollen,  in  order  that  a  few  granules  may  be  wafted  by  a 
chance  breeze  on  to  the  ovules  ? 

Summary  of  Chapter. — We  have  in  this  chapter  dis- 
cussed some  of  the  difficulties  and  objections  which  may  be 
urged  against  my  theory.  Many  of  them  are  very  grave ; 
but, I  think  that  in  the  discussion  light  has  been  thrown 
on  several  facts,  which  on  the  theory  of  independent  acts 
of  creation  are  utterly  obscure.  We  have  seen  that  spe- 
cies at  any  one  period  are  not  indefinitely  variable,  and 
are  not  linked'  together  by  a  multitude  of  intermediate 
gradations,  partly  because  the  process  of  natural  selection 
will  always  be  very  slow,  and  will  act,  at  any  one  time, 
only  on  a  very  few  forms ;  and  partly  because  the  very 
process  of  natural  selection  almost  implies  the  continual 
supplanting  and  extinction  of  preceding  and  intermediate 
gradations.  Closely  allied  species,  now  living  on  a  con- 
tinuous area,  must  often  have  been  formed  when  the  area 
was  not  continuous,  and  when  the  conditions  of  life  did 
not  insensibly  graduate  away  from  one  part  to  another. 
When  two  varieties  are  formed  in  two  districts  of  a  con- 
tinuous area,  an  intermediate  variety  will  often  be  formed, 
fitted  for  an  intermediate  zone ;  but  from  reasons  assigned, 
the  intermediate  variety  will  usually  exist  in  lesser  num- 
bers than  the  two  forms  which  it  connects  ;  consequently 
the  two  latter,  during  the  course  of  further  modification, 
from  existing  in  greater  numbers,  will  have  a  great  ad- 
vantage over  the  less  numerous  intermediate  variety,  and 


J^g2  DIFFICULTIES    OX   THEORY.  [Chap.  VI 

will  thus  generally  succeed  in  supplanting  and  exterminat- 
ing it. 

We  have  seen  in  tliis  chapter  ho"w  cautious  we  should 
he  in  concluding  that  the  most  different  habits  of  life  could 
not  graduate  into  each  other ;  that  a  hat,  for  instance, 
could  not  have  been  formed  by  natural  selection  from  an 
animal  which  at  first  could  only  glide  through  the  air. 

We  have  seen  that  a  species  may  under  new  condi- 
tions of  life  change  its  habits,  or  have  diversified  habits, 
with  some  habits  very  unlike  those  of  its  nearest  con- 
geners. Hence  we  can  understand,  bearing  in  mind  that 
each  organic  being  is  trying  to  live  wherever  it  can  live, 
how  it  has  arisen  that  there  are  upland  geese  with  webbed 
feet,  ground  woodpeckers,  diving  thrushes,  and  petrels 
with  the  habits  of  auks. 

Although  the  belief  that  an  organ  so  perfect  as  the 
eye  could  have  been  formed  by  natural  selection,  is  more 
than  enough  to  stagger  any  one ;  yet  in  the  case  of  any 
organ,  if  we  know  of  a  long  series  of  gradations  in  com- 
plexity, each  good  for  its  possessor,  then,  under  changing 
conditions  of  life,  there  is  no  logical  impossibility  in  the 
acquirement  of  any  conceivable  degree  of  perfection 
through  natural  selection.  In  the  cases  in  "which  we  know 
of  no  intermediate  or  transitional  states,  we  should  be 
very  cautious  in  concludmg  that  none  could  have  existed, 
for  the  homologies  of  many  organs  and  their  intermediate 
estates  show  that  wonderful  metamorj)hoses  in  function  are 
at  least  possible.  For  instance,  a  swimbladder  has  ap- 
parently been  converted  into  an  air-breathing  lung.  The 
same  organ  having  performed  simultaneously  very  different 
functions,  and  then  having  been  specialised  for  one  func- 
tion ;  and  two  very  distinct  organs  having  performed  at 
the  same  time  the  same  function,  the  one  having  been 
perfected  whilst  aided  by  the  other,  must  often  have 
largely  facilitated  transitions. 

We  are  far  too  ignorant,  in  almost  every  case,  to  be 
enabled  to  assert  that  any  part  or  organ  is  so  unimportant 
for  the  welfare  of  a  species,  that  modifications  in  its  struc- 
ture could  not  have  been  slowly  accumulated  by  means 
of  natural  selection,     But  we  may  confidently  believe 


OnAP.  VI.l  SUMMARY.  183 

that  many  modifications,  wholly  due  to  the  laws  of 
growth,  and  at  first  in  no  way  advantageous  to  a  species, 
have  been  subsequently  taken  advantage  of  by  the  still 
further  modified  descendants  of  this  species.  We  may, 
also,  believe  that  a  part  formerly  of  high  importance  has 
often  been  retained  (as  the  tail  of  an  aquatic  animal  by 
its  terrestrial  descendants),  though  it  has  become  of  such 
small  importance  that  it  could  not,  in  its  present  state, 
have  been  acquired  by  natural  selection, — a  power  which 
acts  solely  by  the  preservation  of  profitable  variations  in 
the  struggle  for  life. 

JS^atural  selection  will  ^^I'oduce  nothing  in  one  species 
for  the  exclusive  good  or  injury  of  another ;  though  it 
may  well  produce  parts,  organs,  and  excretions  highly 
useful  or  even  indispensable,  or  highly  injurious  to  another 
species,  but  in  all  cases  at  the  same  time  useful  to  the 
owner.  ISTatural  selection  in  each  well-stocked  country, 
must  act  chiefiy  through  the  comj)etition  of  the  inhabit- 
ants one  with  another,  and  consequently  will  produce  per- 
fection, or  strength  in  the  battle  for  life,  only  according 
to  the  standard  of  that  country.  Hence  the  inhabitants 
of  one  country,  generally  the  smaller  one,  will  often  yield, 
as  we  see  they  do  yield,  to  the  inhabitants  of  another  and 
generally  larger  country.  For  in  the  larger  country  there 
will  have  existed  more  individuals,  and  more  diversified 
forms,  and  the  competition  will  have  been  severer,  and  thus 
the  standard  of  perfection  will  have  been  rendered  higher. 
E'atural  selection  will  not  necessarily  produce  absolute 
perfection ;  nor,  as  far  as  we  can  judge  by  our  limited 
faculties,  can  absolute  perfection  be  everywhere  found. 

On  the  theory  of  natural  selection  we  can  clearly 
understand  the  full  meaning  of  that  old  canon  in  natural 
history,  "  Katura  non  facit  saltum."  This  canon,  if  we 
look  only  to  the  present  inhabitants  of  the  world,  is  not 
strictly  correct,  but  if  we  include  all  those  of  past  times, 
it  must  by  my  theory  be  strictly  true. 

It  is  generally  acknowleged  that  all  organic  beings 
have  been  formed  on  two  great  laws — Unity  of  Type,  and 
the  Conditions  of  Existence.  By  unity  of  type  is  meant 
that  fundamental  agreement  in  structure,  which  we  see  in 


■j^g^  DIFFICULTIES   ON   THEORY.  [Chap.  VI. 

organic  beings  of  tlie  same  class,  and  wliicli  is  quite  inde- 
pendent of  their  habits  of  life.  On  my  theory,  imity  of 
type  is  explained  by  nnity  of  descent.  The  expression 
of  conditions  of  existence,  so  often  insisted  on  by  the 
ilhistrious  Cuvier,  is  fully  embraced  by  the  principle  of 
natural  selection.  For  natural  selection  acts  by  either 
now  adapting  the  varying  parts  of  each  being  to  its 
organic  and  inorganic  conditions  of  life ;  or  by  having 
adapted  them  dui-ing  long-past  periods  of  time :  the 
adaptations  being  aided  in  some  cases  by  use  and  disuse, 
being  slightly  aflected  by  the  direct  action  of  the  external 
conditions  of  life,  and  being  in  all  cases  subjected  to  the 
several  laws  of  growth.  Hence,  in  fact,  the  law  of  the 
Conditions  of  Existence  is  the  higher  law  ;  as  it  includes, 
through  the  inheritance  of  former  adaptations,  that  of 
Unity  of  Type. 


Chip.  VII.]  INSTINCT.  185 


CHAPTER    VII. 

INSTINCT. 

Instiricts  comparable  with  habits,  but  different  in  their  origin— Instincts  graduated— 
Aphides  and  ants— Instincta  variable— Domestic  instincts,  their  origin— Natural 
instincts  of  the  cuckoo,  ostrich,  and  parasitic  bees — Slave-making  ants — Hive-bee, 
its  cell-making  instinct— Difficulties  on  the  theory  of  the  Natural  Selection  of 
instincts — Neuter  or  sterile  insects — Summary. 

The  subject  of  instinct  miglit  liave  been  worked  into  the 
previous  chapters  ;  but  I  have  thought  that  it  would  be 
more  convenient  to  treat  the  subject  separately,  especially 
as  so  wonderful  an  instinct  as  that  of  the  hive-bee  making 
its  cells  will  probably  have  occurred  to  many  readers,  as 
a  difficulty  sufficient  to  overthrow  my  whole  theory.  I 
must  premise,  that  I  have  nothing  to  do  with  the  origin 
of  the  primary  mental  powers,  any  more  than  I  have  with 
that  of  life  itself.  We  are  concerned  only  with  the  diver- 
sities of  instinct  and  of  the  other  mental  qualities  of  ani- 
mals within  the  same  class. 

I  will  not  attempt  any  definition  of  instinct.  It  would 
be  easy  to  show  that  several  distinct  mental  actions  are 
commonly  embraced  by  this  term  ;  but  every  one  under- 
stands what  is  meant,  when  it  is  said  that  instinct  impels 
the  cuckoo  to  migrate  and  to  lay  her  eggs  in  other  birds' 
nests.  An  action,  which  w^e  ourselves  should  require 
experience  to  enable  us  to  perform,  when  performed  by 
an  animal,  more  especially  by  a  very  young  one,  without 
any  experience,  and  when  performed  by  many  individuals 
in  the  same  way,  without  their  knowing  for  what  purpose 
it  is  performed,  is  usually  said  to  be  instinctive.  But  I 
could  show  that  none  of  these  characters  of  instinct  are 
universal.  A  little  dose,  as  Pierre  Huber  expresses  it,  of 
judgment  or  reason,  often  comes  into  play,  even  in  animals 
very  low  in  the  scale  of  nature. 


•j^gg  IITSTIl^CT.  [Chap.  VII 

Frederick  Cuvier  and  several  of  the  older  metaphysi- 
cians have  compared  instinct  with  habit.  This  compar- 
ison gives,  I  think,  a  remarkably  accurate  notion  of  the 
frame  of  mind  under  which  an  instinctive  action  is  per- 
formed, but  not  of  its  origin.  How  unconsciously  many 
habitual  actions  are  performed,  indeed  not  rarely  in  direct 
opposition  to  our  conscious  will !  yet  they  may  be  modi- 
fied by  the  will  or  reason.  Habits  easily  become  associ- 
ated with  other  habits,  and  with  certain  periods  of  time 
and  states  of  the  body.  When  once  acquired,  they  often 
remain  constant  throughout  life.  Several  other  points  of 
resemblance  between  instincts  and  habits  could  be  pointed 
out.  As  in  repeating  a  well-known  song,  so  in  instincts, 
one  action  follows  another  by  a  sort  of  rhythm ;  if  a  person 
be  interrupted  in  a  song,  or  in  repeating  anything  by  rote, 
he  is  generally  forced  to  go  back  to  recover  the  habitual 
train  of  thought  :  so  P.  Huber  found  it  was  Avith  a  cater- 
pillar, which  makes  a  very  complicated  hammock  ;  for  if 
he  took  a  caterpillar  which  had  completed  its  hammock 
up  to,  say,  the  sixth  stage  of  constniction,  and  j)ut  it  into 
a  hammock  completed  up  only  to  the  third  stage,  the  cat- 
erpillar simply  re-performed  the  fourth,  fifth,  and  sixth 
stages  of  construction.  If,  however,  a  caterpillar  were 
taken  out  of  a  hammock  made  up,  for  instance,  to  the 
third  stage,  and  were  put  into  one  finished  up  to  the  sixth 
stage,  so  that  much  of  its  work  was  already  done  for  it, 
far  from  feeling  the  benefit  of  this,  it  was  much  embar- 
rassed, and,  in  order  to  complete  its  hammock,  seemed 
forced  to  start  from  the  third  stage,  where  it  had  left  ofi", 
and  thus  tried  to  complete  the  already  finished  work. 

If  we  suppose  any  habitual  action  to  become  inherited 
— and  I  think  it  can  be  shown  that  this  does  sometimes 
happen — then  the  resemblance  between  what  originally 
was  a  habit  and  an  instinct  becomes  so  close  as  not  to  be 
distinguished.  If  Mozart,  instead  of  playing  the  piano- 
forte at  three  years  old  with  wonderfully  little  practice, 
had  played  a  tune  with  no  practice  at  all,  he  might  truly 
be  said  to  have  done  so  instinctively.  But  it  would  be  the 
most  serious  error  to  suppose  that  the  greater  number  of 
instincts  have  been  acquired  by  habit  in  one  generation, 


Chap.  VI I. j  INSTINCT   LIKE    HABIT.  j^87 

and  tlien  transmitted  by  inheritance  to  succeeding  gene- 
rations. It  can  be  clearly  shown  that  the  most  wonderful 
instincts  with  which  we  are  acquainted,  namely,  those  of 
the  hive~bee  and  of  many  ants,  could  not  possibly  have 
been  thus  acquired. 

It  will  be  universally  admitted  that  instincts  are  as 
important  as  corporeal  structure  for  the  welfare  of  each 
sj)ecies,  under  its  present  conditions  of  life.  Under  changed 
conditions  of  life,  it  is  at  least  possible  that  slight  modifi- 
cations of  instinct  might  be  profitable  to  a  species  ;  and 
if  it  can  be  shown  that  instincts  do  vary  ever  so ,  little, 
then  I  can  see  no  difiiculty  in  natural  selection  preserving 
and  continually  accumulating  variations  of  instinct  to  any 
extent  that  may  be  profitable.  It  is  thus,  as  I  believe, 
that  all  the  most  complex  and  w^onderful  instincts  have 
originated.  As  modifications  of  corporeal  structure  arise 
from,  and  are  increased  by,  use  or  habit,  and  are  dimin- 
ished or  lost  by  disuse,  so  I  do  not  doubt  it  has  been 
with  instincts.  But  I  believe  that  the  eftects  of  habit  are 
of  quite  subordinate  importance  to  the  efi'ects  of  the  natu- 
ral selection  of  what  may  be  called. accidental  variations 
of  instincts  ; — that  is  of  variations  produced  by  the  same 
tmknown  causes  which  produce  slight  deviations  of  bodily 
structure. 

JSTo  complex  instinct  can  possibly  be  produced  through 
natural  selection,  except  by  the  slow  and  gradual  accu- 
mulation of  numerous,  slight,  yet  profitable,  variations. 
Hence,  as  in  the  case  of  corporeal  structures,  we  ought  to 
find  in  nature,  not  the  actual  transitional  gradations  by 
which  each  complex  instinct  has  been  acquired — for  these 
could  be  found  only  in  the  lineal  ancestors  of  each  species 
— but  we  ought  to  find  in  the  collateral  lines  of  descent 
some  evidence  of  such  gradations ;  or  we  ought  at  least  to 
be  able  to  show  that  gradations  of  some  kind  are  ])ossible  ; 
and  this  we  certainly  can  do.  I  have  been  surprised  to 
find,  making  allowance  for  the  instincts  of  animals  having 
been  but  little  observed  except  in  Europe  and  North 
America,  and  for  no  instinct  being  known  amongst  extinct 
species,  how  very  generally  gradations,  leading  to  the 
most  complex  instincts,  can  be  discovered.  The  canon  of 
9* 


288  INSTINCT.  [Chap.  VII. 

"  ITatura  non  facit  saltum  "  applies  with  almost  equal 
force  to  instincts  as  to  bodily  organs.  Changes  of  instinct 
may  sometimes  be  facilitated  by  the  same  species  having 
difierent  instincts  at  different  periods  of  life,  or  at  different 
seasons  of  the  year,  or  when  placed  under  different  cir- 
cumstances, &c.  ;  in  which  case  either  one  or  the  other 
instinct  might  be  preserved  by  natural  selection.  And 
such  instances  of  diversity  of  instinct  in  the  same  species 
can  be  shown  to  occur  in  nature. 

Again  as  in  the  case  of  corporeal  structure,  and  con- 
formably with  my  theory,  the  instinct  of  each  species  is 
good  for  itself,  but  has  never,  as  far  as  we  can  judge,  been 
produced  for  the  exclusive  good  of  others.  One  of  the 
strongest  instances  of  an  animal  apparently  performing 
an  action  for  the  sole  good  of  another,  with  which  I  am 
acquainted,  is  that  of  aphides  voluntarily  yielding  their 
sweet  excretion  to  ants  :  that  they  do  so  voluntarily,  the 
following  facts  show.  I  removed  all  the  ants  from  a 
group  of  about  a  dozen  aphides  on  a  dock-plant,  and  pre- 
vented their  attendance  during  several  hours.  After  this 
interval,  I  felt  sure  that  the  aphides  would  want  to  excrete. 
I  watched  them  for  some  time  through  a  lens,  but  not 
one  excreted;  I  then  tickled  and  stroked  them  with  a  hair 
in  the  same  manner,  as  well  as  I  could,  as  the  ants  do 
with  their  antennae  ;  but  not  one  excreted.  Afterwards  I 
allowed  an  ant  to  visit  them,  and  it  immediately  seemed, 
by  its  eager  way  of  running  about,  to  be  well  aware  what 
a  rich  flock  it  had  discovered ;  it  then  began  to  play  Avith 
its  antennse  on  the  abdomen  first  of  one  aphis  and  then  of 
another ;  and  each  aphis,  as  soon  as  it  felt  the  antennae, 
immediately  lifted  up  its  abdomen  and  excreted  a  limpid 
drop  of  sweet  juice,  which  was  eagerly  devoured  by  the 
ant.  Even  the  quite  young  aphides  behaved  in  this  man- 
ner, showing  that  the  action  was  instinctive,  and  not  the 
result  of  experience.  But  as  the  excretion  is  extremely 
viscid,  it  is  probably  a  convenience  to  the  aphides  to  have 
it  removed  ;  and  therefore  probably  the  aphides  do  not 
mstinctively  excrete  for  the  sole  good  of  the  ants.  Al- 
though I  do  not  believe  that  any  animal  in  the  world  per- 
forms an  action  for  the  exclusive  good  of  another  of  a 


OniP.  Vltl  INSTINCT.  189 

distinct  species,  yet  each  species  tries  to  take  advantage 
of  the  instincts  of  others,  as  each  takes  advantage  of  the 
weaker  bodily  structure  of  others.  So  again,  in  some  few 
cases,  certain  instincts  cannot  be  considered  as  absolutely 
perfect ;  but  as  details  on  this  and  other  such  points  are 
not  indispensable,  they  may  be  here  passed  over. 

As  some  degree  of  variation  in  instincts  under  a  state 
of  nature,  and  the  inheritance  of  such  variations,  are  in- 
dispensable for  the  action  of  natural  selection,  as  many  in- 
stances as  possible  ought  to  have  been  here  given ;  but 
want  of  space  prevents  me.  I  can  only  assert,  that  in- 
stincts certainly  do  vary — for  instance,  the  migratory  in- 
stinct, both  in  extent  and  direction,  and  in  its  total  loss. 
So  it  is  with  the  nests  of  birds,  which  vary  partly  in  de- 
pendence on  the  situations  chosen,  and  on  the  nature  and 
temperature  of  the  country  inhabited,  but  often  from 
causes  wholly  unknown  to  us  :  Audubon  has  given  sever- 
al remarkable  cases  of  differences  in  nests  of  the  same 
species  in  the  northern  and  southern  United  States.  Fear 
of  any  particular  enemy  is  certainly  an  instinctive  quality, 
as  may  be  seen  in  nestling  birds,  though  it  is  strengthened 
by  experience,  and  by  the  sight  of  fear  of  the  same  enemy 
in  other  animals.  But  fear  of  man  is  slowly  acquired,  as  I 
have  elsewhere  sho^vn,  by  various  animals  inhabiting 
desert  islands  ;  and  we  may  see  an  inst^ance  of  this,  even 
in  England,  in  the  greater  wildness  of  all  our  large  birds 
than  of  our  small  birds ;  for  the  large  birds  have  been 
most  persecuted  by  man.  We  may  safely  attribute  the 
greater  wildness  of  our  large  birds  to  this  cause  ;  for  in 
uninhabited  islands  large  birds  are  not  more  fearful  than 
small ;  and  the  magpie,  so  wary  in  England,  is  tame  in 
Korway,  as  is  the  hooded  crow  in  Egypt. 

That  the  general  disposition  of  individuals  of  the  same 
species,  born  in  a  state  of  nature,  is  extremely  diversified, 
can  be  shown  by  a  multitude  of  facts.  Several  cases 
also,  could  be  given,  of  occasional  and  strange  habits  in 
certain  species,  which  might,  if  advantageous  to  the  spe- 
cies, give  rise,  through  natural  selection,  to  quite  new  in- 
stincts. But  I  am  well  aware  that  these  general  statements, 
without  facts  given  in  detail,  can  produce  but  a  feeble 


•^gQ  INSTH^CT.  [CnAT.  VII 

effect  on  the  reader's  raind.     I  can  only  repeat  my  assur- 
ance, that  I  do  not  speak  without  good  evidence. 

The  possibility,  or  even  j)robability,  of  inherited  varia- 
tions of  instinct  in  a  state  of  nature  will  be  strengthened 
by  briefly  considering  a  few  cases  under  domestication. 
"We  shall  thus  also  be  enabled  to  see  the  respective  parts 
which  habit  and  the  selection  of  so-called  accidental  va- 
riations have  played  in  modifying  the  mental  qualities  of 
our  domestic  animals.  A  number  of  curious  and  authen- 
tic instances  could  be  given  of  the  inheritance  of  all  shades 
of  disposition  and  tastes,  and  likewise  of  the  oddest  tricks, 
associated  with  certain  frames  of  mind  or' periods  of  time. 
But  let  us  look  to  the  familiar  case  of  the  several  breeds 
of  dogs  :  it  cannot  be  doubted  that  young  pointers  (I  have 
myself  seen  a  striking  instance)  will  sometimes  point  and 
even  back  other  dogs  the  very  first  time  that  they  are 
taken  out ;  retrieving  is  certainly  in  some  degree  inherited 
by  retrievers ;  and  a  tendency  to  run  round,  instead  of  at, 
a  flock  of  sheep,  by  shepherd-dogs.  I  cannot  see  that  these 
actions,  performed  without  experience  by  the  young,  and 
in  nearly  the  same  manner  by  each  individual,  performed 
with  eager  delight  by  each  breed,  and  without  the  end 
being  known, — for  the  young  pointer  can  no  more  know 
that  he  points  to  aid  his  master,  than  the  white  butterfly 
knows  why  she  lays  her  eggs  on  the  leaf  of  the  cabbage, 
— I  cannot  see  that  these  actions  differ  essentially  from 
true  instincts.  If  we  were  to  see  one  kind  of  wolf,  when 
young  and  without  any  training,  as  soon  as  it  scented  its 
prey,  stand  motionless  like  a  statue,  and  then  slowly  crawl 
forward  with  a  peculiar  gait ;  and  another  kind  of  wolf 
rushing  round,  instead  of  at,  a  herd  of  deer,  and  driving 
them  to  a  distant  point,  we  should  assuredly  call  these 
actions  instinctive.  Domestic  instincts,  as  they  may  be 
called,  are  certainly  far  less  fixed  or  invariable  than  nat- 
ural instincts ;  but  they  have  been  acted  on  by  far  less 
rigorous  selection,  and  have  been  transmitted  for  an  in- 
comparably shorter  period,  under  less  fixed  conditions  of 
life. 

-     How  strongly  these  domestic  instincts,  habits,  and  dis- 
positions are  mherited,  and  how  curiously  they  become 


Chap.  Vll.J  DOMTESTIC   INSTINCTS.  |9| 

mingled,  is  well  shown  when  different  breeds  of  dogs  are 
crossed.  Thus  it  is  known  .that  a  cross  with  a  bnll-dog 
has  affected  for  many  generations  the  courage  and  obsti- 
nacy of  greyhounds ;  and  a  cross  with  a  greyhound  has 
given  to  a  whole  family  of  shepherd-dogs  a  tendency  to 
hunt  hares.  These  domestic  instincts,  when  thus  tested 
by  crossing,  resemble  natural  instincts,  which  in  a  like 
manner  become  curiously  blended  together,  and  for  a  long 
period  exhibit  traces  of  the  instincts  of  either  parent :  for 
example,  Le  Roy  describes  a  dog,  whose  great-grandfather 
was  a  wolf,  and  this  dog  showed  a  trace  of  its  wild  parent- 
age only  in  one  way,  by  not  coming  in  a  straight  line  to 
his  master  when  called. 

Domestic  instincts  are  sometimes  spoken  of  as  actions 
which  have  become  inherited  solely  from  long-continued 
and  compulsory  habit,  but  this,  I  think,  is  not  true,  l^o 
one  would  ever  have  thought  of  teaching,  or  probably 
could  have  taught,  the  tumbler-pigeon  to  tumble, — an 
action  which,  as  I  have  witnessed,  is  performed  by  young 
birds,  that  have  never  seen  a  pigeon  tumble.  We  may 
believe  that  some  one  pigeon  showed  a  slight  tendency  to 
this  strange  habit,  and  that  the  long-continued  selection 
of  the  best  individuals  in  successive  generations  made 
tumblers  what  they  now  are  ;  and  near  Glasgow  there  are 
house-tumblers,  as  I  hear  from  Mr.  Brent,  which  cannot  fly 
eighteen  inches  high  without  going  head  over  heels.  It  may 
be  doubted  whether  any  one  would  have  thought  of  train- 
ing a  dog  to  point,  had  not  some  one  dog  naturally  shown 
a  tendency  in  this  line ;  and  this  is  known  occasionally 
to  happen,  as  I  once  saw  in  a  pure  terrier :  the  act  of 
pointing  is  probably,  as  many  have  thought,  only  the  ex- 
aggerated pause  of  an  animal  preparing  to  spring  on  its 
prey.  When  the  first  tendency  to  point  was  once  dis- 
played, methodical  selection  and  the  inherited  effects  of 
compulsory  training  in  each  successive  generation  would 
soon  complete  the  work ;  and  unconscious  selection  is  still 
at  work,  as  each  man  tries  to  procure,  without  intending 
to  improve  the  breed,  dogs  which  will  stand  and  hunt  best. 
On  the  other  hand,  habit  alone  in  some  cases  has  sufficed  ; 
no  animal  is  more  difficult  to  tame  than  the  young  of  the 
wild  rabbit ;  scarcely  any  animal  is  tamer  than  the  young 


J^92  INSTINCT.  [Chap.  VII. 

of  the  tame  rabbit ;  but  I  do  not  suppose  that  domestic 
rabbits  have  ever  been  selected  for  tameness ;  and  I  pre- 
sume that  we  must  attribute  the  whole  of  the  inherited 
change  from  extreme  wildness  to  extreme  tameness,  sim- 
ply to  habit  and  long-continued  close  confinement. 

l^atural  instincts  are  lost  under  domestication :  a  re- 
markable instance  of  this  is  seen  in  those  breeds  of  fowls 
which  very  rarely  or  never  become  "  broody,"  that  is, 
never  wish  to  sit  on  their  eggs.  Familiarity  alone  pre- 
vents our  seeing  how  universally  and  largely  the  minds 
of  our  domestic  animals  have  been  modified  by  domestica- 
tion. It  is  scarcely  possible  to  doubt  that  the  love  of 
man  has  become  instinctive  in  the  dog.  All  wolves, 
foxes,  jackals,  and  species  of  the  cat  genus,  when  kept 
tame,  are  most  eager  to  attack  poultry,  sheep,  and  pigs ; 
and  this  tendency  has  been  found  incurable  in  dogs  which 
have  been  brought  home  as  puppies  from  countries  such 
as  Tierra  del  Fuego  and  Australia,  where  the  savages  do 
not  keep  these  domestic  animals.  How  rarely,  on  the 
other  hand,  do  our  civilised  dogs,  even  when  quite  young, 
require  to  be  taught  not  to  attack  poultry,  sheep,  and 
pigs !  J^o  doubt  they  occasionally  do  make  an  attack, 
and  are  then  beaten  ;  and  if  not  cured,  they  are  destroy- 
ed ;  so  that  habit,  with  some  degree  of  selection,  has  prob- 
ably concurred  in  civilising  by  inheritance  our  dogs.  On 
the  other  hand,  young  chickens  have  lost,  wholly  by 
habit,  that  fear  of  the  dog  and  cat  which  no  doubt  was 
originally  instinctive  in  them,  in  the  same  way  as  it  is  so 
plainly  instinctive  in  young  pheasants,  though  reared 
under  a  hen.  It  is  not  that  chickens  have  lost  all  fear, 
but  fear  only  of  dogs  and  cats,  for  if  the  hen  gives  the 
danger-chuckle,  they  will  run  (more  especially  young  tur- 
keys) from  under  her,  and  conceal  themselves  in  the  sur- 
rounding grass  or  thickets  ;  and  this  is  evidently  done  for 
the  instinctive  purpose  of  allowing,  as  we  see  in  wild 
ground-birds,  their  mother  to  fiy  away.  But  this  instinct 
retained  by  our  chickens  has  become  useless  under  do- 
mestication, for  the  mother-hen  has  almost  lost  by  disuse 
the  power  of  flight. 

Hence,  we  may  conclude,  that  domestic  instincts  have 
been  acquired  and  natural  instincts  have  been  lost  partly 


Chap.  VII.]  OF   THE    CUCKOO.  j[93 

by  habit,  and  partly  by  man  selecting  and  accunmlating 
during  successive  generations,  peculiai  mental  habits  and 
actions,  which,  at  lirst  appeared  from  what  we  must  in 
our  ignorance  call  an  accident.  In  some  cases  compul- 
sory habit  alone  has  sufficed  to  produce  such  inherited 
mental  changes  ;  in  other  cases  compulsory  habit  has  done 
nothing,  and  all  has  been  the  result  of  selection,  pursued 
both  methodically  and  unconsciously  ;  but  in  most  cases, 
probably,  habit  and  selection  have  acted  together. 

We  shall,  perhaps,  best  understand  how  instincts  in  a 
state  of  nature  have  become  modified  by  selection,  by 
considering  a  few  cases.  I  will  select  only  three,  out  of 
the  several  which  I  shall  have  to  discuss  in  my  future 
work, — namely,  the  instinct  which  leads  the  cuckoo  to  lay 
her  eggs  in  other  birds'  nests  ;  the  slave-making  instinct 
of  certain  ants  ;  and  the  comb-making  power  of  the  hive- 
bee  :  these  two  latter  instincts  have  generally,  and  most 
justly,  been  ranked  by  naturalists  as  the  most  wonderful 
of  all  known  instincts. 

It  is  now  commonly  admitted  that  the  more  immediate 
and  final  cause  of  the  cuckoo's  instinct  is,  that  she  lays 
her  eggs,  not  daily,  but  at  intervals  of  two  or  three  days ; 
so  that,  if  she  were  to  make  her  own  nest  and  sit  on  her 
own  eggs,  those  first  laid  would  have  to  be  left  for  some 
time  unincubated,  or  there  would  be  eggs  and  young 
birds  of  different  ages  in  the  same  nest.  If  this  were  the 
case,  the  process  of  laying  and  hatching  might  be  incon- 
veniently long,  more  especially  as  she  has  to  migrate  at  a 
very  early  period ;  and  the  first  hatched  young  would 
probably  have  to  be  fed  by  the  male  alone.  But  the 
American  cuckoo  is  in  this  predicament ;  for  she  makes 
her  own  nest  and  has  eggs  and  young  successively  hatched, 
all  at  the  same  time.  It  has  been  asserted  that  the  Ameri- 
can cuckoo  occasionally  lays  her  eggs  in  other  birds' 
nests ;  but  I  hear  on  the  high  authority  of  Dr.  Brewer, 
that  this  is  a  mistake.  ISTevertheless,  I  could  give  several 
instances  of  various  birds  which  have  been  known  occa- 
eionally  to  lay  their  eggs  in  other  birds'  nests.  Now  let 
us  suppose  that  the  ancient  progenitor  of  our  European 
cuckoo  had  the  habits  of  the  American  cuckoo.;  but  that 


-j^g^  INSTINCT.  [Chap.  VIL 

occasionally  she  laid  an  egg  in  another  bird's  nest.  If 
the  old  bird  profited  by  this  occasional  habit,  or  if  the 
yonng  were  made  more  vigorous  by  advantage  having 
been  taken  of  the  mistaken  maternal  instinct  of  another 
bird,  than  by  their  own  mother's  care,  encnmbered  as  she 
can  hardly  fail  to  be  by  having  eggs  and  yonng  of  dif- 
ferent ages  at  the  same  time ;  then  the  old  birds  or  the 
fostered  yonng  would  gain  an  advantage.  And  analogy 
would  lead  me  to  believe,  that  the  young  thus  reared 
would  be  apt  to  follow  by  inheritance  the  occasional  and 
aberrant  habit  of  their  mother,  and  in  their  turn  would 
be  apt  to  lay  their  eggs  in  other  birds'  nests,  and  thus  be 
successful  in  rearing'their  young.  By  a  continued  process 
of  this  nature,  I  believe  that  the  strange  instinct  of  our 
cuckoo  could  be,  and  has  been,  generated.  I  may  add 
that,  according  to  Dr.  Gray  and  to  some  other  observers, 
the  European  cuckoo  has  not  utterly  lost  all  maternal 
love  and  care  for  her  own  offspring. 

The  occasional  habit  of  birds  laying  their  eggs  in  other 
birds'  nests,  either  of  the  same  or  of  a  distinct  species,  is 
not  very  uncommon  with  the  Gallinacess  ;  and  this  per- 
haps explains  the  origin  of  a  singular  instinct  in  the  allied 
group  of  ostriches.  For  several  hen  ostriches,  at  least  in 
the  case  of  the  American  species,  unite  and  lay  first  a  few 
eggs  in  one  nest  and  then  in  another ;  and  these  are 
hatched  by  the  males.  This  instinct  may  probably  be 
accounted  for  by  the  fact  of  the  hens  laying  a  large 
number  of  eggs ;  but,  as  in  the  case  of  the  cuckoo,  at 
intervals  of  two  or  three  days.  This  instinct,  however, 
of  the  American  ostrich  has  not  as  yet  been  perfected  ; 
for  a  surprising  number  of  eggs  lie  strewed  over  the  plains, 
so  that  in  one  day's  himting  I  picked  up  no  less  than 
twenty  lost  and  Avasted  eggs. 

Many  bees  are  parasitic,  and  always  lay  their  eggs  in 
the  nests  of  bees  of  other  kinds.  Tliis  case  is  more  remark- 
able than  that  of  the  cuckoo ;  for  these  bees  have  not 
only  their  instincts  but  their  structure  modified  in  accord- 
ance with  their  parasitic  habits  ;  for  they  do  not  j^ossess 
the  pollen-collecting  apparatus  which  would  be  necessary 
if  they  had  to  store  food  for  their  own  young.     Some 


Chap.  VIL]  SLAVE-MAKING    INSTINCT.  ]^95 

species,  likewise,  of  Spliegidse  (wasp-like  insects)  are 
parasitic  on  other  species  ;  and  M.  Fabre  lias  lately  shown 
good  reason  for  believing  that  althongh  the  Tachy tes  nigra 
generally  makes  its  own  burrow  and  stores  it  with  para- 
lysed prey  for  its  own  larvae  to  feed  on,  yet  that  when  this 
insect  finds  a  burrow  already  made  and  stored  by  another 
sphex,  it  takes  advantage  of  the  prize,  and  becomes  for 
the  occasion  parasitic.  In  this  case,  as  with  the  supposed 
case  of  the  cuckoo,  I  can  see  no  difficulty  in  natural  selec- 
tion making  an  occasional  habit  permanent,  if  of  advantage 
to  the  species,  and  if  the  insect  whose  nest  and  stored 
food  are  thus  feloniously  appropriated,  be  not  thus  ex- 
terminated. 

Slave-making  instinct. — ^This  remarkable  instinct  was 
first  discovered  in  the  Formica  (Polyerges)  rufescens  by 
Pierre  Huber,  a  better  observer  even  than  his  celebrated 
father.  This  ant  is  absolutely  dependent  on  its  slaves  ; 
without  their  aid,  the  species  would  certainly  become 
extinct  in  a  single  year.  The  males  and  fertile  females 
do  no  work.  The  workers  or  sterile  females,  though 
most  energetic  and  courageous  in  capturing  slaves,  do  no 
other  work.  They  are  incapable  of  making  their  own 
nests,  or  of  feeding  their  own  larvse.  "When  the  old  nest 
is  found  inconvenient,  and  they  have  to  migrate,  it  is  the 
slaves  which  determine  the  migration,  and  actually  carry 
their  masters  in  their  jaws.  So  utterly  helpless  are  the 
masters,  that  when  Huber  shut  up  thirty  of  them  without 
a  slave,  but  with  plenty  of  the  food  which  they  like  best, 
and  with  their  larvse  and  pupae  to  stimulate  them  to  work, 
they  did  nothing ;  they  could  not  even  feed  themselves, 
and  many  perished  of  hunger.  Huber  then  introduced  a 
single  slave  (F.  fusca),  and  she  instantly  set  to  work,  fed 
and  saved  the  survivors  ;  made  some  cells  and  tended  the 
larvae,  and  put  all  to  rights.  What  can  be  more  extra- 
ordinary than  these  well-ascertained  facts?  If  we  had 
not  known  of  any  other  slave-making  ant,  it  would  have 
been  hopeless  to  have  speculated  how  so  wonderful  an 
instinct  could  have  been  perfected. 

Another  species  (F.  sanguinea)  was  also  discovered  by  P. 
Huber  to  be  a  slave-making  ant.    This  species  is  found  in 


IQQ  INSTINCT.  [CHiP.  VIL 

the  soutliern  parts  of  England,  and  its  habits  have  beer, 
attended  to  bj  Mr.  F.  Smith,  of  the  British  Museum,  to 
whom  I  am  much  indebted  for  information  on  this  and 
other  subjects.  Although  fully  trustmg  to  the  statements 
of  Huber  and  Mr.  Smith,  I  tried  to  approach  the  subject 
in  a  sceptical  frame  of  mind,  as  any  one  may  well  be  ex- 
cused for  doubting  the  truth  of  so  extraordinary  and  odious 
an  instinct  as  that  of  making  slaves.  Hence  I  will  give 
the  observations  which  I  have  myself  made,  in  some  little 
detail.  I  opened  fourteen  nests  of  F.  sanguinea,  and 
found  a  few  slaves  in  all.  Males  and  fertile  females  of  the 
slave-species  are  found  only  in  their  own  proper  commu- 
nities, and  have  never  been  observed  in  the  nests  of  F. 
sanguinea.  The  slaves  are  black  and  not  above  half  the 
size  of  their  red  masters,  so  that  the  contrast  in  their  ap- 
pearance is  very  great.  When  the  nest  is  slightly .  dis- 
turbed, the  slaves  occasionally  come  out,  and  like  their 
masters  are  much  agitated  and  defend  the  nest :  when  the 
nest  is  much  disturbed  and  the  larvae  and  pup^  are  ex- 
posed, the  slaves  work  energetically  with  their  masters  in 
carrying  them  away  to  a  place  of  safety.  Hence,  it  is 
clear,  that  the  slaves  feel  quite  at  home.  During  the 
months  of  June  and  July,  on  three  successive  years,  I 
have  watched  for  many  hours  several  nests  in  Surrey  and 
Sussex,  and  never  saw  a  slave  either  leave  or  enter  a  nest. 
As,  during  these  months,  the  slaves  are  very  few  in  num- 
ber, I  thought  that  they  might  behave  differently  when 
more  numerous ;  but  Mr.  Smith  informs  me  that  he  has 
watched  the  nests  at  various  hours  during  May,  June,  and 
August,  both  in  Surrey  and  Hampshire,  and  has  never 
seen  the  slaves,  though  present  in  large  numbers  in 
August,  either  leave  or  enter  the  nest.  Hence  he  considers 
them  as  strictly  household  slaves.  The  masters,  on  the 
other  hand,  may  be  constantly  seen  bringing  in  materials 
for  the  nest,  and  food  of  all  kinds.  During  the  present 
year,  however,  in  the  month  of  July,  I  came  across  a  com- 
munity with  an  unusually  large  stock  of  slaves,  and  I  ob- 
served a  few  slaves  mingled  with  their  masters  leaving  the 
nest,  and  inarching  along  the  same  road  to  a  tall  Scotch- 
fir-tree,  twenty-five  yards  distant,  which  they  ascended 


Chap.  VII.]  SLAVE-MAKING   INSTINCT.  J^9Y 

together,  probably  in  search  of  aphides  or  cocci.  Accord- 
ing to  Huber,  who  had  ample  opportunities  for  observa- 
tion, in  Switzerland  the  slaves  habitually  work  with  their 
masters  in  making  the  nest,  and  they  alone  open  and  close 
the  doors  in  the  morning  and  evening ;  and,  as  Huber 
expressly  states,  their  principal  office  is  to  search  for 
aphides.  This  difference  in  the  usual  habits  of  the  mas- 
ters and  slaves  in  the  two  countries,  probably  depends 
merely  on  the  slaves  being  captured  in  greater  numbers 
in  Switzerland  than  in  England. 

One  day  I  fortunately  witnessed  a  migration  of  F.  san- 
guinea  from  one  nest  to  another,  and  it  was  a  most  inter- 
esting spectacle  to  behold  the  masters  carefully  carrying 
their  slaves  in  their  jaws,  instead  of  being  carried  by 
them,  as  in  the  case  of  the  F.  rufescens.  Another 
day  my  attention  was  struck  by  about  a  score  of  the 
slave-makers  haunting  the  same  spot,  and  evidently  not 
in  search  of  food  ;  they  approached  and  were  vigorously 
repulsed  by  an  independent  community  of  the  slave 
species  (F.  fusca) ;  sometimes  as  many  as  three  of  these 
ants  clinging  to  the  legs  of  the  slave-making  F.  san- 
guinea.  The  latter  ruthlessly  killed  their  small  oppo- 
nents, and  carried  their  dead  bodies  as  food  to  their  nest, 
twenty-nine  yards  distant ;  but  they  were  prevented  from 
getting  any  pupse  to  rear  as  slaves.  I  then  dug  up  a 
small  parcel  of  the  pupse  of  F.  fusca  from  another  nest, 
and  put  them  down  on  a  bare  spot  near  the  place 
of  combat ;  they  were  eagerly  seized,  and  carried  off  by 
the  tyrants,  who  perhaps  fancied  that,  after  all,  they  had 
been  victorious  in  their  late  combat. 

At  the  same  time  I  laid  on  the  same  place  a  small 
parcel  of  the  pupae  of  another  species,  F  flava,  with  a  few 
of  these  little  yellow  ants  still  clinging  to  the  fragments 
of  the  nest.  This  species  is  sometimes,  though  rarely, 
made  into  slaves,  as  has  been  described  by  Mr.  Smith. 
Although  so  small  a  species,  it  is  very  courageous,  and  1 
have  seen  it  ferociously  attack  other  ants.  In  one  in- 
stance I  found  to  my  surj)rise  an  indej3endent  community 
of  F.  flava  under  a  stone  beneath  a  nest  of  the  slave- 
making  F.  sanguinea ;  and  when  I  had  accidentally  dis- 
tui'bed  both  nests,  the  little  ants  attacked  theii*  big  neigh- 


•£Qg  INSTINCT.  [Chap.  VIL 

bours  witli  surprising  courage.  'Now  I  was  curious  to 
ascertain  wliether  F.  sanguinea  could  distinguish  the 
pupae  of  F.  fusca,  which  they  habitually  make  into  slaves, 
from  those  of  the  little  and  furious  F.  flava,  which  they 
rarely  capture,  and  it  was  evident  that  they  did  at  once 
distinguish  them :  for  we  have  seen  that  they  eagerly  and 
instantly  seized  the  pup 83  of  F.  fusca,  whereas  they  were 
much  terrified  when  they  came  across  the  pupae,  or  even 
the  earth  from  the  nest  of  F.  flava,  and  quickly  ran  away ; 
but  in  about  a  quarter  of  an  hour,  shortly  after  all  the 
little  yellow  ants  had  crawled  away,  they  took  heart  and 
carried  oif  the  pupae. 

One  evening  I  visited  another  community  of  F.  san- 
guinea, and  found  a  number  of  these  ants  entering  their 
nest,  carrying  the  dead  bodies  of  F.  fusca  (showing  that 
it  was  not  a  migration)  and  numerous  pupae.     I  traced 
the  returning  file  burthened  with  booty,  for  about  forty 
yards,  to  a  very  thick  clump  of  heath,  whence  I  saw  the 
last  individual  of  F.  sanguinea  emerge,  carrying  a  pupae  ;• 
but  I  was  not  able  to  find  the  desolated  nest  in  the  thick 
heath.     The  nest,  however,  must  have  been  close  at  hand, 
for  two  or  three  individuals  of  F.  fusca  were  rushing 
about  in  the  greatest  agitation,  and  one  was  perched  mo- 
tionless with  its  own  pupa  in  its  mouth  on  the  top  of  a 
spray  of  heath,  an  image  of  despair,  over  its  ravaged  home. 
Such  are  the  facts,  though  they  did  not  need  confir- 
mation by  me,  in  regard  to  the  wonderful  instinct  of 
making  slaves.     Let  it  be  observed  what  a  contrast  the 
instinctive  habits  of  F.  sanguinea  present  with  those  of 
the  continental  F.  rufescens.     The  latter  does  not  build 
its   own  nest,  does   not  determine  its   own   migrations, 
does  not  collect  food  for  itself  or  its  young,  and  cannot 
even  feed  itself:  it  is  absolutely  dependent  on  its  numer- 
ous  slaves.      Formica    sanguinea,    on    the   other   hand, 
possesses  much  fewer  slaves,  and  in  the  early  part  of 
tlie    summer    extremely   few  :    the    masters    determine 
when  and  where  a  new  nest  shall  be  formed,  and  when 
ihey  migrate,  the   masters   carry  the   slaves.      Both    in 
Switzerland  and   England   the  slaves  seem  to  have  the 
exclusive  care  of  the   larvae,  and   the  masters  alone  go 
on  slave-making  expeditions.     In  Switzerland  the  slaves 


Chap  VII.]  CELLS   OP   THE   HIVE-BEE.  ][99 

and  masters  work  together,  making  and  bringing  materials 
for  the  nest :  both,  but  chiefly  the  slaves,  tend,  and  milk 
as  it  may  be  called,  their  aphides  ;  and  thus  both  collect 
food  for  the  community.  In  England  the  masters  alone 
usually  leave  the  nest  to  collect  building  materials  and 
food  for  themselves,  their  slaves  and  larvse.  So  that  the 
masters  in  this  country  receive  much  less  service  from 
their  slaves  than  they  do  in  Switzerland. 

By  what  steps  the  instinct  of  F.  sanguinea  originated 
I  will  not  pretend  to  conjecture.  But  as  ants,  which  are 
not  slave-makers,  will,  as  I  have  seen,  carry  off  pupae  of 
other  species,  if  scattered  near  their  nests,  it  is  possible 
that  pupse  originally  stored  as  food  might  become  devel- 
oped ;  and  the  ants  thus  imintentionally  reared  would 
then  follow  their  proper  instincts,  and  do  what  work  they 
could.  If  their  presence  proved  useful  to  the  species  which 
had  seized  them — if  it  were  more  advantageous  to  this 
species  to  capture  workers  than  to  procreate  them — ^the 
habit  of  collecting  pupse  originally  for  food  might  by 
natural  selection  be  strengthened  and  rendered  permanent 
for  the  very  different  purpose  of  raising  slaves.  When 
the  instinct  was  once  acquired,  if  carried  out  to  a  much 
less  extent  even  than  in  our  British  F.  sanguinea,  which, 
as  we  have  seen,  is  less  aided  by  its  slaves  than  the  same 
s]3ecies  in  Switzerland,  I  can  see  no  difficulty  in  natural 
selection  increasing  and  modifying  the  instinct — always 
supposing  each  modification  to  be  of  use  to  the  species — 
until  an  ant  was  formed  as  abjectly  dependent  on  its 
slaves  as  is  the  Formica  rufescens. 

Cell-making  instinct  of  the  Hive-Bee. — I  will  not  here 
enter  on  minute  details  on  this  subject,  but  will  merely 
2:ive  an  outline  of  the  conclusions  at  which  I  have  arrived. 
He  must  be  a  dull  man  who  can  examine  the  exquisite 
structure  of  a  comb,  so  beautifully  adapted  to  its  end, 
without  enthusiastic  admiration.  We  hear  from  mathe- 
maticians that  bees  have  practically  solved  a  recondite 
problem,  and  have  made  their  cells  of  the  proper  shape 
to  hold  the  greatest  possible  amount  of  honey,  with  the 
least  possible  consumption  of  precious  wax  in  their  con- 
struction.    It  has  been  remarked  that  a  skilful  workman, 


200  IN-STINCT.  [Chap.  VII. 

witli  fitting  tools  and  measures,  would  find  it  very  difii- 
cult  to  make  cells  of  wax  of  the  true  form,  though  this  is 
perfectly  efi'ected  by  a  crowd  of  bees  working  in  a  dark 
hive.  Grant  whatever  instincts  you  please,  and  it  seems 
at  first  quite  inconceivable  how  they  can  make  all  the 
necessary  angles  and  planes,  or  even  perceive  when  they 
are  correctly  made.  But  the  difficulty  is  not  nearly  so 
great  as  it  at  first  appears :  all  this  beautiful  work  can 
be  shown,  I  think,  to  follow  from  a  few  very  simple  in- 
stincts. 

I  was  led  to  investigate  this  subject  by  Mr.  Water- 
house,  who  has  shown  that  the  form  of  the  cell  stands  in 
close  relation  to  the  presence  of  adjoining  cells  ;  and  the 
following  view  may,  perhaps,  be  considered  only  as  a 
modification  of  his  theory.  Let  us  look  to  the  great  prin- 
ciple of  gradation,  and  see  whether  I^ature  does  not  re- 
veal to  us  her  method  of  work.  At  one  end  of  a  short 
series  we  have  humble-bees,  which  use  their  old  cocoons 
to  hold  honey  sometimes  adding  to  them,  short  tubes  of 
wax,  and  likewise  making  separate  and  very  irregular 
rounded  cells  of  wax.  At  the  other  end  of  the  series  we 
have  the  cells  of  the  hive-bee,  placed  in  a  double  layer : 
each  cell,  as  is  well  known,  is  an  hexagonal  prism,  with 
the  basal  edges  of  its  six  sides  bevelled  so  as  to  join  on  to 
a  pyramid,  formed  of  three  rhombs.  These  rhombs  have 
certain  angles,  and  the  three  which  form  the  pyramidal 
base  of  a  single  cell  on  one  side  of  the  comb,  enter  into 
the  composition  of  the  bases  of  three  adjoining  cells  on  the 
opposite  side.  In  the  series  between  the  extreme  perfec- 
tion of  the  cells  of  the  hive-bee  and  the  simplicity  of  those 
of  the  humble-bee,  we  have  the  cells  of  the  Mexican  Me- 
lipona  domestica,  carefully  described  and  figured  by 
Pierre  Huber.  The  Melipona  itself  is  intermediate  in 
structure  between  the  hive  and  humble  bee,  but  more 
nearly  related  to  the  latter:  it  forms  a  nearly  regular 
waxen  comb  of  cylindrical  cells,  in  which  the  young  are 
Iiatched,  and,  in  addition,  some  large  cells  of  wax  for 
holding  honey.  These  latter  cells  are  nearly  spherical 
and  of  nearly  equal  sizes,  and  are  aggregated  into  an  ii'- 
regular  mass.     But  the  important  point  to  notice,  is  that 


Ghap.  VII.]  CELLS   OF   THE    HIVE-BEE.  201 

these  cells  are  always  made  at  tliat  degree  of  nearness  to 
each  other,  that  they  would  have  intersected  or  broken 
into  each  other,  if  the  spheres  had  been  completed ;  but 
this  is  never  permitted,  the  bees  building  perfectly  flat 
walls  of  wax  between  the  spheres  which  thus  tend  to  in- 
tersect. Hence  each  cell  consists  of  an  outer  spherical 
portion  and  of  two,  three,  or  more  perfectly  flat  surfaces, 
according  as  the  cell  adjoins  two,  three,  or  more  other 
cells.  When  one  cell  comes  into  contact  with  three  other 
cells,  which,  from  the  spheres  being  nearly  of  the  same 
size,  is  very  frequently  and  necessarily  the  case,  the  three 
flat  surfaces  are  united  into  a  pyramid ;  and  this  pyramid, 
as  Huber  has  remarked,  is  manifestly  a  gross  imitation  of 
the  three-sided  pyramidal  basis  of  the  cell  of  the  hive-bee. 
As  in  the  cells  of  the  hive-bee,  so  here,  the  three  plane 
surfaces  in  any  one  cell  necessarily  enter  into  the  con- 
struction of  three  adjoining  cells.  It  is  obvious  that  the 
Melipona  saves  wax  by  this  manner  of  building  ;  for  the 
flat  walls  between  the  adjoining  cells  are  not  double,  but 
are  of  the  same  thickness  as  the  outer  spherical  portions, 
and  yet  each  flat  portion  forms  a  part  of  two  cells. 

Reflecting  on  this  case,  it  occurred  to  me  that  if  the 
Melipona  had  made  its  spheres  at  some  given  distance 
from  each  other,  and  had  made  them  of  equal  sizes  and 
had  arranged  them  symmetrically  in  a  double  layer,  the 
resulting  structure  would  probably  have  been  as  perfect 
as  the  comb  of  the  hive-bee.  Accordingly  I  wrote  to 
Professor  Miller,  of  Cambridge,  and  this  geometer  has 
kindly  read  over  the  following  statement,  drawn  up  from 
his  information,  and  tells  me  that  it  is  strictly  correct : — 

K  a  number  of  equal  spheres  be  described  with  their 
centres  placed  in  two  parallel  layers  ;  with  the  centre  of 
each  sphere  at  the  distance  of  radius  x  4/  2,  or  radius  x 
1-4:1421  (or  at  some  lesser  distance),  from  the  centres  of 
the  six  surrounding  spheres  in  the  same  layer  ;  and  at  the 
same  distance  from  the  centres  of  the  adjoining  spheres  in 
the  other  and  parallel  layer ;  then,  if  planes  of  intersec- 
tion between  the  several  spheres  in  both  layers  be  formed, 
there  will  result  a  double  layer  of  hexagonal  prisms 
united   together    by  pyramidal  bases   formed   of   three 


202  INSTINCT.  [Chap.  VH. 

rliombs  ;  and  the  rhombs  and  the  sides  of  the  hexagonal 
prisms  will  have  every  angle  identically  the  same  with 
the  best  measurements  which  have  been  made  of  the  cells 
of  the  hive-bee. 

Hence  we  may  safely  conclude  that  if  we  could 
slightly  modify  the  instincts  already  possessed  by  the 
Melipona,  and  in  themselves  not  very  wonderful,  this  bee 
would  make  a  structure  as  wonderfully  perfect  as  that  of 
the  hive-bee.  We  must  suppose  the  Melipona  to  make 
her  cells  truly  spherical,  and  of  equal  sizes ;  and  this 
would  not  be  very  sui-prising,  seeing  that  she  already  does 
so  to  a  certain  extent,  and  seeing  what  perfectly  cylindri- 
cal burrows  in  wood  many  insects  can  make,  apparently 
by  turning  round  on  a  fixed  point.  We  must  suppose  the 
Melipona  to  arrange  her  cells  in  level  layers,  as  she  al- 
ready does  her  cylindrical  cells ;  and  we  must  further 
suppose,  and  this  is  the  greatest  difficulty,  that  she  can 
somehow  judge  accurately  at  what  distance  to  stand  from 
her  fellow-labourers  when  several  are  making  their 
spheres  ;  but  she  is  already  so  far  enabled  to  judge  of  dis- 
tance, that  she  always  describes  her  spheres  so  as  to  in- 
tersect largely ;  and  then  she  unites  the  points  of  intersec- 
tion by  perfectly  flat  surfaces.  We  have  further  to  sup- 
pose, but  this  is  no  difficulty,  that  after  hexagonal  prisms 
have  been  formed  by  the  intersection  of  adjoining  spheres 
in  the  same  layer,  she  can  prolong  the  hexagon  to  any 
length  requisite  to  hold  the  stock  of  honey  ;  in  the  same 
way  as  the  rude  humble-bee  adds  cylinders  of  wax  to  the 
circular  mouths  of  her  old  cocoons.  By  such  modifica- 
tions of  instincts  in  themselves  not  very  wonderful, — ^hard- 
ly more  wonderful  than  those  wdiich  guide  a  bird  to  make 
its  nest, — I  believe  that  the  hive-bee  has  acquired,  through 
natural  selection,  her  inimitable  architectural  powers. 

But  this  theory  can  be  tested  by  experiment.  Follow- 
ing the  example  of  Mr.  Tegetmeier,  I  separated  two 
combs,  and  put  between  them  a  long,  thick,  square  strip 
of  wax  :  the  bees  instantly  began  to  excavate  minute  cir- 
cular pits  in  it ;  and  as  they  deepened  these  little  pits, 
they  made  them  wider  and  wider  until  they  were  convert- 
ed into  shallow  basins,  appearing  to  the  eye  perfectly  true 


Chap.  VIL]  CELLS    OF   THE    HIVE-BEE.  203 

or  parts  of  a  sphere,  and  of  about  the  diameter  of  a  cell. 
It  was  most  interesting  to  me  to  observe  that  wherevei 
several  bees  had  begun  to  excavate  these  basins  near  to- 
gether, they  had  begun  their  work  at  such  a  distance  from 
each  other,  that  by  the  time  the  basins  had  acquired  the 
above  stated  width  {i.  e.  about  the  width  of  an  ordinary- 
cell),  and  were  in  depth  about  one  sixth  of  the  diameter 
of  tlie  sphere  of  which  they  formed  a  part,  the  rims  of  the 
basins  intersected  or  broke  into  each  other.  As  soon  as 
this  occurred,  the  bees  ceased  to  excavate,  and  began  to 
build  up  flat  walls  of  wax  on  the  lines  of  intersection  be- 
tween the  basins,  so  that  each  hexagonal  prism  was  built 
upon  the  festooned  edge  of  a  smooth  basin,  instead  of  on 
the  straight  edges  of  a  three-sided  pyramid  as  in  the  case 
of  ordinary  cells. 

I  then  put  into  the  hive,  instead  of  a  thick,  square 
piece  of  wax,  a  thin  and  narrow,  knife-edged  ridge,  col- 
oured with  Vermillion.  The  bees  instantly  began  on  both 
sides  to  excavate  little  basius  near  to  each  other,  in  the 
same  w^ay  as  before ;  but  the  ridge  of  w^ax  was  so  thin, 
that  the  bottoms  of  the  basins,  if  they  had  been  excavated 
to  the  same  depth  as  in  the  former  experiment,  would 
have  broken  into  each  other  from  the  opposite  sides.  The 
bees,  however,  did  not  suffer  this  to  happen,  and  they 
stopped  their  excavations  in  due  time  ;  so  that  the  basins, 
as  soon  as  they  had.  been  a  little  deepened,  came  to  have 
flat  bottoms  ;  and  these  flat  bottoms,  formed  by  thin  little 
plates  of  the  vermillion  wax  having  been  left  ungnaw^ed, 
were  situated,  as  far  as  the  eye  could  judge,  exactly  along 
the  planes  of  imaginary  intersection  between  the  basins  on 
the  opposite  sides  of  the  ridge  of  wax.  In  parts,  only 
little  bits,  in  other  parts,  large  portions  of  a  rhombic  plate 
had  been  left  between  the  opposed  basins,  but  the  work, 
from  the  unnatural  state  of  things,  had  not  been  neatly 
performed.  The  bees  must  have  worked  at  very  nearly 
the  same  rate  on  the  opposite  sides  of  the  ridge  of  vermil- 
lion wax,  as  they  circularly  gnawed  aw^ay  and  deepened 
the  basins  on  both  sides,  in  order  to  have  succeeded  in  thus 
leaving  flat  plates  between  the  basins,  by  stojDping  work 
along  the  intermediate  planes  or  planes  of  intersection. 
10 


2Q4  IN8TINCT.  [Chap.  VII. 

Considering  liow  flexible  thin  wax  is,  I  do  not  see  that 
there  is  any  difficulty  in  the  bees,  whilst  at  work  on  the 
two  sides  of  a  strij)  of  wax,  perceiving  when  they  have 
gnawed  the  wax  away  to  the  proper  thinness,  and  then 
stopping  their  work.  In  ordinary  combs  it  has  appeared 
to  me  that  the  bees  do  not  always  succeed  in  working  at 
exactly  the  same  rate  from  the  opposite  sides  ;  for  I  have 
noticed  half-completed  rhombs  at  the  base  of  a  just-com- 
menced cell,  which  were  slightly  concave  on  one  side, 
where  I  suppose  that  the  bees  had  excavated  too  quickly, 
and  convex  on  the  opposed  side,  where  the  bees  had 
worked  less  quickly  In  one  well-marked  instance,  I  put 
the  comb  back  into  the  hive,  and  allowed  the  bees  to  go 
on  working  for  a  short  time,  and  again  examined  the  cell, 
and  I  found  that  the  rhombic  plate  had  been  completed, 
and  had  \)^(ioviiQ  perfectly  flat :  it  was  absolutely  impossi- 
ble, from  the  extreme  thinness  of  the  little  rhombic  plate, 
that  they  could  have  effected  this  by  gnawing  away  the 
convex  side ;  and  I  suspect  that  the  bees  in  such  cases 
stand  in  the  opposed  cells  and  push  and  bend  the  ductile 
and  warm  wax  (which  as  I  have  tried  is  easily  done)  into 
its  proper  intermediate  plane,  and  thus  flatten  it. 

From  the  experiment  of  the  ridge  of  vei-milion  wax, 
we  can  clearly  see  that  if  the  bees  were  to  build  for  them- 
selves a  thin  wall  of  wax,  they  could  make  their  cells  of 
the  proper  shape,  by  standing  at  the  proper  distance  from 
each  other,  by  excavating  at  the  same  rate,  and  by  en- 
deavouring to  make  equal  spherical  hollows,  but  never 
allowing  the  spheres  to  break  into  each  other.  xS"ow 
bees,  as  may  be  clearly  seen  by  examining  the  edge  of  a 
growing  comb,  do  make  a  rough,  circumferential  wall  or 
rim  all  round  the  comb  ;  and  they  gnaw  into  this  from  the 
opposite  sides,  always  working  circularly  as  they  deepen 
each  cell.  They  do  not  make  the  whole  three-sided  pyra- 
midal base  of  any  one  cell  at  the  same  time,  but  only  the  one 
rhombic  plate  which  stands  on  the  extreme  growing  margin, 
or  the  two  plates,  as  the  case  may  be ;  and  they  never  com- 
plete the  upper  edges  of  the  rhombic  plates,  until  the 
hexagonal  walls  are  commenced.  Some  of  these  statements 
differ  from  those  made  b}^  the  justly  celebrated  elder  Huber, 


Chap.  VII.]  CELLS    OF   THE   HIVE-BEE.  205 

but  I  am  convinced  of  their  acciiracv ;  and  if  I  had  space. 
I  conld  show  that  thej  are  conformable  with  my  theory. 

Huber's  statement  that  the  very  first  cell  is  excavated 
out  of  a  little  parallel-sided  wall  of  wax,  is  not,  as  far  as  T 
have  seen,  strictly  correct ;  the  first  commencement  hav- 
ing always  been  a  little  hood  of  wax  ;  but  I  will  not  here 
enter  on  these  details.  We  see  how  important  a  part  ex- 
cavation plays  in  the  construction  of  the  cells  ;  but  it 
would  be  a  great  error  to  suppose  that  the  bees  cannot 
build  up  a  rough  wall  of  wax  in  the  proper  position — that 
is,  along  the  plane  of  intersection  between  two  adjoining 
spheres.  I  have  several  specimens  showing  clearly  that 
they  can  do  this.  Even  in  the  rude  circumferential  rim 
or  wall  of  wax  round  a  growing  comb,  fiexures  may  some- 
times be  observed,  corresponding  in  position  to  the  planes 
of  the  rhombic  basal  plates  of  future  cells.  But  the  rough 
wall  of  wax  has  in  every  case  to  be  finished  oif,  by  being 
largely  gnawed  away  on  both  sides.  The  manner  in 
which  the  bees  build  is  curious ;  they  always  make  the 
first  rough  wall  from  ten  to  twenty  times  thicker  than 
the  excessively  thin  finished  wall  of  the  cell,  which  will 
ultimately  be  left.  We  shall  understand  how  they  work, 
by  supposing  masons  first  to  pile  up  a  broad  ridge  of 
cement,  and  then  to  begin  cutting  it  away  equally  on  both 
sides  near  the  ground,  till  a  smooth,  very  thin  wall  is  left 
in  the  middle  ;  the  masons  always  piling  up  the  cut-away 
cement,  and  adding  fresh  cement,  on  the  summit  of  the 
ridge.  We  shall  thus  have  a  thin  wall  steadily  growing 
upward  ;  but  always  crowned  by  a  gigantic  coping.  From 
all  the  cells,  both  those  just  commenced  and  those  com- 
pleted, being  thus  crowned  by  a  strong  coping  of  wax, 
the  bees  can  cluster  and  crawl  over  the  comb  without  in- 
iuring  the  delicate  hexagonal  walls,  which  are  only  about 
one  four-hundreth  of  an  inch  in  thickness  ;  the  plates  of 
the  pyramidal  basis  being  about  twice  as  thick.  By  this 
singular  manner  of  building,  strength  is  continually  given 
to  the  comb,  with  the  utmost  ultimate  economy  of  wax. 

It  seems  at  first  to  add  to  the  difiiculty  of  understand- 
ing how  the  cells  are  made,  that  a  multitude  of  bees  all 
work  together  ;  one  bee  after  working  a  short  time  at  one 


205  INSTINCT.  [Chap.  VII. 

cell  going  to  another,  so  that,  as  Hiiber  has  stated,  a  score 
of  individuals  work  even  at  the  commencement  of  the  first 
cell.  I  was  able  practically  to  show  this  fact,  hy  covering 
the  edges  of  the  hexagonal  walls  of  a  single  cell,  or  the 
extreme  margin  of  the  circumferential  rim  of  a  growing 
comb,  with  an  extremely  thin  layer  of  melted  vermilion 
wax  ;  and  I  invariably  found  that  the  colour  was  most 
delicately  difi'used  by  the  bees — as  delicately  as  a  painter 
could  have  done  with  his  brush — by  atoms  of  the  coloured 
wax  having  been  taken  from  the  spot  on  which  it  had 
been  placed,  and  worked  into  the  growing  edges  of  the  cells 
all  round.  Tlie  work  of  construction  seems  to  be  a  sort 
of  balance  struck  between  many  bees,  all  instinctively 
standing  at  the  same  relative  distance  from  each  other,  all 
trying  to  sweep  equal  spheres,  and  then  building  up,  or 
leaving  ungnawecl,  the  planes  of  intersection  between 
these  spheres.  It  was  really  curious  to  note  in  cases  of 
difficulty,  as  when  two  j)ieces  of  comb  met  at  an  angle, 
how  often  the  bees  would  entirely  pull  down  and  rebuild 
in  different  ways  the  same  cell,  sometimes  recurring  to  a 
shape  which  they  had  at  first  rejected. 

When  bees  have  a  place  on  which  they  can  stand  in 
their  proper  positions  for  working — for  instance,  on  a  slip 
of  wood,  placed  directly  under  the  middle  of  a  comb 
growing  downwards  so  that  the  comb  has  to  be  built  over 
one  face  of  the  slip — in  this  case  the  bees  can  lay  the 
foundations  of  one  wall  of  a  new  hexagon,  in  its  strictly 
proper  place,  projecting  beyond  the  other  completed  cells. 
It  suffices  that  the  bees  should  be  enabled  to  stand  at  their 
proper  relative  distances  from  each  other  and  from  the 
walls  of  the  last  completed  cells,  and  then,  by  striking 
imaginary  spheres,  they  can  build  up  a  wall  intermediate 
between  two  adjoining  spheres  ;  but,  as  far  as  I  have 
seen,  they  never  gnaw  away  and  finish  off  the  angles  of  a 
cell  till  a  large  part  both  of  that  cell  and  of  the  adjoining 
cells  has  been  built.  This  capacity  in  bees  of  laying  down 
under  certain  circumstances  a  rough  wall  in  its  proper 
place  between  two  just-commenced  cells,  is  important,  as 
it  bears  on  a  fact,  which  seems  at  first  quite  subversive  of 
the  foregoing  theory  ;  namely,  that  the  cells  on  tlie  ex- 


Chap.  VIL]  CELLS    OF   THE    HIVE-BEE.  ^Q^ 

tremc  margin  of  wasp-combs  are  sometimes  strictly  hex- 
agonal ;  but  I  have  not  space  here  to  enter  on  this  sub- 
ject. I^or  does  there  seem  to  me  any  great  difficulty  in 
a  single  insect  (as  in  the  case  of  a  queen-wasp)  making 
hexagonal  cells,  if  she  work  alternately  on  the  inside  and 
outside  of  two  or  three  cells  commenced  at  the  same 
time,  always  standing  at  the  proper  relative  distance  from 
the  parts  of  the  cells  just  begun,  sweeping  spheres  or  cyl- 
inders, and  building  up  intermediate  planes.  It  is  even 
conceivable  that  an  insect  might,  by  fixing  on  a  point  at 
which  to  commence  a  cell,  and  then  moving  outside,  first 
to  one  point,  and  then  to  five  other  points,  at  the  proper 
relative  distances  from  the  central  point  and  from  each 
otiier,  strike  the  planes  of  intersection,  and  so  make  an 
isolated  liexagon  :  but  I  am  not  aware  that  any  such  case 
has  been  observed  ;  nor  would  any  good  be  derived  from 
a  single  hexagon  being  built,  as  in  its  construction  more 
materials  would  be  required  than  for  a  cylinder. 

As  natural  selection  acts  only  by  the  accumulation  of 
slight  modifications  of  structure  or  instinct,  each  profit- 
able to  the  individual  under  its  conditions  of  life,  it  may 
reasonably  be  asked,  how  a  long  and  graduated  succession 
of  modified  architectural  instincts,  all  tending  towards 
the  present  perfect  plan  of  construction,  could  have 
profited  the  progenitors  of  the  hive-bee  ?  I  think  the 
answer  is  not  difficult :  it  is  known  that  bees  are  often 
hard  pressed  to  get  sufficient  nectar  ;  and  I  am  informed 
by  Mr.  Tegetmeier  that  it  has  been  experimentally  found 
that  no  less  than  from  twelve  to  fifteen  pounds  of  dry  sugar 
are  consumed  by  a  hive  of  bees  for  the  secretion  of  each 
pound  of  wax ;  so  that  a  prodigious  quantity  of  fluid 
nectar  must  be  collected  and  consumed  by  the  bees  in  a 
hive  for  the  secretion  of  the  wax  necessary  for  the  con- 
struction of  their  combs.  Moreover,  many  bees  have  to 
remain  idle  for  many  days  during  the  process  of  secretion. 
A  large  store  of  honey  is  indispensable  to  support  a  large 
stock  of  bees  during  the  winter  ;  and  the  security  of  the 
hive  is  known  mainly  to  depend  on  a  large  number  of 
bee^  being  supported.  Hence  the  saving  of  wax  by 
largely  saving  honey  must  be  a  most  important  element 


208  INSTINCT.  [Chap.  VII. 

of  success  in  any  family  of  bees.  Of  course  the  success  of  any 
species  of  bee  may  be  dependent  on  the  number  of  its  para- 
sites or  other  enemies,  or  on  quite  distinct  causes,  and  so  be 
altogether  independent  of  the  quantity  of  honey  which  the 
bees  could  collect.  But  let  us  suppose  that  this  latter  cir- 
cumstance determined,  as  it  probably  often  does  determine, 
the  numbers  of  a  humble-bee  which  could  exist  in  a  country. 
But  let  us  suppose  (differently  to  what  really  is  the  case)  that 
the  community  lived  throus^hout  the  winter,  and  conse- 
quently required  a  store  of  honey :  there  can  in  this  case 
be  no  doubt  that  it  would  be  an  advantage  to  our  humble- 
bee,  if  a  slight  modification  of  her  instinct  led  her  to  make 
her  waxen  cells  near  together,  so  as  to  intersect  a  little  ; 
for  a  wall  in  common  even  to  two  adjoining  cells,  would 
save  some  little  wax.  Hence  it  would  continually  be 
more  and  more  advantageous  to  our  humble-bee,  if  she 
were  to  make  her  cells  more  and  more  regular,  nearer 
together,  and  aggregated  into  a  mass,  like  the  cells  of  the 
Melipona  ;  for  in  this  case  a  large  j)^i't  of  the  bounding 
surface  of  each  cell  would  serve  to  bound  other  cells,  and 
much  wax  would  be  saved.  Again,  from  the  same  cause, 
it  would  be  advantageous  to  the  Melij)ona,  if  she  were  to 
make  her  cells  closer  together,  and  more  regular  in  every 
w^ay  than  at  present;  for  then,  as  we  have  seen,  the  spher- 
ical surfaces  would  wholly  disappear,  and  would  all  be 
replaced  by  plane  surfaces  ;  and  the  Melipona  would 
make  a  comb  as  perfect  as  that  of  the  hive-bee.  Beyond 
this  stage  of  perfection  in  architecture,  natural  selection 
could  not  lead  ;  for  the  comb  of  the  hive-bee,  as  far  as  we 
can  see,  is  absolutely  perfect  in  economising  wax. 

Thus,  as  I  believe,  the  most  wonderful  of  all  Imown 
instincts,  that  of  the  hive-bee,  can  be  explained  by  natural 
selection  having  taken  ad  v^antage  of  numerous,  successive, 
slight  modifications  of  simpler  instincts  ;  natural  selection 
having  by  slow  degrees,  more  and  more  perfectly,  led  the 
bees  to  sweep  equal  spheres  at  a  given  distance  from  each 
other  in  a  double  layer,  and  to  build  up  and  excavate  the 
wax  along  the  planes  of  intersection.  The  bees,  of  course, 
no  more  knowing  that  they  swept  their  spheres  at  one 
particular  distance  from  each  other,  than  they  know  what 


Chap.  VII.]  NEUTER   INSECTS.  209 

are  the  several  angles  of  the  hexagonal  prisms  and  of  the 
basal  rhombic  plates.  The  motive  power  of  the  process 
of  natural  selection  having  been  economy  of  wax  ;  that 
individual  swarm  which  wasted  least  honey  in  the  secre- 
tion of  wax,  having  succeeded  best,  and  having  transmitted 
by  inheritance  its  newly  acquired  eonomical  instinct  to 
new  swarms,  which  in  their  turn  will  have  had  the  best 
chance  of  succeeding  in  the  struggle  for  existence. 

'No  doubt  many  instincts  of  very  difficult  explanation 
could  be  opposed  to  the  theory  of  natural  selection, — 
cases,  in  which  we  cannot  see  how  an  instinct  could  pos- 
sibly have  originated ;  cases,  in  which  no  intermediate 
gradations  are  known  to  exist ;  cases  of  instinct  of  appar- 
ently such  trifling  importance,  that  they  could  hardly 
have  been  acted  on  by  natural  selection ;  cases  of  instincts 
almost  identically  the  same  in  animals  so  remote  in  the 
scale  of  nature,  that  we  cannot  account  for  their  similarity 
by  inheritance  from  a  common  parent,  and  must  therefore 
believe  that  they  have  been  acquired  by  independent  acts 
of  natural  selection.  I  will  not  here  enter  on  these  several 
cases,  but  will  confine  myself  to  one  special  difficulty, 
which  at  first  appeared  to  me  insuperable,  and  actually 
fatal  to  my  whole  theory.  I  allude  to  the  neuters  or  ster- 
ile females  in  insect  communities  :  for  these  neuters  often 
difler  widely  in  instinct  and  in  structure  from  both  the 
males  and  fertile  females,  and  yet,  from  being  sterile,  they 
cannot  propagate  their  kind. 

The  subject  well  deserves  to  be  discussed  at  great 
length,  but  I  will  here  take  only  a  single  case,  that  of 
working  or  sterile  ants.  How  the  workers  have  been  ren- 
dered sterile  is  a  difficulty  ;  but  not  much  greater  than 
that  of  any  other  striking  modification  of  structure  ;  for 
it  can  be  shown  that  some  insects  and  other  articulate 
animals  in  a  state  of  nature  occasionally  become  sterile  ; 
and  if  such  insects  had  been  social,  and  it  had  been  profit- 
able to  the  community,  that  a  number  should  have  been 
annually  born  capable  of  work,  but  incapable  of  procrea- 
tion, I  can  see  no  very  great  difficulty  in  this  being  efi'ect- 
ed  by  natural  selection.     But  I  must  pass  over  this  pre- 


210  INSTINCT.  [Chap.  VIL 

liminary  difficulty.  The  great  difficulty  lies  in  the  working 
ants  differing  widely  from  both  the  males  and  the  fertile 
females  in  structure,  as  in  the  shape  of  the  thorax  and  in 
being  destitute  of  wings  and  sometimes  of  eyes,  and  in 
instinct.  As  far  as  instinct  alone  is  concerned,  the  prodi- 
gious difference  in  this  respect  between  the  workers  and 
the  perfect  females,  would  have  been  far  better  exempli- 
fied by  the  hive-bee.  If  a  working  ant  or  other  neuter 
insect  had  been  an  animal  in  the  ordinary  state,  I  should 
have  unhesitatingly  assumed  that  all  its  characters  had 
been  slowly  acquired  through  natural  selection ;  namely,  by 
an  individual  having  been  bom  with  some  slight  profitable 
modification  of  structure,  this  being  inherited  by  its  off- 
spring, which  again  varied  and  were  again  selected,  and 
so  onwards.  But  with  the  working  ant  we  have  an  insect 
differing  greatly  from  its  parents,  yet  absolutely  sterile ; 
so  that  it  could  never  have  transmitted  successively  ac- 
quired modifications  of  structure  or  instinct  to  its  progeny. 
It  may  well  be  asked  how  is  it  possible  to  reconcile  this 
case  with  the  theory  of  natural  selection  ? 

First,  let  it  be  remembered  that  we  have  innumerable 
instances,  both  in  our  domestic  productions  and  in  those 
in  a  state  of  nature,  of  all  sorts  of  differences  of  structure 
which  have  become  correlated  to  certain  ages,  and  to 
either  sex.  We  have  differences  correlated  not  only  to 
one  sex,  but  to  that  short  period  alone  when  the  repro- 
ductive system  is  active,  as  in  the  nuptial  plumage  of 
many  birds,  and.  in  the  hooked  jaws  of  the  male  salmon. 
"VVe  have  even  slight  difterences  in  the  horns  of  difterent 
breeds  of  cattle  in  relation  to  an  artificially  imperfect  state  of 
the  male  sex  ;  for  oxen  of  certain  breeds  have  longer  horns 
than  in  other  breeds,  in  comparison  with  the  horns  of  the 
bulls  or  cows  of  these  same  breeds.  Hence  I  can  see  no 
real  difficulty  in  any  character  having  become  correlated 
with  the  sterile  condition  of  certain  members  of  insect- 
communities  :  the  difficulty  lies  in  understanding  how 
such  correlated  modifications  of  structure  could  have  been 
slowly  accumulated  by  natural  selection. 


sened 


This  difficulty,  though  appearing  insuperable,  is  les- 
ed,  or,  as  I  believe,  disappears,  wlien  it  is  remembered 


Chap.  VIL]  NEUTER   INSECTS.  211 

that  selection  may  be  applied  to  the  family,  as  well  as  to  the 
individual,  and  may  thus  gain  the  desired  end.  Thus,  a 
well-flavored  vegetable  is  cooked,  and  the  individual  is 
destroyed  ;  but  the  horticulturist  sows  seeds  of  the  same 
stock,  and  confidently  expects  to  get  nearly  the  same 
variety  ;  breeders  of  cattle  wish  the  flesh  and  fat  to  be 
well-marbled  together  ;  the  animal  has  been  slaughtered, 
but  the  breeder  goes  with  confidence  to  the  same  family, 
I  have  such  faith  in  the  powers  of  selection,  that  I  do  not 
doubt  that  a  breed  of  cattle,  always  yielding  oxen  with 
extraordinarily  long  horns,  could  be  slowly  formed  by 
carefully  watching  which  individual  bulls  and  cows,  when 
matched,  produced  oxen  with  the  longest  horns  ;  and  yet 
no  one  ox  could  ever  have  propagated  its  kind.  Thus  I 
believe  it  has  been  with  social  insects  :  a  slight  modifica- 
tion of  structure,  or  instinct,  correlated  with  the  sterile 
condition  of  certain  members  of  the  community,  has  been 
advantageous  to  the  community  :  consequently  the  fertile 
males  and  females  of  the  same  community  flourished,  and 
trasmitted  to  their  fertile  offspring  a  tendency  to  produce 
sterile  members  having  the  same  modification.  And  I 
believe  that  this  process  has  been  repeated,  until  that 
prodigious  amount  of  diflference  between  the  fertile  aj^d 
sterile  females  of  the  same  species  has  been  proginced, 
which  we  see  in  many  social  insects. 

But  we  have  not  as  yet  touched  on  the  climax  of  the  difiS.- 
culty ;  namely,  the  fact  that  the  neuters  of  several  ants 
differ,  not  only  from  the  fertile  females  and  males,  but  from 
each  other,  sometimes  to  an  almost  incredible  degree,  and  are 
thus  divided  into  two  or  even  three  castes.  The  castes, 
moreover,  do  not  generally  graduate  into  each  other,  but  are 
perfectly  well  defined  ;  being  as  distinct  from  each  other,  as 
are  any  two  species  of  the  same  genus,  or  rather  as  any  two 
genera  of  the  same  family.  Thus  in  Eciton,  there  are 
working  and  soldier  neuters,  with  jaws  and  instincts  ex- 
traordinarily different :  in  Cryptocerus,  the  workers  of 
one  caste  alone  carry  a  wonderful  sort  of  shield  on  their 
heads,  the  use  of  which  is  quite  unknown  :  in  the  Mexican 
Myrmecocystus,  the  workers  of  one  caste  never  leave  the 
nest ;  they  are  fed  by  the  workers  of  another  caste,  and 
10* 


212  INSTINCT.  tCHAP.  vn. 

they  have  an  enormously  developed  abdomen  which  se- 
cretes a  sort  of  honey,  supplying  the  place  of  that  excreted 
by  the  aphides,  or  the  domestic  cattle  as  they  may  be 
called,  which  onr  Em-oj^ean  ants  guard  or  imprison. 

It  will  indeed  be  thought  that  I  have  an  overweening 
confidence  in  the  principle  of  natural  selection,  when  I  do 
not  admit  that  such  wonderful  and  well-established  facts  at 
once  annihilate  my  theory.  In  the  simpler  case  of  neuter 
insects  all  of  one  caste  or  of  the  same  kind,  which  have 
been  rendered  by  natural  selection,  as  I  believe  to  be  quite 
possible,  different  from  the  fertile  males  and  females, — in 
this  case  we  may  safely  conclude  from  the  analogy  of 
ordinary  variations,  that  each  successive,  slight,  profitable 
inodification  did  not  probably  at  first  appear  in  all  the 
individual  neuters  in  the  same  nest,  but  in  a  few  alone ; 
and  that  by  the  long-continued  selection  of  the  fertile 
parents  which  produced  most  neuters  with  the  profitable 
modification,  all  the  neuters  ultimately  came  to  have  the 
desired  character.  On  this  view  we  ought  occasionally 
to  find  neuter-insects  of  the  same  species,  in  the  same 
nest,  presenting  gradations  of  structure ;  and  this  we  do 
find,  even  often,  considering  how  few  neuter-insects  out  of 
Ei^rope  have  been  carefully  examined.  Mr.  F.  Smith  has 
shown  how  surprisingly  the  neuters  of  several  British 
ants  difi'er  from  each  other  in  size  and  sometimes  in 
colour ;  and  that  the  extreme  forms  can  sometimes  be 
perfectly  linked  together  by  individuals  taken  out  of  the 
same  nest :  I  have  myself  compared  perfect  gradations 
of  this  kind.  It  often  happens  that  the  larger  or  the 
smaller  sized  workers  are  the  most  numerous ;  or  that 
both  large  and  small  are  numerous,  with  those  of  an 
intermediate  size  scanty  in  numbers.  Formica  flava  has 
larger  and  smaller  workers,  with  some  of  intermediate 
size ;  and,  in  this  species,  as  Mr.  F.  Smith  has  observed, 
the  larger  workers  have  simple  eyes  (ocelli),  which  though 
small  can  be  plainly  distinguished,  whereas  the  smaller 
workers  have  their  ocelli  rudimentary.  Having  carefully 
dissected  several  specimens  of  these  workers,  I  can  aftirm 
that  the  eyes  are  far  more  rudimentary  in  the  smaller 
workers  than  can  be  accounted  for  merely  by  their  pro- 


Ohap.  Vli.3  K-EUTER   lls*SECTS.  213 

portionally  lesser  size  ;  and  I  fully  believe,  though  I  dare 
not  assert  so  positively,  that  the  workers  of  intermediate 
size  have  their  ocelli  in  an  exactly  intermediate  condition. 
So  that  we  here  have  two  bodies  of  sterile  workers  in  the 
same  nest,  differing  not  only  in  size,  but  in  their  organs 
of  vision,  yet  connected  by  some  few  members  in  an 
intermediate  condition.  I  may  digress  by  adding,  that  if 
the  smaller  workers  had  been  the  most  useful  to  the  com- 
munity, and  those  males  and  females  had  been  continually 
selected,  which  produced  more  and  more  of  the  smaller 
workers,  until  all  the  workers  had  come  to  be  in  this  con- 
dition ;  we  should  then  have  had  a  species  of  ant  with 
neuters  very  nearly  in  the  same  condition  with  those  of 
Myrmica.  For  the  workers  of  Myrmica  have  not  even 
rudiments  of  ocelli,  though  the  male  and  female  ants  of 
this  genus  have  well-developed  ocelli. 

I  may  give  one  other  case :  so  confidently  did  I  expect 
to  find  gradations  in  important  points  of  structure  between 
the  different  castes  of  neuters  in  the  same  species,  that  I 
gladly  availed  myself  of  Mr.  F.  Smith's  offer  of  numerous 
specimens  from  the  same  nest  of  the  driver  ant  (Anomma) 
of  West  Africa.  The  reader  will  perhaps  best  appreciate 
the  amount  of  difference  in  these  workers,  by  my  giving 
not  the  actual  measurements,  but  a  strictly  accurate  illus- 
tration :  the  difference  was  the  same  as  if  we  were  to  see 
a  set  of  workmen  building  a  house,  of  whom  many  were 
five  feet  four  inches  high,  and  many  sixteen  feet  high ; 
but  we  must  suppose  that  the  larger  workmen  had  heads 
four  instead  of  three  times  as  big  as  those  of  the  smaller 
men,  and  jaws  nearly  five  times  as  big.  The  jaws,  more- 
over, of  the  working  ants  of  the  several  sizes  differ 
wonderfully  in  shape,  and  in  the  form  and  number  of  the 
teeth.  But  the  important  fact  for  us  is,  that  though  the 
workers  can  be  grouped  into  castes  of  different  sizes,  yet 
they  graduate  insensibly  into  each  other,  as  does  the  widely- 
different  structure  of  their  jaws.  I  speak  confidently  on 
this  latter  point,  as  Mr.  Lubbock  made  drawings  for  me 
with  the  camera  lucida  of  the  jaws  which  I  had  dissected 
from  the  workers  of  the  several  sizes. 

With  these  facts  before  me,  I  believe  that  natural  se= 


214:  INSTINCT.  [CHAt.  VIL 

lection,  by  acting  on  the  fertile  pare^its,  could  form  a  spe- 
cies which  should  regularly  produce  neuters,  either  all 
of  large  size  with  one  form  of  jaw,  or  all  of  small  size 
with  jaws  having  a  widely  different  structure  ;  or  lastly, 
and  this  is  our  climax  of  difficulty,  one  set  of  workers  of 
one  size  and  structure,  and  simultaneously  another  set  of 
workers  of  a  different  size  and  structure ; — a  graduated 
series  having  been  first  formed,  as  in  the  case  of  the  driver 
ant,  and  then  the  extreme  forms,  from  being  the  most 
useful  to  the  community,  having  been  produced  in  greater 
and  greater  numbers  through  the  natural  selection  of  the 
parents  which  generated  them ;  until  none  with  an  inter- 
mediate structure  were  produced. 

Thus,  as  I  believe,  the  wonderful  fact  of  two  distinctly 
defined  castes  of  sterile  workers  existing  in  the  same  nest, 
both  widely  different  from  each  other  and  from  their 
parents,  has  originated.  We  can  see  how  useful  their 
production  may  have  been  to  a  social  community  of 
insects,  on  the  same  principle  that  the  division  of  labour 
is  useful  to  civilised  man.  As  ants  work  by  inherited 
instincts  and  by  inherited  tools  or  weapons,  and  not  by 
acquired  knowledge  and  manufactured  instniments,  a  per- 
fect division  of  labour  could  be  effected  with  them  only 
by  the  workers  being  sterile  ;  for  had  they  been  fertile, 
they  would  have  intercrossed,  and  their  instincts  and 
structure  would  have  become  blended.  And  nature  has, 
as  I  believe,  effected  this  admirable  division  of  labour  in 
the  communities  of  ants,  by  the  means  of  natural  selec- 
tion. But  I  am  bound  to  confess,  that,  with  all  my  faith 
m  this  principle,  I  should  never  have  anticipated  that 
natural  selection  could  have  been  efficient  in  so  high  a 
degree,  had  not  the  case  of  these  neuter  insects  convinced 
me  of  the  fact.  I  have,  therefore,  discussed  this  case,  at 
some  little  but  wholly  insufficient  length,  in  order  to  show 
the  power  of  natural  selection,  and  likewise  because  this 
is  by  far  the  most  serious  special  difficulty,  which  my 
theory  has  encountered.  The  case,  also,  is  very  interesting, 
as  it  proves  that  with  animals,  as  with  plants,  any  amount 
of  modification  in  structure  can  be  effected  by  the  accu- 
mulation of  numerous,  slight,  and  as  we  must  call  them 


Chap.  Vll.]  BITMMARY.  215 

accidental,  yariations,  whicli  are  in  any  manner  profitable, 
without  exercise  or  habit  having  come  into  play.  For  no 
amount  of  exercise,  or  habit,  or  yolition,  in  the  utterly 
sterile  members  of  a  community  could  possibly  haye 
affected  the  structure  or  instincts  of  the  fertile  members, 
which  alone  leaye  descendants.  I  am  surprised  that  no 
one  has  advanced  this  demonstrative  case  of  neuter  insects, 
against  the  well-known  doctrine  of  Lamarck. 

Summary. — I  have  endeavoured  briefly  in  this  chajDter 
to  show  that  the  mental  qualities  of  our  domestic  animals 
vary,  and  that  the  variations  are  inherited.  Still  more 
briefly  I  have  attempted  to  show  that  instincts  vary 
slightly  in  a  state  of  nature.  ]^o  one  will  dispute  that 
instincts  are  of  the  highest  importance  to  each  animal. 
Therefore  I  can  see  no  difiiculty,  under  changing  condi- 
tions of  life,  in  natural  selection  accumulating  slight 
modifications  of  instinct  to  any  extent,  in  any  useful 
direction.  In  some  cases  habit  or  use  and  disuse  have 
probably  come  into  play.  I  do  not  pretend  that  the  facts 
given  in  this  chapter  strengthen  in  any  great  degree  my 
theory  ;  but  none  of  the  cases  of  difiiculty,  to  the  best 
of  my  judgment,  annihilate  it.  On  the  other  hand,  the 
fact  that  instincts  are  not  always  absolutely  perfect  and 
are  liable  to  mistakes  ; — that  no  instinct  has  been  produced 
for  the  exclusive  good  of  other  animals,  but  that  each 
animal  takes  advantage  of  the  instincts  of  others  ; — that 
the  canon  in  natural  history,  of  "  natura  non  facit  saltum  " 
is  applicable  to  instincts  as  well  as  to  corporeal  structure, 
and  is  plainly  explicable  on  the  foregoing  views,  but  is 
otherwise  inexplicable, — all  tend  to  corroborate  the  theory 
of  natural  selection. 

This  theory  is,  also,  strengthened  by  some  few  other 
facts  in  regard  to  instincts ;  as  by  that  common  case  of 
closely  allied,  but  certainly  distinct,  species,  when  inhab- 
iting distant  parts  of  the  world  and  living  under  consider- 
ably different  conditions  of  life,  yet  often  retaining  nearly 
the  same  instincts.  For  instance,  we  can  understand  on 
the  principle  of  inheritance,  how  it  is  that  the  thrush  of 
South  America  lines  its  nest  with  mud,  in  the  same  pecu- 


216  INSTINCT.  [Chap.  Vll, 

liar  manner  as  does  our  British  thrush :  how  it  is  that  the 
Hornbills  of  Africa  and  India,  though  belonging  to  allied 
but  distinct  genera,  have  the  same  extraordinary  instinct 
of  plastering  up  and  imprisoning  their  hens  whilst  sitting 
on  their  eggs  in  a  hole  in  a  tree,  with  only  a  small  hole 
left  in  the  plaster,  through  which  the  males  feed  the 
hens  and  the  young  when  hatched :  how  it  is  that  the 
male  wrens  (Troglodytes)  of  Korth  America,  build  "  cock- 
nests,"  to  roost  in,  like  the  males  of  our  distinct  Kitty- 
wrens, — a  habit  wholly  unlike  that  of  any  other  known 
bird.  Finally,  it  may  not  be  a  logical  deduction,  but  to 
my  imagiuation  it  is  far  more  satisfactory  to  look  at  such 
instiucts  as  the  young  cuckoo  ejecting  its  foster  brothers, 
— ants  making  slaves, — the  larvae  of  ichneumonidae  feed- 
ing within  the  live  bodies  of  caterpillars, — ^not  as  es23ecial- 
ly  endowed  or  created  instincts,  but  as  small  consequences 
of  one  general  law,  leading  to  the  advancement  of  all  or- 
ganic beings,  namely,  multiply,  vary,  let  the  strongest 
live  and  the  weakest  die. 


Chap.  VIIL]  HYBRIDISM.  217 


CHAPTER   YIII. 

HYBRIDISM. 

Distinction  between  the  sterility  of  iirst  crosses  and  of  hybrids— Sterility  various  in 
degree,  not  universal,  afiected  by  close  interbreeding,  removed  by  domestication — 
Laws  governing  the  sterility  of  hybrids— Sterility  not  a  special  endowment,  but 
incidental  on  other  diiJerences— Causes  of  the  sterility  of  first  crosses  and  of 
hybrids— Parallelism  between  the  effects  of  changed  conditions  of  life  and  cross- 
ing-Fertility of  varieties  when  crossed  and  of  their  mongrel  offspring  not  uni- 
versal—Hybrids and  mongrels  compared  independently  of  their  fertility— Sum- 
mary. 

The  view  generally  entertained  by  naturalists  is  that  spe- 
cies, wlien  intercrossed,  have  been  specially  endowed  with 
the  quality  of  sterility,  in  order  to  prevent  the  confusion 
of  all  organic  forms.  This  view  certainly  seems  at  first 
probable,  for  species  within  the  same  country  could  hard- 
ly have  kept  distinct  had  they  been  capable  of  crossing 
freely.  The  importance  of  the  fact  that  hybrids  are  very 
generally  sterile,  has,  I  think,  been  much  underrated  by 
some  late  writers.  On  the  theory  of  natural  selection  the 
case  is  especially  important,  inasmuch  as  the  sterility  of 
hybrids  could  not  possibly  be  of  any  advantage  to  them, 
and  therefore  could  not  have  been  acquired  by  the  con- 
tinued preservation  of  successive  profitable  degrees  of 
sterility.  I  hope,  however,  to  be  able  to  show  that  ste- 
rility is  not  a  specially  acquired  or  endowed  quality,  but 
is  incidental  on  other  acquired  differences. 

In  treating  this  subject,  two  classes  of  facts,  to  a  large 
extent  fundamentally  different,  have  generally  been  con- 
founded together;  namely,  the  sterility  of  two  species 
when  first  crossed,  and  the  sterility  of  the  hybrids  pro- 
duced from  them. 

Pure  species  have  of  course  their  organs  of  reproduc- 
tion in  a  perfect  condition,  yet  when  intercrossed  they 


2;|^g  HYBRIDISM.  IChap.  VIII. 

produce  either  few  or  no  offspring.  Hybrids,  on  tliG 
other  hand,  have  their  reproductive  organs  functionally 
impotent,  as  may  be  clearly  seen  in  the  state  of  the  male 
element  in  both  plants  and  animals  ;  though  the  organs 
themselves  are  perfect  in  structure,  as  far  as  the  micro- 
scope reveals.  In  the  first  case  the  two  sexual  elements 
which  go  to  form  the  embryo  are  perfect ;  in  the  second 
case  they  are  either  not  at  all  developed,  or  are  imper- 
fectly developed.  This  distinction  is  important,  when  the 
cause  of  the  sterility,  which  is  common  to  the  two  cases, 
has  to  be  considered.  The  distinction  has  probably  been 
slurred  over,  owing  to  the  sterility  in  both  cases  being 
looked  on  as  a  special  endowment,  beyond  the  province 
of  our  reasoning  powers. 

The  fertility  of  varieties,  that  is  of  the  forms  known  or 
believed  to  have  descended  from  common  parents,  when 
intercrossed,  and  likewise  the  fertility  of  their  mongrel 
offspring,  is,  on  my  theory,  of  equal  importance  with  the 
sterility  of  species ;  for  it  seems  to  make  a  broad  and 
clear  distinction  between  varieties  and  species. 

First,  for  the  sterility  of  species  when  crossed  and  of 
their  hybrid  offspring.  It  is  impossible  to  study  the  sev- 
eral memoirs  and  works  of  those  two  conscientious  and 
admirable  observers,  Kolreuter  and  Gartner,  who  almost 
devoted  their  lives  to  this  subject,  without  l)eing  deeply 
impressed  with  the  high  generality  of  some  degree  of  ste- 
rility. Kolreuter  makes  the  rule  universal ;  but  then  he 
cuts  the  knot,  for  in  ten  cases  in  which  he  found  two 
forms,  considered  by  most  authors  as  distinct  species, 
quite  fertile  together,  he  unhesitatingly  ranks  tliem  as  va- 
rieties. Gartner  also,  makes  the  rule  equally  universal ; 
and  he  disputes  the  entire  fertility  of  Kolreuter's  ten  cases. 
But  in  these  and  in  many  other  cases,  Gartner  is  obliged 
carefully  to  count  the  seeds,  in  order  to  show  that  there  is 
any  degree  of  sterility.  He  always  compares  the  maxi- 
mum number  of  seeds  produced  by  two  species  when 
crossed  and  by  their  hybrid  offspring,  Avitli  the  average 
number  produced  by  both  pure-parent  sj^ecies  in  a  state 
of  nature.  But  a  serious  cause  of  error  seems  to  me  to 
be  here  introduced  :  a  plant  to  be  hybridised  must  be  cas- 


Chap.  VIIL]  STERILITY.  219 

tratecl,  and,  what  is  often  more  important,  must  be  se- 
cluded in  order  to  prevent  pollen  being  brought  to  it  by 
insects  from  other  j^lants.  I^early  all  the  plants  experi- 
mentised  on  bj  Gartner  were  potted,  and  apparently  were 
kept  in  a  chamber  in  his  house.  That  these  processes  are 
often  injurious  to  the  fertility  of  a  plant  cannot  be  doubt- 
ed ;  for  Gartner  gives  in  his  table  about  a  score  of  cases 
of  plants  which  he  castrated,  and  artificially  fertilised 
with  their  own  pollen,  and  (excluding  all  cases  such  as  the 
Leguminosse,  in  which  there  is  an  acknowledged  difiiculty 
in  the  manipulation)  half  of  these  twenty  plants  had  their 
fertility  in  some  degree  impaired.  Moreover,  as  Gartner 
during  several  years  repeatedly  crossed  the  primrose  and 
cowslip,  which  we  have  such  good  reasons  to  believe  to 
be  varieties,  and  only  once  or  twice  succeeded  in  getting 
fertile  seed  ;  as  he  found  the  common  red  and  blue  j)im- 
pernels  (Anagallis  arvensis  and  coerulea),  which  the  best 
botanists  rank  as  varieties,  absolutely  sterile  together ; 
and  as  he  came  to  the  same  conclusion  in  several  other 
analogous  cases ;  it  seems  to  me  that  we  may  well  be 
permitted  to  doubt  whether  many  other  species  are  really 
so  sterile,  when  intercrossed,  as  Gartner  believes. 

It  is  certain,  on  the  one  hand,  that  the  sterility  of  va- 
rious species  when  crossed  is  so  different  in  degree  and 
graduates  away  so  insensibly,  and,  on  the  other  hand,  that 
the  fertility  of  pure  species  is  so  easily  affected  by  various 
circumstances,  that  for  all  practical  purposes  it  is  most 
difiicult  to  say  where  perfect  fertility  ends  and  sterility 
begins.  I  think  no  better  evidence  of  this  can  be  required 
than  that  the  two  most  experienced  observers  who  have 
ever  lived,  namely,  Kolreuter  and  Gartner,  should  have 
arrived  at  diametrically  opposite  conclusions  in  regard  to 
the  very  same  species.  It  is  also  most  instructive  to  com- 
pare— but  I  have  not  space  here  to  enter  on  details — the 
evidence  advanced  by  our  best  botanists  on  the  question 
whether  certain  doubtful  forms  should  be  ranked  as  sj)e- 
cies  or  varieties,  with  the  evidence  from  fertility  adduced 
by  different  hybridisers,  or  by  the  same  author,  from  ex- 
periments made  during  different  years.  It  can  thus  be 
shown  that  neither  sterility  nor  fertility  affords  any  clear 


220  HYBRIDISM.  [Chap.  VIII 

distinction  between  species  and  varieties ;  but  tliat  the 
evidence  from  this  source  graduates  away,  and  is  doubt- 
ful in  tlie  same  degree  as  is  the  evidence  derived  from 
other  constitutional  and  structural  differences. 

In  regard  to  the  sterility  of  hybrids  in  successive  gen- 
erations ;  though  Grartner  was  enabled  to  rear  some  hy- 
brids, carefully  guiding  them  from  a  cross  with  either 
pure  parent,  for  six  or  seven,  and  in  one  case  for  ten  gen- 
erations, yet  he  asserts  positively  that  their  fertility  never 
increased,  but  generally  greatly  decreased.  I  do  not 
doubt  that  this  is  usually  tlie  case,  and  that  the  fertility 
often  suddenly  decreases  in  the  first  few  generations. 
^Nevertheless  I  believe  that  in  all  these  experiments  the 
fertility  has  been  diminished  by  an  independent  cause, 
namely,  from  close  interbreeding.  I  have  collected  so 
large  a  body  of  facts,  showing  that  close  interbreeding 
lessens  fertility,  and,  on  the  other  hand,  that  an  occasional 
cross  with  a  distinct  individual  or  variety  increases  fertili- 
ty, that  I  cannot  doubt  the  correctness  of  this  almost  uni- 
versal belief  amongst  breeders.  Hybrids  are  seldom 
raised  by  experimentalists  in  great  numbers ;  and  as  the 
parent-species,  or  other  allied  hybrids,  generally  grow  in 
the  same  garden,  the  visits  of  insects  must  be  carefully 
prevented  during  the  flowering  season :  hence  hybrids 
will  generally  be  fertilised  during  each  generation  by 
their  own  individual  pollen  ;  and  I  am  convinced  that  this 
would  be  injurious  to  their  fertility,  already  lessened  by 
their  hybrid  origin.  I  am  strengthened  in  this  conviction 
by  a  remarkable  statement  repeatedly  made  by  Gartner, 
namely,  that  if  even  the  less  fertile  hybrids  be  artificially 
fertilised  with  hybrid  pollen  of  the  same  kind,  their  fer- 
tility, notwithstanding  the  frequent  ill  eflects  of  manipu- 
lation, sometimes  decidedly  increases,  and  goes  on  increas- 
ing. Now,  in  artificial  fertilisation  pollen  is  as  often 
taken  by  chance  (as  I  know  from  my  own  experience) 
from  the  anthers  of  another  flower,  as  from  the  anthers  of 
the  flower  itself  which  is  to  be  fertilised  ;  so  that  a  cross 
between  two  flowers,  though  probably  on  the  same  plant, 
would  be  thus  efi'ected.  Moreover,  whenever  complicat- 
ed experiments  are  in  progress,  so  careful  an  observer  as 


Chap.  VIIL]  STERILITY.  221 

Gartner  would  have  castrated  his  hybrids,  and  this  would 
have  insured  in  each  generation  a  cross  with  a  pollen  from 
a  distinct  flower,  either  from  the  same  plant  or  from 
another  plant  of  the  same  hybrid  nature.  And  thus,  the 
strange  fact  of  the  increase  of  fertility  in  the  successive 
generations  of  artificially  fertilised  hybrids  may,  I  be- 
lieve, be  accounted  for  by  close  interbreeding  having  been 
avoided. 

]^ow  let  us  turn  to  the  results  arrived  at  by  the  third 
most  experienced  hybridiser,  namely,  the  Hon.  and  Kev. 
"W.  Herbert.  He  is  as  emphatic  in  his  conclusion  that 
some  hybrids  are  perfectly  fertile — as  fertile  as  the  pure 
parent  species — as  are  Kobeuter  and  Gartner  that  some 
degree  of  sterility  between  distinct  species  is  a  universal 
law  of  nature.  He  experimentised  on  some  of  the  very 
same  species  as  did  Gartner.  The  difi'erence  in  their  re- 
sults may,  I  think,  be  in  part  accounted  for  by  Herbert's 
great  horticultural  skill,  and  by  his  having  hothouses  at 
his  command.  Of  his  many  important  statements,  I  will 
here  give  only  a  single  one  as  an  example,  namely,  that 
"  every  ovule  in  a  pod  of  Crinum  capense  fertilised  by  C. 
revolutum  produced  a  plant,  which  (he  says)  I  never  saw 
to  occur  in  a  case  of  its  natural  fecundation."  So  that  we 
here  have  perfect,  or  even  more  than  commonly  perfect, 
fertility  in  a  first  cross  between  two  distinct  species. 

This  case  of  the  Crinum  leads  me  to  refer  to  a  most 
singular  fact,  namely,  that  there  are  individual  plants,  as 
with  certain  species  of  Lobelia,  and  with  all  the  species 
of  the  genus  Hippeastrum,  which  can  be  far  more  easily 
fertilised  by  the  pollen  of  another  and  distinct  species, 
than  by  their  own  pollen.  For  these  plants  have  been 
found  to  yield  seed  to  the  pollen  of  a  distinct  species, 
though  quite  sterile  with  their  own  pollen,  notwithstand- 
ing that  their  own  pollen  was  found  to  be  perfectly  good, 
for  it  fertilised  distinct  species.  So  that  certain  individual 
plants  and  all  the  individuals  of  certain  species  can  ac- 
tually be  hybridised  much  more  readily  than  they  can  be 
self-fertilised !  For  instance,  a  bulb  of  Hippeastrum  auli- 
cum  produced  four  flowers ;  three  were  fertilised  by  Her- 
bert with  their  own  pollen,  and  the  fourth  was  subse- 


222  HYBRIDISM.  [Chap.  VIIL 

quently  fertilised  by  tlie  pollen  of  a  compound  hybrid 
descended  from  three  other  and  distinct  species :  the  result 
was  that  "  the  ovaries  of  the  three  first  flowers  soon  ceased 
to  grow,  and  after  a  few  days  perished  entirely,  whereas 
the  pod  impregnated  by  the  pollen  of  the  hybrid  made 
vigorous  growth  and  rapid  progress  to  maturity,  and  bore 
good  seed,  which  vegetated  freely."  In  a  letter  to  me, 
in  1839,  Mr.  Herbert  told  me  that  he  had  then  tried  the 
experiment  during  five  years,  and  he  continued  to  try  it 
during  several  subsequent  years,  and  always  with  the 
same  result.  This  result  has,  also,  been  confirmed  by 
other  observers  in  the  case  of  Hippeastrum  with  its  sub- 
genera, and  in  the  case  of  some  other  genera,  as  Lobelia, 
Passiflora  and  Yerbascum.  Although  the  plants  in 
these  experiments  appeared  perfectly  healthy,  and  al- 
though both  the  ovules  and  pollen  of  the  same  flower 
were  perfectly  good  with  respect  to  other  species,  yet  as 
they  were  functionally  imperfect  in  their  mutual  self- 
action,  we  must  infer  that  the  plants  were  in  an  unnatural 
state.  ^Nevertheless  these  facts  show  on  what  slight  and 
mysterious  causes  the  lesser  or  greater  fertility  of  species 
when  crossed,  in  comparison  with  the  same  species  when 
self-fertilised,  sometimes  depends. 

The  practical  experiments  of  horticulturists,  though 
not  made  with  scientific  precision,  deserve  some  notice. 
It  is  notorious  in  how  complicated  a  manner  the  species 
of  Pelargonium,  Fuchsia,  Calceolaria,  Petunia,  Rhodo- 
dendron, &c.,  have  been  crossed,  yet  many  of  these  hybrids 
seed  freely.  For  instance,  Herbert  asserts  that  a  hybrid 
from  Calceolaria  integrifolia  and  plantaginea,  species  most 
widely  dissimilar  in  general  habit,  "  reproduced  itself  as 
perfectly  as  if  it  had  been  a  natural  sj^ecies  from  the 
mountains  of  Chile."  I  have  taken  some  pains  to  ascer- 
tain the  degree  of  fertility  of  some  of  the  complex  crosses 
of  Rhododendrons,  and  I  am  assured  that  many  of  them 
are  perfectly  fertile.  Mr.  C.  Noble,  for  instance,  informs 
me  that  he  raises  stocks  for  grafting  from  a  hybrid  be- 
tween lihod.  Ponticum  and  Catawbiense,  and  that  this 
hybrid  "  seeds  as  freely  as  it  is  possible  to  imagine." 
Had  hybrids,  when  fairly  treated,  gone  on  decreasing  in 


Chap.  VIII.]  STERILITY.  223 

fertility  in  each  successive  generation,  as  Gartner  believes 
to  be  the  case,  the  fact  would  have  been  notorious  to  nur- 
serymen. Horticulturists  raise  large  beds  of  the  same 
hybrids,  and  such  alone  are  fairly  treated,  for  by  insect 
agency  the  several  individuals  of  the  same  hybrid  variety 
are  allowed  to  freely  cross  with  each  other,  and  the  in- 
jurious influence  of  close  interbreeding  is  thus  prevented. 
Any  one  may  readily  convince  himself  of  the  efficiency 
of  insect-  agency  by  examining  the  flowers  of  the  more 
sterile  kinds  of  hybrid  rhododendrons,  which  produce  no 
pollen,  for  he  will  find  on  their  stigmas  plenty  of  pollen 
brought  from  other  flowers. 

In  regard  to  animals,  much  fewer  experiments  have 
been  carefully  tried  than  with  plants.  If  our  systematic 
arrangements  can  be  trusted,  that  is  if  the  genera  of  ani- 
mals are  as  distinct  from  each  other,  as  are  the  genera  of 
plants,  then  we  may  infer  that  animals  more  widely  sep- 
arated in  the  scale  of  nature  can  be  more  easily  crossed 
than  in  the  case  of  plants ;  but  the  hybrids  themselves 
are,  I  think,  more  sterile.  I  doubt  whether  any  case  of 
a  perfectly  fertile  hybrid  animal  can  be  considered  as 
thoroughly  well  authenticated.  It  should,  however,  be 
borne  in  mind  that,  owing  to  few  animals  breeding  freely 
under  confinement,  few  experiments  have  been  fairly 
tried :  for  instance,  the  canary-bird  has  been  crossed  with 
nine  other  finches,  but  as  not  one  of  these  nine  species 
breeds  freely  in  confinement,  we  have  no  right  to  expect 
that  the  first  crosses  between  them  and  the  canary,  or 
that  their  hybrids,  should  be  perfectly  fertile.  Again, 
with  respect  to  the  fertility  in  successive  generations  of 
the  more  fertile  hybrid  animals,  I  hardly  know  of  an 
instance  in  which  two  families  of  the  same  hybrid  have 
been  raised  at  the  same  time  from  difi'erent  parents,  so  as 
to  avoid  the  ill  efi'ects  of  close  interbreeding.  On  the 
contrary,  brothers  and  sisters  have  usually  been  crossed 
in  each  successive  generation,  in  opposition  to  the  con- 
stantly repeated  admonition  of  every  breeder.  And  in 
this  case,  it  is  not  at  all  surprising  that  the  inherent 
sterility  in  the  hybrids  should  have  gone  on  increasing. 
If  we  were  to  act  thus,  and  pair  brothers  and  sisters  in 


224  HYBRIDISM.  [Chap.  VHl. 

tlie  case  of  any  pure  animal,  wbicli  from  any  cause  had 
the  least  tendency  to  sterility,  the  breed  would  assuredly 
be  lost  in  a  very  few  generations. 

Although  I  do  not  know  of  any  thoroughly  well- 
authenticated  cases  of  j)erfectly  fertile  hybrid  animals,  I 
have  some  reason  to  believe  that  the  hybrids  from  Cer- 
vulus  vaginalis  and  Reevesii,  and  from  Phasianus  colchicus 
with  P.  torquatus  and  with  P.  versicolor  are  perfectly  fer- 
tile. There  is  no  doubt  that  these  three  pheasants,  namely, 
the  common,  the  true  ring-necked,  and  the  Japan,  inter- 
cross, and  are  becoming  blended  together  in  the  woods  of 
several  parts  of  England.  The  hybrids  from  the  common  and 
Chinese  geese  (A.  cygnoides),  species  which  are  so  different 
that  they  are  generally  ranked  in  distinct  genera,  have  often 
bred  in  this  country  with  either  pure  parent,  and  in  one  sin- 
gle instance  they  have  bred  inter  se.  This  was  effected  by 
Mr.  Eyton,  who  raised  two  hybrids  from  the  same  parents 
but  from  different  hatches  ;  and  from  these  two  birds  he 
raised  no  less  than  eight  hybrids  (grandchildren  of  the 
pure  geese)  from  one  nest.  In  India,  however,  these  cross- 
bred geese  must  be  far  more  fertile  ;  for  I  am  assured  by 
two  eminently  capable  judges,  namely  Mr.  Blyth  and 
Capt.  Hutton,  that  whole  flocks  of  these  geese  are  kept  in 
various  parts  of  the  country  ;  and  as  they  are  kept  for 
profit,  where  neither  pure  parent-species  exists,  they  must 
certainly  be  highly  fertile. 

A  doctrine  which  originated  with  Pallas,  has  been 
largely  accepted  by  modern  naturalists  ;  namely,  that 
most  of  our  domestic  animals  have  descended  from  two 
or  more  aboriginal  species,  since  commingled  by  intercross- 
ing. On  this  view,  the  original  species  must  either  at  first 
have  produced  quite  fertile  hybrids,  or  the  hybrids  must 
have  become  in  subsequent  generations  quite  fertile  under 
domestication.  This  latter  alternative  seems  to  me  the 
most  probable,  and  I  am  inclined  to  believe  in  its  truth, 
although  it  rests  on  no  direct  evidence.  I  believe,  for 
instance,  that  our  dogs  have  descended  from  several  wild 
stocks  ;  yet,  with  perhaps  the  exception  of  certain  indig- 
enous domestic  dogs  of  South  America,  all  are  quite 
fertile  together ;  and  analogy  makes  me  greatly  doubt, 
whether  tlie  several  aboriginal  species  would  at  first  have 


Chap.  VIII.]  LAWS  OF  STERILITY.  225 

freely  bred  together  and  have  produced  quite  fertile 
hybrids.  So  a^ain  there  is  reason  to  believe  that  our 
European  and  tne  humped  Indian  cattle  are  quite  fertile 
together ;  but  from  facts  communicated  to  me  by  Mr 
Blyth,  I  think  they  must  be  considered  as  distinct  species. 
On  this  view  of  the  origin  of  many  of  our  domestic  ani- 
mals, w^e  must  either  give  up  the  belief  of  the  almost 
universal  sterility  of  distinct  species  of  animals  when 
crossed ;  or  we  must  look  at  steriKty,  not  as  an  indelible 
characteristic,  but  as  one  capable  of  being  removed  by 
domestication. 

Finally,  looking  to  all  the  ascertained  facts  on  the 
intercrossing  of  plants  and  animals,  it  may  be  concluded 
that  some  degree  of  sterility,  both  in  first  crosses  and  in 
hybrids,  is  an  extremely  general  result ;  but  that  it  can- 
not, under  our  present  state  of  knowledge,  be  considered 
as  absolutely  universal. 

Laws  governing  the  Sterility  of  first  Crosses  and  of 
Hybrids. — ^We  will  now  consider  a  little  more  in  detail 
the  circumstances  and  rules  governing  the  sterility  of 
first  crosses  and  of  hybrids.  Our  chief  object  will  be  to 
see  whether  or  not  the  rules  indicate  that  species  have 
specially  been  endowed  with  this  quality,  in  order  to  pre- 
vent their  crossing  and  blending  together  in  utter  con- 
fusion. The  following  rules  and  conclusions  are  chiefly 
drawn  up  from  Gartner's  admirable  work  on  the  hybridi- 
sation of  plants.  I  have  taken  much  pains  to  ascertain 
how  far  the  rules  apply  to  animals,  and  considering  how 
scanty  our  knowledge  is  in  regard  to  hybrid  animals,  I 
have  been  surprised  to  find  how  generally  the  same  rules 
apply  to  both  kingdoms. 

It  has  been  already  remarked,  that  the  degree  of  fer- 
tility, both  of  first  crosses  and  of  hybrids,  graduates  from 
zero  to  perfect  fertility.  It  is  surprising  in  how  many 
curious  ways  this  gradation  can  be  shown  to  exist ;  but 
only  the  barest  outline  of  the  facts  can  here  be  given. 
When  pollen  from  a  plant  of  one  family  is  placed  on  the 
stigma  of  a  plant  of  a  distinct  family,  it  exerts  no  more 
influence  than  so  much  inorganic  dust.  From  this  abso- 
lute zero  of  fertility,  the  pollen  of   difi'erent  species   of 


226  HYBRIDISM.  [Chap.  VIII. 

the  same  genus  applied  to  the  stigma  of  some  one  sj^ecies, 
yields  a  perfect  gradation  in  the  number  of  seeds  pro* 
duced,  "up  to  nearly  complete  or  even  quite  complete  fer- 
tility ;  and,  as  we  have  seen,  in  certain  abnormal  cases,  even 
to  an  excess  of  fertility,  beyond  that  which  the  plant's  o^oi 
pollen  will  produce.  So  in  hybrids  themselves,  there  are 
some  which  never  have  produced,  and  probably  never 
would  produce,  even  with  the  pollen  of  either  pure  parent, 
a  single  fertile  seed :  but  in  some  of  these  cases  a  first  trace 
of  fertility  may  be  detected,  by  the  pollen  of  one  of  the 
pure  parent-species  causing  the  flower  of  the  hybrid  to 
wither  earlier  than  it  otherwise  would  have  done ;  and  the 
early  withering  of  the  flower  is  well  known  to  be  a  sign  of 
incipient  fertilisation.  From  this  extreme  degree  of  steril- 
ity we  have  self-fertilised  hybrids  producing  a  greater  and 
greater  number  of  seeds  up  to  perfect  fertility. 

Hybrids  from  two  species  which  are  very  difficult  to 
cross,  and  which  rarely  produce  any  offspring,  are  gener- 
ally very  sterile ;  but  the  parallelism  between  the  dif- 
ficulty of  making  a  first  cross,  and  the  sterility  of  the 
hybrids  thus  produced — two  classes  of  facts  which  are 
generally  confounded  together — is  by  no  means  strict. 
There  are  many  cases,  in  which  two  pure  sj)ecies  can  be 
united  with  unusual  facility,  and  produce  numerous 
hybrid-offspring,  yet  these  hybrids  are  remarkably  sterile. 
On  the  other  hand,  there  are  species  which  can  be  crossed 
very  rarely,  or  with  extreme  difficulty,  but  the  hybrids, 
when  at  last  produced,  are  very  fertile.  Even  within  the 
limits  of  the  same  genus,  for  instance  in  Dianthus,  these 
two  opposite  cases  occur. 

The  fertility,  both  of  first  crosses  and  of  hybrids,  is 
more  easily  aftected  by  unfavourable  conditions,  than  is 
the  fertility  of  pure  species.  But  the  degree  of  fertility 
is  likewise  innately  variable ;  for  it  is  not  always  the 
same  when  the  same  two  species  are  crossed  under  the 
same  circumstances,  but  depends  in  part  upon  the  consti- 
tution of  the  individuals  which  happen  to  have  been 
chosen  for  the  experiment.  So  it  is  with  hybrids,  for  their 
degree  of  fertility  is  often  found  to  difter  greatly  in  the 
several  individuals  raised  from  seed  out  of  the  same 
capsule  and  exposed  to  exactly  the  same  conditions. 


Chap.  VIII.]  LAWS    OF    STERILITY.  227 

Bj  the  term  systematic  affinity  is  meant,  the  resem- 
blance between  species  in  structure  and  in  constitution, 
more  especially  in  the  structure  of  parts  which  are  of 
high  physiological  importance  and  which  differ  little  in 
the  allied  species.  Now  the  fertility  of  first  crosses  be- 
tween species,  and  of  the  hybrids  produced  from  them,  is 
largely  governed  by  their  systematic  affinity.  This  is 
clearly  shown  by  hybrids  never  having  been  raised  be- 
tween species  ranked  by  systematists  in  distinct  families  ; 
and  on  the  other  hand,  by  very  closely  allied  species 
generally  uniting  with  facility.  But  the  correspondence 
between  systematic  affinity  and  the  facility  of  crossing  is 
by  no  means  strict.  A  multitude  of  cases  could  be  given 
of  very  closely  allied  species  which  will  not  unite,  or  only 
with  extreme  difficulty  ;  and  on  the  other  hand  of  very 
distinct  species  which  unite  with  the  utmost  facility.  In 
the  same  family  there  may  be  a  genus,  as  Dianthus,  in 
which  very  many  species  can  most  readily  be  crossed  ;  and 
another  genus,  as  Silene,  in  which  the  most  persevering 
efibrts  have  failed  to  produce  between  extremely  close 
species  a  single  hybrid.  Even  within  the  limits  of  the 
same  genus,  we  meet  with  this  same  difference  ;  for  in- 
stace,  the  many  species  of  Nicotiana  have  been  more 
largely  crossed  than  the  species  of  almost  any  other  genus ; 
but  Gartner  found  that  N.  acuminata,  which  is  not  a  par- 
ticularly distinct  species,  obstinately  failed  to  fertilise,  or 
to  be  fertilised  by,  no  less  than  eight  other  species  of  ISTi- 
cotiana.     Yery  many  analogous  facts  could  be  given. 

IsTo  one  has  been  able  to  point  out  what  kind,  or  what 
amount,  of  difference  in  any  recognisable  character  is 
sufficient  to  prevent  two  species  crossing.  It  can  be 
shown  that  plants  most  widely  different  in  habit  and 
general  appearance,  and  having  strongly  marked  differ- 
ences in  every  part  of  the  flower,  even  in  the  pollen,  in 
the  fruit,  and  in  the  cotyledons,  can  be  crossed.  Annual 
and  pereimial  plants,  deciduous  and  evergreen  trees,  plants 
inhabiting  different  stations  and  fitted  for  extremely  dif- 
ferent climates,  can  often  be  crossed  with  ease. 

By  a  reciprocal  cross  between  two  species,  I  mean  the 
case,  for  instance,  of  a  stallion-horse  being  first  crossed 
11 


228  HYBRIDISM,  [Chap.  VIII. 

with  a  female-ass,  and  tlien  a  male-ass  witli  a  mare :  these 
two  species  may  then  be  said  to  have  been  reciprocally 
crossed.  There  is  often  the  widest  possible  difference  in 
the  facility  of  making  reciprocal  crosses.  Such  cases  are 
highly  important,  for  they  prove  that  the  capacity  in  any 
two  species  to  cross  is  often  completely  independent  of 
their  systematic  affinity,  or  of  any  recognisable  difference 
in  their  whole  organisation.  On  the  other  hand,  these 
cases  clearly  show  that  the  capacity  for  crossing  is  con- 
nected with  constitutional  differences  imperceptible  by  us, 
and  confined  to  the  reproductive  system.  This  difference 
in  the  result  of  reciprocal  crosses  between  the  same  two 
species  was  long  ago  observed  by  Kolreuter.  To  give  an 
instance  :  Mirabilis  jalappa  can  easily  be  fertilised  by  the 
pollen  of  M.  longiflora,  and  the  hybrids  thus  produced 
are  sufficiently  fertile ;  but  Kolreuter  tried  more  than  two 
hundred  times,  during  eight  following  years,  to  fertilise 
reciprocally  M.  longiflora  with  the  pollen  of  M.  jalappa, 
and  utterly  failed.  Several  other  equally  striking  cases 
could  be  given.  Thuret  has  observed  the  same  fact  with 
certain  sea-weeds  or  Fuci.  Gartner,  moreover,  found  that 
this  difference  of  facility  in  making  reciprocal  crosses  is 
extremely  common  in  a  lesser  degree.  He  has  observed 
it  even  between  forms  so  closely  related  (as  Matthiola 
annua  and  glabra)  that  many  botanists  rank  them  only 
as  varieties.  It  is  also  a  remarkable  fact  that  hybrids 
raised  from  reciprocal  crosses,  though  of  course  compound- 
ed of  the  very  same  two  species,  the  one  species  having 
first  been  used  as  the  father  and  then  as  the  mother,  gen- 
erally difter  in  fertility  in  a  small,  and  occasionally  in  a  high 
deo-ree. 

Several  other  singular  i-ules  could  be  given  from  Gart- 
ner :  for  instance,  some  species  have  a  remarkable  power 
of  crossing  with  other  species  ;  other  species  of  the  same 
genus  have  a  remarkable  power  of  impressing  their  like- 
ness on  their  hybrid  oft'spring  ;  but  these  two  powers  do 
not  at  all  necessarily  go  together.  There  are  certain  hy- 
brids which  instead  of  having,  as  is  usual,  an  intermediate 
character  between  their  two  parents,  always  closely  re- 
semble one  of  them  ;  and  such  hybrids,  though  externally 


Chap.  VIII.]  COMPARED   WITH    GRAFTIXG.  229 

SO  like  one  of  tlieir  pure  parent  species,  are  with  rare  ex- 
ceptions extremely  sterile.  So  again  amongst  hybrids 
which  are  usually  intermediate  in  structure  between  their 
parents,  exceptional  and  abnormal  individuals  sometimes 
are  born,  wliicJi  closely  resemble  one  of  their  pure  parents ; 
and  these  hybrids  are  almost  always  utterly  sterile,  even 
when  the  other  hybrids  raised  from  seed  from  the  same 
capsule  have  a  considerable  degree  of  fertility.  These  facts 
sliow  how  completely  fertility  in  the  hybrid  is  indepen- 
dent of  its  external  resemblance  to  either  pure  parent. 

Considering  the  several  rules  now  given,  which  gov- 
ern the  fertility  of  first  crosses  and  of  hybrids,  we  see  that 
when  forms,  which  must  be  considered  as  good  and 
distinct  species,  are  united,  their  fertility  graduates  from 
zero  to  perfect  fertility,  or  even  to  fertility  under  certain 
conditions  in  excess.  That  their  fertility,  besides  being 
eminently  susceptible  to  favourable  and  unfavourable  con- 
ditions, is  innately  variable.  Tliat  it  is  by  no  means 
always  the  same  in  degree  in  the  first  cross  and  in  the 
hybrids  produced  from  this  cross.  That  the  fertility  of 
hybrids  is  not  related  to  the  degree  in  which  they  resemble 
in  external  appearance  either  parent.  And  lastly,  that 
the  facility  of  making  a  first  cross  between  any  two  species 
is  not  always  governed  by  their  systematic  afiinity  or 
degree  of  resemblance  to  each  other.  This  latter  state- 
ment is  clearly  proved  by  reciprocal  crosses  between  the 
same  two  species,  for  according  as  the  one  species  or  the 
other  is  used  as  the  father  or  the  mother,  there  is  generally 
some  difi'erence,  and  occasionally  the  widest  ])ossible  dif- 
ference, in  the  facility  of  effecting  an  union.  The  hybrids 
moreover,  produced  from  reciprocal  crosses  often  differ  in 
fertility. 

JS'ow  do  these  complex  and  singular  rules  indicate 
that  species  have  been  endowed  with  sterility  simply  to 
prevent  their  becoming  confounded  in  nature  ?  I  think 
not.  ^  For  why  should  the  sterility  be  so  extremely  differ- 
ent in  degree,  when  various  species  are  crossed,  all  of 
which  we  must  suppose  it  would  be  equally  important  to 
keep  from  blending  together  ?  Why  shoiild  the  degree 
of  sterility  be  innately  variable  in  the  individuals  of'tho 


230  HYBRIDISM,  [Chap.  VIIl. 

same  species  ?  Why  should  some  species  cross  with  facil- 
ity, and  yet  produce  very  sterile  hybrids ;  and  other 
species  cross  with  extreme  difficulty,  and  yet  produce 
fairly  fertile  hybrids  ?  Why  should  there  often  be  so 
great  a  diflerence  in  the  result  of  a  reciprocal  cross  be- 
tween the  same  two  species  ?  Why,  it  may  even  be  ask- 
ed, has  the  production  of  hybrids  been  j)ermitted  ?  to  grant 
to  species  the  special  power  of  producing  hybrids,  and 
then  to  stop  their  further  propagation  by  different  degrees 
of  sterility,  not  strictly  related  to  the  facility  of  the  first 
union  between  their  parents,  seems  to  be  a  strange  ar- 
rangement. 

The  foregoing  rules  and  facts,  on  the  other  hand, 
appear  to  me  clearly  to  indicate  that  the  sterility  both 
of  first  crosses  and  of  hybrids  is  simply  incidental  or  de- 
pendent on  unknown  differences,  chiefly  in  the  reproduc- 
tive systems  of  the  species  which  are  crossed.  The  differ- 
ences being  of  so  peculiar  and  limited  a  nature,  that,  in 
reciprocal  crosses  between  two  species  the  male  sexual 
element  of  the  one  will  often  freely  act  on  the  female 
sexual  element  of  the  other,  but  not  in  a  reversed  direc- 
tion. It  will  be  advisable  to  explain  a  little  more  fully 
by  an  example  what  I  mean  by  sterility  being  incidental 
on  other  difl'erences,  and  not  a  s]3ecially  endowed  quality. 
As  the  capacity  of  one  plant  to  be  grafted  or  budded  on 
another  is  so  entirely  unimportant  for  its  welfare  in  a  state 
of  nature,  I  presume  that  no  one  will  suppose  that  this 
capacity  is  a  specially  endowed  quality,  but  will  admit 
that  it  is  incidental  on  differences  in  the  laws  of  growth 
of  the  two  plants.  We  can  sometimes  see  the  reason  why 
one  tree  will  not  take  on  another,  from  differences  in  their 
rate  of  growth,  in  the  hardness  of  their  wood,  in  the  period 
of  the  flow  or  nature  of  their  sap,  &c. ;  but  in  a  multitude 
of  cases  we  can  assign  no  reason  whatever.  Great  diver- 
sity in  the  size  of  two  plants,  one  being  woody  and  the 
other  herbaceous,  one  being  evergreen  and  the  other 
deciduous,  and  adaptation  to  widely  different  climates, 
does  not  always  prevent  the  two  grafting  together.  As 
in  hybridisation,  so  with  grafting,  the  capacity  is  limited 
by  systematic  affinity,  for  no  one  has  been  able  to  graft 


Chap.  VIII.]  COMPARED   WITH   GRAFTING.  231 

trees  togctlier  belonging  to  quite  distinct  families  ;  and, 
on  the  other  hand,  closely  allied  species,  and  varieties  of 
the  same  species,  can  usually,  but  not  invariably,  be 
grafted  with  ease.  But  this  capacity,  as  in  hybridisation, 
is  by  no  means  absolutely  governed  by  systematic  affinity. 
Although  many  distinct  genera  within  the  same  family 
have  been  grafted  together,  in  other  cases  species  of  the 
same  genus  will  not  take  on  each  other.  The  pear  can  be 
grafted  far  more  readily  on  the  quince,  which  is  ranked 
as  a  distinct  genus,  than  on  the  apple,  which  is  a  member 
of  the  same  genus.  Even  different  varieties  of  the  pear 
take  with  different  degrees  of  facility  on  the  quince ;  so 
do  different  varieties  of  the  apricot  and  peach  on  certain 
varieties  of  the  plum. 

As  Gartner  found  that  there  was  sometimes  an  innate 
difference  in  different  individuals  of  the  same  two  species 
in  crossing  ;  so  Sagaret  believes  this  to  be  the  case  with 
different  individuals  of  the  same  two  species  in  being 
grafted  together.  As  in  reciprocal  crosses,  the  facility  of 
effecting  an  union  is  often  very  far  from  equal,  so  it  some- 
times is  in  grafting ;  the  common  gooseberry,  for  instance, 
cannot  be  grafted  on  the  currant,  whereas  the  currant 
will  take,  though  with  difficulty,  on  the  gooseberry. 

We  have  seen  that  the  sterility  of  hybrids,  which  have 
their  reproductive  organs  in  an  imperfect  condition,  is  a 
very  different  case  from  the  difficulty  of  uniting  two  pure 
species,  which  have  their  reproductive  organs  perfect ; 
yet  these  two  distinct  cases  run  to  a  certain  extent  paral- 
lel. Something  analogous  occurs  in  grafting ;  for  Thouin 
found  that  three  species  of  Eobinia,  which  seeded  freely 
on  their  own  roots,  and  which  could  be  grafted  with  no 
great  difficulty  on  another  species,  when  thus  grafted  were 
rendered  barren.  On  the  other  hand,  certain  species  of 
Sorbns,  when  grafted  on  other  species,  yielded  twice  as 
much  frnit  as  when  on  their  own  roots.  We  are  remind- 
ed by  this  lattpr  tact  of  the  extraordinary  case  of  Hippe- 
astrum,  Lobelia,  etc.,  which  seeded  much  more  freely 
when  fertilised  with  the  pollen  of  distinct  species,  than 
when  self-fertilised  with  their  own  pollen. 

We  thus  see,  that  although  there  is  a  clear  and  funda- 


232  HYBRIDISM.  [Ghap.  Vni. 

mental  difference  between  the  mere  adliesion  of  grafted 
stocks,  and  tlie  union  of  the  male  and  female  elements  in 
the  act  of  reproduction,  yet  that  there  is  a  rude  degree  of 
parallelism  in  the  results  of  grafting  and  of  crossing  dis- 
tinct species.  And  as  we  must  look  at  the  curious  and 
complex  laws  governing  the  facility  with  which  trees  can 
be  grafted  on  each  other  as  incidental  or  unknown  differ- 
ences in  their  vegetative  systems,  so  I  believe  that  the 
still  more  complex  laws  governing  the  facility  of  first 
crosses,  are  incidental  on  unknown  differences,  chiefly  in 
their  reproductive  systems.  These  differences,  in  both 
cases,  follow  to  a  certain  extent,  as  might  have  been  ex- 
pected, systematic  afiinity,  by  which  every  kind  of  resem- 
blance and  dissimilarity  between  organic  beings  is  at- 
tempted to  be  expressed.  The  fact  by  no  means  seems  to 
me  to  indicate  that  the  greater  or  lesser  difliculty  of  either 
grafting  or  crossing  together  various  species  has  been  a 
special  endowment ;  although  in  the  case  of  crossing,  the 
difliculty  is  as  important  for  the  endurance  and  stability 
of  specific  forms,  as  in  the  case  of  grafting  it  is  unimjDor- 
tant  for  their  welfare. 

Causes  of  the  Sterility  of  first  Crosses  andof  Hyhrids. — • 
We  may  now  look  a  little  closer  at  the  probable  causes  of 
the  sterility  of  first  crosses  and  of  hybrids.  These  two 
cases  are  fundamentally  different,  for,  as  just  remarked, 
in  the  union  of  two  pure  species  the  male  and  female  sex- 
ual elements  are  perfect,  whereas  in  ]iybrids  they  are  im- 
perfect. Even  in  first  crosses,  the  greater  or  lesser  difli- 
culty in  effecting  an  union  apparently  depends  on  several 
distinct  causes.  Tliere  must  sometimes  be  a  physical 
impossibility  in  the  male  element  reaching  the  ovule,  as 
would  be  the  case  with  a  plant  having  a  justil  too  long  for 
the  pollen  tubes  to  reach  tlie  ovarium.  It  has  also  been 
observed  that  when  pollen  of  one  species  is  placed  on  the 
stigma  of  a  distantly  allied  species,  though  the  pollen-tubes 
protrude,  they  do  not  penetrate  the  stigmatic  surface. 
Again,  the  male  clement  may  reach  the  female  clement, 
but  be  incapable  of  causing  an  embryo  to  be  developed, 
as  seems  to  have  been  the  case  with  some  of  Thuret's 


Chap.  VIII.]  CAUSES    OF   STERILITY.  233 

experiments  on  Fuci.  !No  explanation  can  be  given  of 
these  facts,  any  more  than  why  certain  trees  cannot  he 
grafted  on  others.  Lastly,  an  embryo  may  be  developed, 
and  then  perish  at  an  early  period.  This  latter  alternative 
has  not  been  sufficiently  attended  to  ;  but  I  believe,  from 
observations  commmiicated  to  me  by  Mr.  Hewitt,  who  has 
had  great  experience  in  hybridising  gallinaceous  birds, 
that  the  early  death  of  the  embryo  is  a  very  frequent 
cause  of  sterility  in  first  crosses.  I  was  at  first  very  un- 
willing to  believe  in  this  view  ;  as  hybrids,  when  once 
born,  are  generally  healthy  and  long-lived,  as  we  see  in 
the  case  of  the  common  mule.  Hybrids,  however,  are 
difi*erently  circumstanced  before  and  after  birth  :  when 
born  and  living  in  a  country  where  their  two  parents  can 
live,  they  are  generally  placed  under  suitable  conditions 
of  life.  But  a  hybrid  partakes  of  only  half  of  the  nature 
and  constitution  of  its  mother,  and  therefore  before  birth, 
as  long  as  it  is  nourished  within  its  mother's  womb  or 
within  the  egg  or  seed  produced  by  the  mother,  it  may  be 
exposed  to  conditions  in  some  degree  unsuitable,  and  con- 
sequently be  liable  to  perish  at  an  early  period ;  more 
especially  as  all  very  young  beings  seem  eminently  sensi- 
tive to  injurious  or  unnatural  conditions  of  life. 

In  regard  to  the  sterility  of  hybrids,  in  which  the 
sexual  elements  are  imperfectly  developed,  the  case  is 
very  diflferent.  I  have  more  than  once  alluded  to  a  large 
body  of  facts,  which  I  have  collected,  showing  that  where 
animals  and  plants  are  removed  from  their  natural  con- 
ditions, they  are  extremely  liable  to  have  their  reproduc- 
tive systems  seriously  afi'ected.  This,  in  fact,  is  the  great 
bar  to  the  domestication  of  animals.  Between  the  ster- 
ility thus  superinduced  and  that  of  hybrids,  there  are 
many  points  of  similarity.  In  both  cases  the  sterility  is 
independent  of  general  health,  and  is  often  accompanied 
by  excess  of  size  or  great  luxuriance.  In  both  cases,  the 
sterility  occm*s  in  various  degrees ;  in  both,  the  male 
element  is  the  most  liable  to  be  efi'ected  ;  but  sometimes 
the  female  more  than  the  male.  Li  both,  the  tendency 
goes  to  a  certain  extent  with  systematic  affinity,  for  whole 
groups  of  animals  and  plants  are  rendered  impotent  by  the 


234:  HYBRIDISM.  [Chap.  VIII. 

same  iiimatural  conditions  ;  and  whole  groups  of  sj)ecies 
teiad  to  produce  sterile  hybrids.  On  the  other  hand,  one 
species  in  a  group  will  sometimes  resist  great  changes  of 
conditions  with  unimpaired  fertility ;  and  certain  species 
in  a  group  will  produce  unusually  fertile  hybrids.  Ko 
one  can  tell,  till  he  tries,  whether  any  particular  animal 
will  breed  under  confinement  or  any  plant  seed  freel}' 
under  culture  ;  nor  can  he  tell,  till  he  tries,  whether  an;y 
two  species  of  a  genus  will  produce  more  or  less  sterile 
hybrids.  Lastly,  when  organic  beings  are  placed  during 
several  generations  under  conditions  not  natural  to  them, 
they  are  extremely  liable  to  vary,  which  is  due,  as  I  be- 
lieve, to  their  reproductive  systems  having  been  specially 
eflected,  though  in  a  lesser  degree  than  when  sterility 
ensues.  So  it  is  with  hybrids,  for  hybrids  in  successive 
generations  are  eminently  liable  to  vary,  as  every  experi- 
mentalist has  observed. 

Thus  we  see  that  when  organic  beings  are  placed  under 
new  and  unnatural  conditions,  and  when  hybrids  are  pro- 
duced by  the  unnatural  crossing  of  two  species,  the  re- 
productive system,  independently  of  the  general  state  of 
health,  is  affected  by  sterility  in  a  very  similar  manner. 
In  the  one  case,  the  conditions  of  life  have  been  disturbed, 
though  often  in  so  sliglit  a  degree  as  to  be  innappreciable 
by  us  ;  in  the  other  case,  or  that  of  liybrids,  the  external 
conditions  have  remained  the  same,  but  the  organisation, 
has  been  disturbed  by  two  different  structures  and  consti- 
tutions having  been  blended  into  one.  For  it  is  scarcely 
possible  that  two  organisations  should  be  compounded 
into  one,  without  some  disturbance  occurring  in  the  devel- 
opment, or  periodical  action,  or  mutual  relation  of  the 
different  parts  and  organs  one  to  another,  or  to  the  condi- 
tions of  life.  When  liybrids  are  able  to  breed  intei'  se,  they 
transmit  to  their  offspring  from  generation  to  generation 
the  same  com])ounded  organisation,  and  hence  we  need 
not  be  surprised  that  their  sterility,  though  in  some  degree 
variable,  rarely  diminishes. 

It  must,  however,  be  confessed  that  we  cannot  under- 
stand, excepting  on  vague  hypotheses,  several  facts  with 
respect  to  the  sterility  of  hybrids ;  for  instance,  the  im- 


Chap.  VIIL]  CAUSES    OF   STERILITY.  235 

equal  fertility  of  hybrids  produced  from  reciprocal  cross- 
es ;  or  the  increased  sterility  in  those  hybrids  which  oc- 
casionally and  exceptionally  resemble  closely  either  pure 
parent.  Nor  do  I  pretend  that  the  foregoing  remarks  go 
to  the  root  of  the  matter  ;  no  explanation  is  offered  why 
an  organism,  when  placed  under  unnatural  conditions,  is 
rendered  sterile.  All  that  I  have  attempted  to  show,  is 
that  in  two  cases,  in  some  respects  allied,  sterility  is  the 
common  result, — in  the  one  case  from  the  conditions  of 
life  having  been  disturbed,  in  the  other  case  from  the  or- 
ganisation having  been  disturbed  by  two  organisations 
having  been  compounded  into  one. 

It  may  seem  fanciful,  but  I  suspect  that  a  similar 
parallelism  extends  to  an  allied  yet  very  different  class 
of  facts.  It  is  an  old  and  almost  universal  belief,  founded, 
I  think,  on  a  considerable  body  of  evidence,  that  slight 
changes  in  the  conditions  of  life  are  beneficial  to  all  living 
things.  We  see  this  acted  on  by  farmers  and  gardeners 
in  their  frequent  exchanges  of  seed,  tubers,  &c.,  from  one 
soil  or  climate  to  another,  and  back  again.  During  the 
convalescence  of  animals,  we  plainly  see  that  great  benefit 
is  derived  from  almost  any  change  in  the  habits  of  life. 
Again,  both  with  plants  and  animals,  there  is  abundant 
evidence,  that  a  cross  between  very  distinct  individuals 
of  the  same  species,  that  is  between  members  of  different 
strains  or  sub-breeds,  gives  vigor  and  fertility  to  the  oft"- 
spring.  I  believe,  indeed,  from  the  facts  alluded  to  in 
our  fourth  chapter,  that  a  certain  amount  of  crossing  is 
indispensable  even  with  hermaphrodites  ;  and  that  close 
inter-breeding  continued  during  several  generations  be- 
tween the  nearest  relations,  especially  if  these  be  kept 
under  the  same  conditions  of  life,  always  induces  weak- 
ness and  sterility  in  the  progeny. 

Hence  it  seems  that,  on  the  one  hand,  slight  changes 
in  the  conditions  of  life  benefit  all  organic  beings,  and  on 
the  other  hand,  that  slight  crosses,  that  is  crosses  between 
the  males  and  females  of  the  same  species  which  have 
varied  and  become  slightly  different,  give  vigour  and 
fertility  to  the  offspring.  But  we  have  seen  that  greater 
changes,  or  changes  of  a  f>articular  nature,  often  render 
11* 


236  HYBRIDISM.  [Chap.  VIII. 

organic  beings  in  some  degree  sterile ;  and  that  greater 
crosses,  that  is  crosses  between  males  and  females  which 
have  become  widely  or  specifically  different,  produce  hy- 
brids which  are  generally  sterile  in  some  degree.  I  can- 
not persuade  myself  that  this  parallelism  is  an  accident 
or  an  illusion.  Both  series  of  facts  seem  to  be  connected 
together  by  some  common  but  unknown  bond,  which  is 
essentially  related  to  the  principle  of  life. 

Fertility  of  Varieties  when  crossed^  and  of  their  Hon- 
grel  offsirrhig. — It  may  be  urged,  as  a  most  forcible  argu- 
ment, that  there  must  be  some  essential  distinction  be- 
tween spepies  and  varieties,  and  that  there  must  be  some 
error  in  all  the  foregoing  remarks,  inasmuch  as  varieties, 
however  much  they  may  differ  from  each  other  in  external 
appearance,  cross  with  perfect  facility,  and  yield  perfectly 
fertile  offspring.  I  fully  admit  that  this  is  almost  inva- 
riably the  case,  and  that  the  case  offers  a  great  difficulty ; 
probably  something  here  remains  unexplained.  But  if 
we  look  to  varieties  produced  under  nature,  we  are  imme- 
diately involved  in  hopeless  difficulties  ;  for  if  two  hitherto 
reputed  varieties  be  found  in  any  degree  sterile  together, 
they  are  at  once  ranked  by  most  naturalists  as  species. 
For  instance,  the  blue  and  red  pimpernel,  the  primrose  and 
cowslip,  which  are  considered  by  many  of  our  best  bota- 
nists as  varieties,  are  said  by  Gartner  not  to  be  quite  fer- 
tile when  crossed,  and  he  consequently  ranks  them  as  un- 
doubted species.  If  we  thus  argue  in  a  circle,  the  fertility 
of  all  varieties  produced  under  nature  will  assuredly  have 
to  be  granted. 

If  we  turn  to  varieties,  produced,  or  supposed  to  have 
been  produced,  under  domestication,  we  are  still  involved 
in  doubt.  For  when  it  is  stated,  for  instance,  that  the 
German  Spitz  dog  unites  more  easily  than  other  dogs  with 
foxes,  or  that  certain  South  American  indigenous  domes- 
tic dogs  do  not  readily  cross  with  European  dogs,  the  ex- 
phmation  which  will  occur  to  every  one,  and  probably  the 
true  one,  is  that  these  dogs  have  descended  from  several 
aboriginally  distinct  species.  I^evertheless  the  perfect 
fertility  of  so  many  domestic  varieties,  differing  widely 
from  each  other  in  appearance,  for  instance  of  the  pigeon 


CfiAP.  VIII.]  FERTILITY  OF  MOiTGfRELS.  237 

or  of  the  cabbage,  is  a  remarkable  fact ;  more  especially 
when  we  reflect  how   many  species   there  are,  which,  . 
though  resembling  each  other  most  closely,  are  utterly 
sterile  when  intercrossed.     Several  considerations,  how- 
ever, render  the  fertility  of  domestic  varieties  less  remark- 
able than  at  first  appears.     In  the  first  place,  we  must 
remember   how  ignorant  we   are   regarding  the  precise 
cause  of  sterility,  when  species  are  crossed  and  when  spe- 
cies arc  removed  from  their  natural  conditions.     On  this 
latter  head  I  have  not  had  space  to  adduce  the  many  re- 
markable facts  which  could  have  been  given  ;  with  re- 
spect to  sterility  from  crossing,  reflect  on  the  difierence  in 
the  result  of  reciprocal  crosses,— reflect  on  the  singular 
cases  in  which  a  plant  can  be  more  easily  fertilised  by 
foreign  pollen  than  by  its  own.      When  we  think  over 
such  cases  and  on  that  of  the  difi'erent  coloured  varieties 
of  Yerbascum  presently  to  be  given,  Ave  must  feel  how 
ignorant  we  are,  and  how  little  likely  it  is  that  we  should 
luiderstand  why  certain  forms  are  fertile  and  other  forms 
sterile  when  intercrossed.     It  can,  in  the  second  place,  be 
clearly  shown  that  mere  external  dissimilarity  between 
two  species  does  not  determine  their  greater  or  lesser  de- 
gree of  sterility  when  crossed;    and  we  may  apply  the 
same  rule  to  domestic  varieties.     In  the  third  place,  some 
eminent  naturalists  believe  that  a  long  course  of  domesti- 
cation tends  to  eliminate  sterility  in  the  successive  genera- 
tions of  hybrids  which  were  at  first  only  slightly  sterile  ; 
and  if  this  be  so,  we  surely  ought  not  to  expect  to  find 
sterility  both  appearing  and  disappearing  under  nearly 
the  same  conditions  of  life.     Lastly,  and  this  seems  to  me 
the  most  important  consideration,  new  races  of  animals 
and  plants  are  produced  under  domestication  by  man's 
methc^dical  and  imconscious  power  of  selection,  for  his 
own  use  and  pleasure :  he  neither  wishes  to  select,  nor 
could  select,  slight  diflerences  in  the  reproductive  system, 
or  other  constitutional  difi'erences  correlated  with  the  re- 
productive system.     Domestic  productions  have  become 
less  closely  adapted  to  climate  and  to  the  other  physical 
conditions  of  life,  than  are  those  in  a  state  of  nature.     Man 
supplies  his  several  varieties  with  the  same  food ;  treats 
them  nearly  in  the  same  manner,  and  does  not  wish  to 


23S  HYBRIDISM.  [Chap.  VIII. 

alter  their  general  habits  of  life.  iJ^ature  acts  uniformly 
and  slowly  during  vast  periods  of  time  on  the  whole  or- 
ganisation, in  any  way  w'hich  may  be  for  each  creature's 
owm  good ;  and  thus  she  may,  either  directly,  or  more 
probably  indirectly,  through  correlation,  modily  the  re- 
productive system  in  the  several  descendants  from  any 
one  species.  Seeing  this  difference  in  the  process  of  se- 
lection, as  carried  on  by  man  and  nature,  we  need  not  be 
surprised  at  some  difference  in  the  result. 

I  have  as  yet  spoken  as  if  the  varieties  of  the  same 
species  were  invariably  fertile  when  intercrossed.  But 
it  seems  to  me  impossible  to  resist  the  evidence  of  the 
existence  of  a  certain  amount  of  sterility  in  the  few  fol- 
lowing cases,  which  I  will  briefly  abstract.  The  evidence 
is  at  least  as  good  as  that  from  w^hich  we  believe  in  the 
sterility  of  a  multitude  of  species.  The  evidence  is,  also, 
derived  from  hostile  witnesses,  who  in  all  other  cases 
consider  fertility  and  sterility  as  safe  criterions  of  specific 
distinction.  Gartner  kept  during  several  years  a  dwarf 
kind  of  maize  with  yellow  seeds,  and  a  tall  variety  wdth 
red  seeds,,  growing  near  each  other  in  his  garden  ;  and  al- 
though these  plants  have  separated  sexes,  they  never  nat- 
urally crossed.  He  then  fertilised  thirteen  flowers  of  the 
one  with  the  pollen  of  the  other ;  but  only  a  single  head 
produced  any  seed,  and  this  one  head  produced  only  five 
grains.  Manipulation  in  this  case  could  not  have  been 
injurious,  as  the  plants  have  separated  sexes.  Xo  one,  I 
believe,  has  suspected  that  these  varieties  of  maize  are 
distinct  species  ;  and  it  is  important  to  notice  that  the 
hybrid  plants  thus  raised  were  themselves  perfectly  fertile ; 
so  that  even  Gartner  did  not  venture  to  consider  the  two 
varieties  as  specifically  distinct. 

Girou  de  Buzareingues  crossed  three  varieties  of  gourd, 
which  like  the  uiaize  has  separated  sexes,  and  he  asserts 
that  their  mutual  fertilisation  is  by  so  much  the  less  easy 
as  their  difterences  are  greater.  How  far  these  experi- 
ments may  be  trusted,  I  know^  not;  but  the  forms  exj^er- 
imentised  on,  are  ranked  by  Sagaret,  who  mainly  founds 
his  classification  by  the  test  of  infertility,  as  varieties. 

The  following  case  is  far  more  remarkable,  and  seems 
at  first  quite  incredible ;  but  it  is  the  result  of  an  astonish- 


Chap.  VIII.]  FERTILITY   OF   MONGRELS.  239 

ing  number  of  experiments  made  during  many  years  on 
nine  species  of  Ycrbascum,  by  so  good  an  observer  and 
so  hostile  a  witness,  as  Gartner :  namely,  that  yellow  and 
white  varieties  of  the  same  species  of  Yerbascum  when 
intercrossed  produce  less  seed,  than  do  either  coloured 
varieties  when  fertilised  with  pollen  from  their  own  col- 
oured flowers.  Moreover,  he  asserts  that  when  yellow 
and  white  varieties  of  one  species  are  crossed  with  yellow 
and  white  varieties  of  a  distinct  species,  more  seed  is  pro- 
duced by  the  crosses  between  the  same  coloured  flowers, 
than  between  those  which  are  differently  coloured.  Yet 
these  varieties  of  Yerbascum  present  no  other  difi'erence 
besides  the  mere  colour  of  the  flower ;  and  one  variety 
can  sometimes  be  raised  from  the  seed  of  the  other. 

From  observations  which  I  have  made  on  certain 
varieties  of  hollyhock,  I  am  inclined  to  suspect  that  they 
present  analogous  facts. 

Kolreuter,  whose  accuracy  has  been  confirmed  by 
every  subsequent  observer,  has  proved  the  remarkable 
fact,  that  one  variety  of  the  common  tobacco  is  more 
fertile,  when  crossed  with  a  widely  distinct  species,  than 
are  the  other  varieties.  He  experimentised  on  five  forms, 
which  are  commonly  reputed  to  be  varieties,  and  which 
he  tested  by  the  severest  trial,  namely,  by  reciprocal 
crosses,  and  he  found  their  mongrel  offspring  perfectly 
fertile.  But  one  of  these  five  varieties,  when  used  either 
as  father  or  mother,  and  crossed  with  the  l!^icotiana  glu- 
tinosa,  always  yielded  hybrids  not  so  sterile  as  those 
which  were  produced  from  the  four  other  varieties  when 
crossed  with  N.  glutinosa.  Hence  the  reproductive  sys- 
tem of  this  one  variety  must  have  been  in  some  manner 
and  in  some  degree  modified. 

From  these  facts  ;  from  the  great  difficulty  of  ascer- 
taining the  infertility  of  varieties  in  a  state  of  nature,  for 
a  supposed  variety  if  infertile  in  any  degree  would  gener- 
ally be  ranked  as  species;  from  man  selecting  only  ex- 
ternal characters  in  the  production  of  the  most  distinct 
domestic  varieties,  and  from  not  wishing  or  being  able  to 
produce  recondite  and  functional  differences  in  the  repro- 
ductive system ;  from  these  several  considerations  and 
facts,  I  do  not  think  that  the  very  general  fertility  of 


240  HYBRIDISM.  [CSAP.  Vlli, 

Yarieties  can  be  proved  to  be  of  universal  occurrence,  or 
to  form  a  fundamental  distinction  between  varieties  and 
species.  "  The  general  fertility  of  varieties  does  not  seem 
to  me  sufficient  to  overthrow  the  view  which  I  have  taken 
with  respect  to  the  very  general,  but  not  invariable,  steril- 
ity of  first  crosses  and  of  hybrids,  namely,  that  it  is  not 
a  special  endowment-,  but  is  incidental  on  slowly  acquired 
modifications,  more  especially  in  the  re23roductive  systems 
of  the  forms  which  are  crossed. 

Hyhvids  and  Mongrels  compared^  independently  oftJieir 
fertility. — Independently  of  the  question  of  fertility,  the  ofi'- 
spring  of  species  when  crossed  and  of  varieties  when  crossed 
may  be  compared  in  several  other  respects.  Gartner,  whose 
strong  wish  was  to  draw  a  marked  line  of  distinc- 
tion between  species  and  varieties,  could  find  very  few 
and,  as  it  seems  to  me,  quite  unimportant  difi'erences  be- 
tween the  so-called  hybrid  oflspring  of  species,  and  the 
so-called  mongrel  offs]3ring  of  varieties.  And,  on  the 
other  hand,  they  agree  most  closely  in  very  many  im- 
portant respects. 

I  shall  here  discuss  this  subject  with  extreme  brevity. 
The  most  important  distinction  is,  that  in  the  first  gener- 
ation mongrels  are  more  variable  than  hybrids ;  but  Gart- 
ner admits  that  hybrids  from  species  which  have  long 
been  cultivated  are  often  variable  in  the  first  generation ; 
and  I  have  myself  seen  striking  instances  of  this  fact. 
Gartner  further  admits  that  hybrids  between  very  closely 
allied  species  are  more  variable  than  those  from  very  dis- 
tinct species  ;  and  this  shows  that  the  difierence  in  the  de- 
gree of  variability,  graduates  away.  When  mongrels  and 
the  more  fertile  hybrids  are  proj)agated  for  several  gener- 
ations an  extreme  amount  of  variability  in  their  ofifspring 
is  notorious ;  but  some  few  cases  both  of  hybrids  and 
mongrels  long  retaining  uniformity  of  character  could  be 
given.  The  variability,  however,  in  the  successive  gener- 
ations of  mongrels  is,  perhaps,  greater  than  in  hybrids. 

This  greater  variability  of  mongrels  than  of  hybrids 
does  not  seem  to  me  at  all  surprising.  For  the  parents 
of  moii2:rels  are  varieties,  and  mostlv  domestic  varieties 
(very  few  experiments  having  been  tried  on  natural  van- 


Chap.  VIII.]  HYBRIDS  AND  MONGRELS.  24cl 

eties),  and  this  implies  in  most  cases  that  there  has  been  re- 
cent variability  ;  and  therefore  we  might  expect  that  such 
variability  would  often  continue  and  be  superadded  to  that 
arising  from  the  mere  act  of  crossing.  The  slight  degree  of 
variability  in  hybrids  from  the  lirst  cross  or  in  the  lirst  gen- 
eration, in  contrast  with  their  extreme  variability  in  the 
succeeding  generations,  is  a  curious  fact  and  deserves  atten- 
tion. For  it  bears  on  and  corroborates  the  view  which  I  have 
taken  on  the  cause  of  ordinary  variability ;  namely,  that  it  is 
due  to  the  reproductive  system  being  eminently  sensitive  to 
any  change  in  the  conditions  of  life,  being  thus  often  ren- 
dered either  impotent  or  at  least  incapable  of  its  proper 
function  of  producing  offspring  identical  with  the  parent- 
form.  ISTow  hybrids  in  the  first  generation  are  descended 
from  species  (excluding  those  long  cultivated)  which  have 
not  had  their  reproductive  systems  in  any  way  affected, 
and  they  are  not  variable ;  but  hybrids  themselves  have 
their  reproductive  systems  seriously  affected,  and  their 
descendants  are  highly  variable. 

But  to  return  to  our  comparison  of  mongrels  and  hy- 
brids :  Gartner  states  that  mongrels  are  more  liable  than 
hybrids  to  revert  to  either  parent-form ;  but  this,  if  it  be 
true,  is  certainly  only  a  difference  in  degree.  Gartner  fur- 
ther insists  that  when  any  two  species,  although  most  close- 
ly allied  to  each  other,  are  crossed  with  a  third  species, 
the  hybrids  are  widely  different  from  each  other ;  whereas 
if  two  very  distinct  varieties  of  one  species  are  crossed  with 
another  species,  the  hybrids  do  not  differ  much.  But  this 
conclusion,  as  far  as  I  can  make  out,  is  founded  on  a  sin- 
gle experiment ;  and  seems  directly  opj^osed  to  the  results 
of  several  experiments  made  by  Kolreuter. 

These  alone  are  the  unimportant  differences,  which 
Gartner  is  able  to  point  out,  between  hybrid  and  mongrel 
plants.  On  the  other  hand,  the  resemblance  in  mongrels 
and  in  hybrids  to  their  respective  parents,  more  especially 
in  hybrids  produced  from  nearly  related  species,  follows  ac- 
cording to  Gartner  the  same  laws.  When  two  species  are 
crossed,  one  has  sometimes  a  prepotent  power  of  impressing 
its  likeness  on  the  hybrid ;  and  so  I  believe  it  to  be  with 
varieties  of  j^lants.  With  animals  one  variety  certainly 
often  has  this  prepotent  power  over  another  variety.    Hy- 


242  HYBRIDISM.  [Chap.  Vni. 

brid  plants  produced  from  a  reciprocal  cross,  generally 
resemble  each  other  closely ;  and  so  it  is  with  mongrels 
from  a  reciprocal  cross.  Both  hybrids  and  mongrels 
can  be  reduced  to  either  pure  parent-form,  by  repeated 
crosses  in  successive  generations  with  either  parent. 

These  several  remarks  are  apparently  applicable  to 
animals  ;  but  the  subject  is  here  excessively  complicated, 
partly  owing  to  the  existence  of  secondary  sexual  charac- 
ters ;  but  more  especially  owing  to  prepotency  in  trans- 
mitting likeness  running  more  strongly  in  one  sex  than  in 
the  other,  both  when  one  species  is  crossed  with  another, 
and  when  one  variety  is  crossed  with  another  variety. 
For  instance,  I  think  those  authors  are  right,  who  main- 
tain that  the  ass  has  a  prepotent  power  over  the  horse,  so 
that  both  the  mule  and  the  hinny  more  resemble  the  ass 
than  the  horse ;  but  that  the  prepotency  runs  more 
strongly  in  the  male-ass  than  in  the  female,  so  that  the 
mule,  which  is  the  offspring  of  the  male-ass  and  mare,  is 
more  like  an  ass,  than  is  the  hinny,  which  is  the  offspring 
of  the  female-ass  and  stallion. 

Much  stress  has  been  laid  by  some  authors  on  the  sup- 
posed fact  that  mongrel  animals  alone  are  born  closely 
like  one  of  their  parents  ;  but  it  can  be  shown  that  this 
does  sometimes  occur  with  hybrids  ;  yet  I  grant  much 
less  frequently  with  hybrids  than  "^vith  mongrels.  Look- 
ing to  the  cases  which  I  have  collected  of  cross-bred  ani- 
mals closely  resembling  one  parent  the  resemblances  seem 
chiefly  conlined  to  characters  almost  monstrous  in  their 
nature,  and  which  have  suddenly  appeared — such  as 
albinism,  melanism,  deficiency  of  tail  or  horns,  or  addi- 
tional fingers  and  toes  ;  and  do  not  relate  to  characters 
which  have  been  slowly  acquired  by  selection.  Conse- 
quently, sudden  reversions  to  the  perfect  character  of 
either  parent  would  be  more  likely  to  occur  with  mon- 
grels, which  are  descended  from  varieties  often  suddenly 
produced  and  semi-monstrous  in  character,  than  with 
hybrids,  which  are  descended  from  species  slowly  and 
naturally  produced.  On  the  whole  I  entirely  agree  with 
Dr.  Prosper  Lucas,  who,  after  arranging  an  enormous 
body  of  facts  with  respect  to  animals,  comes  to  the  con- 
clusion, that  the  laws  of  resemblance  of  the  child  to  its 


Chap.  VIII.]  SUMMARY.  243 

parents  are  tlie  same,  whether  the  two  parents  differ  much 
or  little  from  each  other,  namely  in  the  nnion  of  individu- 
als of  the  same  variety,  or  of  different  varieties,  or  of  dis- 
tinct species. 

Laying  aside  the  question  of  fertility  and  sterility,  in 
all  other  respects  there  seems  to  be  a  general  and  close 
similarity  in  the  offspring  of  crossed  species,  and  of  crossed 
varieties.  If  we  look  at  species  as  having  been  specially 
created,  and  at  varieties  as  having  been  produced  by  sec- 
ondary laws,  this  similarity  would  be  an  astonishing  fact. 
But  it  harmonises  perfectly  with  the  view  that  there  is  no 
essential  distinction  between  species  and  varieties. 

Summary  of  Chapter. — First  crosses  between  forms  suf- 
ficiently distinct  to  be  ranked  as  species,  and  their  hybrids, 
are  very  generally,  but  not  universally,  sterile.  The  sterility 
is  of  all  degrees,  and  is  often  so  slight  that  the  two  most  care- 
ful experimentalists  who  have  ever  lived,  have  come  to  dia- 
metrically opposite  conclusions  in  ranking  forms  by  this 
test.  The  sterility  is  innately  variable  in  individuals  of  the 
same  species,  and  is  eminently  susceptible  of  favourable  and 
unfavourable  conditions.  The  degree  of  sterility  does  not 
strictly  follow  systematic  afiinity,  but  is  governed  by  sev- 
eral curious  and  complex  laws.  It  is  generally  different,  and 
sometimes  widely  different,  in  reciprocal  crosses  between 
the  same  two  species.  It  is  not  always  equal  in  degree  in  a 
first  cross  and  in  the  hybrid  produced  from  this  cross. 

In  the  same  manner  as  in  grafting  trees,  the  capacity  of 
one  species  or  variety  to  take  on  another,  is  incidental  on 
generally  unknown  differences  in  their  vegetative  systems, 
so  in  crossing,  the  greater  or  less  facility  of  one  species  to 
unite  with  another,  is  incidental  on  unknown  differences  in 
their  reproductive  systems.  There  is  no  more  reason  to 
think  that  species  have  been  specially  endowed  with 
various  degrees  of  sterility  to  prevent  them  crossing  and 
blending  in  nature,  than  to  think  that  trees  have  been  spe- 
cially endowed  with  various  and  somewhat  analogous  de- 
grees of  difficulty  in  being  grafted  together  in  order  to 
prevent  them  becoming  inarched  in  our  forests. 

The  sterility  of  first  crosses  between  pure  species 
which  have  their  reproductive  systems  perfect,  seems  to 


"24:4:  HYBRIDISM.  [Chap.  VIll. 

depend  on  several  circumstances ;  in  some  cases  largel  v 
on  tlie  early  death  of  the  embryo.  The  sterility  of  hy- 
brids, which  have  their  reproductive  systems  imperfect, 
and  which  have  had  this  system  and  their  whole  organisa- 
tion distm'bed  by  being  compounded  of  two  distinct  spe- 
cies, seems  closely  allied  to  that  sterility  which  so  fre- 
quently affects  pure  species,  when  their  natural  conditions 
of  life  have  been  disturbed.  This  view  is  supported  by  a 
parallelism  of  another  kind ; — namely,  that  the  crossing 
of  forms  only  slightly  different  is  favourable  to  the  vigour 
and  fertility  of  their  offspring ;  and  that  slight  changes 
in  the  conditions  of  life  are  aj)parently  favourable  to  the 
vigour  and  fertility  of  all  organic  beings.  It  is  not  sur- 
prising that  the  degree  of  difficulty  in  uniting  two  species, 
and  the  degree  of  sterility  of  their  hybrid-offspring  should 
generally  correspond,  though  due  to  distinct  causes  ;  for 
both  depend  on  the  amount  of  difference  of  some  kind 
between  the  species  which  are  crossed.  ISTor  is  it  surpris- 
ing that  the  facility  of  effecting  a  first  cross,  the  fertility 
of  the  hybrids  produced,  and  the  capacity  of  being  grafted 
together — though  this  latter  capacity  evidently  depends 
on  widely  different  circumstances — should  all  run,  to  a 
certain  extent,  parallel  with  the  systematic  affinity  of  the 
forms  which  are  subjected  to  experiment ;  for  systematic 
affinity  attemj)ts  to  express  all  kinds  of  resemblance  be- 
tween all  species. 

First  crosses  between  fonns  known  to  be  varieties,  or 
sufficiently  alike  to  be  considered  as  varieties,  and  their 
mongrel  offspring,  are  very  generally,  but  not  quite  uni- 
versally, fertile.  I^or  is  this  nearly  general  and  perfect 
fertility  surprising,  when  we  remember  how  liable  we  are 
to  argue  in  a  circle  with  respect  to  varieties  in  a  state  of 
nature  ;  and  when  we  remember  that  the  greater  number 
of  varieties  have  been  produced  under  domestication  by 
the  selection  of  mere  external  differences,  and  not  of  dif- 
ferences in  the  reproductive  system.  In  all  other  respects, 
excluding  fertility,  there  is  a  close  general  resemblance 
between  hybrids  and  mongrels  .  Finally_,  then,  the  facts 
briefly  given  in  this  chapter  do  not  seem  to  me  opposed 
to,  but  even  rather  to  support  the  view,  that  there  is  no 
fundamental  distinction  between  species  and  varieties. 


Chap.  IX.]       IMPERFECTION   OF   GEOLOGICAL   RECORD.  245 


CHAPTER    IX. 

ON  THE  IMPERFECTION  OF  THE  GEOLOGICAL  RECORD. 

On  the  absence  of  intermediate  varieties  at  the  present  day — On  the  nature  of  extinct 
intermediate  varieties  ;  on  their  number— On  the  vast  lapse  of  time,  as  inferred 
from  the  rate  of  deposition  and  of  denudation — On  the  poorness  of  our  palfeonto- 
logical  collections— On  the  intermittence  of  geological  formations— On  the  absence 
of  intermediate  varieties  in  any  one  formation — On  the  sudden  appearance  of 
groups  of  species— On  their  sudden  appearance  in  the  lowest  known  fossiliferous 
strata. 

In  the  sixth  chapter  I  eniimerated  the  chief  objections 
which  might  be  justly  urged  against  the  views  maintained 
in  this  volume.  Most  of  them  have  now  been  discussed. 
One,  namely  the  distinctness  of  specific  forms,  and  their 
not  being  blended  together  by  innumerable  transitional 
links,  is  a  very  obvious  difficulty.  I  assigned  reasons  why 
such  links  do  not  commonly  occur  at  the  present  day, 
under  the  circumstances  apparently  most  favourable  for 
their  presence,  namely  on  an  extensive  and  continuous 
area  with  graduated  physical  conditions.  I  endeavoured 
to  show,  that  the  life  of  each  species  depends  in  a  more 
important  mamier  on  the  presence  of  other  already  defined 
organic  forms,  than  on  climate ;  and,  therefore,  that  the 
really  governing  conditions  of  life  do  not  graduate  aw^ay 
quite  insensibly  like  heat  or  moisture.  I  endeavoured, 
also,  to  show  that  inteiTtiediate  varieties,  from  existing  in 
lesser  numbers  than  the  forms  which  they  connect,  will 
generally  be  beaten  out  and  exterminated  during  the 
course  of  further  modification  and  improvement.  The 
main  cause,  however,  of  innumerable  intermediate  links 
not  now  occurring  everywhere  throughout  nature  depends 
on  the  very  process  of  natural  selection,  through  w^hich 
new  varieties  continually  take  the  places  of  and  extermi- 
nate their  parent-forms.     But  just  in  proportion  as  this 


246  IMPERFECTION    OF   THE  [Chap.  IX. 

process  of  extermination  lias  acted  on  an  enormous  scale, 
so  must  tlie  number  of  intermediate  varieties,  wHcli  have 
formerly  existed  on  the  earth,  be  truly  enormous.  "Why 
then  is  not  every  geological  formation  and  every  stra- 
tum full  of  such  intermediate  links  ?  Geology  assuredly 
does  not  reveal  any  such  finely  graduated  organic  chain  ; 
and  this,  perhaps,  is  the  most  obvious  and  gravest  objec- 
tion which  can  be  urged  against  my  theory.  The  expla- 
nation lies,  as  I  believe,  in  the  extreme  imperfection  of 
the  geological  record. 

Li  the  first  place  it  should  always  be  borne  in  mind 
what  sort  of  intermediate  forms  must,  on  my  theory, 
have  formerly  existed.  I  have  found  it  difiicult,  when 
looking  at  any  two  species,  to  avoid  picturing  to  myself, 
forms  directly  intermediate  between  them.  But  this  is  a 
wholly  false  view ;  we  should  always  look  for  forms  in- 
termediate between  each  species  and  a  common  but  un 
known  progenitor ;  and  the  progenitor  will  generally 
have  diftered  in  some  respects  from  all  its  modified  de- 
scendants. -^To  give  a  simple  illustration  :  the  fantail  and 
pouter  pigeons  have  both  descended  from  the  rock-pigeon ; 
if  we  possessed  all  the  intermediate  varieties  which  have 
ever  existed,  we  should  have  an  extremely  close  series 
between  both  and  the  rock-pigeon ;  but  we  should  have 
no  varieties  directly  intermediate  between  the  fantail  and 
pouter  ;  none,  for  instance,  combining  a  tail  somewhat  ex- 
panded with  a  crop  somewhat  enlarged,  the  characteristic 
features  of  these  two  breeds.  These  two  breeds,  more- 
over, have  become  so  much  modified,  that  if  we  had  no 
historical  or  indirect  evidence  regarding  their  origin,  it 
would  not  have  been  possible  to  have  determined  from  a 
mere  comparison  of  their  structure  with  that  of  the  rock- 
pigeon,  whether  they  had  descended  from  this  species  or 
from  some  other  allied  species,  such  as  C.  oenas. 

So  with  natural  species,  if  we  look  to  forms  very  dis- 
tinct, for  instance  to  the  horse  and  tapir,  we  have  no 
reason  to  suppose  that  links  ever  existed  directly  interme- 
diate between  them,  but  between  each  and  an  unknown 
common  parent.  The  common  parent  will  have  had  in 
its  whole  organisation  much  general  resemblance  to  the 


Chap.  IX.l  GEOLOGICAL   RECORD. 


247 


tapir  and  to  the  horse  ;  but  in  some  points  of  structure 
may  have  differed  considerably  from  both,  even  perhaps 
more  than  they  differ  from  each  other.  Hence  in  all  such 
cases,  we  sliould  be  unable  to  recognise  the  parent-form 
of  any  two  or  more  species,  even  if  we  closely  compared 
the  structure  of  the  parent  with  that  of  its  modified  de- 
scendants, unless  at  the  same  time  we  had  a  nearly  per- 
fect chain  of  the  intermediate  links. 

It  is  just  possible  by  my  theory,  that  one  of  two  living 
forms  might  have  descended  from  the  other ;  for  instance, 
a  horse  from  a  tapir  ;  and  in  this  case  direct  intermediate 
links  will  have  existed  between  them.  But  such  a  case 
would  imply  that  one  form  had  remained  for  a  very  long 
period  unaltered,  whilst  its  descendants  had  undergone  a 
vast  amount  of  change  ;  and  the  principle  of  competition 
between  organism  and  organism,  between  child  and  pa- 
rent, will  render  this  a  very  rare  event ;  for  in  all  cases 
the  new  and  improved  forms  of  life  will  tend  to  supj^lant 
the  old  and  unimproved  forms. 

By  the  theory  of  natural  selection  all  living  species 
have  been  connected  with  the  parent-species  of  each 
genus,  by  differences  not  greater  than  we  see  between 
the  varieties  of  the  same  species  at  the  present  day  ;  and 
these  parent-species,  now  generally  extinct,  have  in  their 
turn  been  similarly  connected  with  more  ancient  species  ; 
and  so  on  backwards,  always  converging  to  the  common 
ancestor  of  each  great  class.  So  that  the  number  of  in- 
termediate and  transitional  links,  between  all  living  and 
extinct  species,  must  have  been  inconceivably  great.  But 
assuredly,  if  this  theory  be  true,  such  have  lived  upon 
this  earth. 

On  the  lapse  of  Time. — ^Independently  of  our  not  find- 
ing fossil  remains  of  such  infinitely  numerous  connecting 
links,  it  may  be  objected,  that  time  will  not  have  sufficed 
for  so  great  an  amount  of  organic  change,  all  changes 
having  been  effected  very  slowly  through  natural  selection. 
It  is  hardly  possible  for  me  even  to  recall  to  the  reader, 
who  may  not  be  a  practical  geologist,  the  facts  leading 
the  mind  feebly  to  comprehend  the  lapse  of  time.     He 


248  IMPERFECTION    OF   THE  [Chap.  IX. 

who  can  read  Sir  Charles  Lyell's  grand  work  on  the  Prin- 
ciples of  Geology,  which  the  future  historian  will  recognise 
as  having  produced  a  revolution  in  natural  science,  yet 
does  not  admit  how  incomprehensibly  vast  have  been  the 
past  periods  of  time,  may  at  once  close  this  volume.  Not 
that  it  suffices  to  study  the  Principles  of  Geology,  or  to 
read  special  treatises  by  different  observers  on  separate 
formations,  and  to  mark  how  each  author  attempts  to  give 
an  inadequate  idea  of  the  duration  of  each  formation  or 
even  each  stratum.  A  man  must  for  years  examine  for 
himself  great  piles  of  superimposed  strata,  and  watch  the 
sea  at  work  grinding  down  old  rocks  and  making  fresh 
sediment,  before  he  can  hope  to  comprehend  anything 
of  the  lapse  of  time,  the  monuments  of  which  we  see 
around  us. 

It  is  good  to  wander  along  lines  of  sea-coast,  when 
formed  of  moderately  hard  rocks,  and  mark  the  process 
of  degradation.  The  tides  in  most  cases  reach  the  clitfs 
only  for  a  short  time  twice  a  day,  and  the  waves  eat  into 
them  only  when  they  are  charged  with  sand  or  pebbles  ; 
for  there  is  reason  to  believe  that  pure  water  can  effect 
little  or  nothing  in  wearing  away  rock.  At  last  the  base 
of  the  cliff  is  undermined,  huge  fragments  fall  down,  and 
these  remaining  fixed,  have  to  be  worn  away,  atom  by 
atom,  until  reduced  in  size  they  can  be  rolled  about  by  the 
waves,  and  then  are  more  quickly  ground  into  pebblesj 
sand,  or  mud  But  how  often  do  we  see  along  the  bases 
of  retreating  cliffs,  rounded  boulders,  all  thickly  clothed 
by  marine  productions,  shewing  how  little  they  are  abrad- 
ed and  how  seldom  they  are  railed  about !  Moreover, 
if  we  follow  for  a  few  miles  any  line  of  rocky  cliff,  which 
is  undergoing  degradation,  we  find  that  it  is  only  here  and 
there,  along  a  short  length  or  round  a  promontory,  that 
the  cliffs  are  at  the  present  time  suffering.  The  appear- 
ance of  the  surface  and  the  vegetation  show  that  else- 
where years  have  elapsed  since  the  waters  w^ashed  their 
base. 

He  who  most  closely  studies  the  action  of  the  sea  on 
our  shores,  will,  I  believe,  be  most  deeply  impressed  with 
the  slowness  with  which  rocky  coasts  are  worn,  away. 


Chap.  IX.]  GEOLOGICAL   RECORD,  249 

The  observations  on  this  head  by  Hugh  Miller,  and  by 
that  excellent  observer  Mr.  Smith  of  Jordan  Hill,  are 
most  impressive.  With  the  mind  thus  impressed,  let  any 
one  examine  beds  of  conglomerate  many  thousand  feet  in 
thickness,  which,  though  probably  formed  at  a  quicker 
rate  than  many  other  deposits,  yet,  from  being  formed  of 
worn  and  rounded  pebbles,  each  of  which  bears  the  stamp 
of  time,  are  good  to  show  how  slowly  the  mass  has  been 
accumulated.  Let  him  remember  Lyell's  profound  remark, 
that  the  thickness  and  extent  of  sedimentary  formations 
are  the  result  and  measure  of  the  degradation  which  the 
earth's  crust  has  elsewhere  suflered.  And  what  an  amount 
of  degradation  is  implied  by  the  sedimentary  deposits  of 
many  countries  !  Professor  Kamsay  has  given  me  the 
maximum  thickness,  in  most  cases  from  actual  measure- 
ment, in  a  few  cases  from  estimate,  of  each  formation  in 
different  parts  of  Great  Britain  ;  and  this  is  the  result : — 

Feet. 
Palceozoic  strata  (not  including  igneous  beds)  ..     .. '   ..     57,154 

Secondary  strata      13,190 

Tertiary  strata 2,240 

— making   altogether   ^2,584  feet ;    that  is,  very  nearly 
thirteen  and  three-quarters  British  miles.     Some  of  these 
formations,  which  are  represented  in  England  by  thin 
beds,  are  thousands  of  feet  in  thickness  on  the  Continent 
Moreover,  between  each  successive  formation,  we  have,  in 
the   opinion  of  most  geologists,  enormously  long  blank 
periods.     So  that  the  lofty  pile  of  sedimentary  rocks  in 
Britain,  gives  but  an  inadequate  idea  of  the  time  which 
has  elapsed  during  their  accumulation ;  yet  what  time 
this  must  have  consumed !     Good  observers  have  esti- 
mated that  sediment  is  deposited  by  the  great  Mississippi 
Eiver  at  the  rate  of  only  600  feet  in  a  hundred  thousand 
years.     This  estimate  may  be  quite  erroneous  ;  yet,  con- 
sidering  over  what  wide   spaces  very  fine  sediment   is 
transported   by  the  currents  of  the  sea,  the  process  of 
accumulation  in  any  one  area  must  be  extremely  slow. 

But  the  amount  of  denudation  which  the  strata  have 
in  many  places  suffered,  independently  of  the  rate  of 
Jiccumulation  of  the  degraded  matter,  probablv  offers  the 


OKQ  IMPERFECTION    OF   THE  [Chap.  IX, 

best  evidence  of  tlie  lapse  of  time.  I  remember  having 
been  much  struck  with  the  evidence  of  denudation,  when 
viewing  volcanic  islands,  which  have  been  worn  by  the 
Vn' aves  and  pared  all  round  into  perpendicular  cliffs  of  one 
or  two  tliousand  feet  in  height ;  for  the  gentle  slope  of 
the  lava-streams,  due  to  their  formerly  liquid  state,  showed 
at  a  glance  how  far  the  hard,  rocky  beds  had  once  extended 
into  the  open  ocean.  The  same  story  is  still  more  plainly 
told  by  faults, — those  great  cracks  along  which  the  strata 
have  been  upheaved  on  one  side,  or  thrown  down  on  the 
other,  to  the  height  or  depth  of  thousands  of  feet ;  for 
since  the  crust  cracked,  the  surface  of  the  land  has  been 
so  completely  planed  down  by  the  action  of  the  sea,  that 
no  trace  of  these  vast  dislocations  is  externally  visible. 

The  Craven  fault,  for  instance,  extends  for  upwards  of 
30  miles,  and  along  this  line  the  vertical  displacement  of 
the  strata  has  varied  from  600  to  3000  feet.  Prof.  Kam- 
say  has  published  an  account  of  a  downthrow  in  Angle- 
sea  of  2300  feet ;  and  he  informs  me  that  he  fully  believes 
there  is  one  in  Merionethshire  of  12,000  feet ;  yet  in  these 
cases  there  is  nothing  on  the  surface  to  show  such  prodi- 
gious movements  ;  the  pile  of  rocks  on  the  one  or  other 
side  having  been  smoothly  swept  away.  The  considera- 
tion of  these  facts  impresses  my  mind  almost  in  the  same 
manner  as  does  the  vain  endeavour  to  grapple  with  the 
idea  of  eternity. 

I  am  tempted  to  give  one  other  case,  the  well-known 
one  of  the  denudation  of  the  Weald.  Though  it  must  be 
admitted  that  the  denudation  of  the  Weald  has  been  a 
mere  trifle,  in  comparison  with  that  which  has  removed 
masses  of  our  palaeozoic  strata,  in  parts  ten  thousand 
feet  in  thickness,  as  shown  in  Prof.  Ramsay's  masterly 
memoir  on  this  subject:  yet  it  is  an  admirable  lesson  to 
stand  on  the  intermediate  hilly  country  and  look  on  the  one 
hand  at  the  Xorth  Downs,  and  on  the  other  hand  at  the 
South  Downs ;  for,  remembering  that  at  no  great  distance  to 
the  west  the  northern  and  southern  escarpments  meet  and 
close,  one  can  safely  picture  to  oneself  the  great  dome  of 
rocks  which  must  have  covered  up  the  Weald  within  so 
limited  a  period  as  since  the  latter  part  of  the  Chalk 
formation.     The  distance  from  the  northern  to  the  south- 


Chap.  IX.]  GEOLOGICAL    RECORD.  251 

ern  Downs  is  about  22  miles,  and  the  thickness  of  the 
several  formations  is  on  an  average  about  1100  feet,  as  I 
am  informed  bj  Prof.  Ramsay,  But  if,  as  some  geologists 
suppose,  a  range  of  older  rocks  underlies  the  AVeald,  on 
the  flanks  of  which  the  overlying  sedimentary  deposits 
might  have  accumulated  in  thinner  masses  than  elsewhere, 
the  above  estimate  would  be  erroneous  ;  but  this  source 
of  doubt  probably  would  not  greatly  affect  the  estimate 
as  ajDplied  to  the  w^estern  extremity  of  the  district.  If, 
then,  we  knew^  the  rate  at  Avhich  tlie  sea  commonly  wears 
away  a  line  of  cliff  of  any  given  height,  we  could  measure 
the  time  requisite  to  have  denuded  the  Weald.  This,  of 
course,  cannot  be  done  ;  but  w^e  may,  in  order  to  form 
some  crude  notion  on  the  subject,  assume  that  the  sea 
would  eat  into  cliffs  500  feet  in  height  at  the  rate  of  one 
inch  in  a  century.  This  will  at  first  appear  much  too 
small  an  allowance  ;  but  it  is  the  same  as  if  we  were  to 
assume  a  cliff"  one  yard  in  height  to  be  eaten  back  along 
a  whole  line  of  coast  at  the  rate  of  one  yard  in  nearly 
every  twenty-two  years.  I  doubt  whether  any  rock,  even 
as  soft  as  chalk,  would  yield  at  this  rate  exce]3ting  on  the 
most  exposed  coasts  ;  though  no  doubt  the  degradation 
of  a  lofty  cliff  would  be  much  more  rapid  from  the  breakage 
of  the  fallen  fragments.  On  the  other  hand,  I  do  not  be- 
lieve that  any  line  of  coast,  ten  or  twenty  miles  in  length, 
ever  suffers  degradation  at  the  same  time  along  its  whole 
indented  length ;  and  we  must  remember  that  almost  all 
strata  contain  harder  layers  or  nodules,  which  from  long  re- 
sisting attrition  form  a  breakwater  at  the  base.  We  may 
at  least  confidently  believe  that  no  rocky  coast  500  feet  in 
height  commonly  yields  at  the  rate  of  a  foot  per  century ; 
for  this  would  be  the  same  in  amount  as  a  cliff' one  yard  in 
height  retreating  twelve  yards  in  twenty-two  years ;  and 
no  one,  I  think,  who  has  carefully  observed  the  shape  of 
old  fallen  fragments  at  the  base  of  cliffs,  will  admit  any 
near  approach  to  such  rapid  wearing  away.  Hence,  un- 
der ordinary  circumstances,  I  should  infer  that  for  a  cliff 
500  feet  in  height,  a  denudation  of  one  inch  per  century 
for  the  whole  length  would  be  a  sufficient  allowance.  At 
this  rate,  on  the  above  data,  the  denudation  of  the  Weald 
must  have  required  306,662,400  years  ;  or  say  three  hun- 
12 


252  IMPERFECTION  OF  THE  [Chap.  IX. 

dred  million  years.  But  perhaps  it  would  be  safer  to  al- 
low two  or  three  inches  per  century,  and  this  would  reduce 
the  number  of  years  to  one  hundred  and  fifty  or  one  hun- 
dred million  years.* 

The  action  of  fresh  water  on  the  gently  inclined  Wealden 
district,  when  upraised,  could  hardly  have  been  great,  but 
it  would  somewhat  reduce  the  above  estimate.  On  the  other 
hand,  during  oscillations  of  level,  which  we  know  this  area 
has  undergone,  the  sm^face  may  have  existed  for  millions  of 
years  as  land,  and  thus  have  escaped  the  action  of  the  sea : 
when  deeply  submerged  for  perhaps  equally  long  periods, 
it  would,  likewise,  have  escaped  the  action  of  the  coast- 
waves. 

I  have  made  these  few  remarks  because  it  is  highly 
important  for  us  to  gain  some  notion,  however  imperfect, 
of  the  lapse  of  years.  During  each  of  these  years,  over 
the  whole  world,  the  land  and  the  water  has  been  peopled 
by  hosts  of  living  forms.  What  an  infinite  number  of 
generations,  which  the  mind  cannot  grasp,  must  have 
succeeded  each  other  in  the  long  roll  of  years !  ISTow.turn 
to  our  richest  geological  museums,  and  what  a  paltry  dis- 
play we  behold ! 

On  the  poorness  of  our  Palceontological  collections. — 
That  our  palseontological  collections  are  very  imperfect,  is 
admitted  by  every  one.     The  remark  of  that  admirable 

*  I  have  left  the  foreo^oing  passages  as  they  stand  in  the  second  edition, 
but  I  confess  that  an  able  and  justly  severe  article,  since  published  in  the 
Saturday  Review  (Dee.  24th,  1859),  shows  that  I  have  been  rash.  I  have 
not  sufficiently  allowed  for  the  softness  of  the  strata  underlying  the  chalk  ; 
the  remarks  made  are  more  truly  applicable  to  denuded  areas  composed  of 
hard  rocks.  Xor  have  I  allowed  for  the  denudation  going  on  on  both  sides 
of  the  ancient  AVeald-Bay  ;  but  the  circumstance  of  the  denudation  having 
taken  place  within  a  protected  bay  would  prolong  the  process.  It  has  long 
been  my  habit  to  observe  the  shape  and  state  of  surface  of  the  fragments  at 
the  bases  of  lofty  retreating  cliffs,  and  I  can  find  no  words  too  strong  to  ex- 
press my  conviction  of  tlie  extreme  slowness  with  which  they  are  worn  away 
and  removed.  I  beg  the  reader  to  observe  that  I  have  expressly  stated 
that  we  cannot  know  ut  what  rate  the  sea  wears  away  a  line  of  cliff:  I  as- 
sumed the  one  inch  per  century  in  order  to  gain  some  crude  idea  of  the  lapse 
of  years ;  but  I  always  supposed  that  the  reader  would  double  or  quadruple 
or  increase  in  any  proportion  which  seemed  to  him  fair  the  probable  rate  of 
denudation  per  century.  But  I  own  that  I  have  been  rash  and  unguarded 
in  the  calculation. 


Chap  IX.]  GEOLOGICAL  RECORD,  253 

palaeontologist,  tlie  late  Edward  Forbes,  should  not  be 
forgotten,  namely,  that  numbers  of  our  fossil  species  are 
known  and  named  from  single  and  often  broken  specimens, 
or  from  a  few  specimens  coflected  on  some  one  spot.  Only 
a  small  portion  of  the  surface  of  the  earth  has  been  geo- 
logically explored,  and  no  part  with  sufficient  care,  as  the 
important  discoveries  made  every  year  in  Europe  prove. 
No  organism  wholly  soft  can  be  preserved.  Shells  and 
bones  will  decay  and  disappear  when  left  on  the  bottom 
of  the  sea,  where  sediment  is  not  accumulating.  I  believe 
we  are  continually  taking  a  most  erroneous  view,  when  we 
tacitly  admit  to  ourselves  that  sediment  is  being  deposited 
over  nearly  the  whole  bed  of  the  sea,  at  a  rate  sufficiently 
quick  to  embed  and  preserve  fossil  remains.  Throughout 
an  enormously  large  proportion  of  the  ocean,  the  bright 
blue  tint  of  the  water  bespeaks  its  purity.  The  many  cases 
on  record  of  a  formation  conformably  covered,  after  an 
enormous  interval  of  time,  by  another  and  later  formation, 
without  the  underlying  bed  having  suffered  in  the  interval 
any  wear  and  tear,  seem  explicable  only  on  the  view  of  the 
bottom  of  the  sea  not  rarely  lying  for  ages  in  an  unaltered 
condition.  The  remains  which  do  become  embedded,  if  in 
sand  or  gravel,  will  when  the  beds  are  upraised  generally 
be  dissolved  by  the  percolation  of  rain-water  charged  with 
carbonic  acid.  Some  of  the  many  kinds  of  animals  which 
live  on  the  beach  between  high  and  low  watermark  seem 
to  be  rarely  preserved.  For  instance,  the  several  species 
of  the  Chthamalinse  (a  sub-family  of  sessile  cirripedes)  coat 
the  rocks  all  over  the  world  in  infinite  numbers :  they  are 
all  strictly  littoral,  with  the  exception  of  a  single  Medi- 
terranean species,  which  inhabits  deep  water  and  has  been 
found  fossil  in  Sicily,  whereas  not  one  other  species  has 
hitherto  been  found  in  any  tertiary  formation :  yet  it  is 
now  known  that  the  genus  Chthamalus  existed  during  the 
chalk  period.  The  moUuscan  genus  Chiton  offers  a  par- 
tially analogous  case. 

With  respect  to  the  terrestrial  productions  which  lived 
during  the  Secondary  and  Palaeozoic  periods,  it  is  super- 
fluous to  state  that  our  evidence  from  fossil  remains  is 
fragmentary  in  an  extreme  degree.     For  instance,  not  a 


254:  IMPERFECTIOX    OF    THE  [Chap.  IX. 

land  shell  is  known  belonging  to  either  of  these  vast 
periods,  with  one  exception  discovered  by  Sir  C.  Lyell  in 
the  carboniferous  strata  of  North  America.  In  regard  to 
mammiferons  remains,  a  single  glance  at  the  historical 
table  j)nblished  in  the  Supplement  to  Lyell's  Manual,  will 
bring  home  the  truth,  how  accidental  and  rare  is  their 
preservation,  far  better  than  pages  of  detail.  JSTor  is  their 
rarity  surprising,  when  we  remember  how  large  a  propor- 
tion of  the  bones  of  tertiary  mammals  have  been  dis- 
covered either  in  caves  or  in  lacustrine  deposits ;  and  that 
not  a  cave  or  true  lacustrine  bed  is  known  belonging  to 
the  age  of  our  secondary  or  palaeozoic  formations. 

But  the  imperfection  in  the  geological  record  mainly 
results  from  another  and  more  important  cause  than  any 
of  the  foregoing ;  namely,  from  the  several  formations 
being  separated  from  each  other  by  wide  intervals  of  time. 
When  we  see  the  formations  tabulated  in  written  works, 
or  when  we  follow  them  in  natiu-e,  it  is  difficult  to  avoid 
believing  that  they  are  closely  consecutive.  But  we 
know,  for  instance  from  Sir  B.  Murchison's  great  work  on 
Russia,  what  wide  gaps  there  are  in  that  country  between 
the  superimposed  formations  ;  so  it  is  in  ISTorth  America, 
and  in  many  other  parts  of  the  world.  The  most  skilful 
geologist,  if  his  attention  had  been  exclusively  confined 
to  these  large  territories,  would  never  have  suspected  that 
during  the  periods  which  were  blank  and  barren  in  his 
own  country,  great  piles  of  sediment,  charged  with  new 
and  peculiar  forms  of  life,  had  elsewhere  been  accumulated. 
And  if  in  each  separate  territory,  hardly  any  idea  can  be 
formed  of  the  length  of  time  which  has  elapsed  between 
the  consecutive  formations,  we  may  infer  that  this  could 
nowhere  be  ascertained.  The  frequent  and  great  changes 
in  the  mineralogical  composition  of  consecutive  formations, 
generally  implying  great  changes  in  the  geograj)hy  of  the 
surrounding  lands,  whence  the  sediment  has  been  derived, 
accords  with  the  belief  of  vast  intervals  of  time  having 
elapsed  between  each  formation. 

But  we  can,  I  think,  see  why  the  geological  formations 
of  each  region  are  almost  invariably  intermittent ;  that  is, 
have  not  followed  each  other  in  close  sequence.     Scarcely 


1 


Uhap.  IX.]  GEOLOGICAL   RECORD.  255 

any  fact  struck  me  more  when  examining  many  hundred 
miles  of  the  South  American  coasts,  which  have  been  up- 
raised several  hundred  feet  within  the  recent  period,  than 
the  absence  of  any  recent  deposits  sufficiently  extensive 
to  last  for  even  a  short  geological  period.  Along  the 
whole  west  coast,  which  is  inhabited  by  a  peculiar  marine 
fauna,  tertiary  beds  are  so  scantily  developed,  that  no 
record  of  several  successive  and  peculiar  marine  faunas 
will  probably  be  preserved  to  a  distant  age.  A  little  re- 
flection will  explain  why  along  the  rising  coast  of  the 
western  side  of  South  America,  no  extensive  formations 
with  recent  or  tertiary  remains  can  anywhere  be  found, 
though  the  supply  of  sediment  must  for  ages  have  been 
great,  from  the  enormous  degradation  of  the  coast-rocks 
and  from  muddy  streams  entering  the  sea.  The  explana- 
tion, no  doubt,  is,  that  the  littoral  and  sub-littoral  deposits 
are  continually  worn  away,  as  soon  as  they  are  brought 
up  by  the  slow  and  gradual  rising  of  the  land  within  the 
grinding  action  of  the  coast- weaves. 

We  may,  I  think,  safely  conclude  that  sediment  must 
be  accumulated  in  extremely  thick,  solid,  or  extensive 
masses,  in  order  to  withstand  the  incessant  action  of  the 
waves,  when  first  upraised  and  during  subsequent  oscilla- 
tions of  level.  Such  thick  and  extensive  accumulations 
of  sediment  may  be  formed  in  two  ways ;  either,  in  pro- 
found depths  of  the  sea,  in  which  case,  judging  from  the 
researches  of  E.  Forbes,  we  may  conclude  that  the  bottom 
will  be  inhabited  by  extremely  few  animals,  and  the  mass 
when  upraised  will  give  a  most  imperfect  record  of  the 
forms  of  life  which  then  existed  ;  or,  sediment  may  be  ac- 
cumulated to  any  thickness  and  extent  over  a  shallow 
bottom,  if  it  continue  slowly  to  subside.  In  this  latter 
case,  as  long  as  the  rate  of  subsidence  and  supply  of  sed- 
iment nearly  balance  each  other,  the  sea  will  remain  shal- 
low and  favourable  for  life,  and  thus  a  fossiliferous  forma- 
tion thick  enough,  when  upraised,  to  resist  any  amount  of 
degradation,  may  be  formed. 

I  am  convinced  that  all  our  ancient  formations,  which 
are  rich  in  fossils,  have  thus  been  formed  during  subsi- 
dence.     Since   publishing  my  views  on   this  subject  in 


256  IMPERFECTION    OF    THE  [Chap.  IX. 

1845,  I  have  watched  the  progress  of  Geology,  and  have 
been  surprised  to  note  how  author  after  author,  in  treating 
of  this  or  that  great  formation,  has  come  to  the  conclusion 
that  it  was  accumulated  during  subsidence.  I  may  add, 
that  the  only  ancient  tertiary  formation  on  the  west  coast 
of  South  America,  which  has  been  bulky  enough  to  resist 
such  degradation  as  it  has  as  yet  suffered,  but  which  will 
hardly  last  to  a  distant  geological  age,  was  certainly  de- 
posited during  a  downward  oscillation  of  level,  and  thus 
gained  considerable  thickness. 

All  geological  facts  tell  us  plainly  that  each  area  has 
undergone  numerous  slow  oscillations  of  level,  and  appar- 
ently these  oscillations  have  affected  wide  spaces.  Con- 
sequently formations  rich  in  fossils  and  sufficiently  thick 
and  extensive  to  resist  subsequent  degradation,  may  have 
been  formed  over  wide  spaces  during  periods  of  subsi- 
dence, but  only  where  the  supply  of  sediment  was  suffi- 
cient to  keep  the  sea  shallow  and  to  embed  and  preserve 
the  remains  before  they  had  time  to  decay.  On  the  other 
hand,  as  long  as  the  bed  of  the  sea  remained  stationary, 
thick  deposits  could  not  have  been  accumulated  in  the 
shallow  parts,  which  are  the  most  favourable  to  life. 
Still  less  could  this  have  happened  during  the  alternate 
periods  of  elevation ;  or,  to  speak  more  accurately,  the 
beds  which  were  then  accumulated  will-  have  been  de- 
stroyed by  being  upraised  and  brought  within  the  limits 
of  the  coast-action. 

Thus  the  geological  record  will  almost  necessarily  be 
rendered  intermittent.  I  feel  much  confidence  in  the 
truth  of  these  views,  for  they  are  in  strict  accordance  with 
the  general  principles  inculcated  by  Sir  C.  Lyell ;  and  E. 
Forbes  independently  arrived  at  a  similar  conclusion. 

One  remark  is  here  worth  a  passing  notice.  During 
periods  of  elevation  the  area  of  the  land  and  of  the  adjoin- 
ing shoal  parts  of  the  sea  will  be  increased,  and  new  sta- 
tions will  often  be  formed ; — all  circumstances  most  fa- 
vourable, as  previously  explained,  for  the  formation  of 
new  varieties  and  species ;  but  during  such  periods  there 
will  generally  be  a  blank  in  the  geological  record.  On 
the  other  hand,  during  subsidence,  the  inhabited  area  and 


Chap.  IX.]  GEOLOGICAL  RECORD.  257 

number  of  inhabitants  will  decrease  (excepting  the  pro- 
ductions on  the  shores  of  a  continent  when  first  broken 
up  into  an  archipelago),  and  consequently  during  subsi- 
dence, though  there  will  be  much  extinction,  fewer  new 
varieties  or  species  will  be  formed  ;  and  it  is  during  these 
very  periods  of  subsidence,  that  our  great  deposits  rich  in 
fossils  have  been  accumulated.  Nature  may  almost  be 
said  to  have  guarded  against  the  frequent  discovery  of 
her  transitional  or  linking  forms. 

From  the  foregoing  considerations  it  cannot  be  doubted 
that  the  geological  record,  viewed  as  a  whole,  is  extremely 
imperfect ;  but  if  we  confine  our  attention  to  any  one 
formation,  it  becomes  more  diflicult  to  understand,  Avhy 
we  do  not  therein  find  closely  graduated  varieties  between 
the  allied  sjDecies  which  lived  at  its  commencement  and 
at  its  close.  Some  cases  are  on  record  of  the  same  species 
presenting  distinct  varieties  in  the  upper  and  lower  parts 
of  the  same  formation,  but,  as  they  are  rare,  they  may  be 
here  passed  over.  Although  each  formation  has  indis- 
putably requii'ed  a  vast  number  of  years  for  its  deposition, 
I  can  see  several  reasons  why  each  should  not  include  a 
graduated  series  of  links  between  the  species  which  then 
lived ;  but  I  can  by  no  means  pretend  to  assign  due  pro- 
portional weight  to  the  following  considerations. 

Although  each  formation  may  mark  a  very  long  lapse 
of  years,  each  perhaps  is  short  compared  with  the  j)eriod 
requisite  to  change  one  species  into  another.  I  am  aware 
that  two  palaeontologists,  whose  opinions  are  worthy  of 
much  deference,  namely  Bronn  and  Woodward,  have  con- 
cluded that  the  average  duration  of  each  formation  is 
twice  or  thrice  as  long  as  the  average  duration  of  specific 
forms.  But  insuperable  difficulties,  as  it  seems  to  me, 
prevent  us  coming  to  any  just  conclusion  on  this  head. 
\Vhen  we  see  a  species  first  appearing  in  the  middle  of  any 
formation,  it  would  be  rash  in  the  extreme  to  infer  that  it 
had  not  elsewhere  previously  existed.  So  again  when  we 
find  a  species  disappearing  before  the  uppermost  layers 
have  been  deposited,  it  would  be  equally  rash  to  suppose 
that  it  then  became  wholly  extinct.  AVe  forget  how  small 
the  area  of  Europe  is  compared  with  the  rest  of  the  world ; 


258  IMPEKFECTIOX   OF   THE  [Chap.  IX. 

nor  haye  the  several  stages  of  the  same  formation  throngh- 
out  Europe  been  correlated  with  perfect  accm-acy. 

AVith  marine  animals  of  all  kinds,  we  maj  safely  infer 
a  large  amount  of  migration  during  climatal  and  other 
changes ;  and  when  we  see  a  species  hrst  appearing  in  any 
formation,  the  probability  is  that  it  only  then  first  immi- 
grated into  that  area.  It  is  well  known,  for  instance,  that 
several  species  appeared  somewhat  earlier  in  the  palseozoic 
beds  of  North  America  than  in  those  of  Eiiroj)e ;  time 
having  apparently  been  required  for  their  migration  from 
the  American  to  the  European  seas.  In  examining  the 
latest  deposits  of  various  quarters  of  the  world,  it  has 
everywhere  been  noted,  that  some  few  still  existing  spe- 
cies are  common  in  the  deposit,  but  have  become  extinct 
in  the  immediately  surrounding  sea ;  or,  conversely,  that 
some  are  now  abundant  in  the  neighbouring  sea,  but  are 
rare  or  absent  in  this  particular  deposit.  It  is  an  excel- 
lent lesson  to  reflect  on  the  ascertained  amount  of  migra- 
tion of  the  inhabitants  of  Europe  during  the  Glacial  period, 
w^hich  forms  only  a  j)art  of  one  whole  geological  period ; 
aud  likewise  to  reflect  on  the  great  changes  of  level,  on 
the  inordinately  great  change  of  climate,  on  the  pro- 
digious lapse  of  time,  all  included  within  this  same  gla- 
cial period.  Yet  it  may  be  doubted  whether  in  any 
quarter  of  the  world,  sedimentary  deposits,  including 
fossil  remains^  have  gone  on  accumulating  within  the 
same  area  durmg  the  whole  of  this  period.  It  is  not,  for 
instance,  probable  that  sediment  was  deposited  durino-  the 
whole  of  the  glacial  period  near  the  mouth  of  the  Missis- 
sippi, within  that  limit  of  depth  at  which  marine  animals 
can  flourish;  for  we  know  what  vast  geographical  changes 
occurred  in  other  parts  of  America  during  this  space  of 
time.  AVhen  such  beds  as  were  deposited  in  shallow 
water  near  the  mouth  of  the  Mississippi  during  some  part 
of  the  glacial  period  shall  have  been  upraised,  organic  re- 
mains will  probably  at  first  appear  and  disappear  at.  dif- 
ferent levels,  owing  to  the  migration  of  species  and  to 
geographical  changes.  And  in  the  distant  future,  a  geol- 
ogist examining  these  beds  might  be  tempted  to  conclude 
that  the  averao-e  duration  of  life  of  the  embedded  fossils 


Chap.  IX.]  .   GEOLOGICAL  RECORD.  259 

had  been  less  tlian  that  of  the  glacial  period,  instead  of 
having  been  really  far  greater,  that  is  extending  from  be- 
fore the  glacial  ejjocli  to  the  present  day. 

Ill  order  to  get  a  perfect  gradation  between  two  forms 
in  the  npper  and  lower  parts  of  the  same  formation,  the 
deposit  must  have  gone  on  accumulating  for  a  very  long 
period,  in  order  to  have  given  sufficient  time  for  the  slow 
process  of  variation ;  hence  the  deposit  will  generally  have 
to  be  a  very  thick  one ;  and  the  species  undergoing  modi- 
fication will  have  had  to  live  on  the  same  area  throughout 
this  whole  time.  But  we  have  seen  that  a  thick  fossil- 
iferous  formation  can  only  be  accumulated  during  a  period 
of  subsidence  ;  and  to  keep  the  depth  approximately  the 
same,  which  is  necessary  in  order  to  enable  the  same  spe- 
cies to  live  on  the  same  space,  the  suj)ply  of  sediment  must 
nearly  have  counterbalanced  the  amount  of  subsidence. 
But  this  same  movement  of  subsidence  will  often  tend  to 
sink  the  area  whence  the  sediment  is  derived,  and  thus 
diminish  the  supply  whilst  the  downward  movement  con- 
tinues. In  fact,  this  nearly  exact  balancing  between  the 
supply  of  sediment  and  the  amount  of  subsidence  is  prob- 
ably a  rare  contingency  ;  for  it  has  been  observed  by 
more  than  one  palaeontologist,  that  very  thick  deposits 
are  usually  barren  of  organic  remains,  except  near  their 
upper  or  lower  limits. 

It  would  seem  that  each  separate  formation,  like  the 
wliole  pile  of  formations  in  any  country,  has  generally  been 
intermittent  in  its  accumulation.  When  we  see,  as  is  so 
often  the  case,  a  formation  composed  of  beds  of  different 
mineralogical  composition,  we  may  reasonably  suspect 
that  the  process  of  deposition  has  been  much  interrupted, 
as  a  change  in  the  currents  of  the  sea  and  a  supply  of  sed- 
iment of  a  different  nature  will  generally  have  been  due  to 
geographical  changes  requiring  much  time.  'Nor  will 
the  closest  inspection  of  a  formation  give  any  idea  of  the 
time  which  its  deposition  has  consumed.  Many  in- 
stances could  be  given  of  beds  only  a  few  feet  in  thickness, 
representing  formations,  elsewhere  thousands  of  feet  in 
thickness,  and  which  must  have  required  an  enormous 
period  for  their  accumulation  ;  vet  no  one  ia'norant  of  this 


260  IMPERFECTlOis-    OF   THE   •  [Chap.  IX. 

fact  would  have  suspected  the  vast  lapse  of  time  represent- 
ed bj  the  thinner  formation.  Many  cases  could  be  given 
of  the  lower  beds  of  a  formation  having  been  upraised, 
denuded,  submerged,  and  then  re-covered  by  the  upper 
beds  of  the  same  formation,— facts,  showing  what  wide, 
yet  easily  overlooked,  intervals  have  occurred  in  its  accu- 
mulation. In  other  cases  we  have  the  plainest  evidence 
in  great  fossilised  trees,  still  standing  upright  as  they 
grew,  of  many  long  intervals  of  time  and  changes  of  level 
during  the  process  of  deposition,  which  would  never  even 
have  been  suspected,  had  not  the  trees  chanced  to  have 
been  preserved:  thus  Messrs.  Lyell  and  Dawson  found 
carboniferous  beds  1400  feet  thick  in  N"ova  Scotia,  with 
ancient  root-bearing  strata,  one  above  the  other,  at  no  less 
than  sixty-eight  different  levels.  Hence,  when  the  same 
species  occur  at  the  bottom,  middle,  and  top  of  a  forma- 
tion, the  probability  is,  that  they  have  not  lived  on  the 
same  spot  during  the  whole  period  of  deposition,  but  have 
disappeared  and  reap]Deared,  perhaps  many  times,  during 
the  same  geological  period.  So  that  if  such  species  were 
to  undergo  a  considerable  amount  of  modification  during 
any  one  geological  period,  a  section  would  not  probably 
include  all  the  fine  intermediate  gradations  which  must  on 
my  theory  have  existed  between  them,  but  abrupt,  though 
perhaps  very  slight,  changes  of  form. 

It  is  all-imjDortant  to  remember  that  naturalists  have 
no  golden  rule  by  which  to  distinguish  species  and  varie- 
ties ;  they  grant  some  little  variability  to  each  species, 
but  when  they  meet  with  a  somewhat  greater  amoimt  of 
difference  between  any  two  forms,  they  rank  both  as 
species,  unless  they  are  enabled  to  connect  them  together. 
by  close  intei-mediate  gradations.  And  this  from  the 
reasons  just  assigned  we  can  seldom  hope  to  effect  in  any 
one  geological  section.  Supposing  B  and  C  to  be  two 
species,  and  a  third.  A,  to  be  found  in  an  underlying  bed  ; 
even  if  A  were  strictly  intermediate  between  B\and  C,  it 
would  simply  be  ranked  as  a  third  and  distinct  species, 
unless  at  the  same  time  it  could  be  most  closely  connected 
with  either  one  or  both  forms  by  intermediate  varieties. 
Nor  should  it  be  forgotten,  as  before  explained,  that  A 


OHAt>.  1X.1  GEOLOGICAL   RECORD.  261 

tniglit  be  tlie  actual  progenitor  of  B  and  C,  and  yet  might 
not  at  all  necessarily  be  strictly  intermediate  between 
them  in  all  points  of  structure.  So  that  we  might  obtain 
the  parent-species  and  its  several  modified  descendants 
from  the  lower  and  upper  beds  of  a  formation,  and  unless 
we  obtained  numerous  transitional  gradations,  we  should 
not  recognise  their  relationship,  and  should  consequently 
be  compelled  to  rank  them  all  as  distinct  species. 

It  is  notorious  on  what  excessively  slight  differences 
many  palaeontologists  have  founded  their  species  ;  and 
they  do  this  the  more  readily  if  the  specimens  come  from 
difterent  sub-stages  of  the  same  formation.  Some  ex- 
perienced conchologists  are  now  sinking  many  of  the  very 
fine  species  of  D'Orbigny  and  others  into  the  rank  of 
varieties ;  and  on  this  view  we  do  find  the  kind  of  evi- 
dence of  change  which  on  my  theory  we  ought  to  find. 
Moreover,  if  we  look  to  rather  wide  intervals,  namely,  the 
distinct  but  consecutive  stages  of  the  same  great  forma- 
tion, we  find  that  the  embedded  fossils,  though  almost 
universally  ranked  as  specifically  different,  yet  are  far 
more  closely  allied  to  each  other  than  are  the  species 
found  in  more  widely  separated  formations  ;  but  to  this 
subject  I  shall  have  to  return  in  the  following  chapter. 

One  other  consideration  is  worth  notice  :  with  animals 
and  plants  that  can  propagate  rapidly  and  are  not  highly 
locomotive,  there  is  reason  to  suspect,  as  we  have  former- 
ly seen,  that  their  varieties  are  generally  at  first  local ; 
and  that  such  local  varieties  do  not  spread  widely  and 
supplant  their  parent-forms  until  they  have  been  modified 
and  perfected  in  some  considerable  degree.  According 
to  this  view,  the  chance  of  discovering  in  a  formation  in 
any  one  country  all  the  early  stages  of  transition  between 
any  two  forms,  is  small,  for  the  successive  changes  are 
supposed  to  have  been  local  or  confined  to  some  one  spot. 
Most  marine  animals  have  a  wide  range  ;  and  we  have 
seen  that  with  plants  it  is  those  which  have  the  widest 
range,  that  oftenest  present  varieties  ;  so  that  with  shells 
and  other  marine  animals,  it  is  probably  those  which  have 
had  the  widest  range,  far  exceeding  the  limits  of  the 
known  geological  formations  of  Europe,  which  have  often- 


252  IMPERFECTIONS    OE   tHE  [Chap.  IX, 

est  given  rise,  first  to  local  varieties  and  ultimately  to 
new  species ;  and  this  again  would  greatly  lessen  the 
chance  of  our  being  able  to  trace  the  stages  of  transition 
in  any  one  geological  formation. 

It  should  not  be  forgotten,  that  at  the  present  day, 
with  perfect  specimens  for  examination,  two  forms  can  sel- 
dom be  connected  by  intermediate  varieties  and  thus 
proved  to  be  the  same  species,  until  many  specimens  have 
been  collected  from  many  places ;  and  in  the  case  of  fossil 
species  this  could  rarely  be  eftected  by  palaeontologists. 
"We  shall,  perhaps,  best  perceive  the  improbability  of  our 
being  enabled  to  connect  species  by  numerous,  fine,  inter- 
mediate, fossil  links,  by  asking  ourselves  whether,  for  in- 
stance, geologists  at  some  future  period  will  be  able  to 
prove,  that  our  diflerent  breeds  of  cattle,  sheep,  horses, 
and  dogs  have  descended  from  a  single  stock  or  from  sev- 
eral aboriginal  stocks ;  or,  again,  whether  certain  sea- 
shells  inhabiting  the  shores  of  I^orth  America,  which  are 
ranked  by  some  conchologists  as  distinct  species  from  their 
European  representatives,  and  by  other  conchologists  as 
only  varieties,  are  really  varieties  or  are,  as  it  is  called, 
specifically  distinct.  This  could  be  efi'ected  only  by  the 
future  geologist  discovering  in  a  fossil  state  numerous  in- 
termediate gradations  ;  and  such  success  seems  to  me  im- 
probable in  the  highest  degree. 

Geological  research,  though  it  has  added  numerous 
species  to  existing  and  extinct  genera,  and  has  made  the 
intervals  between  some  few  groups  less  wide  than  they 
otherwise  would  have  been,  yet  has  done  scarcely  anything 
in  breaking  down  the  distinction  between  species,  by  con- 
necting them  together  by  numerous,  fine,  intermediate 
varieties  ;  and  this  not  having  been  efi'ected,  is  j^robably 
the  gravest  and  most  obvious  of  all  the  many  objections 
which  may  be  urged  against  my  views.  Hence  it  will 
be  worth  while  to  sum  up  the  foregoing  remarks,  under 
an  imaginary  illustration.  The  Malay  Achipelago  is  of 
about  the  size  of  Europe  from  the  North  Cape  to  the 
Mediterranean,  and  from  Britain  to  Russia  ;  and  therefore 
equals  all  the  geological  formations  which  may  have  been 
examined  with  any  accuracy,  excepting  those  of  the  United 


CHAP.  IX.]  GEOLOGICAL   HECOflD.  ggg 

States  of  America.  I  fully  agi-ee  witli  Mr.  Godwin- Aus- 
ten, that  the  present  condition  of  the  Malay  Archipelago, 
with  its  nnmerous  large  islands  separated  by  wide  and 
shallow  seas,  probably  represents  the  former  state  of 
Europe,  when  most  of  our  formations  were  accumulating. 
The  Malay  Archipelago  is  one  of  the  richest  regions  of 
the  whole  world  in  organic  beings ;  yet  if  all  the  species 
were  to  be  collected  which  have  ever  lived  there,  how 
imperfectly  would  they  represent  the  natural  history  of 
the  world ! 

But  we  have  every  reason  to  believe  that  the  terres- 
trial productions  of  the  archipelago  would  be  ]3reserved 
in  an  excessively  imperfect  manner  in  the  formations 
which  we  suppose  to  be  there  accumulating.  I  suspect 
that  not  many  of  the  strictly  littoral  animals,  or  of  those 
which  lived  on  naked  submarine  rocks,  would  be  em- 
bedded ;  and  those  embedded  in  gravel  or  sand,  would 
not  endure  to  a  distant  epoch.  Wherever  sediment  did 
not  accumulate  on  the  bed  of  the  sea,  or  where  it  did  not 
accumulate  at  a  sufficient  rate  to  protect  organic  bodies 
from  decay,  no  remains  could  be  preserved. 

In  our  archipelago,  I  believe  that  fossiliferous  forma- 
tions could  be  formed  of  sufficient  thickness  to  last  to  an 
age,  as  distant  in  futurity  as  the  secondary  formations  lie 
in  the  past,  only  during  periods  of  subsidence.  These 
periods  of  subsidence  would  be  separated  from  each  other 
by  enormous  intervals,  during  which  the  area  w^ould  be 
either  stationary  or  rising ;  whilst  rising,  each  fossiliferous 
formation  would  be  destroyed,  almost  as  soon  as  accumu- 
lated, by  the  incessant  coast-action,  as  we  now  see  on  the 
shores  of  South  America.  During  the  periods  of  subsi- 
dence there  would  probably  be  much  extinction  of  life ; 
during  the  periods  of  elevation,  there  would  be  much 
variation,  but  the  geological  record  would  then  be  least 
perfect. 

It  may  be  doubted  whether  the  duration  of  any  one 
great  period  of  subsidence  over  the  whole  or  part  of  the 
archipelago,  together  with  a  contemporaneous  accumula- 
tion of  sediment,  would  exceed  the  average  duration  of  the 
same  specific  forms ;    and  these  contingencies  are  indis- 


2g4:  IMPERFEOTIOK   OF   THE  [Ohap.  1X> 

pensable  for  tlie  preservation  of  all  the  transitional  grada- 
tions between  any  two  or  more  species.  If  such  grada- 
tions were  not  fully  preserved,  transitional  varieties  would 
merely  appear  as  so  many  distinct  species.  It  is,  also, 
probable  that  each  great  period  of  subsidence  would  be 
interrupted  by  oscillations  of  level,  and  that  slight  cli- 
matal  changes  would  intervene  during  such  lengthy 
periods ;  and  in  these  cases  the  inhabitants  of  the  archi- 
pelago would  have  to  migrate,  and  no  closely  consecutive 
record  of  their  modifications  could  be  preserved  in  any 
one  formation. 

Yery  many  of  the  marine  inhabitants  of  the  archipe- 
lago now  range  thousands  of  miles  beyond  its  confines ; 
and  analogy  leads  me  to  believe  that  it  would  be  chiefly 
these  far-ranging  species  which  would  oftenest  produce 
new  varieties ;  and  the  varieties  would  at  first  generally 
be  local  or  confined  to  one  place,  but  if  possessed  of  any 
decided  advantage,  or  when  further  modified  and  im- 
proved, they  would  slowly  spread  and  supplant  their 
parent-forms.  "When  such  varieties  returned  to  their 
ancient  homes,  as  they  would  differ  from  their  former 
state,  in  a  nearly  umform,  though  perhaps  extremely 
slight  degree,  they  would,  according  to  the  principles  fol- 
lowed by  many  palgeontologists,  be  ranked  as  new  and 
distinct  species. 

If  then,  there  be  some  degree  of  truth  in  these  re- 
marks, we  have  no  right  to  expect  to  find  in  our  geologi- 
cal formations,  an  infinite  number  of  those  fine  transitional 
forms,  which  on  my  theory  assuredly  have  connected  all 
the  past  and  present  species  of  the  same  group  into  one 
long  and  branching  chain  of  life.  We  ought  only  to  look 
for  a  few  links,  some  more  closely,  some  more  distantly 
related  to  each  other ;  and  these  links,  let  them  be  ever 
so  close,  if  found,  in  diflerent  stages  of  the  same  formation, 
would,  by  most  palaeontologists,  be  ranked  as  distinct 
species.  But  I  do  not  pretend  that  I  should  ever  have 
suspected  how  poor  a  record  of  the  mutations  of  life,  the 
best  preserved  geological  section  presented,  had  not  the 
difficulty  of  our  not  discovering  innumerable  transitional 
links  between  the  species  which  appeared  at  the  com- 


Chap.  IX.]  GEOLOGICAL   HECORD.  265 

mencement  and  close  ot*  each  formatioiij  pressed  so  hardly 
on  my  theory. 

On  the  sudden  appearance  of  whole  groups  of  Allied 
Species. — ^The  abrupt  manner  in  which  whole  groups  of 
species  suddenly  appear  in  certain  formations,  has  been 
urged  by  several  palaeontologists,  for  instance,  by  Agassiz, 
Pictet,  and  by  none  more  forcibly  than  by  Professor 
Sedgwick,  as  a,  fatal  objection  to  the  belief  in  the  trans- 
mutation of  species.  If  numerous  species,  belonging  to 
the  same  genera  or  families,  have  really  started  into  life 
all  at  once,  the  fact  would  be  fatal  to  the  theory  of  de- 
scent with  slow  modification  through  natural  selection. 
For  the  development  of  a  group  of  forms,  all  of  which 
have  descended  from  some  one  progenitor,  must  have 
been  an  extremely  slow  process ;  and  the  progenitors 
must  have  lived  long  ages  before  their  modified  descend- 
ants. But  we  continually  over-rate  the  perfection  of  the 
geological  record,  and  falsely  infer,  because  certain  genera 
or  families  have  not  been  found  within  a  certain  stage, 
that  they  did  not  exist  before  that  stage.  "We  continually 
forget  how  large  the  world  is,  compared  with  the  area 
over  which  our  geological  formations  have  been  carefully 
examined  ;  we  forget  that  groups  of  species  may  elsewhere 
have  long  existed  and  have  slowly  multiplied  before  they 
invaded  the  ancient  archipelagoes  of  Europe  and  of  the 
United  States.  We  do  not  make  due  allowance  for  the 
enormous  intervals  of  time,  which  have  probably  elapsed 
between  our  consecutive  formations,*^ — longer  perhaps  in 
some  cases  than  the  time  required  for  the  accumulation  of 
each  formation.  These  intervals  will  have  given  time  for 
the  multiplication  of  species  from  some  one  or  some  few 
parent-forms  ;  and  in  the  succeeding  formation  such  spe- 
cies will  a23pear  as  if  suddenly  created. 

I  may  here  recall  a  remark  formerly  made,  namely 
that  it  might  require  a  long  succession  of  ages  to  adapt 
an  organism  to  some  new  and  peculiar  line  of  life,  for  in- 
stance to  fly  through  the  air;  but  that  when  this  had  been 
eflected,  and  a  few  species  had  thus  acquired  a  great  ad- 
vantage over  other  organisms,  a  comparatively  short  time 


2QQ  IMPEHFECTON  OF  THE  [Chap.  IX. 

would  be  necessary  to  produce  many  divergent  forms, 
which  would  be  able  to  spread  rapidly  and  widely 
throughout  the  world. 

I  will  now  give  a  few  examples  to  illustrate  these  re- 
marks, and  to  show  how  liable  we  are  to  error  in  suppos- 
ing that  whole  groups  of  species  have  suddenly  been  pro- 
duced. I  may  recall  the  well-known  fact  that  in  geological 
treatises,  jjublished  not  many  years  ago,  the  great  class  of 
mammals  was  always  spoken  of  as  having  abruptly  come 
in  at  the  commencement  of  the  tertiary  series.  And  now 
one  of  the  richest  known  accumulations  of  fossil  mammals, 
for  its  thickness,  belongs  to  the  middle  of  the  secondary 
series  ;  and  one  true  mammal  has  been  discovered  in  the 
new  red  sandstone  at  nearly  the  commencement  of  this 
great  series.  Cuvier  used  to  urge  that  no  monkey  oc- 
curred in  any  tertiary  stratum ;  but  now  extinct  species 
have  been  discovered  in  India,  South  America,  and  in 
Europe,  even  as  far  back  as  the  eocene  stage.  Had  it  not 
been  for  the  rare  accident  of  the  preservation  of  footsteps 
in  the  new  red  sandstone  of  the  United  States,  who  would 
have  ventured  to  suppose  that,  besides  reptiles,  no  less 
than  at  least  thirty  kinds  of  birds,  some  of  gigantic  size, 
existed  during  that  period  ?  Not  a  fragment  of  bone  has 
been  discovered  in  these  beds.  Notwithstanding  that 
the  number  of  joints  shown  in  the  fossil  impressions  cor- 
respond with  the  number  in  the  several  toes  of  living  birds' 
feet,  some  authors  doubt  whether  the  animals  which  left 
the  impressions  were  really  birds.  ^  Until  quite  recently 
these  authors  might  have  maintained,  and  some  have 
maintained,  that  the  whole  class  of  birds  came  suddenly 
into  existence  during  an  early  tertiary  period ;  but  now 
we  know,  on  the  authority  of  Professor  Owen  (as  may  be 
seen  in  Lyell's  '  Manual '),  that  a  bird  certainly  lived  dur- 
ing the  deposition  of  the  upper  green-sand. 

I  may  give  another  instance,  which  from  having  passed 
under  my  own  eyes  has  much  struck  me.  In  a  memoir 
on  Fossil  Sessile  Cirripedes,  I  have  stated  that,  from  the 
number  of  existing  and  extinct  tertiary  species  ;  from  the 
extraordinary  abundance  of  the  individuals  of  many  spe- 
cies all  over  the  world,  from  the  Arctic  regions  to  the 


Chap.  IX.]  GEOLOGICAL   RECORD.  2^7 

equator,  inliabiting  various  zones  of  depths  from  the  upper 
tidal  limits  to  50  fathoms  ;  from  the  perfect  manner  in 
which  specimens  are  preserved  in  the  oldest  tertiary 
beds  ;  from  the  ease  with  which  even  a  fragment  of  a 
valve  can  be  recognised  ;  from  all  these  circumstances,  I 
inferred  that  had  sessile  cirrij)edes  existed  dm-ing  the  sec- 
ondary periods,  they  would  certainly  have  been  preserved 
and  discovered  ;  and  as  not  one  species  has  been  dis- 
covered in  beds  of  this  age,  I  concluded  that  this  great 
group  had  been  suddenly  developed  at  the  commencement 
of  the  tertiary  series.  This  was  a  sore  trouble  to  me, 
adding  as  I  thought  one  more  instance  of  the  abrupt  ap- 
pearance of  a  great  group  of  species.  But  my  work  had 
hardly  been  published,  when  a  skilful  palseontologist,  M. 
Bosquet,  sent  me  a  drawing  of  a  perfect  specimen  of  an 
unmistakeable  sessile  cirripede,  which  he  had  himself  ex- 
tracted from  the  chalk  of  Belgium.  And,  as  if  to  make 
the  case  as  striking  as  possible,  this  sessile  cirripede  was 
a  Chthamalus,  a  very  common,  large,  and  ubiquitous 
genus,  of  which  not  one  specimen  has  as  yet  been  found 
even  in  any  tertiary  stratum.  Hence  we  now  positively 
know  that  sessile  cirripedes  existed  during  the  secondary 
period  ;  and  these  cirripedes  might  have  been  the  pro- 
genitors of  our  many  tertiary  and  existing  species. 

The  case  most  frequently  insisted  on  by  palaeontolo- 
gists of  the  apparently  sudden  appearance  of  a  whole 
group  of  species,  is  that  of  the  teleostean  fishes,  low  down 
in  the  Chalk  period.  This  group  includes  the  large  ma- 
jority of  existing  species.  Lately,  Professor  Pictet  has 
carried  their  existence  one  sub-stage  further  back  ;  and 
some  palaeontologists  believe  that  certain  much  older 
fishes,  of  which  the  afiinities  are  as  yet  imperfectly 
known,  are  really  teleostean.  Assuming,  however,  that 
the  Avhole  of  them  did  appear,  as  Agassiz  believes,  at  the 
commencement  of  the  chalk  formation,  the  fact  would 
certainly  be  highly  remarkable ;  but  I  cannot  see  that  it 
would  be  an  insuperable  diificulty  on  my  theory,  unless 
it  could  likewise  be  shown  that  the  species  of  this  group 
appeared  suddenly  and  simultaneously  throughout  the 
world  at  this  same  period.     It  is  almost  superfiuous  to 


2g8  IMPERFECTION   OF   THE  [Chap.  IX. 

remark  that  hardly  any  fossil-fish  are  known  from  south 
of  the  equator ;  and  by  running  through  Pictet's  Palaeon- 
tology it  will  be  seen  that  very  few  species  are  known 
from  several  formations  in  Europe.  Some  few  families 
of  fish  now  have  a  confined  range  ;  the  teleostean  fish 
might  formerly  have  had  a  similarly  confined  range,  and 
after  having  been  largely  developed  in  some  one  sea, 
might  have  spread  widely.  JS^or  have  we  any  right  to 
suppose  that  the  seas  of  the  world  have  always  been  so 
freely  open  from  north  to  south  as  they  are  at  present. 
Even  at  this  day,  if  the  Malay  Archipelago  were  con- 
verted into  land,  the  tropical  parts  of  the  Indian  Ocean 
would  form  a  large  and  perfectly  enclosed  basin,  in  which 
any  great  group  of  marine  animals  might  be  multij)lied  ; 
and  here  they  would  remain  confined,  until  some  of  the 
species  became  adapted  to  a  cooler  climate,  and  were  en- 
abled to  double  the  southern  capes  of  Africa  or  Australia, 
and  thus  reach  other  and  distant  seas. 

From  these  and  similar  considerations,  but  chiefly 
from  our  ignorance  of  the  geology  of  other  countries  be- 
yond the  confines  of  Europe  and  the  United  States ;  and 
from  the  revolution  in  our  palseontological  ideas  on  many 
points,  which  the  discoveries  of  even  the  last  dozen  years 
have  efi'ected,  it  seems  to  me  to  be  about  as  rash  in  us  to 
dogmatize  on  the  succession  of  organic  beings  throughout 
the  world,  as  it  would  be  for  a  naturalist  to  land  for  five 
minutes  on  some  one  barren  point  in  Australia,  and  then 
to  discuss  the  number  and  range  of  its  ^productions. 

On  the  sudden  appearance  of  groujps  of  Allied  Species 
in  the  loioest  known  fossiliferoxis  strata. — ^There  is  another 
and  allied  difficulty,  w^hich  is  much  graver.  I  allude  t£> 
the  manner  in  which  numbers  of  species  of  the  same  group, 
suddenly  appear  in  the  lowest  known  fossiliferous  rocks. 
Most  of  the  arguments  which  have  convinced  me  that  all 
the  existing  species  of  the  same  group  have  descended 
from  one  progenitor,  apply  with  nearly  equal  force  to  the 
earliest  known  species.  For  instance,  I  cannot  doubt  that 
all  the  Silurian  trilobites  have  descended  from  some  one 
crustacean,  which  must  have  lived  long  before  the  Silu- 


Chap.  IX.]  GEOLOGICAL  RECORD.  269 

rian  age,  and  wMcli  probably  differed  greatly  from  any 
known  animal.  Some  of  tlie  most  ancient  Silurian  ani- 
mals, as  the  Kantilus,  Lingula,  &c.,  do  not  differ  mucb 
from  living  species ;  and  it  cannot  on  my  theory  be  sup- 
posed, that  these  old  species  were  the  progenitors  of  all 
the  species  of  the  orders  to  which  they  belong,  for  they 
do  not  present  characters  in  any  degree  intermediate  be- 
tween them.  If,  moreover,  they  had  been  the  progenitors 
of  these  orders,  they  would  almost  certainly  have  been 
long  ago  supplanted  and  exterminted  by  their  numerous 
and  improved  descendants. 

Consequently,  if  my  theory  be  true,  it  is  indisputable 
that  before  the  lowest  Silui-ian  stratum  was  dej)osited,  long 
periods  elapsed,  as  long  as,  or  probably  far  longer  than, 
the  whole  interval  from  the  Silurian  age  to  the  present 
day  ;  and  that  during  these  vast,  yet  quiie  unknown, 
periods  of  time,  the  world  swarmed  with  living  crea- 
tures. 

To  the  question  why  we  do  not  find  records  of  these 
vast  primordial  periods,  I  can  give  no  satisfactory  answer. 
Several  of  the  most  eminent  geologists,  with  Sir  R.  Mur- 
chison  at  their  head,  are  convinced  that  we  see  in  the  or- 
ganic remains  of  the  lowest  Silurian  stratum  the  dawn  of 
life  on  this  planet.  Other  highly  competent  judges,  as 
Lyell  and  the  late  E.  Forbes,  dispute  this  conclusion.  We 
should  not  forget  that  only  a  small  portion  of  the  world  is 
known  with  accuracy.  M.  Barrande,  has  lately  added 
another  and  lower  stage  to  the  Silurian  system,  aboundinsj 
with  new  and  peculiar  species.  Traces  of  life  have  been 
detected  in  the  Longmynd  beds  beneath  Barrande's  so- 
called  primordial  zone.  The  presence  of  phosphatic  nod- 
ules and  bituminous  matter  in  some  of  the  lowest  azoic 
rocks,  probably  indicates  the  former  existence  of  life  at 
these  periods.  But  the  difficulty  of  understanding  the 
absence  of  vast  piles  of  fossiliferous  strata,  which  on  my 
theory  no  doubt  were  somewhat  accumulated  before  the 
Silurian  epoch,  is  very  great.  If  these  most  ancient  beds 
had  been  wholly  worn  away  by  denudation,  or  obliterated 
by  metamorphic  action,  we  ought  to  find  only  small  rem- 
nants of  the  formations  next  succeeding  them  in  age,  and 


270    ■  IMPERFECTION-   OF   THE  [Chap.  IX. 

these  ought  to  be  very  generally  in  a  metoniorphosed  con- 
dition. Bnt  the  descrij^tions  which  we  now  possess  of  the 
Silurian  deposits  over  immense  territories  in  Kussia  and 
in  North  America,  do  not  support  the  view,  that  the  older 
a  formation  is,  the  more  it  has  sufiered  the  extremity  of 
denudation  and  metamorphism. 

The  case  at  present  must  remain  inexplicable ;  and 
may  be  truly  urged  as  a  valid  argument  against  the  views 
here  entertained.  To  show  that  it  may  hereafter  receive 
some  explanation,  I  will  give  the  following  hypothesis. 
From  the  nature  of  the  organic  remains,  which  do  not  ap- 
pear to  have  inhabited  profound  depths,  in  the  several 
formations  of  Europe  and  of  the  United  States  ;  and  from 
the  amount  of  sediment,  miles  in  thickness,  of  w^hich  the 
formations  are  composed,  we  may  infer  that  from  first  to 
last  large  islands  or  tracts  of  land,  whence  the  sediment 
was  derived,  occurred  in  the  neighbourhood  of  the  exist- 
ing continents  of  Europe  and  iNorth  America.  But  we 
do  not  know  what  was  the  state  of  things  in  the  intervals 
between  the  successive  formations  ;  whether  Europe  and 
the  United  States  during  these  intervals  existed  as  dry 
land,  or  as  a  submarine  surface  near  land,  on  which  sedi- 
ment was  not  deposited,  or  again  as  the  bed  of  an  open 
and  unfathomable  sea. 

Looking  to  the  existing  oceans,  which  are  thrice  as 
extensive  as  the  land,  we  see  them  studded  with  many 
islands  ;  but  not  one  oceanic  island  is  as  yet  known  to 
afford  even  a  remnant  of  any  palaeozoic  or  secondary  for- 
mation. Hence  we  may  perhaps  infer,  that  during  the 
palaeozoic  and  secondary  periods,  neither  continents  nor 
continental  islands  existed  where  our  oceans  now  extend  ; 
for  had  they  existed  there,  palaeozoic  and  secondary  forma- 
tions would  in  all  probability  have  been  accumulated  from 
sediment  derived  from  their  wear  and  tear ;  and  would  have 
been  at  least  partially  uj)heaved  by  the  oscillations  of  level, 
which  we  may  fairly  conclude  must  have  intervened  dur- 
ing these  enormously  long  periods.  If  then  we  may  infer 
anything  from  these  facts,  Ave  may  infer  that  where  our 
oceans  now  extend,  oceans  have  extended  from  the  remot 
est  period  of  wliich  we  have  any  record  ;  and  on  the  other 


Chap.  IX.]  GEOLOGICAL   RECORD.  .         271 

hand,  that  where  continents  now  exist,  large  tracts  of  land 
have  existed,  subjected  no  doubt  to  great  oscillations  of 
level,  since  the  earliest  silurian  period.  The  coloured 
map  appended  to  my  volume  on  Coral  Keefs,  led  me  to 
conclude  that  the  great  oceans  are  still  mainly  areas  of 
subsidence,  the  great  archipelagoes  still  areas  of  oscilla- 
tions of  level,  and  the  continents  areas  of  elevation.  But 
have  we  any  right  to  assume  that  things  have  thus  re- 
mained from  eternity?  Our  continents  seem  to  have  been 
formed  by  a  preponderance,  during  many  oscillations  of 
level,  of  the  force  of  elevation  ;  but  may  not  the  areas  of 
preponderant  movement  have  changed  in  the  lapse  of 
ages  ?  At  a  period  immeasurably  antecedent  to  the  silu- 
rian epoch,  continents  may  have  existed  where  oceans  are 
now  spread  out ;  and  clear  and  open  oceans  may  have  ex- 
isted where  our  continents  now  stand.  JSTor  should  we  be 
justified  in  assuming  that  if,  for  instance,  the  bed  of  the 
Pacific  Ocean  were  now  converted  into  a  continent,  we 
should  there  find  formations  older  than  the  silurian  strata, 
supposing  such  to  have  been  formerly  deposited  ;  for  it 
might  well  happen  that  strata  which  had  subsided  some 
miles  nearer  to  the  centre  of  the  earth,  and  which  had 
been  pressed  on  by  an  enormous  weight  of  superincum- 
bent water,  might  have  undergone  far  more  metamorphic 
action  than  strata  which  have  always  remained  nearer  to 
the  surface.  The  immense  areas  in  some  parts  of  the 
world,  for  instance  in  South  America,  of  bare  metamor- 
phic rocks,  which  must  have  been  heated  under  great 
pressure,  have  always  seemed  to  me  to  require  some 
special  explanation  ;  and  we  may  perhaps  believe  that  we 
see  in  these  large  areas,  the  many  formations  long  anterior 
to  the  silurian  epoch  in  a  completely  metamorphosed  con- 
dition. 

The  several  difficulties  here  discussed,  namely  our  not 
finding  in  the  successive  formations  infinitely  numerous 
transitional  links  between  the  many  species  which  now 
exist  or  have  existed  ;  the  sudden  manner  in  which  whole 
groups  appear  in  our  European  formations  ;  the  almost 
entire  absence,  as  at  present  known,  of  fossiliferous  for- 


272  IMPERFECTIO^r    OF    GEOLOGICAL    llECORD.        [Chap.  IX, 

mations  beneath  the  Silurian  strata,  are  all  undoubtedly 
of  the  gravest  nature.  We  see  this  in  the  plainest  manner 
bj  the  fact  that  all  the  most  eminent  palaeontologists, 
namely  Cuvier,  Owen,  Agassiz,  Barrande,  Falconer,  E. 
Forbes,  &c.,  and  all  our  greatest  geologists,  as  Ljell,  Mur- 
chison,  Sedgwick,  &c., have  unanimously,  often  vehemently, 
maintained  the  immutability  of  species.  But  I  have  rea- 
son to  believe  that  one  great  authority,  Sir  Charles  Lyell, 
from  further  reflexion  entertains  grave  doubts  on  this 
subject.  I  feel  how  rash  it  is  to  difler  from  these  great 
authorities,  to  whom,  with  others,  we  owe  all  our  knowl- 
edge. Those  who  think  the  natural  geological  record  in 
any  degree  perfect,  and  who  do  not  attach  much  weight 
to  the  facts  and  arguments  of  other  kinds  given  in  this 
volume,  will  undoubtedly  at  once  reject  my  theory.  For 
my  part,  following  out  Lyell's  metaphor,  I  look  at  the 
natural  geological  record,  as  a  history  of  the  world  imper- 
fectly kept,  and  written  in  a  changing  dialect ;  of  this 
history  we  j)ossess  the  last  volume  alone,  relating  only  to 
two  or  three  countries.  Of  this  volume,  only  here  and 
there  a  short  chapter  has  been  preserved  ;  and  of  each 
page,  only  here  and  there  a  few  lines.  Each  word  of  the 
slowly  changing  language,  in  which  the  history  is  supposed 
to  be  written,  being  more  or  less  diflerent  in  the  inter- 
rujDted  succession  of  chapters,  may  represent  the  appar- 
ently abruptly  changed  forms  of  life,  entombed  in  our 
consecutive,  but  widely  sej^arated,  formations.  On  this 
view,  the  difficulties  above  discussed  are  greatly  diminish- 
ed, or  even  disappear. 


Ohap.  X.]  GEOLOGICAL   SUCCESSION.  273 


CHAPTER    X. 

ON    THE    GEOLOGICAL    SUCCESSION    OF  ORGANIC    BEINGS. 

On  the  slow  and  successive  appearance  of  new  species— On  their  different  rates  of 
change— Species  once  lost  do  not  reappear— Groups  of  species  follow  the  same  gen- 
eral  rules  in  their  appearance  and  disappearance  as  do  single  species— On  Extinc- 
tion—On simultaneous  changes  in  the  forms  of  life  throughout  the  world— On  the 
affinities  of  extinct  species  to  each  other  and  to  living  species— On  the  state  of  de- 
velopment of  ancient  forms— On  the  succession  of  the  same  types  within  the  same 
areas— Summary  of  preceding  and  present  chapters. 

Let  us  now  see  whether  the  several  facts  and  rules  re- 
lating to  the  geological  succession  of  organic  beings,  better 
accord  with  the  common  view  of  the  immutability  of  spe- 
cies, or  with  that  of  their  slow  and  gradual  modification, 
through  descent  and  natural  selection. 

'New  species  have  appeared  very  slowly,  one  after  an- 
other, both  on  the  land  and  in  the  waters.  Lyell  has 
shown  that  it  is  hardly  possible  to  resist  the  evidence  on 
this  head  in  the  case  of  the  several  tertiary  stages ;  and 
every  year  tends  to  fill  up  the  blanks  between  them,  and 
to  make  the  percentage  system  of  lost  and  new  forms  more 
gradual.  Li  some  of  the  most  recent  beds,  though  un- 
doubtedly of  high  antiquity  if  measured  by  years,  only  one 
or  two  species  are  lost  forms,  and  only  one  or  two  are  new 
forms,  having  here  appeared  for  the  first  time,  either  lo- 
3ally,  or,  as  far  as  we  know,  on  the  face  of  the  earth.  If 
we  may  trust  the  observations  of  Philippi  in  Sicily,  the 
successive  changes  in  the  marine  inhabitants  of  that  island 
liavG  been  many  and  most  gradual.  The  secondary  for- 
mations are  more  broken ;  but,  as  Bronn  has  remarked, 
neither  the  appearance  nor  disappearance  of  their  many 
now  extinct  species  has  been  simultaneous  in  each  sepa- 
rate formation. 


274:  GEOLOGICAL    SUCCESSION  [Chap.  X. 

Species  of  different  genera  and  classes  have  not 
changed  at  the  same  rate,  or  in  the  same  degree.  In  the 
oldest  tertiary  beds  a  few  living  shells  may  snll  be  found 
in  the  midst  of  a  multitude  of  extinct  forms.  Falconer 
has  given  a  striking  instance  of  a  similar  fact,  in  an  ex- 
isting crocodile  associated  with  many  strange  and  lost 
mammals  and  reptiles  in  the  sub-Himalayan  dejDosits. 
The  Silurian  Lingula  differs  but  little  from  the  living  spe- 
cies of  this  genus  ;  whereas  most  of  the  other  Silurian 
Molluscs  and  all  the  Crustaceans  have  changed  greatly. 
The  productions  of  the  land  seem  to  change  at  a  quicker 
rate  than  those  of  the  sea,  of  which  a  striking  instance  has 
lately  been  observed  in  Switzerland.  There  is  some 
reason  to  believe  that  organisms,  considered  high  in  the 
scale  of  nature,  change  more  quickly  than  those  that  are 
low :  though  there  are  exceptions  to  this  rule.  The 
amount  of  organic  change,  as  Pictet  has  remarked,  does 
not  strictly  correspond  with  the  succession  of  our  geologi- 
cal formations;  so  that  between  each  two  consecutive 
formations,  the  forms  of  life  have  seldom  changed  in  ex- 
actly the  same  degree.  Yet  if  we  compare  any  but  the 
most  closely  related  formations,  all  the  species  will  be 
found  to  have  imdergone  some  change.  When  a  species 
has  once  disapj)eared  from  the  face  of  the  earth,  we  have 
reason  to  believe  that  the  same  identical  form  never  re- 
a23pears.  The  strongest  apparent  exception  to  this  latter 
rule,  is  that  of  the  so-called  "  colonies  "  of  M.  Barrande, 
which  intrude  for  a  period  in  the  midst  of  an  older  forma- 
tion, and  then  allow  the  pre-existing  fauna  to  reappear ; 
but  Ly ell's  explanation,  namely,  that  it  is  a  case  of  tem- 
porary migration  from  a  distinct  geographical  province, 
seems  to  me  satisfactory. 

These  several  facts  accord  well  with  my  theory.  I  be- 
lieve in  no  fixed  law  of  development,  causing  all  the  in- 
habitants of  a  country  to  change  abruptly,  or  simulta- 
neously, or  to  an  equal  degree.  Tlie  process  of  modifica- 
tion must  be  extremely  slow.  The  variability  of  each 
species  is  quite  independent  of  that  of  all  others. 
Whether  such  variability  be  taken  advantage  of  by  nat- 
ural selection,  and  whether  the  variations  be  accumulated 


Chap.  X.]  GEOLOGICAL   SUCCESSIOlSr.  275 

to  a  greater  or  lesser  amount,  thus  causing  a  greater  or 
lesser  amount  of  modification  in  the  varying  species,  de- 
pends on  many  complex  contingencies, — on  the  variability 
Leing  of  a  beneficial  nature,  on  the  power  of  intercrossing, 
on  the  rate  of  breeding,  on  the  slowly  changing  physical 
conditions  of  the  country,  and  more  especially  on  the 
nature  of  the  other  inhabitants  with  which  the  varying 
species  come  into  competition.  Hence  it  is  by  no  means 
surprising  that  one  species  should  retain  the  same  identi- 
cal form  much  longer  than  others  ;  or,  if  changing,  that  it 
should  change  less.  We  see  the  same  fact  in  geographical 
distribution;  for  instance,  in  the  land-shells  and  coleop- 
terous insects  of  Madeira  having  come  to  difier  consider- 
ably from  their  nearest  allies  on  the  continent  of  Europe, 
whereas  the  marine  shells  and  birds  have  remained  un- 
altered. We  can  perhaps  understand  the  apparently 
quicker  rate  of  change  in  terrestrial  and  in  more  highly 
organised  productions  compared  with  marine  and  lower 
productions,  by  the  more  complex  relations  of  the  higher 
beings  to  their  organic  and  inorganic  conditions  of  life,  as 
explained  in  a  former  chapter.  When  many  of  the  inhab- 
itants of  a  country  have  become  modified  and  improved, 
we  can  understand,  on  the  principle  of  competition,  and 
on  that  of  the  many  all-important  relations  of  organism 
to  organism,  that  any  form  which  does  not  become  in 
some  degree  modified  and  improved,  will  be  liable  to  be 
exterminated.  Hence  we  can  see  why  all  the  species  in 
the  same  region  do  at  last,  if  we  look  to  wide  enough  in- 
tervals of  time,  become  modified  ;  for  those  which  do  not 
change  will  become  extinct. 

In  members  of  the  same  class  the  average  amount  of 
change,  during  long  and  equal  periods  of  time,  may,  per- 
haps, be  nearly  the  same ;  but  as  the  accumulation  of  long- 
enduring  fossiliferous  formations  depends  on  great  masses 
of  sediment  having  been  deposited  on  areas  whilst  sub- 
siding, our  formations  have  been  almost  necessarily  accu- 
mulated at  wide  and  irregularly  intermittent  intervals ; 
consequently  the  amount  of  organic  change  exhibited  by 
the  fossils  embedded  in  consecutive  formations  is  not 
equal.  Each  formation,  on  this  view,  does  not  mark  a 
13 


276  GEOLOGICAL   SUCCESSION.  [Chap.  X. 

new  and  complete  act  of  creation,  but  only  an  occasional 
scene,  taken  almost  at  hazard,  in  a  slowlj  changing 
drama. 

We  can  clearly  understand  why  a  species  when  once 
lost  should  never  reappear,  even  if  the  very  same  con- 
ditions of  life,  organic  and  inorganic,  should  recur.  For 
though  the  offspring  of  one  species  might  be  adapted 
(and  no  doubt  this  has  occurred  in  innumerable  instances) 
to  fill  the  exact  place  of  another  species  in  the  economy 
of  nature,  and  thus  supplant  it ;  yet  the  two  forms — the 
old  and  the  new — would  not  be  identically  the  same  ;  for 
both  would  almost  certainly  inherit  difi'erent  characters 
from  their  distinct  progenitors.  Eor  instance,  it  is  just 
possible,  if  our  fantail-pigeons  were  all  destroyed,  that 
fanciers,  by  striving  during  long  ages  for  the  same  object, 
might  make  a  new  breed  hardly  distinguishable  from  our 
present  fantail ;  but  if  the  parent  rock-pigeon  were  also 
destroyed,  and  in  nature  we  have  every  reason  to  believe 
that  the  parent-form  will  generally  be  supplanted  and  ex- 
terminated by  its  improved  ofi'spring,  it  is  quite  incredible 
that  a  fantail,  identical  with  the  existing  breed,  could  be 
raised  from  any  other  species  of  pigeon,  or  even  from  the 
other  well-established  races  of  the  domestic  j)igeon,  for 
newly-formed  fantail  would  be  almost  sure  to  inherit 
from  its  new  progenitor  some  slight  characteristic  difi:er- 
ences. 

Grouj)S  of  species,  that  is,  genera  and  families,  follow 
the  same  general  rules  in  their  appearance  and  disappear- 
ance as  do  single  species,  changing  more  or  less  quickly, 
and  in  a  greater  or  lesser  degree.  A  group  does  not  re- 
appear after  it  has  once  disappeared  ;  or  its  existence,  as 
long  as  it  lasts,  is  continuous.  I  am  aware  that  there  are 
some  apparent  exceptions  to  this  rule,  but  the  exceptions 
are  surprisingly  few,  so  few,  that  E.  Forbes,  Pictet,  and 
"Woodward  (though  all  strongly  opposed  to  such  views  as 
I  maintain)  admit  its  truth ;  and  the  rule  strictly  accords 
with  my  theory.  For  as  all  the  species  of  the  same  group 
have  descended  from  some  one  species,  it  is  clear  that  as 
long  as  any  species  of  the  group  have  appeared  in  the  long 
Buccession  of  ages,  so  long  must  its  members  have  contin- 


Chap.  X.]  EXTINCTIONS^.  277 

uonsly  existed,  in  order  to  have  generated  either  new  and 
modified  or  the  same  old  and  unmodified  forms.  Species 
of  the  genus  Lingula,  for  instance,  must  have  continu- 
ously existed  by  an  unbroken  succession  of  generations, 
from  the  lowest  Silurian  stratum  to  the  present  day. 

We  have  seen  in  the  last  chapter  that  the  species  of  a 
group  sometimes  falsely  appear  to  have  come  in  abruptly ; 
and  I  have  attempted  to  give  an  explanation  of  this  fact, 
which  if  true  would  have  been  fatal  to  my  views.  But 
such  cases  are  certainly  exceptional ;  the  general  rule  be- 
ing a  gradual  increase  in  number,  till  the  group  reaches  its 
maximum,  and  then,  sooner  or  later,  it  gradually  de- 
creases. If  the  number  of  the  species  of  a  genus,  or  the 
number  of  the  genera  of  a  family,  be  represented  by  a 
vertical  line  of  varying  thickness,  crossing  the  successive 
geological  formations  in  which  the  species  are  found,  the 
line  will  sometimes  falsely  appear  to  begin  at  its  lower 
end,  not  in  a  sharp  point,  but  abruptly  ;  it  then  gradually 
thickens  upwards,  sometimes  keeping  for  a  space  of  equal 
thickness,  and  ultimately  thins  out  in  the  upper  beds, 
marking  the  decrease  and  final  extinction  of  the  species. 
This  gradual  increase  in  number  of  the  species  of  a  group 
is  strictly  conformable  with  my  theory ;  as  the  species  of 
the  same  genus,  and  the  genera  of  the  same  family,  can 
increase  only  slowly  and  progressively ;  for  the  process  of 
modification  and  the  production  of  a  number  of  allied 
forms  must  be  slow  and  gradual, — one  species  giving  rise 
first  to  two  or  three  varieties,  tliese  being  slowly  con- 
verted into  species,  which  in  their  turn  produce  by 
equally  slow  steps  other  species,  and  so  on,  like  the 
branching  of  a  great  tree  from  a  single  stem,  till  the 
group  becomes  large. 

O71  Extinction. — "We  have  as  yet  spoken  only  inci- 
dentally of  the  disappearance  of  species  and  of  groups 
of  species.  On  the  theory  of  natural  selection  the  extinc- 
tion of  old  forms  and  the  production  of  new  and  improved 
forms  are  intimately  connected  together.  Tlie  old  notion 
of  all  the  inhabitants  of  the  earth  having  been  swept 
away  at  successive  periods  by  catastrophes,  is  very  gene- 


2Y8  GEOLOGICAL   SUCCESSIOIS".  [Chap.  X. 

rally  given  up,  even  by  those  geologists,  as  Elie  de  Beau- 
mont, Murchison,  Barrande,  (fee.,  whose  general  views 
wonld  naturally  lead  them  to  this  conclusion.  On  the 
contrary,  we  have  every  reason  to  believe,  from  the  study 
of  the  tertiary  formations,  that  species  and  groups  of 
species  gradually  disappear,  one  after  another,  first  from 
one  sj)ot,  then  from  another,  and  finally  from  the  world. 
Both  single  species  and  whole  groups  of  species  last  for 
very  unequal  periods  ^  some  groups  as  we  have  seen,  hav- 
ing endured  from  the  earliest  known  dawn  of  life  to  the 
present  day  ;  some  having  disappeared  before  the  close 
of  the  palaeozoic  period,  ffo  fixed  law  seems  to  deteiTaine 
the  length  of  time  during  which  any  single  species  or  any 
single  genus  endures.  There  is  reason  to  believe  that  the 
complete  extinction  of  the  species  of  a  group  is  generally 
a  slower  process  than  their  production :  if  the  appearance 
and  disappearance  of  a  group  of  species  be  represented, 
as  before,  by  a  vertical  line  of  varying  thickness,  the  line 
is  found  to  taper  more  gradually  at  its  upper  end,  which 
marks  the  progress  of  extermination,  than  at  its  lower 
end,  whicli  marks  the  first  appearance  and  increase  in 
numbers  of  the  species.  In  some  cases,  however,  the 
extermination  of  whole  groups  of  beings,  as  of  ammon- 
ites towards  the  close  of  the  secondary  period,  has  been 
wonderfully  sudden. 

The  whole  subject  of  the  extinction  of  species  has 
been  involved  in  the  most  gratuitous  mystery.  Some 
authors  have  even  supposed  that  as  the  individual  has  a 
definite  length  of  life,  so  have  species  a  definite  duration. 
No  one  I  think  can  have  marvelled  more  at  the  extinction 
of  species,  than  I  have  done.  When  I  found  in  La  Plata 
the  tooth  of  a  horse  embedded  with  the  remains  of  Masto- 
don, Megatherium,  Toxodon,  and  other  extinct  monsters, 
which  all  co-existed  with  still  living  shells  at  a  very  late 
geological  period,  I  was  filled  with  astonishment ;  for 
seeing  that  the  horse,  since  its  introduction  by  the  Span- 
iards into  South  America,  has  run  wild  over  the  whole 
country  and  has  increased  in  numbers  at  an  unparalleled 
rate,  I  asked  myself  what  could  so  recently  have  exter- 
minated the  former  horse  under  conditions  of  life  appar- 


Chap.  X.]  EXTINCTION".  279 

ently  so  favourable.  But  liow  utterly  groundless  was  my 
astonishment !  Professor  Owen  soon  ]3erceived  that  the 
tooth,  though  so  like  that  of  the  existing  horse,  belonged 
to  an  extinct  species.  Had  this  horse  be^n  still  living, 
but  in  some  degree  rare,  no  naturalist  would  have  felt  the 
least  surprise  at  its  rarity  ;  for  rarity  is  the  attribute  of  a 
vast  number  of  species  of  all  classes,  in  all  countries.  If 
we  ask  ourselves  why  this  or  that  species  is  rare,  we  answer 
that  something  is  unfavourable  in  its  conditions  of  life ; 
but  what  that  something  is,  we  can  hardly  ever  tell.  On 
the  supposition  of  the  fossil  horse  still  existing  as  a  rare 
species,  we  might  have  felt  certain  from  the  analogy  of  all 
otlier  mammals,  even  of  the  slow-breeding  elephant,  and 
from  the  history  of  the  naturalisation  of  the  domestic 
horse  in  South  America,  that  under  more  favourable  con- 
ditions it  would  in  a  very  few  years  have  stocked  the 
whole  continent.  But  we  could  not  have  told  what  the 
unfavourable  conditions  were  which  checked  its  increase, 
whether  some  one  or  several  contingencies,  and  at  what 
period  of  the  horse's  life,  and  in  what  degree,  they  sever- 
ally acted.  If  the  conditions  had  gone  on,  however  slow- 
ly, becoming  less  and  less  favourable,  we  assuredly  should 
not  have  perceived  the  fact,  yet  the  fossil  horse  would 
certainly  have  become  rarer  and  rarer,  and  finally  ex- 
tinct ; — its  place  being  seized  on  by  some  more  successful 
competitor. 

It  is  most  difficult  always  to  remember  that  the  increase 
of  every  living  being  is  constantly  being  checked  by  unper- 
ceived  injurious  agencies ;  and  that  these  same  unperceived 
agencies  are  amply  sufficient  to  cause  rarity,  and  finally 
extinction.  AVe  see  in  many  cases  in  the  more  recent 
tertiary  formations,  that  rarity  precedes  extinction ;  and 
we  know  that  this  has  been  the  progress  of  events  with 
those  animals  which  have  been  exterminated,  either  locally 
or  wholly,  through  man's  agency.  I  may  repeat  what  I 
published  in  184:5,  namely,  that  to  admit  that  species 
generally  become  rare  before  they  become  extinct — to 
feel  no  surprise  at  the  rarity  of  a  species,  and  yet  to 
marvel  greatly  when  it  ceases  to  exist,  is  much  the  same 
as  to  admit  that  sickness  in  the  individual  is  the  forerunner 


280  GEOLOGICAL   SUCCESSION.  [Chap.  X, 

of  deatli — to  feel  no  surprise  at  sickness,  but  when  ttie  sick 
man  dies,  to  wonder  and  to  snspect  that  he  died  by  some 
unknown  deed  of  violence. 

The  theoiy  of  natural  selection  is  grounded  on  the 
belief  that  each  new  variety,  and  ultimately  each  new 
species,  is  j)roduced  and  maintained  by  having  some  ad- 
vantage over  those  with  which  it  comes  into  competition ; 
and  the  consequent  extinction  of  less-favoured  forms 
almost  inevitably  follows.  It  is  the  same  with  our  do- 
mestic productions  :  when  a  new  and  slightly  improved 
variety  has  been  raised,  it  at  first  suj)plants  the  less  im- 
proved varieties  in  the  same  neighbourhood  ;  when  much 
improved  it  is  transported  far  and  near,  like  our  short- 
horned  cattle,  and  takes  the  place  of  other  breeds  in  other 
countries.  Thus  the  appearance  of  new  forms  and  the 
disappearance  of  old  forms,  both  natural  and  artificial, 
are  bound  together.  In  certain  flourishing  groups,  the 
number  of  new  specific  forms  which  have  been  produced 
within  a  given  time  is  probably  greater  than,  that  of  the 
old  forms  which  have  been  exterminated  ;  but  we  know 
that  the  number  of  species  has  not  gone  on  indefinitely 
increasing,  at  least  during  the  later  geological  periods,  so 
that  looking  to  later  times,  we  may  believe  that  the  pro- 
duction of  new  forms  has  caused  the  extinction  of  about 
the  same  number  of  old  forms. 

The  competition  will  generally  be  most  severe,  as 
formerly  explained  and  illustrated  by  examples,  between 
the  forms  which  are  most  like  each  other  in  all  respects. 
Hence  the  improved  and  modified  descendants  of  a  species 
will  generally  cause  the  extermination  of  the  parent- 
species  ;  and  if  many  new  forms  have  been  developed  from 
any  one  species,  the  nearest  allies  of  that  species,  i.  e.  the 
species  of  the  same  genus,  will  be  the  most  liable  to  ex- 
termination. Thus,  as  I  believe,  a  number  of  new  species 
descended  from  one  species,  that  is  a  new  genus,  comes  to 
supplant  an  old  genus,  belonging  to  the  same  family. 
But  it  must  often  have  haj^pcDcd  that  a  new  species  belong- 
ing to  some  one  group  will  have  seized  on  the  place  occu- 
pied by  a  species  belonging  to  a  distinct  group,  and  thus 
caused  its  extermination ;    and  if  many  allied  forms  be 


Chap.  X.]  EXTINCTION.  281 

developed  from  the  successful  intruder,  many  will  have  to 
yield  their  places  ;  and  it  will  generally  be  allied  forms, 
which  will  sufier  from  some  inherited  inferiority  in  com- 
mon. But  whether  it  be  species  belonging  to  the  same  or 
to  a  distinct  class,  which  yield  their  places  to  other  species 
which  have  been  modified  and  improved,  a  few  of  the 
sufl'erers  may  often  long  be  preserved,  from  being  fitted  to 
some  peculiar  line  of  life,  or  from  inhabiting  some  distant 
and  isolated  station,  where  they  have  escaped  severe  com- 
petition. For  instance,  a  single  species  of  Trigonia,  a 
great  genus  of  shells  in  the  secondary  formations,  survives 
in  the  Australian  seas ;  and  a  few  members  of  the  great 
and  almost  extinct  group  of  Ganoid  fishes  still  inhabit  our 
fresh  waters.  Therefore  the  utter  extinction  of  a  group 
is  generally,  as  we  have  seen,  a  slower  process  than  its 
production. 

With  respect  to  the  apparently  sudden  extermination 
of  whole  families  or  orders,  as  of  Trilobites  at  the  close 
of  the  palaeozoic  period  and  of  Ammonites  at  the  close  of 
the  secondary  period,  we  must  remember  what  has  been 
already  said  on  the  probable  wide  intervals  of  time  be- 
tween our  consecutive  formations  ;  and  in  these  intervals 
there  may  have  been  much  slow  extermination.  More- 
over, when  by  sudden  immigration  or  by  unusually  rapid 
development,  many  species  of  a  new  group  have  taken 
possession  of  a  new  area,  they  will  have  exterminat-ed  in  a 
correspondingly  rapid  manner  many  of  the  old  inhabit- 
ants ;  and  the  forms  which  thus  yield  their  places  will 
commonly  be  allied,  for  they  will  partake  of  some  inferiority 
in  common. 

Thus,  as  it  seems  to  me,  the  manner  in  which  single 
species  and  whole  groups  of  species  become  extinct, 
accords  well  with  the  theory  of  natural  selection.  We 
need  not  marvel  at  extinction  ;  if  we  must  marvel,  let  it 
be  at  our  presumption  in  imagining  for  a  moment  that  we 
understand  the  many  complex  contingencies,  on  which 
the^  existence  of  each  species  depends.  If  we  forget  for 
an  instant,  that  each  species  tends  to  increase  inordinately, 
and  that  some  check  is  always  in  action,  yet  seldom  per- 
ceived by  us,  the  whole  economy  of  nature  will  be  utterly 


282  GEOLOGICAL   SUCCESSIOlSr,  [Chap.  X. 

obscured.  Whenever  we  can  precisely  say  why  this  spe- 
cies is  more  abundant  in  individuals  than  that  •  why  this 
species  and  not  another  can  be  naturalised  m  a  given 
country  ;  then,  and  not  till  then,  we  may  justly  feel  sur- 
prise why  we  cannot  account  for  the  extinction  of  this  par- 
ticular species  or  group  of  species. 

On  the  Forms  of  Life  changing  almost  simultaneously 
throughout  the  World. — Scarcely  any  palseontological  dis- 
covery is  more  striking  than  the  fact,  that  the  forms  of 
life  change  almost  simultaneously  throughout  the  world. 
Thus  our  European  Chalk  formation  can  be  recognised  in 
many  distant  parts  of  the  world,  under  the  most  different 
climates,  where  not  a  fragment  of  the  mineral  chalk  itself 
can  be  found  ;  namely,  in  l^orth  America,  in  equatorial 
South  America,  in  Tierra  del  Fuego,  at  the  Cape  of  Good 
Hope,  and  in  the  peninsula  of  India.  For  at  these  distant 
poiuts,  the  organic  remains  in  certain  beds  present  an 
unmistakeable  degree  of  resemblance  to  those  of  the 
Chalk;  It  is  not  that  the  same  species  are  met  with  ; 
for  in  some  cases  not  one  species  is  identically  the 
same,  but  they  belong  to  the  same  families,  genera,  and 
sections  of  genera,  and  sometimes  are  similarly  character- 
ised in  such  trifling  points  as  mere  superficial  sculpture. 
Moreover  other  forms,  which  are  not  found  in  the  Chalk 
of  Europe,  but  which  occur  in  the  formations  either  above 
or  below,  are  similarly  absent  at  these  distant  points 
of  the  world.  In  the  several  successive  palaeozoic  forma- 
tions of  Russia,  Western  Europe  and  North  America,  a 
similar  parallelism  in  the  forms  of  life  has  been  observed 
by  several  authors  :  so  it  is,  according  to  Lyell,  with  the 
several  European  and  JSTorth  American  tertiary  deposits. 
Even  if  the  few  fossil  species  which  are  common  to  the 
Old  and  jS^ew  Worlds  be  kept  wholly  out  of  view,  the 
general  parallelism  in  the  successive  forms  of  life,  in  the 
stages  of  the  widely  separated  palaeozoic  and  tertiary 
periods,  would  still  be  manifest,  and  the  several  formations 
could  be  easily  correlated. 

These  observations,  however,  relate  to  the  marine  in- 
habitants of  distant  parts  of  the  world :  we  have  not  suffi- 


Chap.  X.]  THROUGHOUT    THE    WORLD.  283 

cient  data  to  judge  whether  the  productions  of  the  land 
and  of  fresh  water  change  at  distant  points  in  the  same 
parallel  manner.  We  may  donbt  whether  thej  have  thns 
changed  :  if  the  Megatherium,  Mylodon,  Macrauchenia, 
and  Toxodon  had  been  brought  to  Europe  from  La  Plata, 
without  any  information  in  regard  to  their  geological  po- 
sition, no  one  would  have  suspected  that  they  had  coex- 
isted with  still  living  sea-shells  ;  but  as  these  anomalous 
monsters  coexisted  with  the  Mastodon  and  Horse,  it  might 
at  least  have  been  inferred  that  they  had  lived  during  one 
of  the  later  tertiary  stages. 

When  the  marine  forms  of  life  are  spoken  of  as  having 
changed  simultaneously  throughout  the  world,  it  must  not 
be  supposed  that  this  expression  relates  to  the  same  thou- 
sandth or  hundred-thousandth  year,  or  even  that  it  has  a 
very  strict  geological  sense  ;  for  if  all  the  marine  animals 
which  live  at  the  present  day  in  Europe,  and  all  those 
that  lived  in  Europe  during  the  pleistocene  period  (an 
enormously  remote  period  as  measured  by  years,  includ- 
ing the  whole  glacial  epoch),  were  to  be  comj^ared  with 
those  now  living  in  South  America  or  in  Australia,  the 
most  skilful  naturalist  would  hardly  be  able  to  say 
whether  the  existing  or  the  pleistocene  inhabitants  of  Eu- 
rope resembled  most  closely  those  of  the  southern  hemis- 
phere. So.  again,  several  highly  competent  observers 
believe  that  the  existing  productions  of  the  United  States 
are  more  closely  related  to  those  which  lived  in  Europe 
during  certain  later  tertiary  stages,  than  to  those  which 
now  live  here  ;  and  if  this  be  so,  it  is  evident  that  fossil- 
iferous  beds  deposited  at  the  present  day  on  the  shores  of 
ISTorth  America  would  hereafter  be  liable  to  be  classed 
with  somewhat  older  Euro]3ean  beds.  ISTevertheless,  look- 
ing to  a  remotely  future  epoch,  there  can,  I  think,  be  little 
doubt  that  all  the  more  modern  marine  formations,  name- 
ly, the  upper  pliocene,  the  pleistocene  and  strictly  modern 
beds,  of  Europe,  ISTorth  and  South  America,  and  Australia, 
from  containing  fossil  remains  in  some  degree  allied,  and 
from  not  including  those  forms  which  are  only  found  in 
the  older  underlying  deposits,  would  be  correctly  ranked 
as  simultaneous  in  a  geological  sense. 
13-^ 


284  GEOLOaiCAL  SUCCESSION,  [CfiAf.  X 

The  fact  of  the  forms  of  life  changing  simultaneously,  in 
the  above  large  sense,  at  distant  parts  of  the  world,  has 
greatly  struck  those  admirable  observers,  MM.  de  Yerneuil 
and  d'Archiac.  After  referring  to  the  parallelism  of  the 
palaeozoic  forms  of  life  in  various  parts  of  Euroj^e,  they 
add,  "  If  struck  by  this  strange  sequence,  we  turn  our  at- 
tention to  North  America,  and  there  discover  a  series  of 
analogous  phenomena,  it  will  appear  certain  that  all  these 
modifications  of  species,  their  extinction,  and  the  intro- 
duction of  new  ones,  cannot  be  owing  to  mere  changes  in 
marine  currents  or  other  causes  more  or  less  local  and 
temporary,  but  depend  on  general  laws  which  govern  the 
whole  animal  kingdom."  M.  Barrande  has  made  forcible 
remarks  to  precisely  the  same  effect.  It  is,  indeed,  quite 
futile  to  look  to  changes  of  currents,  climate,  or  other 
physical  conditions,  as  the  cause  of  these  great  mutations 
in  the  forms  of  life  throughout  the  world,  under  the  most 
different  climates.  We  must,  as  Barrande  has  remarked, 
look  to  some  special  law.  We  shall  see  this  more  clearly 
when  we  treat  of  the  present  distribution  of  organic  beings, 
and  find  how  slight  is  the  relation  between  the  physical 
conditions  of  various  countries,  and  the  nature  of  their  in- 
habitants. 

This  great  fact  of  the  parallel  succession  of  the  forms 
of  life  throughout  the  world,  is  explicable  on  the  theory 
of  natural  selection.  ISTew  species  are  formed  by  new  va- 
rieties arising,  which  have  some  advantage  over  older 
forms  ;  and  those  forms,  which  are  already  dominant,  or 
have  some  advantage  over  the  other  forms  in  their  own 
country,  would  naturally  oftenest  give  rise  to  new  varieties 
or  incipient  species  ;  for  these  latter  must  be  victorious 
in  a  still  higher  degree  in  order  to  be  preserved  and  to 
survive.  We  have  distinct  evidence  on  this  head,  in  the 
plants  which  are  dominant,  that  is,  which  are  commonest 
in  their  own  homes,  and  aremost  widely  diflused,  having 
produced  the  greatest  number  of  new  varieties.  It  is  also 
natural  that  the  dominant,  varying,  and  far-spreading 
species,  which  already  have  invaded  to  a  certain  exten't 
the  territories  of  other  species,  should  be  those  which 
would  have  the  best  chance  of  spreading  still  further,  and 


Chap.  X.]  THROUGHOUT   THE   WORLD.  285 

of  giving  rise  in  new  countries  to  new  varieties  and  species. 
The  process  of  diffusion  may  often  be  very  slow,  being 
dependent  on  cliniatal  and  geographical  changes,  or  on 
strange  accidents,  but  in  the  long  run  the  dominant 
forms  will  generally  succeed  in  spreading.  The  diffusion 
would,  it  is  probable,  be  lower  with  the  terrestrial  inhab- 
itants of  distinct  continents  than  with  the  marine  inhab- 
itants of  the  continuous  sea.  We  might  therefore  expect 
to  find,  as  we  apparently  do  find,  a  less  strict  degree  of 
parallel  succession  in  the  productions  of  the  land  than 
of  the  sea. 

Dominant  species  spreading  from  any  region  might  en- 
counter still  more  dominant  s]3ecies,  and  then  their  trium- 
phant course,  or  even  their  existence,  would  cease.  We 
know  not  at  all  precisely  what  are  all  the  conditions  most 
favourable  for  the  multiplication  of  new  and  dominant 
species  ;  but  we  can,  I  think,  clearly  see  that  a  number 
of  individuals,  from  giving  a  better  chance  of  the  appear- 
ance of  favourable  variations,  and  that  severe  competition 
with  many  already  existing  forms,  w^ould  be  highly  fa- 
vourable, as  would  be  the  power  of  spreading  into  new 
territories>  A  certain  amount  of  isolation,  recurring  at 
long  intervals  of  time,  would  probably  be  also  favourable 
as  before  explained.  One  quarter  of  the  world  may  have 
been  most  favourable  for  the  production  of  new  and  dom- 
inant species  on  the  land,  and  another  for  these  in  the 
waters  of  the  sea.  If  two  great  regions  had  been  for  a 
long  period  favourably  circumstanced  in  an  equal  degree, 
whenever  their  inhabitants  met,  the  battle  would  be  pro- 
longed and  severe ;  and  some  from  one  birthplace  and 
some  from  the  other  might  be  victorious.  Bat  in  the 
course  of  time,  the  forms  dominant  in  tlie  highest  degree, 
wherever  produced,  would  tend  everywhere  to  prevail. 
As  they  prevailed,  they  would  cause  the  extinction  of 
other  and  inferior  forms  ;  and  as  these  inferior  forms  would 
be  allied  in  groups  by  inheritance,  whole  groups  would 
tend  slowly  to  disappear  ;  though  here  and  there  a  single 
member  might  long  be  enabled  to  survive. 

Thus,  as  it  seems  to  me,  the  parallel,  and,  taken  in  a 
large  sense,  simultaneous,  succession  of  the  same  forms  of 


2§g  GEOLOGICAL   StTCCESSlON",  [Chap.  X. 

life  througlioiit  the  world,  accords  well  witli  the  principle 
of  new  s]jecies  having  been  formed  by  dominant  species 
spreading  widely  and  varying  ;  the  nevv  species  thns  pro- 
duced being  themselves  dominant  owing  to  inheritance, 
and  to  having  already  had  some  advantage  over  their 
parents  or  over  other  species  ;  these  again  spreading,  vary- 
ing, and  producing  new  species.  The  forms  which  are 
beaten  and  which  yield  their  places  to  the  new  and  victo- 
rious forms,  will  generally  be  allied  in  groups,  from  in- 
heriting some  inferiority  in  common ;  and  therefore  as 
new  and  improved  groups  spread  throughout  the  world, 
old  groups  will  disappear  from  the  world  ;  and  the  succes- 
sion of  forms  in  both  ways  will  everywhere  tend  to  cor- 
respond. 

There  is  one  other  remark  connected  with  this  subject 
worth  making.  I  have  given  my  reasons  for  believing 
that  all  our  greater  fossiliferous  formations  were  deposited 
during  periods  of  subsidence ;  and  that  blank  intervals 
of  vast  duration  occurred  during  the  j)eriods  when  the 
bed  of  the  sea  was  either  stationary  or  rising,  and  like- 
wise when  sediment  was  not  thrown  do^vn  quickly  enough 
to  embed  and  preserve  organic  remains.  During  these 
long  and  blank  intervals  I  suppose  that  the  inhabitants 
of  each  region  underwent  a  considerable  amount  of  modi- 
fication and  extinction,  and  that  there  was  much  migration 
from  other  parts  of  the  world.  As  we  have  reason  to  be- 
lieve that  large  areas  are  affected  by  the  same  movement, 
it  is  probable  that  strictly  contemporaneous  formations 
have  often  been  accumulated  over  very  wide  spaces  in  the 
same  quarter  of  the  world  ;  but  we  are  far  from  having 
any  right  to  conclude  that  this  has  invariably  been  the  case, 
and  that  large  areas  have  invariably  been  affected  by  the 
same  movements.  When  two  formations  have  been  de- 
posited in  two  regions  during  nearly,  but  not  exactly  the 
same  period,  we  should  find  in  both,  from  the  causes 
explained  in  the  foregoing  paragraphs,  the  same  general 
succession  in  the  forms  of  life  ;  but  the  species  would  not 
exactly  correspond  ;  for  there  will  have  been  a  little  more 
time  in  the  one  region  than  in  the  other  for  modification, 
extinction,  and  immigration. 


Chap,  X.J  THROUGHOUT  THE  WORLD.  ggj 

I  suspect  that  cases  of  this  nature  have  occurred  in 
Europe.  Mr.  Prestwich,  in  his  admirable  Memoirs  on  the 
eocene  deposits  of  England  and  France,  is  able  to  draw  a 
close  general  parallelism  between  the  successive  stages  in 
the  two  countries  ;  but  when  he  compares  certain  stages 
in  England  with  those  in  France,  although  he  finds  in 
both  a  curious  accordance  in  the  numbers  of  the  species 
belonging  to  the  same  genera,  yet  the  species  themselves 
differ  in  a  manner  very  difficult  to  account  for,  considering 
the  proximity  of  the  two  areas, — unless,  indeed,  it  be 
assumed  that  an  isthmus  separated  two  seas  inhabited  by 
distinct,  but  contemporaneous,  faunas.  Lyell  has  made 
similar  observations  on  some  of  the  later  tertiary  forma- 
tions. Barrande,  also,  shows  that  there  is  a  striking 
general  parallelism  in  the  successive  Silurian  deposits  of 
Bohemia  and  Scandinavia ;  nevertheless  he  finds  a  sur- 
prising amount  of  difference  in  the  species.  If  the  several 
formations  in  these  regions  have  not  been  deposited  during 
the  same  exact  periods, — a  foiTQation  in  one  region  often 
corresponding  with  a  blank  interval  in  the  other, — and  if 
in  both  regions  the  species  have  gone  on  slowly  changing 
during  the  accumulation  of  the  several  formations  and 
during  the  long  intervals  of  time  between  them  ;  in  this 
case,  the  several  formations  in  the  two  regions  could  be 
aiTanged  in  the  same  order,  in  accordance  with  the  general 
succession  of  the  form  of  life,  and  the  order  would  falsely 
appear  to  be  strictly  parallel ;  nevertheless  the  species 
would  not  all  be  the  same  in  the  apparently  corresponding 
stages  in  the  two  regions. 

On  the  Affinities  of  extinct  Species  to  each  othei\  and 
to  living  forms. — Let  us  now  look  to  the  mutual  affinities 
of  extinct  and  living  species.  They  all  fall  into  one  grand 
natural  system  ;  and  this  fact  is  at  once  explained  on  the 
principle  of  descent.  The  more  ancient  any  form  is,  the 
more,  as  a  general  rule,  it  diflers  from  living  forms.  But, 
as  Buckland  long  ago  remarked,  all  fossils  can  be  classed 
either  in  still  existing  groups,  or  between  them.  That  the 
extinct  forms  of  life  help  to  fill  up  the  wide  intervals  be- 
tween existing  genera,  families,  and  orders,  cannot  be  dis- 


2gg  GEOLOGICAL   SUCCESSION.  [Chap.  X. 

puted.  For  if  we  confine  our  attention  either  to  the 
living  or  to  the  extinct  alone,  the  series  is  far  less  perfect 
than  if  we  combine  both  into  one  general  system.  With 
respect  to  the  Yertebrata,  whole  pages  conld  be  filled 
with  striking  illustrations  from  our  great  palaeontologist) 
Owen,  showing  how  extinct  animals  fall  in  between  exist- 
ing groups.  Cuyier  ranked  the  Ruminants  and  Pachy- 
derms, as  the  two  most  distinct  orders  of  mammals  ;  but 
Owen  has  discovered  so  many  fossil  links,  that  he  has  had 
to  alter  the  whole  classification  of  these  two  orders  ;  and 
has  placed  certain  pachyderms  in  the  same  sub-order  with 
ruminants :  for  example,  he  dissolves  by  fine  grada- 
tions the  apparently  wide  difference  between  the  pig  and 
the  camel.  In  regard  to  the  Invertebrata,  Barrande,  and 
a  higher  authority  could  not  be  named,  asserts  that  he  is 
every  day  taught  that  palseozoic  animals,  though  belong- 
ing to  the  same  orders,  families^  or  genera  with  those 
living  at  the  present  day,  were  not  at  this  epoch  limited 
In  such  distinct  groups  as  they  now  are. 

Some,  writers  have  objected  to  any  extract  species  or 
group  of  species  being  considered  as  intermediate  between 
living  species  or  groups.  If  by  this  term  it  is  meant  that 
an  extinct  form  is  directly  intermediate  in  all  its  char- 
acters between  two  living  forms,  the  objection  is  probably 
valid.  But  I  apprehend  that  in  a  perfectly  natural  classi- 
fication many  fossil  species  would  have  to  stand  between 
living  species,  and  some  extinct  genera  between  living 
genera,  even  between  genera  belonging  to  distinct  families. 
The  most  common  case,  especially  with  respect  to  very 
distinct  groups,  such  as  fish  and  reptiles,  seems  to  be,  that 
supposing  them  to  be  distinguished  at  the  present  day 
from  each  other  by  a  dozen  characters,  the  ancient  mem- 
bers of  the  same  two  groups  would  be  distiaguished  by  a 
somewhat  lesser  number  of  characters,  so  that  the  two 
groups,  though  formerly  quite  distinct,  at  that  period 
made  some  small  approach  to  each  other. 

It  is  a  common  belief  that  the  more  ancient  a  form  is. 
by  so  much  the  more  it  tends  to  connect  by  some  of  its 
characters  groups  now  widely  separated  from  each  other* 
This  remark  no  doubt  must  be  restricted  to  those  groups 


Chap.  X.J  AFFINITIES   OF   EXTINCT   SPECIES.  £89 

whicli  have  undergone  much  change  in  the  course  of 
geological  ages  ;  and  it  would  be  difficult  to  prove  the 
truth  of  the  proposition,  for  every  now  and  then  even  a 
living  animal,  as  the  Lepidosiren,  is  discovered  having 
affinities  directed  towards  veiy  distinct  groups.  Yet  if 
we  compare  the  older  Eeptiles  and  Batrachians,  the  older 
Fish,  the  older  Cej)halopods,  and  the  eocene  Mammals, 
with  the  more  recent  members  of  the  same  classes,  we 
must  admit  that  there  is  some  truth  in  the  remark. 

Let  us  see  how  far  these  several  facts  and  inferences 
accord  with  the  theory  of  descent  with  modification.  As 
the  subject  is  somewhat  complex,  I  must  request  the  reader 
to  turn  to  the  diagram  in  the  fourth  chapter.  We  may 
suppose  that  the  numbered  letters  represent  genera,  and 
the  dotted  lines  diverging  from  them  the  species  in  each 
genus.  The  diagram  is  much  too  simple,  too  few  genera 
and  too  few  species  being  given,  but  this  is  unimportant 
for  us.  The  horizontal  lines  may  represent  successive 
geological  formations,  and  all  the  forms  beneath  the  upper- 
most line  may  be  considered  as  extinct.  The  three  exist- 
ing genera,  ^^*,  ^^*,  ^^*,  will  form  a  small  family  ;  J'*,  and 
f^\  a  closely  allied  family  or  sub-family ;  and  6>^*,  6^*,  m^^^ 
a  third  family.  Tliese  three  families,  together  with  the 
many  extinct  genera  on  the  several  lines  of  descent 
diverging  from  the  parent-form  A,  will  form  an  order ; 
for  all  will  have  inherited  something  in  common  from  their 
ancient  and  common  progenitor.  On  the  principle  of  the 
continued  tendency  to  divergence  of  character,  which  was 
formerly  illustrated  by  this  diagram,  the  more  recent  any 
form  is,  the  more  it  will  generally  differ  from  its  ancient 
progenitor.  Hence  we  can  understand  the  rule  that  the 
most  ancient  fossils  differ  most  from  existing  forms.  We 
must  not,  however,  assume  that  divergence  of  character 
is  a  necessary  contingency  ;  it  depends  solely  on  the 
descendants  from  a  species  being  thus  enabled  to  seize  on 
many  and  different  places  in  the  economy  of  nature. 
Therefore  it  is  quite  possible,  as  we  have  seen  in  the  case 
of  some  Silurian  forms,  that  a  sj)ecies  might  go  on  being 
slightly  modified  in  relation  to  its  slightly  altered  condi- 
tions of  life,  and  yet  retain  throughout  a  vast  period  the 


290  GEOLOGICAL   SUCCESSION.  [Ca.ip.  X 

same  general  characteristics.  This  is  represented  in  the 
diagram  by  the  letter  f^\ 

All  the  many  forms,  extinct  and  recent,  descended 
from  A,  make,  as  before  remarked,  one  order ;  and  this 
order,  from  the  continued  effects  of  extinction  and  diver- 
gence of  character,  has  become  divided  into  several  sub- 
families and  families,  some  of  wliich  are  supposed  to  have 
perished  at  different  periods,  and  some  to  have  endured  to 
the  present  day. 

By  looking  at  the  diagram  we  can  see  that  if  many 
of  the  extinct  forms,  supposed  to  be  embedded  in  the 
successive  formations,  were  discovered  at  several  points 
low  down  in  the  series,  the  three  existing  families  on  the 
uppermost  line  would  be  rendered  less  distinct  from  each 
other.  If,  for  instance,  the  genera  «\  d^  a^\  /" ^,  m^,  011% 
r)%\  were  disinterred,  these  three  families  would  be  so 
closely  linked  together  that  they  probably  would  have  to 
be  united  into  one  great  family,  in  nearly  the  same  manner 
as  has  occurred  with  ruminants  and  pachyderms.  Yet  he 
who  objected  to  call  the  extinct  genera,  which  thus  linked 
the  living  genera  of  three  families  together,  intermediate 
in  character,  would  be  justified,  as  they  are  intermediate, 
not  directly,  but  only  by  a  long  and  circuitous  course 
through  many  widely  different  Ibrms.  If  many  extinct 
forms  were  to  be  discovered  above  one  of  the  middle 
horizontal  lines  or  geological  formations — for  instance, 
above  !No.  YI. — but  none  from  beneath  this  line,  then 
only  the  two  families  on  the  left  hand  (namely,  a^\  etc., 
and  &^\  (fee.)  would  have  to  be  united  into  one  family  ; 
and  the  two  other  families  (namely,  a^^  ^of^*  now  includ- 
ing five  genera,  and  0'*  to  iii"^)  would  yet  remain  distinct. 
These  two  families,  however,  would  be  less  distinct  from 
each  other  than  they  were  before  the  discovery  of  the 
fossils.  If,  for  instance,  we  suppose  the  existing  genera 
of  the  two  families  to  differ  from  each  other  by  a  dozen 
characters,  in  this  case  the  genera,  at  the  early  period 
marked  YL,  would  differ  by  a  lesser  number  of  characters ; 
for  at  this  early  stage  of  descent  they  have  not  diverged 
in  character  from  tlie  common  progenitor  of  the  order, 
nearly  bo  much  as  they  subsequently  diverged.     Tluis  it 


Chap.  X.]  AFFINITIES    OF   EXTIN"CT    SPECIES.  29j^ 

comes  that  ancient  and  extinct  genera  are  often  in  some 
sliglit  degree  intermediate  in  character  between  their 
modified  descendants,  or  between  their  collateral  relations. 

In  nature  the  case  will  be  far  more  complicated  than 
is  represented  in  the  diagram ;  for  the  groups  'svill  have 
been  more  numerous,  they  will  have  endured  for  extremely 
unequal  lengths  of  time,  and  will  have  been  modified  in 
various  degrees.  As  we  possess  only  the  last  volume  of 
the  geological  record,  and  that  in  a  very  broken  condition, 
we  have  no  right  to  expect,  except  in  very  rare  cases,  to 
fill  up  wide  intervals  in  the  natural  system,  and  thus  unite 
distinct  families  or  orders.  All  that  we  have  a  right  to 
expect,  is  that  those  groups,  which  have  within  known 
geological  periods  undergone  much  modification,  should  in 
the  older  formations  make  some  slight  approach  to  each 
other ;  so  that  the  older  members  should  diflfer  less  from 
each  other  in  some  of  their  characters  than  do  the  existing 
members  of  the  same  groups  ;  and  this  by  the  concurrent 
evidence  of  our  best  palseontologists  seems  frequently  to 
be  the  case. 

Thus,  on  the  theory  of  descent  with  modification,  the 
main  facts  with  respect  to  the  mutual  affinities  of  the 
extinct  forms  of  life  to  each  other  and  to  living  forms, 
seem  to  me  explained  in  a  satisfactory  manner.  And  they 
are  wholly  inexplicable  on  any  other  view. 

On  this  same  theory,  it  is  evident  that  the  fauna  of  any 
great  period  in  the  earth's  history  will  be  intermediate 
in  general  character  between  that  which  preceded  and  that 
which  succeeded  it.  Thus,  the  species  which  lived  at  the 
sixth  great  stage  of  descent  in  the  diagram  are  the  modi- 
fied offspring  of  those  which  lived  at  the  fifth  stage,  and 
are  the  parents  of  those  which  became  still  more  modi- 
fied at  the  seventh  stage  ;  hence  they  could  hardly  fail 
to  be  nearly  intermediate  in  character  between  the  forms 
of  life  above  and  below.  We  must,  however,  allow  for 
the  entire  extinction  of  some  preceding  forms,  and  for  the 
coming  in  of  quite  new  forms  by  immigration,  and  for  a 
large  amount  of  modification,  during  the  long  and  blank 
intervals  between  the  successive  formations.  Subject  to 
these  allowances,  the  fauna  of  each  geological  period  un- 


292  GEOLOGICAL    BUCCESSION.  [Chap.  X. 

doubtedly  is  intermediate  in  cliaracter,  between  the  pre- 
ceding and  succeeding  faunas.  I  need  give  only  one 
instance,  namely,  the  manner  in  wliicli  the  fossils  of  the 
Devonian  system,  when  this  system  was  first  discovered, 
were  at  once  recognised  by  paleontologists  as  intermediate 
in  character  between  those  of  the  overlying  carboniferous, 
and  underlying  Silurian  system.  But  each  fauna  is  not 
necessarily  exactly  intermediate,  as  unequal  intervals  of 
time  have  elapsed  between  consecutive  formations. 

It  is  no  real  objection  to  the  truth  of  the  statement,  that 
the  fauna  of  each  period  as  a  whole  is  nearly  intermediate 
in  character  between  the  preceding  and  succeeding  faunas, 
that  certain  genera  ofter  exceptions  to  the  rule.  For  in- 
stance, mastodons  and  elephants,  when  arranged  by  Dr. 
Falconer  in  two  series,  first  according  to  their  mutual  afii- 
nities  and  then  according  to  their  periods  of  existence,  do 
not  accord  in  arrangement.  The  species  extreme  in  char- 
acter are  not  the"  oldest,  or  the  most  recent ;  nor  are  those 
which  are  intermediate  in  character,  intermdiate  in  age. 
But  supposing  for  an  instant,  in  this  and  other  such  cases, 
that  the  record  of  the  first  appearance  and  disappearance 
of  the  species  was  perfect,  we  have  no  reason  to  believe 
that  forms  succssively  produced  necessarily  endure  for 
corresponding  lengths  of  time ;  a  very  ancient  form  might 
occasionally  last  much  longer  than  a  form  elsewhere  sub- 
sequently produced,  especially  in  the  case  of  terrestrial 
productions  inhabiting  separated  districts.  To  compare 
small  things  with  great :  if  the  principal  living  and  extinct 
races  of  the  domestic  pigeon  were  arranged  as  well  as  they 
could  be  in  serial  affinity,  this  arrangement  would  not 
closely  accord  with  the  order  in  time  ot  their  production, 
and  still  less  with  the  order  of  their  disappearance ;  for  the 
parent  rock-pigeon  now  lives ;  and  many  varieties  be- 
tween the  rock-pigeon  and  the  carrier  have  become  ex- 
tinct ;  and  carriers  which  are  extreme  in  the  important 
character  of  length  of  beak  have  originated  earlier  than 
short-beaked  tumblers,  which  are  at  the  opjDOsite  end  of 
the  series  in  this  same  respect. 

Closely  connected  with  the  statement,  that  the  organic 
remains  from  an  intermediate  formation  are  in  some  de- 


Chap.  X.]  AFFINITIES   OF   EXTINCT   SPECIES.  293 

gree  intermediate  in  character,  is  the  fact,  insisted  on  by 
all  palaeontologists,  that  fossils  from  two  consecutive  for- 
mations are  far  more  closely  related  to  each  other,  than 
are  the  fossils  from  two  remote  formations.     Pictet  gives 
as  a  well-known  instance,  the  general  resemblance  of  the 
organic  remains  from  the  several  stages  of  the  chalk  for- 
mation, thongh  the   species  are  distinct  in  each  stage. 
Tliis  fact  alone,  from  its  generality,  seems  to  have  shaken 
Professor  Pictet  in  his  firm  belief  in  the  immutability  of 
species.     He  who  is  acquainted  with  the  distribution  of 
existing  species  over  the  globe,  will  not  attempt  to  ac- 
count for  the  close  resemblance  of  the  distinct  species  in 
closely  consecutive  formations,  by  the  physical  conditions 
of  the  ancient  areas  having  remained  nearly  the  same. 
Let  it  be  remembered  that  the  forms  of  life,  at  least  those 
inhabiting  the  sea,  have  changed  almost  simultaneously 
throughout  the  world,  and  therefore  under  the  most  diflfer- 
ent  climates  and  conditions.     Consider  the  prodigious  vi- 
cissitudes of  climate  during  the  pleistocene  period,  which  in- 
cludes the  whole  glacial  period,  and  note  how  little  the  spe- 
cific forms  of  the  inhabitants  of  the  sea  have  been  affected. 
On  the  theory  of  descent,  the  full  meaning  of  the  fact 
of  fossil   remains   from    closely   consecutive   formations, 
though  ranked  as  distinct  species,  being  closely  related,  is 
obvious.     As  the  accumulation  of  each  formation  has  often 
been  interrupted,  and  as  long  blank  intervals  have  inter- 
vened between  successive  formations,  we  ought  not  to  ex- 
pect to  find,  as  I  attempted  to  show  in  the  last  chapter,  in 
any  one  or  two  formations,  all  the  intermediate  varieties 
between  the  species  which  appeared  at  the  commence- 
ment and  close  of  these  periods ;  but  we  ought  to  find 
after  intervals,  very  long  as  measured  by  years,  but  only 
moderately  long  as  measured  geologically,  closely  allied 
forms,  or,  as  they  have  been  called  by  some  authors,  repre- 
sentative species ;  and  these  we  assuredly  do  find.     We 
find,  in  short,  such  evidence  of  the  slow  and  scarcely  sen- 
sible mutation  of  specific  forms,  as  we  have  a  just  right  to 
expect  to  find. 

0)1  the  state  of  Development  of  Ancient  Forms. — 
There  has  been  much  discussion  whether  recent  forms  are 


294  GEOLOGICAt  SUCCESSION-.  [Chap.  X 

more  highly  developed  than  ancient.  I  will  not  here  en- 
ter on  this  subject,  for  naturalists  have  not  as  yet  defined 
to  each  other's  satisfaction  what  is  meant  by  high  and  low 
forms.  The  best  definition  probably  is,  that  the  higher 
forms  have  their  organs  more  distinctly  specialised  for 
different  functions  ;  and  as  such  division  of  physiological 
labour  seems  to  be  an  advantage  to  each  being,  natural 
selection  will  constantly  tend  in  so  far  to  make  the  later 
and  more  modified  forms  higher  than  their  early  progeni- 
tors, or  than  the  slightly  modified  descendants  of  such  pro- 
genitors. In  a  more  general  sense  the  more  recent  forms 
must,  on  my  theory,  be  higher  than  the  more  ancient ;  for 
each  new  species  is  formed  by  having  had  some  advan- 
tage in  the  struggle  for  life  over  other  and  preceding  forms. 
If  under  a  nearly  similar  climate,  the  eocene  inhabitants 
of  one  quarter  of  the  world  were  put  into  competition 
with  the  existing  inhabitants  of  the  same  or  some  other 
quarter,  the  eocene  fauna  or  flora  would  certainly  be  beaten 
and  exterminated ;  as  would  a  secondary  fauna  by  an 
eocene,  and  a  palaeozoic  fauna  by  a  secondary  fauna.  I 
do  not  doubt  that  this  process  of  improvement  has  afifect- 
ed  in  a  marked  and  sensible  manner  the  organisation  of 
the  more  recent  and  victorious  forms  of  life,  in  compari- 
son with  the  ancient  and  beaten  forms  ;  but  I  can  see  no 
way  of  testing  this  sort  of  progress.  Crustaceans,  for  in- 
stance, not  the  highest  in  their  own  class,  may  have  beaten 
the  highest  molluscs.  From  the  extraordinary  manner  in 
which  European  productions  have  recently  spread  over 
ISTew  Zealand,  and  have  seized  on  places  which  must  have 
been  previously  occupied,  we  may  believe,  if  all  the  ani- 
mals and  plants  of  Great  Britain  were  set  free  in  I^ew 
Zealand,  that  in  the  course  of  time  a  multitude  of  British 
forms  would  become  thoroughly  naturalized  there,  and 
would  exterminate  many  of  the  natives.  On  the  other 
hand,  from  what  we  see  now  occurring  in  Is'ew  Zealand, 
and  from  hardly  a  single  inhabitant  of  the  southern  hem- 
isphere having  l)ccome  wild  in  any  part  of  Europe,  we 
may  doubt,  if  all  the  productions  of  jN^ew  Zealand  were  set 
free  in  Great  Britain,  whether  any  considerable  number 
would  be  enabled  to  seize  on  places  now  occupied  by  our 


Chap.  X.]  STATE    OF   DEVELOPMEIsT.  295 

native  plants  and  animals.  Under  this  point  of  view,  tlie 
productions  of  Great  Britain  may  be  said  to  be  higher 
than  those  of  Zealand.  Yet  the  most  skilful  naturalist 
from  an  examination  of  the  species  of  the  two  countries 
could  not  have  foreseen  this  result. 

Agassiz  insists  that  ancient  animals  resemble  to  a  cer- 
tain extent  the  embryos  of  recent  animals  of  the  same 
classes  ;  or  that  the  geological  succession  of  extinct  forms 
is  in  some  degree  parallel  to  the  embryo-logical  develop- 
ment of  recent  forms.  I  must  follow  Pictet  and  Huxley 
in  thinking  that  the  truth  of  this  doctrine  is  very  far  from 
proved.  Yet  I  fully  expect  to  see  it  hereafter  confirmed, 
at  least  in  regard  to  subordinate  groups,  which  have 
branched  off  from  each  other  within  comparatively  recent 
times.  For  this  doctrine  of  Agassiz  accords  well  with  the 
theory  of  natural  selection.  In  a  future  chapter  I  shall 
attempt  to  show  that  the  adult  differs  from  its  embryo, 
owing  to  variations  supervening  at  a  not  early  age,  and 
being  inherited  at  a  corresponding  age.  This  process, 
whilst  it  leaves  the  embryo  almost  unaltered,  continually 
adds,  in  the  course  of  successive  generations,  more  and 
more  difference  to  the  adult. 

Thus  the  embryo  comes  to  be  left  as  a  sort  of  picture, 
preserved  by  nature,  of  the  ancient  and  less  modified  con- 
dition of  each  animal.  This  view  may  be  true,  and  yet 
it  may  never  be  capable  of  full  proof.  Seeing,  for  in- 
stance, that  the  oldest  known  mammals,  reptiles,  and  fish 
strictly  belong  to  their  own  proper  classes,  though  some 
of  these  old  forms  are  in  a  slight  degree  less  distinct  from 
each  other  than  are  the  typical  members  of  the  same 
groups  at  the  present  day,  it  would  be  vain  to  look  for 
animals  having  the  common  embryological  character  of 
the  Yertebrata,  until  beds  far  beneath  the  lowest  Silurian 
strata  are  discovered — a  discovery  of  which  the  chance  is 

verv  small. 

»/ 

On  the  Succession  of  the  same  Types  within  the  same 
areas,  cluring  the  later  tertiary  periods . — Mr.  Clift  many 
years  ago  showed  that  the  fossil  mammals  from  the  Aus- 
tralian caves  were  closely  allied  to  the  living  marsupials 


29g  GEOLOGICAL   SUCCESSION-.  [Chap.  X 

of  that  continent.  In  Sontli  America,  a  similar  relation- 
ship is  manifest,  even  to  an  uneducated  eye,  in  the  gi- 
gantic pieces  of  armour  like  those  of  the  armadillo,  found 
in  several  parts  of  La  Plata ;  and  Professor  Owen  has 
shown  in  the  most  striking  manner  that  most  of  the  fossil 
mammals,  buried  there  in  such  numbers,  are  related  to 
South  American  types.  This  relationship  is  even  more 
clearly  seen  in  the  wonderful  collection  of  fossil  bones 
made  by  MM.  Lund  and  Clausen  in  the  caves  of  Brazil. 
I  was  so  much  impressed  with  these  facts  that  I  strongly 
insisted,  in  1839  and  1845,  on  this  "  law  of  the  succession 
of  types," — on  "  this  wonderful  relationship)  in  the  same 
continent  between  the  dead  and  the  living."  Professor 
Owen  has  subsequently  extended  the  same  generalisation 
to  the  mammals  of  the  Old  World.  We  see  the  same  law 
in  this  author's  restoration  of  the  extinct  and  gigantic  l)ird3 
of  'New  Zealand.  We  see  it  also  in  the  birds  of  the  caves 
of  Brazil.  Mr.  Woodward  has  shown  that  the  same  law 
holds  good  with  sea-shells,  but  from  the  wide  distribution 
of  most  genera  of  molluscs,  it  is  not  well  displayed  by 
them.  Other  cases  could  be  added,  as  the  relation  be- 
tween the  extinct  and  living  land-shells  of  Madeira  ;  and 
between  the  extinct  and  living  brackish-water  shells  of 
the  Aralo-Caspian  sea. 

Now  what  does  this  remarkable  law  of  the  succession 
of  the  same  types  within  the  same  areas  mean?  He 
would  be  a  bold  man,  who  after  comparing  the  present 
climate  of  Australia  and  of  parts  of  South  America  under 
the  same  latitude,  would  attempt  to  account,  on  the  one 
hand,  by  dissimilar  physical  conditions  for  the  dissimilari- 
ty of  the  inhabitants  of  these  two  continents,  and,  on  the 
other  hand,  by  similarity  of  conditions,  for  the  uniformity 
of  the  same  types  in  each  during  the  later  tertiary  periods. 
Nov  can  it  be  pretended  that  it  is  an  immutable  law  that 
marsupials  should  have  been  chiefly  or  solely  produced  in 
Australia ;  or  that  Edentata  and  other  American  types 
should  have  been  solely  produced  in  Somth  America. 
For  we  know  that  Euro]3e  in  ancient  times  was  peopled  by 
numerous  marsupials ;  and  I  liave  shown  in  the  publica- 
tions above  alluded  to,  that  in  America  the  law  of  distri- 


Chap.  X.J  SAME   TYPES   IN    SAME    AREAS.  297 

bution  of  terrestrial  mammals  was  formerly  different  from 
what  it  now  is.  l^orth.  America  formerly  partook  strong- 
ly of  the  present  character  of  the  southern  half  of  the  con- 
tinent ;  and  the  southern  half  was  formerly  more  closely 
allied,  than  it  is  at  present,  to  the  northern  half.  In  a 
similar  manner  we  know  from  Falconer  and  Cantley's  dis- 
coveries, that  northern  India  was  formerly  more  closely 
related  in  its  mammals  to  Africa  than  it  is  at  the  present 
time.  Analogous  facts  could  be  given  in  relation  to  the 
distribution  of  marine  animals. 

On  the  theory  of  descent  with  modiJElcation,  the  great 
law  of  the  long  enduring,  but  not  immutable,  succession  of 
the  same  types  within  the  same  areas,  is  at  once  explained ; 
for  the  inhabitants  of  each  quarter  of  the  world  will  ob- 
viously tend  to  leave  in  that  quarter,  during  the  next  suc- 
ceeding period  of  time,  closely  allied  though  in  some  de- 
gree modiiied  descendants.  If  the  inhabitants  of  one  con- 
tinent formerly  differed  greatly  from  those  of  another  con- 
tinent, so  will  their  modified  descendants  still  differ  in 
nearly  the  same  manner  and  degree.  But  after  very  long 
intervals  of  time  and  after  great  geographical  changes, 
permitting  much  inter-migration,  the  feebler  will  yield  to 
the  more  dominant  forms,  and  there  will  be  nothing  im- 
mutable in  the  laws  of  past  and  present  distribution. 

It  may  be  asked  in  ridicule,  whether  I  suppose  that 
the  megatherium  and  other  allied  huge  monsters  have  left 
behind  them  in  South  America  the  sloth,  armadillo,  and 
anteater,  as  their  degenerate  descendants.  This  cannot 
for  an  instant  be  admitted.  These  huge  animals  have  be- 
come wholly  extinct,  and  have  left  no  progeny.  But  in 
the  caves  of  Brazil,  there  are  many  extinct  species  which 
are  closely  allied  in  size  and  in  other  characters  to  the 
species  still  living  in  South  America  ;  and  some  of  these 
fossils  may  be  the  'actual  progenitors  of  living  species. 
It  must  not  be  forgotten  that,  on  my  theory,  all  the  spe- 
cies of  the  same  genus  have  descended  from  some  one 
species  ;  so  that  if  six  genera,  each  having  eight  species, 
be  found  in  one  geological  formation,  and  in  the  next  suc- 
ceeding formation  there  be  six  other  allied  or  representa- 
tive genera  with  the  same  number  of  species,  then  we 


2Qg       ,  GEOLOGICAL   SUCCESSION.  [Chap.  X. 

may  conclude  that  only  one  species  of  eacli  of  the  six 
older  genera  has  left  modified  descendants,  constituting 
the  six  new  genera.  The  other  seven  species  of  the  old 
genera  have  all  died  out  and  have  left  no  progeny.  Or, 
which  would  probably  be  a  far  commoner  case,  two  or 
three  species  of  t^vo  or  three  alone  of  the  six  older  genera 
will  have  been  the  parents  of  the  six  new  genera ;  the 
other  old  species  and  the  other  whole  genera  having  be- 
come utterly  extinct.  In  failing  orders,  with  the  genera 
and  species  decreasing  in  numbers,  as  apparently  is  the 
case  of  the  Edentata  of  South  America,  still  fewer  genera 
and  species  will  have  left  modified  blood-descendants. 

SuriiTnary  of  the  preceding  and  present  Chapters. — I 
have  attempted  to  show  that  the  geological  record  is  ex- 
tremely imperfect ;  that  only  a  small  portion  of  the  globe 
has  been  geologically  explored  with  care  ;  that  only  cer- 
tain classes  of  organic  beings  have  been  largely  preserved 
in  a  fossil  state  ;  that  the  number  both  of  specimens  and 
of  species,  preserved  in  our  museums,  is  absolutely  as 
nothing  compared  with  the  incalculable  number  of  gen- 
erations which  must  have  passed  away  even  during  a 
single  formation  ;  that,  owing  to  subsidence  being  neces- 
sary for  the  accumulation  of  fossiliferous  deposits  thick 
enough  to  resist  future  degradation,  enormous  intervals 
of  time  have  elapsed  between  the  successive  formations  ; 
that  there  has  probably  been  more  extinction  during  the 
periods  of  subsidence,  and  more  variation  during  the  pe- 
riods of  elevation,  and  during  the  latter  the  record  will 
have  been  least  perfectly  kept ;  that  each  single  formation 
has  not  been  continuously  deposited  ;  that  the  duration  of 
each  formation  is,  perhaps,  short  compared  with  the  aver- 
age duration  of  specific  forms  ;  that  migration  has  played 
an  important  part  in  the  first  appearance  of  new  forms  in 
any  one  area  and  formation  ;  that  widely  ranging  species 
are  those  which  have  varied  most,  and  have  oftenest  given 
rise  to  new  species  ;  and  that  varieties  have  at  first  often 
been  local.  All  these  causes  taken  conjointly,  must  have 
tended  to  make  the  geological  record  extremely  imperfect, 
and  will  to  a  large  extent  explain  why  we  do  not  find  in- 


Chap.  X..1  SUMMARY.  299 

terminable  varieties,  connecting  together  all  the  extinct 
and  existing  forms  of  life  by  the  finest  graduated  steps. 

He  who  rejects  these  views  on  the  nature  of  the  geo- 
logical record,  will  rightly  reject  my  whole  theory.  For 
he  may  ask  in  vain  where  are  the  numberless  transitional 
links  which  must  formerly  have  connected  the  closely 
allied  or  representative  species,  found  in  the  several  stages 
of  the  same  great  formation.  He  may  disbelieve  in  the 
enormous  intervals  of  time  which  have  elapsed  between 
our  consecutive  formations  ;  he  may  overlook  how  im- 
portant a  part  migration  must  have  played,  when  the  for- 
mations of  any  one  great  region  alone,  as  that  of  Europe, 
are  considered  ;  he  may  urge  the  apparent,  but  often 
falsely  apparent,  sudden  coming  in  of  whole  groups  of 
species.  He  may  ask  where  are  the  remains  of  those  in- 
finitely numerous  organisms  w^hich  raust  have  existed  long 
before  the  first  bed  of  the  Silurian  system  was  deposited  : 
I  can  answer  this  latter  question  only  hypothetically,  by 
saying  that  as  far  as  we  can  see,  where  our  oceans  now 
extend  they  have  for  an  enormous  period  extended,  and 
where  our  oscillating  continents  now  stand  they  have 
stood  over  since  the  Silurian  epoch  ;  but  that  long  before 
that  period,  the  world  may  have  presented  a  wholly  dif- 
ferent aspect ;  and  that  the  older  continents,  formed  of 
formations  older  than  any  known  to  us,  may  now  all  be  in 
a  metamorphosed  condition,  or  may  lie  buried  under  the 
ocean. 

Passing  from  these  difiiculties,  all  the  other  great 
leading  facts  in  palaeontology  seem  to  me  simply  to  fol- 
low on  the  theory  of  descent  wdth  modification  through 
natural  selection.  We  can  thus  understand  how  it  is  that 
new  species  come  in  slowly  and  successively  ;  how  species 
of  difterent  classes  do  not  necessarily  change  together,  or 
at  the  same  rate,  or  in  the  same  degree ;  yet  in  the  long 
run  that  all  undergo  modification  to  some  extent.  The 
extinction  of  old  forms  is  the  almost  inevitable  conse- 
quence of  the  production  of  new  forms.  We  can  under- 
stand why  when  a  species  has  once  disappeared  it  never 
reappears.  Groups  of  species  increase  in  numbers  slowly, 
and  endure  for  unequal  periods  of  time :  for  the  process 
14 


gQQ  GEOLOGICAL    SUCCESSION.  IUhap.  X. 

of  modification  is  necessarily  slow,  and  depends  on  many 
complex  contingencies.  The  dominant  species  of  tlie 
larger  dominant  groups  tend  to  leave  many  modified  de- 
scendants, and  thus  new  sub-groups  and  groups  are 
formed.  As  these  are  formed,  the  species  of  the  less 
vigorous  groups,  from  tlieir  inferiority  inherited  from  a 
common  progenitor,  tend  to  become  extinct  together,  and 
to  leave  no  modified  offspring  on  the  face  of  the  earth. 
But  the  utter  extinction  of  a  whole  group  of  species  may 
often  be  a  very  slow  process,  from  the  survival  of  a  few 
descendants,  lingering  in  protected  and  isolated  situations. 
"When  a  group  has  once  wholly  disappeared,  it  does  not 
reappear ;  for  the  link  of  generation  has  been  broken. 

We  can  understand  how  the  spreading  of  the  domi- 
nant forms  of  life,  which  are  those  that  oftenest  vary,  will 
in  the  long  run  tend  to  people  the  world  with  allied,  but 
modified,  descendants ;  and  these  will  generally  succeed 
in  taking  the  places  of  those  groups  of  species  which  are 
their  inferiors  in  the  struggle  for  existence.  Hence,  after 
long  intervals  of  time,  the  productions  of  the  world  will 
appear  to  have  changed  simultaneously. 

We  can  understand  how  it  is  that  all  the  forms  of  life, 
ancient  and  recent,  make  together  one  grand  system ;  for 
all  are  connected  by  generation.  We  can  understand, 
from  the  continued  tendency  to  divergence  of  character, 
why  the  more  ancient  a  form  is,  the  more  it  generally 
differs  from  those  now  living.  AVhy  ancient  and  extinct 
forms  often  tend  to  fill  up  gaps  between  existing  forms, 
sometimes  blending  two  groups  previously  classed  as  dis- 
tinct into  one ;  but  more  commonly  only  bringing  them  a 
little  closer  together.  The  more  ancient  a  form  is,  the 
more  often,  aj^parently,  it  displays  characters  in  some  de- 
gree intermediate  between  groups  now  distinct ;  for  the 
more  ancient  a  form  is,  the  more  nearly  it  will  be  related 
to,  and  consequently  resemble,  the  common  progenitor  of 
groups,  since  become  widely  divergent.  Extinct  forms 
are  seldom  directly  intermediate  between  existing  forms  ; 
but  are  intermediate  only  by  a  long  and  circuitous  course 
through  many  extinct  and  very  difierent  forms.  We  can 
clearly  see  why  the  organic  remains  of  closely  consecutive 


CuAP.  X.]  SUMMARY.  -  3()J_ 

formations  are  more  closelj  allied  to  eacli  other,  tlian  are 
those  of  remote  formations  ;  for  the  forms  are  more  closely 
linlied  together  by  generation :  we  can  clearly  see  why 
the  remains  of  an  intermediate  formation  are  intermediate 
in  character. 

The  inhabitants  of  each  successive  period  in  the  world's 
history  have  beaten  their  predecessors  in  the  race  for  life, 
and  are,  in  so  far,  higher  in  the  scale  of  natnre  ;  and  this 
may  account  for  that  vague  yet  ill-defined  sentiment,  felt 
by  many  palaeontologists,  that  organisation  on  the  whole 
has  progressed.  If  it  should  hereafter  be  proved  that 
ancient  animals  resemble  to  a  certain  extent  the  embryos 
of  more  recent  animals  of  the  same  class,  the  fact  will  be 
intelligible.  The  succession  of  the  same  types  of  structure 
within  the  same  areas  during  the  later  geological  periods 
ceases  to  be  mysterious,  and  is  simply  explained  by  in- 
heritance. 

If  then  the  geological  record  be  as  imperfect  as  I  be- 
lieve it  to  be,  and  it  may  at  least  be  asserted  that  the  rec- 
ord cannot  be  proved  to  be  much  more  perfect,  the  main 
objections  to  the  theory  of  natural  selection  are  greatly 
diminished  or  disappear.  On  the  other  hand,  all  the  chief 
laws  of  palaeontology  plainly  proclaim,  as  it  seems  to  me, 
that  species  have  been  produced  by  ordinary  generation  : 
old  forms  having  been  supplanted  by  new  and  improved 
forms  of  life,  produced  by  the  laws  of  variation  still  acting 
round  us,  and  preserved  by  ITatural  Selection. 


302  GEOGRAPHICAL   DISTRIBUTION,  TChap.  XL 


CHAPTER    XI. 

GEOGRAPHICAL    DISTRIBUTION. 

Present  distribution  cannot  he  accounted  for  by  differences  in  physical  conditions— Im- 
portance of  barriers — Affinity  of  the  productions  of  the  same  continent — Centres 
of  creation — Means  of  dispersal,  by  changes  of  climate  and  of  the  level  of  the 
land,  and  by  occasional  means — Dispersal  during  the  Glacial  period  co-extensive 
■\vith  the  world. 

In  considering  tlie  distribution  of  organic  beings  over  tbe 
face  of  the  globe,  tbe  first  great  fact  wbicli  strikes  lis  is, 
tbat  neither  the  similarity  nor  the  dissimilarity  of  the  in- 
habitants of  various  regions  can  be  accounted  for  by  their 
climatal  and  other  physical  conditions.  Of  late,  almost 
every  author  who  has  studied  the  subject  has  come  to  this 
conclusion.  The  case  of  America  alone  would  almost 
suffice  to  prove  its  truth  :  for  if  we  exclude  the  northern 
parts  where  the  circumpolar  land  is  almost  continuous, 
all  authors  agree  that  one  of  the  most  fundamental  divi- 
sions in  geographical  distribution  is  that  between  the 
Kew  and  Old  Worlds  ;  yet  if  we  travel  over  the  vast 
American  continent,  from  the  central  parts  of  the  United 
States  to  its  extreme  southern  point,  we  meet  with  the 
most  diversified  conditions  ;  the  most  humid  districts,  arid 
deserts,  lofty  mountains,  grassy  plains,  forests,  marshes, 
lakes,  and  great  rivers,  under  almost  every  temperature. 
There  is  hardly  a  climate  or  condition  in  the  Old 
World  which  cannot  be  paralleled  in  the  l^ew — at  least 
as  closely  as  the  same  species  generally  require  ;  for  it  is 
a  most  rare  case  to  find  a  group  of  organisms  confined  to 
any  small  spot,  having  conditions  peculiar  in  only  a  slight 
degree  ;  for  instance,  small  areas  in  the  Old  World  could 
be  pointed  out  hotter  than  any  in  the  Kew  World,  yet 


Chap,  XI.]  GEOGRAPHICAL   DISTRIBUTION.  3Q3 

tliese  are  not  inhabited  by  a  peculiar  fauna  or  flora.  I^ot- 
withstandin^  this  parallelism  in  the  conditions  of  the  Old 
and  New  Worlds,  how  widely  diflerent  are  their  living 
productions  ! 

In  the  southern  hemisphere,  if  we  compare  large  tracts 
of  land  in  Australia,  South  Africa,  and  western  South 
America,  between  latitudes  25°  and  35°,  we  shall  find 
parts  extremely  similar  in  all  their  conditions,  yet  it  would 
not  be  possible  to  point  out  three  faunas  and  floras  more 
utterly  dissimilar.  Or  again  we  may  compare  the  pro- 
ductions of  South  America  south  of  lat.  35^  with  those 
north  of  25°,  which  consequently  inhabit  a  considerably 
difi'erent  climate,  and  they  will  be  found  incomparably 
more  closely  related  to  each  other,  than  they  are  to  the 
productions  of  Australia  or  Africa  under  nearly  the  same 
climate.  Analogous  facts  could  be  given  with  respect  to 
the  inhabitants  of  the  sea. 

A  second  great  fact  which  strikes  us  in  our  general 
review  is,  that  barriers  of  any  kind,  or  obstacles  to  free 
migration,  are  related  in  a  close  and  important  manner  to 
the  differences  between  the  productions  of  various  regions. 
We  see  this  in  the  great  difference  of  nearly  all  the  ter- 
restrial productions  of  the  ITew  and  Old  Worlds,  except- 
ing in  the  northern  parts,  where  the  land  almost  joins,  and 
where,  under  a  slightly  different  climate,  there  might  have 
been  free  migration  for  the  northern  temperate  forms,  as 
there  now  is  for  the  strictly  arctic  productions.  We  see 
the  same  fact  in  the  great  difference  between  the  inhabit- 
ants of  Australia,  Africa,  and  South  America  under  the 
same  latitude :  for  these  countries  are  almost  as  much  iso- 
lated from  each  other  as  is  possible.  On  each  continent, 
al^o,  we  see  the  same  fact ;  for  on  the  opposite  sides  of 
lofty  and  continuous  mountain-ranges,  and  of  great  deserts, 
and  sometimes  even  of  large  rivers,  we  find  different  pro- 
ductions ;  though  as  mountain-chains,  deserts,  &c.,  are 
not  as  impassable,  or  likely  to  have  endured  so  long  as 
the  oceans  separating  continents,  the  differences  are  very 
inferior  in  degree  to  those  characteristic  of  distinct  conti- 
nents. 

Turning  to  the  sea,  we  find  the  same  law.     'No  two 


304  GEOGRAPHICAL   DISTRIBUTION.  [Chap.  XL 

marine  faunas  are  more  distinct,  with  hardly  a  fish,  shell, 
or  crab  in  common,  than  those  of  the  eastern  and  western 
shores  of  South  and  Central  America,  yet  these  great 
faunas  are  separated  only  by  the  narrow,  but  impassable, 
isthmus  of  Panama.  Westward  of  the  shores  of  America, 
a  wide  space  of  open  ocean  extends,  with  not  an  island  as  a 
halting-place  for  emigrants  ;  here  we  have  a  barrier  of 
another  kind,  and  as  soon  as  this  is  passed  we  meet  in  the 
eastern  islands  of  the  Pacific,  with  another  and  totally 
distinct  fauna.  So  that  here  three  marine  faunas  range 
far  northward  and  southward,  in  parallel  lines  not  far  from 
each  other,  under  corresponding  climates ;  but  from  being 
separated  from  each  other,  by  impassable  barriers,  either 
of  land  or  open  sea,  they  are  wholly  distinct.  On  the 
other  hand,  proceeding  still  further  westward  from  the 
eastern  islands  of  the  tropical  parts  of  the  Pacific,  we  en- 
counter no  impassable  barriers,  and  we  have  innumerable 
islands  as  halting-places,  until  after  travelling  over  a 
hemisphere  we  come  to  the  shores  of  Africa ;  and  over 
this  vast  space  we  meet  with  no  well-defined  and  distinct 
marine  faunas.  Although  hardly  one  shell,  crab  or  fish  is 
common  to  the  above-named  three  approximate  faunas  of 
Eastern  and  Western  America  and  the  eastern  Pacific 
islands,  yet  many  fish  range  from  the  Pacific  into  the  In- 
dian Ocean,  and  many  shells  are  common  to  the  eastern 
islands  of  the  Pacific  and  the  eastern  shores  of  Africa,  on 
almost  exactly  opposite  meridians  of  longitude. 

A  third  great  fact,  partly  included  in  the  foregoing 
statements,  is  the  affinity  of  the  productions  of  the  same 
continent  or  sea,  though  the  species  themselves  are  distinct 
at  difi'erent  points  and  stations.  It  is  a  law  of  the  widest 
generality,  and  every  continent  ofi*ers  innumerable  in- 
stances. iSTevertheless  the  naturalist  in  travelling,  for  in 
stance,  from  north  to  south,  never  fails  to  be  struck  by  the 
manner  in  which  successive  groups  of  beings,  specifically 
distinct,  yet  clearly  related,  replace  each  other.  He  hears 
from  closely  allied,  yet  distinct  kinds  of  birds,  notes  near- 
ly similar,  and  sees  their  nests  similarly  constructed,  but 
not  quite  alike,  with  eggs  coloured,  in  nearly  the  same 
manner.     The  plains  near  the  Straits  of  Magellan  are  in- 


Chap.  XI.]  OEOGRAPHICAL   DISTRIBUTION  206 

habited  Ly  one  species  of  Rliea  (American  ostricli),  and 
northward  the  plains  of  La  Plata  by  another  species  of 
the  same  genus  ;  and  not  by  a  true  ostrich  or  emeu,  like 
those  found  in  Africa  and  Australia  under  the  same  lati- 
tude. On  these  same  plains  of  La  Plata,  we  see  the 
agouti  and  bizcacha,  animals  having  nearly  the  same 
habits  as  our  hares  and  rabbits  and  belonging  to  the  same 
order  of  Kodents,  but  they  plainly  display  an  American 
type  of  structure.  We  ascend  the  lofty  peaks  of  the  Cor- 
dillera and  we  find  an  alpine  species  of  bizcacha ;  we  look 
to  the  waters,  and  we  do  not  find  the  beaver  and  musk-rat, 
but  the  coypu  and  capybara,  rodents  of  the  American  type. 
Innumerable  other  instances  could  be  given.  If  we  look 
to  the  islands  off  the  American  shore,  however  much  they 
may  differ  in  geological  structure,  the  inhabitants,  though 
they  may  be  all  peculiar  species,  are  essentially  American. 
We  may  look  back  to  past  ages,  as  shown  in  the  last 
chapter,  and  we  find  American  types  then  prevalent  on 
the  American  continent  and  in  the  American  seas.  We 
see  in  these  facts  some  deep  organic  bond,  prevailing 
throughout  space  and  time,  over  the  same  areas  of  land 
and  water,  and  independent  of  their  physical  conditions. 
The  naturalist  must  feel  little  curiosity,  who  is  not  led  to 
inquire  what  this  bond  is. 

This  bond,  on  my  theory,  is  simply  inheritance,  that 
cause  which  alone,  as  far  as  we  positively  know,  produces 
organisms  quite  like,  or,  as  we  see  in  the  case  of  varieties, 
nearly  like  each  other.  The  dissimilarity  of  the  inhab- 
itants of  different  regions  may  be  attributed  to  modifica- 
tion through  natural  selection,  and  in  a  quite  subordinate 
degree  to  the  du-ect  influence  of  different  physical  condi- 
tions. The  degree  of  dissimilarity  will  depend  on  the  mi- 
gration of  the  more  dominant  forms  of  life  from  one  region 
into  another  having  been  effected  with  more  or  less  ease, 
at  periods  more  or  less  remote  ; — on  the  nature  and  num- 
ber of  the  former  immigrants  ; — and  on  their  action  and 
reaction,  in  their  mutual  struggles  for  life  ; — the  relation 
of  organism  to  organism  being,  as  I  have  already  often 
remarked,  the  most  important  of  all  relations.  Thus  the 
high  importance  of  barriers  comes  into  play  by  checking 


3Qg  GEOGRAPHICAL    DISTRIBUTION.  [Chap.  XI, 

migration  ;  as  does  time  for  tlie  slow  process  of  modifica- 
tion throngli  natural  selection.  Widely-ranging  species, 
abounding  in  individuals,  which  have  already  triumphed 
over  many  competitors  in  their  own  widely-extended 
homes,  will  have  the  best  chance  of  seizing  on  new  places, 
when  they  spread  into  new  countries.  In  their  new  homes 
they  will  be  exposed  to  new  conditions,  and  will  frequent- 
ly undergo  further  modification  and  improvement ;  and 
thus  they  will  become  still  further  victorious,  and  will 
produce  groups  of  modified  descendants.  On  this  principle 
of  inheritance  with  modification,  we  can  understand  how 
it  is  that  sections  of  genera,  whole  genera,  and  even  fami- 
lies are  confined  to  the  same  areas,  as  is  so  commonly  and 
notoriously  the  case. 

I  believe,  as  was  remarked  in  the  last  chapter,  in  no 
law  of  necessary  development.  As  the  variability  of  each 
species  is  an  independent  property,  and  will  be  taken  ad- 
vantage of  by  natural  selection,  only  so  far  as  it  profits 
the  individual  in  its  complex  struggle  for  life,  so  the  de- 
gree of  modification  in  different  species  will  be  no  uniform 
quantity.  If,  for  instance,  a  number  of  species,  which 
stand  in  direct  competition  with  each  other,  migrate  in  a 
body  into  a  new  and  afterwards  isolated  country,  they 
will  be  little  liable  to  modification  ;  for  neither  migration 
nor  isolation  in  themselves  can  do  anything.  These  prin- 
ciples come  into  play  only  by  bringing  organisms  into 
new  relations  with  each  other,  and  in  a  lesser  degree  with 
the  surrounding  physical  conditions.  As  we  have  seen 
in  the  last  chapter  that  some  forms  have  retained  nearly 
the  same  character  from  an  enormously  remote  geological 
period,  so  certain  species  have  migrated  over  vast  spaces, 
and  have  not  become  greatly  modified. 

On  these  views,  it  is  obvious,  that  the  several  species 
of  the  same  genus,  though  inhabiting  the  most  distant 
quarters  of  the  world,  must  originally  have  proceeded 
from  the  same  source,  as  they  have  descended  from  the 
same  progenitor.  In  the  case  of  those  species,  which  have 
undergone  during  whole  geological  periods  but  little  mod- 
ification, there  is  not  much  difiiculty  in  believing  that 
they  may  have  migrated  from  the  same  region  ;  for  dm*- 


Chap.  XI.]  SINGLE    CENTRES    OF    CREATION.  3QY  ' 

ing  the  vast  geographical  and  climatal  changes  which 
will  have  supervened  since  ancient  times,  almost  any 
amount  of  migration  is  ^^ossible.  But  in  many  other 
cases,  in  which  we  have  reason  to  believe  that  the  species 
of-  a  genus  have  been  produced  within  comparatively  re- 
cent times,  there  is  great  difficulty  on  this  head.  It  is 
also  obvious  that  the  individuals  of  the  same  species, 
though  now  inhabiting  distant  and  isolated  regions,  must 
have  proceeded  from  one  spot,  where  their  parents  were 
first  produced :  for,  as  explained  in  the  last  chapter,  it  is 
incredible  that  individuals  identically  the  same  should 
ever  have  been  produced  through  natural  selection  from 
parents  specifically  distinct. 

We  are  thus  brought  to  the  question  which  has  been 
largely  discussed  by  naturalists,  namely,  whether  species 
have  been  created  at  one  or  more  points  of  the  earth's 
surface.  Undoubtedly  there  are  very  many  cases  of  ex- 
treme difficulty,  in  understanding  how  the  same  species 
could  possibly  have  migrated  from  some  one  point  to  the 
several  distant  and  isolated  points,  where  now  found. 
JSTevertheless  the  simplicity  of  the  view  that  each  species 
was  first  produced  within  a  single  region  captivates  the 
mind.  He  who  rejects  it,  rejects  the  vera  causa  of  ordi- 
nary generation  with  subsequent  migration,  and  calls  in 
the  agency  of  a  miracle.  It  is  universally  admitted,  that 
in  most  cases  the  area  inhabited  by  a  species  is  continu- 
ous ;  and  when  a  plant  or  animal  inhabits  two  points  so 
distant  from  each  other,  or  with  an  interval  of  such  a 
nature,  that  the  space  could  not  be  easily  passed  over  by 
migration,  the  fact  is  given  as  something  remarkable  and 
exceptional.  Tlie  capacity  of  migrating  across  the  sea  is 
more  distinctly  limited  in  terrestrial  mammals,  than  per- 
haps in  any  other  organic  beings  ;  and,  accordingly,  we 
find  no  inexplicable  cases  of  the  same  mammal  inhabiting 
distant  points  of  the  world.  ISTo  geologist  will  feel  any 
difficulty  in  such  cases  as  Great  Britain  having  been  for- 
merly united  to  Europe,  and  consequently  possessing  the 
same  quadrupeds.  But  if  the  same  species  can  be  pro- 
duced at  two  separate  points,  why  do  we  not  find  a  single 
mammal  common  to  Europe  and  Australia  or  South 
14* 


3Q3  GEOGRAPHICAL  DISTRIBUTION.  [Chap.  XI. 

America  ?  The  conditions  of  life  are  nearly  the  same,  so 
that  a  multitude  of  European  animals  and  plants  have  be- 
come naturalised  in  America  and  Australia  ;  and  some  of 
the  aboriginal  plants  are  identically  the  same  at  these 
distant  points  of  the  northern  and  southern  hemispheres  ? 
The  answer,  as  I  believe,  is,  that  mammals  have  not  been 
able  to  migrate,  whereas  some  plants  from  their  varied 
means  of  dispersal,  have  migrated  across  the  vast  and 
broken  intersj)ace.  The  great  and  striking  influence 
which  barriers  of  every  kind  have  had  on  distribution,  is 
intelligible  only  on  the  view  that  the  great  majority  of 
sj)ecies  have  been  produced  on  one  side  alone,  and  have 
not  been  able  to  migrate  to  the  other  side.  Some  few 
families,  many  sub-families,  very  many  genera,  and  a  still 
greater  number  of  sections  of  genera  are  confined  to  a 
single  region  ;  and  it  has  been  observed  by  several  natu- 
ralists, that  the  most  natural  genera,  or  those  genera  in 
which  the  species  are  most  closely  related  to  each  other, 
are  generally  local,  or  confined  to  one  area.  What  a 
strange  anomaly  it  would  be,  if,  when  coming  one  step 
lower  in  the  series,  to  the  individuals  of  the  same  spe- 
cies, a  directly  opposite  rule  j^revailed ;  and  species  were 
not  local,  but  had  been  produced  in  two  or  more  distinct 
areas ! 

Hence  it  seems  to  me,  as  it  has  to  many  other  natu- 
ralists, that  the  view  of  each  species  having  been  pro- 
duced in  one  area  alone,  and  having  subsequently  mi- 
grated from  that  area  as  far  as  its  powers  of  migration 
and  subsistence  under  past  and  present  conditions  per- 
mitted, is  the  most  probable.  Undoubtedly  many  cases 
occur,  in  which  we  cannot  explain  how  the  same  species 
could  have  passed  from  one  point  to  the  other.  But 
the  geographical  and  climatal  changes,  which  have  cer- 
tainly occurred  within  recent  geological  times,  must  have 
interrupted  or  rendered  discontinuous  the  formerly  con- 
tinuous range  of  many  species.  So  that  we  are  reduced 
to  consider  whether  the  exceptions  to  continuity  of  range 
are  so  numerous  and  of  so  grave  a  nature,  that  we  ought 
to  give  up  the  belief,  rendered  probable  by  general  con- 
siderations, that  each  species  has  been  produced  within 


Chap.  XI.]  SINGLE    CENTRES    OF    CREATION.  3()f) 

one  area,  and  has  migrated  thence  as  far  it  could.  It 
would  be  hopelessly  tedious  to  discuss  all  the  exceptional 
cases  of  the  same  species,  now  living  at  distant  and  sep- 
arated points  ;  nor  do  I  for  a  moment  j)retend  that  any 
explanation  could  be  offered  of  many  such  cases.  But 
after  some  preliminary  remarks,  I  will  discuss  a  few  of 
the  most  striking  classes  of  facts  ;  namely,  the  existence 
of  the  same  species  on  the  summits  of  distant  mountain- 
ranges,  and  at  distant  points  in  the  arctic  and  antarctic 
regions  ;  and  secondly  (in  the  following  chapter),  the  wide 
distribution  of  fresh-water  productions  ;  and  thirdly,  the 
occurrence  of  the  same  terrestrial  species  on  islands  and 
on  the  mainland,  though  separated  by  hundreds  of  miles 
of  open  sea.  If  the  existence  of  the  same  species  at  dis- 
tant and  isolated  j)oints  of  the  earth's  surface,  can  in  many 
instances  be  explained  on  the  view  of  each  species  having 
migrated  from  a  single  birthplace  ;  then,  considering  our 
ignorance  with  respect  to  former  climatal  and  geographi- 
cal changes  and  various  occasional  means  of  transport,  the 
belief  that  this  has  been  the  universal  lavf,  seems  to  me 
incomparably  the  safest. 

In  discussing  this  subject,  we  shall  be  enabled  at  the 
same  time  to  consider  a  point  equally  important  for  us, 
namely,  whether  the  several  distinct  species  of  a  genus, 
which  on  my  theory  have  all  descended  from  a  common 
progenitor,  can  have  migrated  (undergoing  modification 
during  some  part  of  their  migration)  from  the  area  inhab- 
ited by  their  progenitor.  If  it  can  be  shown  to  be  almost 
invariablv  the  case,  that  a  reofion,  of  which  most  of  its  in- 
habitants  are  closely  related  to,  or  belong  to  the  same 
genera  with  the  species  of  a  second  region,  has  probably 
received  at  some  former  period  immigrants  from  this  other 
region,  my  theory  will  be  strengthened  ;  for  we  can  clear- 
ly understand,  on  the  principle  of  modification,  why  the 
inhabitants  of  a  region  should  be  related  to  those  of 
another  region,  whence  it  has  been  stocked.  A  volcanic 
island,  for  instance,  upheaved  and  formed  at  the  distance 
of  a  few  hundreds  of  miles  from  a  continent,  w^ould  prob- 
ably receive  from  it  in  the  course  of  time  a  few  colonists," 
and  their  descendants,  though  modified,  would  still  be 


320  GEOGRAPHICAL   DISTRIBUTION.  [Chap.  XI. 

plainly  related  by  inheritance  to  the  inhabitants  of  the 
continent.  Cases  of  this  nature  are  common,  and  are,  as 
we  shall  hereafter  more  fnlly  see,  inexplicable  on  the  theory 
of  independent  creation.  This  view  of  the  relation  of 
sj)ecies  in  one  region  to  those  in  another,  does  not  differ 
much  (by  substituting  the  word  variety  for  species)  from 
that  lately  advanced  in  an  ingenious  paper  by  Mr.  "Wal- 
lace, in  which  he  concludes,  that  "  every  species  has  come 
into  existence  coincident  both  in  space  and  time  with  a 
pre-existing  closely  allied  species."  And  I  now  know 
from  correspondence,  that  this  coincidence  he  attributes 
to  generation  with  modification. 

The  previous  remarks  on  "  single  and  multiple  centres 
of  creation  "  do  not  directly  bear  on  another  allied  ques- 
tion,— namely  whether  all  the  individuals  of  the  same 
species  have  descended  from  a  single  pair,  or  single  her- 
maphrodite, or  whether,  as  some  authors  suppose,  from 
many  individuals  simultaneously  created.  "With  those  or- 
ganic beings  which  never  intercross  (if  such  exist),  the 
species,  on  my  theory,  must  have  descended  from  a  suc- 
cession of  improved  varieties,  which  will  never  have 
blended  with  other  individuals  or  varieties,  but  will  have 
supplanted  each  other  ;  so  that,  at  each  successive  stage 
of  modification  and  improvement,  all  the  individuals  of 
each  variety  will  have  descended  from  a  single  parent. 
But  in  the  majority  of  cases,  namely,  with  all  organisms 
which  habitually  unite  for  each  birth,  or  which  often  in- 
tercross, I  believe  that  during  the  slow  process  of  modifi- 
cation the  individuals  of  the  species  will  have  been  kept 
nearly  uniform  by  intercrossing ;  so  that  many  individ- 
uals will  liave  gone  on  sijnultaneously  changing,  and  the 
whole  amount  ot  modification  will  not  have  been  due,  at 
each  stage,  to  descent  from  a  single  parent.  To  illustrate 
what  I  mean  :  our  English  race-horses  differ  slightly  from 
the  horses  of  every  other  breed  ;  but  they  do  not  owe  their 
difference  and  superiority  to  descent  from  any  single  pair, 
but  to  continued  care  in  selecting  and  training  many  in- 
dividuals during  many  generations. 

Before  discussing  the  three  classes  of  facts,  which  I 
have  selected  as  presenting  the  greatest  amomit  of  diffi- 


Ohap.  XL]  MEANS   OF   DISPERSAL,  ^l^ 

culty  on  the  theory  of  "  single  centres  of  creation,"  I 
must  say  a  few  words  on  the  means  of  dispersal. 

Means  of  Dispersal. — Sir  C.  Lyell  and  other  authors 
have  ably  treated  this  subject.  I  can  give  here  only  the 
briefest  abstract  of  the  more  important  facts.  Change 
of  climate  must  have  had  a  powerful  influence  on  migra- 
tion :  a  region  when  its  climate  was  different  may  have 
been  a  high  road  for  migration,  but  now  be  impassable  : 
I  shall,  however,  presently  have  to  discuss  this  branch  of 
the  subject  in  some  detail.  Changes  of  level  in  the  land 
must  also  have  been  highly  influential :  a  narrow  isthmus 
now  separates  two  marine  faunas  ;  submerge  it,  or  let  it 
formerly  have  been  submerged,  and  the  two  faunas  will 
now  blend  or  may  formerly  have  blended  :  where  the  sea 
now  extends,  land  may  at  a  former  period  have  connected 
islands  or  possibly  even  continents  together,  and  thus 
have  allowed  terrestrial  productions  to  pass  from  one  to 
the  other,  l^o  geologist  will  dispute  that  great  mutations 
of  level  have  occurred  within  the  period  of  existing  or- 
ganisms. Edward  Forbes  insisted  that  all  the  islands  in 
the  Atlantic  must  recently  have  been  connected  with 
Europe  or  Africa,  and  Europe  likewise  with  America. 
Other  authors  have  thus  hypothetically  bridged  over  every 
ocean,  and  have  united  almost  every  island  to  some  main- 
land. K  indeed  the  arguments  used  by  Forbes  are  to  be 
trusted,  it  must  be  admitted  that  scarcely  a  single  island 
exists  which  has  not  recently  been  united  to  some  conti- 
nent. This  view  cuts  the  Gordian  knot  of  the  dispersal 
of  the  same  species  to  the  most  distant  points,  and  removes 
many  a  difficulty :  but  to  the  best  of  my  judgment  we 
are  not  authorized  in  admitting  such  enormous  geograph- 
ical changes  within  the  period  of  existing  species.  It 
seems  to  me  that  we  have  abundant  evidence  of  great 
oscillations  of  level  in  our  continents ;  but  not  of  such 
vast  changes  in  their  position  and  extension,  as  to  have 
united  them  within  the  recent  period  to  each  other  and  to 
the  several  intervening  oceanic  islands.  I  freely  admit 
the  former  existence  of  many  islands,  now  buried  beneath 
the  sea,  which  may  have  served   as  halting  places  for 


gj|^2  GEOGRAPHICAL   DISTRIBtJTiOlT.  [Chap.  XL 

plants  and  for  many  animals  during  tlieir  migration.  In 
the  coral-producing  oceans  sucli  sunken  islands  are  now 
marked,  as  I  believe,  by  rings  of  coral  or  atolls  standing 
over  them.  Whenever  it  is  fully  admitted,  as  I  believe  it 
will  some  day  be,  that  each  species  has  proceeded  from  a 
single  birthplace,  and  when  in  the  course  of  time  we  know 
something  definite  about  the  means  of  distribution,  we 
shall  be  enabled  to  speculate  with  security  on  the  former 
extension  of  the  land.  But  I  do  not  believe  that  it  will 
ever  be  proved  that  within  the  recent  period  continents 
which  are  now  quite  separate,  have  been  continuously,  or 
almost  continuously,  united  with  each  other,  and  with  the 
many  existing  oceanic  islands.  Several  facts  in  distribu- 
tion,— such  as  the  great  difi'erence  in  the  marine  faunas  on 
the  opposite  sides  of  almost  every  continent, — the  close 
relation  of  the  tertiary  inhabitants  of  several  lands  and 
even  seas  to  their  present  inhabitants, — a  certain  degree 
of  relation  (as  we  shall  hereafter  see)  between  the  distri- 
bution of  mammals  and  the  depth  of  the  sea, — these  and 
other  such  facts  seem  to  me  opposed  to  the  admission  of 
such  prodigious  geographical  revolutions  within  the  recent 
period,  as  are  necessitated  on  the  view  advanced  by  Forbes 
and  admitted  by  his  many  followers.  The  nature  and 
relative  proportions  of  the  inhabitants  of  oceanic  islands 
likewise  seem  to  me  opposed  to  the  belief  of  their  former 
continuity  with  continents.  Nor  does  their  almost  uni- 
versally volcanic  composition  favour  the  admission  that 
they  are  the  wrecks  of  sunken  continents  ; — if  they  had 
originally  existed  as  mountain-ranges  on  the  land,  some  at 
least  of  the  islands  would  have  been  formed,  like  other 
*mountain-summits,  of  granite,  metamorphic  schists,  old 
fossiliferous  or  other  such  rocks,  instead  of  consisting  of 
mere  piles  of  volcanic  matter. 

I  must  now  say  a  few  words  on  what  are  called  acci- 
dental means,  but  which  more  properly  might  be  called 
occasional  means  of  distribution.  I  shall  here  confine 
myself  to  plants.  In  botanical  works,  this  or  that  plant 
is  stated  to  be  ill  adapted  for  wide  dissemination ;  but 
for  trans2)ort  across  the  sea,  the  greater  or  less  facilities 
may  be  said  to  be  almost  wholly  unknown.  Until  I  tried, 
witii  Mr.  Berkeley's  aid,  a  few  experiments,  it  was  not 


Ohap.  XL)  MEANS  OF  DISPERSAL.  3]^3 

even  known  how  far  seeds  could  resist  the  injurious  action 
of  sea-water.  To  my  surprise  I  found  that  out  of  87  kinds, 
64  germinated  after  an  immersion  of  28  days,  and  a  few 
survived  an  immersion  of  137  days.  It  deserves  notice 
that  certain  orders  were  far  more"  affected  than  others ; 
nine  Leguminosse  were  tried,  and  with  one  exception  all 
resisted  the  salt-water  badly :  seven  species  of  the  allied 
orders  Hydrophyllaceae  and  Polemoniacese  were  killed 
by  a  month's  immersion.  For  convenience'  sake  I  chiefly 
tried  small  seeds,  without  the  capsule  or  fruit ;  and 
as  all  of  these  sank  in  a  few  days,  they  could  not 
be  floated  across  wide  spaces  of  the  sea,  whether  or 
not  they  were  injured  by  the  salt-water.  Afterwards  I 
tried  some  larger  fruits,  capsules,  &c.,  and  some  of  these 
floated  for  a  long  time.  It  is  well  known  Avhat  a  difference 
there  is  in  the  buoyancy  of  green  and  seasoned  timber ; 
and  it  occurred  to  me  that  floods  might  wash  down  plants 
or  branches,  and  that  these  might  be  dried  on  the  banks, 
and  then  by  a  fresh  rise  in  the  stream  be  washed  into  the 
sea.  Hence  I  was  led  to  dry  stems  and  branches  of  94 
plants  with  ripe  fniit,  and  to  place  them  on  sea  water. 
The  majority  sank  quickly,  but  some  which  w^hilst  green 
floated  for  a  very  short  time,  when  dried  floated  much 
longer ;  for  instance,  ripe  hazel-nuts  sank  immediately, 
but  when  dried,  they  floated  for  90  days  and  afterwards 
when  planted  they  germinated  ;  an  asparagus  plant  with 
ripe  berries  floated  for  23  days,  when  dried  it  floated  for 
85  days,  and  the  seeds  afterwards  germinated :  the  ripe 
seeds  of  Helosciadium  sank  in  two  days,  when  dried  they 
floated  for  above  90  days,  and  afterwards  germinated. 
Altogether  out  of  the  94  dried  plants,  18  floated  for  above 
28  days,  and  some  of  the  18  floated  for  a  very  much  longer 
period.  So  that  as  f  ^  seeds  germinated  after  an  immer- 
sion of  28  days ;  and  as  ^f  plants  with  ripe  fruit  (but  not 
all  the  same  species  as  in  the  foregoing  experiment)  floated, 
after  being  dried,  for  above  28  days,  as  far  as  we  may  infer 
anything  from  these  scanty  facts,  we  may  conclude  that 
the  seeds  of  yVo  plants  of  any  country  might  be  floated 
by  sea-currents  during  28  days,  and  would  retain  their 
power  of  germination.  In  Johnston's  Physical  Atlas,  the 
average  rate  of  the  several  Atlantic  currents  is  33  miles 


g-j^^  GEOGRAPHICAL  DISTRIBUTION.  [Chap.  XL 

per  diem  (some  currents  running  at  tlie  rate  of  60  miles  per 
diem) ;  on  this  average,  the  seeds  of  jW  plants  belonging 
to  one  country  might  be  floated  across  924  miles  of  sea  to 
another  country ;  and  when  stranded,  if  blown  to  a  fa- 
vourable spot  by  an  inland  gale,  they  would  germinate. 

Subsequently  to  my  experiments,  M.  Martens  tried 
similar  ones,  but  in  a  much  better  manner,  for  he  placed 
the  seeds  in  a  box  in  the  actual  sea,  so  that  they  were 
alternately  wet  and  exposed  to  the  air  like  really  floating 
plants.  He  tried  98  seeds,  mostly  difi'erent  from  mine ; 
but  he  chose  many  large  fruits  and  likewise  seeds  from 
plants  which  live  near  the  sea  ;  and  this  would  have 
favoured  the  average  length  of  their  flotation  and  of  their 
resistance  to  the  injurious  action  of  the  salt-water.  On 
the  other  hand  he  did  not  previously  dry  the  plants  or 
branches  with  the  fruit ;  and  this,  as  we  have  seen,  would 
have  caused  some  of  them  to  have  floated  much  longer. 
The  result  was  that  -^f  of  his  seeds  floated  for  42  days, 
and  were  then  capable  of  germination.  But  I  do  not 
doubt  that  plants  exposed  to  the  waves  would  float  for  a 
less  time  than  those  protected  from  violent  movement  as 
in  our  experiments.  Therefore  it  would  perhaps  be  safer 
to  assume  that  the  seeds  of  about  yVo  plants  of  a  flora, 
after  having  been  dried,  could  be  floated  across  a  sj^ace 
of  sea  900  miles  in  width,  and  would  then  germinate. 
The  fact  of  the  larger  fruits  often  floating  longer  than  the 
small,  is  interesting ;  as  plants  with  large  seeds  or  fruit 
could  hardly  be  transported  by  any  other  means  ;  and 
Alph.  de  Candolle  has  shown  that  such  plants  generally 
have  restricted  ranges. 

But  seeds  may  be  occasionally  transported  in  another 
manner.  Drift  timber  is  thrown  up  on  most  islands,  even 
on  those  in  the  midst  of  the  widest  oceans ;  and  the  natives 
of  the  coral-islands  in  the  Pacific,  procure  stones  for  their 
tools,  solely  from  the  roots  of  drifted  trees,  these  stones 
being  a  valuable  royal  tax.  I  find  on  examination,  that 
when  irregularly  shaped  stones  are  embedded  in  the  roots 
of  trees,  small  parcels  of  earth  are  very  frequently  enclosed 
in  their  interstices  and  behind  them, — so  perfectly  that 
Dot  a  particle  could  be  washed  away  in  the  longest  trans- 
port :    out  of  one  small  portion  of  earth  thus  completely/ 


Chap.  XL]  MEANS  OF  DISPERSAL.  g25 

enclosed  by  wood  in  an  oak  about  50  years  old,  three 
dicotyledonous  plants  germinated :  I  am  certain  of  the 
accuracy  of  this  observation.  Again,  I  can  show  that  the 
carcasses  of  birds,  when  floating  on  the  sea,  sometimes 
escape  being  immediately  devoured  ;  and  seeds  of  many 
kinds  in  the  crops  of  floating  birds  long  retain  their 
vitality  :  peas  and  vetches,  for  instance,  are  killed  by  even 
a  few  days'  immersion  in  sea-water ;  but  some  taken 
out  of  the  crop  of  a  pigeon,  which  had  floated  on  artificial 
salt-water  for  30  days,  to  my  surprise  nearly  all  germi- 
nated. 

Living  birds  can  hardly  fail  to  be  highly  efi'ective 
agents  in  the  transportation  of  seeds.  I  could  give  many 
facts  showing  how  frequently  birds  of  many  kinds  are 
blown  by  gales  to  vast  distances  across  the  ocean.  We 
may  I  think  safely  assume  that  under  such  circumstances 
their  rate  of  flight  would  often  be  35  miles  an  hour  ;  and 
some  authors  have  given  a  far  higher  estimate.  I  have 
never  seen  an  instance  of  nutritious  seeds  passing  through 
the  intestines  of  a  bird  ;  but  hard  seeds  of  fruit  will  pass 
uninjured  through  even  the  digestive  organs  of  a  turkey. 
In  the  course  of  two  months,  I  picked  up  in  my  garden 
12  kinds  of  seeds,  out  of  the  excrement  of  small  birds,  and 
these  seemed  perfect,  and  some  of  them,  which  I  tried, 
germinated.  But  the  following  fact  is  more  important : 
the  crops  of  birds  do  not  secrete  gastric  juice,  and  do  not 
in  the  least  injure,  as  I  know  by  trial,  the  germination  of 
seeds ;  now  after  a  bird  has  found  and  devoured  a  large 
supply  of  food,  it  is  positively  asserted  that  all  the  grains 
do  not  pass  into  the  gizzard  for  12  or  even  18  hours.  A 
bird  in  this  interval  might  easily  be  blown  to  the  distance 
of  500  miles,  and  hawks  are  known  to  look  out  for  tired 
birds,  and  the  contents  of  their  torn  crops  might  thus 
readily  get  scattered.  Mr.  Brent  informs  me  that  a  friend 
of  his  had  to  give  up  flying  carrier-pigeons  from  France 
to  England,  as  the  hawks  on  the  English  coast  destroyed 
so  many  on  their  arrival.  Some  hawks  and  owls  bolt 
their  prey  whole,  and  after  an  interval  of  from  twelve  to 
twenty  hours,  disgorge  pellets,  which,  as  I  know  from  ex- 
periments made  in  the  Zoological  Gardens,  include  seeds 
capable  of  germination.     Some  seeds  of  the  oat,  wheat, 


3Xg  GEOGRAPHICAL   DISTRIBUTION.  [Chap.  XI. 

millet,  canary,  liemjD,  clover,  and  beet  germinated  after 
having  been  from  twelve  to  twentj-one  hours  in  the 
stomachs  of  difierent  birds  of  prey ;  and  two  seeds  of 
beet  grew  after  having  been  thus  retained  for  two  days 
and  fourteen  hours.  Fresh-water  fish,  I  find,  eat  seeds  of 
many  land  and  water  plants  ;  fish  are  frequently  devoured 
by  birds,  and  thus  the  seeds  might  be  transported  from 
place  to  place.  I  forced  many  kinds  of  seeds  into  the 
stomachs  of  dead  fish,  and  then  gave  their  bodies  to  fish- 
ing-eagles, storks,  and  pehcans ;  these  birds  after  an  in- 
terval of  many  hours,  either  rejected  the  seeds  in  pellets 
or  passed  them  in  their  excrement ;  and  several  of  these 
seeds  retained  their  power  of  germination.  Certain  seeds, 
however,  were  always  killed  by  this  process. 

Although  the  beaks  and  feet  of  bii'ds  are  generally 
quite  clean,  I  can  show  that  earth  sometimes  adheres  to 
them  ;  in  one  instance  I  removed  twenty-two  grains  of 
dry  argillaceous  earth  from  one  foot  of  a  partridge,  and  in 
this  earth  there  was  a  pebble  quite  as  large  as  the  seed  of 
a  vetch.  Thus  seeds  might  occasionally  be  transported  to 
great  distances ;  for  many  facts  could  be  given  showing 
that  soil  almost  everywhere  is  charged  with  seeds.  Re- 
flect for  a  moment  on  the  millions  of  quails  which  annual- 
ly cross  the  Mediterranean;  and  can  we 'doubt  that  the 
earth  adhering  to  their  feet  would  sometimes  include  a  few 
minute  seeds  ?  But  I  shall  presently  have  to  recur  to  this 
subject. 

As  icebergs  are  known  to  be  sometimes  loaded  with 
earth  and  stones,  and  have  even  carried  brushwood,  bones, 
and  the  nest  of  a  land-bird,  I  can  hardly  doubt  that  they 
must  occasionally  have  transported  seeds  from  one  part  to 
another  of  the  arctic  and  antarctic  regions,  as  suggested 
by  Lyell ;  and  during  the  Glacial  period  from  one  part  of 
the  now  temperate  regions  to  another.  In  the  Azores, 
from  the  large  number  of  the  species  of  plants  common 
to  Europe,  in  comparison  with  the  plants  of  other  oceanic 
islands  nearer  to  the  mainland,  and  (as  remarked  by  Mr. 
H.  C.  Watson)  from  the  somewhat  northern  character  of 
the  flora  in  comparison  with  the  latitude,  I  suspected  that 
these  islands  had  been  partly  stocked  by  ice-bome  seeds, 


Chap.  XL]  MEANS   OF  DISPERSAL.  3JL7 

during  the  Glacial  epoch.  At  my  request  Sir  C.  Lyell 
wrote  to  M.  Hartung  to  inquire  whether  he  had  observed 
erratic  boulders  on  these  islands,  and  he  answered  that  he 
had  found  large  fragments  of  granite  and  other  rocks, 
which  do  not  occur  in  the  archipelago.  Hence  we  may 
safely  infer  that  icebergs  formerly  landed  their  rocky  bur- 
thens on  the  shores  of  these  mid-ocean  islands,  and  it  is  at 
least  possible  that  they  may  have  brought  thither  the 
seeds  of  northern  plants. 

Considering  that  the  several  above  means  of  transport, 
and  that  several  other  means,  which  without  doubt  remain 
to  be  discovered,  have  been  in  action  year  after  year,  for 
centuries  and  tens  of  thousands  of  years,  it  would  I  think 
be  a  marvellous  fact  if  many  plants  had  not  thus  become 
widely  transported.  These  means  of  transport  are  some- 
times called  accidental,  but  this  is  not  strictly  correct : 
the  currents  of  the  sea  are  not  accidental,  nor  is  the  direc- 
tion of  prevalent  gales  of  wind.  It  should  be  observ- 
ed that  scarcely  any  means  of  transport  would  carry  seeds 
for  very  great  distances  ;  for  seeds  do  not  retain  their  vi- 
tality when  exposed  for  a  great  length  of  time  to  the 
action  of  sea-water  ;  nor  could  they  be  long  carried  in  the 
crops  or  intestines  of  birds.  These  means,  however,  would 
suliice  for  occasional  transport  across  tracts  of  sea  some 
hundred  miles  in  breadth,  or  from  island  to  island,  or  from 
a  continent  to  a  neighbouring  island,  but  not  from  one 
distant  continent  to  another.  The  floras  of  distant  conti- 
nents would  not  by  such  means  become  mingled  in  any 
great  degree ;  but  would  remain  as  distinct  as  we  now 
see  them  to  be.  The  currents,  from  their  course,  would 
never  bring  seeds  from  E'orth  America  to  Britain,  though 
they  might  and  do  bring  seeds  from  the  West  Indies  to 
our  western  shores,  where,  if  not  killed  by  so  long  an  im- 
mersion in  salt-water,  they  could  not  endure  our  climate. 
Almost  every  year,  one  or  two  land-birds  are  blown  across 
the  whole  Atlantic  Ocean,  from  ^North  America  to  the 
western  shores  of  Ireland  and  England  ;  but  seeds  could 
be  transported  by  these  wanderers  only  by  one  means, 
namely,  in  dirt  sticking  to  their  feet,  which  is  in  itself  a 
rare  accident.     Even  in  this  case,  how  small  would  the 


f 

3][^g  GEOGRAPHICAL   DISTRIBUTIOIT,  [CnAP.  XI. 

chance  be  of  a  seed  falling  on  favourable  soil,  and  coming 
to  maturity  ?  But  it  would  be  a  great  error  to  argue  that 
because  a  well-stocked  island,  like  Great  Britain,  has  not, 
as  far  as  is  known  (and  it  would  be  very  difficult  to  prove 
this),  received  within  the  last  few  centuries,  through  occa- 
sional means  of  transport,  immigrants  from  Europe  or  any 
other  continent,  that  a  poorly-stocked  island,  thougn 
standing  more  remote  from  the  mainland,  would  not  re- 
ceive colonists  by  similar  means.  I  do  not  doubt  that  out 
of  twenty  seeds  or  animals  transported  to  an  island,  even 
if  far  less  well-stocked  than  Britain,  scarcely  more  than 
one  would  be  so  well  fitted  to  its  new  home,  as  to  become 
naturalised.  But  this,  as  it  seems  to  me,  is  no  valid  argu- 
ment against  what  would  be  efi'ected  by  occasional  means 
of  transport,  during  the  long  lapse  of  geological  time, 
whilst  an  island  was  being  upheaved  and  formed,  and  be- 
fore it  had  become  fully  stocked  with  inhabitants.  On 
almost  bare  land,  with  few  or  no  destructive  insects  or 
birds  living  there,  nearly  every  seed,  which  chanced  to 
arrive,  would  be  sure  to  germinate  and  survive. 

Dispersal  during  the  Glacial  period. — ^The  identity  of 
many  plants  and  animals,  on  mountain-summits,  sepa- 
rated from  each  other  by  hundreds  of  miles  of  lowlands, 
where  the  Alpine  species  could  not  possibly  exist,  is  one 
of  the  most  striking  cases  known  of  the  same  species  living 
at  distant  points,  without  the  apparent  possibiHty  of  their 
having  migrated  from  one  to  the  other.  It  is  indeed  a 
remarkable  fact  to  see  so  many  of  the  same  plants  living 
on  the  snowy  regions  of  the  Alps  or  Pyrenees,  and  in  the 
extreme  northern  parts  of  Europe  ;  but  it  is  far  more  re- 
markable, that  the  plants  on  the  White  Mountains,  in  the 
United  States  of  America,  are  all  the  same  with  those  of 
Labrador,  and  nearly  all  the  same,  as  we  hear  from  Asa 
Gray,  with  those  on  the  loftiest  mountains  of  Europe. 
Even  as  long  ago  as  1747,  such  facts  led  Gmelin  to  con- 
clude that  the  same  sj^ecies  must  have  been  independently 
created  at  several  distinct  points  ;  and  we  might  have  re- 
mained in  this  same  belief,  had  not  Agassiz  and  others 
called  vivid  attention  to  the  Glacial  period,  which,  as  we 


Cfap.  XL]  DURING   THE    GLACIAL   PERIOD.  3-^9 

shall  immediately  see,  affords  a  simple  explanation  of 
these  facts.  We  have  evidence  of  almost  every  conceiv- 
able kind,  organic  and  inorganic,  that  within  a  very 
recent  geological  period,  central  Europe  and  JSTorth 
America  suffered  under  an  Arctic  climate.  The  ruins 
of  a  house  burnt  by  fire  do  not  tell  their  tale  more 
plainly,  than  do  the  mountains  of  Scotland  and  Wales, 
with  their  scored  flanks,  polished  surfaces,  and  perched 
boulders,  of  the  icy  streams  with  which  their  valleys 
were  lately  filled.  So  greatly  has  the  climate  of  Europe 
changed,  that  in  ]^orthern  Italy,  gigantic  moraines,  left 
by  old  glaciers,  are  now  clothed  by  the  vine  and  maize. 
Throughout  a  large  part  of  the  TJnited  States,  erratic 
boulders,  and  rocks  scored  by  drifted  icebergs  and  coast- 
Ice,  plainly  reveal  a  former  cold  period. 

The  former  influence  of  the  glacial  climate  on  the  dis- 
tribution of  the  inhabitants  of  Europe,  as  explained  with 
remarkable  clearness  by  Edward  Forbes,  is  substantially 
as  follows.  But  we  shall  follow  the  changes  more  readily, 
by  supposing  a  new  glacial  period  to  come  slowly  on,  and 
then  pass  aw^ay,  as  formerly  occurred.  As  the  cold  came 
on,  and  as  each  more  southern  zone  became  fitted  for  arc- 
tic beings  and  ill-fitted  for  their  former  more  temperate 
inhabitants,  the  latter  would  be  supplanted  and  arctic 
productions  would  take  their  places.  The  inhabitants  of 
the  more  temperate  regions  would  at  the  same  time  travel 
southward,  unless  they  were  stopped  by  barriers,  in  which 
case  they  would  perish.  The  mountains  would  become 
covered  with  snow  and  ice,  and  their  former  Alpine  in- 
habitants would  descend  to  the  plains.  By  the  time  that 
the  cold  had  reached  its  maximum,  we  should  have  a  uni' 
form  arctic  fauna  and  flora,  covering  the  central  parts  of 
Europe,  as  far  south  as  the  Alps  and  Pyrenees,  and  even 
stretching  into  Spain.  The  now  temperate  regions  of  the 
United  States  would  likewise  be  covered  by  arctic  plants 
and  animals,  and  these  would  be  nearly  the  same  witli 
those  of  Europe  ;  for  the  present  circumpolar  inhabitants, 
which  we  suppose  to  have  everywhere  travelled  south- 
ward, are  remarkably  uniform  round  the  world.  We 
may  suppose  that  the  Glacial  period  came  on  a  little 


320  GEOGRAPHICAL   DISTRIBUTION,  [Chap.  XL 

earlier  or  later  in  ISTorth  America  than  in  Europe,  so  will 
the  southern  migration  there  have  been  a  little  earlier  or 
later  ;  but  this  will  make  no  difference  in  the  final  result. 

As  the  warmth  returned,  the  arctic  forms  would  re- 
treat northward,  closely  followed  up  in  their  retreat  by  the 
productions  of  the  more  temperate  regions.  And  as  the 
snow  melted  from  the  bases  of  the  mountains,  the  arctic 
forms  would  seize  on  the  cleared  and  thawed  ground,  al- 
ways ascending  higher  and  higher,  as  the  warmth  in- 
creased, whilst  their  brethren  were  pursuing  their  north- 
ern journey.  Hence,  when  the  warmth  had  fully  returned, 
the  same  arctic  species,  which  had  lately  lived  in  a  body 
together  on  the  lowlands  of  the  Old  and  !New  Worlds^ 
would  be  left  isolated  on  distant  mountain-summits  (having 
been  exterminated  on  all  lesser  heights)  and  in  the  arctic 
regions  of  both  hemispheres. 

Thus  we  can  understand  the  identity  of  many  plants 
at  points  so  immensely  remote  as  on  the  mountains  of  the 
United  States  and  of  Europe.  We  can  thus  also  under- 
stand the  fact  that  the  Alj)ine  plants  of  each  mountain- 
range  are  more  especially  related  to  the  arctic  forms  living 
due  north  or  nearly  due  north  of  them  :  for  the  migration 
as  the  cold  came  on,  and  the  re-migration  on  the  returning 
warmth,  will  generally  have  been  due  south  and  north. 
The  Alpine  plants,  for  example,  of  Scotland,  as  remarked 
by  Mr  H.  C.  "Watson,  and  those  of  the  Pyrenees,  as  re- 
marked by  Ramond,  are  more  especially  allied  to  the 
plants  of  northern  Scandinavia ;  those  of  the  United 
States  to  Labrador  ;  those  of  the  mountains  of  Siberia  to 
the  arctic  regions  of  that  country.  These  views,  grounded 
as  they  are  on  the  perfectly  well-ascertained  occurrence 
of  a  former  Glacial  period,  seem  to  me  to  explain  in  so 
satisfactory  a  manner  the  present  distribution  of  the  Al- 
pine and  Arctic  productions  of  Europe  and  America,  that 
when  in  other  regions  we  find  the  same  species  on  distant 
mountain-summits,  we  may  also  conclude  without  other 
evidence,  that  a  colder  climate  permitted  their  former 
migration  across  the  low  intervening  tracts,  since  become 
too  warm  for  theii'  existence. 

If  the  climate,  since  the  Glacial  period,  has  ever  been 


Chap.  XI.]  DURING   THE   GLACIAL   PERIOD.  321 

ill  any  degree  warmer  than  at  present  (as  some  geologists 
in  the  United  States  believe  to  have  been  the  case,  chiefly 
from  the  distribution  of  the  fossil  Gnathodou),  then  the 
arctic  and  temperate  productions  will  at  a  very  late  period 
have  marched  a  little  further  north,  and  subsequently 
have  retreated  to  their  present  homes ;  but  I  have  met 
with  no  satisfactory  evidence  with  respect  to  this  inter- 
calated slightly  warmer  period,  since  the  Glacial  period. 

The  arctic  forms,  during  their  long  southern  migration 
and  re-migration  northward,  will  have  been  exposed  to 
nearly  the  same  climate,  and,  as  is  especially  to  be  noticed, 
they  will  have  kept  in  a  body  together ;  consequently 
their  mutual  relations  will  not  have  been  much  disturbed, 
and,  in  accordance  with  the  principles  inculcated  in  this 
volume,  they  will  not  have  been  liable  to  much  modifica- 
tion. But  with  our  Alpine  productions,  left  isolated  from 
the  moment  of  the  returning  warmth,  first  at  the  bases 
and  ultimately  on  the  summits  of  the  mountains,  the  case 
will  have  been  somewhat  different ;  for  it  is  not  likely 
that  all  the  same  arctic  species  will  have  been  left  on 
mountain  ranges  distant  from  each  other,  and  have  sur- 
vived there  ever  since ;  they  will,  also,  in  all  probability 
have  become  mingled  with  ancient  Alpine  species,  which 
must  have  existed  on  the  mountains  before  the  commence- 
ment of  the  Glacial  epoch,  and  which  during  its  coldest 
period  will  have  been  temporarily  driven  down  to  the 
plains ;  they  will,  also,  have  been  exposed  to  somewhat 
different  climatal  influences.  Their  mutual  relations  will 
thus  have  been  in  some  degree  disturbed ;  consequently 
they  will  have  been  liable  to  modification ;  and  this  we 
find  has  been  the  case;  for  if  we  compare  the  present 
Alpine  plants  and  animals  of  the  several  great  European 
mountain-ranges,  though  very  many  of  the  species  are 
identically  the  same,  some  present  varieties,  some  are 
ranked  as  doubtful  forms,  and  some  few  are  distinct  yet 
closely  allied  or  representative  species. 

In  illustrating  what,  as  I  believe,  actually  took  place 
during  the  Glacial  period,  I  assumed  that  at  its  com- 
mencement the  arctic  productions  were  as  uniform  round 
the  polar  regions  as  they  are  at  the  present  day.     But  the 


322.  GEOGRAPHICAL   DISTRIBUTION,  [Chap.  XI. 

foregoing  remarks  on  distribution  apply  not  only  to  strictly 
arctic  forms,  but  also  to  many  sub-arctic  and  to  some  few 
northern  temperate  forms,  for  some  of  these  are  the  same 
on  the  louver  mountains  and  on  the  plains  of  JSTorth 
America  and  Europe;  and.it  may  be  reasonably  asked 
how  I  account  for  the  necessary  degree  of  uniformity  of 
the  sub-arctic  and  northern  temperate  forms  round  the 
world,  at  the  commencement  of  the  Glacial  period.  At 
the  present  day,  the  sub-arctic  and  northern  temperate 
productions  of  the  Old  and  J^ew  Worlds  are  separated 
from  each  other  by  the  Atlantic  Ocean  and  by  the  ex- 
treme northern  part  of  the  Pacific.  During  the  Glacial 
period,  when  the  inhabitants  of  the  Old  and  Xew  "Worlds 
lived  further  southwards  than  at  present,  they  must  have 
been  still  more  completely  separated  by  wider  spaces  of 
ocean.  I  believe  the  above  difficulty  may  be  surmounted 
by  looking  to  still  earlier  changes  of  climate  of  an  oppo- 
site nature.  We  have  good  reason  to  believe  that  during 
the  newer  Pliocene  period,  before  the  Glacial  epoch,  and 
whilst  the  majority  of  the  inhabitants  of  the  world  were 
specifically  the  same  as  now,  the  climate  was  warmer  than 
at  the  present  day.  Hence  we  may  suppose  that  the  or- 
ganisms now  living  under  the  climate  of  latitude  60°, 
during  the  Pliocene  period  lived  further  north  under  the 
Polar  Circle,  in  latitude  66°-67°  ;  and  that  the  strictly 
arctic  productions  then  lived  on  the  broken  land  still 
nearer  to  the  pole.  Now  if  we  look  at  a  globe,  we  shall 
see  that  under  the  Polar  Circle  there  is  almost  continuous 
land  from  western  Europe,  through  Siberia,  to  eastern 
America.  And  to  this  continuity  of  the  circumpolar 
land,  and  to  the  consequent  freedom  for  inter -migration 
under  a  more  favourable  climate,  I  attribute  the  necessary 
amount  of  uniformity  in  the  sub-arctic  and  northern  tem^ 
perate  productions  of  the  Old  and  ISTew  Worlds,  at  a 
period  anterior  to  the  Glacial  epoch. 

Believing,  from  reasons  before  alluded  to,  that  our 
continents  have  long  remained  in  nearly  the  same  relative 
position,  though  subjected  to  large,  but  partial  oscillations 
of  level,  I  am  strongly  inclined  to  extend  the  above  view, 
and  to  infer  that  during  some  earlier  and  still  warmer  pe- 


Chap.  XI.]  DURING   THE    GLACIAL   PERIOD.  323 

riod,  such  as  the  older  Pliocene  period,  a  large  number  of 
the  same  plants  and  animals  inhabited  the  almost  contimi- 
ous  circnmpolar  land  ;  and  that  these  plants  and  animals, 
both  in  the  Old  and  New  Worlds,  began  slowly  to  migrate 
southwards  as  the  climate  became  less  warm,  long  before 
the  commencement  of  the  Glacial  period.  We  now  see, 
as  I  believe,  their  descendants,  mostly  in  a  modified  con- 
dition, in  the  central  parts  of  Europe  and  the  United 
States.  On  this  view  we  can  understand  the  relationship, 
with  very,  little  identity,  between  the  productions  of 
ISTorth  America  and  Europe, — a  relationship  which  is  most 
remarkable,  considering  the  distance  of  the  two  areas,  and 
their  separation  by  the  Atlantic  Ocean.  "We  can  further 
understand  the  singular  fact  remarked  on  by  several  ob- 
servers, that  the  productions  of  Europe  and  America 
during  the  later  tertiary  stages  were  more  closely  related 
to  each  other  than  they  are  at  the  present  time  ;  for  during 
these  warmer  j)eriods  the  northern  parts  of  the  Old  and 
New  Worlds  will  have  been  almost  continuously  united 
by  land,  serving  as  a  bridge,  since  rendered  impassable 
by  cold,  for  the  inter-migration  of  their  inhabitants. 

During  the  slowly  decreasing  warmth  of  the  Pliocene 
period,  as  soon  as  the  species  in  common,  which  inhabited 
the  New  and  Old  Worlds,  migrated  south  of  the  Polar 
Circle,  they  must  have  been  completely  cut  off  from  each 
other.  Tliis  separation,  as  far  as  the  more  temperate  pro- 
ductions are  concerned,  took  place  long  ages  ago.  And 
as  the  plants  and  animals  migrated  southward,  they  will 
have  become  mingled  in  the  one  great  region  with  the 
native  American  productions,  and  have  had  to  compete 
with  them ;  and  in  the  other  great  region,  with  those  of 
the  Old  AYorld.  Consequently  we  have  here  every-thing 
favourable  for  much  modification, — for  far  more  modifica- 
tion than  with  the  Alpine  productions,  left  isolated,  with- 
in a  much  more  recent  period,  on  the  several  mountain- 
ranges  and  on  the  arctic  lands  of  the  two  Worlds.  Hence 
it  has  come,  that  when  we  compare  the  now  living  pro- 
ductions of  the  temperate  regions  of  the  New  and  Old 
Worlds,  we  find  very  few  identical  species  (though  Asa 
Gray  has  lately  shown  that  more  plants  are  identical  than 
15 


024:  GEOGRAPHICAL   DISTRIBUTION,  [Chap   XL 

was  formerly  supposed),  but  we  find  in  every  great  class 
many  forms,  wliich  some  naturalists  rank  as  geographical 
races,  and  others  as  distinct  species  ;  and  a  host  of  closely 
allied  or  representative  forms  which  are  ranked  by  all  nat- 
uralists as  specifically  distinct. 

As  on  the  land,  so  in  the  waters  of  the  sea,  a  slow 
southern  migration  of  a  marine  fauna,  which  during  the 
Pliocene  or  even  a  somewhat  earlier  period,  was  nearly 
uniform  along  the  continuous  shores  of  the  Polar  Circle, 
will  account,  on  the  theory  of  modification,  for  many 
closely  allied  forms  now  living  in  areas  completely  sun- 
dered. Thus,  I  think,  we  can  understand  the  presence  of 
many  existing  and  tertiary  representative  forms  on  the 
eastern  and  western  shores  of  temperate  ISTorth  America  ; 
and  the  still  more  striking  case  of  many  closely  allied 
crustaceans  (as  described  in  Dana's  admirable  work),  of 
some  fish  and  other  marine  animals,  in  the  Mediterranean 
and  in  the  seas  of  Japan, — areas  now  separated  by  a  con- 
tinent and  by  nearly  a  hemisphere  of  equatorial  ocean. 

These  cases  of  relationship,  without  identity,  of  the  in- 
habitants of  seas  now  disjoined,  and  likewise  of  the  past 
and  present  inhabitants  of  the  temperate  lands  of  l^orth 
America  and  Europe,  are  inexplicable  on  the  theory  of 
creation.  We  cannot  say  that  they  have  been  created 
alike,  in  correspondence  with  the  nearly  similar  physical 
conditions  of  the  areas  ;  for  if  we  compare,  for  instance, 
certain  parts  of  South  America  with  the  southern  conti- 
nents of  the  Old  World,  we  see  countries  closely  corre- 
sponding in  all  their  physical  conditions,  but  with  their  in- 
habitants utterly  dissimilar. 

But  we  must  return  to  our  more  immediate  subject, 
the  Glacial  period.  I  am  convinced  that  Porbes's  view 
may  be  largely  extended.  In  Europe  we  have  the  plain- 
est evidence  of  the  cold  period,  from  the  western  shores 
of  Britain  to  the  Oural  range,  and  southward  to  the  Py- 
renees. We  may  infer,  from  the  frozen  mammals  and 
nature  of  the  mountain  vegetation,  that  Sibei'ia  was  simi- 
larly aff'ected.  Along  the  Himalaya,  at  points  900  miles 
apart,  glaciers  have  left  the  marks  of  their  former  low 
descent ;  and  in  Sikkim,  Pr,  Hooker  saw  maize  growing 


J 


Chap.  XL]  DURING   THE    GLACIAL   PERIOD.  325 

on  gigantic  ancient  moraines.  Sontli  of  the  equator,  we 
have  some  direct  evidence  of  former  glacial  action  in  ISTew 
Zealand  ;  and  the  same  plants,  found  on  widely  separated 
mountains  in  this  island,  tell  the  same  stoiy.  If  one  ac- 
count which  has  been  published  can  be  trusted,  we  have 
direct  evidence  of  glacial  action  in  the  south-eastern  cor- 
ner of  Australia. 

Looking  to  America  ;  in  the  northern  half,  ice-borne 
fragments  of  rock  have  been  observed  on  the  eastern  side 
as  far  south  as  lat.  36°-37°,  and  on  the  shores  of  the  Pa- 
cific, where  the  climate  is  now  so  difi'erent,  as  far  south 
as  lat.  46°  ;  erratic  boulders  have,  also,  been  noticed  on 
the  rocky  mountains.  In  the  Cordillera  of  Equatorial 
South  America,  glaciers  once  extended  far  below  their 
present  level.  In  central  Chile  I  was  astonished  at  the 
structure  of  a  vast  mound  of  detritus,  about  800  feet  in 
height,  crossing  a  valley  of  the  Andes  ;  and  this  I  now 
feel  convinced  was  a  gigantic  moraine,  left  far  below  any 
existing  glacier.  Further  south  on  both  sides  of  the  con- 
tinent, from  lat.  41°  to  the  southernmost  extremity,  we 
have  the  clearest  evidence  of  former  glacial  action,  in 
huge  boulders  transported  far  from  their  parent  source. 

"We  do  not  know  that  the  Glacial  epoch  was  strictly 
simultaneous  at  these  several  far-distant  points  on  opposite 
sides  of  the  world.  But  we  have  good  evidence  in  almost 
every  case,  that  the  epoch  was  included  within  the  latest 
geological  period.  We  have,  also,  excellent  evidence 
that  it  endured  for  an  enormous  time,  as  measured  by 
years,  at  each  point.  The  cold  may  have  come  on,  or 
have  ceased,  earlier  at  one  point  of  the  globe  than  at  an- 
other, but  seeing  that  it  endured  for  long  at  each,  and 
that  it  was  contemporaneous  in  a  geological  sense,  it  seems 
to  me  probable  that  it  was,  during  a  part  at  least  of 
the  period,  actually  simultaneous  throughout  the  world. 
Without  some  distinct  evidence  to  the  contrary,  we  may  at 
least  admit  as  probable  that  the  glacial  action  was  simul- 
taneous on  the  eastern  and  western  sides  of  ISTorth  Amer- 
ica, in  the  Cordillera  under  the  equator  and  under  the 
warmer  temperate  zones,  and  on  both  sides  of  the  south- 
ern extremity  of  the  continent.     If  this  be  admitted,  it  is 


326  GEOGRAPHICAL   DISTRIBUTION,  [Chap.  XL 

difficult  to  avoid  "believing  that  the  temperature  of  the 
whole  world  was  at  this  period  simultaneously  cooler. 
But  it  would  suffice  for  my  purpose,  if  the  temperature 
was  at  the  same  time  lower  along  certain  broad  belts  of 
longitude. 

On  this  view  of  the  whole  world,  or  at  least  of  broad 
longitudinal  belts,  having  been  simultaneously  colder  from 
pole  to  pole,  much  light  can  be  thrown  on  the  present 
distribution  of  identical  and  allied  species.  In  America, 
Dr.  Hooker  has  shown  that  between  forty  and  fifty  of  the 
flowering  plants  of  Tierra  del  Fuego,  forming  no  incon- 
siderable part  of  its  scanty  flora,  are  common  to  Europe, 
enormously  remote  as  these  two  points  are ;  and  there 
are  many  closely  allied  species.  On  the  lofty  mountains 
of  equatorial  America  a  host  of  peculiar  sj)ecies  belonging 
to  European  genera  occur.  On  the  highest  mountains  of 
Brazil,  some  few  European  genera  were  found  by  Gard- 
ner, which  do  not  exist  in  the  wide  intervening  hot  coun- 
tries. So  on  the  Silla  of  Caraccas  the  illustrious  Hum- 
boldt long  ago  found  species  belonging  to  genera  charac- 
teristic of  the  Cordillera.  On  the  mount^ns  of  Abyssinia, 
several  European  forms  and  some  few  representatives  of 
the  peculiar  flora  of  the  Cape  of  Good  Hope  occur.  At 
the  Cape  of  Good  Hope  a  very  few  European  sj)ecies,  be- 
lieved not  to  have  been  introduced  by  man,  and  on  the 
mountains,  some  few  representative  European  forms  are 
found,  which  have  not  been  discovered  in  the  intertropi- 
cal parts  of  Africa.  On  the  Himalaya,  and  on  the  isolat- 
ed mountain-ranges  of  the  peninsula  of  India,  on  the 
heights  of  Ceylon,  and  on  the  volcanic  cones  of  Java, 
many  plants  occur,  either  identically  the  same  or  repre- 
senting each  other,  and  at  the  same  time  representing 
plants  of  Europe,  not  found  in  the  intervening  hot  low- 
lands. A  list  of  the  genera  collected  on  the  loftier  peaks 
of  Java  raises  a  picture  of  a  collection  made  on  a  hill  in 
Europe  !  Still  more  striking  is  the  fact  that  southern 
Australian  forms  are  clearly  represented  by  plants  grow- 
ing on  the  summits  of  the  mountains  of  Borneo.  Some 
of  these  Australian  forms,  as  I  hear  from  Dr.  Hooker,  ex- 
tend along  the  heights  of  the  peninsula  of  Malacca,  and 


Chap.  XL]  DURING   THE    GLACIAL   PERIOD.  32^ 

are  thinly  scattered,  on  the  one  hand  over  India  and  on 
the  other  as  far  north  as  Japan. 

On  the  southern  mountains  of  Australia,  Dr.  F. 
Miiller  has  discovered  several  European  species  ;  other 
species,  not  introduced  by  man,  occur  on  the  lov\^lands  ; 
and  a  long  list  can  be  given,  as  I  am  informed  by  Dr. 
Hooker,  of  European  genera,  found  in  Australia,  but  not 
in  the  intermediate  torrid  regions.  In  the  admirable  '  In- 
troduction to  the  Flora  of  New  Zealand,'  by  Dr.  Hooker, 
analogous  and  striking  facts  are  given  in  regard  to  the 
plants  of  that  large  island.  Hence  we  see  that  through- 
out the  world,  the  plants  growing  on  the  more  lofty 
mountains,  and  on  the  temperate  lowlands  of  the  northern 
and  southern  hemispheres,  are  sometimes  identically  the 
same ;  but  they  are  much  oftener  specifically  distinct, 
though  related  to  each  other  in  a  most  remarkable 
manner. 

This  brief  abstract  applies  to  plants  alone  :  some  strict- 
ly analogous  facts  could  be  given  on  the  distribution  of 
terrestrial  animals.  In  marine  productions,  similar  cases 
occur  ;  as  an  example,  I  may  quote  a  remark  by  the  high- 
est authority.  Prof.  Dana,  that  "  it  is  certainly  a  wonderful 
fact  that  New  Zealand  should  have  a  closer  resemblance 
in  its  Crustacea  to  Great  Britain,  its  antipode,  than  to  any 
other  part  of  the  world."  Sir  J.  Kichardson,  also,  speaks 
of  the  re-appearance  on  the  shores  of  New  Zealand,  Tas- 
mania, (fee,  of  northern  forms  of  fish.  Dr.  Hooker  in- 
forms me  that  twenty-five  species  of  Algse  are  common  to 
New  Zealand  and  to  Europe,  but  have  not  been  found  in 
the  intermediate  tropical  seas. 

It  should  be  observed  that  the  northern  species  and 
forms  found  in  the  southern  parts  of  the  southern  hemi- 
sphere, and  on  the  mountain-ranges  of  the  intertropical 
regions,  are  not  arctic,  but  belong  to  the  northern  tempe- 
rate zones.  As  Mr.  H.  C.  Watson  has  recently  remarked, 
"  In  receding  from  polar  towards  equatorial  latitudes,  the 
Alpine  or  mountain  floras  really  become  less  and  less  arc- 
tic' Many  of  the  forms  living  on  the  mountains  of  the 
warmer  regions  of  the  earth  and  in  the  southern  hemi- 
sphere are  of  doubtful  value,  being  ranked  by  some  natu- 


328  GEOGRAPHICAL   DISTRIBUTION,  [Chap.  XI 

ralists  as  specifically  distinct,  by  others  as  varieties  ;  but 
some  are  certainly  identical,  and  many,  thongli  closely 
related  to  northern  forms,  must  be  ranked  as  distinct 
species. 

IS^ow  let  lis  see  what  light  can  be  thrown  on  the  fore- 
going facts,  on  the  belief,  supported  as  it  is  by  a  large 
body  of  geological  evidence,  that  the  whole  world,  or  a 
large  part  of  it,  was,  during  the  Glacial  period,  simulta- 
neously much  colder  than  at  present.  The  Glacial  period, 
as  measured  by  years,  must  have  been  very  long ;  and 
when  we  remember  over  what  vast  spaces  some  natural- 
ised plants  and  animals  have  spread  within  a  few  centu- 
ries, this  period  will  have  been  ample  for  any  amount  of 
migration.  As  the  cold  came  slowly  on,  all  tlie  tropical 
plants  and  other  productions  will  have  retreated  from  both 
sides  towards  the  equator,  followed  in  the  rear  by  the 
temperate  productions,  and  these  by  the  arctic  ;  but  with 
the  latter  we  are  not  now  concerned.  The  tropical  plants 
probably  suffered  much  extinction ;  how  much  no  one 
can  say  ;  perhaps  formerly  the  tropics  supported  as  many 
species  as  we  see  at  the  present  day  crowded  together  at 
the  Cape  of  Good  Hope,  and  in  parts  of  temperate  Aus- 
stralia.  As  we  know  that  many  troj)ical  plants  and  ani- 
mals can  withstand  a  considerable  amount  of  cold,  many 
might  have  escaped  extermination  during  a  moderate  fall 
of  temperature,  more  especially  by  escaping  into  the 
warmest  spots.  But  the  great  fact  to  bear  in  mind  is, 
that  all  tropical  productions  will  have  suffered  to  a  cer- 
tain extent.  On  the  other  hand,  the  temperate  produc- 
tions, after  migrating  nearer  to  the  equator,  though  they 
will  have  been  placed  under  somewhat  new  conditions, 
will  have  suffered  less.  And  it  is  certain  that  many  tem- 
perate plants,  if  protected  from  the  inroads  of  competi 
tors,  can  withstand  a  much  warmer  climate  than  their 
own.  Hence,  it  seems  to  me  possible,  bearing  in  mind 
that  the  tropical  productions  were  in  a  suffering  state  and 
could  not  have  presented  a  firm  front  against  intruders, 
that  a  certain  number  of  the  more  vigorous  and  dominant 
temperate  forms  might  have  penetrated  the  native  ranks, 
and  have  reached  or  even  crossed  the  equar(/i.     The  in- 


Chap.  XI.]  DURING   THE   GLACIAL   PERIOD.  329 

Yasion  would,  of  course,  have  been  greatly  favoured  hj 
high  land,  and  perhaps  by  a  dry  climate  ;  for  Dr.  Fal- 
coner informs  me  that  it  is  the  damp,  with  the  heat  of  the 
tropics,  which  is  so  destructive  to  perennial  plants  from  a 
temperate  climate.  On  the  other  hand,  the  most  humid 
and  hottest  districts  will  have  afforded  an  asylum  to  the 
tropical  natives.  The  mountain-ranges  north-west  of  the 
Himalaya,  and  the  long  line  of  the  Cordillera,  seem  to 
have  afforded  two  great  lines  of  invasion  :  and  it  is  a 
striking  fact,  lately  communicated  to  me  by  Dr.  Hooker, 
that  all  the  flowering  plants,  about  forty-six  in  number, 
common  to  Tierra  del  Fuego  and  to  Europe  still  exist  in 
North  America,  which  must  have  lain  on  the  line  of 
march.  But  I  do  not  doubt  that  some  temperate  produc- 
tions entered  and  crossed  even  the  lowlands  of  the  tropics 
at  the  period  when  the  cold  was  most  intense, — when  arc- 
tic forms  had  migrated  some  twenty-five  degi'ees  of  lati- 
tude from  their  native  country  and  covered  the  land  at 
the  foot  of  the  Pyrenees.  At  this  period  of  extreme  cold, 
I  beheve  that  the  climate  under  the  equator  at  the  level 
of  the  sea  was  about  the  same  with  that  now  felt  there  at 
the  height  of  six  or  seven  thousand  feet.  During  this  the 
coldest  period,  I  suppose  that  large  spaces  of  the  tropical 
lowlands  were  clothed  with  a  mingled  tropical  and  tem- 
perate vegetation,  like  that  now  growing  with  strange 
luxuriance  at  the  base  of  the  Himalaya,  as  graphically  de- 
scribed by  Hooker. 

Thus,  as  I  believe,  a  considerable  number  of  plants,  a 
few  terrestrial  animals,  and  some  marine  productions,  mi- 
grated during  the  Glacial  period  from  the  northern  and 
southern  temperate  zones  into  the  intertropical  regions, 
and  some  even  crossed  the  equator.  As  the  warmth  re- 
turned, these  temperate  forms  would  naturally  ascend 
the  higher  mountains,  being  exterminated  on  the  low- 
lands ;  those  which  had  not  reached  the  equator,  would 
re-migrate  northward  or  southward  towards  their  former 
homes  ;  but  the  forms,  chiefly  northern,  which  had  crossed 
the  equator,  would  travel  still  further  from  their  homes 
into  the  more  temperate  latitudes  of  the  opposite  hemi- 
sphere.    Although  we  have  reason  to  believe  from  geo- 


QQQ  GEOGRAPHICAL   DISTRIBUTION",  [Chap.  XL 

logical  evidence  tliat  the  whole  body  of  arctic  shells  imder- 
went  scarcely  any  modification  during  their  long  southern 
migration  and  re-migration  northward,  the  case  may  have 
been  wholly  different  with  those  intruding  forms  which 
settled  themselves  on  the  intertropical  mountains,  and  in 
the  southern  hemisphere.  These  being  surrounded  by 
strangers  will  have  had  to  compete  with  many  new  forms 
of  life ;  and  it  is  probable  that  selected  modifications  in 
their  structure,  habits,  and  constitutions  will  have  profited 
them.  Thus  many  of  these  wanderers,  though  still  j)]ainly 
related  by  inheritance  to  their  brethren  of  the  northern 
or  southern  hemispheres,  now  exist  in  their  new  homes  as 
well-marked  varieties  or  as  distinct  species. 

It  is  a  remarkable  fact,  strongly  insisted  on  by  Hooker 
in  regard  to  America,  and  by  Alph.  de  Candolle  in  re- 
gard to  Australia,  that  many  more  identical  plants  and 
allied  forms  have  apparently  migrated  from  the  north  to 
the  south,  than  in  a  reversed  direction.  We  see,  how- 
ever, a  few  southern  vegetable  forms  'on  the  mountains  of 
Borneo  and  Abyssinia.  I  suspect  that  this  prcjDonderant 
migration  from  north  to  south  is  due  to  the  greater  extent 
of  land  in  the  north,  and  to  the  northern  forms  having 
existed  in  their  own  homes  in  greater  numbers,  and  hav- 
ing consequently  been  advanced  through  natural  selection 
and  competition  to  a  higher  stage  of  perfection  or  domi- 
nating power,  than  the  southern  forms.  And  thus,  when 
they  became  commingled  during  the  Glacial  period,  the 
northern  forms  were  enabled  to  beat  the  less  2^o"^erful 
southern  forms.  Just  in  the  same  manner  as  we  see  at 
the  present  day,  that  very  many  European  productions 
cover  the  ground  in  La  Plata,  and  in  a  lesser  degree  in 
Australia,  and  have  to  a  certain  extent  beaten  the  natives; 
whereas  extremely  few  southern  forms  have  become  nat- 
uralised in  any  j^art  of  Europe,  though  hides,  wool,  and 
other  objects  likely  to  carry  seeds,  have  been  largely  im- 
ported into  Europe  during  the  last  two  or  three  centuries 
from  La  Plata,  and  during  the  last  thirty  or  forty  years 
from  Australia.  Something  of  the  same  kind  must  have 
occurred  on  the  intertropical  mountains  :  no  doubt  before 
the  Glacial  period  they  were  stocked  with  endemic  Alpine 


Chap,  Xl.J  DUUmG   THE   GLACIAL   PERIOD.  33J 

forms  ;  but  these  have  almost  everywhere  largely  yielded 
to  the  more  dominant  forms,  generated  in  the  larger  areas 
and  more  efficient  workshops  of  the  north.  In  many  isl- 
ands the  native  productions  are  nearly  equalled  or  even 
outnumbered  by  the  naturalised  ;  and  if  the  natives  have 
not  been  actually  exterminated,  their  numbers  have  been 
greatly  reduced,  and  this  is  the  first  stage  towards  ex- 
tinction. A  mountain  is  an  island  on  the  land  ;  and  the 
intertropical  mountains  before  the  Glacial  period  must 
have  been  completely  isolated ;  and  I  believe  that  the 
productions  of  these  islands  on  the  land  yielded  to  those 
produced  within  the  larger  areas  of  the  north,  just  in  the 
same  way  as  the  productions  of  real  islands  have  every- 
where lately  yielded  to  continental  forms,  naturalised  by 
man's  agency. 

I  am  far  from  supposing  that  all  difficulties  are  re- 
moved on  the  view  here  given  in  regard  to  the  range  and 
affinities  of  the  allied  species  v^hich  live  in  the  northern 
and  southern  temperate  zones  and  on  the  mountains  of 
the  intertropical  regions.  Yery  many  difficulties  remain 
to  be  solved.  I  do  not  pretend  to  indicate  the  exact  lines 
and  means  of  migration,  or  the  reason  why  certain  spe- 
cies and  not  others  have  migrated  ;  why  certain  species 
have  been  modified  and  have  given  rise  to  new  groups  of 
forms,  and  others  have  remained  unaltered.  We  cannot 
hope  to  explain  such  facts,  until  we  can  say  why  one  spe- 
cies and  not  another  becomes  naturalised  by  man's  agency 
in  a  foreign  land  ;  why  one  ranges  twice  or  thrice  as  far, 
and  is  twice  or  thrice  as  common,  as  another  species 
within  their  own  homes. 

I  have  said  that  many  difficulties  remain  to  be  solved : 
some  of  the  most  remarkable  are  stated  with  admirable 
clearness  by  Dr.  Hooker  in  his  botanical  works  on  the 
antarctic  regions.  These  cannot  be  here  discussed.  I 
will  only  say  that  as  far  as  regards  the  occurrence  of 
identical  species  at  points  so  enormously  remote  as  Ker- 
guelen  Land,  New  Zealand,  and  Fuegia,  I  believe  that 
towards  the  close  of  the  Glacial  period,  icebergs,  as 
suggested  by  Lyell,  have  been  largely  concerned  in  their 
dispersal.  But  the  existence  of  several  quite  distinct 
15* 


332  GEOGRAPHICAL   DISTRIBUTION,  [Chap.  XI 

species,  belonging  to  genera  exclusively  confined  to  the 
south,  at  these  and  other  distant  points  of  the  southern 
hemisphere,  is,  on  my  theory  of  descent  with  modification, 
a  far  more  remarkable  case  of  difiiculty.  For  some  of 
these  species  are  so  distinct,  that  we  cannot  suppose  that 
there  has  been  time  since  the  commencement  of  the  Glacial 
period  for  their  migration,  and  for  their  subsequent  modi- 
fication to  the  necessary  degree.  The  facts  seem  to  me  to 
indicate  that  peculiar  and  very  distinct  species  have 
migrated  in  radiating  lines  from  some  common  centre  ; 
and  I  am  inclined  to  look  in  the  southern,  as  in  the  north- 
ern hemisphere,  to  a  former  and  warmer  period,  before 
the  commencement  of  the  Glacial  period,  when  the  an- 
tarctic lands,  now  covered  with  ice,  supported  a  highly 
peculiar  and  isolated  flora.  I  suspect  that  before  this  flora 
was  exterminated  by  the  Glacial  epoch,  a  few  forms  were 
widely  dispersed  to  various  points  of  the  southern  hemi- 
sphere by  occasional  means  of  transport,  and  by  the  aid, 
as  halting-places,  of  existing  and  now  sunken  islands,  and 
perhaps  at  the  commencement  of  the  Glacial  period,  by 
icebergs.  By  these  means,  as  I  believe,  the  southern 
shores  of  America,  Australia,  New  Zealand,  have  become 
slightly  tinted  by  the  same  peculiar  forms  of  vegetable 
life. 

Sir  C.  Lyell  in  a  striking  passage  has  speculated,  in 
language   almost   identical  with  mine,  on  the  efi'ects  of 

freat  alternations  of  climate  on  geographical  distribution, 
believe  that  the  world  has  recently  felt  one  of  his  great 
cycles  of  change ;  and  that  on  this  view,  combined  with 
modification  through  natural  selection,  a  multitude  of 
facts  in  the  present  distribution  both  of  the  same  and  of 
allied  forms  of  life  can  be  explained.  The  living  waters 
may  be  said  to  have  flowed  during  one  short  period  from 
the  north  and  from  the  south,  and  to  have  crossed  at  the 
equator  ;  but  to  have  flowed  with  greater  force  from  the 
north  so  as  to  have  freely  inundated  the  south.  As  the 
tide  leaves  its  drift  in  horizontal  lines,  though  rising  higher 
on  the  shores  where  the  tide  rises  highest,  so  liave  the 
living  waters  left  their  living  drift  on  our  mountain- 
Bummits,  in  a  line  gently  rising  from  the  arctic  lowlands 


Chap.  XI.]  DURING   THE    GLACIAL   PERIOD.  333 

to  a  great  height  under  the  equator.  The  various  beings 
thus  left  stranded  may  be  compared  with  savage  races  of 
man,  driven  up  and  surviving  in  the  mountain-fastnesses 
of  almost  every  land,  which  serve  as  a  record,  full  of 
interest  to  us,  of  the  former  inhabitants  of  the  surround- 
ing lowlands. 


334  GEOGRAPHICAL  DISTRIBUTION.  [Chap.  XIL 


CHAPTEB   XII, 

GEOGRAPHICAL  DISTRIBUTION — Continued. 

Distribution  of  frcBli-water  productions — On  the  inhabitants  of  oceanic  islands — Ab» 
eence  of  Batrachiails  and  of  terrestrial  mammals — On  the  relation  of  the  inhabit- 
ants of  islands  to  those  of  the  nearest  mainland — On  colonisation  from  the  nearest 
source  with  subsequent  modification — Summary  of  the  last  and  present  chap- 
ters. 

As  lakes  and  river-systems  are  separated  from  eacli  other 
by  barriers  of  land,  it  might  have  been  tbonglit  that  fresh- 
water productions  wonld  not  have  ranged  widely  within 
the  same  country,  and  as  the  sea  is  apparently  a  still  more 
impassable  barrier,  that  they  never  would  have  extended 
to  distant  countries.  But  the  case  is  exactly  the  reverse. 
IS^ot  only  have  many  fresh-water  species,  belonging  to 
quite  different  classes,  an  enormous  range,  but  allied  spe- 
cies prevail  in  a  remarkable  manner  throughout  the 
world.  I  well  remember,  when  first  collecting  in  the 
fresh  waters  of  Brazil,  feeling  much  surprise  at  the  simi- 
larity of  the  fresh-water  insects,  shells,  &c.,  and  at  the 
dissimilarity  of  the  surrounding  terrestrial  beings,  com- 
pared with  those  of  Britain. 

But  this  power  in  fresh- water  productions  of  ranging 
widely,  though  so  unexjDected,  can,  I  think,  in  most  cases 
be  explained  by  their  having  become  fitted,  in  a  manner 
highly  useful  to  them,  for  short  and  frequent  migrations 
from  pond  to  pond,  or  from  stream  to  stream  ;  and  liabil- 
ity to  wide  dispersal  would  follow  from  this  capacity  as 
an  almost  necessary  consequence.  We  can  here  consider 
only  a  few  cases.  In  regard  to  fish,  I  believe  that  the 
same  species  never  occur  in  the  fresh  waters  of  distant 
continents.  But  on  the  same  continent  the  species  often 
range  widely  and  almost  capriciously ;    for  two  river- 


Chap.  XIl.l  FRESH- WATER   tROBtlCTlONS.  33^ 

systems  will  have  some  fish  in  common  and  some  different. 
A  few  facts  seem  to  favour  tlie  possibility  of  their  occa- 
sional transport  by  accidental  means  ;  like  that  of  the 
live  fish  not  rarely  dropped  by  whirlwinds  in  India,  and 
the  vitality  of  their  ova  when  removed  from  the  water. 
But  I  am  inclined  to  attribute  the  dispersal  of  fresh- water 
fish  mainly  to  slight  changes  within  the  recent  period  in 
the  level  of  the  land,  having  caused  rivers  to  flow  into 
each  other.  Instances,  also,  could  be  given  of  this  having 
occurred  during  floods,  without  any  change  of  level.  We 
have  evidence  in  the  loess  of  the  Rhine  of  considerable 
changes  of  level  in  the  land  within  a  very  recent  geolog- 
ical period,  and  when  the  surface  was  peopled  by  existing 
land  and  fresh-water  shells.  Tlie  wide  difi'erence  of  the 
fish  on  opposite  sides  of  continuous  mountain-ranges, 
which  from  an  early  period  must  have  parted  river-systems 
and  completely  prevented  their  inosculation,  seems  to  lead 
to  this  same  conclusion.  With  respect  to  allied  fresh- 
water fish  occurring  at  very  distant  points  of  the  world, 
no  doubt  there  are  many  cases  which  cannot  at  present 
be  explained  :  but  some  fresh-water  fish  belong  to  very 
ancient  forms,  and  in  such  cases  there  will  have  been 
ample  time  for  great  geographical  changes,  and  conse- 
quently time  and  means  for  much  migration.  In  the 
second  place,  salt-water  fish  can  with  care  be  slowly 
accustomed  to  live  in  fresh  water ;  and,  according  to 
Yalenciennes,  there  is  hardly  a  single  group  of  fishes 
confined  exclusively  to  fresh  water,  so  that  we  may  imagine 
that  a  marine  member  of  a  fresh- water  group  might  travel 
far  along  the  shores  of  the  sea,  and  subsequently  become 
modified  and  adapted  to  the  fresh  waters  of  a  distant 
land. 

Some  species  of  fresh-water  shells  have  a  very  wide 
range,  and  allied  species,  which,  on  my  theory,  are  de- 
scended from  a  common  parent  and  must  have  proceeded 
from  a  single  source,  prevail  throughout  the  world.  Their 
distribution  at  first  perplexed  me  much,  as  their  ova  are 
not  likely  to  be  transported  by  birds,  and  they  are  imme- 
diately killed  by  sea-water,  as  are  the  adults.  I  could 
not  even  understand  how  some  naturalised  species  have 


336  GEOGRAPHICAL   DISTRIBUTIOK-.  [Chap.  XIL 

rapidly  spread  througliout  the  same  country.  But  two 
facts,  whicli  I  have  observed — and  no  doubt  many  others 
remain  to  be  observed — throw  some  light  on  this  subject. 
When  a  duck  suddenly  emerges  from  a  pond  covered  with 
duck-weed,  I  have  twice  seen  these  little  plants  adhering 
to  its  back ;  and  it  has  happened  to  me,  in  removing  a 
little  duck-weed  from  one  aquarium  to  another,  that  I  have 
quite  unintentionally  stocked  the  one  with  fresh-water 
shells  from  the  other.  But  another  agency  is  perhaps 
more  effectual :  I  suspended  a  duck's  feet,  which  might 
represent  those  of  a  bird  sleeping  in  a  natural  pond,  in  an 
aquarium,  where  many  ova  of  fresh-water  shells  were 
hatching ;  and  I  found  that  numbers  of  the  extremely 
minute  and  just  hatched  shells  crawled  on  the  feet,  and 
clung  to  them  so  firmly  that  when  taken  out  of  the  water 
they  could  not  be  jarred  off,  though  at  a  somewhat  more 
advanced  age  they  would  voluntarily  drop  off.  These 
just  hatched  molluscs,  though  aquatic  in  their  nature, 
survived  on  the  duck's  feet,  in  damp  air,  from  twelve  to 
twenty  hours  ;  and  in  this  length  of  time  a  duck  or  heron 
might  fly  at  least  six  or  seven  hundred  miles,  and  would 
be  sure  to  alight  on  a  pool  or  rivulet,  if  blown  across  the 
sea  to  an  oceanic  island  or  to  any  other  distant  point.  Sir 
Charles  Lyell  also  informs  me  that  a  Dyticus  has  been 
caught  with  an  Ancylus  (a  fresh-water  she'll  like  a  limpet) 
firmly  adhering  to  it ;  and  a  water-beetle  of  the  same 
family,  a  Colymbetes,  once  flew  on  board  the  '  Beagle,' 
when  forty-five  miles  distant  from  the  nearest  land  :  how 
much  farther  it  might  have  flown  with  a  favouring  gale 
no  one  can  tell. 

With  respect  to  j^lants,  it  has  long  been  known  what 
enormous  ranges  many  fresh-water  and  even  marsh-species 
have,  both  over  continents  and  to  the  most  remote  oceanic 
islands.  This  is  strikingly  shown,  as  remarked  by  Alph. 
de  Candolle,  in  large  groups  of  terrestrial  plants,  which 
have  only  a  very  few  aquatic  members ;  for  these  latter 
seem  immediately  to  acquire,  as  if  in  consequence,  a  very 
w^ide  range.  I  think  favourable  means  of  dispersal  ex- 
plain this  fact.  I  have  before  mentioned  that  earth  occa- 
sionally, though  rarely,  adheres  in  some  quantity  to  the 


Chap.  XII.]  FRESH-WATER  PRODtTCTIONS.  33^^ 

feet  and  beaks  of  "birds.  Wading  birds,  which  frequent 
the  muddy  edges  of  ponds,  if  suddenly  flushed,  would  be 
the  most  likely  to  have  muddy  feet.  Birds  of  this  order 
I  can  show  are  the  greatest  wanderers,  and  are  occasion- 
ally found  on  the  most  remote  and  barren  islands  in  the 
open  ocean ;  they  would  not  be  likely  to  alight  on  the 
surface  of  the  sea,  so  that  the  dirt  would  not  be  washed 
off  their  feet ;  when  making  land,  they  would  be  sure  to 
fly  to  their  natural  fresh-water  haunts.  I  do  not  believe 
that  botanists  are  aware  how  charged  the  mud  of  ponds 
is  with  seeds  :  I  have  tried  several  little  experiments,  but 
will  here  give  only  the  most  striking  case  :  I  took  in  Feb- 
ruary three  table-spoonfuls  of  mud  from  three  different 
points,  beneath  water,  on  the  edge  of  a  little  pond ;  this 
mud  when  dry  weighed  only  6f  ounces  ;  I  kept  it  covered 
up  in  my  study  for  six  months,  pulling  up  and  counting 
each  plant  as  it  grew  ;  the  plants  were  of  many  kinds,  and 
were  altogether  53Y  in  number  ;  and  yet  the  viscid  mud 
was  all  contained  in  a  breakfast  cup  !  Considering  these 
facts,  I  think  it  would  be  an  inexplicable  circumstance  if 
water-birds  did  not  transport  the  seeds  of  fresh-water 
plants  to  vast  distances,  and  if  consequently  the  range  of 
these  plants  was  not  very  great.  The  same  agency  may 
have  come  into  play  with  the  eggs  of  some  of  the  smaller 
fresh-water  animals. 

Other  and  unknown  agencies  probably  have  also 
played  a  part.  I  have  stated  that  fresh-water  flsh  eat 
some  kinds  of  seeds,  though  they  reject  many  other  kinds 
after  having  swallowed  them  ;  even  small  fish  swallow 
seeds  of  moderate  size,  as  of  the  yellow  water-lily  and 
Potamogeton.  Herons  and  other  birds,  century  -after 
century,  have  gone  on  daily  devouring  fish  ;  they  then 
take  flight  and  go  to  other  waters,  or  are  blown  across 
the  sea  ;  and  we  have  seen  that  seeds  retain  their  power 
of  germination,  when  rejected  in  pellets  or  in  excrement, 
many  hours  afterwards.  Wlien  I  saw  the  great  size  of 
the  seeds  of  that  fine  water-lily,  the  ]N"elumbium,  and  re- 
membered Alph.  de  CandoUe's  remarks  on  this  plant,  I 
thought  that  its  distribution  must  remain  quite  inexplica- 
ble ;  but  Audubon  states  that  he  found  the  seeds  of  the 


338  GEOaRAPHICAL   DlSTRIBtJTlOK  [Chap.  XlL 

great  southern  water-lilj  (probably,  according  to  Dr. 
Hooker,  the  Kelumbmm  lutenm)  in  a  heron's  stomach ; 
although  I  do  not  know  the  fact,  yet  analogy  makes  me 
believe  that  a  heron  flying  to  another  pond  and  getting  a 
hearty  meal  of  fish,  would  probably  reject  from  its  stom- 
ach a  pellet  containing  the  seeds  of  the  !N"elumbium  un- 
digested ;  or  the  seeds  might  be  dropped  by  the  bird 
whilst  feeding  its  young,  in  the  same  way  as  fish  are 
known  sometimes  to  be  drop]3ed. 

In  considering  these  several  means  of  distribution,  it 
should  be  remembered  that  when  a  pond  or  stream  is  first 
formed,  for  instance,  on  a  rising  islet,  it  will  be  unoccu- 
pied ;  and  a  single  seed  or  egg  will  have  a  good  chance 
of  succeeding.  Although  there  will  always  be  a  struggle 
for  life  between  the  individuals  of  the  species,  however 
few,  already  occupying  any  pond,  yet  as  the  number  of 
kinds  is  small,  compared  w^ith  those  on  the  land,  the  com- 
petition will  probably  be  less  severe  between  aquatic 
than  between  terrestrial  species  ;  consequently  an  intrud- 
er from  the  waters  of  a  foreign  country,  would  have  a 
better  chance  of  seizing  on  a  place,  than  in  the  case  of 
terrestrial  colonists.  We  should,  also,  remember  that 
some,  perhaps  many,  fresh-water  productions  are  low  in 
the  scale  of  nature,  and  that  we  have  reason  to  believe 
that  such  low  beings  change  or  become  modified  less 
quickly  than  the  high  ;  and  this  will  give  longer  time 
than  the  average  for  the  migration  of  the  same  aquatic 
species.  We  should  not  forget  the  probability  of  many 
species  having  fomerly  ranged  as  continuously  as  fresh- 
water productions  ever  can  range,  over  immense  areas, 
and  having  subsequently  become  extinct  in  intermediate 
regions.  But  the  wide  distribution  of  fresh-water  plants 
and  of  the  lower  animals,  whether  retaining  the  same 
identical  form  or  in  some  degree  modified,  I  believe  main- 
ly depends  on  the  wide  dispersal  of  their  seeds  and  eggs 
by  animals,  more  especially  by  fresh-water  birds,  which 
have  large  powers  of  flight,  and  naturally  travel  from  one 
to  another  and  often  distant  piece  of  water.  ^Nature,  like 
a  careful  gardener,  thus  takes  her  seeds  from  a  bed  of  a 
particular  nature,  and  drops  them  in  another  equally  well 
fitted  for  them. 


Chap.  XII.]  OCEANIC   ISLANDS.  33^. 

On  the  Inhcobitants  of  Oceanic  Islands. — We  now 
come  to  tlie  last  of  the  three  classes  of  facts,  which  I  have 
selected  as  presenting  the  greatest  amount  of  difficult j,  on 
the  view  that  all  the  individuals  both  of  the  same  and  of 
allied  species  have  descended  from  a  single  parent ;  and 
therefore  have  all  proceeded  from  a  common  birthplace, 
notwithstandmg  that  in  the  course  of  time  thej  have  come 
to  inhabit  distant  points  of  the  globe.  I  have  already 
stated  that  I  cannot  honestly  admit  Forbes's  view  on  con- 
tinental extensions,  which,  if  legitimately  followed  out, 
would  lead  to  the  belief  that  within  the  recent  period  all 
existing  islands  have  been  nearly  or  quite  joined  to  some 
continent.  This  view  would  remove  many  difficulties, 
but  it  would  not,  I  think,  explain  all  the  facts  in  regard 
to  insular  productions.  In  the  following  remarks  I  shall 
not  confine  myself  to  the  mere  question  of  dispersal ;  but 
shall  consider  some  other  facts,  which  bear  on  the  truth 
of  the  two  theories  of  independent  creation  and  of  descent 
with  modification. 

The  species  of  all  kinds  which  inhabit  oceanic  islands 
are  few  in  number  compared  with  those  on  equal  conti- 
nental areas  :  Alph.  de  CandoUe  admits  this  for  plants, 
and  Wollaston  for  insects.  If  we  look  to  the  large  size 
and  varied  stations  of  ]N^ew  Zealand,  extending  over  'TSO 
miles  of  latitude,  and  compare  its  flowering  plants,  only 
^50  in  number,  with  those  on  an  equal  area  at  the  Cape 
of  Good  Hope  or  in  Australia,  we  must,  I  think,  admit 
that  something  quite  independently  of  any  difference  in 
physical  conditions  has  caused  so  great  a  difference  in 
number.  Even  the  uniform  county  of  Cambridge  has 
84:7  plants,  and  the  little  island  of  Angiesea  Y64,  but  a  few 
ferns  and  a  few  introduced  plants  are  included  in  these 
numbers,  and  the  comparison  in  some  other  respects  is  not 
quite  fair.  We  have  evidence  that  the  barren  island  of 
Ascension  aboriginally  possessed  under  half-a-dozen  flow- 
ering plants  ;  yet  many  have  become  naturalised  on  it, 
as  they  have  on  IN^ew  Zealand  and  on  every  other  oceanic 
island  which  can  be  named.  In  St.  Helena  there  is  reason 
to  believe  that  the  naturalised  plants  and  animals  have 
nearly  or  quite  exterminated  many  native  productions. 


.g^Q  GEOGRAPHICAL   DISTRIBUTION.  [Chap.  XII. 

He  who  admits  the  doctrine  of  the  creation  of  each  sepa- 
rate sj)ecies,  will  have  to  admit,  that  a  sufficient  nnmber 
of  the  best  adapted  plants  and  animals  have  not  been 
created  on  oceanic  islands  ;  for  man  has  nnintentionally 
stocked  them  from  various  sources  far  more  fully  and  per- 
fectly than  has  nature. 

Although  in  oceanic  islands  the  number  of  kinds  of 
inhabitants  is  scanty,  the  proportion  of  endemic  species 
{i.  e.  those  found  nowhere  else  in  the  world)  is  often  ex- 
tremely large.  If  we  compare,  for  instance,  the  number 
of  the  endemic  land-shells  in  Madeira,  or  of  the  endemic 
birds  in  the  Galapagos  Archipelago,  with  the  number 
found  on  any  continent,  and  then  compare  the  area  of  the 
islands  with  that  of  the  continent,  we  shall  see  that  this  is 
true.  This  fact  might  have  been  expected  on  my  theory, 
for,  as  already  explained,  sj)ecies  occasionally  arriving  after 
long  intervals  in  a  new  and  isolated  district,  and  having  to 
compete  with  new  associates,  will  be  eminently  hable  to 
modification,  and  will  often  produce  groups  of  modified 
descendants.  But  it  by  no  means  follows,  that,  because  in 
an  island  nearly  all  the  species  of  one  class  are  peculiar,  those 
of  another  class,  or  of  another  section  of  the  same  class,  are 
peculiar  ;  and  this  difi'erence  seems  to  depend  on  the  spe- 
cies which  do  not  become  modified  having  immigrated 
with  facility  and  in  a  body,  so  that  their  mutual  relations 
have  not  been  much  disturbed ;  and  partly  on  the  frequent 
arrival  of  unmodified  immigrants  from  the  mother-country, 
and  the  consequent  intercrossing  with  them.  With  re- 
spect to .  the  effects  of  this  intercrossing,  it  should  be  re- 
membered that  the  ofi'spring  of  such  crosses  would  almost 
certainly  gain  in  vigour ;  so  that  even  an  occasional  cross 
would  produce  more  effect  than  might  at  first  have  been 
anticipated.  To  give  a  few  examples :  in  the  Galapagos 
Islands  there  are  twenty-six  land-birds,  of  these  twenty- 
one  (or  perhaps  twenty-three)  are  peculiar,  whereas  of  the 
eleven  marine  birds  only  two  are  j)eculiar ;  and  it  is  ob- 
vious that  marine  birds  could  arrive  at  these  islands  more 
easily  than  land-birds.  Bermuda,  on  the  other  hand,  which 
lies  at  about  the  same  distance  from  North  America  as 
the  Galapagos  Islands  do  from  South  America,  and  which 
has  a  very  peculiar  soil,  does  not  possess  one  endemic 


Chap.  XIL]  OCEANIC    ISLAJCDS.  341 

land-bird  ;  and  we  know  from  Mr.  J .  M.  Jones's  admira- 
ble account  of  Bermuda,  that  very  many  E^ortli  American 
birds,  during  their  great  annual  migrations,  visit  either 
periodically  or  occasionally  this  island.  Madeira  does 
not  possess  one  peculiar  bird,  and  many  European  and 
African  birds  are  almost  every  year  blbwn  there,  as  I  am 
informed  by  Mr.  E.  Y.  Harcourt.  So  that  these  two 
islands  of  Bermuda  and  Madeira  have  been  stocked  by 
birds,  which  for  long  ages  have  struggled  together  in 
their  former  homes,  and  have  become  mutually  adapted 
to  each  other  ;  and  when  settled  in  their  new  homes,  each 
kind  will  have  been  kept  by  the  others  to  their  proper 
places  and  habits,  and  will  consequently  have  been  little 
liable  to  modification.  Madeira,  again,  is  inhabited  by  a 
wonderful  number  of  peculiar  land-shells,  whereas  not  one 
species  of  sea-shell  is  confined  to  its  shores  :  now,  though 
we  do  not  know  how  sea-shells  are  dispersed,  yet  we  can 
see  that  their  eggs  or  larvse,  perhaps  attached  to  seaweed 
or  floating  timber,  or  to  the  feet  of  wading-birds,  might  be 
transported  far  more  easily  than  land-shells,  across  three 
or  four  hundred  miles  of  open  sea.  The  difi'erent  orders 
of  insects  in  Madeira  apparently  present  analogous  facts. 

Oceanic  islands  are  sometimes  deficient  in  certain 
classes,  and  their  places  are  apparently  occupied  by  the 
other  inhabitants  ;  in  the  Galapagos  Islands  reptiles,  and 
in  ISTew  Zealand  gigantic  wingless  birds,  take  the  place 
of  mammals.  In  the  plants  of  the  Galapagos  islands.  Dr. 
Hooker  has  shown  that  the  proportional  numbers  of  the 
difi'erent  orders  are  very  difi'erent  from  what  they  are 
elsewhere.  Such  cases  are  generally  accounted  for  by 
the  physical  conditions  of  the  islands ;  but  this  explana- 
tion seems  to  me  not  a  little  doubtful.  Facility  of  immi- 
gration, I  believe,  has  been  at  least  as  important  as  the 
nature  of  the  conditions. 

Many  remarkable  little  facts  could  be  given  with  re- 
spect to  the  inhabitants  of  remote  islands.  For  instance, 
in  certain  islands  not  tenanted  by  mammals,  some  of  the 
endemic  plants  have  beautifully  hooked  seeds  ;  yet  few 
relations  are  more  striking  than  the  adaptation  of  hooked 
seeds  for  transportal  by  the  wool  and  fur  of  quadrupeds. 
This  case  presents  no  difficulty  on  my  view,  for  a  hooked 


34:2  GEOGRAPUICAL    DISTllIBUTION.  [Chap.  Xll. 

seed  might  be  transported  to  an  island  by  some  other 
means  ;  and  the  plant  then  becoming  slightly  modified, 
but  still  retaining  its  hooked  seeds,  wonld  form  an  en- 
demic species,  having  as  useless  an  appendage  as  any  ru- 
dimentary organ, — for  instance,  as  the  shrivelled  wings 
under  the  soldered  elytra  of  many  insular  beetles.  Again, 
islands  ofteo  possess  trees  or  bushes  belonging  to  orders 
which  elsewhere  include  only  herbaceous  species ;  now 
trees,  as  Alph.  de  CandoUe  has  shown,  generally  have, 
whatever  the  cause  may  be,  confined  ranges.  Hence  trees 
would  be  little  likely  to  reach  distant  oceanic  islands ; 
and  an  herbaceous  plant,  though  it  would  have  no  chance 
of  successfully  competing  in  stature  with  a  fully  developed 
tree,  w^ien  established  on  an  island  and  having  to  com- 
pete with  herbaceous  plants  alone,  might  readily  gain  an 
advantage  by  growing  taller  and  taller  and  overtopping 
the  other  ^^lants.  If  so,  natural  selection  would  often  tend 
to  add  to  the  stature  of  herbaceous  plants  when  growing 
on  an  island,  to  whatever  order  they  belonged,  and  thus 
convert  them  first  into  bushes  and  ultimately  into  trees. 

With  respect  to  the  absence  of  whole  orders  on  oceanic 
islands,  Bory  St.  Yincent  long  ago  remarked  that  Batra- 
chians  (frogs,  toads,  newts)  have  never  been  found  on  any 
of  the  many  islands  with  which  the  great  oceans  are  stud- 
ded. I  have  taken  pains  to  verify  this  assertion,  and  I 
have  found  it  strictly  true.  I  have,  however,  been  as- 
sured that  a  frog  exists  on  the  mountains  of  the  great 
island  of  Kew  Zealand  ;  but  I  suspect  that  this  exception 
(if  the  information  be  correct)  may  be  explained  through 
glacial  agency.  This  general  absence  of  frogs,  toads,  and 
newts  on  so  many  oceanic  islands  cannot  be  accounted  for 
by  their  physical  conditions  ;  indeed  it  seems  that  islands 
are  peculiarly  well  fitted  for  these  animals  ;  for  frogs  have 
been  introduced  into  Madeira,  the  Azores,  and  Mauri- 
tius, and  have  multiplied  so  as  to  become  a  nuisance. 
But  as  these  animals  and  their  spawn  are  known  to  be 
immediately  killed  by  sea-water,  on  my  view  we  can  see 
that  there  would  be  great  difiiculty  in  their  transportal 
across  the  sea,  and  therefore  why  they  do  not  exist  on  any 
oceanic  island.     But  why,  on  the  theory  of  creation,  they 


Chap.  XIL]  OCEANIC    ISLANDS.  343 

should  not  have  been  created  there,  it  would  be  very 
difficult  to  explain. 

Mammals  offer  another  and  similar  case.  I  have  care- 
fullj  searched  the  oldest  voyages,  but  have  not  finished 
my  search  ;  as  yet  I  have  not  found  a  single  instance,  free 
from  doubt,  of  a  terrestrial  mammal  (excluding  domesti- 
3ated  animals  kept  by  the  natives)  inhabiting  an  island 
situated  above  800  miles  from  a  continent  or  great  con- 
tinental island  ;  and  many  islands  situated  at  a  much  less 
distance  are  equally  barren.  The  Falkland  Islands,  which 
are  inhabited  by  a  wolf-like  fox,  come  nearest  to  an  excep- 
tion ;  but  this  group  cannot  be  considered  as  oceanic,  as 
it  lies  on  a  bank  connected  with  the  mainland  ;  moreover, 
icebergs  formerly  brought  boulders  to  its  western  shores, 
and  they  may  have  formerly  transported  foxes,  as  so  fre- 
quently now  happens  in  the  arctic  regions.  Yet  it  cannot 
be  said  that  small  islands  will  not  support  small  mammals, 
for  they  occur  in  many  parts  of  the  world  on  very  small 
islands,  if  close  to  a  continent ;  and  hardly  an  island  can  be 
named  on  which  our  smaller  quadrupeds  have  not  become 
naturalised  and  greatly  multiplied.  It  cannot  be  said,  on 
the  ordinary  view  of  creation,  that  there  has  not  been  time 
for  the  creation  of  mammals  ;  many  volcanic  islands  are 
sufficiently  ancient,  as  shown  by  the  stupendous  degrada- 
tion which  they  have  suffered  and  by  their  tertiary  strata  : 
there  has  also  been  time  for  the  production  of  endemic 
species  belonging  to  other  classes  ;  and  on  continents  it  is 
thought  that  mammals  appear  and  disappear  at  a  quicker 
rate  than  other  and  lower  animals.  Though  terrestrial 
mammals  do  not  occur  on  oceanic  islands,  aerial  mammals 
do  occur  on  almost  every  island.  ISTew  Zealand  possesses 
two  bats  found  nowhere  else  in  the  world  :  I^orfolk  Island, 
the  Yiti  Archipelago,  the  Bonin  Islands,  the  Caroline  and 
Marianne  Archipelagoes,  and  Mauritius,  all  possess  their 
peculiar  bats.  Why,  it  may  be  asked,  has  the  supposed 
creative  force  produced  bats  and  no  other  mammals  on 
remote  islands  ?  On  my  view  this  question  can  easily  be 
answered ;  for  no  terrestrial  mammal  can  be  transported 
across  a  wide  space  of  sea,  but  bats  can  fly  across.  Bats 
have  been  seen  wandering  by  day  far  over  the  Atlantic 
Ocean  ;  and  two  North  American  species  either  regularly 


344  GEOGRAPHICAL   DISTRIBUTION.  [Chap.  XD 

or  occasionally  visit  Bermuda,  at  tlie  distance  of  600  miles 
from  the  mainland.  I  hear  from  Mr.  Tomes,  who  has 
specially  studied  this  family,  that  many  of  the  same  spe- 
cies have  enormous  ranges,  and  are  found  on  continents 
and  on  far  distant  islands.  Hence  we  have  only  to  sup- 
pose that  such  wandering  species  have  been  modified 
through  natural  selection  in  their  new  homes  in  relation 
to  their  new  position,  and  we  can  understand  the  presence 
of  endemic  bats  on  islands,  with  the  absence  of  all  terres- 
trial mammals. 

Besides  the  absence  of  terrestrial  mammals  in  relation 
to  the  remoteness  of  islands  from  continents,  there  is  also 
a  relation,  to  a  certain  extent  independent  of  distance, 
between  the  depth  of  the  sea  separating  an  island  from 
•the  neighouring  mainland,  and  the  presence  in  both  of 
the  same  mammiferous  species  or  of  allied  species  in  a  more 
or  less  modified  condition.  Mr.  "Windsor  Earl  has  made 
some  striking  observations  on  this  head  in  regard  to  the 
great  Malay  Archipelago,  which  is  traversed  near  Celebes 
by  a  space  of  deep  ocean  ;  and  this  space  separates  two 
widely  distinct  mammalian  faunas.  On  either  side  the 
islands  are  situated  on  moderately  steep  submarine  banks, 
and  they  are  inhabited  by  closely  allied  or  identical 
quadrupeds.  No  doubt  some  few  anomalies  occur  in  this 
great  archipelago,  and  there  is  much  difiiculty  in  forming 
a  judgment  in  some  cases  owing  to  the  probable  naturali- 
sation of  certain  mammals  through  man's  agency  ;  but  we 
shall  soon  have  much  light  thrown  on  the  natural  history 
of  this  archipelago  by  the  admirable  zeal  and  researches 
of  Mr.  Wallace.  I  have  not  as  yet  had  time  to  follow  up 
this  subject  in  all  other  quarters  of  the  world  ;  but  as  far 
as  I  have  gone,  the  relation  generally  holds  good.  We 
see  Britain  separated  by  a  shallow  channel  from  Europe, 
and  the  mammals  are  the  same  on  both  sides  ;  we  meet 
with  analogous  facts  on  many  islands  separated  by  simi- 
lar channels  from  Australia.  The  West  Indian  Islands 
stand  on  a  deeply  submerged  bank,  nearly  1000  fathoms 
in  depth,  and  here  we  find  American  forms,  but  the 
species  and  even  the  genera  are  distinct.  As  the 
amount  of  modification  in  all  cases  depends  to  a  certain 
degree  on  the  lapse  of  time,  and  as  during  changes  of 


Chap.  XII.}  OCEANIC   ISLANDS,  3J.5 

level  it  is  obvious  that  islands  separated  by  shallow  chan- 
nels are  more  likely  to  have  been  continuously  nnited 
within  a  recent  period  to  the  mainland  than  islands  sepa- 
rated by  deeper  channels,  we  can  understand  the  freqnent 
relation  between  the  depth  of  the  sea  and  the  degree  of 
affinity  of  the  mammalian  inliabitants  of  islands  with 
those  of  a  neighbouring  continent, — an  inexplicable  rela- 
tion on  the  view  of  independent  acts  of  creation. 

All  the  foregoing  remarks  on  the  inhabitants  of  oceanic 
islands, — namely,  the  scarcity  of  kinds, — the  richness  in 
endemic  forms  in  particular  classes  or  sections  of  classes, 
— the  absence  of  whole  groups,  as  of  batrachians,  and  of 
terrestrial  mammals  notwithstanding  the  ^^resence  of  aerial 
bats, — the  singular  proportions  of  certain  orders  of  plants, 
— herbaceous  forms  having  been  developed  into  trees, 
&c., — seem  to  me  to  accord  better  with  the  view  of  occa- 
sional means  of  transport  having  been  largely  efficient  in 
the  long  course  of  time,  than  with  the  view  of  all  our 
oceanic  islands  having  been  formerly  connected  by  con- 
tinuous land  with  the  nearest  continent ;  for  on  this  latter 
view  the  migration  would  probably  have  been  more  com- 
plete ;  and  if  modification  be  admitted,  all  the  forms  of 
life  would  have  been  more  equally  modified,  in  accord- 
ance with  the  ]3aramount  importance  of  the  relation  of  or- 
ganism to  organism. 

I  do  not  deny  that  there  are  many  and  grave  difficulties 
in  understanding  how  several  of  the  inhabitants  of  the 
more  remote  islands,  whether  still  retaining  the  same  spe- 
cific form  or  modified  since  their  arrival,  could  have 
reach-ed  their  present  homes.  But  the  probability  of 
many  islands  having  existed  as  halting-places,  of  which 
not  a  wreck  now  remains,  must  not  be  overlooked.  I 
will  here  give  a  single  instance  of  one  of  the  cases  of  diffi- 
culty. Almost  all  oceanic  islands,  even  the  most  isolated 
and  smallest,  are  inhabited  by  land-shells,  generally  by 
endemic  species,  but  sometimes  by  species  found  elsewhere. 
Dr.  Aug.  A.  Gould  has  given  several  interesting  cases  in 
regard  to  the  land-shells  of  the  islands  of  the  Pacific. 
Kow  it  is  notorious  that  land-shells  are  very  easily  killed 
by  salt ;  their  eggs,  at  least  such  as  I  have  tried,  sink  in 
sea-water  and  are  killed  by  it.     Yet  there  must  be  on  mv 


346  GEOGRAPHICAL  DISTRIBUTION.  [Chap.  XII. 

view,  some  unknown,  but  highly  efficient  means  for  their 
transportal.  Would  the  just-hatched  young  occasionally 
crawl  on  and  adhere  to  the  feet  of  birds  roosting  on  the 
ground,  and  thus  get  transported  ?  It  occurred  to  me  that 
land-shells,  when  hybernating  and  having  a  membranous 
diaphragm  over  the  mouth  of  the  shell,  might  be  floated 
in  chinks  of  drifted  timber  across  moderately  w4de  arms 
of  the  sea.  And  I  foimd  that  several  species  did  in  this 
state  withstand  uninjured  an  immersion  in  sea-water  dur- 
ing seven  days  :  one  of  these  shells  was  the  Helix  poma- 
tia,  and  after  it  had  again  hybernated  I  put  it  in  sea-water 
for  twenty  days,  and  it  perfectly  recovered.  As  this  species 
has  a  thick  calcareous  operculum,  I  removed  it,  and  when 
it  had  formed  a  new  membranous  one,  I  immersed  it  for 
fourteen  days  in  sea-water,  and  it  recovered  and  crawled 
away  :  but  more  experiments  are  wanted  on  this  head. 

Tlie  most  striking  and  important  fact  for  us  in  regard 
to  the  inhabitants  of  islands,  is  their  affinity  to  those  of 
the  nearest  mainland,  without  being  actually  the  same 
species.  I^umerous  instances  could  he  given  of  this  fact. 
I  will  give  only  one,  that  of  the  Galapagos  Archipelago, 
situated  under  the  equator,  between  500  and  600  miles 
from  the  shores  of  South  America.  Here  almost  every 
product  of  the  land  and  water  bears  the  unmistakeable 
stamp  of  the  American  continent.  There  are  twenty-six 
land-birds,  and  twenty-one  or  perhaps  twenty-three  of 
these  are  ranked  as  distinct  species,  and  are  supj^osed  to 
have  been  created  here;  yet  the  close  affinity  of  most  of 
these  birds  to  American  species  in  every  character,  in  tlieir 
habits,  gestures,  and  tones  of  voice,  was  manifest.  So  it  is 
with  the  other  animals,  and  with  nearly  all  the  plants,  as 
shown  by  Dr.  Hooker  in  his  admirable  memoir  on  the  Flora 
of  this  archipelago.  The  naturalist,  looking  at  the  inhabi- 
tants of  these  volcanic  islands  in  the  Pacific,  distant  several 
hundred  miles  from  the  continent,  yet  feels  that  he  is  stand- 
ing on  American  land.  Why  should  tliis  be  so?  why 
should  the  species  which  are  supposed  to  have  been  created 
in  the  Galapagos  Archipelago,  and  nowhere  else,  bear  so 
plain  a  stamp  of  affinity  to  those  created  in  America? 
There  is  nothing  in  the  conditions  of  life,  in  the  geological 
nature  of  the  islands,  in  their  height  or  climate,  or  in  the 


Chap.  XII.]  OCEANIC  ISLANDS.  g^^ 

proportions  in  wliicli  the  several  classes  are  associated  to- 
gether, which  resembles  closely  the  conditions  of  the  South 
American  coast :  in  fact  there  is  a  considerable  dissimilar- 
ity in  all  these  respects.  On  the  other  hand,  there  is  a 
considerable  degree  of  resemblance  in  the  volcanic  nature 
of  the  soil,  in  climate,  height  and  size  of  the  islands,  be- 
tween the  Galapagos  and  Cape  de  Yerde  Archipelagos  : 
but  what  an  entire  and  absolute  difterence  in  their  inhab- 
itants !  The  inhabitants  of  the  Cape  de  Yerde  Islands  are 
related  to  those  of  Africa,  like  those  of  the  Galapagos  to 
America.  I  believe  this  grand  fact  can  receive  no  sort  of 
explanation  on  the  ordinary  view  of  independent  creation  ; 
"^vhereas  on  the  vie-w  here  maintained,  it  is  obvious  that 
the  Galapagos  Islands  would  be  likely  to  receive  colonists, 
whether  by  occasional  means  of  transport  or  by  formerly 
continuous  land,  from  America  ;  and  the  Cape  de  Yerde 
Islands  from  Africa ;  and  that  such  colonists  would  be 
liable  to  modification  ; — the  principle  of  inheritance  still 
betraying  their  original  birthplace. 

Many  analogous  facts  could  be  given  :  indeed  it  is  an 
almost  universal  rule  that  the  endemic  productions  of 
islands  are  related  to  those  of  the  nearest  continent,  or  of 
other  near  islands.  The  exceptions  are  few,  and  most  of 
them  can  be  explained.  Thus  the  plants  of  Kerguelen 
Land,  though  standing  nearer  to  Africa  then  to  America, 
are  related,  and  that  very  closely,  as  we  know  from  Dr. 
Hooker's  account,  to  those  of  America :  but  on  the  view 
that  this  island  has  been  mainly  stocked  by  seeds  brought 
with  earth  and  stones  on  icebergs,  drifted  by  the  prevail- 
ing currents,  this  anomaly  disappears.  ISTew  Zealand  in 
its  endemic  plants  is  much  more  closely  related  to  Austra- 
lia, the  nearest  mainland,  than  to  any  other  region  :  and 
this  is  what  might  have  been  expected  ;  but  it  is  also 
plainly  related  to  South  America,  which,  although  the 
next  nearest  continent,  is  so  enormously  remote,  that  the 
fact  becomes  an  anomaly.  But  this  difiiculty  almost  disaj)- 
pears  on  the  view  that  both  New  Zealand,  South  America, 
and  other  southern  lands  were  long  ago  partially  stocked 
from  a  nearly  intermediate  though  distant  point,  namely 
from  the  antarctic  islands,  when  they  were  clothed  with 
vegetation,  before  the  commencement  of  the  Glacial  period. 
16 


g^g  GEOGRAPHICAL  DISTRIBUTION.  lChap.  XII. 

The  affinity,  wliicli,  tliougli  feeble,  I  am  assured  by  Dr. 
Hooker  is  real,  between  the  flora  of  the  south-western 
corner  of  Australia  and  of  the  Cape  of  Good  Hope,  is  a 
far  more  remarkable  case,  and  is  at  present  inexplicable : 
but  this  affinity  is  confined  to  the  plants,  and  will,  I  do  not 
doubt,  be  some  day  explained. 

The  law  which  causes  the  inhabitants  of  an  archi- 
pelago, though  specifically  distinct,  to  be  closely  allied  to 
those  of  the  nearest  continent,  we  sometimes  see  displayed 
on  a  small  scale,  yet  in  a  most  interesting  manner,  within 
the  limits  of  the  same  archipelago.  Thus  the  several 
islands  of  the  Galapagos  Archipelago  are  tenanted,  as  I 
have  elsewhere  shown,  in  a  quite  marvellous  manner,  by 
very  closely  related  species ;  so  that  the  inhabitants  of 
each  separate  island,  though  most  distinct,  are  related  in 
an  incomparably  closer  degree  to  each  other  than  to  the 
inhabitants  of  any  other  part  of  the  world.  And  this  is 
just  what  might  have  been  expected  on  my  view,  for  the 
islands  are  situated  so  near  each  other  that  they  would 
almost  certainly  receive  immigrants  from  the  same  origi- 
nal source,  or  from  each  other.  But  this  dissimilarity 
between  the  endemic  inhabitants  of  the  islands  may  be 
used  as  an  argument  against  my  views  ;  for  it  may  be 
asked,  how  has  it  happened  in  the  several  islands  situated 
within  sight  of  each  other,  having  the  same  geological 
nature,  the  same  height,  climate,  &c.,  that  many  of  the 
immigrants  should  have  been  differently  modified,  though 
only  in  a  small  degree.  This  long  appeared  to  me  a  great 
difficulty  :  but  it  arises  in  chief  part  from  the  deeply- 
seated  error  of  considering  the  physical  conditions  of  a 
country  as  the  most  important  for  its  inhabitants  ;  where- 
as it  cannot,  I  think,  be  disputed  that  the  nature  of  the 
other  inhabitants,  with  which  each  has  to  compete,  is  at 
least  as  important,  and  generally  a  far  more  important 
element  of  success.  ]^ow  if  we  look  to  those  inhabitants 
of  the  Galapagos  Archipelago  which  are  found  in  other 
parts  of  the  world  (laying  on  one  side  for  the  moment  the 
endemic  species,  which  cannot  be  here  fairly  included,  as  we 
are  considering  how  they  have  come  to  be  modified  since 
their  arrival),  we  find  a  considerable  amount  of  difference  in 
the  several  islands.    This  difference  might  indeed  have  been 


Chap,  XII.  1  OCEANIC   ISLANDS.  3^9 

expected  on  tlie  view  of  tlie  islands  having  been  stocked 
by  occasional  means  of  transport — a  seed,  for  instance,  of 
one  plant  having  been  brought  to  one  island,  and  that 
of  another  plant  to  another  island.  Hence  when  in  former 
times  an  immigrant  settled  on  any  one  or  more  of  the 
islands,  or  when  it  subsequently  spread  from  one  island 
to  another,  it  would  undoubtedly  be  exposed  to  difierent 
conditions  of  life  in  the  different  islands,  for  it  would  have 
to  compete  with  different  sets  of  organisms  :  a  plant^  for 
instance,  would  find  the  best-fitted  ground  more  perfectly 
occuj)ied  by  distinct  plants  in  one  island  than  in  another, 
and  it  would  be  exposed  to  the  attacks  of  somewhat 
different  enemies.  If  then  it  varied,  natural  selection 
would  probably  favour  different  varieties  in  the  different 
islands.  Some  species,  however,  might  spread  and  yet 
retain  the  same  character  throughout  the  group,  just  as 
we  see  on  continents  some  species  spreading  widely  and 
remaining  the  same. 

The  really  surprising  fact  in  this  case  of  the  Galapagos 
Archipelago,  and  in  a  lesser  degree  in  some  analogous 
instances,  is  that  the  new  species  formed  in  the  separate 
islands  have  not  quickly  spread  to  the  other  islands.  But 
the  islands,  though  in  sight  of  each  other,  are  separated 
by  deep  arms  of  the  sea,  in  most  cases  wider  than 
the  British  Channel,  and  there  is  no  reason  to  suppose 
that  they  have  at  any  former  period  been  continuously 
united.  The  currents  of  the  sea  are  rapid  and  sweep 
across  the  arcliipelago,  and  gales  of  wind  are  extraor- 
dinarily rare  ;  so  that  the  islands  are  far  more  effectually 
separated  from  each  other  than  they  appear  to  be  on  a 
map.  Nevertheless  a  good  many  species,  both  those  found 
in  other  parts  of  the  world  and  those  confined  to  the  archi- 
pelago, are  common  to  the  several  islands,  and  we  may 
infer  from  certain  facts  that  these  have  probably  spread 
from  some  one  island  to  the  others.  But  we  often  take,  I 
think,  an  erroneous  view  of  the  probability  of  closely 
allied  species  invading  each  other's  territory,  when  put 
into  free  intercommunication.  Undoubtedly  if  one  spe- 
cies has  any  advantage  whatever  over  another,  it  will  in 
a  very  brief  time  wholly  or  in  part  supplant  it ;  but  if 


25Q  GEOGRAPHICAL   DISTRIBUTION.  [Chap.  XH. 

both  are  equally  well  fitted  for  their  own  places  in  nature, 
both  probably  will  hold  their  own  places  and  keep  sepa- 
rate for  almost  any  length  of  time.  Being  familiar  with 
the  fact  that  many  species,  naturalised  through  man's 
agency,  have  spread  with  astonishing  rapidity  over  new 
countries,  we  are  apt  to  infer  that  most  species  would  thus 
spread  ;  but  we  should  remember  that  the  forms  which 
become  naturalised  in  new  countries  are  not  generally 
closely  allied  to  the  aboriginal  inhabitants,  but  are  very 
distinct  species,  belonging  in  a  large  proportion  of  cases, 
as  shown  by  Alph.  de  Candolle,  to  distinct  genera.  In 
the  Galapagos  Archipelago,  many  even  of  the  birds, 
though  so  well  adapted  for  flying  from  island  to  island, 
are  distinct  on  each  ;  thus  there  are  three  closely-allied 
species  of  mocking-thrush,  each  confined  to  its  own  island. 
Now  let  us  suppose  the  mocking-thrush  of  Chatham 
Island  to  be  blown  to  Charles  Island,  which  has  its  own 
mocking-thrush  :  why  should  it  succeed  in  establishing 
itself  there  ?  We  may  safely  infer  that  Charles  Island  is 
well  stocked  with  its  own  species,  for  annually  more  eggs 
are  laid  there  than  can  possibly  be  reared  ;  and  we  may 
infer  that  the  mocking-thrush  peculiar  to  Charles  Island 
is  at  least  as  well  fitted  for  its  home  as  is  the  species  pecu- 
liar to  Chatham  Island.  Sir  C.  Lyell  and  Mr.  Wollaston 
have  communicated  to  me  a  remarkable  fact  bearing  on 
this  subject ;  namely,  that  Madeira  and  the  adjoining  islet 
of  Porto  Santo  possess  many  distinct  but  representative 
land-shells,  some  of  which  live  in  crevices  of  stone  ;  and 
although  large  quantities  of  stone  are  annually  transported 
from  Porto  Santo  to  Madeira,  yet  this  latter  island  has 
not  become  colonised  by  the  Porto  Santo  species  :  never- 
theless both  islands  have  been  colonised  by  some  European 
land-shells,  which  no  doubt  had  some  advantage  over  the 
indigenous  S]Decies.  From  these  considerations  I  think  we 
need  not  greatly  marvel  at  the  endemic  and  representative 
species,  which  inhabit  the  several  islands  of  the  Galapagos 
Archipelago,  not  having  universally  spread  from  island  to 
island.  In  many  other  instances,  as  in  the  several  districts 
of  the  same  continent,  pre-occupation  has  probably  played 
an  important  part  in  checking  the  commingling  of  species 


Chap.  XIL]  OCEANIC    ISLANDS.  ggjj^ 

under  the  same  conditions  of  life.  Thus,  the  south-east 
and  sonth-west  corners  of  Australia  have  nearly  the  same 
physical  conditions,  and  are  united  by  continnons  land, 
yet  they  are  inhabited  by  a  vast  number  of  distinct  mam- 
mals, birds,  and  plants. 

Tlie  principle  which  determines  the  general  character 
of  the  fauna  and  flora  of  oceanic  islands,  namely,  that  the 
inhabitants,  when  not  identically  the  same,  yet  are  plainly 
related  to  the  inhabitants  of  that  region  whence  colonists 
could  most  readily  have  been  derived, — the  colonists  hav- 
ing been  subsequently  modified  and  better  fitted  to  their 
new  homes, — is  of  the  widest  application  throughout 
nature.  We  see  this  on  every  mountain,  in  every  lake 
and  marsh.  For  Alpine  species,  excepting  in  so  far  as 
the  same  forms,  chiefly  of  plants,  have  spread  widely 
throughout  the  world  during  the  recent  Glacial  epoch,  are 
related  to  those  of  the  surrounding  lowlands  ; — thus  we 
have  in  South  America,  Alpine  humming-birds,  Alpine 
rodents,  Alpine  plants,  &c.,  all  of  strictly  American  forms, 
and  it  is  obvious  that  a  mountain,  as  it  became  slowly  up- 
heaved, would  naturally  be  colonised  from  the  surround- 
ing lowlands.  So  it  is  with  the  inhabitants  of  lakes  and 
marshes,  excepting  in  so  far  as  great  facility  of  transport 
has  given  the  same  general  forms  to  the  whole  world. 
"We  see  this  same  principle  in  the  blind  animals  inhabit- 
ing the  caves  of  America  and  of  Europe.  Other  analo- 
gous facts  could  be  given.  And  it  will,  I  believe,  be 
universally  found  to  be  true,  that  wherever  in  two  re- 
gions, let  them  be  ever  so  distant,  many  closely  allied  or 
representative  species  occur,  there  will  likewise  be  found 
some  identical  species,  showing,  in  accordance  with  the 
foregoing  view,  that  at  some  former  period  there  has  been 
intercommunication  or  migration  between  the  two  regions. 
And  wherever  many  closely-allied  species  occur,  there 
will  be  found  many  forms  which  some  naturalists  rank  as 
distinct  species,  and  some  as  varieties ;  these  doubtful 
forms  showing  us  the  steps  in  the  process  of  modification. 

This  relation  between  the  power  and  extent  of  migra- 
tion of  a  species,  either  at  the  present  time  or  at  some 
former  period  under  difi'erent  physical  conditions,  and  the 


352  GEOGRAPHICAL   DISTRIBUTIOIJ?".  [Chap.  XII. 

existence  at  remote  points  of  the  world  of  other  species 
allied  to  it,  is  shown  in  another  and  more  general  way. 
Mr.  Gould  remarked  to  me  long  ago,  that  in  those  genera 
of  birds  which  range  oyer  the  world,  many  of  the  species 
have  very  wide  ranges.  I  can  hardly  doubt  that  this  rule 
is  generally  true,  though  it  would  be  difficult  to  prove  it. 
Amongst  mammals,  we  see  it  strikingly  displayed  in 
Bats,  and  in  a  lesser  degree  in  the  Felidse  and  Canidse. 
"We  see  it,  if  we  compare  the  distribution  of  butterflies  and 
beetles.  So  it  is  with  most  fresh-water  productions,  in 
which  so  many  genera  range  over  the  world,  and  many 
individual  species  have  enormous  ranges.  It  is  not  meant 
that  in  world-ranging  genera  all  the  species  have  a  wide 
range,  or  even  that  they  have  on  an  average  a  wide  range ; 
but  only  that  some  of  the  species  range  very  widely  ;  for 
the  facility  with  which  widely-ranging  species  vary  and 
give  rise  to  new  forms  will  largely  determine  their  aver- 
age range.  For  instance,  two  varieties  of  the  same  species 
inhabit  America  and  Europe,  and  the  species  thus  has  an 
immense  range ;  but,  if  the  variation  had  been  a  little 
greater,  the  two  varieties  would  have  been  ranked  as  dis- 
tinct species,  and  the  common  range  would  have  been 
greatly  reduced.  Still  less  is  it  meant,  that  a  species 
which  apparently  has  the  capacity  of  crossing  barriers 
and  ranging  widely,  as  in  the  case  of  certain  powerfully- 
winged  birds,  will  necessarily  range  widely ;  for  we  should 
never  forget  that  to  range  widely  implies  not  only  the 
power  of  crossing  barriers,  but  the  more  important  power 
of  being  victorious  in  distant  lands  in  the  struggle  for  life 
with  foreign  associates.  But  on  the  view  of  all  the  s^dc- 
cies  of  a  genus  having  descended  from  a  single  j)arent, 
though  now  distributed  to  the  most  remote  points  of  the 
world,  we  ought  to  And,  and  I  believe  as  a  general  rule 
we  do  find,  that  some  at  least  of  the  species  range  very 
widely  ;  for  it  is  necessary  that  the  unmodified  parent 
should  range  widely,  undergoing  modification  during  its 
diflusion,  and  should  place  itself  under  diverse  conditions 
favourable  for  the  conversion  of  its  ofl'spring,  firstly  into 
new  varieties  and  ultimately  into  new  species. 

In  considering  the  wide  distribution  of  certain  genera, 


Chap.  XII.l  OCEANIC    ISLANDS.  353 

We  should  bear  in  mind  that  some  are  extremely  ancient, 
and  must  have  branched  off  from  a  common  parent  at  a 
remote  epoch  ;  so  that  in  such  cases  there  will  have  been 
ample  time  for  great  climatal  and  geographical  changes 
and  for  accidents  of  transport ;  and  consequently  for  the 
migration  of  some  of  the  species  into  all  quarters  of  the 
world,  where  they  may  have  become  slightly  modiiied  in 
relation  to  their  new  conditions.  There  is,  also,  some 
reason  to  believe  from  geological  evidence  that  organisms 
low  in  the  scale  within  each  great  class,  generally  change 
at  a  slower  rate  than  the  higher  forms  ;  and  consequently 
the  lower  forms  will  have  had  a  better  chance  of  ranging 
widely  and  of  still  retaining  the  same  specific  character. 
This  fact,  together  with  the  seeds  and  eggs  of  many  low 
forms  being  very  minute  and  better  fitted  for  distant 
transportation,  probably  accounts  for  a  law  which  has 
long  been  observed,  and  which  has  lately  been  admirably 
discussed  by  Alph.  de  Candolle  in  regard  to  plants, 
namely,  that  the  lower  any  group  of  organisms  is,  the 
more  widely  it  is  apt  to  range. 

The  relations  just  discussed, — namely,  low  and  slowly- 
changing  organisms  ranging  more  widely  than  the  high, 
— some  of  the  species  of  widely-ranging  genera  them- 
selves ranging  widely, — such  facts,  as  alpine,  lacustrine, 
and  marsh  productions  being  related  (with  the  exceptions 
before  specified)  to  those  on  the  surrounding  low  lands 
and  dry  lands,  though  these  stations  are  so  different — the 
very  close  relation  of  the  distinct  species  which  inhabit 
the  islets  of  the  same  archipelago, — and  especially  the 
striking  relation  of  the  inhabitants  of  each  whole  archi- 
pelago or  island  to  those  of  the  nearest  mainland, — are,  1 
think,  utterly  inexplicable  on  the  ordinary  view  of  the  in- 
dependent creation  of  each  species,  but  are  explicable  on 
the  view  of  colonisation  from  the  nearest  and  readiest 
source,  together  with  the  subsequent  modification  and 
better  adaptation  of  the  colonists  to  their  new  homes. 

Summary  of  last  and  present  Chapters. — In  these 
chapters  I  have  endeavoured  to  show,  that  if  we  make 
due  allowance  for  our  ignorance  of  the  full  effects  of  all 


354  GEOGRAPHICAL    DISTRIBUTION.  [Chap.  XIl. 

the  changes  of  climate  and  of  the  level  of  the  land,  whicE 
have  certainly  occurred  within  the  recent  period,  and  of 
other  similar  changes  which  may  have  occnrred  within 
the  same  period  ;  if  we  remember  how  profoundly  igno- 
rant we  are  with  respect  to  the  many  and  curious  means 
of  occasional  transport, — a  subject  which  has  hardly  ever 
been  properly  experimentised  on  ;  if  we  bear  in  mind  how 
often  a  species  may  have  ranged  continuously  over  a  wide 
area,  and  then  have  become  extinct  in  the  intermediate 
tracts,  I  think  the  difficulties  in  believing  that  all  the  in- 
dividuals of  the  same  species,  wherever  located,  have  de- 
scended from  the  same  parents,  are  not  insuperable.  And 
we  are  led  to  this  conclusion,  which  has  been  arrived  at 
by  many  naturalists  under  the  designation  of  single  cen- 
tres of  creation,  by  some  general  considerations,  more 
especially  from  the  importance  of  barriers  and  from  the 
analogical  distribution  of  sub-genera,  genera,  and  families. 

With  respect  to  the  distinct  species  of  the  same  genus, 
which  on  my  theory  must  have  spread  from  one  parent- 
source  ;  if  we  make  the  same  allowances  as  before  for  our 
ignorance,  and  remember  that  some  forms  of  life  change 
most  slowly,  enormous  periods  of  time  being  thus  gi-anted 
for  their  migration,  I  do  not  think  that  the  difficulties  are 
insuperable  ;  though  they  often  are  in  this  case,  and  in  that 
of  the  individuals  of  the  same  species,  extremely  grave. 

As  exemplifying  the  effects  of  climatal  changes  on 
distribution,  I  have  attempted  to  show  how  important 
has  been  the  influence  of  the  modern  Glacial  period, 
which  I  am  fully  convinced  simultaneously  aflected  the 
whole  world,  or  at  least  great  meridional  belts.  As 
showing  how  diversified  are  the  means  of  occasional 
transport,  I  have  discussed  at  some  little  length  the  means 
of  dispersal  of  fresh-water  productions. 

If  the  difficulties  be  not  insuperable  in  admitting  that 
in  the  long  course  of  time  the  individuals  of  the  same 
species,  and  likewise  of  allied  species,  have  proceeded 
from  some  one  source  ;  then  I  think  all  the  grand  leading 
facts  of  geographical  distribution  are  explicable  on  the 
theory  of  migration  (generally  of  the  moi'e  dominant 
forms  of  life),  together  with  subsequent  modification  and 


I 


Chap.  XII.]  SUMMARY.  qkK 

the  multiplication  of  new  forms.  We  can  thus  under- 
stand the  high  importance  of  barriers,  whether  of  land  or 
water,  which  separate  our  several  zoological  and  botan- 
ical j^rovinces.  We  can  thus  understand  the  localisation 
of  sub-genera,  genera,  and  families  ;  and  how  it  is  that ' 
under  different  latitudes,  for  instance  in  South  America, 
the  inhabitants  of  the  plains  and  mountains,  of  the  forests, 
marshes,  and  deserts,  are  in  so  mysterious  a  manner  Imked 
together  by  affinity,  and  are  likewise  linked  to  the  extinct 
beings  which  formerly  inhabited  the  same  continent. 
Bearing  in  mind  that  the  mutual  relations  of  organism  to 
organism  are  of  the  highest  importance,  we  can  see  why 
two  areas  having  nearly  the  same  physical  conditions 
should  often  be  inhabited  by  very  difierent  forms  of  life  ; 
for  according  to  the  length  of  time  which  has  elapsed 
since  new  inhabitants  entered  one  region  ;  according  to 
the  nature  of  the  communication  which  allowed  certain 
forms  and  not  others  to  enter,  either  in  greater  or  lesser 
numbers  ;  according  or  not,  as  those  which  entered  hap- 
j^ened  to  come  in  more  or  less  direct  competition  with 
each  other  and  with  the  aborigines  ;  and  according  as  the 
immigrants  were  capable  of  varying  more  or  less  raj^idly, 
there  would  ensue  in  difierent  regions,  independently  of 
their  physical  conditions,  infinitely  diversified  conditions 
of  life, — there  would  be  an  almost  endless  amount  of  or- 
ganic action  and  reaction, — and  we  should  find,  as  we  do 
find,  some  groups  of  beings  greatly,  and  some  only  slight- 
ly modified, — some  developed  in  great  force,  some  exist- 
ing in  scanty  numbers — in  the  difierent  great  geographi- 
cal provinces  of  the  world. 

On  these  same  principles,  we  can  understand,  as  I 
have  endeavoured  to  show,  why  oceanic  islands  should 
have  few  inliabitants,  but  of  these  a  great  number  should 
be  endemic  or  peculiar ;  and  why,  in  relation  to  the 
means  of  migration,  one  group  of  beings,  even  within  the 
same  class,  should  have  all  its  species  endemic,  and  an- 
other group  should  have  all  its  species  common  to  other 
quarters  of  the  world.  We  can  see  why  whole  groups  of 
organisms,  as  batrachians  and  terrestrial  mammals,  should 
be  absent  from  oceanic  islands,  whilst  the  most  isolated 
16* 


356  GEOGRAPHICAL  DISTRIBUTION.  [Chap.  Xll. 

islands  possess  their  own  peculiar  species  of  aerial  mam- 
mals  or  bats.  We  can  see  why  there  should  be  some  re- 
lation between  the  presence  of  mammals,  in  a  more  or 
less  modified  condition,  and  the  depth  of  the  sea  between 
'  an  island  and  the  mainland.  We  can  clearly  see  why  all 
the  inhabitants  of  an  archipelago,  thongh  specifically  dis- 
tinct on  the  several  islands,  should  be  closely  related  to 
each  other,  and  likewise  be  related,  bnt  less  closely,  to 
those  of  the  nearest  continent  or  other  source  whence  im- 
migrants were  probably  derived.  We  can  see  why  in  two 
areas,  however  distant  from  each  other,  there  should  be  a 
correlation,  in  the  presence  of  identical  species,  of  varie- 
ties, of  doubtful  species,  and  of  distinct  but  representative 
species. 

As  the  late  Edward  Forbes  often  insisted,  there  is  a 
striking  parallelism  in  the  laws  of  life  throughout  time 
and  space  :  the  laws  governing  the  succession  of  forms  in 
past  times  being  nearly  the  same  with  those  governing  at 
the  present  time  the  differences  in  different  areas.  We 
see  this  in  many  facts.  The  endurance  of  each  species 
and  group  of  species  is  continuous  in  time  ;  for  the  excep- 
tions to  the  rule  are  so  few,  that  they  may  faii-ly  be  at- 
tributed to  our  not  having  as  yet  discovered  in  an  inter- 
mediate deposit  the  forms  which  are  therein  absent,  but 
which  occur  above  and  below  :  so  in  space,  it  certainly  is 
the  general  rule  that  the  area  inhabited  by  a  single  spe- 
cies, or  by  a  group  of  sj^ecies,  is  continuous  ;  and  the  ex- 
ceptions, which  are  not  rare,  may,  as  I  have  attemjDted  to 
show,  be  accounted  for  by  migration  at  some  former 
period  under  different  conditions  or  by  occasional  means 
of  transport,  and  by  the  species  having  become  extinct  in 
the  intermediate  tracts.  Both  in  time  and  space,  species 
and  grouj)s  of  species  have  their  points  of  maximum  de- 
velopment. Groups  of  species,  belonging  either  to  a  cer- 
tain period  of  time,  or  to  a  certain  area,  are  often  charac- 
terised by  trifling  characters  in  common,  as  of  sculpture 
or  colour.  In  looking  to  the  long  succession  of  ages,  as  in 
now  looking  to  distant  provinces  throughout  the  world, 
we  find  that  some  organisms  differ  little,  whilst  others 
belonging  to  a  different  class,  or  to  a  diflerent  order,  or 


CHAi>.  XII. >  SUMMARY. 


357 


even  only  to  a  different  family  of  the  same  order,  differ 
greatly.  In  both  time  and  space  the  lower  members  of 
each  class  generally  change  less  than  the  higher ;  but 
there  are  in  both  cases  marked  exceptions  to  the  rule. 
On  my  theory  these  several  relations  throughout  time 
and  space  are  intelligible ;  for  whether  we  look  to  the 
forms  of  life  which  have  changed  during  successive  ages 
within  the  same  quarter  of  the  world,  or  to  those  which 
have  changed  after  having  migrated  into  distant  quarters, 
in  both  cases  the  forms  within  each  class  have  been  con- 
nected by  the  same  bond  of  ordinary  generation  ;  and  the 
more  nearly  any  two  forms  are  related  in  blood,  the  near- 
er they  will  generally  stand  to  each  other  in  time  and 
space  ;  in  both  cases  the  laws  of  variation  have  been  the 
same,  and  modifications  have  been  accumulated  by  the 
same  power  of  natural  selection. 


558  CLASSIFICATIOK-.  [Chxp.  XIIL 


CHAPTEE    XIII. 

MUTUAL    AFFINITIES    OF    ORGANIC    BEINGS  :     MORPHOLOGY  :     EMBRI*- 
OLOGY  :      RUDIMENTARY    ORGANS. 

Classification,  groups  subordinate  to  groups— Natural  system— Rules  and  difficul- 
ties in  classification,  explained  on  the  theory  of  descent  -with  modification — Classi- 
fication of  varieties — Descent  always  used  in  classification — Analogical  or  adaptive 
characters — Affinities,  general,  complex  and  radiating — Extinction  separates  and 
defines  groups — Morphology,  between  members  of  the  same  class,  between  parts 
of  the  same  individual — Embryology,  laws  of,  explained  by  variations  not  super- 
vening at  an  early  age,  and  being  inherited  at  a  corresponding  age— Rudimentary 
ORGANS  •,  their  origin  explained — Summary. 

From  the  first  dawn  of  life,  all  organic  beings  are  fonnd 
to  resemble  eacb  other  in  descending  degrees,  so  that  they 
can  be  classed  in  groups  nnder  groups.  This  classification 
is  evidently  not  arbitrary  like  the  grouj)ing  of  the  stars  in 
constellations.  The  existence  of  groups  would  have  been 
of  simj)le  signification  if  one  group  had  been  exclusively 
fitted  to  inhabit  the  land,  and  another  the  water  ;  one  to 
feed  on  flesh,  another  on  vegetable  matter,  and  so  on ; 
but  the  case  is  widely  diff'erent  in  nature  ;  for  it  is  notori- 
ous how  commonly  members  of  even  the  same  sub-group 
have  difi'erent  habits.  In  our  second  and  fourth  chapters, 
on  Variation  and  on  I^atural  Selection,  I  have  attempted 
to  show  that  it  is  the  widely  ranging,  the  much  diftused 
and  common,  that  is  the  dominant  species  belonging  to 
the  larger  genera,  which  vary  most.  The  varieties,  or  in- 
cipient species,  thus  produced  ultimately  become  convert- 
ed, as  I  believe,  into  new  and  distinct  species  ;  and  these, 
on  the  principle  of  inheritance,  tend  to  produce  other  new 
and  dominant  species.  Consequently  the  groups  which 
are  now  large,  and  which  generally  include  many  domi- 
nant species,  tend  to  go  on  increasing  indefinitely  in  size. 
I  further  attempted  to  show  that  from  the  varying  de- 


Chap.  XIII.I  CLASSIFICATIOS".  359 

scendants  of  each  species  trying  to  occupy  as  many  and 
as  different  places  as  possible  in  the  economy  of  nature, 
there  is  a  constant  tendency  in  their  characters  to  diverge. 
This  conclusion  was  supported  by  looking  at  the  great 
diversity  of  the  forms  of  life  which,  in  any  small  area^ 
come  into  the  closest  competition,  and  by  looking  to  cer- 
tain facts  in  naturalisation. 

I  attempted  also  to  show  that  there  is  a  constant  ten- 
dency in  the  forms  which  are  increasing  in  number  and 
diverging  in  character,  to  supplant  and  exterminate  the 
less  divergent,  the  less  improved,  and  preceding  forms. 
I  request  the  reader  to  turn  to  the  diagram  illustrating 
the  action,  as  formerly  explained,  of  these  several  princi- 
ples, and  he  will  see  that  the  inevitable  result  is  that  the 
modified  descendants  proceeding  from  one  progenitor 
become  broken  up  into  groups  subordinate  to  groups.  In 
the  diagram  each  letter  on  the  uppermost  line  may  repre- 
sent a  genus  including  several  species  ;  and  all  the  genera 
on  this  line  form  together  one  class,  for  all  have  descend- 
ed from  one  ancient  but  unseen  parent,  and,  consequently, 
have  inherited  something  in  common.  But  the  three 
genera  on  the  left  hand  have,  on  this  same  principle,  much 
in  common,  and  form  a  sub-family,  distinct  from  that  in- 
cluding the  next  two  genera  on  the  right  hand,  which 
diverged  from  a  common  parent  at  the  lifth  stage  of  de- 
scent. These  five  genera  have  also  much,  though  less,  in 
common  ;  and  they  form  a  family  distinct  from  that  includ- 
ing the  three  genera  still  further  to  the  right  hand,  which 
diverged  at  a  still  earlier  period.  And  all  these  genera, 
descended  from  (A),  form  an  order  distinct  from  the  genera 
descended  from  (I).  So  that  we  here  have  many  species 
descended  from  a  single  progenitor  grouped  into  genera  ; 
and  the  genera  are  included  in,  or  subordinate  to,  sub- 
families, and  orders,  all  united  into  one  class.  Thus,  the 
grand  fact  in  natural  history  of  the  subordination  of  group 
under  group,  which,  from  its  familiarity,  does  not  always 
sufficiently  strike  us,  is  in  my  judgment  fully  explained. 

"Naturalists  try  to  arrange  the  species,  genera,  and 
families  in  each  class,  on  what  is  called  the  ^Natural  Sys- 
tem.    But  what  is  meant  by  this  system  ?     Some  authors 


3gQ  CLASSlFlCA'TlON.  [Chap.  XIll. 

look  at  it  merely  as  a  scheme  for  arranging  together  those 
living  objects  which  are  most  alike,  and  for  separating 
those  which  are  most  unlike  ;  or  as  an  artificial  means  for 
enunciating,  as  briefly  as  possible,  general  propositions, — 
that  is,  by  one  sentence,  to  give  the  characters  common, 
for  instance,  to  all  mammals,  by  another  those  common  to 
all  carnivora,  by  another  those  common  to  the  dog-genus, 
and  then  by  adding  a  single  sentence,  a  full  description  is 
given  of  each  kind  of  dog.  The  ingenuity  and  utility  of 
this  system  are  indisputable.  But  many  naturalists  think 
that  something  more  is  meant  by  the  I^atural  System ; 
they  believe  that  it  reveals  the  plan  of  the  Creator ;  but 
unless  it  be  specified  whether  order  in  time  or  space,  or 
what  else  is  meant  by  the  plan  of  the  Creator,  it  seems  to 
me  that  nothing  is  thus  added  to  our  knowledge.  Such 
expressions  as  that  famous  one  of  Linnaeus,  and  which  we 
often  meet  with  in  a  more  or  less  concealed  form,  that  the 
characters  do  not  make  the  genus,  but  that  the  genus 
gives  the  characters,  seem  to  imply  that  something  more 
is  included  in  our  classification,  than  mere  resemblance. 
I  believe  that  something  more  is  included  ;  and  that  pro- 
pinquity of  descent, — the  only  known  cause  of  the  simi- 
larity of  organic  beings,-— is  the  bond,  hidden  as  it  is  by 
various  degrees  of  modification,  which  is  partially  revealed 
to  us  by  oui'  classifications. 

Let  us  now  consider  the  rules  followed  in  classification, 
and  the  difliculties  which  are  encountered  on  the  view 
that  classification  either  gives  some  unknown  plan  of  crea- 
tion, or  is  simply  a  scheme  for  enunciating  general  pro- 
positions and  of  placing  together  the  forms  most  like  each 
other.  It  might  have  been  thought  (and  was  in  ancient 
times  thought)  that  those  parts  of  the  structure  which  de- 
termined the  habits  of  life,  and  the  general  place  of  each 
being  in  the  economy  of  nature  would  be  of  very  high 
importance  in  classification.  [N^othing  can  be  more  false. 
Ko  one  regards  the  external  similarity  of  a  mouse  to  a 
shrew,  of  a  dugong  to  a  whale,  of  a  whale  to  a  fish,  as  of 
any  importance.  These  resemblances,  though  so  intimate- 
ly connected  with  the  whole  life  of  the  being,  are  ranked 
as  merely  "  adaptive  or  analogical  characters  ;  "  but  to 


Chap.  XIII.J  CLASSIFICATION-.  3gj[ 

the  consideration  of  these  resemblances  we  shall  have  to 
recur.  It  may  even  be  given  as  a  general  rule,  that  the 
less  any  part  of  the  organisation  is  concerned  with  special 
habits,  the  more  important  it  becomes  for  classification. 
As  an  instance :  Owen,  in  speaking  of  the  dugong,  says, 
"  The  generative  organs  being  those  which  are  most  re- 
motely related  to  the  habits  and  food  of  an  animal,  I  have 
always  regarded  as  affording  very  clear  indications  of  its 
true  affinities.  We  are  least  likely  in  the  modifications  of 
these  organs  to  mistake  a  merely  adaptive  for  an  essential 
character."  So  with  plants,  how  remarkable  it  is  that 
the  organs  of  vegetation,  on  which  their  whole  life  de- 
pends, are  of  little  signification,  excepting  in  the  first  main 
divisions  ;  whereas  the  organs  of  reproduction,  with  their 
product  the  seed,  are  of  paramount  importance  ! 

"VVe  must  not,  therefore,  in  classifying,  trust  to  resem- 
blances in  parts  of  the  organisation,  however  important 
they  may  be  for  the  welfare  of  the  being  in  relation  to  the 
outer  world.  Perhaps  from  this  cause  it  has  partly  arisen, 
that  almost  all  naturalists  lay  the  greatest  stress  on  resem- 
blances in  organs  of  high  vital  or  physiological  impor- 
tance. 1^0  doubt  this  view  of  the  classificatory  importance 
of  organs  which  are  important  is  generally,  but  by  no 
means  always,  true.  But  their  importance  for  classifica- 
tion, I  believe,  depends  on  their  greater  constancy  through- 
out large  groups  of  species ;  and  this  constancy  depends 
on  such  organs  having  generally  been  subjected  to  less 
change  in  the  adaptation  of  the  species  to  their  conditions 
of  life.  Tliat  the  mere  physiological  importance  of  an 
organ  does  not  determine  its  classificatory  value,  is  almost 
shown  by  the  one  fact,  that  in  allied  groups,  in  which  the 
same  organ,  as  we  have  every  reason  to  suppose,  has 
nearly  the  same  physiological  value,  its  classificatory 
value  is  widely  different,  ^o  naturalist  can  have  worked 
at  any  group  without  being  struck  with  this  fact ;  and  it 
has  been  most  fully  acknowledged  in  the  writings  of  almost 
every  author.  It  will  suffice  to  quote  the  highest  authori- 
ty, Robert  Brown,  who  in  speaking  of  certain  organs  in 
the  Proteaceae,  says  their  generic  importance,  "  like  that 
of  all  their  parts,  not  only  in  this  but,  as  I  apprehend,  in 


302  CLASSIFICATIOIf.  [Chap.  XIII. 

every  natural  family,  is  very  uneqiial,  and  in  some  cases 
seems  to  be  entirely  lost."  Again  in  another  work  he 
says,  the  genera  of  the  Connaraceae  "  difter  in  having  one 
or  more  ovaria,  in  the  existence  or  absence  of  albumen,  in 
the  imbricate  or  valvular  aestivation.  Any  one  of  these 
characters  singly  is  frequently  of  more  than  generic  im- 
portance, though  here  even  when  all  taken  together  they 
appear  insufficient  to  separate  Cnestis  from  Connarus." 
To  give  an  example  amongst  insects,  in  one  great  division 
of  the  Hymenoptera,  the  antennae,  as  Westwood  has  re- 
marked, are  most  constant  in  structure  ;  in  another  divi- 
sion they  differ  much,  and  the  differences  are  of  quite 
subordinate  value  in  classification  ;  yet  no  one  probably 
will  say  that  the  antennae  in  these  two  divisions  of  the 
same  order  are  of  unequal  physiological  importance.  Any 
number  of  instances  could  be  given  of  the  varying  im- 
portance for  classification  of  the  same  important  organ 
within  the  same  group  of  beings. 

Again,  no  one  will  say  that  rudimentary  or  atrophied 
organs  are  of  high  physiological  or  vital  imj)ortance ; 
yet,  undoubtedly,  organs  in  this  condition  are  often  of 
high  value  in  classification.  'No  one  will  dispute  that  the 
rudimentary  teeth  in  the  upper  jaws  of  young  ruminants, 
and  certain  rudimentary  bones  of  the  leg,  are  highly  ser- 
viceable in  exhibiting  the  close  affinity  between  Rumi- 
nants and  Pachyderms.  Robert  Brown  has  strongly  in- 
sisted on  the  fact  that  the  rudimentary  florets  are  of  the 
highest  importance  in  the  classification  of  the  Grasses. 

IS'umerous  instances  could  be  given  of  characters  de- 
rived from  parts  which  must  be  considered  of  very  trifling 
physiological  importance,  but  which  are  universally  ad- 
mitted as  highly  serviceable  in  the  definition  of  whole 
groups.  For  instance  whether  or  not  there  is  an  open 
passage  from  the  nostrils  to  the  mouth,  the  only  character, 
according  to  Owen,  which  absolutely  distinguishes  fishes 
and  reptiles — the  infiection  of  the  angle  of  the  jaws  in 
Marsupials — the  manner  i]i  which  the  wings  of  insects  arc 
folded — mere  colour  in  certain  Algae — mere  pubescence 
on  the  parts  of  the  flower  in  grasses — the  nature  of  the 
deraial  covering,  as  hair  or  feathers,  in  the  Yertebrata. 


Chap.  XIII.]  CLASSIFICATION.  3gg 

If  the  Ornitliorhynclnis  had  been  covered  with  feathers 
instead  of  hair,  this  external  and  trifling  character  would, 
I  think,  have  been  considered  by  naturalists  as  important 
an  aid  in  determining  the  degree  of  affinity  of  this  strange 
creature  to  birds  and  reptiles,  as  an  approach  in  structure 
in  any  one  internal  and  important  organ. 

The  importance,  for  classification,  of  trifling  characters, 
mainly  depends  on  their  being  correlated  with  several 
other  characters  of  more  or  less  importance.  The  value 
indeed  of  an  aggregate  of  characters  is  very  evident  in 
natural  history.  Hence,  as  has  often  been  remarked,  a 
species  may  depart  from  its  allies  in  several  characters, 
both  of  high  physiological  importance  and  of  almost  uni- 
versal prevalence,  and  yet  leave  us  in  no  doubt  where  it 
should  be  ranked.  Hence,  also,  it  has  been  found,  that  a 
classification  founded  on  any  single  character,  however 
important  that  may  be,  has  always  failed  ;  for  no  part  of 
the  organisation  is  universally  constant.  The  importance 
of  an  aggregate  of  characters,  even  when  none  are  im- 
portant, alone  explains,  I  think,  that  saying  of  Linngeus, 
that  the  characters  do  not  give  the  genus,  but  the  genus 
gives  the  characters  ;  for  this  saying  seems  founded  on  an 
appreciation  of  many  trifling  points  of  resemblance,  too 
slight  to  be  defined.  Certain  plants,  belonging  to  the 
Malpighiacese,  bear  perfect  and  degraded  flowers  ;  in  the 
latter,  as  A.  de  Jussieu  has  remarked,  "the  greater  number 
of  the  characters  proper  to  the  species,  to  the  genus,  to 
the  family,  to  the  class,  disappear,  and  thus  laugh  at  our 
classification."  But  when  Aspicarpa  produced  in  France, 
during  several  years,  only  degraded  flowers,  departing  so 
wonderfully  in  a  number  of  the  most  important  points  of 
structure  from  the  proper  type  of  the  order,  yet  M. 
Eichard  sagaciously  saw,  as  Jussieu  observes,  that  this 
genus  should  still  be  retained  amongst  the  Malpighiacese. 
This  case  seems  to  me  well  to  illustrate  the  spirit  with 
which  our  classifications  are  sometimes  necessarily  founded. 

Practically  when  naturalists  are  at  work,  they  do  not 
trouble  themselves  about  the  physiological  value  of  the 
characters  which  they  use  in  defining  a  group,  or  in  allo- 
cating any  particular  species.     K  they  find  a  character 


364:  CLASSIFICATION.  [Chap.  XIII. 

nearly  uniform,  and  common  to  a  great  nnmber  of  forms, 
and  not  common  to  others,  they  use  it  as  one  of  high 
value ;  if  common  to  some  lesser  number,  they  use  it  as  of 
subordinate  value.  Tliis  principle  has  been  broadly  con- 
fessed by  some  naturalists  to  be  the  true  one ;  and  by 
none  more  clearly  than  by  that  excellent  botanist,  Aug. 
St.  Hilaire.  If  certain  characters  are  always  found  cor- 
related with  others,  though  no  apparent  bond  of  connexion 
can  be  discovered  between  them,  es]3ecial  value  is  set  on 
them.  As  in  most  groups  of  animals,  important  organs, 
such  as  those  for  propelling  the  blood,  or  for  aerating  it, 
or  those  for  propagating  the  race,  are  found  nearly  uni- 
form, they  are  considered  as  highly  serviceable  in  classifica- 
tion ;  but  in  some  groups  of  animals  all  these,  the  most  im- 
portant vital  organs,  are  found  to  offer  characters  of  quite 
subordinate  value. 

We  can  see  why  characters  derived  from  the  embryo 
should  be  of  equal  importance  with  those  derived  from 
the  adult,  for  our  classifications  of  course  include  all  ages 
of  each  species.  But  it  is  by  no  means  obvious,  on  the 
ordinary  view,  why  the  structure  of  the  embryo  should 
be  more  important  for  this  purpose  than  that  of  the  adult, 
which  alone  plays  its  full  part  in  the  economy  of  nature. 
Yet  it  has  been  strongly  urged  by  those  great  naturalists, 
Milne  Edwards  and  Agassiz,  that  embryonic  characters 
are  the  most  important  of  any  in  the  classification  of  ani- 
mals ;  and  this  doctrine  has  very  generally  been  admitted 
as  true.  The  same  fact  holds  good  with  flowering  plants, 
of  which  the  two  main  divisions  have  been  founded  on 
characters  derived  from  the  embryo, — on  the  number  and 
position  of  the  embryonic  leaves  or  cotyledons,  and  on 
the  mode  of  develoj^ment  of  the  plumule  and  radicle.  In 
our  discussion  on  embryology,  we  shall  see  why  such 
characters  are  so  valuable,  on  the  view  of  classification 
tacitly  including  the  idea  of  descent. 

Our  classifications  are  often  plainly  influenced  by 
chains  of  afiinities.  Nothing  can  be  easier  than  to  define 
a  number  of  characters  common  to  all  birds  ;  but  in  the 
case  of  crustaceans,  such  definition  has  hitherto  been 
found  impossible.     There  are  crustaceans  at  the  opposite 


Chap.  XIII.]  CLASSIFICATION.  3^5 

ends  of  the  series,  which  have  hardly  a  character  in  com- 
mon ;  yet  the  species  at  both  ends,  from  being  plainly 
allied  to  others,  and  these  to  others,  and  so  onwards,  can 
be  recognised  as  unequivocally  belonging  to  this,  and  to 
no  other  class  of  the  Articulata. 

Geographical  distribution  has  often  been  used,  though 
perhaps  not  quite  logically,  in  classification,  more  espe- 
cially in  very  large  groups  of  closely  allied  forms.  Tem- 
minck  insists  on  the  utility  or  even  necessity  of  this  prac- 
tice in  certain  groups  of  birds  ;  and  it  has  been  followed 
by  several  entomologists  and  botanists. 

Finally,  with  respect  to  the  comparative  value  of  the 
various  groups  of  species,  such  as  orders,  sub-orders,  fam- 
ilies, sub-families  and  genera,  they  seem  to  be,  at  least  at 
present  almost  arbitrary.  Several  of  the  best  botanists,  such 
as  Mr.  Bentham,  and  others,  have  strongly  insisted  on  their 
arbitrary  value.  Instances  could  be  given  amongst  plants 
and  insects,  of  a  group  of  forms,  first  ranked  by  practised 
naturalists  as  only  a  genus,  and  then  raised  to  the  rank  of 
a  sub-family  or  family  ;  and  this  has  been  done,  not  be- 
cause further  research  has  detected  important  structural 
differences,  at  first  overlooked,  but  because  numerous  al- 
lied species,  with  slighty  difi'erent  grades  of  difl*erence, 
have  been  subsequently  discovered. 

All  the  foregoing  rules  and  aids  and  difficulties  in 
classification  are  explained,  if  I  do  not  greatly  deceive 
myself,  on  the  view  that  the  natural  system  is  founded 
on  descent  with  modification ;  that  the  characters  which 
naturalists  consider  as  showing  true  affinity  between  any 
two  or  more  species,  are  those  which  have  been  inherited 
from  a  common  parent,  and,  in  so  far,  all  true  classifica- 
tion is  genealogical ;  that  community  of  descent  is  the 
hidden  bond  which  naturalists  have  been  unconsciously 
seeking,  and  not  some  unknown  plan  of  creation,  or  the 
enunciation  of  general  propositions,  and  the  mere  putting 
together  and  separating  objects  more  or  less  alike. 

But  I  must  explain  my  meaning  more  fully.  I  be- 
lieve that  the  arrangement  of  the  groups  within  each  class, 
in  due  subordination  and  relation  to  the  other  groups, 
must  be  strictly  genealogical  in  order  to  be  natural ;  but 


ggg  CLASSIFICATION.  [Chap.  XIIL 

that  the  amount  of  difference  in  tlie  several  branches  or 
gro-iips,  though  allied  in  the  same  degree  in  blood  to 
their  common  progenitor,  may  differ  greatly,  being  due 
to  the  different  degrees  of  modification  which  they  have 
undergone  ;  and  this  is  expressed  by  the  forms  being 
ranked  under  different  genera,  families,  sections,  or  or- 
ders. The  reader  will  best  understand  what  is  meant,  if 
he  will  take  the  trouble  of  referring  to  the  diagram  in  the 
fourth  chapter.  We  will  suppose  the  letters  A  to  L  to 
represent  allied  genera,  which  lived  during  the  Silurian 
epoch,  and  these  have  descended  from  a  species  which  ex- 
isted at  an  unknown  anterior  period.  Species  of  three  of 
these  genera  (A,  F,  and  I)  have  transmitted  modified  de- 
scendants to  the  present  day,  represented  by  the  fifteen 
genera  {p}^  to  0")  on  the  uppermost  horizontal  line.  JN'ow 
all  these  modified  descendants  from  a  single  species,  are 
represented  as  related  in  blood  or  descent  to  the  same 
degree  ;  they  may  metaphorically  be  called  cousins  to  the 
same  millionth  degree  ;  yet  they  differ  widely  and  in  dif- 
ferent degrees  from  each  other.  The  forms  descended  from 
A,  now  broken  up  into  two  or  three  families,  constitute  a 
distinct  order  from  those  descended  from  I,  also  broken 
up  into  two  families.  !Nor  can  the  existing  species,  de- 
scended from  A,  be  ranked  in  the  same  genus  with  the 
parent  A  ;  or  those  from  I,  with  the  parent  I.  But  the 
existing  genus  F'*  may  be  supposed  to  have  been  but 
slightly  modified  ;  and  it  will  then  rank  with  the  parent- 
genus  F  ;  just  as  some  few  still  living  organic  beings 
belong  to  Silurian  genera.  So  that  the  amount  or  value 
of  the  differences  between  organic  beings  all  related  to 
each  other  in  the  same  degree  in  blood,  has  come  to  be 
widely  different.  ^Nevertheless  their  genealogical  arrange' 
ment  remains  strictly  true,  not  only  at  the  present  time, 
but  at  each  successive  period  of  descent.  All  the  modified 
descendants  from  A  will  have  inherited  something  in 
common  from  their  common  parent,  as  will  all  the  descend- 
ants from  I ;  so  will  it  be  with  each  subordinate  branch 
of  descendants,  at  each  successive  period.  If,  however, 
we  choose  to  suppose  that  any  of  the  descendants  of  A 
or  of  I  have  been  so  much  modified  as  to  have  more  or 


Chap.  XIII.]  CLASSIFICATION.  gg^ 

less  completely  lost  traces  of  tlieir  parentage,  in  this  case, 
their  places  in  a  natural  classification  will  have  been  more 
or  less  completely  lost,' — as  sometimes  seems  to  have 
occurred  with  existing  organisms.  All  the  descendants  of 
the  genus  F,  along  its  whole  line  of  descent,  are  supposed 
to  have  been  but  little  modified,  and  they  yet  form  a 
single  genus.  But  this  genus,  though  much  isolated,  will 
still  occu23y  its  proper  intermediate  position  ;  for  F  origi- 
nally was  intermediate  in  character  between  A  and  I,  and 
the  several  genera  descended  from  these  two  genera  will 
have  inherited  to  a  certain  extent  their  characters.  This 
natural  arrangement  is  shown,  as  far  as  is  possible  on 
paper,  in  the  diagram,  but  in  much  too  simple  a  manner. 
K  a  branching  diagram  had  not  been  used,  and  only  the 
names  of  the  groups  had  been  written  in  a  linear  series, 
it  would  have  been  still  less  possible  to  have  given  a  natural 
arrangement ;  and  it  is  notoriously  not  possible  to  repre- 
sent in  a  series,  on  a  flat  surface,  the  affinities  which  we 
discover  in  nature  amongst  the  beings  of  the  same  group. 
Thus,  on  the  view  which  I  hold,  the  natural  system  is 
genealogical  in  its  arrangement,  like  a  pedigree  ;  but  the 
degrees  of  modification  which  the  difi'erent  groups  have 
undergone,  have  to  be  expressed  by  ranking  them  under 
difi'erent  so-called  genera,  sub-families,  families,  sections, 
orders,  and  classes. 

It  may  be  worth  while  to  illustrate  this  view  of  classi- 
fication, by  taking  the  case  of  languages.  If  we  possessed 
a  perfect  pedigree  of  mankind,  a  genealogical  arrange- 
ment of  the  races  of  man  would  afi'ord  the  best  classifica- 
tion of  the  various  languages  now  spoken  throughout  the 
world  ;  and  if  all  extinct  languages,  and  all  intermediate 
and  slowly  changing  dialects,  had  to  be  included,  such  an 
arrangement  would,  I  think,  be  the  only  possible  one. 
Yet  it  might  be  that  some  very  ancient  language  had 
altered  little,  and  had  given  rise  to  few  new  languages, 
whilst  others  (owing  to  the  spreading  and  subsequent 
isolation  and  states  of  civilisation  of  the  several  races, 
descended  from  a  common  race)  had  altered  much,  and 
had  given  rise  to  many  new  languages  and  dialects.  The 
various  degrees  of  difference  in  the  languages  from  the 


353  CLASSIFICATION.  [Chap.  XIIL 

same  stock,  would  have  to  be  expressed  by  groups  sub- 
ordinate to  groups  ;  but  the  proj^er  or  even  only  possible 
arrangement  would  still  be  genealogical ;  and  this  would 
be  strictly  natural,  as  it  would  connect  together  all  lan- 
guages, extinct  and  modern,  by  the  closest  affinities,  and 
would  give  the  filiation  and  origin  of  each  tongue. 

In  confirmation  of  this  view,  let  us  glance  at  the 
classification  of  varieties,  which  are  believed  or  known  to 
have  descended  from  one  species.  These  are  grouped 
under  species,  with  sub-varieties  under  varieties  ;  and  with 
our  domestic  productions,'  several  other  grades  of  difierence 
are  requisite,  as  we  have  seen  with  pigeons.  The  origin 
of  the  existence  of  groups  subordinate  to  groups,  is  the 
same  with  varieties  as  with  species,  namely,  closeness  of 
descent  with  various  degrees  of  modification.  Xearly 
the  same  rules  are  followed  in'  classifying  varieties,  as 
with  species.  Authors  have  insisted  on  the  necessity  of 
classing  varieties  on  a  natural  instead  of  an  artificial 
system  ;  we  are  cautioned,  for  instance,  not  to  class  two 
varieties  of  the  pine-apple  together,  merely  because  their 
fruit,  though  the  most  important  part,  happens  to  be 
nearly  identical ;  no  one  j^uts  the  Swedish  and  common 
turnips  together,  though  the  esculent  and  thickened  stems 
are  so  similar.  Whatever  part  is  found  to  be  most  con- 
stant, is  used  in  classing  varieties  :  thus  the  great  agri- 
culturist Marshall  says  the  horns  are  very  useful  for  tliis 
purpose  with  cattle,  because  they  are  less  variable  than 
the  shape  or  colour  of  the  body,  &c. ;  whereas  with  sheep 
the  horns  are  much  less  serviceable,  because  less  constant. 
In  classing  varieties,  I  apprehend  if  we  had  a  real  pedi- 
gree, a  genealogical  classification  would  be  universally 
preferred ;  and  it  has  been  attempted  by  some  authors. 
For  we  might  feel  sure,  whether  there  had  been  more  or 
less  modification,  the  principle  of  inheritance  would  keep 
the  forms  together  which  were  allied  in  the  greatest  num- 
ber of  points.  In  tumbler  j^igeons,  though  some  sub- 
varieties  difi*er  from  the  others  in  the  important  character 
of  having  a  longer  beak,  yet  all  are  kept  together  from 
having  the  common  habit  of  tumbling  ;  but  the  short- 
faced  breed  lias  nearly  or  quite  lost  this  habit ;  neverthe- 


Chap.  XIII.]  CLASSIFICATIOX.  ggQ 

less,  wittLont  any  reasoning  or  thinking  on  tlie  subject, 
these  tumblers  are  kept  in  the  same  group,  because  allied 
in  blood  and  alike  in  some  other  respects.  If  it  could  be 
proved  that  the  Hottentot  had  descended  from  the  IS'egro, 
I  think  he  would  be  classed  under  the  Kegro  group,  how- 
ever much  he  might  differ  in  colour  and  other  iniportant 
characters  from  negroes. 

With  species  in  a  state  of  nature,  every  naturalist  has 
in  fact  brought  descent  into  his  classification  ;  for  he 
includes  in  his  lowest  grade,  or  that  of  a  species,  the  two 
sexes  ;  and  how  enormously  these  sometimes  differ  in  the 
most  important  characters,  is  known  to  every  naturalist : 
scarcely  a  single  fact  can  be  predicated  in  common  of  the 
males  and  hermaphrodites  of  certain  cirripedes,  when  adult, 
and  yet  no  one  dreams  of  separating  them.  The  natural- 
ist includes  as  one  species  the  several  larval  stages  of  the 
same  individual,  however  much  they  may  differ  from  each 
other  and  from  the  adult ;  as  he  likewise  includes  the  so- 
called  alternate  generations  of  Steenstrup,  which  can  only 
in  a  technical  sense  be  considered  as  the  same  individual. 
He  includes  monsters  ;  he  includes  varieties,  not  solely  be- 
cause they  resemble  the  parent-form,  but  because  they  are 
descended  from  it.  He  who  believes  that  the  cowslip  is 
descended  from  the  primrose,  or  conversely,  ranks  them 
together  as  a  single  species,  and  gives  a  single  definition. 
As  soon  as  three  Orchidean  forms  (Monochanthus,  Myan- 
thus,  and  Catasetum),  which  had  previously  been  ranked 
as  three  distinct  genera,  were  known  to  be  sometimes  jyvo- 
duced  on  the  same  spike,  they  were  immediately  included 
as  a  single  specieS;  But  it  may  be  asked,  what  ought  wo 
to  do,  if  it  could  be  proved  that  one  species  of  kangaroo 
had  been  produced,  by  a  long  course  of  modification,  from 
a  bear  ?  Ought  we  to  rank  this  one  species  with  bears, 
and  what  should  we  do  with  the  other  species  ?  The  sup- 
position is  of  course  preposterous  ;  and  I  might  answer  by 
the  argumentum  ad  Jiominem,  and  ask  what  should  be 
done  if  a  perfect  kangaroo  were  seen  to  come  out  of  the 
womb  of  a  bear  ?  According  to  all  analogy,  it  would  be 
ranked  with  bears ;  but  then  assuredly  all  the  other  species 
of  the  kangaroo  family  would  have  to  be  classed  under 


gYQ  CLASSIFICATION.  [Csap.  XIIL 

tlie  bear  genus.  Tbe  whole  case  is  preposterous ;  for 
where  there  has  been  close  descent  in  common,  there  will 
certainly  be  close  resemblance  or  affinity. 

As  descent  has  universally  been  used  in  classing  to- 
gether the  individuals  of  the  same  species,  though  the 
males  and  females  and  larvae  are  sometimes  extremely 
different ;  and  as  it  has  been  used  in  classing  varieties 
which  have  undergone  a  certain,  and  sometimes  a  consider- 
able amount  of  modification,  may  not  this  same  element 
of  descent  have  been  unconsciously  used  in  grouping  spe- 
cies under  genera,  and  genera  under  higher  groups,  though 
in  these  cases  the  modification  has  been  greater  in  degree, 
and  has  taken  a  longer  time  to  complete  ?  I  believe  it 
has  thus  been  unconsciously  used ;  and  only  thus  can  I 
understand  the  several  rules  and  guides  which  have  been 
followed  by  our  best  systematists.  We  have  no  written 
pedigrees  ;  we  have  to  make  out  community  of  descent 
by  resemblances  of  any  kind.  Therefore  we  choose  those 
characters  which,  as  far  as  we  can  judge,  are  the  least 
likely  to  have  been  modified  in  relation  to  the  conditions 
of  life  to  which  each  sj)ecies  has  been  recently  exposed. 
Rudimentary  structures  on  this  view  are  as  good  as,  or 
even  sometimes  better  than,  other  parts  of  the  organisa- 
tion. We  care  not  how  trifling  a  character  may  be — ^let 
it  be  the  mere  inflection  of  the  angle  of  the  jaw,  the 
manner  in  which  an  insect's  wing  is  folded,  whether  the 
skin  be  covered  by  hair  or  feathers — if  it  prevail  through- 
out many  and  different  species,  especially  those  having 
very  different  habits  of  life,  it  assumes  high  value  ;  for  we 
can  account  for  its  j)i'esence  in  so  many  forms  with  such 
different  habits,  only  by  its  inheritance  from  a  common 
parent.  We  may  err  in  this  respect  in  regard  to  single 
points  of  structure,  but  when  several  characters,  let  them 
be  ever  so  trifling,  occur  together  throughout  a  large  group 
of  beings  having  different  habits,  we  may  feel  almost  sure, 
on  the  theory  of  descent,  that  these  characters  have  been 
inherited  from  a  common  ancestor.  And  we  know  that 
such  correlated  or  aggregated  characters  have  especial 
value  in  cloysification. 

We  can  understand  why  a  species  or  a  group  of  species 


Chap.  XIIL]  CLASSIFICATION.  3^1 

may  depart,  in  several  of  its  most  important  character- 
istics, from  its  allies,  and  yet  be  safely  classed  with  them. 
This  may  be  safely  done,  and  is  often  done,  as  long  as  a 
sufficient  number  of  characters,  let  them  be  ever  so  unim- 
portant, betrays  the  hidden  bond  of  community  of  descent. 
Let  two  forms  have  not  a  single  character  in  common,  yet 
if  these  extreme  forms  are  connected  together  by  a  chain 
of  intermediate  groups,  we  may  at  once  infer  their  com- 
munity of  descent,  and  we  put  them  all  into  the  same 
class.  As  we  find  organs  of  high  physiological  importance 
— those  which  serve  to  preserve  life  under  the  most  diverse 
conditions  of  existence — are  generally  the  most  constant, 
we  attach  especial  value  to  them ;  but  if  these  same 
organs,  in  another  group  or  section  of  a  group,  are  found 
to  differ  much,  we  at  once  value  them  less  in  our  classifi- 
cation. We  shall  hereafter,  I  think,  clearly  see  why  em- 
bryological  characters  are  of  such  high  classificatory  im- 
portance. Geographical  distribution  may  sometimes  be 
brought  usefully  into  play  in  classing  large  and  widely- 
distributed  genera,  because  all  the  species  of  the  same 
genus,  inhabiting  any  distinct  and  isolated  region,  have  in 
all  probability  descended  from  the  same  parents. 

We  can  understand,  on  these  views,  the  very  impor- 
tant distinction  between  real  affinities  and  analogical  or 
adaptive  resemblances.  Lamarck  first  called  attention  to 
this  distinction,  and  he  has  been  ably  followed  by  Macleay 
and  others.  The  resemblance,  in  the  shape  of  the  body 
and  in  the  fin-like  anterior  limbs,  between  the  dugong, 
which  is  a  pachydermatous  animal,  and  the  whale,  and 
between  both  these  mammals  and  fishes,  is  analogical. 
Amongst  insects  there  are  innumerable  instances  :  thus 
Linnaeus,  misled  by  external  appearances,  actually  classed 
an  homopterous  insect  as  a  moth.  We  see  something 
of  the  same  kind  even  in  our  domestic  varieties,  as 
in  the  thickened  stems  of  the  common  and  Swedish 
turnip.  Tlie  resemblance  of  the  greyhound  and  racehorse 
is  hardly  more  fanciful  than  the  analogies  which  have 
been  drawn  by  some  authors  between  very  distinct  ani- 
mals. On  my  view  of  characters  being  of  real  impor- 
tance for  classification,  only  in  so  far  as  they  reveal 
17 


nfj2  CLASSIFICATION.  [Chap.  XIII. 

descent,  we  can  clearly  understand  why  analogical  or 
adaptive  character,  although  of  the  utmost  importance  to 
the  welfare  of  the  being,  are  almost  valueless  to  the  sys- 
tematist.  For  animals,  belonging  to  two  most  distinct 
lines  of  descent,  may  readily  become  adapted  to  similar 
conditions,  and  thus  assume  a  close  external  resemblance ; 
but  such  resemblances  will  not  reveal — will  rather  tend 
to  conceal  their  blood-relationship  to  their  proj)er  lines  of 
descent.  We  can  also  understand  the  apparent  paradox, 
that  the  very  same  characters  are  analogical  when  one 
class  or  order  is  compared  with  another,  but  give  true 
affinities  when  the  members  of  the  same  class  or  order  are 
compared  one  with  another  :  thus  the  shape  of  the  body 
and  fin-like  limbs  are  only  analogical  when  whales  are 
comiDared  with  fishes,  being  adaptations  in  both  classes 
for  swimming  through  the  water ;  but  the  shape  of  the 
body  and  fin-like  limbs  serve  as  characters  exhibiting  true 
affinity  between  the  several  members  of  the  whale  family ; 
for  these  cetaceans  agree  in  so  many  characters,  great  and 
small,  that  we  cannot  doubt  that  they  have  inherited  theii' 
general  shape  of  body  and  structure  of  limbs  from  a  com- 
mon ancestor.     So  it  is  with  fishes. 

As  members  of  distinct  classes  have  often  been  adapt- 
ed by  successive  slight  modifications  to  live  under  nearly 
similar  circumstances, — to  inhabit  for  instance  the  three 
elements  of  land,  air,  and  water, — we  can  perhaps  under- 
stand how  it  is  that  a  numerical  parallelism  has  some- 
times been  observed  between  the  sub-groups  in  distinct 
classes.  A  naturalist,  struck  by  a  parallelism  of  this 
nature  in  any  one  class,  by  arbitrarily  raising  or  sinking 
the  value  of  the  groups  in  other  classes  (and  all  our  ex- 
perience shows  that  this  valuation  has  hitherto  been  arbi- 
trary), could  easily  extend  the  parallelism  over  a  wide 
range  ;  and  thus  the  septenary,  quinary,  quaternary,  and 
ternary  classifications  have  probably  arisen. 

As  the  modified  descendants  of  dominant  species,  be- 
longing to  the  larger  genera,  tend  to  inherit  the  advan- 
tages, which  made  the  groups  to  which  they  belong  large 
and  their  parents  dominant,  tliey  are  almost  sure  to 
spread  widely,  and  to  seize  cm  more  and  more  places  in 


Chap.  XIII.]  CLASSIFICATION.  3^3 

the  economy  of  nature.  The  larger  and  more  dominant 
groups  thus  tend  to  go  on  increasing  in  size ;  and  they 
consequently  supplant  many  smaller  and  feebler  groups. 
Thus  we  can  account  for  the  fact  that  all  organisms, 
recent  and  extinct,  are  included  under  a  few  great  orders, 
under  still  fewer  classes,  and  all  in  one  great  natural  sys- 
tem. As  showing  how  few  the  higher  groups  are  in 
number,  and  how  widely  spread  they  are  throughout  the 
world,  the  fact  is  striking,  that  the  discovery  of  Australia 
has  not  added  a  single  insect  belonging  to  a  new  order ; 
and  that  in  the  vegetable  kingdom,  as  I  learn  from  Dr. 
Hooker,  it  has  added  only  two  or  three  orders  of  small 
size. 

In  the  chapter  on  geological  succession  I  attempted  to 
show,  on  the  principle  of  each  group  having  generally 
diverged  much  in  character  during  the  long-continued 
process  of  modification,  how  it  is  that  the  more  ancient 
forms  of  life  often  present  characters  in  some  slight 
degree  intermediate  between  existing  groups.  A  few  old 
and  intermediate  parent-forms  having  occasionally  trans- 
mitted to  the  present  day  descendants  but  little  modified, 
will  give  to  us  our  so-called  osculant  or  aberrant  groups. 
The  more  aberrant  any  form  is,  the  greater  must  be  the 
number  of  connecting  forms  which  on  my  theory  have 
been  exterminated  and  utterly  lost.  And  we  have  some 
evidence  of  aberrant  forms  having  suflered  severely  from 
extinction,  for  they  are  generally  represented  by  extreme- 
ly few  species  ;  and  such  species  as  do  occur  are  generally 
very  distinct  from  each  otlier,  which  again  implies  extinc- 
tion. The  genera  Ornithorhynchus  and  Lepidosiren,  for 
example,  would  not  have  been  less  aberrant  had  each 
been  represented  by  a  dozen  species  instead  of  by  a  single 
one  ;  but  such  richness  in  species,  as  I  find  after  some  in- 
vestigation, does  not  commonly  fall  to  the  lot  of  aberrant 
genera.  We  can,  I  think,  account  for  this  fact  only  by 
looking  at  aberrant  forms  as  failing  groups  conquered  by 
more  successful  competitors,  with  a  few  members  pre- 
served by  some  unusual  coincidence  of  favourable  circum- 
stances. 

Mr.  "Waterhouse  has  remarked  that,  when  a  member 


^^^  CLASSIFICATION.  [Chap.  XIIL 

belonging  to  one  group  of  animals  exhibits  an  affinity  to 
a  quite  distinct  group,  tbis  affinity  in  most  cases  is  gen- 
eral and  not  special :  thus,  according  to  Mr.  Waterbonse, 
of  all  Rodents,  tbe  bizcacba  is  most  nearly  related  to  Mar- 
supials ;  but  in  tbe  points  in  wbicb  it  approaches  tbis 
order,  its  relations  are  general,  and  not  to  any  one  mar- 
supial species  more  tban  to  another.  As  tbe  points  of 
affinity  of  tbe  bizcacba  to  Marsupials  are  believed  to  be 
real  and  not  merely  adaptive,  they  are  due  on  my  theory 
to  inheritance  in  common.  Therefore  we  must  suppose 
either  that  all  Rodents,  including  the  bizcacba,  branched 
off  from  some  very  ancient  Marsupial,  which  will  liave 
bad  a  character  in  some  degree  intermediate  with  respect 
to  all  existing  Marsupials  ;  or  that  both  Rodents  and 
Marsupials  branched  off  from  a  common  progenitor,  and 
that  both  groups  have  since  undergone  much  modification 
in  divergent  directions.  On  either  view  we  may  suppose 
that  the  bizcacba  has  retained,  by  inheritance,  more  of 
the  character  of  its  ancient  progenitor  than  have  other 
Rodents  ;  and  therefore  it  will  not  be  specially  related 
to  any  one  existing  Marsupial,  but  indirectly  to  all  or 
nearly  all  Marsupials,  from  having  partially  retained  the 
character  of  their  common  j)rogenitor,  or  of  an  early 
member  of  the  group.  On  the  other  band,  of  all  Marsu- 
pials, as  Mr.  Waterbouse  has  remarked,  the  pbascolomys 
resembles  most  nearly,  not  any  one  species,  but  the  gene- 
ral order  of  Rodents.  In  tbis  case,  however,  it  may  be 
strongly  suspected  that  the  resemblance  is  only  analogi- 
cal, owing  to  the  pbascolomys  having  become  adapted  to 
habits  like  those  of  a  Rodent.  Tbe  elder  De  Candolle 
has  made  nearly  similar  osbservations  on  tbe  general 
nature  of  the  affinities  of  distinct  orders  of  plants. 

On  the  principle  of  the  multiplication  and  gradual  di- 
vergence in  character  of  the  species  descended  from  a  com- 
mon parent,  together  with  their  retention  by  inheritance 
of  some  characters  in  common,  we  can  understand  the 
excessively  complex  and  radiating  affinities  by  which  all 
the  members  of  the  same  family  or  higher  group  are  con- 
nected together.  For  the  common  parent  of  a  whole 
family  of  species,  now  broken  up  by  extinction  into  dis- 


Chap.  XIII.]  CLASSIFICATION". 


375 


tinct  groiij^s  and  sub-groups,  will  have  transmitted  some 
of  its  characters,  modified  in  various  ways  and  degrees, 
to  all ;  and  the  several  species  will  consequently  be  related 
to  each  other  by  circuitous  lines  of  affinity  of  various 
lengths  (as  may  be  seen  in  the  diagram  so  often  referred 
to),  mounting  up  through  many  predecessors.  As  it  is 
difficult  to  show  the  blood-relationship  between  the  nu- 
merous kindred  of  any  ancient  and  noble  family,  even  by 
the  aid  of  a  genealogical  tree,  and  almost  impossible  to  do 
this  without  this  aid,  we  can  understand  the  extraor- 
dinary difficulty  which  naturalists  have  experienced  in 
describing,  without  the  aid  of  a  diagram,  the  various 
affinities  which  they  perceive  between  the  many  Kving 
and  extinct  members  of  the  same  great  natural  class. 

Extinction,  as  we  have  seen  in  the  fourth  chapter,  has 
played  an  important  part  in  defining  and  widening  the 
intervals  between  the  several  groups  in  each  class.  We 
may  thus  account  even  for  the  distinctness  of  whole  classes 
from  each  other — for  instance,  of  birds  from  all  other  ver- 
tebrate animals — by  the  belief  that  many  ancient  forms 
of  life  have  been  utterly  lost,  through  which  the  early 
progenitors  of  birds  were  formerly  connected  with  the 
early  progenitors  of  the  other  vertebrate  classes.  There 
has  been  less  entire  extinction  of  the  forms  of  life  which 
once  connected  fishes  with  batrachians.  There  has  been 
still  less  in  some  other  classes,  as  in  that  of  the  Crustacea, 
for  here  the  most  wonderfully  diverse  forms  are  still  tied 
together  by  a  long,  but  broken,  chain  of  affinities.  Ex- 
tinction has  only  separated  groups  :  it  has  by  no  means 
made  them  ;  for  if  every  form  which  has  ever  lived  on 
this  earth  were  suddenly  to  reappear,  though  it  would  be 
quite  impossible  to  give  definitions  by  which  each  group 
could  be  distinguished  from  other  groups,  as  all  would 
blend  together  by  steps  as  fine  as  those  between  the  finest 
existing  varieties,  nevertheless  a  natural  classification,  or 
at  least  a  natural  arrangement,  would  be  possible.  We 
shall  see  this  by  turning  to  the  diagram  :  the  letters,  A  to 
L,  may  represent  eleven  Silurian  genera,  some  of  which 
have  produced  large  groups  of  modified  descendants. 
Every  intermediate  link  between  these  eleven  genera  and 


3>7g  CLASSIFICATION  [Chap.  Xlll. 

their  primordial  parent,  and  every  intermediate  link  in 
eacli  branch  and  sub-branch  of  their  descendants,  may  be 
sujDposed  to  be  still  alive  ;  and  the  links  to  be  as  fine  as 
those  between  the  finest  varieties.  In  this  case  it  wonld 
be  qnite  impossible  to  give  any  definition  by  which  the 
several  members  of  the  several  gronps  conld  be  distin- 
guished from  their  more  immediate  parents  ;  or  these 
parents  from  their  ancient  and  unknown  progenitor.  Yet 
the  natural  arrangement  in  the  diagram  would  still  hold 
good  ;  and,  on  the  principle  of  inheritance,  all  the  foniis 
descended  from  A,  or  from  I,  would  have  something  in 
common.  In  a  tree  we  can  specify  this  or  that  branch, 
though  at  the  actual  fork  the  two  unite  and  blend  together. 
We  could  not,  as  I  have  said,  define  the  several  groups  ; 
but  we  could  pick  out  types,  or  forms,  representing  most 
of  the  characters  of  each  group,  whether  large  or  small, 
and  thus  give  a  general  idea  of  the  value  of  the  difi'erences 
between  them.  This  is  what  we  should  be  driven  to,  if 
we  were  ever  to  succeed  in  collecting  all  the  forms  in  any 
class  which  have  lived  throughout  all  time  and  space. 
We  shall  certainly  never  succeed  in  making  so  perfect  a 
collection  :  nevertheless,  in  certain  classes,  we  are  tending 
in  this  direction  ;  and  Milne  Edwards  has  lately  insisted, 
in  an  able  paper,  on  the  high  importance  of  looking  to 
types,  whether  or  not  we  can  separate  and  define  the 
groups  to  which  such  types  belong. 

Finally,  we  have  seen  that  natural  selection,  which 
results  from  the  struggle  for  existence,  and  which  almost 
inevitably  induces  extinction  and  divergence  of  character 
in  the  many  descendants  from  one  dominant  parent-spe- 
cies, explains  that  great  and  universal  feature  in  the 
affinities  of  all  organic  beings,  namely,  their  subordination 
in  group  under  group.  We  use  the  element  of  descent  in 
classing  the  individuals  of  both  sexes  and  of  all  ages,  al- 
though having  few  characters  in  common,  under  one  spe- 
cies ;  we  use  descent  in  classing  acknowledged  varieties, 
however  difi'erent  they  may  be  from  their  j^arent ;  and  I 
believe  this  element  of  descent  is  the  hidden  bond  of  con- 
nexion which  naturalists  have  sought  under  the  teiTQ  of 
the  Natural  System.     On  this  idea  of  the  natural  system 


Chap.  XIIL]  '  MORPHOLOGY.  3^7 

being,  in  so  far  as  it  has  been  perfected,  genealogical  in 
its  arrangement,  witb  the  grades  of  difference  between  tlie 
descendants  from  a  common  parent,  expressed  by  the 
terms  genera,  families,  orders,  &c.,  we  can  understand  the 
rules  which  w^e  are  compelled  to  follow  in  our  classifica- 
tion. We  can  understand  why  we  value  certain  resem- 
blances far  more  than  others  ;  why  we  are  permitted  to 
use  rudimentary  and  useless  organs,  or  others  of  trifling 
physiological  importance  ;  why,  in  comparing  one  group 
with  a  distinct  group,  we  summarily  reject  analogical  or 
adaptive  characters,  and  yet  use  these  same  characters 
within  the  limits  of  the  same  group.  We  can  clearly  see 
how  it  is  that  all  living  and  extinct  forms  can  be  grouped 
together  in  one  great  system  ;  and  how  the  several  mem- 
bers of  each  class  are  connected  together  by  the  most  com- 
plex and  radiating  lines  of  affinities.  We  shall  never, 
probably,  disentangle  the  inextricable  web  of  affinities 
between  the  members  of  any  one  class  ;  but  when  we  have  a 
distinct  object  in  view,  and  do  not  look  to  some  unknown 
plan  of  creation,  we  may  hope  to  make  sure  but  slow 
progress. 

Morphology. — ^We  have  seen  that  the  members  of  the 
same  class,  independently  of  their  habits  of  life,  resemble 
each  other  in  the  general  plan  of  their  organisation.  This  re- 
semblance is  often  expressed  by  the  term  "  unity  of  type ; " 
or  by  saying  that  the  several  parts  and  organs  in  the  dif- 
ferent species  of  the  class  are  homologous.  The  whole 
•subject  is  included  under  the  general  name  of  Morphology. 
This  is  the  most  interesting  department  of  natural  history, 
and  may  be  said  to  be  its  very  soul.  What  can  be  more 
curious  than  that  the  hand  of  a  man,  formed  for  grasping, 
that  of  a  mole  for  digging,  the  leg  of  the  horse,  the  paddle 
of  the  porpoise,  and  the  wing  of  the  bat,  should  all  be 
constructed  on  the  same  pattern,  and  should  include  the 
same  bones,  in  the  same  relative  positions  ?  Geoftroy  St. 
Hilaire  has  insisted  strongly  on  the  high  importance  of 
relative  connexion  in  homologous  organs  :  the  parts  may 
change  to  almost  any  extent  in  form  and  size,  and  yet 
they  always  remain  connected  together  in  the  same  order. 


Q'7g  ■  MORPHOLOGY.  [Chap.  XIU, 

We  never  find,  for  instance,  the  bones  of  the  arm  and 
forearm,  or  of  the  thigh  and  leg,  transposed.  Hence  the 
same  names  can  he  given  to  the  homologous  bones  in 
widely  different  animals.  AYe  see  the  same  great  law  in 
the  construction  of  the  mouths  of  insects. :  what  can  be 
more  different  than  the  immensely  long  spiral  proboscis 
of  a  sphinx-moth,  the  curious  folded  one  of  a  bee  or  bug, 
and  the  great  jaws  of  a  beetle  ? — yet  all  these  organs,  serv- 
ing for  such  different  purposes,  are  formed  by  infinitely 
numerous  modifications  of  an  upper  lip,  mandibles,  and 
two  pairs  of  maxillae.  Analogous  laws  govern  the  con- 
struction of  the  mouths  and  limbs  of  crustaceans.  So  it  is 
with  the  flowers  of  plants. 

l^othing  can  be  more  hopeless  than  to  attempt  to  ex- 
plain this  similarity  of  pattern  in  members  of  the  same 
class,  by  utility  or  by  the  doctrine  of  final  causes.  The 
hopelessness  of  the  attempt  has  been  expressly  admitted 
by  Owen  in  his  most  interesting  work  on  the  '  jSTature  of 
Limbs.'  On  the  ordinary  view  of  the  independent  crea- 
tion of  each  being,  we  can  only  say  that  so  it  is  ; — that  it 
has  so  pleased  the  Creator  to  construct  each  animal  and 
plant. 

The  explanation  is  manifest  on  the  theory  of  the 
natural  selection  of  successive  slight  modifications, — each 
modification  being  profitable  in  some  way  to  the  modified 
form,  but  often  affecting  by  correlation  of  growth  other 
parts  of  the  organisation.  In  changes  of  this  nature, 
there  will  be  little  or  no  tendency  to  modify  the  original 
pattern,  or  to  transpose  parts.  The  bones  of  a  limb  might 
be  shortened  and  widened  to  any  extent,  and  become 
gradually  enveloped  in  thick  membrane,  so  as  to  serve  as 
a  fin ;  or  a  webbed  foot  might  have  all  its  bones,  or  certain 
bones,  lengthened  to  any  extent,  and  the  membrane  con- 
necting them  increased  to  any  extent,  so  as  to  serve  as  a 
wing :  yet  in  all  this  great  amount  of  modification  there 
will  be  no  tendency  to  alter  the  framework  of  bones  or 
the  relatiye  connexion  of  the  several  parts.  If  we  sup- 
pose that  the  ancient  progenitor,  the  archetype  as  it  may 
be  called,  of  all  mammals,  had  its  limbs  constructed  on 
the  existing  general  pattern,  for  whatever  purpose  they 


Chap.  XIIIJ  MORPHOLOGY. 


379 


served,  we  can  at  once  perceive  the  plain  signification  of 
the  homologous  construction  of  the  limbs  throughout  the 
whole  class.  So  with  the  mouths  of  insects,  we  have 
only  to  suppose  that  their  common  progenitor  had  an 
upper  lip,  mandibles,  and  two  pair  of  maxillae,  these  parts 
being  perhaps  very  simple  in  form  ;  and  then  natural  selec- 
tion will  account  for  the  infinite  diversity  in  structure  and 
function  of  the  mouths  of  insects.  i^NTevertheless,  it  is 
conceivable  that  the  general  pattern  of  an  organ  might 
become  so  much  obscured  as  to  be  finally  lost,  by  the 
atrophy  and  ultimately  by  the  complete  abortion  of  certain 
parts,  by  the  soldering  together  of  other  parts,  and  by  the 
doubling  or  multiplication  of  others, — variations  which 
we  know  to  be  within  the  limits  of  possibility.  In  the 
paddles  of  the  extinct  gigantic  sea-lizards,  and  in  the 
mouths  of  certain  suctorial  crustaceans,  the  general  pattern 
seems  to  have  been  thus  to  a  certain  extent  obscured. 

There  is  another  and  equally  curious  branch  of  the 
present  subject ;  namely,  the  comparison  not  of  the 
same  part  in  difierent  members  of  a  class,  but  of  the 
difierent  parts  or  organs  in  the  same  individual.  Most 
physiologists  believe  that  the  bones  of  the  skull  are 
homologous  with — that  is  correspond  in  number  and  in 
relative  connection  with — the  elemental  parts  of  a  certain 
number  of  vertebrae.  The  anterior  and  posterior  limbs  in 
each  member  of  the  vertebrate  and  articulate  classes  are 
plainly  homologous.  We  see  the  same  law  in  compariug 
the  wonderfully  complex  jaws  and  legs  in  crustaceans. 
It  is  familiar  to  almost  every  one,  that  in  a  flower  the 
relative  position  of  the  sepals,  petals,  stamens,  and  j)istils, 
as  well  as  their  intimate  structure,  are  intelligible  on  the 
view  that  they  consist  of  metamorphosed  leaves,  arranged 
in  a  spire.  In  monstrous  plants,  we  often  get  direct  evi- 
dence of  the  possibility  of  one  organ  being  transformed 
into  another ;  and  we  can  actually  see  in  embryonic 
crustaceans  and  in  many  other  animals,  and  in  flowers, 
that  organs,  which  when  mature  become  extremely  diflfer- 
ent,  are  at  an  early  stage  of  growth  exactly  alike. 

How  inexplicable  are  these  facts  on  the  ordinary  view 
of  creation  !     Why  should  the  brain  be  enclosed  in  a  box 
17* 


380  MORPHOLOGY.  [Chap.  XIII. 

composed  of  sucli  numerous  and  such,  extraordinarily 
shaped  pieces  of  bone  ?  As  Owen  has  remarked,  the 
benefit  derived  from  the  yielding  of  the  several  pieces  in 
the  act  of  parturition  of  mammals,  will  by  no  means  ex- 
plain the  same  construction  in  the  skulls  of  birds.  Why 
should  similar  bones  have  been  created  in  the  formation 
of  the  wing  and  leg  of  a  bat,  used  as  they  are  for  such 
totally  different  purposes  ?  Why  should  one  crustacean, 
which  has  an  extremely  comj)lex  mouth  formed  of  many 
parts,  consequently  always  have  fewer  legs ;  or  con- 
versely, those  with  many  legs  have  simpler  mouths? 
Why  should  the  sepals,  petals,  stamens,  and  pistils 
in  any  individual  flower,  though  fitted  for  such  wide- 
ly different  purposes,  be  all  constructed  on  the  same 
pattern  ? 

On  the  theory  of  natural  selection,  we  can  satisfactorily 
answer  these  questions.  In  the  vertebrata,  we  see  a  series 
of  internal  vertebrae  bearing  certain  processes  and  appen- 
dages ;  in  the  articulata,  we  see  the  body  divided  into  a 
series  of  segments,  bearing  external  appendages ;  and  in 
flowering  plants,  we  see  a  series  of  successive  spiral 
whorls  of  leaves.  An  indefinite  repetition  of  the  same 
part  or  organ  is  the  common  characteristic  (as  Owen  has 
observed)  of  all  low  or  little-modified  forms ;  therefore  we 
may  readily  believe  that  the  unknown  progenitor  of  the 
vertebrata  possessed  many  vertebrae  ;  the  unknown  pro- 
genitor of  the  articulata,  many  segments ;  and  the  un- 
known progenitor  of  flowering  plants,  many  spiral  whorls 
of  leaves.  We  have  formerly  seen  that  parts  many  times 
repeated  are  eminently  liable  fo  vary  in  number  and 
structure  ;  consequently  it  is  quite  probable  that  natural 
selection,  during  a  long-continued  course  of  modificatioUj 
should  have  seized  on  a  certain  number  of  the  primordi- 
ally  similar  elements,  many  times  repeated,  and  have 
adapted  them  to  the  most  diverse  purposes.  And  as  the 
whole  amount  of  modification  will  have  been  effected  by 
slight  successive  steps,  we  need  not  wonder  at  discover- 
ing in  such  parts  or  organs,  a  certain  degree  of  fundamen- 
tal resemblance,  retained  by  the  strong  ]3rinciple  of  in- 
heritance. 


Chap.  XIII.]  EMBRYOLOGY.  33]^ 

In  the  great  class  of  molluscs,  thougli  we  can  homolo- 
gise  the  parts  of  one  species  with  those  of  another  and 
distinct  species,  we  can  indicate  but  few  serial  homolo- 
gies ;  that  is,  we  are  seldom  enabled  to  say  that  one  part 
or  organ  is  homologous  with  another  in  the  same  indi- 
vidual. And  we  can  understand  this  fact ;  for  in  mol- 
luscs, even  in  the  lowest  members  of  the  class,  we  do  not 
find  nearly  so  much  indefinite  repetition  of  any  one  part, 
as  we  find  in  the  other  great  classes  of  the  animal  and 
vegetable  kingdoms. 

^N'aturalists  frequently  speak  of  the  skull  as  formed  of 
metamorphosed  vertebrae  :  the  jaws  of  crabs  as  metamor- 
phosed legs  ;  the  stamens  and  pistils  of  flowers  as  meta- 
morphosed leaves  ;  but  it  would  in  these  cases  probably 
be  more  correct,  as  Professor  Huxley  has  remarked,  to 
speak  of  both  skull  and  vertebrae,  both  jaws  and  legs, 
&c., — as  having  been  metamorphosed,  not  one  from  the 
other,  but  from  some  common  element.  l!Taturalists, 
however,  use  such  language  only  in  a  metaphorical  sense  : 
they  are  far  from  meaning  that  during  a  long  course  of 
descent,  primordial  organs  of  any  kind — vertebrae  in  the 
one  case  and  legs  in  the  other — have  actually  been  modi- 
fied into  skulls  or  jaws.  Yet  so  strong  is  the  appearance 
of  a  modification  of  this  nature  having  occurred,  that  nat- 
uralists can  hardly  avoid  employing  language  having  this 
plain  signification.  On  my  view  these  terms  may  be  used 
literally  ;  and  the  wonderful  fact  of  the  jaws,  for  instance, 
of  a  crab  retaining  numerous  characters,  which  they 
would  probably  have  retained  through  inheritance,  if  they 
had  really  been  metamorphosed  during  a  long  course  of 
descent  from  true  legs,  or  from  some  simple  appendage,  is 
explained. 

EiiibryoTogy. — It  has  already  been  casually  remarked 
that  certain  organs  in  the  individual,  which  when  mature 
become  widely  diflerent  and  serve  for  difi'erent  purposes, 
are  in  the  embryo  exactly  alike.  The  embryos,  also,  of 
distinct  animals  within  the  same  class  are  often  strikingly 
similar :  a  better  proof  of  this  cannot  be  given,  than  a 
statement  by  Yon  Baer,  namely,  that,  "  The  embryos  of 


Qg2  EMBRYOLOGY.  [Chap.  XIII. 

mammalia,  of  birds,  lizards,  and  snakes,  probably  also 
of  cbelonia,  are  in  tbeir  earliest  states  exceedingly  like  one 
anotber,  botb  as  a  wbole  and  in  tbe  mode  of  development 
of  tbeir  parts ;  so  mucb  so,  in  fact,  that  we  can  often  dis- 
tinguish tbe  embryos  only  by  tbeir  size.  In  my  possession 
are  two  little  embr^^os  in  spirit,  whose  names  I  have  omit- 
ted to  attach,  and  at  present  I  am  quite  unable  to  say  to 
what  class  they  belong.  They  may  be  lizards,  or  small 
birds,  or  very  young  mammalia,  so  complete  is  the  simi- 
larity in  the  mode  of  formation  of  the  head  and  trunk  in 
these  animals.  The  extremities,  however,  are  still  absent 
in  these  embryos.  But  even  if  they  existed  in  the  earliest 
stage  of  their  development,  we  should  learn  nothing ;  for  the 
feet  of  lizards  and  mammals,  the  wings  and  feet  of  birds,  no 
less  than  the  hands  and  feet  of  man,  all  arise  from  the  same 
fundamental  form."  The  vermiform  larvae  of  moths,  flies, 
beetles,  &c.,  resemble  each  other  much  more  closely  than  do 
the  mature  insects ;  but  in  the  case  of  larvae,  the  embryos  are 
active,  and  have  been  adapted  for  special  lines  of  life.  A 
trace  of  the  law  of  embryonic  resemblance,  sometimes 
lasts  till  a  rather  late  age  :  thus  birds  of  the  same  genus, 
and  of  closely  allied  genera,  often  resemble  each  other  in 
their  first  and  second  plumage  ;  as  we  see  in  the  spotted 
feathers  in  the  thrush  group.  In  the  cat  tribe,  most  of 
the  species  are  striped  or  spotted  in  lines ;  and  stripes  can 
be  plainly  distinguished  in  the  whelj)  of  the  lion.  "We 
occasionally  though  rarely  see  something  of  this  kind  in 
plants  :  thus  the  embryonic  leaves  of  the  ulex  or  furze, 
and  the  first  leaves  of  the  phyllodineous  acacias,  are 
pinnate  or  divided  like  the  ordinary  leaves  of  the  legumi- 
nosae. 

The  points  of  structure,  in  which  the  embryos  of  wide- 
ly difi'erent  animals,  of  the  same  class  resemble  each 
other,  often  have  no  direct  relation  to  their  conditions  of 
existence.  We  cannot,  for  instance,  suppose  that  in  the 
embryos  of  the  vertebrata  the  peculiar  loop-like  course  of 
the  arteries  near  the  branchial  slits  are  related  to  similar 
conditions, — in  the  young  mammal  which  is  nourished  in 
the  womb  of  its  mother,  in  the  egg  of  the  bird  which  is 
hatched  in  a  nest,  and  in  the  spawn  of  a  frog  under  water. 


Chap.  XIII.]  EMBRYOLOGY.  353 

"We  have  no  more  reason  to  believe  in  such  a  relation, 
than  we  have  to  believe  that  the  same  bones  in  the  hand 
of  a  man,  wing  of  a  bat,  and  fin  of  a  porpoise,  are  related 
to  similar  conditions  of  life.  'No  one  will  suppose  that 
the  stripes  on  the  whelp  of  a  lion,  or  the  spots  on  the 
young  blackbird,  are  of  any  use  to  these  animals,  or  are 
related  to  the  conditions  to  which  they  are  exposed. 

The  case,  however,  is  different  when  an  animal  during 
any  part  of  its  embryonic  career  is  active,  and  has  to 
provide  for  itself.  The  period  of  activity  may  come  on 
earlier  or  later  in  life ;  but  whenever  it  comes  on,  the 
adaptation  of  the  larva  to  its  conditions  of  life  is  just  as 
perfect  and  as  beautiful  as  in  the  adult  animal.  From 
such  special  adaptations,  the  similarity  of  the  larvse  or 
active  embryos  of  allied  animals  is  sometimes  much  obscur- 
ed ;  and  cases  could  be  given  of  the  larvae  of  two  species, 
or  of  two  groups  of  species,  difl'ering  quite  as  much,  or  even 
more,  from  each  other  than  do  their  adult  parents.  In  most 
cases,  however,  the  larvse,  though  active,  still  obey  more  or 
less  closely  the  law  of  common  embryonic  resemblance.  Cir- 
ripedes  afford  a  good  instance  of  this  :  even  the  illustrious 
Cuvier  did  not  perceive  that  a  barnacle  was,  as  it  certainly 
is,  a  crustacean  ;  but  a  glance  at  the  larva  shows  this  to 
be  the  case  in  an  unmistakeable  manner.  So  again  the 
two  main  divisions  of  cirripedes,  the  pedunculated  and 
sessile,  which  differ  widely  in  external  appearance,  have 
larvae  in  all  their  several  stages  barely  distinguishable. 

The  embryo  in  the  course  of  development  generally 
rises  in  organisation  :  I  use  this  expression,  though  I  am 
aware  that  it  is  hardly  possible  to  define  clearly  what  is 
meant  by  the  organisation  being  higher  or  lower.  But 
no  one  probably  will  dispute  that  the  butterfly  is  higher 
than  the  caterpillar.  In  some  cases,  however,  the  mature 
animal  is  generally  considered  as  lower  in  the  scale  than 
the  larva,  as  with  certain  parasitic  crustaceans.  To  refer 
once  again  to  cirripedes  :  the  larvae  in  the  first  stage  have 
three  pairs  of  legs,  a  very  simple  single  eye,  and  a  probos- 
ciformed  mouth,  with  which  they  feed  largely,  for  they 
increase  much  in  size.  In  the  second  stage,  answering  to 
the  chrysalis  stage  of  butterflies,  they  have  six  pairs  of 


384  EMBRYOLOGY.  [Chap.  Xlll. 

beautifully  constructed  natatory  legs,  a  pair  of  magnificent 
compound  eyes,  and  extremely  complex  antennae ;  but 
they  have  a  closed  and  imperfect  mouth,  and  cannot  feed: 
tlieir  function  at  this  stage  is,  to  search  by  their  well-de- 
veloped organs  of  sense,  and  to  reach  by  their  active 
powers  of  swimming,  a  proper  place  on  which  to  become 
attached  and  to  undergo  their  final  metamorphosis.  "When 
this  is  completed  they  are  fixed  for  life :  their  legs  are 
now  converted  into  prehensile  organs  ;  they  again  obtain 
a  well-constructed  mouth  ;  but  they  have  no  antennae,  and 
their  two  eyes  are  now  reconverted  into  a  minute,  single, 
and  very  simple  eye-spot.  In  this  last  and  complete  state, 
cirripedes  may  be  considered  as  either  more  highly  or  more 
lowly  organised  than  they  were  in  the  larval  condition. 
But  in  some  genera  the  larvae  become  developed  either 
into  hermaphrodites  having  the  ordinary  structure,  or  into 
what  I  have  called  complemental  males  :  and  in  the  latter, 
the  development  has  assuredly  been  retrograde ;  for  the 
male  is  a  mere  sack,  which  lives  for  a  short  time,  and  is 
destitute  of  mouth,  stomach,  or  other  organ  of  importance, 
excepting  for  rejDroduction. 

We  are  so  much  accustomed  to  see  dififerences  in  struc- 
ture between  the  embryo  and  the  adult,  and  likewise  a 
close  similarity  in  the  embryos  of  widely  different  animals 
withm  the  same  class,  that  we  might  be  led  to  look  at 
these  facts  as  necessarily  contingent  in  some  manner  on 
growth.  But  there  is  no  obvious  reason  why,  for  instance, 
the  wing  of  a  bat,  or  the  fin  of  a  porpoise,  should  not 
have  been  sketched  out  with  all  the  parts  in  proper  pro- 
portion, as  soon  as  any  structure  became  visible  in  the 
embryo.  And  in  some  whole  groups  of  animals  and  in 
certain  members  of  other  groups,  the  embryo  does  not  at 
any  period  differ  widely  from  the  adult :  thus  Owen  has 
remarked  in  regard  to  cuttle-fish,  "  there  is  no  metamor- 
phosis ;  the  cephalopodic  character  is  manifested  long  be- 
fore the  parts  of  the  embryo  are  completed  ;  "  and  again 
in  spiders,  "  there  is  nothing  worthy  to  be  called  a  meta- 
morphosis." ThelarvfB  of  insects,  whether  adapted  to  the 
most  diverse  and  active  habits,  or  quite  inactive,  being  fed 
by  their  parents  or  placed  in  the  midst  of  proper  nutri- 


Othp    Xr\i,]  EMBRYOLOGY.  3§5 

nient,  jet  nearly  all  pass  tlirougli  a  similar  worm-like 
stage  of  development ;  but  in  some  few  cases,  as  in  that 
of  Apliis,  if  we  look  to  the  admirable  drawings  by  Profes- 
sor Huxley  of  the  development  of  this  insect,  we  see  no 
trace  of  the  vermiform  stage. 

How,  then,  can  we  explain  these  several  facts  in  em- 
bryology,— namely  the  very  general,  but  not  universal 
difference  in  structure  between  the  embryo  and  the  adult ; 
— of  parts  in  the  same  individual  embryo,  which  ulti- 
mately become  very  unlike  and  serve  for  diverse  purposes, 
being  at  this  early  period  of  growth  alike  ; — of  embryos 
of  different  species  witliin  the  same  class,  generally,  but 
not  universally,  resembling  each  other  ; — of  the  structure 
of  the  embryo  not  being  closely  related  to  its  conditions 
of  existence,  excej^t  when  the  embryo  becomes  at  any 
period  of  life  active  and  has  to  provide  for  itself ;  of  the 
embryo  apparently  having  sometimes  a  higher  organisa- 
tion than  the  mature  animal,  into  which  it  is  developed  ? 
I  believe  that  all  these  facts  can  be  explained,  as  follows, 
on  the  view  of  descent  with  modification. 

It  is  commonly  assumed,  perhaps  from  monstrosities 
often  affecting  the  embryo  at  a  very  early  period,  that 
slight  variations  necessarily  appear  at  an  equally  early 
period.  But  we  have  little  evidence  on  this  head — indeed 
the  evidence  rather  points  the  other  way  ;  for  it  is  noto- 
rious that  breeders  of  cattle,  horses,  and  various  fancy 
animals,  cannot  positively  tell,  until  some  time  after  the 
animal  has  been  born,  what  its  merits  or  form  will  ulti- 
mately turn  out.  We  see  this  plainly  in  our  own  chil- 
dren ;  we  cannot  always  tell  whether  the  child  will  be 
tall  or  short,  or  what  its  precise  features  will  be.  The 
question  is  not,  at  what  period  of  life  any  variation  has  been 
caused,  but  at  what  period  it  is  fully  displayed.  The 
cause  may  have  acted,  and  I  believe  generally  has  acted, 
even  before  the  embryo  is  formed  ;  and  the  variation  may 
be  due  to  the  male  and  female  sexual  elements  having 
been  affected  by  the  conditions  to  which  either  parent,  or 
their  ancestors,  have  been  exposed.  ^STevertheless  an 
effect  thus  caused  at  a  very  early  period,  even  before  the 
formation  of  the  embrj^o,  may  appear  late  in  life  ;  as  when 


386  EMBRYOLOGY,  [Chap.  XIIL 

an  hereditary  disease,  whicli  appears  in  old  age  alone, 
has  been  communicated  to  the  offspring  from  the  repro- 
ductive element  of  one  parent.  Or  again,  as  when  the 
horns  of  cross-bred  cattle  have  been  affected  by  the  shape 
of  the  horns  of  either  parent.  For  the  welfare  of  a  very 
young  animal,  as  long  as  it  remains  in  its  mother's  womb, 
or  in  the  egg,  or  as  long  as  it  is  nourished  and  protected 
by  its  parent,  it  must  be  quite  unimportant  whether  most 
of  its  characters  are  fully  acquired  a  little  earlier  or  later 
in  life.  It  would  not  signify,  for  instance,  to  a  bird  which 
obtained  its  food  best  by  having  a  long  beak,  whether  or 
not  it  assumed  a  beak  of  this  particular  length,  as  long  as 
it  was  fed  by  its  parents.  Hence,  I  conclude,  that  it  If 
quite  possible,  that  each  of  the  many  successive  modifica- 
tions, by  which  each  species  has  acquired  its  present  struc- 
ture, may  have  supervened  at  a  not  very  early  period  of 
life  ;  and  some  direct  evidence  from  our  domestic  animals 
supports  this  view.  But  in  other  cases  it  is  quite  possible 
that  each  successive  modification  or  most  of  them  may  have 
appeared  at  an  extremely  early  period. 

I  have  stated  in  the  first  chapter,  that  there  is  some 
evidence  to  render  it  probable,  that  at  whatever  age  any 
variation  first  appears  in  the  parent,  it  tends  to  reappear 
at  a  corresponding  age  in  the  offspring.  Certain  varia- 
tions can  only  appear  at  corresponding  ages,  for  instance, 
peculiarities  in  the  caterpillar,  cocoon,  or  imago  states  of 
the  silk-moth  ;  or,  again,  in  the  horns  of  almost  full-grown 
cattle.  But  further  than  this,  variations  which,  for  all 
that  we  can  see,  might  have  appeared  earlier  or  later  in 
life,  tend  to  appear  at  a  corresponding  age  in  the  ofl'spring 
and  parent.  I  am  far  from  meaning  that  this  is  invari- 
ably the  case  ;  and  I  could  give  a  good  many  cases  of  va- 
riations (taking  the  word  in  the  largest  sense)  which  have 
supervened  at  an  earlier  age  in  the  child  than  in  tho 
parent. 

Tliese  two  principles,  if  their  truth  be  admitted,  will, 
I  believe,  explain  all  the  above  specified  leading  facts  in 
embryology .  But  first  let  us  look  at  a  few  analogous 
cases  in  domestic  varieties.  Some  authors  who  have 
written  on  Dogs,  maintain  that  the  greyhound  and  bull- 


Chap.  XIII.]  EMBRYOLOGY.  387 

dog,  though  appearing  so  different,  are  really  varieties 
most  closely  allied,  and  have  probably  descended  from 
the  same  wild  stock  ;  hence  I  was  cm-ions  to  see  how  far 
their  puppies  differed  from  each  other :  I  was  told  by 
breeders  that  they  differed  just  as  much  as  their  parents, 
and  this,  judging  by  the  eye,  seemed  almost  to  be  the 
case  ;  but  on  actually  measuring  the  old  dogs  and  their 
six-days  old  puppies,  I  found  that  the  puppies  had  not 
nearly  acquired  their  full  amount  of  proportional  differ- 
ence. So  again,  I  was  told  that  the  foals  of  cart  and  race- 
horses differed  as  much  as  the  full-grown  animals ;  and 
this  surprised  me  greatly,  as  I  think  it  probable  that  the 
difference  between  these  two  breeds  has  been  wholly 
caused  by  selection  under  domestication  ;  but  having  had 
careful  measurements  made  of  the  dam,  and  of  a  three- 
days  old  colt  of  a  race  and  heavy  cart-horse,  I  find  that 
the  colts  have  by  no  means  acquired  their  full  amount  of 
proportional  difference. 

As  the  evidence  appears  to  me  conclusive,  that  the 
several  domestic  breeds  of  Pigeon  have  descended  from 
one  wild  species,  I  compared  young  pigeons  of  various 
breeds,  within  twelve  hours  after  being  hatched ;  I  care- 
fully measured  the  proportions  (but  will  not  here  give 
details)  of  the  beak,  width  of  mouth,  length  of  nostril 
and  of  eyelid,  size  of  feet  and  length  of  leg,  in  the  wild 
stock,  in  pouters,  fantails,  runts,  barbs,  dragons,  carriers, 
and  tumblers.  'Now  some  of  these  birds,  when  mature, 
differ  so  extraordinarily  in  length  and  form  of  beak,  that 
they  would,  I  cannot  doubt,  be  ranked  in  distinct  genera, 
had  they  been  natural  productions.  But  when  the  nest- 
ling birds  of  these  several  breeds  were  placed  in  a  row, 
though  most  of  them  could  be  distinguished  from  each 
other,  yet  their  proportional  differences  in  the  above 
specified  several  points  were  incomparably  less  than  in 
the  full-grown  birds.  Some  characteristic  points  of  dif- 
ference— for  instance,  that  of  the  width  of  mouth — could 
hardly  be  detected  in  the  young.  But  there  was  one 
remarkable  exception  to  this  rule,  for  the  young  of  the 
short-faced  tumbler  differed  from  the  young  of  the  wild 
rock-pigeon  and  of  the  other  breeds,  in  all  its  proportions, 
almost  exactly  as  much  as  in  the  adult  state. 


3gg  EMBRYOLOGY.  [Chap.  XllL 

The  two  principles  above  given  seem  to  me  to  explain 
these  facts  in  regard  to  the  later  embryonic  stages  of  our 
domestic  varieties.  Fanciers  select  their  horses,  dogs, 
and  pigeons,  for  breeding,  when  they  are  nearly  grown 
up  :  they  are  indifferent  whether  the  desired  qualities  and 
structures  have  been  acquired  earlier  or  later  in  life,  if  the 
full-grown  animal  possesses  them.  And  the  cases  just 
given,  more  especially  that  of  pigeons,  seem  to  show  that 
the  characteristic  differences  which  give  value  to  each 
breed,  and  which  have  been  accumulated  by  man's  selec- 
tion, have  not  generally  first  appeared  at  an  early  period 
of  life,  and  have  been  inherited  by  the  offspring  at  a  cor- 
responding not  early  period.  But  the  case  of  the  short- 
faced  tumbler,  which  when  twelve  hours  old  had  acquired 
its  proper  proportions,  proves  that  this  is  not  the  universal 
rule ;  for  here  the  characteristic  differences  must  either 
have  appeared  at  an  earlier  period  than  usual,  or,  if  not 
so,  the  differences  must  have  been  inherited,  not  at  the 
corresponding,  but  at  an  earlier  age. 

]S[ow  let  us  apply  these  facts  and  the  above  two  prin- 
ciples— which  latter,  though  not  j^roved  true,  can  be 
shown  to  be  in  some  degree  probable — to  species  in  a 
state  of  nature.  Let  us  take  a  genus  of  birds,  descended 
on  my  theory  from  some  one  parent-species,  and  of  which 
the  several  new  species  have  become  modified  through 
natural  selection  in  accordance  with  their  diverse  habits. 
Then,  from  the  many  slight  successive  steps  of  variation 
having  supervened  at  a  rather  late  age,  and  having  been 
inherited  at  a  corresponding  age,  the  young  of  the  new 
species  of  our  supposed  genus  will  manifestly  tend  to 
resemble  each  other  much  more  closely  than  do  the  adults, 
just  as  we  have  seen  in  the  case  of  pigeons.  We  may 
extend  this  view  to  whole  families  or  even  classes.  The 
fore-limbs,  for  instance,  which  served  as  legs  in  the  parent- 
sj)ecies,  may  become,  by  a  long  course  of  modification, 
adapted  in  one  descendant  to  act  as  hands,  in  another  as 
paddles,  in  another  as  wings ;  and  on  the  above  two  prin- 
ciples— namely  of  each  successive  modification  superven- 
ing at  a  rather  late  age,  and  being  inherited  at  a  corre- 
sponding late  age — 'the  fore-limbs  in  the  embryps  of  the 


Chap.  XIII.]  EMBRYOLOGY.  389 

several  descendants  of  the  parent- species  will  still  resemble 
each  other  closely,  for  they  will  not  have  been  modified. 
But  in  each  individual  new  species,  the  embryonic  fore- 
limbs  will  difi'er  greatly  from  the  fore-limbs  in  the  mature 
animal ;  the  limbs  in  the  latter  having  undergone  much 
modification  at  a  rather  late  period  of  life,  and  having 
thus  been  converted  into  hands,  or  paddles,  or  wings. 
Whatever  infiuence  long-continued  exercise  or  use  on  the 
one  hand,  and  disuse  on  the  other,  may  have  in  modifying 
an  organ,  such  influence  will  mainly  affect  the  mature 
animal,  which  has  come  to  its  full  powers  of  activity  and 
has  to  gain  its  own  living  ;  and  the  effects  thus  produced 
will  be  inherited  at  a  corresponding  mature  age.  Where- 
as the  young  will  remain  unmodified,  or  be  modified  in  a 
lesser  degree,  by  the  effects  of  use  and  disuse. 

In  certain  cases  the  successive  steps  of  variation  might 
supervene,  from  causes  of  which  we  are  wholly  ignorant, 
at  a  very  early  period  of  life,  or  each  step  might  be  in- 
herited at  an  earlier  period  than  that  at  which  it  first 
appeared.  In  either  case  (as  with  the  short-faced  tumbler) 
the  yoimg  or  embryo  would  closely  resemble  the  mature 
parent-form.  We  have  seen  that  this  is  the  rule  of  de- 
velopment in  certain  whole  groups  of  animals,  as  with 
cuttle-fish  and  spiders,  and  with  a  few  members  of  the 
great  class  of  insects,  as  with  Aphis.  With  respect  to 
the  final  cause  of  the  young  in  these  cases  not  undergoing 
any  metamorphosis,  or  closely  resembling  their  parents 
from  their  earliest  age,  we  can  see  that  this  would  result 
from  the  two  following  contingencies  :  firstly,  from  the 
young,  during  a  course  of  modification  carried  on  for 
many  generations,  having  to  provide  for  their  own  wants 
at  a  very  early  stage  of  development,  and  secondly,  from 
their  following  exactly  the  same  habits  of  life  with  their 
parents  ;  for  in  this  case,  it  would  be  indispensable  for  the 
existence  of  the  species,  that  the  child  should  be  modified 
at  a  very  early  age  in  the  same  manner  with  its  parents, 
in  accordance  with  their  similar  habits.  Some  further 
explanation,  however,  of  the  embryo  not  undergoing  any 
metamorphosis  is  perhaps  requisite.  If,  on  the  other 
hand,  it  profited  the  young  to  follow  habits  of  life  in  any 


390  EMBRYOLOGY.  [Chap.  XHl. 

degree  different  from  those  of  their  parent,  and  conse- 
quently to  be  constructed  in  a  slightly  different  manner, 
then,  on  the  principle  of  inheritance  at  corresponding 
ages,  the  active  young  or  larvae  might  easily  be  rendered 
by  natural  selection  different  to  any  conceivable  extent 
from  their  parents.  Such  differences  might,  also,  become 
correlated  with  successive  stages  of  development ;  so  that 
the  larvse,  in  the  first  stage,  might  differ  greatly  from  the 
larvae  in  the  second  stage,  as  we  have  seen  to  be  the  case 
with  cirripedes.  The  adult  might  become  fitted  for  sites 
or  habits,  in  which  organs  of  locomotion  or  of  the  senses, 
&c.,  would  be  useless ;  and  in  this  case  the  final  meta- 
morphosis would  be  said  to  be  retrograde. 

As  all  the  organic  beings,  extinct  and  recent,  which 
have  ever  lived  on  this  earth  have  to  be  classed  together, 
and  as  all  have  been  connected  by  the  finest  gradations, 
the  best,  or  indeed,  if  oiir  collections  were  nearly  perfect, 
the  only  possible  arrangement,  would  be  genealogical; 
descent  being  on  my  view  the  hidden  bond  of  connection 
which  naturalists  have  been  seeking  under  the  term  of 
the  natural  system.     On  this  view  we  can  understand 
how  it  is  that,  in  the  eyes  of  most  naturalists,  the  structure 
of  the  embryo  is  even  more  important  for  classification 
than  that  of  the  adult.     For  the  embryo  is  the  animal  in 
its  less  modified  state  ;  and  in  so  far  it  reveals  the  struc- 
ture of  its  progenitor.     In  two  groups  of  animals,  however 
much  they  may  at  present  differ  from  each  other  in  struc- 
ture and  habits,  if  they  pass  through  the  same  or  similar 
embryonic  stages,  we  may  feel  assured  that  they  have  both 
descended  from  the  same  or  nearly  similar  parents,  and 
are  therefore  in  that  degree  closely  related.     Thus,  com- 
munity in   embryonic   structure  reveals   community  of 
descent.     It  will  reveal  this  community  of  descent,  how- 
ever much  the  structure  of  the  adult  may  have  been 
modified  and  obscured ;  we  have  seen,  for  instance,  that 
cirripedes  can  at  once  be  recognised  by  their  larvse  as 
belonging  to  the  great  class  of  crustaceans.     As  the  em- 
bryonic state  of  each  sj^ecies  and  group  of  species  partially 
shows  us  the  structure  of  their  less  modified  ancient  pro- 
genitors, we   can   clearly  see   why  ancient   and   extinct 


Chap.  XIII.]  RUDIMENTARY    ORGANS.  391 

forms  of  life  should  resemble  the  embryos  of  tlieir  de- 
scendants,— onr  existing  species.  Agassiz  believes  this 
to  be  a  law  of  nature ;  but  I  am  bound  to  confess  that  I 
only  hope  to  see  the  law  hereafter  proved  true.  It  can 
be  proved  true  in  those  cases  alone  in  which  the  ancient 
state,  now  supposed  to  be  represented  in  many  embryos, 
has  not  been  obliterated,  either  by  the  successive  varia- 
tions in  a  long  course  of  modification  having  supervened 
at  a  very  early  age,  or  by  the  variations  having  been 
inherited  at  an  earlier  period  than  that  at  which  they  first 
appeared.  It  should  also  be  borne  in  mind,  that  the  sup- 
posed law  of  resemblance  of  ancient  forms  of  life  to  the 
embryonic  stages  of  recent  forms,  may  be  true,  but  yet, 
owing  to  the  geological  record  not  extending  far  enough 
back  in  time,  may  remain  for  a  long  period,  or  for  ever, 
incapable  of  demonstration. 

Thus,  as  it  seems  to  me,  the  leading  facts  in  embryol- 
ogy, which  are  second  in  importance  to  none  in  natural 
history,  are  explained  on  the  principle  of  slight  modifi- 
cations not  appearing,  in  the  many  descendants  from  some 
one  ancient  progenitor,  at  a  very  early  period  in  the  life 
of  each,  though  perhaps  caused  at  the  earliest,  and  being 
inherited  at  a  corresponding  not  early  period.  Embryol- 
ogy rises  greatly  in  interest,  when  we  thus  look  at  the 
embryo  as  a  picture,  more  or  less  obscured,  of  the  com- 
mon parent-form  of  each  great  class  of  animals. 

Rudimentary^  atrophied^  or  aborted  organs. — Organs 
or  parts  in  this  strange  condition,  bearing  the  stamp  of 
inutility,  are  extremely  common  throughout  nature.  For 
instance,  rudimentary  mammse  are  very  general  in  the 
males  of  mammals  :  I  presume  that  the  "  bastard-wing  " 
in  birds  may  be  safely  considered  as  a  digit  in  a  rudi- 
mentary state :  in  very  many  snakes  one  lobe  of  the  lungs 
is  rudimentary  ;  in  other  snakes  there  are  rudiments  of 
the  pelvis  and  hind  limbs.  Some  of  the  cases  of  rudi- 
mentary organs  are  extremely  curious  ;  for  instance,  the 
presence  of  teeth  in  foetal  whales,  which  when  grown  up 
have  not  a  tooth  in  their  heads  ;  and  the  presence  of  teeth, 
which  never  cut  through  the  gums,  in  the  upper  jaws  of 


g92  RUDIMENTARY   ORGANS.  [Chap.  XHL 

our  unborn  calves.  It  lias  even  been  stated  on  good 
autliority  that  rndiments  of  teetli  can  be  detected  in  the 
beaks  of  certain  embryonic  birds.  Nothing  can  be  plainer 
than  that  wings  are  formed  for  flight,  yet  in  how  many 
insects  do  we  see  wings  so  reduced  in  size  as  to  be  utterly 
incapable  of  flight,  and  not  rarely  lying  under  wing-cases, 
firmly  soldered  together ! 

The  meaning  of  rudimentary  organs  is  often  quite  un- 
mistakeable :  for  instance  there  are  beetles  of  the  same 
genus  (and  even  of  the  same  species)  resembling  each 
other  most  closely  in  all  respects,  one  of  which  will  have 
full-sized  wings,  and  another  mere  rudiments  of  mem- 
brane ;  and  here  it  is  impossible  to  doubt,  that  the  rudi- 
ments represent  wmgs.  Kudimentary  organs  sometimes 
retain  their  potentiality,  and  are  merely  not  developed : 
this  seems  to  be  the  case  with  the  mammae  of  male  mam- 
mals, for  many  instances  are  on  record  of  these  organs 
having  become  well  developed  in  full-grown  males,  and 
having  secreted  milk.  So  again  there  are  normally  four 
developed  and  two  rudimentary  teats  in  the  udders  of  the 
genus  Bos,  but  in  our  domestic  cows  the  two  sometimes 
become  developed  and  give  milk.  In  individual  plants  of 
the  same  species  the  petals  sometimes  occur  as  mere 
rudiments,  and  sometimes  in  a  well-developed  state.  In 
plants  with  separated  sexes,  the  male  flowers  often  have 
a  rudiment  of  a  pistil ;  and  Kolreuter  found  that  by  cross- 
ing such  male  plants  with  an  hermaphrodite  species,  the 
rudiment  of  the  jjistil  in  the  hybrid  ofispring  was  much 
increased  in  size  ;  and  this  shows  that  the  rudiment  and 
the  perfect  pistil  are  essentially  alike  in  nature. 

An  organ  serving  for  two  purposes,  may  become  rudi- 
mentary or  utterly  aborted  for  one,  even  the  more  impor- 
tant purpose ;  and  remain  perfectly  efficient  for  the  other. 
Thus  in  plants,  the  office  of  the  pistil  is  to  allow  the 
pollen-tubes  to  reach  the  ovules  protected  in  the  ovarium 
at  its  base.  The  pistil  consists  of  a  stigma  supported  on 
the  style ;  but  in  some  Compositse,  the  male  florets, 
which  of  course  cannot  be  fecundated,  have  a  pistil, 
which  is  in  a  rudimentary  state,  for  it  is  not  crowned 
with  a  stigma ;   but  the  style  remains  well  developed, 


Chap.  XIII.]  RUDIMENTARY  ORGANS.  390 

and  is  clothed  with  hairs  as  in  other  compositse,  for  the  pur- 
pose of  brushing  the  pollen  out  of  the  surrounding  anthers. 
Again,  an  organ  may  become  rudimentary  for  its  proper 
purpose,  and  be  used  for  a  distinct  object :  in  certain  fish  the 
swim-bladder  seems  to  be  nearly  rudimentary  for  its  proper 
function  of  giving  buoyancy,  but  has  become  converted  into 
a  nascent  breathing  organ  or  lung.  Other  similar  instances 
could  be  given. 

Organs,  however  little  developed,  if  of  use,  should  not  be 
called  rudimentary ;  they  cannot  properly  be  said  to  be  in  an 
atrophied  condition ;  they  may  be  called  nascent,  and  may 
hereafter  be  developed  to  any  extent  by  natural  selection. 
Rudimentary  organs,  on  the  other  hand,  are  essentially  use- 
less, as  teeth  which  never  cut  through  the  gums  ;  in  a  still 
less  developed  condition,  they  would  be  of  still  less  use. 
They  cannot,  therefore,  under  their  present  condition,  have 
been  formed  by  natural  selection,  which  acts  solely  by  the 
preservation  of  useful  modifications ;  they  have  been  re- 
tained, as  we  shall  see,  by  inheritance,  and  relate  to  a  former 
condition  of  their  possessor.  It  is  difficult  to  know  what  are 
nascent  organs  ;  looking  to  the  future,  we  cannot  of  course 
tell  how  any  part  will  be  developed,  and  whether  it  is  now 
nascent ;  looking  to  the  past,  creatures  with  an  organ  in  a 
nascent  condition  will  generally  have  been  supplanted  and 
exterminated  by  their  successors  with  the  organ  in  a  more 
perfect  and  developed  condition.  The  wing  of  the  penguin 
is  of  high  service,  and  acts  as  a  fin ;  it  may,  therefore,  repre- 
sent the  nascent  state  of  the  wings  of  birds ;  not  that  I  be- 
lieve this  to  be  the  case,  it  is  more  probably  a  reduced  or- 
gan, modified  for  a  new  function :  the  wing  of  the  Apteryx 
is  useless,  and  is  truly  rudimentary.  The  mammary  glands 
of  the  Ornithorhynchus  may,  perhaps,  be  considered,  in 
comparison  with  the  udder  of  a  cow,  as  in  a  nascent  state. 
The  ovigerous  frena  of  certain  cirripedes,  which  are  only 
slightly  developed  and  which  have  ceased  to  give  attach- 
ment to  the  ova,  are  nascent  branchiae. 

Rudimentary  organs  in  the  individuals  of  the  same 
species  are  very  liable  to  vary  in  degree  of  development 
and  in  other  respects.  Moreover,  in  closely  allied  species, 
the  degree  to  which  the  same  organ  has  been  rendered 
rudimentary  occasionally  difi'ers  much.     This  latter  fact 


394  RUDIMENTARY  ORGANS.  [Chap.  XIII. 

is  well  exemplified  in  the  state  of  the  wings  of  the  female 
moths  in  certain  groups.  Rudimentary  organs  may  be  ut- 
terly aborted ;  and  this  implies,  that  we  find  in  an  ani- 
mal or  plant  no  trace  of  an  organ,  which  analogy  would 
lead  us  to  expect  to  find,  and  which  is  occasionally  found 
in  monstrous  individuals  of  the  species.  Thus  in  the 
snapdragon  (antirrhinum)  we  generally  do  not  find  a  ru- 
diment of  a  fifth  stamen ;  but  this  may  sometimes  be 
seen.  In  tracing  the  homologies  of  the  same  part  in  dif- 
ferent members  of  a  class,  nothing  is  more  common,  or 
more  necessary,  than  the  use  and  discovery  of  rudiments. 
This  is  well  shown  in  the  drawings  given  by  Owen  of  the 
bones  of  the  leg  of  the  horse,  ox,  and  rhinoceros. 

It  is  an  important  fact  that  rudimentary  organs,  such 
as  teeth  in  the  upper  jaws  of  whales  and  ruminants,  can 
often  be  detected  in  the  embryo,  but  afterwards  wholly 
disappear.  It  is  also,  I  believe,  a  universal  rule,  that  a 
rudimentary  part  or  organ  is  of  greater  size  relatively  to 
the  adjoining  parts  in  the  embryo,  than  in  the  adult ;  so 
that  the  organ  at  this  early  age  is  less  rudimentary,  or 
even  cannot  be  said  to  be  in  any  degree  rudimentary. 
Hence,  also,  a  rudimentary  organ  in  the  adult,  is  often 
said  to  have  retained  its  embryonic  condition. 

I  have  now  given  the  leading  facts  with  respect  to  ru- 
dimentary organs.  In  reflecting  on  them,  every  one  must 
be  struck  with  astonishment :  for  the  same  reasoning 
power  which  tells  us  plainly  that  most  parts  and  organs 
are  exquisitely  adapted  for  certain  purposes,  tells  us  with 
equal  plainness  that  these  rudimentary  or  atrophied  or- 
gans, are  imperfect  and  useless.  In  works  on  natural  his- 
tory rudimentary  organs  are  generally  said  to  have  been 
created  "  for  the  sake  of  symmetry,"  or  in  order  "  to  com- 
plete the  scheme  of  nature  ;"  but  this  seems  to  me  no  ex- 
planation, merely  a  restatement  of  the  fact.  Would  it  be 
thought  sufficient  to  say  that  because  planets  revolve  in 
elliptic  courses  round  the  sun,  satellites  follow  the  same 
course  round  the  planets,  for  the  sake  of  symmetry,  and 
to  complete  the  scheme  of  nature  ?  An  eminent  physiolo- 
gist accounts  for  the  presence  of  rudimentary  organs,  by 
supposing  that  they  serve  to  excrete  matter  in  excess,  or 


Chap.  XIII.]  RUDIMENTARY  ORGANS,  395 

injurious  to  the  system ;  but  can  we  supjDose  that  the 
minute  papilla,  which  often  represents  the  pistil  in  male 
flowers,  and  which  is  formed  merely  of  cellular  tissue, 
can  thus  act  ?  Can  we  suppose  that  the  formation  of  ru- 
dimentary teeth  which  are  subsequently  absorbed,  can  be 
of  any  service  to  the  rapidly  gr(3wing  embryonic  calf  by  the 
excretion  of  precious  phosphate  of  lime  ?  When  a  man's 
fingers  have  been  amputated,  imperfect  nails  sometimes 
appear  on  the  stumps  :  I  could  as  soon  believe  that  these 
vestiges  of  nails  have  appeared,  not  from  unknown  laws 
of  growth,  but  in  order  to  excrete  horny  matter,  as  that 
the  rudimentary  nails  on  the  fin  of  the  manatee  were 
formed  for  this  purpose. 

On  my  view  of  descent  with  modification,  the  origin 
of  rudimentary  organs  is  simple.  We  have  plenty  of 
cases  of  rudimentary  organs  in  our  domestic  productions, 
— as  the  stump  of  a  tail  in  tailless  breeds, — the  vestige  of 
an  ear  in  earless  breeds, — the  reappearance  of  minute 
dangling  horns  in  hornless  breeds  of  cattle,  more  especial- 
ly, according  to  Youatt,  in  young  animals, — and  the  state 
of  the  whole  flower  in  the  cauliflower.  We  often  see  ru- 
diments of  various  parts  in  monsters.  But  I  doubt 
whether  any  of  these  cases  throw  light  on  the  origin  of 
rudimentary  organs  in  a  state  of  nature,  further  than  by 
showing  that  rudiments  can  be  produced  ;  for  I  doubt 
whether  species  under  nature  ever  undergo  abrupt  changes. 
I  believe  that  disuse  has  been  the  main  agency  ;  that  it 
has  led  in  successive  generations  to  the  gradual  reduc- 
tion of  various  organs,  until  they  have  become  ru-diment- 
ary, — as  in  the  case  of  the  eyes  of  animals  inhabiting 
dark  caverns,  and  of  the  wings  of  birds  inhabiting  oceanic 
islands,  which  have  seldom  been  forced  to  take  flight,  and 
have  ultimately  lost  the  power  of  flying.  Again,  an 
organ  useful  under  certain  conditions  might  become  inju- 
rious under  others,  as  with  the  wings  of  beetles  living  on 
small  and  exposed  islands  ;  and  in  this  case  natural  selec- 
tion would  continue  slowly  to  reduce  the  organ,  until  it 
was  rendered  harmless  and  rudimentary. 

Any  change  in  function,  which  can  be  efi'ected  by 
insensibly  small  steps,  is  within  the  power  of  natural  se- 


396  RUDIMENTARY  ORGANS.  [Chap.  XIIL 

lection ;  so  that  an  organ  rendered,  during  changed  habits 
of  life,  useless  or  injurious  for  one  purpose,  might  easily 
be  modified  and  used  for  another  purpose.  Or  an  organ 
might  be  retained  for  one  alone  of  its  former  functions. 
An  organ,  when  rendered  useless,  may  well  be  variable, 
for  its  variations  cannot  be  checked  by  natural  selection. 
At  whatever  period  of  life  disuse  or  selection  reduces  an 
organ,  and  this  will  generally  be  when  the  being  has  come 
to  maturity  and  to  ij:s  full  powers  of  action,  the  principle 
of  inheritance  at  corresponding  ages  will  reproduce  the 
organ  in  its  reduced  state  at  the  same  age,  and  consequent- 
ly will  seldom  affect  or  reduce  it  in  the  embryo.  Thus 
we  can  understand  the  greater  relative  size  of  rudiment- 
ary organs  in  the  embryo,  and  their  lesser  relative  size 
in  the  adult.  But  if  each  step  of  the  process  of  reduction 
were  to  be  inherited,  not  at  the  corresponding  age,  but  at 
an  extremely  early  period  of  life,  (as  we  have  good  reason 
to  believe  to  be  possible,)  the  rudimentary  part  would 
tend  to  be  wholly  lost,  and  we  should  have  a  case  of  com- 
plete abortion.  The  principle,  also,  of  economy,  explained 
in  a  former  chapter,  by  which  the  materials  forming  any 
part  or  structure,  if  not  useful  to  the  possessor,  will  be 
saved  as  far  as  is  possible,  will  probably  often  come  into 
play ;  and  this  will  tend  to  cause  the  entire  obliteration 
of  a  rudimentary  organ. 

As  the  presence  of  rudimentary  organs  is  thus  due  to 
the  tendency  in  every  part  of  the  organisation,  which  has 
long  existed,  to  be  inherited — we  can  understand,  on  the 
genealogical  view  of  classification,  how  it  is  that  systema- 
tists  have  found  rudimentary  parts  as  useful  as,  or  even 
sometimes  more  useful  than,  parts  of  high  physiological 
importauce.  Rudimentary  organs  may  be  compared  with 
the  letters  in  a  word,  still  retained  in  the  spelling,  but  be- 
come useless  in  the  pronunciation,  but  which  serve  as  a 
clue  in  seeking  for  its  derivation.  On  the  view  of  descent 
with  modification,  we  may  conclude  that  the  existence  of 
organs  in  a  rudimentary,  imperfect,  and  useless  condition, 
or  quite  aborted,  far  from  presenting  a  strange  difliculty, 
as  they  assuredly  do  on  the  ordinary  doctrine  of  creation, 


Chap.  XIIL]  SUMMARY.  397 

migtit  even  have  been  anticipatedj  and  can  be  accounted 
for  by  the  laws  of  inheritance. 

Summary. — In  this  chapter  I  have  attempted  to  show, 
that  the  subordination  of  group  to  group  in  all  organisms 
throughout  all  time  ;  that  the  nature  of  the  relationship, 
by  which  all  living  and  extinct  beings  are  united  by  com- 
plex, radiating,  and  circuitous  lines  of  affinities  into  one 
grand  system  ;  the  rules  followed  and  the  difficulties  en- 
countered by  naturalists  in  their  classifications ;  the  value 
set  upon  characters,  if  constant  and  prevalent,  whether 
of  high  vital  importance,  or  of  the  most  trifling  impor- 
tance, or,  as  in  rudimentary  organs,  of  no  importance ; 
the  wide  opposition  in  value  between  analogical  or  adap- 
tive characters,  and  the  characters  of  true  affinity  ;  and 
other  such  rules  ; — all  naturally  follow  on  the  view  of  the 
common  parentage  of  those  forms  which  are  considered 
by  naturalists  as  allied,  together  with  their  modification 
through  natural  selection,  with  its  contmgencies  of  extinc- 
tion and  divergence  of  character.  In  considering  this 
view  of  classification,  it  should  be  borne  in  mind  that  the 
element  of  descent  has  been  universally  used  in  ranking 
together  the  sexes,  ages,  and  acknowledged  varieties  of 
the  same  species,  however  difi'erent  they  may  be  in  struc- 
ture. If  w^e  extend  the  use  of  this  element  of  descent, — ■ 
the  only  certainly  known  cause  of  similarity  in  organic 
beings,  we  shall  understand  what  is  meant  by  the  natu- 
ral system  :  it  is  genealogical  in  its  attempted  arrange- 
ment, with  the  grades  of  acquired  diflerence  marked  by 
the  terms  varieties,  species,  genera,  families,  orders,  and 
classes. 

On  this  same  view  of  descent  with  modification,  all 
the  great  facts  in  Morphology  become  intelligible, — 
whether  we  look  to  the  same  pattern  displayed  in  the 
homologous  organs,  to  whatever  purpose  applied,  of  the 
dififerent  sj)ecies  of  a  class  ;  or  to  the  homologous  parts 
constructed  on  the  same  pattern  in  each  individual  ani- 
mal and  plant. 

On  the  principle  of  successive  slight  variations,  not 
necessarily  or  generally  supervening  at  a  very  early  period 


398  8UMMART.  [Chap.  XIIL 

of  life,  and  being  inherited  at  a  corresponding  period,  we 
can  understand  the  great  leading  facts  in  Embryology ; 
namely,  the  resemblance  in  an  individual  embryo  of  the 
homologous  parts,  which  when  matured  will  become 
widely  different  from  each  other  in  structure  and  func- 
tion ;  and  the  resemblance  in  different  species  of  a  class 
of  the  homologous  parts  or  organs,  though  fitted  in  the 
adult  members  for  purposes  as  different  as  possible. 
Larvse  are  active  embryos,  which  have  become  specially 
modified  in  relation  to  their  habits  of  life,  through  the 
principle  of  modifications  being  inherited  at  corresponding 
ages.  On  this  same  principle — and  bearing  in  mind,  that 
when  organs  are  reduced  in  size,  either  from  disuse  or  se- 
lection, it  will  generally  be  at  that  period  of  life  when  the 
being  has  to  provide  for  its  own  wants,  and  bearing  in 
mind  how  strong  is  the  principle  of  inheritance — the  oc- 
currence of  rudimentary  organs  and  their  final  abortion, 
present  to  us  no  inexplicable  difficulties  ;  on  the  contrary, 
their  presence  might  have  been  even  anticipated.  The 
importance  of  embryological  characters  and  of  rudiment- 
ary organs  in  classification  is  intelligible,  on  the  view  that 
an  arrangement  is  only  so  far  natural  as  it  is  genealogical. 
Finally,  the  several  classes  of  facts  which  have  been 
considered  in  this  chapter,  seem  to  me  to  proclaim  so 
plainly,  that  the  innumerable  species,  genera,  and  families 
of  organic  beings,  with  which  this  world  is  peopled,  have 
all  descended,  each  within  its  own  class  or  group,  from 
common  parents,  and  have  all  been  modified  in  the  course 
of  descent,  that  I  should  without  hesitation  adopt  this 
view,  even  if  it  were  unsupported  by  other  facts  or  argu- 
ments. 


CuAP.  XIV.]  RECAPITULATION.  399 


CHAPTEEXIY. 

RECAPITULATION    AND    CONCLUSION. 

Kecapitulation  of  the  difficulties  on  the  theory  of  Natural  Selection— Recapitulation 
of  the  general  and  special  circumstances  in  its  favour — Causes  of  the  general 
helief  in  the  immutability  of  species — How  far  the  theory  of  natural  selection  may 
be  extended— Eflects  of  its  adoption  on  the  study  of  Natural  History — Concluding 
remarks. 

As  this  whole  volume  is  one  long  argument,  it  maj  be 
convenient  to  the  reader  to  have  the  leading  facts  and  in- 
ferences briefly  recapitulated. 

That  many  and  grave  objections  may  be  advanced 
against  the  theory  of  descent  with  modification  through 
natural  selection,  I  do  not  deny.  I  have  endeavoured  to 
give  to  them  their  full  force.  Nothing  at  first  can  appear 
more  difficult  to  believe  than  that  the  more  complex  or- 
gans and  instincts  should  have  been  perfected,  not  by 
means  superior  to,  though  analogous  with  human  reason, 
but  by  the  accumulation  of  innumerable  slight  variations, 
each  good  for  the  individual  possessor.  Nevertheless,  this 
difficulty,  though  appearing  to  our  imagination  insupera- 
bly great,  cannot  be  considered  real,  if  we  admit  the  follow- 
ing propositions,  namely, — that  gradations  in  the  perfec- 
tion of  any  organ  or  instinct,  which  we  may  consider, 
either  do  now  exist  or  could  have  existed,  each  good  of 
its  kind, — that  all  organs  and  instincts  are,  in  ever  so 
slight  a  degree,  variable, — and,  lastly,  that  there  is  a  strug 
gle  for  existence  leading  to  the  preservation  of  each  prof- 
itable deviation  of  structure  or  instinct.  The  truth  of 
these  propositions  cannot,  I  think,  be  disputed. 

It  is,  no  doubt,  extremely  difficult  even  to  conjecture 
by  what  gradations  many  structures  have  been  perfected, 
more  especially  amongst  broken  and  failing  groups  of  or- 


400  RECAPITULATION.  LCbap.  XIV. 

gauic  beings ;  but  we  see  so  many  strange  gradations  in 
nature,  as  is  proclaimed  by  the  canon,  "  Shatura  non  facit 
saltum,"  that  we  ought  to  be  extremely  cautious  in  saying 
that  any  organ  or  instinct,  or  any  whole  being,  could  not 
have  arrived  at  its  present  state  by  many  graduated  steps. 
There  are,  it  must  be  admitted,  cases  of  special  difficulty 
on  the  theory  of  natural  selection ;  and  one  of  the  most 
curious  of  these  is  the  existence  of  two  or  three  defined 
castes  of  workers  or  sterile  females  in  the  same  community 
of  ants  ;  but  I  have  attempted  to  show  how  this  difficulty 
can  be  mastered. 

With  respect  to  the  almost  universal  sterility  of  spe- 
cies when  first  crossed,  which  forms  so  remarkable  a 
contrast  with  the  almost  universal  fertility  of  varieties 
when  crossed,  I  must  refer  the  reader  to  the  recapitula- 
tion of  the  facts  given  at  the  end  of  the  eighth  chapter, 
which  seem  to  me  conclusivel}^  to  show  that  this  sterility 
is  no  more  a  special  endowment  than  is  the  incapacity 
of  two  trees  to  be  grafted  together ;  but  that  it  is  inci- 
dental on  constitutional  dift'erences  in  the  reproductive 
systems  of  the  intercrossed  species.  We  see  the  truth  of 
this  conclusion  in  the  vast  difference  in  the  result,  when 
the  same  two  species  are  crossed  reciprocally ;  that  is, 
when  one  species  is  first  used  as  the  father  and  then  as 
the  mother. 

The  fertility  of  varieties  when  intercrossed  and  of  their 
mongrel  offspring  cannot  be  considered  as  universal ;  nor 
is  their  very  general  fertility  surprising  when  we  remem- 
ber that  it  is  not  likely  that  either  their  constitutions  or 
their  reproductive  systems  should  have  been  profoundly 
modified.  Moreover,  most  of  the  varieties  which  have 
been  experimentised  on  have  been  produced  under  do- 
mestication ;  and  as  domestication  apparently  tends  to 
eliminate  sterility,  we  ought  not  to  expect  it  also  to  pro- 
duce sterility. 

The  sterility  of  hybrids  is  a  very  difierent  case  from 
that  of  first  crosses,  for  their  reproductive  organs  are 
more  or  less  functionally  impotent ;  whereas  in  first 
crosses  the  organs  on  both  sides  are  in  a  perfect  con- 
dition.    As  we  continually  see  that  organisms  of  all  kinds 


Chap.  XIV.]  RECAPITULATION.  4QJ[ 

are  rendered  in  some  degree  sterile  from  theii'  constitutions 
having  been  disturbed  by  sligbtlj  different  and  new  con- 
ditions of  life,  we  need  not  feel  surprise  at  hybrids  being 
in  some  degree  sterile,  for  their  constitutions  can  hardly 
fail  to  have  been  disturbed  from  being  compounded  of 
two  distinct  organisations.  This  parallelism  is  supported 
by  another  parallel,  but  directly  opposite,  class  of  facts ; 
namely,  that  the  vigour  and  fertility  of  all  organic  beings 
are  increased  by  slight  changes  in  their  conditions  of  life, 
and  that  the  offspring  of  slightly  modified  forms  or  varie- 
ties acquire  from  being  crossed  increased  vigour  and  fer- 
tility. So  that,  on  the  one  hand,  considerable  changes  in 
the  conditions  of  life  and  crosses  between  greatly  modified 
forms,  lessen  fertility ;  and  on  the  other  hand,  lesser  changes 
in  the  conditions  of  life  and  crosses  between  less  modified 
forms,  increase  fertility. 

Turning  to  geographical  distribution,  the  difficulties 
encountered  on  the  theory  of  descent  with  modification 
are  grave  enough.  All  the  individuals  of  the  same  spe- 
cies, and  all  the  species  of  the  same  genus,  or  even  higher 
group,  must  have  desoended  from  common  parents  ;  and 
therefore,  in  however  distant  and  isolated  parts  of  the 
world  they  are  now  found,  they  must  in  the  course  of  suc- 
cessive generations  have  passed  from  some  one  part  to  the 
others.  We  are  often  wholly  unable  even  to  conjecture 
how  this  could  have  been  effected.  Yet,  as  we  have  rea- 
son to  believe  that  some  species  have  retained  the  same 
specific  form  for  very  long  periods,  enormously  long  as 
measured  by  years,  too  much  stress  ought  not  to  be  laid 
on  the  occasional  wide  diffusion  of  the  same  species  ;  foi 
during  very  long  periods  of  time  there  will  always  be  a 
good  chance  for  wide  migration  by  many  means.  A 
broken  or  interrupted  range  may  often  be  accounted  foi 
by  the  extinction  of  the  species  in  the  intermediate  re- 
gions. It  cannot  be  denied  that  we  are  as  yet  very  igno- 
rant of  the  full  extent  of  the  various  climatal  and  geo- 
graphical changes  which  have  affected  the  earth  during 
modern  periods  ;  and  such  changes  will  obviously  haA^e 
greatly  facilitated  migration.  As  an  example,  I  have  at- 
tempted to  show  how  potent  has  been  the  influence  of  the 


402  RECAPITULATION.  [Chap.  XIV. 

Glacial  period  on  the  distribution  both  of  the  same  and 
of  representative  species  thronghont  the  world.  We  are 
as  yet  profoundly  ignorant  of  the  many  occasional  means 
of  transport.  With  resj)ect  to  distinct  species  of  the  same 
genus. inhabiting  very  distant  and  isolated  regions,  as  the 
process  of  modification  has  necessarily  been  slow,  all  the 
means  of  migration  will  have  been  possible  during  a  very 
long  period  ;  and  consequently  the  difficulty  of  the  wide 
diffusion  of  species  of  the  same  genus  is  in  some  degree 
lessened. 

As  on  the  theory  of  natural  selection  an  interminable 
number  of  intermediate  forms  must  have  existed,  linking 
together  all  the  species  in  each  group  by  gradations  as 
fine  as  our  present  varieties,  it  may  be  asked,  Why  do 
we  not  see  these  linking  forms  all  around  us  ?  Why  are 
not  all  organic  beings  blended  together  in  an  inextricable 
chaos  ?  AV^ith  respect  to  existing  forms,  we  should  re- 
member that  we  have  no  right  to  expect  (excepting  in 
rare  cases)  to  discover  directly  connecting  links  between 
them,  but  only  between  each  and  some  extinct  and  sup- 
planted form.  Even  on  a  wide  area,  which  has  during  a 
long  period  remained  continuous,  and  of  which  the  climate 
and  other  conditions  of  life  change  insensibly  in  going 
from  a  district  occupied  by  one  species  into  another  dis- 
trict occupied  by  a  closely  allied  species,  we  have  no  just 
right  to  expect  often  to  find  intermediate  varieties  in  the 
intermediate  zone.  For  we  have  reason  to  believe  that 
only  a  few  species  are  undergoing  change  at  any  one 
period  ;  and  all  changes  are  slowly  effected.  I  have  also 
shown  that  the  intermediate  varieties  which  will  at  first 
probably  exist  in  the  intermediate  zones,  will  be  liable 
to  be  supplanted  by  the  allied  forms  on  either  hand ;  and 
the  latter,  from  existing  in  greater  numbers,  will  generally 
be  modified  and  improved  at  a  quicker  rate  than  the  in- 
termediate varieties,  which  exist  in  lesser  numbers ;  so 
that  the  intermediate  varieties  will,  in  the  long  run,  be 
supplanted  and  exterminated. 

On  this  doctrine  of  the  extermination  of  an  infinitude 
of  connecting  links,  between  the  living  and  extinct  in- 
habitants of  the  wo  rid,  and  at  each  successive  period  be- 


Chap.  XIV.]  RECAPITULATION.  4.()3 

tween  the  extinct  and  still  older  species,  why  is  not  every 
geological  formation  charged  with  such  links  ?  Why  does 
not  every  collection  of  fossil  remains  afford  plain  evidence 
of  the  gradation  and  mutation  of  the  forms  of  life  ?  We 
meet  with  no  such  evidence,  and  this  is  the  most  obvious 
and  forcible  of  the  many  objections  which  may  be  urged 
against  my  theory.  Why,  again,  do  whole  groups  of 
allied  species  aj)pear,  though  certainly  they  often  falsely 
appear,  to  have  come  in  suddenly  on  the  several  geologi- 
cal stages  ?  Why  do  we  not  find  great  piles  of  strata  be- 
neath the  Silurian  system,  stored  with  the  remains  of  the 
progenitors  of  the  Silurian  groups  of  fossils  ?  For  cer- 
tainly on  my  theory  such  strata  must  somewhere  have 
been  deposited  at  these  ancient  and  utterly  unknown 
epochs  in  the  world's  history. 

I  can  answer  these  questions  and  grave  objections 
only  on  the  supposition  that  the  geological  record  is  far 
more  imperfect  than  most  geologists  beheve.  It  cannot 
be  objected  that  there  has  not  been  time  sufficient  for  any 
amount  of  organic  change  ;  for  the  lapse  of  time  has  been 
so  great  as  to  be  utterly  inappreciable  by  the  human  in- 
tellect. The  number  of  specimens  in  all  our  museums  is 
absolutely  as  nothing  compared  with  the  countless  gen- 
erations of  countless  s]3ecies  which  certainly  have  existed. 
We  should  not  be  able  to  recognise  a  species  as  the  parent 
of  any  one  or  more  species  if  we  were  to  examine  them 
ever  so  closely,  unless  we  likewise  possessed  many  of  the 
intermediate  links  between  their  past  and  present  states  ; 
and  these  many  links  we  could  hardly  ever  expect  to  dis- 
cover, owing  to  the  imperfection  of  the  geological  record, 
j^umerous  existing  doubtful  forms  could  be  named  which 
are  probably  varieties ;  but  who  will  pretend  that  in  future 
ages  so  many  fossil  links  will  be  discovered,  that  natural- 
ists will  be  able  to  decide,  on  the  common  view,  whether 
or  not  these  doubtful  forms  are  varieties  ?  As  long  as 
most  of  the  links  between  any  two  species  are  unknown, 
if  any  one  link  or  intermediate  variety  be  discovered,  it 
will  simply  be  classed  as  another  and  distinct  species. 
Only  a  small  portion  of  the  world  has  been  geologically 
explored.  Only  organic  beings  of  certain  classes  can  be 
18* 


404  RECAPITULATION.  [Chap.  XIV. 

preserved  in  a  fossil  condition,  at  least  in  any  great  num- 
ber. "Widely  ranging  species  vary  most,  and  varieties 
are  often  at  first  local,- — both  canses  rendering  the  discov- 
ery of  intermediate  links  less  likely.  Local  varieties  will 
not  spread  into  other  and  distant  regions  until  they  are 
considerably  modified  and  improved  ;  and  when  they  do 
spread,  if  discovered  in  a  geological  formation,  they  will 
appear  as  if  suddenly  created  there,  and  will  be  simply 
classed  as  new  species.  Many  formations  have  been  in- 
termittent in  their  accumulation  ;  and  their  duration,  I 
am  inclined  to  believe,  has  been  shorter  than  the  average 
duration  of  specific  forms.  Successive  formations  are 
separated  from  each  other  by  enormous  blank  intervals  of 
time ;  for  fossiliferous  formations,  thick  enough  to  resist 
future  degradation,  can  be  accumulated  only  where  much 
sediment  is  dej)osited  on  the  subsiding  bed  of  the  sea. 
During  the  alternate  periods  of  elevation  and  of  station- 
ary level  the  record  will  be  blank.  During  these  latter 
periods  there  will  probably  be  more  variability  in  the 
forms  of  life  ;  during  periods  of  subsidence,  more  ex- 
tinction. 

With  respect  to  the  absence  of  fossiliferous  formations 
beneath  the  lowest  Silurian  strata,  I  can  only  recur  to  the 
hypothesis  given  in  the  ninth  chapter.  That  the  geologi- 
cal record  is  imperfect  all  will  admit ;  but  that  it  is  im- 
perfect to  the  degree  which  I  require,  few  will  be  inclined 
to  admit.  If  we  look  to  long  enough  intervals  of  time, 
geology  plainly  declares  that  all  species  have  changed  ; 
and  they  have  changed  in  the  manner  wliich  my  theory 
requires,  for  they  have  changed  slowly  and  in  a  graduated 
manner.  We  clearly  see  this  in  the  fossil  remains  from 
consecutive  formations  invariably  being  much  more  close- 
ly related  to  each  other,  than  are  the  fossils  from  forma- 
tions distant  from  each  other  in  time. 

Such  is  the  sum  of  the  several  chief  objections  and 
difficulties  which  may  justly  be  urged  against  my  theory  ; 
and  I  have  now  briefly  recapitulated  the  answers  and  ex- 
planations which  can  be  given  to  them.  I  have  felt  these 
difficulties  far  too  heavily  during  many  years  to  doubt 
their  weight.     But  it   deserves  especial  notice  that  the 


Chap.  XIV.]  RECAPITULATION.  4Q5 

more  important  objections  relate  to  questions  on  whicli  we 
are  confessedly  ignorant ;  nor  do  we  know  how  ignorant 
we  are.  We  do  not  know  all  tlie  possible  transitional 
gradations  between  tlie  simplest  and  the  most  perfect 
organs  ;  it  cannot  be  pretended  that  we  know  all  the 
varied  means  of  Distribution  during  the  long  lapse  of 
years,  or  that  we  know  how  imperfect  the  Geological 
Record  is.  Grave  as  these  several  difficulties  are,  in  my 
judgment  they  do  not  overthrow  the  theory  of  descent 
with  modification, 

Kow  let  us  turn  to  the  other  side  of  the  argument. 
Under  domestication  we  see  much  variability.  Tliis 
seems  to  be  mainly  due  to  the  reproductive  system  being 
eminently  susceptible  to  changes  in  the  conditions  of  life  ; 
80  that  this  system,  when  not  rendered  impotent,  fails  to 
reproduce  ofispring  exactly  like  the  parent-form.  Ya- 
riability  is  governed  by  many  complex  laws, — by  correla- 
tion of  growth,  by  use  and  disuse,  and  by  the  direct  action 
of  the  physical  conditions  of  life.  There  is  much  difficulty 
in  ascertaining  how  much  modification  our  domestic  pro- 
ductions have  imdergone ;  but  we  may  safely  infer  that 
the  amount  has  been  large,  and  that  modifications  can  be 
inherited  for  long  periods.  As  long  as  the  conditions  of 
life  remain  the  same,  we  have  reason  to  believe  that 
modification,  which  has  already  been  inlierited  for  many 
generations,  may  continue  to  be  inherited  for  an  almost 
infinite  number  of  generations.  On  the  other  hand  we 
have  evidence  that  variability,  when  it  has  once  come 
into  play,  does  not  wholly  cease  ;  for  new  varieties  are 
still  occasionally  produced  by  our  most  anciently  domesti- 
cated productions. 

Man  does  not  actually  produce  variability  ;  he  only 
unintentionally  exposes  organic  beings  to  new  conditions 
of  life,  and  then  nature  acts  on  the  organisation,  and  causes 
variability.  But  man  can  and  does  select  the  variations 
given  to  him  by  natm-e,  and  thus  accumulate  them 
in  any  desired  manner.  He  thus  adapts  animals  and 
plants  for  his  own  benefit  or  pleasure.  He  may  do  this 
methodically,  or  he  may  do  it  unconsciously  by  preserv- 


406  RECAPITULATION  [Chap.  XIV. 

ing  the  individuals  most  useful  to  liim  atthetime,  without 
any  thought  of  altering  the  breed.  It  is  certain  that  he 
can  largely  influence  the  character  of  a  breed  by  selecting, 
in  each  successive  generation,  individual  differences  so 
slight  as  to  be  quite  inappreciable  by  an  uneducated  eye. 
This  process  of  selection  has  been  the  great  agency  in  the 
production  of  the  most  distinct  and  useful  domestic  breeds. 
That  many  of  the  breeds  produced  by  man  have  to  a  large 
extent  the  character  of  natural  sj^ecies,  is  shown  by  the 
inextricable  doubts  whether  very  many  of  them  are  va- 
rieties or  aboriginal  species. 

There  is  no  obvious  reason  why  the  principles  which 
have  acted  so  efficiently  under  domestication  should  not 
have  acted  under  nature.  In  the  preservation  of  favoured 
individuals  and  races,  during  the  constantly-recurrent 
Struggle  for  Existence,  we  see  the  most  powerful  and 
ever-acting  means  of  selection.  The  struggle  for  existence 
inevitably  follows  from  the  high  geometrical  ratio  of  in- 
crease which  is  common  to  all  organic  beings.  This  high 
rate  of  increase  is  proved  by  calculation,  by  the  effects  of 
a  succession  of  peculiar  seasons,  and  by  the  results  of  nat- 
uralisation, as  explained  in  the  third  chapter.  More  in- 
dividuals are  born  than  can  possibly  survive.  A  grain 
in  the  balance  will  determine  which  individual  shall  live 
and  which  shall  die, — which  variety  or  species  shall  in- 
crease in  number,  and  which  shall  decrease,  or  finally 
become  extinct.  As  the  individuals  of  the  same  species 
come  in  all  respects  into  the  closest  competition  with  each 
other,  the  struggle  will  generally  be  most  severe  between 
them  ;  it  will  be  almost  equally  severe  between  the  varie- 
ties of  the  same  species,  and  next  in  severity  between  the 
species  of  the  same  genus.  But  the  struggle  will  often  be 
very  severe  between  beings  most  remote  in  the  scale  of 
nature.  The  slightest  advantage  in  one  being,  at  any  age 
or  during  any  season,  over  those  with  which  it  comes  into 
competition,  or  better  adaptation  in  however  slight  a  de- 
gree to  the  surrounding  physical  conditions,  will  turn  the 
balance. 

With  animals  having  separate  sexes  there  will  in  most 
cases  be  a  struggle  between  the  males  for  possession  of  the 


Chap.  XIV.]  RECAPITULATION.  407 

females.  The  most  vigorous  individuals,  or  those  which 
have  most  successfully  struggled  with  their  conditions  of 
life,  will  generally  leave  most  progeny.  But  success  will 
often  depend  on  having  special  weapons  or  means  of  de- 
fence, or  on  the  charms  of  the  males ;  and  the  slightest 
advantage  will  lead  to  victory. 

As  geology  plainly  proclaims  that  each  land  has  un- 
dergone great  physical  changes,  w^e  might  have  expected 
that  organic  beings  would  have  varied  under  nature,  in 
the  same  way  as  they  generally  have  varied  under  the 
changed  conditions  of  domestication.  And  if  there  be  any 
variability  under  nature,  it  would  be  an  unaccountable 
fact  if  natural  selection  had  not  come  into  play.  It  has 
often  been  asserted,  but  the  assertion  is  quite  incapable  of 
proof,  that  the  amount  of  variation  under  nature  is  a 
strictly  limited  quantity.  Man,  though  acting  on  exter- 
nal characters  alone  and  often  capriciously,  can  produce 
within  a  short  period  a  great  result  by  adding  \\]y  mere 
individual  differences  in  his  domestic  productions  ;  and 
every  one  admits  that  there  are  at  least  individual  differ- 
ences in  species  under  nature.  But,  besides  such  differ- 
ences, all  naturalists  have  admitted  the  existence  of  varie- 
ties, which  they  think  sufficiently  distinct  to  be  worthy  of 
record  in  systematic  works.  'No  one  can  draw  any  clear 
distinction  between  individual  difi'erences  and  slight  varie- 
ties ;  or  between  more  plainly  marked  varieties  and  sub- 
species, and  species.  Let  it  be  observed  how  naturalists 
differ  in  the  rank  which  they  assign  to  the  many  repre- 
sentative forms  in  Europe  and  l^orth  America. 

If  then  we  have  under  nature  variability  and  a  ^^owe)*- 
ful  agent  always  ready  to  act  and  select,  why  should  we 
doubt  that  variations  in  any  way  useful  to  beings,  under 
their  excessively  complex  relations  of  life,  would  be  pre- 
served, accumulated,  and  inherited  ?  Why,  if  man  can 
by  patience  select  variations  most  useful  to  himself,  should 
nature  fail  in  selecting  variations  useful,  under  changing 
conditions  of  life,  to  her  living  products  ?  What  limit 
can  be  put  to  this  power,  acting  during  long  ages  and 
rigidly  scrutinising  the  whole  constitution,  structure,  and 
habits  of  each  creature, — favouring  the  good  and  rejecting 


408  RECAPITULATION.  tCHAP  XIV. 

the  bad  ?  I  can  see  no  limit  to  this  poAver,  in  slowly  and 
beautifully  adapting  each  form  to  the  most  complex  rela- 
tions of  life.  The  theory  of  natural  selection,  even  if  we 
look  no  further  than  this,  seems  to  me  to  be  in  itself  prob- 
able. I  have  already  recapitulated,  as  fairly  as  I  could, 
the  opposed  difficulties  and  objections  ;  now  let  us  turn  to 
the  special  acts  and  arguments  in  favour  of  the  theory. 

On  the  view  that  sj)ecies  are  only  strongly  marked  and 
permanent  varieties,  and  that  each  species  first  existed  as 
a  variety,  we  can  see  why  it  is  that  no  line  of  demarca- 
tion can  be  drawn  between  species,  commonly  supposed  to 
have  been  produced  by  special  acts  of  creation,  and  varie- 
ties which  are  acknowledged  to  have  been  produced  by 
secondary  laws.  On  this  same  view  we  can  understand 
how  it  is  that  in  each  region  where  many  species  of  a 
genus  have  been  produced,  and  where  they  now  flourish, 
these  same  species  should  present  many  varieties ;  for 
where  the  manufactory  of  species  has  been  active,  we 
might  expect,  as  a  general  rule,  to  find  it  still  in  action ; 
and  this  is  the  case  if  varieties  be  incipient  species.  More- 
over, the  species  of  the  larger  genera,  which  aflord  the 
greater  number  of  varieties  or  incipient  species,  retain  to 
a  certain  degree  the  character  of  varieties  ;  for  they  difi'er 
from  each  other  by  a  less  amount  of  difference  than  do 
the  species  of  smaller  genera.  The  closely  allied  species 
also  of  the  larger  genera  apparently  have  restricted  ranges, 
and  they  are  clustered  in  little  groups  round  other  species 
— in  which  respect  they  resemble  varieties.  These  are 
strange  relations  on  the  view  of  each  s]3ecies  having  been 
independently  created,  but  are  intelligible  if  all  species 
first  existed  as  varieties. 

As  each  species  tends  by  its  geometrical  ratio  of  repro- 
duction to  increase  inordinately  in  number ;  and  as  the 
modified  descendants  of  each  species  will  be  enabled  to  in- 
crease by  so  much  the  more  as  they  become  more  diversi- 
fied in  habits  and  structure,  so  as  to  be  enabled  to  seize  on 
many  and  widely  diflerent  places  in  the  economy  of  na- 
ture, there  will  be  a  constant  tendency  in  natural  selection 
to  preserve  the  most  divergent  offspring  of  any  one  spe- 
cies.    Hence  during  a  long-continued  course  of  modifica' 


Chap.  XIV.  1  RECAPITULATION.  ^QQ 

tion,  the  slight  differences  characteristic  of  varieties  of  the 
same  species,  tend  to  he  augmented  into  the  greater  differ- 
ences characteristic  of  species  of  the  same  genus.  New 
and  improved  varieties  will  inevitably  supplant  and  exter- 
minate the  older,  less  improved  and  intermediate  varie- 
ties ;  and  thus  species  are  rendered  to  a  large  extent 
defined  and  distinct  objects.  Dominant  species  belong- 
ing to  the  larger  groups  tend  to  give  birth  to  new 
and  dominant  forms ;  so  that  each  large  group  tends  to 
become  still  larger,  and  at  the  same  time  more  divergent 
in  character.  But  as  all  groups  cannot  thus  succeed  in 
increasing  in  size,  for  the  world  would  not  hold  them,  the 
more  dominant  groups  beat  the  less  dominant.  This  tend- 
ency in  the  large  groups  to  go  on  increasing  in  size  and 
diverging  in  character,  together  with  the  almost  inevitable 
contingency  of  much  extinction,  explains  the  arrangement 
of  all  the  forms  of  life,  in  groups  subordinate  to  gi'oups, 
all  within  a  few  great  classes,  which  we  now  see  every- 
where around  us,  and  which  has  prevailed  throughout  all 
time.  This  grand  fact  of  the  grouping  of  all  organic  beings 
seems  to  me  utterly  inexplicable  on  the  theory  of  creation. 

As  natural  selection  acts  solely  by  accumulating  slight, 
successive,  favourable  variations,  it  can  produce  no  great 
or  sudden  modification;  it  can  act  only  by  very  short 
and  slow  steps.  Hence  the  canon  of  "  Natura  non  facit 
saltum,"  which  every  fresh  addition  to  our  knowledge 
tends  to  make  more  strictly  correct,  is  on  this  theory  sim- 
ply intelligible.  We  can  plainly  see  why  nature  is  prod- 
igal in  variety,  though  niggard  in  innovation.  But  why 
this  should  be  a  law  of  nature  if  each  species  has  been  in- 
dependently created,  no  man  can  explain. 

Many  other  facts  are,  as  it  seems  to  me,  explicable  on 
this  theory.  How  strange  it  is  that  a  bird,  under  the  form 
of  a  woodpecker,  should  have  been  created  to  prey  on  in- 
sects on  the  ground  ;  that  upland  geese,  which  never  or 
rarely  swim,  should  have  been  created  with  webbed  feet ; 
that  a  thrush  should  have  been  created  to  dive  and  feed 
on  sub-aquatic  insects  ;  and  that  a  petrel  should  have  been 
created  with  habits  and  structure  fitting  it  for  the  life  of 
an  auk  or  grebe  !  and  so  on  in  endless  other  cases.     But 


4:10  RECAPITULATION.  [CHAP.  XIV. 

on  tlie  view  of  each  species  constantly  trying  to  increase 
in  number,  with  natural  selection  always  ready  to  adapt 
the  slowly  varying  descendants  of*  each  to  any  nnoccu]3ied 
or  ill-occupied  place  in  nature,  these  facts  cease  to  be 
strange,  or  perhaps  might  even  have  been  anticipated. 

As  natural  selection  acts  by  competition,  it  adapts  the 
inhabitants  of  each  country  only  in  relation  to  the  degree 
of  perfection  of  their  associates  ;  so  that  we  need  feel  no 
surprise  at  the  inhabitants  of  any  one  country,  although 
on  the  ordinary  view  su]3posed  to  have  been  specially 
created  and  adapted  for  that  country,  being  beaten  and 
supplanted  by  the  naturalised  productions  from  another 
land.  Xor  ought  we  to  marvel  if  all  the  contrivances  in 
nature  be  not,  as  far  as  we  can  judge,  absolutely  perfect ; 
and  if  some  of  them  be  abhorrent  to  our  ideas  of  fitness. 
We  need  not  marvel  at  the  sting  of  the  bee  causing  the 
bee's  own  death  ;  at  drones  being  produced  in  such  vast 
numbers  for  one  single  act,  and  being  then  slaughtered  by 
their  sterile  sisters ;  at  the  astonishing  waste  of  j)ollen  by 
our  fir-trees  ;  at  the  instinctive  hatred  of  the  queen  bee 
for  her  own  fertile  daughters ;  at  ichneumonidee  feeding 
within  the  live  bodies  of  caterpillars  ;  and  at  other  such 
cases.  The  wonder  indeed  is,  on  the  theory  of  natural 
selection,  that  more  cases  of  the  want  of  absolute  perfec- 
tion have  not  been  observed. 

The  complex  and  little  known  laws  governing  varia- 
tion are  the  same,  as  far  as  we  can  see,  with  the  laws 
which  have  governed  the  production  of  so-called  specific 
forms.  In  both  cases  physical  conditions  seem  to  have 
produced  but  little  direct  efi'ect ;  yet  when  varieties  enter 
any  zone,  they  occasionally  assume  some  of  the  characters 
of  the  species  proper  to  that  zone.  Li  both  varieties  and 
species,  use  and  disuse  seem  to  have  produced  some  efiect ; 
for  it  is  difficult  to  resist  this  conclusion  when  we  look, 
for  instance,  at  the  logger-headed  duck,  which  has  wings, 
incapable  of  flight,  in  nearly  the  same  condition  as  in  the 
domestic  duck ;  or  when  we  look  at  the  burrowing  tueu- 
tucu,  which  is  occasionally  blind,  and  then  at  certain 
moles,  which  are  habitually  blind  and  have  their  eyes 
covered  with  skin  ;  or  when  we  look  at  the  blind  animals 


Chap.  S.1V.]  RECAPITULATIOIir.  ^][|^ 

inhabiting  the  dark  caves  of  America  and  Europe.  In 
both  varieties  and  species  correlation  of  growth  seems  to 
have  j^layed  a  most  important  part,  so  that  when  one  part 
has  been  modified  other  parts  are  necessarily  modified. 
In  both  varieties  and  species  reversions  to  long-lost  charac- 
ters occur.  How  inexplicable  on  the  theory  of  creation  is 
the  occasional  appearance  of  stripes  on  the  shonlder  and 
legs  of  the  several  species  of  the  horse-genns  and  in  their 
hybrids  !  How  simply  is  this  fact  explained  if  we  believe 
that  these  S2:)ecies  have  descended  from  a  striped  progeni- 
tor, in  the  same  manner  as  the  several  domestic  breeds  of 
pigeon  have  descended  from  the  blue  and  barred  rock- 
pigeon  ! 

On  the  ordinary  view  of  each  species  having  been 
independently  created,  w^hy  should  the  specific  characters, 
or  those  by  which  the  species  of  the  same  genus  dififer 
from  each  other,  be  more  variable  than  the  generic  char- 
acters in  which  they  all  agree  ?  Why,  for  instance,  should 
the  colour  of  a  flower  be  more  likely  to  vary  in  any 
one  species  of  a  genus,  if  the  other  species,  supposed  to 
have  been  created  independently,  have  differently  coloured 
flowers,  than  if  all  the  species  of  the  genus  have  the  same 
coloured  flowers?  If  species  are  only  well-marked  va- 
rieties, of  which  the  characters  have  become  in  a  high 
degree  permanent,  we  can  understand  this  fact ;  for  they 
have  already  varied  since  they  branched  oft'  from  a  com- 
mon progenitor  in  certain  characters,  by  which  they  have 
come  to  be  specifically  distinct  from  each  other  ;  and 
therefore  these  same  characters  would  be  more  likely  still 
to  be  variable  than  the  generic  characters  which  have 
been  inherited  without  change  for  an  enormous  period. 
It  is  inexplicable  on  the  theory  of  creation  why  a  part 
developed  in  a  very  unusual  manner  in  any  one  sj)ecies 
of  a  genus,  and  therefore,  as  we  may  naturally  infer,  of 
great  importance  to  the  species,  should  be  eminently  liable 
to  variation  ;  but,  on  my  view,  this  part  has  undergone, 
since  the  several  species  branched  off  from  a  common 
progenitor,  an  unusual  amount  of  variability  and  modifi- 
cation, and  therefore  we  might  expect  this  part  generally 
to  be  still  variable.     But  a  part  may  be  developed  in  the 


4-12  RECAPITVLATIOX.  [Chap.  XIV. 

most  unusual  manner,  like  the  wing  of  a  bat,  and  yet  not 
to  be  more  variable  than  any  other  structure,  if  the  part 
be  common  to  many  subordinate  forms,  that  is,  if  it  has 
been  inherited  for  a  very  long  period  ;  for  in  this  case  it 
will  have  been  rendered  constant  by  long-continued 
natural  selection. 

Glancing  at  instincts,  marvellous  as  some  are,  they 
offer  no  greater  difficulty  than  does  corporeal  structure  on 
the  theory  of  the  natural  selection  of  successive,  slight, 
but  profitable  modifications.  We  can  thus  imderstand 
why  nature  moves  by  graduated  steps  in  endowing  differ- 
ent animals  of  the  same  class  with  their  several  instincts. 
I  have  attempted  to  show  how  much  light  the  principle 
of  gradation  throws  on  the  admirable  architectural  powers 
of  the  hive-bee.  Habit  no  doubt  sometimes  comes  into 
play  in  modifying  instincts  ;  but  it  certainly  is  not  indis- 
pensable, as  we  see,  in  the  case  of  neuter  insects,  which 
leave  no  progeny  to  inherit  the  effects  of  long-continued 
habit.  On  the  view  of  all  the  species  of  the  same  genus 
having  descended  from  a  common  parent,  and  having 
inherited  much  in  common,  we  can  understand  how  it  is 
that  allied  species,  when  placed  under  considerably  differ- 
ent conditions  of  life,  yet  should  follow  nearly  the  same 
instincts  ;  why  the  thrush  of  South  America,  for  instaijce, 
lines  her  nest  with  mud  like  our  British  species.  On  the 
view  of  instincts  having  been  slowly  acquired  through 
natural  selection,  we  need  not  marvel  at  some  instincts 
being  apparently  not  perfect  and  liable  to  mistakes,  and 
at  many  instincts  causing  other  animals  to  suffer. 

If  species  be  only  well-marked  and  permanent  varie- 
ties, we  can  at  once  see  why  their  crossed  offspring  should 
follow  the  same  complex  laws  in  their  degrees  and  kinds 
of  resemblance  to  their  parents, — in  being  absorbed  into 
each  other  by  successive  crosses,  and  in  other  such  points, 
■ — 'as  do  the  crossed  offspring  of  acknowledged  varieties. 
On  the  other  hand,  these  would  be  strange  facts  if  species 
have  been  independently  created,  and  varieties  have  been 
produced  by  secondary  laws. 

K  we  admit  that  the  geological  record  is  imperfect  in 
an  extreme  degree,  then  such  facts  as  the  record  gives. 


Chap.  XIV.]  RECAPITULATION.  4^3 

support  the  theory  of  descent  with  modification.  'New 
species  have  come  on  the  stage  slowly  and  at  successive 
intervals  ;  and  the  amount  of  change,  after  equal  inter- 
vals of  time,  is  widely  different  in  different  groups.  The 
extinction  of  species  and  of  whole  groups  of  species, 
which  has  played  so  conspicuous  a  part  in  the  history  of 
the  organic  world,  almost  inevitably  follows  on  the  prin- 
ciple of  natural  selection  ;  for  old  forms  will  be  supplanted 
by  new  and  improved  forms.  ISTeither  single  species  nor 
groups  of  species  reappear  when  the  chain  of  ordinary 
generation  has  once  been  broken.  The  gradual  diffusion 
of  dominant  forms,  with  the  slow  modification  of  their 
descendants,  causes  the  forms  of  life,  after  long  intervals 
of  time,  to  appear  as  if  they  had  changed  simultaneously 
throughout  the  world.  The  fact  of  the  fossil  remains  of 
each  formation  being  in  some  degree  intermediate  in 
character  between  the  fossils  in  the  formations  above  and 
below,  is  simply  explained  by  their  intermediate  position 
in  the  chain  of  descent.  The  grand  fact  that  all  extinct 
organic  beings  belong  to  the  same  system  with  recent 
beings,  falling  either  into  the  same  or  into  intermediate 
groups,  follows  from  the  living  and  the  extinct  being  the 
offspring  of  common  parents.  As  the  groups  which  have 
descended  from  an  ancient  progenitor  have  generally 
diverged  in  character,  the  progenitor  with  its  early  de- 
scendants will  often  be  intermediate  in  character  in  com- 
parison with  its  later  descendants  ;  and  thus  we  can  see 
why  the  more  ancient  a  fossil  is,  the  oftener  it  stands  in 
some  degree  intermediate  between  existing  and  allied 
groups.  Recent  forms  are  generally  looked  at  as  being, 
in  some  vague  sense,  higher  than  ancient  and  extinct 
forms  ;  and  they  are  in  so  far  higher  as  the  later  and 
more  improved  forms  have  conquered  the  older  and  less 
improved  organic  beings  in  the  struggle  for  life.  Lastly, 
the  law  of  the  long  endurance  of  allied  forms  on  the  same 
continent, — of  marsupials  in  Australia,  of  edentata  in 
America,  and  other  such  cases, — is  intelligible,  for  within 
a  confined  country,  the  recent  and  the  extinct  will  natu- 
rally be  allied  by  descent. 

Looking  to  geographical  distribution,  if  we  admit  that 


414  RECAPITULATION.  [Chap.  XIV. 

there  lias  been  during  the  long  course  of  ages  much 
migration  from  one  part  of  the  world  to  another,  owing  to 
fonner  climatal  and  geographical  changes,  and  to  the 
many  occasional  and  unknown  means  of  dispersal,  then 
we  can  understand,  on  the  theory  of  descent  with  modi- 
fication, most  of  the  great  leading  facts  in  Distribution. 
"We  can  see  why  there  should  be  so  striking  a  parallelism 
in  the  distribution  of  organic  beings  throughout  space, 
and  in  their  geological  succession  throughout  time ;  for 
in  both  cases  the  beings  have  been  connected  by  the  bond 
of  ordinary  generation,  and  the  means  of  modification 
have  been  the  same.  We  see  the  full  meaning  of  the 
wonderful  fact,  which  must  have  struck  every  traveller, 
namely,  that  on  the  same  continent,  under  the  most  diverse 
conditions,  under  heat  and  cold,  on  mountain  and  lowland, 
on  deserts  and  marshes,  most  of  the  inhabitants  within 
each  great  class  are  plainly  related ;  for  they  will  generally 
be  descendants  of  the  same  progenitors  and  early  colo- 
nists. On  this  same  principle  of  former  migration,  com- 
bined in  most  cases  with  modification,  we  can  understand, 
by  the  aid  of  the  Glacial  period,  the  identity  of  some 
few  plants,  and  the  close  alliance  of  many  others,  on  the 
most  distant  mountains,  under  the  most  different  climates  ; 
and  likewise  the  close  alliance  of  some  of  the  inhabitants 
of  the  sea  in  the  northern  and  southern  temperate  zones, 
though  separated  by  the  whole  intertropical  ocean.  Al- 
though two  areas  may  present  the  same  physical  condi- 
tions of  life,  we  need  feel  no  surprise  at  their  inhabitants 
being  widely  different,  if  they  have  been  for  a  long  period 
completely  separated  from  each  other  ;  for  as  the  relation 
of  organism  to  organism  is  the  most  important  of  all  rela- 
tions, and  as  the  two  areas  will  have  received  colonists  from 
some  third  source  or  from  each  other,  at  various  periods 
and  in  different  proportions,  the  course  of  modification  in 
the  two  areas  will  inevitably  be  different. 

On  this  view  of  migration,  with  subsequent  modifica- 
tion, we  can  see  why  oceanic  islands  should  be  inhabited 
by  few  species,  but  of  these,  that  many  should  be  peculiar. 
"We  can  clearly  see  why  those  animals  which  cannot  cross 
wide  spaces  of  ocean,  as  frogs  and  terrestrial  mammals, 


Chap.  XIV.]  RECAPITULATION.  •         ^^^5 

should  not  inhabit  oceanic  islands  ;  and  why,  on  the  other 
hand,  new  and  peculiar  species  of  bats,  which  can  traverse 
the  ocean,  should  so  often  be  found  on  islands  far  distant 
from  any  continent.  Such  facts  as  the  presence  of  pecu- 
liar species  of  bats,  and  the  absence  of  all  other  mammals, 
on  oceanic  islands,  are  utterly  inexplicable  on  the  tlieory 
of  independent  acts  of  creation. 

The  existence  of  closely  allied  or  representative  spe- 
cies in  any  two  areas,  implies,  on  the  theory  of  descent 
with  modification,  that  the  same  parents  formerly  in- 
habited both  areas  ;  and  we  almost  invariably  find  that 
wherever  many  closely  allied  species  inhabit  two  areas, 
some  identical  species  common  to  both  still  exist.  Wher- 
ever many  closely  allied  yet  distinct  species  occur,  many 
doubtful  forms  and  varieties  of  the  same  S23ecies  likewise 
occur.  It  is  a  rule  of  high  generality  that  the  inhabitants 
of  each  area  are  related  to  the  inhabitants  of  the  nearest 
source  whence  immigrants  might  have  been  derived.  We 
see  this  in  nearly  all  the  plants  and  animals  of  the  Gala- 
pagos archipelago,  of  Juan  Fernandez,  and  of  the  other 
American  islands  being  related  in  the  most  striking  man- 
ner to  the  plants  and  animals  of  the  neighbouring  Ameri- 
can mainland ;  and  those  of  the  Cape  de  Yerde  archipel- 
ago and  other  African  islands  to  the  African  mainland. 
It  must  be  admitted  that  these  facts  receive  no  explanation 
on  the  theory  of  creation. 

The  fact,  as  we  have  seen,  that  all  past  and  present 
organic  beings  constitute  one  grand  natural  system,  with 
group  subordinate  to  group,  and  with  extinct  groups  often 
falling  in  between  recent  groups,  is  intelligible  on  the 
theory  of  natural  selection  with  its  contingencies  of  ex- 
tinction and  divergence  of  character.  On  these  same 
principles  we  see  how  it  is,  that  the  mutual  af&nities  of 
the  species  and  genera  within  each  class  are  so  complex 
and  circuitous.  We  see  why  certain  characters  are  far 
more  serviceable  than  others  for  classification ; — why 
adaptive  characters,  though  of  paramount  importance  to 
the  being,  are  of  hardly  any  importance  in  classification ; 
why  characters  derived  from  rudimentary  parts,  though 
of  no  service  to  the  being,  are  often  of  high  classificatory 


416  RECAPITULATION.  [Chap.  XIV. 

value ;  and  wliy  embiyological  characters  are  the  most 
vahiable  of  all.  The  real  affinities  of  all  organic  beings 
are  due  to  inheritance  or  community  of  descent.  The 
natural  system  is  a  genealogical  arrangement,  in  which 
we  have  to  discover  the  lines  of  descent  bj  the  most  per- 
manent characters,  however  slight  their  vital  imj)ortance 
may  be. 

The  framework  of  bones  being  the  same  in  the  hand 
of  a  man,  wing  of  a  bat,  fin  of  the  porpoise,  and  leg  of 
the  horse, — ^the  same  number  of  vertebrse  forming  the 
neck  of  the  giraffe  and  of  the  elephant, — and  innumerable 
other  such  facts,  at  once  explain  themselves  on  the  theory 
of  descent  with  slow  and  slight  successive  modifications. 
The  similarity  of  pattern  in  the  wing  and  leg  of  a  bat, 
though  used  for  such  different  purposes, — in  the  jaws  and 
legs  of  a  crab, — ^in  the  petals,  stamens,  and  pistils  of  a 
flower,  is  likewise  intelligible  on  the  view  of  the  gradual 
modification  of  parts  or  organs,  which  were  alike  in  the 
early  progenitor  of  each  class.  On  the  principle  of  suc- 
cessive T  ariations  not  always  supervening  at  an  early  age, 
and  being  inherited  at  a  corresponding  not  early  period 
of  life,  we  can  clearly  see  why  the  embryos  of  mammals, 
birds,  reptiles,  and  fishes  should  be  so  closely  alike,  and 
should  be  so  unlike  the  adult  forms.  We  may  cease 
marvelling  at  the  embryo  of  an  air-breathing  mammal  or 
bird  having  branchial  slits  and  arteries  running  in  loops, 
like  those  in  a  fish  which  has  to  breathe  the  air  dissolved 
in  water,  by  the  aid  of  well-developed  branchiae. 

Disuse,  aided  sometimes  by  natural  selection,  will 
often  tend  to  reduce  an  organ,  when  it  has  become  useless 
by  changed  habits  or  nnder  changed  conditions  of  life ; 
and  we  can  clearly  understand  on  this  view  the  meaning 
of  rudimentary  organs.  But  disuse  and  selection  will 
generally  act  on  each  creature,  when  it  has  come  to  matu- 
rity and  has  to  play  its  full  part  in  the  struggle  for  exist- 
ence, and  will  thus  have  little  power  of  acting  on  an  or- 
gan during  early  life  ;  hence  the  organ  will  not  be  much 
reduced  or  rendered  rudimentary  at  this  early  age.  The 
calf,  for  instance,  has  inherited  teeth,  which  never  cut 
through  the  gums  of  the  upper  jaw,  from  an  early  progen- 


Chap.  XIV.]  CONCLUSION.  ^^fj 

itor  having  well-developed  teetli ;  and  we  may  Relieve, 
that  the  teeth  in  the  mature  animal  were  reduced,  during 
successive  generations,  by  disuse,  or  by  the  tongue  and 
j)alate  having  been  fitted  by  natural  selection  to  browse 
without  their  aid  ;  whereas  in  the  calf,  the  teeth  have  been 
left  untouched  by  selection  or  disuse,  and  on  the  j^rinciple 
of  inheritance  at  corresponding  ages  have  been  inherited 
from  a  remote  period  to  the  present  day.  On  the  view 
of  each  organic  being  and  each  separate  organ  having 
been  specially  created,  how  utterly  inexplicable  it  is  that 
parts,  like  the  teeth  in  the  embryonic  calf,  or  like  the 
shrivelled  wings  under  the  soldered  wing-covers  of  some 
beetles,  should  thus  so  frequently  bear  the  plain  stamp  of 
inutility  !  ]N"ature  may  be  said  to  have  taken  pains  to  re- 
veal, by  rudimentary  organs  and  by  homologous  struc- 
tures, her  scheme  of  modification,  which  it  seems  that  we 
wilfully  will  not  understand. 

1  have  now  recapitulated  the  chief  facts  and  consider- 
ations which  have  thoroughly  convinced  me  that  species 
have  been  modified,  during  a  long  course  of  descent,  by 
the  preservation  or  the  natural  selection  of  many  succes- 
sive slight  favourable  variations.  I  cannot  believe  that 
a  false  theory  would  explain,  as  it  seems  to  me  that  the 
theory  of  natural  selection  does  explain,  the  several  large 
classes  of  facts  above  specified.  I  see  no  good  reason  why 
the  views  given  in  this  volume  should  shock  the  religious 
feelings  of  any  one.  A  celebrated  author  and  divine  has 
written  to  me  that  "  he  has  gradually  learnt  to  see  that  it 
is  just  as  noble  a  conception  of  the  Deity  to  believe  that 
He  created  a  few  original  forms  capable  of  self-develop- 
ment into  other  and  needful  forms,  as  to  believe  that  He 
required  a  fresh  act  of  creation  to  supply  the  voids  caused 
by  the  action  of  His  laws." 

Why,  it  may  be  asked,  have  nearly  all  the  most 
eminent  living  naturalists  and  geologists  rejected  this 
view  of  the  mutability  of  species  ?  It  cannot  be  asserted 
that  organic  beings  in  a  state  of  nature  are  subject  to  no 
variation ;  it  cannot  be  proved  that  the  amount  of  varia- 
tion in  the  course  of  long  ages  is  a  limited  quantity;  no 


418  CONCLUSION.  [Chap.  XIV. 

clear  distinction  has  been,  or  can  be,  drawn  between  spe- 
cies and  well-marked  varieties.  It  cannot  be  maintained 
that  species  when  intercrossed  are  invariably  sterile,  and 
varieties  invariably  fertile ;  or  that  sterility  is  a  special 
endowment  and  sign  of  creation.  The  belief  that  species 
were  immutable  productions  was  almost  unavoidable  as 
long  as  the  history  of  the  world  was  thought  to  be  of 
short  duration ;  and  now  that  we  have  acquired  some 
idea  of  the  lapse  of  time,  we  are  too  apt  to  assume,  with- 
out proof,  that  the  geological  record  is  so  perfect  that  it 
would  have  afforded  us  plain  evidence  of  the  mutation  of 
epecies,  if  they  had  undergone  mutation. 

But  the  chief  cause  of  our  natural  unwillingness  to 
admit  that  one  species  has  given  birth  to  other  and  distinct 
species,  is  that  we  are  always  slow  in  admitting  any  great 
change  of  which  we  do  not  see  the  intermediate  steps. 
The  difficulty  is  the  same  as  that  felt  by  so  many  geolo- 
gists, when  Lyell  first  insisted  that  long  lines  of  inland 
cliffs  had  been  formed,  and  great  valleys  excavated,  by 
the  slow  action  of  the  coast-waves.  The  mind  cannot 
possibly  grasp  the  full  meaning  of  the  term  of  a  hundred 
million  years  ;  it  cannot  add  up  and  perceive  the  full 
effects  of  many  slight  variations,  accumulated  during  an 
almost  infinite  number  of  generations. 

Although  I  am  fully  convinced  of  the  truth  of  the 
views  given  in  this  volume  under  the  form  of  an  abstract, 
I  by  no  means  expect  to  convince  experienced  naturalists 
whose  minds  are  stocked  with  a  multitude  of  facts  all 
viewed,  during  a  long  course  of  years,  from  a  point  of 
view  directly  opposite  to  mine.  It  is  so  easy  to  hide  our 
ignorance  under  such  expressions  as  the  "  plan  of  crea- 
tion," "  unity  of  design,"  &c.,  and  to  think  that  we  give 
an  explanation  when  we  only  restate  a  fact.  Any  one 
whose  disposition  leads  him  to  attach  more  weight  to 
unexplained  difficulties  than  to  the  explanation  of  a  certain 
number  of  facts  will  certainly  reject  my  theory.  A  few 
naturalists,  endowed  with  much  flexibility  of  mind,  and 
who  have  already  begun  to  doubt  on  the  immutability  of 
species,  may  be  mfluenced  by  this  volume ;  but  I  look 
with  confidence  to  the  future,  to  young  and  rising  natu- 


Chap.  XIV.]  CON^CLUSION.  4;[9 

ralists,  who  will  be  able  to  view  both  sides  ol  the  question 
with  impartiality.  Whoever  is  led  to  believe  that  species 
are  mutable  will  do  good  service  by  conscientiously  ex- 
pressing his  conviction  ;  for  only  thus  can  the  load  of 
prejudice  by  which  this  subject  is  overwhelmed  be  re- 
moved. 

Several  eminent  naturalists  have  of  late  published  their 
belief  that  a  multitude  of  reputed  species  in  each  genus 
are  not  real  species  ;  bat  that  other  species  are  real,  that 
is,  have  been  independently  created.  This  seems  to  me 
a  strange  conclusion  to  arrive  at.  They  admit  that  a 
multitude  of  forms,  which  till  lately  they  themselves 
thought  were  special  creations,  and  which  are  still  thua 
looked  at  by  the  majority  of  naturalists,  and  which  conse- 
quently have  every  external  characteristic  feature  of  true 
S]3ecies, — they  admit  that  these  have  been  produced  by 
variation,  but  they  refuse  to  extend  the  same  view  to  other 
and  very  slightly  different  forms.  Nevertheless  they  do 
not  pretend  that  they  can  define,  or  even  conjecture,  which 
are  the  created  forms  of  life,  and  Avhich  are  those  pro- 
duced by  secondary  laws.  They  admit  variation  as  a 
liera  cau^a  in  one  case,  they  arbitrarily  reject  it  in  an- 
other, without  assigning  any  distinction  in  the  two  cases. 
The  day  will  come  when  this  will  be  given  as  a  curious 
illustration  of  the  blindness  of  preconceived  opinion. 
These  authors  seem  no  more  startled  at  a  miraculous  act 
of  creation  than  at  an  ordinary  birth.  But  do  they  really 
believe  that  at  innumerable  periods  in  the  earth's  history 
certain  elemental  atoms  have  been  commanded  suddenly 
to  flash  into  living  tissues  ?  Do  they  believe  that  at  each 
supposed  act  of  creation  one  individual  or  many  were 
produced  ?  Were  all  the  infinitely  numerous  kiuds  of 
animals  and  plants  created  as  eggs  or  seed,  or  as  full 
grown  ?  and  in  the  case  of  mammals,  were  they  created 
bearing  the  false  marks  of  nourishment  from  the  mother's 
womb  i  Although  naturalists  very  properly  demand  a 
full  explanation  of  every  difficulty  from  those  who  believe 
in  the  mutability  of  species,  on  their  own  side  they  ignore 
the  whole  subject  of  the  first  appearance  of  species  in 
what  they  consider  reverent  silence. 
19 


420  COXCLUSIOX.  [Chap.  XIV. 

It  may  be  asked  liow  far  I  extend  the  doctrine  of  the 
modification  of  species.  The  question  is  difficult  to  an- 
swer, because  the  more  distinct  the  forms  are  which  we 
may  consider,  by  so  much  the  arguments  fall  away  in 
force.  But  some  arguments  of  the  greatest  weight  extend 
very  far.  All  the  members  of  whole  classes  can  be  con- 
nected together  by  chains  of  afiinities,  and  all  can  be 
classified  on  the  same  principle,  in  groups  subordinate  to 
groups.  Fossil  remains  sometimes  tend  to  fill  up  very 
wide  intervals  between  existing  orders.  Organs  in  a  ru- 
dimentary condition  ]3lainly  show  that  an  early  progenitor 
had  the  organ  in  a  fully  developed  state  ;  and  this  in  some 
instances  necessarily  implies  an  enormous  amount  of  mod- 
ification in  the  descendants.  Throughout  whole  classes 
various  structures  are  formed  on  the  same  pattern,  and  at 
an  embryonic  age  the  species  closely  resemble  each  other. 
Therefore  I  cannot  doubt  that  the  theory  of  descent  with 
modification  embraces  all  the  members  of  the  same  class. 
I  believe  that  animals  have  descended  from  at  most  only 
four  or  five  progenitors,  and  plants  from  an  equal  or  lesser 
number. 

Analogy  would  lead  me  one  step  further,  namely,  to 
the  belief  that  all  animals  and  plants  have  descended  from 
some  one  prototype.  But  analogy  may  be  a  deceitful 
guide.  ^Nevertheless  all  living  things  have  much  in  com- 
mon, in  their  chemical  composition,  their  germinal  vesicles, 
their  cellular  structure,  and  their  laws  of  growth  and  re- 
production. We  see  this  even  in  so  trifling  a  circumstance 
as  that  the  same  poison  often  similarly  affects  j^lants  and 
animals  ;  or  that  the  poison  secreted  by  the  gall-fly  pro- 
duces monstrous  growths  on  the  wild  rose  or  oak-tree. 
Therefore  I  should  infer  from  analogy  that  probably  all 
the  organic  beings  which  have  ever  lived  on  this  earth 
have  descended  from  some  one  primordial  form,  into 
which  life  was  first  breathed. 

When  the  views  entertained  in  this  volume  on  the 
origin  of  species,  or  when  analogous  views  are  generally 
admitted,  we  can  dimly  foresee  that  there  will  be  a  con- 
siderable revohition  in  natural  historv.     Svstematists  will 


Chap.  XIV.]  CONCLUSIOX.  X91 

be  able  to  pursue  their  labours  as  at  present ;  but  they 
will  not  be  incessantly  haunted  by  the  shadowy  doubt 
whether  this  or  that  form  be  in  essence  a  species.  This  I 
feel  sure,  and  I  speak  after  experience,  will  be  no  slight 
relief.  The  endless  disputes  whether  or  not  some  fifty 
species  of  British  brambles  are  true  species  will  cease. 
Systematists  will  have  only  to  decide  (not  that  this  will 
be  easy)  whether  any  form  be  sufiiciently  constant  and 
distinct  from  other  forms,  to  be  capable  of  definition  ;  and 
if  definable,  whether  the  differences  be  sufficiently  imjDor- 
tant  to  deserve  a  specific  name.  This  latter  point  will 
become  a  far  more  essential  consideration  than  it  is  at 
present ;  for  differences,  however  slight,  between  any  two 
forms,  if  not  blinded  by  intermediate  gradations,  are  looked 
at  by  most  naturalists  as  sufficient  to  raise  both  forms  to 
the  rank  of  species.  Hereafter  we  shall  be  compelled  to 
acknowledge  that  the  only  distinction  between  species  and 
well-marked  varieties  is,  that  the  latter  are  known,  or 
believed,  to  be  connected  at  the  present  day  by  interme- 
diate gradations,  whereas  species  were  formerly  thus  con- 
nected. Hence,  without  quite  rejecting  the  consideration 
of  the  present  existence  of  intermediate  gradations  between 
any  two  forms,  we  shall  be  led  to  weigh  more  carefully 
and  to  value  higher  the  actual  amount  of  difference  be- 
tween them.  It  is  quite  possible  that  forms  now  general- 
ly acknowledged  to  be  merely  varieties  may  hereafter  be 
thought  worthy  of  specific  names,  as  with  the  primrose 
and  cowslip ;  and  in  this  case  scientific  and  common  lan- 
guage will  come  into  accordance.  In  short,  we  shall  have 
to  treat  species  in  the  same  manner  as  those  naturalists 
treat  genera,  who  admit  that  genera  are  merely  artificial 
combinations  made  for  convenience.  This  may  not  be  a 
cheering  prospect ;  but  we  shall  at  least  be  freed  from  the 
vain  search  for  the  undiscovered  and  undiscoverable  es- 
sence of  the  term  species. 

The  other  and  more  general  departments  of  natural 
history  will  rise  greatly  in  interest.  The  terms  used  by 
naturalists  of  affinity,  relationship,  community  of  type, 
paternity,  morphology,  adaptive  characters,  rudimentary 
and  abortive  organs,  etc.,  will  cease  to  be  metaphorical, 


^22  C0XCLUSI02s\  [Chap.  XIV. 

and  will  have  a  plain  signification.  When  we  no  longer 
look  at  an  organic  being  as  a  savage  looks  at  a  ship,  as  at 
something  wholly  beyond  his  comprehension ;  when  we 
regard  every  production  of  nature  as  one  which  has  had  a 
history ;  when  we  contemplate  every  complex  structure 
and  instinct  as  the  summing  up  of  many  contrivances, 
each  useful  to  the  ]DOssessor,  nearly  in  the  same  way  as 
when  we  look  at  any  great  mechanical  invention  as  the 
summing  up  of  the  labour,  the  experience,  the  reason,  and 
even  the  blunders  of  numerous  workmen  ;  when  we  thus 
view  each  organic  being,  how  far  more  interesting,  I  speak 
from  experience,  will  the  study  of  natural  history  become ! 

A  grand  and  almost  untrodden  field  of  inquiry  will  be 
opened,  on  the  causes  and  laws  of  variation,  on  correla- 
tion of  growth,  on  the  effects  of  use  and  disuse,  on  the 
direct  action  of  external  conditions,  and  so  forth.  The 
study  of  domestic  productions  will  rise  immensely  in  value. 
A  new  variety  raised  by  man  will  be  a  far  more  impor- 
tant and  interesting  subject  for  study  than  one  more  spe- 
cies added  to  the  infinitude  of  already  recorded  species. 
Our  classifications  will  come  to  be,  as  far  as  they  can  be 
so  made,  genealogies ;  and  will  then  truly  give  what 
may  be  called  the  plan  of  creation.  The  rules  for  classify- 
ing will  no  doubt  become  sim]3ler  when  we  have  a  definite 
object  in  view.  We  possess  no  pedigrees  or  armorial 
bearings  ;  and  we  have  to  discover  and  trace  the  many 
diverging  lines  of  descent  in  our  natural  genealogies  by 
characters  of  any  kind  which  have  long  been  inherited. 
Eudimentary  organs  will  speak  infallibly  with  respect  to 
the  nature  of  long-lost  structures.  Species  and  groups  of 
species,  which  are  called  aberrant,  and  which  may  fanci- 
fully be  called  living  fossils,  will  aid  us  in  forming  a  pic- 
ture of  the  ancient  forms  of  life.  Embryology  will  reveal 
to  us  the  structure,  in  some  degree  obscured,  of  the  pro- 
totypes of  each  great  class. 

When  we  can  feel  assured  that  all  the  individuals  of 
the  same  species,  and  all  the  closely  allied  species  of  most 
genera,  have  within  a  not  very  remote  period  descended 
from  one  parent,  and  have  migrated  from  some  one  birth- 
place; and  when  we  better  know  the  manv  means  of  mi- 


Chap.  XIV.]  CONCLUSION.  423 

gration,  then,  by  the  liglit  wliicli  geology  now  throws, 
and  will  continue  to  throw,  on  former  changes  of  climate 
and  of  the  level  of  the  land,  we  shall  surely  be  enabled  to 
trace  in  an  admirable  manner  the  former  migrations  of 
the  inhabitants  of  the  whole  world.  Even  at  present,  by 
comparing  the  differences  of  the  inhabitants  of  the  sea  on 
the  opposite  sides  of  a  continent,  and  the  nature  of  the 
various  inhabitants  of  that  continent  in  relation  to  their 
apparent  means  of  immigration,  some  light  can  be  thrown 
on  ancient  geography. 

The  noble  science  of  Geology  loses  glory  from  the  ex- 
treme imperfection  of  the  record.  The  crust  of  the  earth 
with  its  embedded  remains  must  not  be  looked  at  as  a 
well-filled  museum,  but  as  a  poor  collection  made  at 
hazard  and  at  rare  intervals.  The  accumulation  of  each 
great  fossiliferous  formation  will  be  recognised  as  having 
depended  on  an  unusual  concurrence  of  circumstances, 
and  the  blank  intervals  between  the  successive  stages  as 
having  been  of  vast  duration.  But  we  shall  be  able  to 
guage  with  some  security  the  duration  of  these  intervals 
by  a  comparison  of  the  preceding  and  succeeding  organic 
forms.  We  must  be  cautious  in  attempting  to  correlate 
as  strictly  contemporaneous  two  formations,  which  include 
few  identical  species,  by  the  general  succession  of  their 
forms  of  life.  As  species  are  produced  and  exterminated 
by  slowly  acting  and  still  existing  causes,  and  not  by 
miraculous  acts  of  creation  and  by  catastrophes  ;  and  as 
the  most  important  of  all  causes  of  organic  change  is  one 
which  is  almost  independent  of  altered  and  perhaps  sud- 
denly altered  physical  conditions,  namely,  the  mutual  re- 
lation of  organism  to  organism, — the  improvement  of  one 
being  entailing  the  improvement  or  the  extermination  of 
others ;  it  follows,  that  the  amount  of  organic  change  in 
the  fossils  of  consecutive  formations  probably  serves  as  a 
fair  measure  of  the  lapse  of  actual  time.  A  number  of 
species,  however,  keeping  in  a  body  might  remain  for  a 
long  period  unchanged,  whilst  within  this  same  period, 
several  of  these  species,  by  migrating  into  new  countries 
and  coming  into  competition  with  foreign  associates, 
might  become  modified ;  so  that  we  must  not  overrate  the 


424:  CDXCLUSION.  [Chap.  XIV, 

accuracy  of  organic  cliarige  as  a  measure  of  time.  During 
earlj  periods  of  the  eartli's  history,  vrhen  the  forms  of 
h'fe  were  probably  fewer  and  simpler,  the  rate  of  change 
was  i^robably  slow^er  ;  and  at  the  first  dawn  of  life,  when 
very  few  forms  of  the  simj^lest  structure  existed,  the  rate 
of  change  may  have  been  slow  in  an  extreme  degree. 
The  w^liole  history  of  the  Avorld,  as  at  present  known,  al- 
though of  a  length  quite  incomprehensible  by  us,  will 
hereafter  be  recognised  as  a  mere  fragment  of  time,  com- 
pared Avith  the  ages  which  have  elapsed  since  the  first 
creature,  the  progenitor  of  innumerable  extinct  and  living 
descendants,  was  created. 

In  the  distant  future  I  see  open  fields  for  far  more 
important  researches.  Fsychology  will  be  based  on  a 
new  foundation,  that  of  the  necessary  acquirement  of  each 
mental  power  and  capacity  by  gradation.  Light  will  be 
thrown  on  the  origin  of  man  and  his  history. 

Authors  of  the  highest  eminence  seem  to  be  fully  sat 
isfied  with  the  view  that  each  sj)ecies  has  been  independ- 
ently created.  To  my  mind  it  accords  better  with  what 
we  know  of  the  laws  impressed  on  matter  by  the  Creator, 
that  the  production  and  extinction  of  the  past  and  present 
inhabitants  of  the  w^orld  should  have  been  due  to  second- 
ary causes,  like  those  determining  the  birth  and  death  of 
the  individual.  When  I  view  all  beings  not  as  sj^ecial 
creations,  but  as  the  lineal  descendants  of  some  few  be- 
ings which  lived  long  before  the  first  bed  of  the  Silm-ian 
system  w^as  de230sited,  they  seem  to  me  to  become  en- 
nobled. Judging  from  the  past,  w^e  may  safely  infer  that 
not  one  living  species  will  transmit  its  unaltered  likeness 
to  a  distant  futurity.  And  of  the  species  now  living  very 
few  w^ill  transmit  progeny  of  any  kind  to  a  far  distant 
futurity  ;  for  the  manner  in  wdiich  all  orgaidc  beings  are 
grouped,  shows  that  the  greater  number  of  species  of  each 
genus,  and  all  the  species  of  many  genera,  have  left  no 
descendants,  but  have  become  utterly  extinct.  We  can 
so  far  take  a  proplietic  glance  into  futurity  as  to  foretel 
tliat  it  wdll  be  the  common  and  widely-spread  species,  be- 
longing to  the  larger  and  dominant  groups,  which  will 
ultimately  prevail  and  procreate  new  and  dominant  spe- 


Chap.  XIV.J  CONCLTJSION.  425 

cies.  As  all  the  living  forms  of  life  are  the  lineal  descend- 
ants of  those  which  lived  long  before  the  Silurian  epoch, 
we  may  feel  certain  that  the  ordinary  succession  by  gen- 
eration has  never  once  been  broken,  and  that  no  cataclysm 
has  desolated  the  whole  world.  Hence  we  may  look  with 
some  confidence  to  a  secure  future  of  equally  inapprecia- 
ble length.  And  as  natural  selection  works  solely  by  and 
for  the  good  of  each  being,  all  corporeal  and  mental  en- 
dowments will  tend  to  progress  towards  perfection. 

It  is  interesting  to  contemplate  an  entangled  bank, 
clothed  with  many  plants  of  many  kinds,  with  birds  sing- 
ing on  the  bushes,  with  various  insects  flitting  about,  and 
with  worms  crawling  through  the  damp  earth,  and  to  re- 
flect that  these  elaborately  constructed  forms,  so  difi*erent 
from  each  other,  and  dependent  on  each  other  in  so  com- 
plex a  manner,  have  all  been  produced  by  laws  acting 
around  us.  These  laws,  taken  in  the  largest  sense,  being 
Growth  with  Reproduction  ;  Inheritance  which  is  almost 
implied  by  reproduction  ;  Yariability  from  the  indirect  and 
direct  action  of  the  external  conditions  of  life,  and  from  use 
and  disuse  ;  a  Ratio  of  Increase  so  high  as  to  lead  to  a  Strug- 
gle for  Life,  and  as  a  consequence  to  ^Natural  Selection, 
entailing  Divergence  of  Character  and  the  Extinction  of 
less-improved  forms.  Thus,  from  the  war  of  nature,  from 
famine  and  death,  the  most  exalted  object  which  we  are 
capable  of  conceiving,  namely,  the  production  of  the  higher 
animals,  directly  follows.  There  is  a  grandeur  in  this 
view  of  life,  wdth  its  several  powers,  having  been  original- 
ly breathed  into  a  few  forms  or  into  one  ;  and  that,  whilst 
this  planet  has  gone  cycling  on  according  to  the  fixed 
law  of  gravity,  from  so  simple  a  beginning  endless  forms 
most  beautiful  and  most  wonderful  have  been,  and  are 
being,  evolved. 


SUPPLEMENT. 


The  following  additions  and  alterations,  prepared  bj  the  author  ex- 
pressly for  this  edition,  were  received  too  late  to  be  incorporated  in 
their  proper  places. 

Page  46,  eight  lines  from  bottom,  after  "  not  generally  propagated," 
insert : 

If  it  could  be  shown  that  monstrosities  were  even  propa- 
gated for  a  succession  of  generations  in  a  state  of  nature, 
moditications  might  be  effected  (with  the  aid  of  natural 
selection)  more  abruptly  than  I  am  inclined  to  believe 
they  are. 

Page  79,  six  lines  from  bottom,  after  word  "  nature,"  insert  paren- 
thesis— reading  the  whole  sentence  thus  : 

Man  can  act  only  on  external  and  visible  characters  :  na- 
ture (if  I  may  be  allowed  for  brevity-sake  to  personify  the 
natural  preservation  of  favoured  individuals  during  the 
struggle  for  existence)  cares  nothing  for  appearances,  ex- 
cept in  so  far  as  they  may  be  useful  to  any  being. 

Page  168,  first  line,  after  "structure  of  the  eye,"  insert: 

(though  in  tlie  fish  Amphioxus,  the  eye  is  in  an  extremely 
simple  condition  without  a  lens) 

Page  108,  sixth  line  from  top,  omit  all  seventeen  lines  beginning 
with  "In  the  Articulata."  and  ending  with  '•  living  crustaceans,  and 
bearing  in  mind,"  and  insert  as  follows : 

[In  the  great  kingdom  of  the  Articulata  we  can  start 


StrPPLEMENT, 


427 


from  an  optic  nerve,  simply  coated  witli  pigment,  whicli 
sometimes  forms  a  sort  of  pupil,  but  is  destitute  of  a  lens 
or  any  other  optical  mechanism.  From  this  rndimentaiy 
eye  which  can  distinguish  light  from  darkness,  but  noth- 
ing else,  tiiere  is  an  advance  towards  perfection  along  two 
lines  of  structure,  which  Miiller  thought  were  fundamen- 
tally different ;  namely,  lirstly,  stemmata,  or  the  so-called 
"simple  eyes,"  whicli  have  a  lens  and  cornea;  and  sec- 
ondly, "  compound  eyes,"  which  seem  to  act  mainly  or 
solely  by  excluding  all  the  rays  from  eacli  point  of  the 
viewed  object,  except  the  pencil  that  comes  in  a  line  per- 
pendicular to  the  convex  retina.  In  the  class  of  com- 
pound eyes,  besides  endless  differences  in  the  form,  pro- 
portion, number  and  position  of  the  transparent  cones 
coated  by  pigment  which  act  by  exclusion,  we  have  addi- 
tions of  a  more  or  less  perfect  concentrating  apparatus ; 
thus  in  the  eyes  of  the  meloe  the  facets  of  the  cornea  are 
"  slightly  convex  both  externally  and  internally ;  that  is, 
lens-shaped."  *  In  many  crustaceans  there  are  two  cornea, 
the  external  smooth  and  the  internal  divided  into  facets, 
within  the  substance  of  which,  as  Milne  Edwards  says, 
"renflemens  lenticulaires  paraissent  s'etre  developpes  ; " 
and  sometimes  these  lenses  can  be  detached  in  a  layer  dis- 
tinct from  the  cornea.  The  transparent  cones,  which  were 
supposed  by  Miiller  to  act  solely  by  excluding  the  diverg- 
ent pencils  of  light,  usually  adhere  to  the  cornea,  but  not 
rarely  they  are  detached  from  it,  and  have  their  free  ends 
convex,  and  in  this  case  they  must  act,  I  presume,  as  con- 
verging lenses.  Altogether,  so  diversified  is  the  structure 
of  the  compound  eyes,  that  Miiller  makes  three  main 
classes,  with  no  less  than  seven  subdivisions  of  structure. 
He  makes  a  fourth  main  class — namely,  "  aggregates  "  of 
stemmata;  and  he  adds  that  "this  is  the  transition-form 
between  the  mosaic-like  compound  eyes,  unprovided  with 
a  concentrating  apparatus  and  organs  of  vision  with  such 
an  apparatus." 

AVith  these  facts,  here  too  briefly  and  imperfectly 
given,  which  show  how  much  graduated  diversity'-  there  is 
in  the  eye  of  our  existing  articulata,  and  bearing  in  mind, 
&c.,  &c. 

19* 


^2S  SUPPLEMENT. 

Page  1G9,  tenth  line  from  top,  after  "  transparent  tissue,"  add  : 

•with  spaces  filled  with  fluid  and  with  a  nerve  sensitive, 
&c.,  &c. 

Page  169,  sixteenth  line  from  top,  after  "there  is  a  power,"  insert 
in  brackets : 

[natural  selection] 

Page  170,  twenty-first  line  from  top,  after  "  insensible  steps,"  in- 
sert: 

Certain  plants,  as  some  Legmninosse,  Yiolacese,  (fee,  bear 
two  kinds  of  flowers ;  one  having  the  normal  structure  of 
the  order,  the  other  kind  being  degraded,  though  some- 
times more  fertile  than  the  perfect  flowers ;  if  the  plant 
ceased  to  bear  its  perfect  flowers,  and  this  did  occur  dur- 
ing several  years  with  an  imported  specimen  of  Aspicarpa 
in  France,  a  great  and  sudden  transition  would  in  fact  be 
efl'ected  in  the  nature  of  the  plant.  .  • 

Pnges  293  and  294.  Omit  thirty  lines,  beginning,  "  On  the  state 
of  Development  ^^^  and  ending  >with  "class,  may  have  beaten  the  highest 
molluscs,"  and  insert  as  follows: 

On  the  state  of  Development  of  ancient  compared  with 
living  Forms. — We  have  seen  in  the  Fourth  Chapter  that 
the  degree  of  difl'erentiation  and  specialisation  of  the  parts 
of  all  organic  beings,  when  come  to  maturity,  is  the  best 
standard  as  3"et  suggested  of  their  degree  of  jDcrfection  or 
highness.  We  have  also  seen  that,  as  the  specialisation 
of  parts  or  organs  is  an  advantage  to  each  being,  so  natu- 
ral selection  will  constantly  tend  thus  to  render  the  or- 
ganisation of  each  more  specialised  and  perfect,  and  in 
this  sense  higher ;  not  but  that  it  may,  and  will,  leave 
many  creatures  fltted  for  simple  conditions  of  life  with 
simple  and  unimproved  structures.  In  another  and  more 
general  manner  we  can  see  that,  on  the  theory  of  natural 
selection,  the  more  recent  forms  will  tend  to  be  higher 
than  their  progenitors  ;  for  each  new  species  is  formed  by 
having  had  some  advantage  in  the  struggle  for  life  over 
other  and  preceding  forms.     If,  under  a  nearly  similar 


SUPPLEMENT. 


429 


climate,  the  eocene  inhabitants  of  one  quarter  of  the  world 
were  put  into  competition  with  the  existing  inhabitants  of 
the  same  or  some  other  quarter,  the  eocene  fauna  or  flora 
would  certainly  be  beaten  and  exterminated ;  as  would  a 
secondary  fauna  by  an  eocene,  and  a  palaeozoic  fauna  by 
a  secondary  fauna.  So  that  by  this  fundamental  test  of 
victory  in  the  battle  for  life,  as  well  as  by  the  standard  of 
the  specialisation  of  organs,  modern  forms  ought,  on  the 
theory  of  natural  selection,  to  stand  higher  than  an- 
cient forms.  Is  this  the  case?  A  large  majority  of  pa- 
laeontologists would  certainly  answer  in  the-  affirmative  ; 
but  in  my  imperfect  judgment,  I  can,  after  having  read 
the  discussions  on  this  subject  by  Lyell  and  by  Hooker  in 
regard  to  plants,  concur  only  to  a  cretain  limited  extent. 
Nevertheless,  it  may  be  anticipated  that  the  evidence  Avill 
be  rendered  more  decisive  by  future  geological  research. 

The  problem  is  in  many  ways  excessively  intricate. 
The  geological  record,  at  all  times  imperfect,  does  not  ex- 
tend far  enough  back,  as  I  believe,  to  show  with  unmis- 
takable clearness  that  within  the  known  history  of  the 
world  organisation  has  largely  advanced.  Even  at  the 
present  day,  looking  to  members  of  the  same  class,  natu- 
ralists are  not  unanimous  which  forms  are  highest ;  thus 
some  look  at  the  Selaceans  or  sharks  from  their  approach 
in  some  important  point  of  structure  to  reptiles  as  the 
highest  fish ;  others  look  at  the  teleosteans  as  the  highest. 
The  ganoids  stand  intermediate  between  the  selaceans  and 
teleosteans  ;  the  latter,  at  the  present  day,  are  largely 
preponderant  in  number,  but  formerly  selaceans  and  ga- 
noids alone  existed;  and  in  this  case,  according  to  the 
standard  of  highness  chosen,  so -will  it  be  said  that  fishes 
have  advanced  or  have  retrograded  in  organisation.  To 
attempt  to  compare  in  the  scale  of  highness  members  of 
distinct  types  seems  hopeless ;  who  will  decide  whether  a 
cuttle-fish  be  higher  than  a  bee  ?  that  insect  which  the 
great  Yon  Baer  believed  to  be  "  in  fact  more  highly  or- 
ganised than  a  fish,  although  upon  another  type."  lii  the 
complex  struggle  for  life  it  is  quite  credible  that  crusta- 
ceans, for  instance,  not  very  high  in  their  own  class,  might 
beat  the  cephalopods  or  highest  molluscs  ;  and  such  eras- 


430 


SUPPLEMENT. 


taceans,  thongli  not  liighly  developed,  would  stand  very 
high  in  the  scale  of  invertebrate  animals,  if  judged  by  the 
most  decisive  of  all  trials, — the  law  of  battle. 

Besides  this  inherent  difficnlty  in  deciding  which  forms 
are  the  most  advanced  in  oi'ganization,  we  ought  not 
solely  to  compare  the  highest  members  of  a  class  at  any 
two  distant  periods, — though  undoubtedly  tliis  is  one  and 
perhaps  the  most  important  element  in  striking  a  balance 
— but  we  ought  to  compare  all  the  members,  high  and 
low,  at  the  two  periods.  At  an  ancient  epoch  the  highest 
and  lowest  molluscs — namely,  cephalopods  and  brachio- 
pods — swarmed  in  numbers  ;  at  the  present  time,  both 
these  orders  have  been  greatly  reduced,  whereas  otlier  or- 
ders, intermediate  in  grade  of  organisation,  have  largely 
increased  ;  consequently  some  naturalists  have  niaintained 
that  molluscs  were  formerly  more  highly  developed  than 
at  present ;  but  a  stronger  case  can  be  made  out  on  the 
other  side  by  considering  the  vast  reduction  at  the  present 
day  of  the  lowest  molluscs ;  more  especially  as  the  exist- 
ing cephalopods,  though  so  few  in  number,  are  more 
highly  organised  than  their  ancient  representatives.  We 
ought,  also,  to  consider  the  relative  proportional  numbers 
of  the  high  and  low  classes  in  the  population  of  the  world 
at  the  two  periods;  if,  for  instance,  at  the  present  day 
there  were  fifty  thousand  kinds  of  vertebrate  animals,  and 
if  we  had  reason  to  believe  that  at  some  former  period 
there  were  only  ten  thousand  kinds,  we  ought  to  look  at 
this  increase  in  number  of  the  highest  class,  which  implies 
a  great  displacement  of  lower  forms,  as  a  decided  advance 
in  tlie  organisation  of  the  world,  whether  or  not  it  were 
the  higher  vertebrata  wh?ch  had  thus  largely  increased. 
We  can  thus  see  how  hopelessly  difficult  it  will  appa- 
rently forever  be  to  compare  wi^li  perfect  fairness  under 
such  extremely  complex  relations  the  standard  of  organi- 
sation of  the  imperfectly  known  faunas  of  successive  pe- 
riods of  the  earth's  history. 

We  shall  appreciate  (under  one  important  point  of 
view)  this  difficulty  the  more  clearly,  by  looking  to  the 
case  of  certain  existing  faunas  and  floras.  From  the  ex- 
traordinary manner  in  which  European  productions  have 
recently  spread  over  l^ew  Zealand,  &c.,  &c. 


SUPPLEMENT.  ^^1 

Page  417, 25th  line,  after  "facts  above  specified,"  insert: 

It  is  no  valid  objection  that  science  as  jet  throws  no 
light  on  the  origin  of  Lite.  Who  can  explain  what  is  the 
essence  of  the  Attraction  of  gravity  ?  Althongh  Leibnitz 
accused  Newton  of  introducing  "occult  qualities  and 
miracles  into  philosophy;"  yet  this  unknown  element  of 
attraction  is  now  universally  looked  at  as  a  vera  causa 
perfectly  well  established.] 

[I  see  no  good  reason  why  the  views  given  in  this 
volume  should  shock  the  religious  feelings  of  any  one.  It 
is  satisfactory,  as  showing  how  transient  such  impressions 
are,  to  remember  that  the  greatest  discovery  ever  made 
by  man^  namely,  the  law  of  gravity,  was  attacked  by 
Leibnitz,  "as  subversive  of  natural  and  inferentially  of 
revealed  religion,"  A  celebrated  author  and  divine,  &c., 
&c. 

Page  420,    fifteen    lines  from  top,   after  "deceitful  guide,"  omit 
whole  remainder  of  paragraph,  and  insert,  instead,  as  follows : 

Nevertheless,  all  living  things  have  much  in  common ; 
in  their  chemical  composition,  their  cellular  structtn*e, 
their  laws  of  growth,  and  their  liability  to  injurious  inllu- 
ences.  We" see  this  in  so  trifling  a  circumstance  as  that 
the  same  poison  often  similarly  affects  plants  and  animals, 
or  that  the  poison  secreted  by  the  gall-fly  produces  mon- 
strous growths  on  the  wild  rose  or  oak  tree.  In  all  or- 
ganic beings  the  union  of  a  male  and  female  elemental 
cell  seems  occasionally  to  be  necessary  for  the  production 
of  a  new  being.  In  all,  as  far  as  is  at  present  known,  the 
germinal  vesicle  is  the  same.  So  that  every  individual 
organic  being  starts  from  a  common  origin.  If  we  look 
even  to  the  two  main  divisions — namely,  to  the  animal 
and  vegetable  kingdoms — certain  low  forms  are  so  far 
intermediate  in  character  that  naturalists  have  disputed 
to  which  kingdom  they  should  be  referred  ;  and  on  the 
principle  of  natural  selection  with  divergence  of  charac- 
ter, it  does  not  seem  utterly  incredible  that  from  some 
such  intermediate  production  both  animals  and  plants 
might  possibly  have  been  developed.  Therefore  I  should 
inter  that  probably  all  the  organic  beings  which  have 


4:32 


SUPPLEMENT. 


ever  lived  on  tliis  earth  have  descended  from  some  one 
primordial  form,  into  which  life  was  first  breathed  by  the 
Creator.  But  this  inference  is  chiefly  grounded  on  anal- 
ogy, and  it  is  immaterial  whether  or  not  it  be  accepted. 
The  case  is  different  with  the  members  of  each  great  class, 
as  the  Yertebrata  or  Articulata ;  for  here,  as  has  just  been 
remarked,  we  have  in  the  laws  of  homology  and  embry- 
ology, &c.,  some  distinct  evidence  that  all  have  descended 
from  a  single  primordial  parent.] 


INDEX. 


Aberbant  groups,  373. 
Abj-ssioia,  plants  of,  326. 
Acclimatisation,  127. 
Afliaities  of  extinct  species,  287. 

of  organic  beings,  358. 
Agassiz  on  Amblyopsis,  127. 

on  groups  of  species  suddenly  ap- 
pearing, 264,  267. 

on  embryological  succession,  295. 

on  the  glacial  period,  319. 

ou  embryological  characters,  364. 

on  the  embryos  of  vertebrata,  382. 

on  parallelism  of  embryological  de- 
velopment and  geological  succes- 
sion, 390. 
Algas  of  New  Zealand,  327. 
Alligators,  males,  fighting,  84. 
Amblyopsis,  blind  fish,  127. 
America,    North,    productions    allied  to 
those  of  Europe,  323. 

boulders  and  glaciers  of,  325. 

South,   no    modern  formations    on 
west  coast,  254. 
Ammonites,  sudden  extinction  of,  281. 
Anagallis,  sterility  of,  219. 
Analogy  of  variations,  143. 
Ancylus,  336, 

Animals,  not    domesticated    from  being 
variable,  23. 

domestic,  descended    from    several 
stocks,  24. 

acclimatisation  of,  129. 

of  Australia,  108. 

■with  thicker  fur  in  cold  climates,  122. 

blind,  in  caves,  125. 

extinct,  of  Australia,  296. 
Anomma,  213. 

Antarctic  islands,  ancient  flora  of,  347. 
Antirrhinum,  145. 
Ants  attending  aphides,  188. 

slave-making  instinct,  195. 
Ants,  neuter,  structure  of,  209. 
Aphides  attended  by  ants,  188. 
Aphis,  development  of,  384. 
Apteryx,  163. 
Arab  horses,  38. 
Aralo-Caspian  Sea,  296. 
Archiac,  M.  de,  on  succession  of  species, 
284. 


Artichoke,  Jerusalem,  129. 

Ascension,  plants  of,  339. 

Asclepias,  pollen  of,  173. 

Asparagus,  313. 

Aspicarpa,  363. 

Asses,  striped,  147. 

Ateuchus,  123. 

Audubon  on  habits  of  frigate-bird,  169 

on  variation  in  birds'-nests,  189. 

on  heron  eating  seeds,  338. 
Australia,  animals  of,  108, 

dogs  of,  192. 

extinct  animals  of,  296. 

European  plants  in,  327. 
Azara  on  flies  destroying  cattle,  70. 
Azores,  flora  of,  316. 

Babington,  Mr.,  on  British  plants,  49. 

Balancement  of  growth,  133. 

Bamboo  with  hooks,  176. 

Barberry,  flowers  of,  92. 

Barrande,  M.,  on  Silurian  colonies,  274. 

on  the  succession  of  species,  284. 

on  parallelism  of  palaeozoic  forma- 
tions, 287. 

on  affinities  of  ancient  species,  288. 
Barriers,  importance  of,  303. 
Batrachians  on  islands,  342. 
Bats,  how  structure  acquired,  163. 

distribution  of,  343. 
Bear,  catching  water-insects,  165. 
Bee,  sting  of,  ISO. 

queen,  killing  rivals,  180. 
Bees  fertilising  flowers,  71. 

hive,  not    sucking  the   red  clover, 
89. 

hive,  cell-making  instinct,  200. 

humble,  cells  of,  200. 

parasitic,  195. 
Beetles,  wingless,  in  Madeira,  124. 

with  deficient  tarsi,  123. 
Bentham,  Mr.,  on  British  plants,  49. 

on  classification,  365. 
Berkeley,  Mr.,  on  seeds  in  salt-water,  31Z 
Bermuda,  birds  of,  341. 
Birds  acquiring  fear,  189. 

annually  cross  the  Atlantic,  317. 

colour  of,  on  continents,  121. 

fossil,  in  caves  of  Brazil,  296. 


434 


INDEX. 


Birds  of   Madeira,   Bermuda,  and    Gala- 
pagos, 340. 

song  of  males,  84. 

transporting  seeds,  315. 

waders,  337. 

wingless,  123,  163. 

with  traces  of  embryonic  teeth,  391. 
Bizcacha,  305. 

affinities  of,  373. 
Bladder  for  s-wimming  in  fish,  170. 
Blindness  of  cave  animals,  126. 
Blvtb,  Mr.,  on  distinctness  of  Indian  cat- 
tle, 23. 

on  striped  Hemionus,  147. 

on  crossed  geese,  224. 
Boar,  shoulder-pad  of,  84. 
Borrow,  Mr.,  on  the  Spanish  pointer,  38. 
Bory  St.  Vincent  on  Batrachians,  342. 
Bosquet,  M.,  on  fossil  Chthamalus,  266. 
Boulders,  erratic,  on  the  Azores,  316. 
Branch^,  170. 
Brent,  Mr.,  on  house-tumhlers,  191. 

on  hawks  killing  pigeons,  315. 
Brewer,  Dr.,  on  American  cuckoo,  193. 
Britain,  mammals  of,  344. 
Bronn  on  duration  of  specific  forms,  257. 
Brown,  Robert,  on  classification,  361. 
Buckman  on  variation  in  plants,  17. 
Buzareingues  on  sterility  of  varieties,  238. 

Cabbage,  varieties  of,  crossed,  93. 

Calceolaria,  222. 

Canary-birds,  sterility  of  hybrids,  223. 

Cape  de  Verde  islands,  347. 

Cape  of  Good  Hope,  plants  of,  102,  326. 

Carrier-pigeons  killed  by  hawks,  315. 

Cassini  on  flowers  of  compositae.  131. 

Catasetum,  369. 

Cats,  with  blue  eyes,  deaf,  18. 

variation  in  habits  of,  86. 

curling  tail  when  going  to  spring,  179. 
Cattle  destroying  fir-trees,  69. 

destroyed  by  flies  in  La  Plata,  70. 

breeds  of,  locally  extinct,  103. 

fertility   of   Indian  and    European 
breeds,  225. 
Cave,  inhabitants  of,  blind,  125. 
Centres  of  creation,  307. 
Cephalopodae,  development  of,  384. 
Cervulus,  224. 

Cetacea,  teeth  and  hair,  131. 
Ceylon,  plants  of,  326. 
Chalk  formation,  282. 
Characters,  divergence  of,  103. 

sexual,  varialjle,  141. 

adaptive  or  analogical,  371. 
Charlock,  74. 
Checks  to  increase,  66. 

mutual,  69. 
Chickens,  instinctive  tameness  of,  192. 
Chthamalinae,  253. 

Chthamalus,  cretacean  species  of,  266. 
Circumstances  favourable  to  selection  of 
domestic  products,  42. 

to  natural  selection,  95. 
Cirripedes  capable  of  crossing,  95. 

carapace  aborted,  134. 

their  ovigerous  freua,  172. 

fossil,  266. 

larvje  of,  383. 


Classification,  360. 

Clift,  Mr.,  on  the  succession  of  types,  295. 
Climate,  effects  of,  in  checking  increase  ol 
beings,  67. 

adaptation  of,  to  organisms,  127. 
Cobites,  intestine  of,  170. 
Cockroach,  74. 

Collections,  palseontological,  poor,  252. 
Colour,  influenced  by  climate,  121. 

in  relation  to  attacks  by  flies,  177. 
Columbalivia,  parent  of  domestic  pigeons, 

27. 
Colymbetes,  336. 
Compensation  of  growth,  134. 
Compositae,  outer  and  inner  florets  of,  131. 

male  flowers  of,  392. 
Conclusion,  general,  416. 
Conditions,  slight  changes  in,  favourable 

to  fertility,  235. 
Coot,  166. 
Coral-islands,  seeds  drifted  to,  315. 

reefs,  indicating  movements  of  earth, 
270. 
Corn-crake,  166. 

Correlation  of  growth  in  domestic  produc- 
tions, 18. 

of  growth,  130, 177. 
Cowslip,  51. 

Creation,  single  centres  of,  307. 
Crinum,  221. 
Crosses,  reciprocal,  228. 
Crossing  of  domestic  animals,  importance 
in  altering  breeds,  25. 

advantaees  of,  91. 

unfavourable  to  selection,  96. 
Crustacea  of  New  Zealand,  327. 
Crustacean,  blind,  125. 
Cryptocerus,  211. 
Ctenomys,  blind,  125. 
Cuckoo,  instinct  of,  193. 
Currants,  grafts  of,  231. 
Currents  of  sea,  rate  of,  313. 
Cuvier  on  conditions  of  existence,  184. 

on  fossil  monkeys,  265. 

Fred.,  on  instinct,  186. 

Dana,  Prof.,  on  blind  cave-animals,  126. 

on  relations  of  crustaceans  of  Japan, 

324. 
on  crustaceans  of  New  Zealand,  327. 
De  Candolle  on  struggle  for  existence,  61. 
on  umbelliferce,  132. 
on  general  afiiuities,  374. 
Alph,   on    low  plants,   widely   dis- 
persed, 353. 
on  widely-ranging  plants  being  va- 
riable, 54. 
on  naturalisation,  107. 
on  winged  seeds,  133. 
on  Alpme  species  suddenly  becom- 
ing rare,  157. 
on  distribntion  of  plants  witli  large 

seeds,  314. 
on  vegetation  of  Australia,  330. 
on  fresh-water  plants,  336. 
on  insular  plants,  339. 
Degradation  of  coast  rocks,  248. 
Denudation,  rate  of,  250. 
of  oldest  rocks,  269. 
Development  of  ancient  forms,  293. 


INDEX. 


435 


Devonian  system,  292.  I 

Dianthus,  fertility  of  crosses,  226.  j 

Dirt  on  feet  of  birds,  316, 
Dispersal,  means  of,  311.  I 

during  glacial  period,  318.  j 

Distribution,  geographical,  302. 

means  of,  311. 
Disuse,  etJtcts  of,  under  nature,  122. 
Divergence  of  character,  103.  1 

Division,  physiological,  of  labour,  107.  ] 

Dogs,  hairless,  witli  impeifect  teeth,  18.       I 

descended  from  several  wild  stocks, 
2o. 

domestic  instincts  of,  190. 

inherited  civilization  of,  192. 

fertility  of  breeds  together,  224. 

of  crosses,  236. 

proportions  of,  when  young,  386. 
Domestication,  variation  urder,  14. 
Dowi.ing,  Mr.,  on  fruit-trees  in  America,81. 
Downs, ''North  and  South,  250. 
Dragon-flies,  intestines  of,  170. 
Drift-timber,  314. 
Driver-ai.t.  213. 

Drones  killed  by  other  bees,  180. 
Duck,  domestic,  wings  of,  reduced,  17. 

louger-headcd,  163. 
Duckweed,  336. 
Dngong,  alliiiities  of,  360. 
Dur:g-beetlcs  with  deficient  tarsi,  124. 
Dyticus,  336. 

Earl,  Mr.  "W.,  on  the  Malay  Archipelago, 

344. 
Ears,  drooping,  in  domestic  auimalB,  17. 

Rudimer.tarj-,  394. 
Earth,  seeds  in  roots  of  trees,  314. 
Eciton,  211. 

Economy  of  organisation,  134. 
Edentata,  teeth  ai.dhair,  131. 

fossil  species  of,  296. 
Edwards,  Milne,  on  physiological  divisions 
of  labonr,  107. 

on  gradations  of  structure,  173. 

on  embryological  characters,  364. 
Eggs,  young  birds  escaping  from,  83. 
Electric  organs,  172. 
Elephant,  rate  of  increase,  63. 

of  glacial  period,  128. 
Embryology,  381. 
Existence,  struggle  for,  60. 

coi  ditions  of,  184. 
Extinction,  277. 

as  bearing  on  natural  selection,  102. 

of  domestic  varieties,  103. 
Eye,  structure  of,  167. 

correction  for  aberration,  180. 
Eyes  reduced  in  moles,  125. 

Fabre,  M.,  on  parasitic  sphex,  195. 
Falconer,  Dr.,  on  raturahsation  of  plants 
in  India,  64. 

on  fossil  crocodile,  274. 

on  ele]ihants  and  mastodons,  292. 
Falkland  Island,  wolf  of,  343. 
Faults,  250. 
Faunas,  marine,  304. 
Fear,  instinctive,  in  birds,  189. 
Feet  of  birds,  young  molluscs  adhering  to, 
836. 


Fertility  of  hybrids,  221. 

from  slight  changes  in   conditions, 
235. 

of  crossed  varieties,  230. 
Fir-trees  destroyed  by  cattle,  69. 

pollen  of,  181. 
Fish,  flying,  163. 

teleo^tcan,  pudden  appearance  of,  267. 

eating  seeds,  337. 

fresh-w.nter,  distribution  of,  335. 
Fishes,    ganoid,  now    confiued    to  fresb 
water,  100. 

electric  organs  of,  172. 

ganoid,  living  in  fresh  water,  281. 

of  southern  hemisphere,  327. 
Flight,  powers  of,  how  acquired,  163. 
Flowers,  structure  of,  in  relation  to  cross- 
ing, 91. 

of  compositas  and  umbelliferae,  131. 
Forbes,  E.,  on  colours  of  shells,  121. 

on  abrupt  range  of  shells  in  depth. 
157. 

on  poorness  of  paloeontological  col- 
lections, 252. 

on  continuous  succession  of  genera, 
276. 

on  continental  extensions,  311. 

on  distribution  during  glacial  period, 
319. 

on  parallelism  in  time  and  space,356. 
Forests,  changes  in,  in  America,  72. 
Formation,  Devonian,  292. 
Formations,  thickness  of,  in  Britain,  249. 

intermittent,  254. 
Formica  rufescens,  195. 

sanguinea,  195. 

flava,  neuter  of,  212. 
Frena,  ovigerous,  of  cirripedes,  172. 
Fresh-water    productions,    dispersal     of, 

334. 
Fries  on   species   in   large    genera   being 

closely  allied  to  other  species,  57. 
Frigate-bird,  166. 
Frogs  on  islands,  342. 
Fruit-trees,  gradual  improvement  of,  40. 

in  United  States,  81. 

varieties  of,  acclimatised  in  United 
States,  129. 
Fuci,  crossed,  228. 
Fur,  thicker  in  cold  climates,  132. 
Furze,  382. 

Galapagos  Archipelago,  birds  of,  340. 

productions  of, "347,  348. 
Galeopithecus,  162. 

Game,  increase  of,  checked  by  vermin,  67. 
Gartner  on  sterility  of  hybrids,  219,  225. 

on  reciprocal  crosses,  228. 

on  crossed  maize  and  verbascum, 
238. 

on  comparison  of  hybrids  and  mon 
grels,  240. 
Geese,  fertility  when  crossed,  224. 

upland,  166. 
Genealogy  important  in  classitlcation,  370. 
Geoftroy  St.  Hilaire  on  balancement,  1S3. 

on  homologous  organs,  378. 

Isidore,  on  variability  of  repeated 
parts,  135. 

on  correlation  in  monstrosities,  18. 


436 


INDEX. 


Geoffroy  on  correlation,  131. 

on  variable  parts  being  often  mon- 
strous, 140. 
Geographical  distribution,  302. 
Geography,  ancient,  422. 
Geology,  future  progress  of,  421. 

imperfection  of  the  record,  245. 
Girafle,  tail  of,  174. 
Glacial  period,  318. 
Gmelin  on  distribution,  318. 
Gnathodon,  fossil,  321. 
Godwin-Austen,  Mr.,  on  the  Malay  Archi- 
pelago, 262. 
Goethe  on  conapensation  of  growth,  133. 
Gooseberry,  grafts  of,  231. 
Gould,  Dr.  A.,  on  land-shells,  345. 

Mr.,  on  colours  of  birds,  121. 

on  birds  of  the  Galapagos,  347. 

on   distribution  of  genera  of  birds, 
352. 
Gourds,  crossed,  238. 
Grafts,  capacity  of,  231. 
Grasses,  varieties  of,  105. 
Gray,  Dr.  Asa,  on  trees  of  United  States, 
94. 

on  naturalised  plants  in  the  United 
States,  107. 

on  rarity  of  intermediate  varieties, 
158. 

on  Alpine  plants,  318. 

Dr.  J.  E.,  oa  striped  n'ule,  149. 
Grebe,  165. 

Groups,  aberrant,  373. 
Grouse,  colours  of,  81. 

red,  a  doubtful  species,  50. 
Growth,  compensation  of,  134. 

correlation  of,  in  domestic  products, 
18. 

correlation  of,  130 

Habit,  effect  of,  under  domestication,  17. 
effect  of,  under  nature,  122. 
diversified,  of  same  species,  164. 

Hair  and  teeth,  correlated,  131. 

Harcourt,  Mr.  E.  V.,  oa  the  birds  of  Ma- 
deira, 340. 

Hartung,  M.,  on  boulders  in  the  Azores, 
317. 

Hazel-nuts,  313. 

Hearne  on  habits  of  bears,  165. 

Heath,  changes  in  vegetation,  70. 

Heer,  O.,  on  plants  of  Madeira,  100. 

Helix  pomatia,  346. 

Helosciadium,  313. 

Hemionus,  striped,  147. 

Herbert,  W., on  struggle  for  existence,  61. 
on  sterility  of  hybrids,  220. 

Hermaphrodites  crossing,  91. 

Heron  eating  seed,  338. 

Heron,  Sir  R.,  on  peacocks,  84. 

Heusinger  on  white  animals  not  poi-soned 
by  certain  plants,  18. 

Hewitt,  Mr.,  on  sterility  of  first  crosses, 
233. 

Himalaya,  glaciers  of,  324. 
plants  of,  326. 

Hippeastrum,  221. 

Hollj'-trees,  sexes  of,  88. 

Hollyhock,  varieties  of,  crossed,  239. 

Hooker,  Dr.,  on  trees  of  New  Zealand,  94. 


Hooker,  Dr. ,  on  acclimatisation  of  Hima- 
layan trees,  127. 
on  flowers  of  umbelliferae,  132. 
on  glaciers  of  Himalaya,  324. 
on  algas  of  New  Zealand,  327. 
on  vegetation  at   the   base  of  the 

Himalaya,  329. 
on  plants  of  Tierra  del  Euego,  326, 

329. 
on  Australian  plants,  327,  347. 
on  relations  of  flora  of  South  Amer- 
ica, 330. 
on  flora  of  the  Antarctic  lands,  341, 

347. 
on  the  plants  of  the  Galapagos,  341, 
347. 
Hooks  on  bamboos,  176. 

to  seeds  on  islands,  342. 
Horner,  Mr.,  on  the  antiquity  of  Egyp- 
tians, 23. 
Horns,  rudimentary,  394. 
Horse,  fossil,  in  La  Plata,  278. 
Horses  destroyed  by  flies  in  La  I  lata,  70. 
striped,  147. 

proportions  of,  when  young,  386. 
Horticulturists,  selection  applied  by,  35. 
Huber  on  cells  of  bees,  205. 

P.,  on  reason  blended  with  instinct, 

186. 
on  habitual  nature  of  instincts,  186. 
on  slave-making  ants,  195. 
on  Melipona  domestica,  200. 
Humble-bees,  cells  of,  200. 
Hunter,  J.,  on  secondary  sexual  charac- 
ters, 136. 
Huttou,  Captain,  on  crossed  geese,  224. 
Huxlej',  Prof.,  on  structure  of  hermaph- 
rodites, 94. 
on  erabryological  succession,  295, 
on  homologous  organs,  381. 
on  the  development  of  aphis,  384. 
Hybrids  and  mongrels  compared,  239. 
Hybridism,  217. 
Hydra,  structure  of,  170. 

Ibla,  134. 

Icebergs  transporting  seeds,  316. 
Increase,  rate  of,  63. 

Individuals,  numbers  favourable  to  selec- 
tion, 96. 

manj',  whether  simultaneously  cre- 
ated, 310. 
Inheritance,  laws  of,  19. 

at  corresponding  ages,  20,  82. 
Insects,  colour  of,  fitted  for  habitations. 
81. 

sea-side,  colours  of,  121. 

blind,  in  cavea,  126. 

luminous,  173. 

neuter,  209. 
Instinct,  185. 
Instincts,  domestic,  190. 
Intercrossing,  advantages  of,  90. 
Islands,  oceanic,  338. 
Isolation  favourable  to  selection,  97. 

Japan,  productions  of,  324. 
Java,  plants  of,  326. 

Jones,  Mr.  J.  M.,  on  the  birds  of  Bermu- 
da, 340. 


INDEX. 


437 


Jussieu  on  classification,  363. 

Kentucky,  caves  of,  125. 
Kerguelen-land,  flora  of,  331,  347. 
Kidney-bean,  acclimatisation  of,  129. 
Kidneys  of  birds,  131. 
Kirby  on  tarsi  deficient  in  beetles,  123. 
Knight,  Andrew,  on  causeof  variation,  14. 
Kolreuier  on  the  barberry,  92. 

oa  sterility  of  hybrids,  218. 

on  reciprocal  crosses,  228. 

on  crossed  varieties  of  nicotiana,  239. 

on  crossing  male  and  hermaplirodite 
flowers,  392. 

Lamarck  on  adaptive  characters,  371. 
Land-shells,  distribution  of,  346. 

of  Madeira,  naturalised,  350. 
Languages,  classification  of,  367. 
Lapse,  great,  of  time,  247. 
Larvae,  382. 

Laurel,  nectar  secreted  by  the  leaves,  88. 
Laws  of  variation,  120. 
Leech,  varieties  of,  73. 
Leguminosas,  nectar  secreted  by  glands,  88. 
Lepidosiren,  100,  288. 
Life,  struggle  for,  60. 
Lingula,  Silurian,  268. 
Linnaeus,  aphorism  of,  360. 
Lion,  mane  of,  84. 

young  of,  striped,  382 
Lobelia  fulgens,  71,  92. 
Lobelia,  sterility  of  crosses,  221, 
Loess  of  the  Rhine,  335. 
Lowness  of  structure  connected  with  va- 
riability, 135. 
Lowness,  related  to  wide  distribution,  353. 
Lubbock,  Mr.,  on  the  nerves  of  coccus,  47. 
Lucas,  Dr.  P.,  on  inheritunce,  19. 

on  resemblance  of  child  to  parent, 
242. 
Lund  and  Clausen  on  fossils  of  Brazil,  296. 
Lyell,  Sir  C,  on  the  struggle  for  existence, 
61. 
on  modern  changes  of  the  earth,  90. 
on  measure  of  denudation,  249. 
on  a  carboniferous  land-shell,  253. 
on  fossil  whales,  265. 
on  strata  beneath  Silurian  system, 

268. 
on  the  imperfection  of  the  geological 

record,  271. 
on  the  appearance  of  species,  273. 
on  Barrande's  colonies,  274. 
on  tertiary  formations  of  Europe  and 

North  America,  282. 
on  parallelism  of  tertiary  formations, 
287.  ' 

on  transport  of  seeds  by  iceberes. 
317.  ' 

on  great  alternations  of  climate,  332. 
on  the  distribution  of  fresh-water 

shells,  336. 
on  land-shells  of  Madeira,  350. 
Lyoll  and  Dawson  on  fossUised  trees  in 
Nova  Scotia,  259. 

Macleay  on  analogical  characters,  371. 
Madeira,  plants  of,  100. 

beetles  of,  wingless,  124. 


Madeira,  fossil  land-shells  of,  296. 

birds  of,  340. 
Magpie  tame  in  Norway,  189. 
Maize,  crossed,  238. 

Malay  Archipelago  compared  with   Eu- 
rope, 262. 
mammals  of,  344. 
Malpighiacesie,  363. 
Mamma?,  rudimentary,  392. 
Mammals,  fossil,  in  secondary  formation, 
265. 
insular,  343. 
Man,  origin  of  races  of,  178. 
Manatee,  rudimentary  nails  of,  394. 
Marsupials  of  Australia,  107. 

fossil  species  of,  296. 
Martens,  M.,  experiment  on  seeds,  315. 
Martin,  Mr.  W.  C,  on  striped  mules,  148. 
Matteuchi  on  the  electric  organs  of  ravs. 
172.  ^  ' 

Matthiola,  reciprocal  crosses  of,  228. 
Means  of  dispersal,  311. 
Melipona  domestica,  200. 
Metamorphism  of  oldest  rocks,  269. 
Mice  destroying  bees,  72. 

acclimatisation  of,  128. 
Migration,  bears  on  first  appearance  of 

fossils,  259. 
Miller,  Prof,  on  the  cells  of  bees,  201. 
Mirabilis,  crosses  of,  228. 
Missel-thrush,  74. 
Misseltoe,  complex  relations  of,  11. 
Mississippi,  rate  of  deposition  at  mouth, 

249. 
Mocking-thrush  of  the  Galapagos,  350. 
Modification  of  species,  how  far  applica- 
ble, 418.  ^^ 
Moles,  blind,  125. 
Mongrels,  fertility  and  sterility  of,  236. 

and  hybrids  compared,  239. 
Monkeys,  fossil,  265. 
Monocanthus,  369. 

Mons,  Van,  oa  the  origin  of  fruit-trees,  32. 
Moquin-Tandon  on  sea-side  plants,  121. 
Morphology,  377. 
Mozart,  musical  powers  of,  186. 
Mud,  seeds  in,  337. 
Mules,  striped,  148. 
Muller,    Dr.   F.,    on    Alpine    Australian 

plants,  327. 
Murchison,  Sir  R.,  on  the  formations  of 
Russia,  253. 
on  azoic  formations,  268. 
on  extinction,  277. 
Mustela  vison,  161. 
Myanthus,  369. 
Myrmecocystus,  211. 
Myrmica,  eyes  of,  213. 

Nails,  rudimentary,  393. 

Natural  history,  future  progress  of,  419. 

selection,  77. 

system,  360. 
Nattzralisation  of  forms  distinct  from  the 
indigenous  species,  107. 

in  New  Zealand,  180. 
Nautilus,  Silurian,  268. 
Nectar  of  plants,  88. 
Nectaries,  how  formed,  88. 
Nelumbium  luteum,  337. 


438 


II7DEX. 


N'ests,  variation  in,  189. 
Neuter  insects,  209. 
Newman,  Mr.,  on  tiumble-beea,  72. 
New  Zealand,  productions  of,  not  perfect, 
ISO. 

naturalised  products  of,  294. 

fossil  birds  of,  296. 

glacial  action  in,  325. 

crustaceans  of,  '628. 

alg£e  of,  328. 

number  of  plants  of,  339. 

flora  of,  347. 
Nicotiaua,  crossed  varieties  of,  239. 

certain  species  very  .sterile,  227. 
Noble,  Mr.,  on  fertility  of  Rhododendron, 

222. 
Nodules,  phospbatic,  in  azoic  rocks,  269. 

Oak,  varieties  of,  51. 

Onites  apelles,  123. 

Orchis,  pollen  of,  173. 

Organs  of  extreme  perfection,  167. 

electric,  of  tishes,  172 

of  little  importance,  174. 

homologous,  377. 

rudiments  of,  391. 
Ornithorhynchus,  100,  362. 
Ostrich  not  capable  of  flight,  123. 

habit  of  laying  eggs  together,  194. 

American,  two  species  of,  305. 
Otter,  habits  of,  how  acquired,  161. 
Ouzel,  water,  166. 
Owen,  Prof.,  on  birds  not  flying,  123. 

on  vegetative  repetition,  135. 

on  variable  length  of  arms  in  ourang- 
outang,  136. 

on  the  swim-bladder  of  fishes,  171. 

on  electric  organs,  172. 

on  fossil  horse  of  La  Plata,  279. 

on  relations  of  ruminants  and  pachy- 
derms, 288. 

on  fossil  birds  of  New  Zealand,  296. 

on  succession  of  types,  296. 

on  affinities  of  the  dugong,  361. 

on  homologous  organs,  378. 

on  the  metamorphosis  of  cephalo- 
pods  and  spiders,  384. 

Pacific  Ocean,  faunas  of,  304. 

Paley  on  no  organ  formed  to  give  pain, 

179. 
Pallas  on  the  fertility  of  the  wild  stocks 

of  domestic  animals,  224. 
Paraguay,  cattle  destroyed  by  flies,  71. 
Parasites,  194. 
Partridge,  dirt  on  feet,  316. 
Parts  greatly  developed,  variable,  136. 

degrees  of  utility  of,  179. 
ParuB  major,  104. 
Passiflora,  221. 
Peaches  in  United  States,  81. 
Pear,  grafts  of,  231. 
Pelargonium,  flowers  of,  132. 

sterility  of,  222. 
Pelvis  of  women,  131. 
Peloria,  132. 
Period,  glacial,  318. 
Petrels,  habits  of,  165. 
Fhasianus,  fertility  of  hj'brids,  224. 
Pheasant,  young,  wild,  192. 


Philippi  on  tertiary  species  in  Sicily,  273, 
Pictet,  Prof.,  on  groups  of  species  sudden- 
ly appearing,  264,  267. 
on  rate  of  orgaidc  change,  274. 
on  continuous  succession  of  genera, 

277. 
on  close  alliance  of  fossils  in  con- 
secutive formations,  293. 
on  embryological  succession,  295. 
Pierce,  Mr.,  on  varieties  of  Avolves.  87. 
Pigeons  with  feathered  feet  and  skin  be- 
tween toes,  18. 
breeds  described,  and  origin  of.  25. 
breeds  of,  how  produced,  41,  44. 
tumbler,  not  being  able  to  get  out  of 

egg,  83. 
reverting  to  blue  color,  144. 
instinct  of  tumbling,  191. 
carriers,  killed  by  hawks,  315. 
young  of,  387. 
Pistil,  rudimentary,  392. 
Plants,    poisonous,  not  afiecting   certain 
coloured  animals,  18. 
selection  applied  to,  36. 
gradual  improvement  of,  40. 
not  improved  in  barbarous  countries, 

40. 
destroyed  by  insects,  66. 
in  midst  of  rarge,  have  to  struggle 

with  other  plants,  75. 
nectar  of,  87. 
fleshy,  on  sea-shores,  121. 
fresh-water,  distribution  of,  336. 
low  in  scale,  widely  distri)  ated,  353. 
Plumage,  laws  of  change  in  sexes  of  birds, 

85. 
Plums  in  the  United  States,  81. 
Pointer  dog,  origin  of,  38. 

habits  of,  190. 
Poison  not  aftecting  certain  co«oured  ani- 
mals, 18. 
Poison,  similar  etiect  of,  on  animals  and 

plants,  419. 
Pollen  of  fir-trees,  181. 
Poole,  Col.,  on  striped  hemionus,  147. 
Potamogeton,  337. 
Prestwich,  Mr.,  on  English  and  French 

eocene  formations,  287. 
Primrose,  51. 

sterility  of,  219. 
Primula,  varieties  of,  51. 
Proteolepas,  134. 
Proteus,  127. 
Psychology,  future  progress  of,  423. 

Quagga,  striped,  149. 
Quince,  grafts  of,  231. 

Rabbit,  disposition  of  young,  192. 
Races,  domestic,  characters  of,  21. 
Race-horses,  Arab,  38. 

Ei.glish,  310. 
Ramond  on  plants  of  Pyrenees,  320. 
Ramsay,  Prof.,  on  thickness  of  the  Britisil 
formations.  249. 

on  faults,  250. 
Ratio  of  increase,  63. 
Rats,  supplanting  each  other,  74. 

acclimatisation  of,  128. 

blind  in  cave,  125. 


INDEX. 


43y 


Rattle-snake,  179, 

Reason  and  instinct,  186. 

Recapitulation,  general,  398. 

Reciprocity  of  crosses,  228. 

Record,  geological,  imperfect,  245. 

Rengger  on  flies  destroying  cattle,  70. 

Reproduction,  rate  of,  63. 

Resemblance  to  jiarents  in  mongreiS  and 
hybrids,  241. 

Reversion,  law  of  inheritance,  20. 
in  pigeons  to  blue  colour,  144. 

Rhododendron,  sterility  of,  222. 

Richard,  Prof.,  on  Aspicarpa,  363. 

Richardson,  Sir  J.,  on  structure  of  squir- 
rels, 162. 
on  fishes  of  the  southernhemisphere, 
327. 

Robinia,  grafts  of,  231. 

Rodents,  blind,  125. 

Rudimentary  organs,  391. 

Rudiments    imx^ortaut    for  classification, 
362. 

Sageret  on  grafts,  231. 

Salmons,  males  fighting,  and  hooked  jaws 

of,  84. 
Salt  water,  how  far  injurious  to  seeds,  312. 
Saurophagus  sulphuratus,  164. 
Schiodte  on  blind  insects,  126. 
Schlegel  on  snakes,  131. 
Sea-water,  how  far  injurious  to  seeds,  312. 
Sebright,  Sir  J.,  on  crossed  animals,  25. 

on  selection  of  pigeons,  34. 
Sedgwick,  Prof.,  on  groups  of  species  sud- 
denly appearing,  264. 
Seedlings  destroyed  by  insects,  68 
Seeds,  nutriment  iu,  75. 

winged,  133. 

power  of  resisting  salt  water,  312. 

in  crops  and  intestines  of  birds,  315. 

eaten  by  fish,  316,  337. 

in  mud,  337. 

hooked,  on  islands,  341. 
Selection  of  domestic  products,  33. 

principle  not  of  recent  origin,  36. 

unconscious,  37. 

natural,  77. 

sexual,  83. 

natural,    circumstances    favourable 
to,  95. 
Sexes,  relations  of,  83. 
Sexual  characters  variable,  141. 

selection,  83. 
Sheep,  Merino,  their  selection,  35. 

two  sub-breeds  unLntentionally  pro- 
duced, 39. 

mountain,  varieties  of,  73. 
Shells,  colours  of,  121. 

littoral,  seldom  embedded,  253. 

rresh-water,  dispersal  of,  335. 

of  Madeira,  341. 

land,  distribution  of,  346. 
Silene,  fertility  of  crosses,  227. 
Silliman,  Prof.,  on  blind  rat,  125. 
Skulls  of  j-oung  mammals,  176,  380. 
Slave-making  instinct,  195. 
Smith,  Col.  Hamilton,  on  striped  horses, 
148. 

Mr.   Fred.,  on   slave-making   ants, 
195. 


Smith,  Mr.  Fred.,  on  neuter  ants,  212. 

Mr.,  of  Jordan  Hill,  on  the  degrada- 
tion of  coast-rocks,  248. 
Snap-dragon,  145. 
Somerville,  Lord,  on  selection  of  sheep, 

34. 
Sorbus,  grafts  of,  231. 
Spaniel,  King  Charles's  breed,  38. 
Species,  polymorphic,  48. 

common,  variable,  54. 

in  large  genera  variable,  55. 

groups  of,  suddenly  appearing,  264, 
2o8. 

heneath  Silurian  formations,  208. 

successively  appearing,  273. 

changing  siraultaneouoly  throughout 
the  world,  282. 
Spencer,  Lord,  on  increase  in  size  of  cattle, 

38. 
Sphex,  parasitic,  195. 
Spiders,  development  of,  384. 
Spitz-dog  crossed  with  fox,  236. 
Sports  in  plants,  16. 
Sprengle,  C.  C,  on  crossing,  92. 

on  ray-florets,  132. 
Squirrels,  gradations  in  structure,  162. 
Staflbrdshire,  heath,  changes  in,  70. 
Stag-beetles,  fighting,  84. 
Sterility  from  changed  conditions  of  life, 
16. 

of  hybrids,  218. 
laws  of,  225. 
causes  of,  232. 

from  unfavourable  conditions,  234. 

of  certain  varieties,  237. 
St.  Helena,  productions  of,  339. 
St.  Hilaire.  Aug.,  on  classification,  364. 
St.  John,  Mr.,  on  habits  of  cats,  86. 
Sting  of  bee,  ISO. 

Stocks,  aboriginal,  of  domestic  animals,  23. 
Strata,  thickness  of,  in  Britain,  249. 
Stripes  on  horses,  147. 
Structure,  degrees  of  utility  of,  179. 
Struggle  for  existence,  60. 
Succession,  geological,  273. 
Succession  of  types  in  same  areas,  295. 
Swallow,  one  species  supplanting  another, 

74. 
Swim-bladder,  170. 
System,  natural,  360. 

Tail  of  girafte,  174. 

of  aquatic  animals,  175. 

rudimentary,  394. 
Tarsi  deficient,  123. 
Tausch  on  umbelliferous  flowers,  132. 
Teeth  and  hair  correlated,  131. 

embryonic,  traces  of,  in  birds,  391. 

rudimentary,  in  embryonic  calf,  391, 
416. 
Tegetmeier,  Mr.,  on  cells  of  bees,  202,  207. 
Temminck  on  distribution  aiding  classifi- 
cation, 365. 
Tfcouin  on  grafts,  231. 
Thrush,  aquatic  species  of,  166. 

mocking,  of  the  Galapagos,  350. 

5'oung  of,  spotted,  382. 

]iest  of,  215. 
Thurot,  M.,  on  crossed  fusi;  228. 
Thwaites,  Mr.,  on  acclimatisation,  128. 


MO 


INDEX. 


Tierra  del  Fuego,  dogs  of,  192. 

plants  of,  326,  329. 
Timber-drift,  314. 
Time,  lapse  of,  247. 
Titmouse,  164. 
Toads  on  islands,  342. 
Tobacco,  crossed  varieties  of,  239. 
Tomes,  Mr.,  on  the  distribution  of  bats, 

343. 
Transitions  in  varieties  rare,  15-5. 
Trees  on  islands  belong  to  peculiar  orders, 
342. 

■with  separated  sexes,  93. 
Trifolium  pratense,  71,  89. 

incarnatum,  89. 
Trigonia,  281. 
Trilobites,  268. 

sudden  extinction  of,  281. 
Troglodj-tes,  216. 
Tucutucu,  blind,  125. 

Tumbler  pigeons,  habits   of,   hereditary, 
191. 

young  of,  387. 
Turkey-cocli,  brush  of  hair  on  breast,  85. 
Tui'key,  naked  skin  on  head,  176. 

young,  wild,  192. 
Turnip  and  cabbage,  analogous  variations 

of,  144. 
Tji^e,  unity  of,  184. 
Types,  succession  of,  in  same  areas,  295. 

Udders  enlarged  by  use,  17. 
rudimentarj',  392. 

Ulex,  young  leaves  of,  382. 

Umbelliferce,  outer  and  inner  florets  of,  131. 

Unity  of  type,  184. 

Use,  effects  of,  under  domestication,  17. 

effects  of,  in  a  state  of  nature,  122, 
123, 

Utilit}',    how  far  important  in  the  con- 
struction of  each  part,  178. 

Valenciennes  on  fresh -water  fish,  335. 
VariabiUty  of  mongrels  and  hybrids,  241. 
Variation  under  domestication,  14. 

caused  by  reproductive  system  being 
affected  by  conditions  of  life,  15. 

under  nature,  46. 

laws  of,  120. 
Variations  appear  at  corresponding  ages, 
20,  82. 

analogous  in  distinct  species,  144. 
Varieties,  natural,  46. 

struggle  between,  73. 

domestic,  extinction  of,  104. 

transitional,  rarity  of,  154. 

when  crossed,  fertile,  236. 

when  crossed,  sterile,  237. 

classification  of,  368. 
Verbascum,  sterility  of,  222. 

varieties  of,  crossed,  238. 
Verneuil,  M.  de,  on  the  succession  of  spe- 
cies, 284.  * 
Viola  tricolor,  71. 

Volcanic  islands,  denudation  of,  249. 
Vulture,  naked  skin  on  head,  176. 

V\''ading-bird9,  337. 


"Wallace,  Mr.,  on  origin  of  species,  10. 

on  law  of  geographical  distribution, 

310. 
on  the  Malay  Archipelago,  344. 
"Wasp,  sting  of,  ISO. 
"Water,  fresh,  productions  of,  334. 
Water-hen,  166. 

"Waterhouse,  Mr.,  on  Australian  marsu- 
pials, 108. 
on    greatly  developed  parts   being 

variable,  136. 
on  cells  of  bees,  200. 
on  general  affinities,  373. 
"Water-ouzel,  166. 

"Watson,  Mr.  H.  C,  on  range  of  varieties 
of  British  plants,  68. 
on  acclimatisation,  128. 
on  flora  of  Azores,  316. 
on  Alpine  plants,  320,  327. 
on  rarity  of  intermediate  varieties. 
158. 
"Weald,  denudation  of,  250. 
"Web  of  feet  in  water-birds,  166. 
"West  Indian  islands,  mammals  of,  344. 
"Westwood  on  species  in  large  genera  being 
closely  allied  to  others,  57. 
on  the  tarsi  of  Engidas,  142. 
on  the  antenna!  of  hymenopterous 
insects,  362. 
Whales,  fossil,  265. 
Wheat,  varieties  of,  105. 
"White  Mountains,  flora  of,  318. 
"Wings,  reduction  of  size,  123. 

of  insects  homologous  with  bran- 

chias,  171. 
rudimentary,  in  insects,  391. 
"Wolf  crossed  with  dog,  191. 
of  Falkland  Isles,  343. 
W'ollaston,  Mi-.,  on  varieties  of  insects,  50. 
on  fossil  varieties  of  land-shells  in 

Madeira,  53. 
on  colours  of  insects  on  sea-shore, 

121. 
on  wingless  beetles,  124. 
on  rarity  of  intermediate  varieties, 

158. 
on  insular  insects,  339. 
on     land-shells    of    Madeira,    natu- 
ralised, 350. 
"Wolves,  varieties  of,  86. 
"Woodpecker,  habits  of,  165. 

green  colour  of,  176. 
"Woodward,  Mr.,  on  the  duration  of  spe- 
cific forms,  257. 
on  the  continuous  succession  of  gen- 

er.a,  276. 
on  the  succession  of  types,  296. 
"World,  species  chanffing  simultaneously 

throughout,  282. 
"Wrens,  nest  of,  215. 

Youatt,  Mr.,  on  selection,  34. 

on  sub-breeds  of  sheep,  39. 
on  rudimentary  horns  in  young  cat- 
tle, 394. 

Zebra,  stripes  on,  147. 


D.  Appleton  cfc  Company's  Publications. 


MODERN  BRITISH  ESSAYISTS, 

COliIPKISING 

t  Critical  ^  'Wkttiimtms  Wuh 


AlilSON,  CAKLiYIiE, 

JEFFKEY,  MACAUIiAY, 

MACKINTOSH,  SYDNEY  SMITH, 

STEPHEN,  TAH-FOUBD, 

And  Prof.  WIIiSON, 

In  8  vols.,  large  8vo.,  uniform  Cloth,  S13.  Sheep,  $17.  Half  Calf  Ext, 

Each  Volume  to  be  had  separately. 


Alison's  Essays. 

Miscellaneous  Essays.  By  Archibald  Alison,  F.  E.  S.  Eeprinted  from  the 
EDglish  originals,  witli  the  author's  corrections  for  this  edition.  1  large  voL 
8vo.    Portrait    Cloth,  $1  25 ;  sheep,  $1  75. 

€arlyle's  Essays. 

Critical  and  Miscellaneous  Essays.  By  Thomas  Caeltle.  Complete  in  one 
volume.    1  large  vol.  8vo.    Portrait.    Cloth,  $2 ;  sheep,  $2  50. 

Jeffrey's  Essays, 

Contributions  to  the  Edinburgh  Eevlew.  By  Feancis  Jeffrey.  The  four 
volumes  complete  in  one.  1  very  large  vol.  Svo.  Portrait.  Cloth,  $2  ;  sheep, 
$2  50. 

Macaulay's  Essays. 

Essays,  Critical  and  Miscellaneous.  By  T.  Babington  Macatjlat,  New  and 
Eevised  edition.    1  very  large  vol.  Svo.    Portrait.    Cloth,  $2 ;  sheep,  $2  50. 

Mackintosli's  Essays. 

The  Miscellaneous  "Works  of  the  Eight  Honorable  Sir  James  Mackintosh. 
The  three  volumes  in  one.  1  vol.  large  Svo,  Portrait.  Cloth,  $2;  sheep, 
$2  50. 

Sydney  Smitli's  Works. 

The  "Works  of  the  Eev.  Sydney  Smith.  Three  volumes  complete  in  one.  1 
large  vol.  Svo.    Portrait.    Cloth,  $1  25 ;  sheep,  $1  75. 

Talfourd's  and  Stephen's  Essays. 

Critical  and  Miscellaneous  "Writings  of  T.  Noon  Talfoued,  author  of  "  Ion," 
&c.    Critical  and  Miscellaneous  Essays  of  James  Stephen.    In  1  vol.  large  Svo. 
Portrait.    Cloth,  $1  25 ;   sheep,  $1  75. 
Wilson's  Essays. 

Tho  Eecreations  of  Christopher  North  [Prof.  John  "Wilson.]  Complete  In  1 
vol.  large  Svo,    Portrait.    Cloth,  $1  25 ;  sheep,  $1  75. 


D.  Appleton  &  CoJ's  Publications. 


a?H:E 


EDITED    BY 

GEO.  RIPLEY  and  C.  A.  DANA, 

ASSISTED  BY  A  NUMEROUS  BUT  SELECT  COEPS  OF  'WEITEES. 

The  design  of  The  Nirw  American  Cyclopedia  is  to  furnish  the  great  body 
of  intelligent  readers  in  this  country  with  a  popular  Dictionary  of  General 
Knowledge. 

The  New  American  Cyclopedia  is  not  founded  on  any  European  model; 
in  its  plan  and  elaboration  it  is  strictly  original,  and  strictly  American.  Many  of 
the  writers  employed  on  the  work  have  enriched  it  with  their  personal  researches, 
observations  and  discoveries ;  and  every  article  has  been  written,  or  re-written, 
expressly  for  its  pages. 

It  is  intended  that  the  work  shall  bear  such  a  character  of  practical  utility  as 
to  make  it  indispensable  to  every  American  library. 

Throughout  its  successive  volumes  TIie  New  Ameeioan  Cyclopedia  will 
present  a  fund  of  accurate  and  copious  information  on  Science,  Aet,  Ageiculttjee, 
Commerce,  Manufactures,  Law,  Medicine,  Literature,  Philosophy,  Mathe- 
matics, Astronomy,  History,  Biography,  Geography,  Eeligion,  Politics, 
Travels,  Chemistry,  Mechanics,  Inventions,  and  Trades. 

Abstaining  from  all  doctrinal  discussions,  from  all  sectional  and  sectarian  argu 
ments,  it  will  maintain  the  position  of  absolute  impartiality  on  the  great  contro- 
Terted  questions  which  have  divided  opinions  in  every  age. 

PRICE. 

This  work  is  published  exclusively  by  subscription,  In  fifteen  large  octp.vt 
volumes,  each  containing  750  two-column  pages.  Vols.  I.  to  IX.  are  now  ready. 
Price  per  volume,  cloth,  $3 ;  library  style,  leather,  $3  50 ;  half  morocco,  $4 ;  half 
Russia,  extra,  $4  50. 

HOW  TO  OBTAIN  THE   CYCLOPEDIA. 

1,  By  applying  to  the  nearest  regularly-constituted  agent  in  a  city  or  town. 

2.  By  remitting  to  the  publishers  the  amount  for  oue  volume  or  more.  Im- 
mediately upon  receipt  of  the  money,  the  book  will  be  sent  by  mail,  postage  paid 
in  strong  wrappers,  to  any  address,  within  8,000  miles,  in  the  United  States. 

IMPORTANT    NOTICE. 

Any  one  procuring  four  subscribers  to  the  Cyclopsed5a,  and  sending  the  amount, 
$3  per  volume,  to  the  publishers,  will  be  entitled  to  a  copy  or  the  work  gratify,  to 
be  sent  at  the  remitter's  expense  for  carriage,  or  if  ten^  subscribers  are  obtained, 
eleven  copies  will  be  sent  at  our  expense,  for  carriage. 

%*  Agents  wanted  in  almost  all  sections  of  the  United  States.  Liberal  tenoj 
Mid  exclusive  territory  given.  ^ 


^/z 


H^ 


7/.  XOO^.O^^.  Ooil^