The factors of organic evolution

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THE FACTORS

ORGANIC EVOLUTION.

BY

HERBERT SPENCER.

REPRINTED, WITH ADDITIONS, FROM
THE NINETEENTH CENTURY.

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1887.

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PREFACE.

THE two parts of which this Essay consists, originally
published in The Nineteenth Century for April and May
1886 respectively, now reappear with the assent of the
proprietor and editor of that periodical, to whom my
thanks are due for his courtesy in giving it. Some
passages of considerable length which, with a view to
needful brevity, were omitted when the articles first
appeared, have been restored.

Though the direct bearings of the arguments contained
in this Essay are biological, the argument contained in its
first half has indirect bearings upon Psychology, Ethics,
and Sociology. My belief in the profound importance of
these indirect bearings, was originally a chief prompter
to set forth the argument; and it now prompts me to
re-issue it in permanent form.

Though mental phenomena of many kinds, and especially
of the simpler kinds, are explicable only as resulting from
the natural selection of favourable variations ; yet there
are, I believe, still more numerous mental phenomena,
including all those of any considerable complexity, which
cannot be explained otherwise than as results of the '
inheritance of functionally-produced modifications. What
theory of psychological evolution is espoused, thus depends

VI PREFACE.

on acceptance or rejection of the doctrine that not only
in the individual, but in the successions of individuals,
use and disuse of parts produce respectively increase and
decrease of them.
*-"" Of course there are involved the conceptions we form

' of the genesis and nature of our higher emotions ;
and, by implication, the conceptions we form of our
moral intuitions. If functionally-produced modifications
are inheritable, then the mental associations habitually
produced in individuals by experiences of the relations
between actions and their consequences, pleasurable or
painful, may, in the successions of individuals, generate
innate tendencies to like or dislike such actions. But if
not, the genesis of such tendencies is, as we shall see, not

\ ..satisfactorily explicable.

That our sociological beliefs must also be profoundly
affected by the conclusions we draw on this point, is
obvious. If a nation is modified en masse by transmission
of the effects produced on the natures of its members
by those modes of daily activity which its institutions
and circumstances involve ; then we must infer that
such institutions and circumstances mould its members
far more rapidly and comprehensively than they can do if
the sole cause of adaptation to them is the more frequent
survival of individuals who happen to have varied in
favourable ways.

I will add only that, considering the width and depth
of the effects which acceptance of one or other of these
hypotheses must have on our views of Life, Mind, Morals,
and Politics, the question — Which of them is true ? demands,
beyond all other questions whatever, the attention of
scientific men.

Brighton, January, 1887.

THE FACTORS OF ORGANIC EVOLUTION.

[April and May, 1886.]
I.

WITHIN the recollection of men now in middle life, opinion
concerning the derivation of animals and plants was in
a chaotic state. Among the unthinking there was tacit
belief in creation by miracle, which formed an essential
part of the creed of Christendom; and among the thinking
there were two parties, each of which held an indefensible
hypothesis. Immensely the larger of these parties, includ
ing nearly all whose scientific culture gave weight to their
judgments, though not accepting literally the theologically-
orthodox doctrine, made a compromise between that doctrine
and the doctrines which geologists had established; while
opposed to them were some, mostly having no authority iu
science, who held a doctrine which was heterodox both
theologically and scientifically. Professor Huxley, in his
lecture on " The Coming of Age of the Origin of Species,"
remarks concerning the first of these parties as follows : —

" One-and-twenty years ago, in spite of the work commenced by Hutton
and continued with rare skill and patience by Lyell, the dominant view of the
past history of the earth was catastrophic. Great and sudden physical
revolutions, wholesale creations and extinctions of living beings, were the
ordinary machinery of the geological epic brought into fashion by the mis
applied genius of Cuvier. It was gravely maintained and taught that the
end of every geological epoch was signalised by a cataclysm, by which every
living being on the globe was swept away, to be replaced by a brand-new
creation when the world returned to quiescence. A scheme of nature which

2 THE FACTORS OF ORGANIC EVOLUTION.

appeared to be modelled on the likeness of a succession of rubbers of whist,
at the end of each of which the players upset the table and called for a new
pack, did not seem to shock anybody.

I may be wrong, but I doubt if, at the present time, there is a single
responsible representative of these opinions left. The progress of scientific
geology has elevated the fundament principle of uniformitarianism. that the
explanation of the past is to be sought in the study of the present, into the
position of an axiom ; and the wild speculations of the catastrophists, to
which we all listened with respect a quarter of a century ago, would hardly
find a single patient hearer at the present day."

Of the party above referred to as not satisfied with this
conception described by Professor Huxley, there were two
classes. The great majority were admirers of the Vestiges
of the Natural History of Creation — a work which, while it
sought to show that organic evolution has taken place,
contended that the cause of organic evolution, is "an
impulse " supernaturally " imparted to the forms of life,
advancing them, . . . through grades of organization."
Being nearly all very inadequately acquainted with the
facts, those who accepted the view set forth in the Vestiges
were ridiculed by the well-instructed for being satisfied
with evidence, much of which was either invalid or easily
cancelled by counter-evidence, and at the same time they
exposed themselves to the ridicule of the more philosophical
for being content with a supposed explanation which was
in reality no explanation: the alleged " impulse" to advance
giving us no more help in understanding the facts than
does Nature's alleged " abhorrence of a vacuum " help
us to understand the ascent of water in a pump. The
remnant, forming the second of these classes, was very
small. While rejecting this mere verbal solution, which
both Dr. Erasmus Darwin and Lamarck had shadowed
forth in other language, there were some few who, rejecting
also the hypothesis indicated by both Dr. Darwin and
Lamarck, that the promptings of desires or wants produced
growths of the parts subserving them, accepted the single
vera causa assigned by these writers — the modification of
structures resulting from modification of functions. They

THE FACTORS OF ORGANIC EVOLUTION. 3

recognized as the sole process in organic development, the
adaptation of parts and powers consequent on the effects of
use and disuse — that continual moulding and re-moulding of
organisms to suit their circumstances, which is brought
about by direct converse with such circumstances.

But while this cause accepted by these few is a true
cause, since unquestionably during the . life of the indi
vidual organism changes of function produce changes of
structure; and while it is a tenable hypothesis that
changes of structure so produced are inheritable^; yet it was
manifest to those not prepossessed, that this cause cannot
with reason be assigned for the greater part of the facts.
Though in plants there are some characters which may not
irrationally be ascribed to the direct effects of modified
functions consequent on modified circumstances, yet the
majority of the traits presented by plants are not to be
thus explained. It is impossible that the thorns by which
a briar is in large measure defended against browsing
animals, can have been developed and moulded by the
continuous exercise of their protective actions ; for in the
first place, the great majority of the thorns are never
touched at all, and, in the second place, we have no ground
whatever for supposing that those which are touched are
thereby made to grow, and to take those shapes which
render them efficient. Plants which are rendered uneatable
by the thick woolly coatings of their leaves, cannot have
had these coatings produced by any process of reaction
against the action of enemies; for there is no imaginable
reason why, if one part of a plant is eaten, the rest should
thereafter begin to develop the hairs on its surface. By
what direct effect of function on structure, can the shell of
a nut have been evolved ? Or how can those seeds which
contain essential oils, rendering them unpalatable to birds,
have been made to secrete such essential oils by these
actions of birds which they restrain ? QrJ[K>w_ caij_ the
delicate plumes borne by some seeds, and giving the wind

4 THE FACTOKS OP ORGANIC EVOLUTION.

power to waft them to new stations, be due to any imme
diate influences of surrounding conditions ? Clearly in these
and in countless other cases, change of structure cannot
have been directly caused by change of function. So
is it with animals to a large extent, if not to the same
extent. Though we have proof that by rough usage the
dermal layer may be so excited as to produce a greatly
thickened epidermal layer, sometimes quite horny; and
though it is a feasible hypothesis that an effect of this kind
persistently produced may be inherited ; yet no such cause
can explain the carapace of the turtle, the armour of the
armadillo, or the imbricated covering of the manis. The
skins of these animals are no more exposed to habitual
hard usage than are those of animals covered by hair.
The strange excrescences which distinguish the heads of
the hornbills, cannot possibly have arisen from any reaction
against the action of surrounding forces; for even were
they clearly protective, there is no reason to suppose that
the heads of these birds need protection more than the
heads of other birds. If, led by the evidence that in
animals the amount of covering is in some cases affected by
the degree of exposure, it were admitted as imaginable that
the development of feathers from preceding dermal growths
had resulted from that extra nutrition caused by extra
superficial circulation, we should still be without explana
tion of the structure of a feather. Nor should we have any
clue to the specialities of feathers — the crests of various
birds, the tails sometimes so enormous, the curiously placed
plumes of the bird of paradise, &c., &c. Still more
obviously impossible is it to explain as due to use or disuse
the colours of animals. No direct adaptation to function
could have produced the blue protuberances on a mandril's
face, or the striped hide of a tiger, or the gorgeous plumage
of a kingfisher, or the eyes in a peacock's tail, or the
multitudinous patterns of insects' wings. One single case,
that of a deer's horns, might alone have sufficed to show

THE FACTORS OP ORGANIC EVOLUTION. O

how insufficient was the assigned cause. During their
growth, a deer's horns are not used at all; and when,
having been cleared of the dead skin and dried-up blood
vessels covering them, they are ready for use, they are
nerveless and non-vascular, and hence are incapable of
undergoing any changes of structure consequent on changes
of function.

Of these few then, who rejected the belief described by
Professor Huxley, and who, espousing the belief in a
continuous evolution, had to account for this evolution, it
must be said that though the cause assigned was a true
cause, yet, even admitting that it operated through successive
generations, it left unexplained the greater part of the facts.
Having been myself one of these few, I look back with
surprise at the way in which the facts which were congruous
with the espoused view monopolized consciousness and kept
out the facts which were incongruous with it — conspicuous
though many of them were. The misjudgment was not
unnatural. Finding it impossible to accept any doctrine
which implied a breach in the uniform course of natural
causation, and, by implication, accepting as unquestionable
the origin and development of all organic forms by
accumulated modifications naturally caused, that which
appeared to explain certain classes of these modifications,
was supposed to be capable of explaining the rest : the
tendency being to assume that these would eventually be
similarly accounted for, though it was not clear how.

Returning from this parenthethic remark, we are con
cerned here chiefly to remember that, as said at the outset,
there existed thirty years ago, no tenable theory about
the genesis of living things. Of the two alternative beliefs,
neither would bear critical examination.

Out of this dead lock we were released — in large measure,
though not I believe entirely — by the Origin of Species.
That work brought into view a further factor ; or rather,

0 THE FACTORS OF ORGANIC EVOLUTION.

such factor, recognized as in operation by here and there
an observer (as pointed out by Mr. Darwin in his intro
duction to the second edition), was by him for the first time
seen to have played so immense a part in the genesis of
plants and animals.

Though laying myself open to the charge of telling a
thrice-told tale, I feel obliged here to indicate briefly the
several great classes of facts which Mr. Darwin's hypothesis
explains; because otherwise that which follows would
scarcely be understood. And I feel the less hesitation in
doing this because the hypothesis which it replaced, not
very widely known at any time, has of late so completely
dropped into the background, that the majority of readers
are scarcely aware of its existence, and do not therefore
understand the relation between Mr. Darwin's successful
interpretation and the preceding unsuccessful attempt at
interpretation. Of these classes of facts, four chief ones
may be here distinguished.

(j) In the first place, such adjustments as those exemplified
above are made comprehensible^ Though it is inconceiv
able that a structure like that of the pitcher-plant could
have been produced by accumulated effects of function
on structure ; yet it is conceivable that successive selections
of favourable variations might have produced it; and the
like holds of the no less remarkable appliance of the
Venus's Fly-trap, or the still more astonishing one of that
water-plant by which infant-fish are captured. Though it is
impossible to imagine how, by direct influence of increased
use, such dermal appendages as a porcupine's quills could
have been developed ; yet, profiting as the members of a
species otherwise defenceless might do by the stiffness of
their hairs, rendering them unpleasant morsels to eat, it is
a feasible supposition that from successive survivals of
individuals thus defended in the greatest degrees, and the
consequent growth in successive generations of hairs into
bristles, bristles into spines, spines into quills (for all these

THE FACTORS OP ORGANIC EVOLUTION. 7

are homologous), this change could have arisen. In like
manner, the odd inflatable bag of the bladder-nosed seal, the
curious fishing-rod with its worm-like appendage carried on
the head of the lophius or angler, the spurs on the wings of
certain birds, the weapons- of the sword-fish and saw-fish,
the wattles of fowls, and numberless such peculiar struc
tures, though by no possibility explicable as due to effects
of use or disuse, are explicable as resulting from natural
^ selection operating in one or other way.

^Y in the second place, while showing us how there have \
arisen countless modifications in the forms, structures, ;
and colours of each part, Mr. Darwin has shown us how,
by the establishment of favourable variations, there may
arise new parts.^ Though the first step in the production i
of horns on the heads of various herbivorous animals, may j
have been the growth of callosities consequent on the--''
habit of butting — such callosities thus functionally initiated
being afterwards developed in the most advantageous ways
by selection ; yet no explanation can be thus given of the
sudden appearance of a duplicate set of horns, as occasion
ally happens in sheep : an addition which, where it proved
beneficial, might readily be made a permanent trait by^
natural selection. ' Again, the modifications which follow use
and disuse can by no possibility account for changes in the
numbers of vertebras ; but after, recognizing spontaneous,
or rather fortuitous, variation as a factor, we can see
that where an additional vertebra hence resulting (as
in some pigeons) proves beneficial, -survival of the fittest
may make it a constant character ; j and there may, by
further like additions, be produced extremely long strings
of vertebrae, such as snakes show us. Similarly with the
mammary glands. It is not an unreasonable supposition
that by the effects of greater or less function, inherited
through successive generations, these may be enlarged or
diminished in size ; but it is out of the question to allege
such a cause for changes in their numbers. There is no

THE FACTORS OP ORGANIC EVOLUTION.

imaginable explanation of these save the establishment by
inheritance of Lsponta.negi]LS._Yaiiations, such as are known
to occur in the human race.

^ So too, in the third place, with certain alterations in the

connexions of parts. According to the greater or smaller

demands made on this or that limb, the muscles moving

it may be augmented or diminished in bulk ; and, if there

is inheritance of changes so wrought, the limb may, in

course of generations, be rendered larger or smaller. But

changes in the arrangements or attachments of muscles

cannot be thus accounted for. It is found, especially at

r^the extremities, that the relations of tendons to bones and

j to one another are not always the same. Variations in

/ their modes of connexion may occasionally prove advan-

/ tageous, and may thus become established. Here again,

y then, wre have a class of structural changes to which

Mr. Darwin's hypothesis gives us the key, and to which

there is no other key.

Once more there are the phenomena of jniimicry^ Per
haps in a more striking way than any others, these show
how traits w^hich seem inexplicable are explicable as due
to the more frequent survival of individuals that have
varied in favourable ways. J We are enabled to understand
such marvellous simulations as those of the leaf-insect,
those of beetles which " resemble glittering dew-drops upon
the leaves;" those of caterpillars which, when asleep,
stretch themselves out so as to look like twigs. And we
are shown how there have arisen still more astonishing
imitations — those of one insect by another. As Mr. Bates
has proved, there are cases in which a species of butter
fly, rendered so unpalatable to insectivorous birds by its
disagreeable taste that they will not catch it, is simulated
in its colours and markings by a species which is struc
turally quite different — so simulated that even a practised
entomologist is liable to be deceived : the explanation being
that an original slight resemblance, leading to occasional

THE FACTOES OP ORGANIC EVOLUTION. 9

mistakes on the part of birds, was increased generation
after generation by the more frequent escape of the most-
like individuals, until the likeness became thus great.

But now, recognizing in full this process brought into
clear view by Mr. Darwin, and traced out by him with so
much care and skill, can we conclude that, taken alone, it
accounts for organic evolution ? Has the natural selection
of favourable variations been the sole factor ? On critically
examining the evidence, we shall find reason to think that
it by no means explains all that has to be explained.
Omitting for the present any consideration of a factor
which may be distinguished as primordial, it may be con
tended that the above-named factor alleged by Dr. Erasmus
Darwin and by Lamarck, must be recognized as a (co
-operator. Utterly inadequate to explain the major part of
the facts as is the hypothesis of the inheritance of func
tionally-produced modifications, yet there is a minor part
of the facts, very extensive though less, which must be I
ascribed to this cause.

When discussing the question more than twenty years
ago (Principles of Biology, § 166), I instanced the decreased
size of the jaws in the civilized races of mankind, as a
change not accounted for by the natural selection of
favourable variations ; since no one of the decrements by
which, in thousands of years, this reduction has been
effected, could have given to an individual in which it
occurred, such advantage as would cause his survival,
either through diminished cost of local nutrition or dimi
nished weight to be carried. I did not then exclude, as I
might have done, two other imaginable causes. It may
be said that there is some organic correlation between
increased size of brain and decreased size of jaw : Camper's
doctrine of the facial angle being referred to in proof.
But this argument may be met by pointing to the many
examples of small-jawed people who are also small-brained,

10 THE FACTORS OF ORGANIC EVOLUTION.

and by citing not infrequent cases of individuals remark
able for their mental powers, and at the same time
distinguished by jaws not less than the average but
greater. Again, if sexual selection be named as a possible
cause, there is the reply that, even supposing such slight
diminution of jaw as took place in a single generation to
have been an attraction, yet the other incentives to choice
on the part of men have been too many and great to allow
this one to weigh in an adequate degree ; while, during
the greater portion of the period, choice on the part of
women has scarcely operated : in earlier times they were
stolen or bought, and in later times mostly coerced by
parents. Thus, reconsideration of the facts does not show
me the invalidity of the conclusion drawn, that this
decrease in size of jaw can have had no other cause than
continued inheritance of those diminutions consequent
/ on diminutions of function, implied by the use of
selected and well-prepared food. Here, ~^oW5Tef7" my
chief purpose is to add an instance showing, even
more clearly, the connexion between change of func
tion and change of structure. This instance, allied in
nature to the other, is presented by those varieties, or
rather sub-varieties, of dogs, which, having been household
pets, and habitually fed on soft food, have not been called
on to use their jaws in tearing and crunching, and have
been but rarely allowed to use them in catching prey and in
fighting. No inference can be drawn from the sizes of the
jaws themselves, which, in these dogs, have probably been
shortened mainly by selection. To get direct proof pf the
decrease of the muscles concerned in closing the jaws or
biting, would require a series of observations very difficult
to make. But it is not difficult to get indirect proof of this
decrease by looking at the bony structures witli which
these muscles are connected. Examination of the skulls
of sundry indoor dogs contained in the Museum of the
College of Surgeons, proves the relative smallness of such

THE FACTOES OF OEGANIC EVOLUTION. 11

parts. The only pug-dog's skull is that of an individual
not perfectly adult; and though its traits are quite to the
point they cannot with safety be taken as evidence. The
skull of a toy-terrier has much restricted areas of insertion
for the temporal muscles ; has weak zygomatic arches ; and
has extremely small attachments for the masseter muscles.
Still more significant is the evidence furnished by the skull
of a King Charles's spaniel, which, if we allow three years
to a generation, and bear in mind that the variety must
have existed before Charles the Second's reign, we may
assume belongs to something approaching to the hundredth
generation of these household pets. The relative breadth
between the outer surfaces of the zygomatic arches is con
spicuously small ; the narrowness of the temporal fossae is
also striking; the zygomata are very slender; the temporal
muscles have left no marks whatever, either by limiting
lines or by the character of the surfaces covered ; and the
places of attachment for the masseter muscles are very
feebly developed. At the Museum of Natural History,
among skulls of dogs there is one which, though unnamed,
is shown by its small size and by its teeth, to have belonged
to one variety or other of lap-dogs, and which has the same
traits in an equal degree with the skull just described.
Here, then, we have two if not three kinds of dogs which,
similarly leading protected and pampered lives, show that
in the course of generations the parts concerned in clench
ing the jaws have dwindled. To what cause must this
decrease be ascribed ? Certainly not to artificial selection ;
for most of the modifications named make no appreciable
external signs : the width across the zygomata could alone
be perceived. Neither can natural selection have had any
thing to do with it; for even were there any struggle for
existence among such dogs, it cannot be contended that
any advantage in the struggle could be gained by an
individual in which a decrease took place. Economy of
nutrition, too, is excluded. Abundantly fed as such dogs

12 THE FACTORS OP OEGANIC EVOLUTION.

are, the constitutional tendency is to find places where
excess of absorbed nutriment may be conveniently deposited,
rather than to find places where some cutting down of the
supplies is practicable. Nor again can there be alleged a
possible correlation between these diminutions and that
shortening of the jaws which has probably resulted from
selection ; for in the bull-dog, which has also relatively
short jaws, these structures concerned in closing them
are unusually large. Thus there remains as the only con
ceivable cause, the diminution of size which results from
diminished use. The dwindling of a little-exercised part
has, by inheritance, "^ecn made more and more marked in
successive generations.

Difficulties of another class may next be exemplified —
those which present themselves when we ask how there can
be effected by the selection of favourable variations, such
changes of structure as adapt an organism to some useful
action in which many different parts corpperate. None can
fail to see how a simple part may, in course of generations,
be greatly enlarged, if each enlargement furthers, in some
decided way, maintenance of the species. • It is easy to
understand, too, how a complex part, as an entire limb,
may be increased as a whole by the simultaneous due
increase of its co-operative parts ; since if, while it is
growing, the channels of supply bring to the limb an
unusual quantity of blood, there will naturally result a
proportionately greater size of all its components — bones,
muscles, arteries, veins, &c. But though in cases like this,
the co-operative parts forming some large complex part
may be expected to vary together, nothing implies that
they necessarily do so ; and we have proof that in various
cases, even when closely united, they do not do so. An
example is furnished by those blind crabs named in the
Origin of Species which inhabit certain dark caves of Ken
tucky, and which, though they have lost their eyes, have

THE FACTORS OP ORGANIC EVOLUTION. 13

not lost the foot-stalks which carried their eyes. In
describing the varieties which have been produced by
pigeon-fanciers, Mr. Darwin notes the fact that along with
changes in length of beak produced by selection, there have
not gone proportionate changes in length of tongue. Take
again the case of teeth and jaws. In mankind these have
not varied together. During civilization the jaws have
decreased, but the teeth have not decreased in propor
tion; and hence that prevalent crowding of them, often
remedied in childhood by extraction of some, and in
other cases causing that imperfect development which is
followed by early decay. But the absence of proportionate
variation in co-operative parts that are close together, and
are even bound up in the same mass, is best seen in those
varieties of dogs named above as illustrating the inherited
effects of disuse. We see in them, as we see in the human
race, that diminution in the jaws has not been accompanied
by corresponding diminution in the teeth. In the catalogue
of the College of Surgeons Museum, there is appended to
the entry which identifies a Blenheim Spaniel's skull, the
words — "the teeth are closely crowded together," and to
the entry concerning the skull of a King Charles's Spaniel
the words — " the teeth are closely packed, p. 3, is placed
quite transversely to the axis of the skull." It is further
noteworthy that in a case where there is no diminished use
of the jaws, but where they have been shortened by selection,
r a like want of concomitant variation is manifested : the case
being that of the bull-dog, in the upper jaw of which also,
" the premolars . . . are excessively crowded, and placed
obliquely or even transversely to the long axis of the skull. "*
If, then, in cases where we can test it, we find no con-

* It is probable that this shortening has resulted not directly but indirectly,
from the selection of individuals which were noted for tenacity of hold ; for
the bull-dog's peculiarity in this respect seems due to relative shortness of
the upper jaw, giving the underhung structure which, involving retreat of
the nostrils, enables the dog to continue breathing while holding.

14 THE FACTORS OF ORGANIC EVOLUTION.

comitant variation in co-operative parts that are near
together — if we do not find it in parts which, though
belonging to different tissues, are so closely united as teeth
and jaws — if we do not find it even when the co-operative
parts are not only closely united, but are formed out of the
same tissue, like the crab's eye and its peduncle; what shall
we say of co-operative parts which, besides being composed
of different tissues, are remote from one another? Not only
are we forbidden to assume that they vary together, but
we are warranted in asserting that they can have no
tendency to vary together. And what are the implications
in cases where increase of a structure can be of no service
unless there is concomitant increase in many distant
structures, which have to join it in performing the action
for which it is useful ?

As far back as 1864 (Principles of Biology, § 166) I named
in illustration an animal carrying heavy horns — t!ie extinct
Irish elk ; and indicated the many changes in bones,
muscles, blood-vessels, nerves, composing the fore-part of
the body, which would be required to make an increment
of size in such horns advantageous. Here let me take
another instance — that of the giraffe : an instance which
I take partly because, in the sixth edition of the Origin
of Species, issued in 1872, Mr. Darwin has referred to this
animal when effectually disposing of certain arguments
urged against his hypothesis. He there says : —

" In order that an animal should acquire some structure specially and
largely developed, it is almost indispensable that several other parts should
be modified and co-adapted. Although every part of the body varies
slightly, it does not follow that the necessary parts should always vary in
the right direction and to the right degree " (p. 179).

And in the summary of the chapter, he remarks concerning
the adjustments in the same quadruped, that "the pro
longed use of all the parts together with inheritance will
have aided in an important manner in their co-ordination "
(p. 199) : a remark probably having reference chiefly to

THE FACTORS OP ORGANIC EVOLUTION. 15

the increased massiveness of the lower part of tlie neck ;
the increased size and strength of the thorax required to
bear the additional burden ; and the increased strength
of the fore-legs required to carry the greater weight of
both. But now I think that further consideration suggests
the belief that the entailed modifications are much more
numerous and remote than at first appears; and that the
greater part of these are such as cannot be ascribed in any
rdegree to the selection of favourable variations, but must
/ be ascribed exclusively to the inherited effects of changed
v functions. Whoever has • seen a giraffe gallop will long
remember the sight as a ludicrous one. The reason for the
strangeness of the motions is obvious. Though the fore
limbs and the hind limbs differ so much in length, yet in
galloping they have to keep pace — must take equal strides.
The result is that at each stride, the angle which the hind
limbs describe round their centre of motion is much larger
than the angle described by the fore limbs. And beyond
this, as an aid in equalizing the strides, the hind part of
the back is at each stride bent very much downwards and
forwards. Hence the hind-quarters appear to be doing
nearly all the work. Now a moment's observation shows that
the bones and muscles composing the hind-quarters of the
giraffe, perform actions differing in one or other way and
degree, from the actions performed by the homologous
bones and muscles in a mammal of ordinary proportions,
and from those in the ancestral mammal which gave origin
to the giraffe. Each further stage of that growth which
produced the large fore-quarters and neck, entailed some
adapted change in sundry of the numerous parts composing
the hind-quarters; since any failure in the adjustment of
their respective strengths would entail some defect in speed
and consequent loss of life when chased. It needs but to
remember how, when continuing to walk with a blistered
foot, the taking of steps in such a modified way as to
diminish pressure on the sore point, soon produces aching

16 THE FACTORS OF ORGANIC EVOLUTION.

of muscles which are called into unusual action, to see that
over-straining of any one of the muscles of the giraffe's hind
quarters might quickly incapacitate the animal when putting
out all its powers to escape ; and to be a few yards behind
others would cause death. Hence if we are debarred from
assuming that co-operative parts vary together even when
adjacent and closely united — if we are still more debarred
from assuming that with increased length of fore-legs or
/of neck, there will go an appropriate change in any one
/ muscle or bone in the hind-quarters ; how entirely out of
! the question it is to assume that there will simultaneously
take place the appropriate changes in all those many
components of the hind-quarters which severally require
re-adjustment. It is useless to reply that an increment of
length in the fore-legs or neck might be retained and
transmitted to posterity, waiting an appropriate variation
in a particular bone or muscle in the hind-quarters, which,
being made, would allow of a further increment. For
besides the fact that until this secondary variation occurred
the primary variation would be a disadvantage often fatal;
and besides the fact that before such an appropriate
secondary variation might be expected in the course of
generations to occur, the primary variation would have
died out ; there is the fact that the appropriate variation of
one bone or muscle in the hind-quarters would be useless
j without appropriate variations of all the rest — some in
j this way and some in that — a number of appropriate
variations which it is impossible to suppose.

Nor is this all. Far more numerous appropriate varia
tions would be indirectly necessitated. The immense
change in the ratio of fore-quarters to hind-quarters would
make requisite a corresponding change of ratio in the
appliances carrying on the nutrition of the two. The
entire vascular system, arterial and veinous, would have to
undergo successive unbuildings and rebuildings to make its
channels everywhere adequate to the local requirements;

THE FACTOKS OP ORGANIC EVOLUTION. 17

since any want of adjustment in the blood-supply in this
or that set of muscles, would entail incapacity, failure of
speed, and loss of life. Moreover the nerves supplying the
various sets of muscles would have to be proportionately
changed ; as well as the central nervous tracts from which
they issued. Can we suppose that all these appropriate
changes, too, would be step by step simultaneously made
by_fortunate spontaneous variations, occurring along with
all the other fortunate spontaneous variations ? Consider
ing how immense must be the number of these required
changes, added to the changes above enumerated, the
chances against any adequate re-adjustments fortuitously
arising must be infinity to one.

If the effects of use and disuse of parts are inheritable,
then any change in the fore parts of the giraffe which
affects the action of the hind limbs and back, will simul
taneously cause, by the greater or less exercise of it, a
re-moulding of each component in the hind limbs and
back in a way adapted to the new demands; and generation
after generation the entire structure of the hind-quarters
will be progressively fitted to the changed structure of the
fore-quarters : all the appliances for nutrition and innerva-
tion being at the same time progressively fitted to both.
But in the absence of this inheritance of functionally-
produced modifications, there is no seeing how the required
re-adjustments can be made.

Yet a third class of difficulties stands in the way of the
belief that the natural selection of useful variations is the
sole factor of organic evolution. This class of difficulties,
already pointed out in § 166 of the Principles of Biology,
I cannot more clearly set forth than in the words there
used. Hence I may perhaps be excused for here quoting
them.

" Where the life is comparatively simple, or where surrounding circum
stances render some one function supremely important, the survival of the
fittest may readily bring about the appropriate structural change, without any

18 THE FACTORS OP ORGANIC EVOLUTION.

aid from the transmission of functionally-acquired modifications. But in
proportion as the life grows complex — in proportion as a healthy existence
cannot be secured by a large endowment of some one power, but demands
many powers ; in the same proportion do there arise obstacles to the increase
of any particular power, by " the preservation of favoured races in the
struggle for life." As fast as the faculties are multiplied, so fast does it
become possible for the several members of a species to have various kinds
of superiorities over one another. While one saves its life by higher speed,
another does the like by clearer vision, another by keener scent, another by
quicker hearing, another by greater strength, another by unusual power of
enduring cold or hunger, another by special sagacity, another by special
timidity, another by special courage ; and others by other bodily and mental
attributes. Now it is unquestionably true that, other things equal, each of
these attributes, giving its possessor an extra chance of life, is likely to be
transmitted to posterity. But there seems no reason to suppose that it will
be increased in subsequent generations by natural selection. That it may be
thus increased, the individuals not possessing more than average endow
ments of it, must be more frequently killed off than individuals highly
endowed with it ; and this can happen only when the attribute is one of
greater importance, for the time being, than most of the other attributes. If
those members of the species which have but ordinary shares of it, neverthe
less survive by virtue of other superiorities which they severally possess ;
then it is not easy to see how this particular attribute can be developed by
natural selection in subsequent generations. The probability seems rather
to be, that by gamogenesis, this extra endowment will, on the average, be
diminished in posterity— just serving in the long run to compensate the
deficient endowments of other individuals, whose special powers lie in other
directions ; and so to keep up the normal structure of the species. The
working out of the process is here somewhat difficult to follow ; but it appears
to me that as fast as the number of bodily and mental faculties increases,
and as fast as the maintenance of life comes to depend less on the amount
of any one, and more on the combined action of all ; so fast does the pro
duction of specialities of character by natural selection alone, become
difficult. Particularly does this seem to be so with a species so multitudinous
in its powers as mankind ; and above all does it seem to be so with such of
the human powers as have but minor shares in aiding the struggle for life —
the aesthetic faculties, for example."

Dwelling for a moment on this last illustration of the
class of difficulties described, let us ask how we are to
interpret the development of the musical faculty. I will
not enlarge on the family antecedents of the great com
posers. I will merely suggest the inquiry whether the
greater powers possessed by Beethoven and Mozart, by
Weber and Rossini, than by their fathers, were not due

THE FACTORS OP ORGANIC EVOLUTION. 19

in larger measure to the inherited effects of daily exercise
of the musical faculty by their fathers, than to inheritance,
with increase, of spontaneous variations ; and whether the
diffused musical powers of the Bach clan, culminating in
those of Johann Sebastian, did not result in part from
constant practice ; but I will raise the more general
question — How came there that endowment of musical
faculty which characterizes modern Europeans at large, as
compared with their remote ancestors. The monotonous
chants of low savages cannot be said to show any melodic
inspiration; and it is not evident that an individual
savage who had a little more musical perception than the
rest, would derive any such advantage in the maintenance
of life as would secure the spread of his superiority by
inheritance of the variation. And then what are we to
say of harmony ? We cannot suppose that the appreciation
of this, which is relatively modern, can have arisen by
descent from the men in whom successive variations
increased the appreciation of it — the composers and musical
performers ; for on the whole, these have been men whose
worldly prosperity was not such as enabled them to rear
many children inheriting their special traits. Even if we
count the illegitimate ones, the survivors of these added to
the survivors of the legitimate ones, can hardly be held to
have yielded more than average numbers of descendants ;
and those who inherited their special traits have not often
been thereby so aided in the struggle for existence as to
further the spread of such traits. Rather the tendency
seems to have been the reverse.

Since the above passage was written, I have found in the
second volume of Animals and Plants under Domestication,
a remark made by Mr. Darwin, practically implying
that among creatures which depend for their lives on the
efficiency of numerous powers, the increase of any one by
the natural selection of a variation is necessarily difficult.

Here it is.
3

20 THE FACTORS OF ORGANIC EVOLUTION.

" Finally, as indefinite and almost illimitable variability is the usual result
of domestication and cultivation, with the same part or organ varying in
different individuals in different or even in directly opposite ways ; and as
the same variation, if strongly pronounced, usually recurs only after long
intervals of time, any particular variation would generally be lost by
crossing, reversion, and the accidental destruction of the varying individuals,
unless carefully preserved by man." — Vol. ii, 292.

Remembering that mankind, subject as they are to this
domestication and cultivation, are not, like domesticated
animals, under an agency which picks out and preserves
particular variations ; it results that there must usually be
among them, under the influence of natural selection alone,
a continual disappearance of any useful variations of
particular faculties which may arise. Only in cases of
variations which are specially preservative, as for example,
great cunning during a relatively barbarous state, can we
expect increase from natural selection alone. We cannot
suppose that minor traits, exemplified among others by the
aesthetic perceptions, can have been evolved by natural
selection. But if there is inheritance of functionally-
produced modifications of structure, evolution of such minor
traits is no longer inexplicable.

Two remarks made by Mr. Darwin have implications
from which the same general conclusion must, I think, be
drawn. Speaking of the variability of animals and plants
under domestication, he says : —

"Changes of any kind in the conditions of life, even extremely slight
changes, often suffice to cause variability. . . Animals and plants continue
to be variable for an immense period after their first domestication ; . . .
In the course of time they can be habituated to certain changes, so as to
become less variable ; . . . There is good evidence that the power of
changed conditions accumulates ; so that two, three, or more generations
must be exposed to new conditions before any effect is visible. . . .
Some variations are induced by the direct action of the surrounding
conditions on the whole organization, or on certain parts alone, and other
variations are induced indirectly through the reproductive system being
affected in the same manner as is so common with organic beings when
removed from their natural conditions." — (Animals and Plants under
Domestication, vol. ii, 270.)

THE FACTORS OF ORGANIC EVOLUTION. 21

There are to be recognized two modes of this effect
produced by changed conditions on the reproductive system,
and consequently on offspring. Simple arrest of develop
ment is one. But beyond the variations of offspring arising
from imperfectly developed reproductive systems in parents
— variations which must be ordinarily in the nature of
imperfections — there are others due to a changed balance
of functions caused by changed conditions.' The fact noted
by Mr. Darwin in the above passage, " that the power of
changed conditions accumulates; so that two, three, or
more generations must be exposed to new conditions before
any effect is visible," implies that during these generations
there is going on some change of constitution consequent
on the changed proportions and relations of the functions.
I will not dwell on the implication, which seems tolerably
clear, that this change must consist of such modifications
of organs as adapt them to their changed functions ; and
that if the influence of changed conditions " accumulates,"
it must be through the inheritance of such modifications.
Nor will I press the question — What is the nature of the
effect registered in the reproductive elements, and which
is subsequently manifested by variations ? — Is it an effect
entirely irrelevant to the new requirements of tlue variety ?
— Or ?s it an effect which makes the variety less fit for the
new requirements ? — Or is it an effect which makes it more
fit for the new requirements? But not pressing these
questions, it suffices to point out the necessary implication
that changed functions of organs do, in some way or other,
register themselves in changed proclivities of the repro
ductive elements. In face of these facts it cannot be denied
that the modified action of a part produces an inheritable
effect — be the nature of that effect what it may.

The second of the remarks above adverted to as made
by Mr. Darwin, is contained in his sections dealing with
I correlated variations In the Oriyin of Species, p. 114,
he says — •

22 THE FACTORS OF OEQANIC EVOLUTION.

" The whole organization is so tied together during its growth and develop
ment, that when slight variations in any one part occur, and are accumu
lated through natural selection, other parts become modified."
And a parallel statement contained in Animals and Plants
under Domestication, vol. ii, p. 320, runs thus —
V/ '^Correlated variation is an important subject for us ; for when one part
is modified through continued selection, either by man or under nature,
other parts of the organization will be unavoidably modified. From this
correlation it apparently follows that, with our domesticated animals and
plants, varieties rarely or never differ from each other by some single
character alone."

v/ By what process does a changed part modify other
parts ? By modifying their functions in some way or
degree, seems the necessary answer. It is indeed, imagin
able, that where the part changed is some dermal appen
dage which, becoming larger, has abstracted more of the
needful material from the general stock, the effect may
consist simply in diminishing the amount of this material
available for other dermal appendages, leading to diminu
tion of some or all of them, and may fail to affect in
appreciable ways the rest of the organism : save perhaps
the blood-vessels near the enlarged appendage. But where
the part is an active one — a limb, or viscus, or any organ
which constantly demands blood, produces waste matter,
secretes, or absorbs — then all the other active organs
become implicated in the change. The functions per
formed by them have to constitute a moving equilibrium ;
and the function of one cannot, by alteration of the struc
ture performing it, be modified in degree or kind, without
modifying the functions of the rest — some appreciably and
others inappreciably, according to the directness or indi
rectness of their relations. Of such inter-dependent changes,1/
the normal ones are naturally inconspicuous; but those
which are partially or completely abnormal, sufficiently
carry home the general truth. Thus, unusual cerebral
excitement affects the excretion through the kidneys in
quantity or quality or both. Strong emotions of disagree
able kinds check or arrest the flow of bile. A considerable

THE FACTORS OF ORGANIC EVOLUTION. 23

obstacle to the circulation offered by some important
structure in a diseased or disordered state, throwing more
strain upon the heart, causes hypertrophy of its muscular
walls; and this change which is, so far as concerns the
primary evil, a remedial one, often entails mischiefs in
other organs. "Apoplexy and palsy, in a scarcely credible
number of cases, are directly dependent on hypertropic
enlargement of the heart." And in other cases, asthma,
dropsy, and epilepsy are caused. Now if a result of this
inter-dependence as seen in the individual organism, is that
a local modification of one part produces, by changing their
functions, correlative modifications of other parts, then the
question here to be put is — Are these correlative modifica
tions, when of a kind falling within normal limits, inheritable
or not. If they are inheritable, then the fact stated by Mr.
Darwin that " when one part is modified through continued
selection," " other parts of the organization will be una
voidably modified" is perfectly intelligible : these entailed
secondary modifications are transmitted pari passu with the
successive modifications produced by selection. But what if
they are not inheritable ? Then these secondary modifications
caused in the individual, not being transmitted to descend
ants, the descendants must commence life with organiza
tions out of balance, and with each increment of change
in the part affected by selection, their organizations must
get more out of balance — must have a larger and larger
amounts of re-organization to be made during their lives.
Hence the constitution of the variety must become more
and more unworkable.

The only imaginable alternative is that the re-adjust-
ments are effected in course of time by natural selection.
But, in the first place, as we find no proof of concomitant
variation among directly co-operative parts which are
closely united, there cannot be assumed any concomitant
variation among parts which are both indirectly co-opera
tive and far from one another. And, in the second place,

24 THE FACTORS OF ORGANIC EVOLUTION.

before all the many required re-adjustments could be made,
the variety would die out from defective constitution.
Even were there no such difficulty, we should still have to
entertain a strange group of propositions, which would
stand as follows : — 1. Change in one part entails, by
reaction on the organism, changes, in other parts, the func
tions of which are necessarily changed. 2. Such changes
worked in the individual, affect, in some way, the repro
ductive elements : these being found to evolve unusual
structures when the constitutional balance has been con
tinuously disturbed. 3. But the changes in the reproduc
tive elements thus caused, are not such as represent these
functionally-produced changes : the modifications conveyed
to offspring are irrelevant to these various modifications
functionally produced in the organs of the parents. 4.
Nevertheless, while the balance of functions cannot be re
established through inheritance of the effects of disturbed
functions on structures, wrought throughout the individual
organism; it can be re-established by the inheritance
of fortuitous variations which occur in all the affected
organs without reference to these changes of function.

Now without saying that acceptance of this group of
propositions is impossible, we may certainly say that it is
not easy.

" But where are the direct proofs that inheritance of
functionally-produced modifications takes place?" is a
question which will be put by those who have committed
themselves to the current exclusive interpretation. " Grant
that there are difficulties ; still, before the transmitted
effects of use and disuse can be legitimately assigned in
explanation of them, we must have good evidence that the
effects of use and disuse are transmitted."

Before dealing directly with this demurrer, let me deal
with it indirectly, by pointing out that the lack of recog
nized evidence may be accounted for without assuming

THE FACTORS OF ORGANIC EVOLUTION. 25

that there is not plenty of it. Inattention and reluctant
attention lead to the ignoring of facts which really exist in
abundance ; as is well illustrated in the case of pre-historic
implements. Biassed by the current belief that no traces
of man were to be found on the Earth's surface, save in
certain superficial formations of very recent date, geologists
and anthropologists not only neglected to seek such traces,
but for a long time continued to pooh-pooh those who said
they had found them. When M. Boucher de Perthes at
length succeeded in drawing the eyes of scientific men to
the flint implements discovered by him in the quarternary
deposits of the Somme valley; and when geologists and
anthropologists had thus been convinced that evidences
of human existence were to be found in formations of
considerable age, and thereafter began to search for them ;
they found plenty of them all over the world. Or again,
to take an instance closely germane to the matter, we may
recall the fact that the contemptuous attitude towards
the hypothesis of organic evolution which naturalists in
general maintained before the publication of Mr. Darwin's
work, prevented them from seeing the multitudinous facts
by_ which^ it_ia^.^upp.orted. Similarly, it is very possible
that their alienation from the belief that there is a trans- /
mission of those changes of structure which are produced
by changes of action, makes naturalists slight the evidence
which supports that belief and refuse to occupy themselves
in seeking further evidence.

If it be asked how it happens that there have been
recorded multitudinous instances of variations fortuitously
arising and re-appearing in offspring, while there have not
been recorded instances of the transmission of changes
functionally produced, there are three replies. The first
is that changes of the one class are many of them con
spicuous, while those of the other class are nearly all
inconspicuous. If a child is born with six fingers, the
anomaly is not simply obvious but so startling as to attract

26 TEE FACTORS OF ORGANIC EVOLUTION.

much notice ; and if this child, growing up, has six-
fingered descendents, everybody in the locality hears of
it. A pigeon with specially-coloured feathers, or one
distinguished by a broadened and upraised tail, or by a
protuberance of the neck, draws attention by its oddness ;
and if in its young the trait is repeated, occasionally with
increase, the fact is remarked, and there follows the thought
of establishing the peculiarity by selection. A lamb dis
abled from leaping by the shortness of its legs, could not
fail to be observed; and the fact that its offspring were
similarly short-legged, and had a consequent inability to
get over fences, would inevitably become widely known.
Similarly with plants. That this flower had an extra
number of petals, that that was unusually symmetrical,
and that another differed considerably in colour from the
average of its kind, would be easily seen by an observant
gardener; and the suspicion that such anomalies are
inheritable having arisen, experiments leading to further
proofs that they are so, would frequently be made. JBut it.
is not thus with functionally-produced modifications. Tho
seats of these are in nearly all cases the muscular, osseous,
and nervous systems, and the viscera — parts which are
either entirely hidden or greatly obscured. Modification
in a nervous centre is inaccessible to vision ; bones may be
considerably altered in size or shape without attention
being drawn to them; and, covered with thick coats as
are most of the animals open to continuous observation, tho
increases or decreases in muscles must be great before they
become externally perceptible.

A further important difference between the two inquiries
is that to ascertain whether a fortuitous variation is
inheritable, needs merely a little attention to the selection
of individuals and the observation of offspring; while to
ascertain whether there is inheritance of a functionally-
produced modification, it is requisite to make arrangements
which demand the greater or smaller exercise of some part

THE PACTOES OF ORGANIC EVOLUTION. 27

or parts; and it is difficult in many cases to find such
arrangements, troublesome to maintain them even for one
generation, and still more through successive generations.

Nor is this all. There exist stimuli to inquiry in the one
case which do not exist in the other. The money-interest
and the interest of the fancier, acting now separately and
now together, have prompted multitudinous individuals to
make experiments which have brought out clear evidence
that fortuitous variations are inherited. The cattle-breeders
who profit by producing certain shapes and qualities ; the
keepers of pet animals who take pride in the perfections
of those they have bred; the florists, professional and
amateur, who obtain new varieties and take prizes ; form a
body of men who furnish naturalists with countless of the
required proofs. But there is no such body of men, led
either by pecuniary interest or the interest of a hobby, to
ascertain by experiments whether the effects of use and
disuse are inheritable.

Thus, then, there are amply sufficient reasons why there
is a great deal of direct evidence in the one case and but
little in the other : such little being that which comes out
incidentally. Let us look at what there is of it.

Considerable weight attaches to a fact which Brown-
Sequard discovered, quite by accident, in the course of
his researches. He found that certain artificially-produced
lesions of the nervous system, so small even as a section of
the sciatic nerve, left, after healing, an increasing excit
ability which ended in liability to epilepsy; and there
afterwards came out the unlooked-for result that the
offspring of guinea-pigs which had thus acquired an
epileptic habit such that a pinch on the neck would produce
a fit, inherited an epileptic habit of like kind. It has,
indeed, been since alleged that guinea pigs tend to epilepsy,
and that phenomena of the kind described, occur where
there have been no antecedents like those in Brown-

23 THE FACTORS OP OEGANIC EVOLUTION.

Sequard's case. But considering the improbability that
the phenomena observed by him happened to be nothing
more than phenomena which occasionally arise naturally,
we may, until there is good proof to the contrary, assign
some -value to his results.

Evidence not of this directly experimental kind, but
nevertheless of considerable weight, is furnished by other
nervous disorders. There is proof enough that insanity
admits of being induced by circumstances which, in one or
other way, derange the nervous functions — excesses of this
or that kind; and no one questions the accepted belief
that insanity is inheritable. Is it alleged that the insanity
which is inheritable is that which spontaneously arises, and
that the insanity which follows some chronic perversion of
functions is not inheritable ? This does not seem a very
reasonable allegation ; and until some warrant for it is
forthcoming, we may fairly assume that there is here a
further support for belief in the transmission of functionally-
produced changes.

Moreover, I find among physicians the belief that
nervous disorders of a less severe kind are inheritable.
Men who have prostrated their nervous systems by prolonged
overwork or in some other way, have children more or less
prone to nervousness. It matters not what may be the
form of inheritance — whether it be of a brain in some way
imperfect, or of a deficient blood-supply ; it is in any caso
the inheritance of functionally-modified structures.

Verification of the reasons above given for the paucity
of this direct evidence, is yielded by contemplation of it ;
for it is observable that the cases named are cases which,
from one or other cause, have thrust themselves on
observation. They justify the suspicion that it is not
"because such cases are rare that many of them cannot be
cited ; Imfc simply because they are mostly unobtrusive, and
to be found only by that deliberate search which nobody
makes. I say nobody, but I am wrong. Successful search

THE FACTORS OP ORGANIC EVOLUTION. 29

has been made by one whose competence as an observer is
beyond question, and whose testimony is less liable than
that of all others to any bias towards the conclusion that
such inheritance takes place. I refer to the author of
the Origin of Species.

Now-a-dayjj_.most naturalists are more Darwinian than
MrrParwrfl frrmpplf- I do not mean that their beliefs in
organic evolution are more decided ; though I shall be
supposed to mean this by the mass of readers, who identify
Mr. Darwin's great contribution to the theory of organic
evolution, with the theory of organic evolution itself, and
even with the theory of evolution at large. But I mean
that the particular factor which he first recognized as
having played so immense a part in organic evolution, has r
come to be regarded by his followers as the sole factor, |
though it was not so regarded by him. It is true that he
apparently rejected altogether the causal agencies alleged
by earlier inquirers. In the Historical Sketch prefixed to
the later editions of his Origin of Species (p. xiv, note),
he writes : — " It is curious how largely my grandfather,
Dr. Erasmus Darwin, anticipated the views and erroneous
grounds of opinion of Lamarck in his f Zoonomia ' (vol. i,
pp. 500-510), published in 1794." And since, among the
views thus referred to, was the view that changes of
structure in organisms arise by the inheritance of function
ally-produced changes, Mr. Darwin seems, by the above
sentence, to have implied his disbelief in such inheritance.
But he did not mean to imply this; for his belief in it as (,
a cause of evolution, if not an important cause, is proved
by many passages in his works. In the first chapter of
the Origin of Species (p. 11 of the first edition), he says '••
respecting the inherited effects of habit, that "with
animals the increased use or disuse of parts has had a
marked influence ; " and he gives as instances the changed
relative weights of the wing bones and leg bones of the

30 THE FACTORS OP ORGANIC EVOLUTION.

wild duck and the domestic duck, " the great and inher
ited development of the udders in cows and goats," and
the drooping ears of various domestic animals. Here are
other passages taken from the latest edition of the work.

" I think there can be no doubt that use in our domestic animals has
strengthened and enlarged certain parts, and disuse diminished them ; and
that such modifications are inherited " (p. 108). [And on the following
pages he gives five further examples of such effects.] " Habit in producing
constitutional peculiarities and use in strengthening and disuse in weaken
ing and diminishing organs, appear in many cases to have been potent in
their effects " (p. 131). '* When discussing special cases, Mr. Mivart passes
over the effects of the increased use and disuse of parts, which I have
always maintained to be highly important, and have treated in my ' Varia
tion under Domestication ' at greater length than, as I believe, any other
writer " (p. 176). " Disuse, on the other hand, will account for the less
developed condition of the whole inferior half of the body, including the
lateral fins " (p. 188). "1 may give another instance of a structure which
apparently owes its origin exclusively to use or habit " (p. 188). " It
appears probable that disuse has been the main agent in rendering organs
rudimentary " (pp. 400 — 401). " On the whole, we may conclude that habit,
or use and disuse, have, in some cases, played a considerable part in the
modification of the constitution and structure ; but that the effects have
often been largely combined with, and sometimes overmastered by, the
natural selection of innate variations " (p. 114).

In his subsequent work, The Variation of Animals and
Plants under Domestication, where he goes into full detail,
Mr. Darwin gives more numerous illustrations of the
inherited effects of use and disuse. The following are some
of the cases, quoted from volume i of the first edition.

Treating of domesticated rabbits, he says: — "the want of exercise has
apparently modified the proportional length of the limbs in comparison with
the body " (p. 116). " We thus see that the most important and complicated
organ [the brain] in the whole organization is subject to the law of decrease
in size from disuse " (p. 129). He remarks that in birds of the oceanic
islands " not persecuted by any enemies, the reduction of their wings has
probably been caused by gradual disuse." After comparing one of these, the
water-hen of Tristan d'Acunha, with the European water-hen, and showing
that all the bones concerned in flight are smaller, he adds — " Hence in the
skeleton of this natural species nearly the same changes have occurred, only
carried a little further, as with our domestic ducks, and in this latter case I
presume no one will dispute that they have resulted from the lessened use of
the wings and the increased use of the legs " (pp. 286-7). "As with other
long-domesticated animals, the instincts of the silk-moth have suffered. The

THE PACTOES OP ORGANIC EVOLUTION. 31

caterpillars, when placed on a mulberry-tree, often commit the strange mis
take of devouring the base of the leaf on which they are feeding, and
consequently fall down ; but they are capable, according to M. Eobinet, of
again crawling up the trunk. Even this capacity sometimes fails, for
M. Martins placed some caterpillars on a tree, and those which fell were
not able to remount and perished of hunger ; they were even incapable of
passing from leaf to leaf " (p. 304).

Here are some instances of like meaning from volume ii.

" In many cases there is reason to believe that the lessened use of various
organs has affected the corresponding parts in the offspring. But there is no
good evidence that this ever follows in the course of a single generation. . .
Our domestic fowls, ducks, and geese have almost lost, not only in the
individual but in the race, their power of flight ; for we do not see a chicken,
when frightened, take flight like a young pheasant. . . . With domestic
pigeons, the length of the sternum, the prominence of its crest, the length of
the scapulae and f urcula, the length of the wings as measured from tip to tip
of the radius, are all reduced relatively to the same parts in the wild pigeon."
[After detailing kindred diminutions in fowls and ducks, Mr. Darwin adds]
" The decreased weight and size of the bones, in the foregoing cases, is
probably the indirect result of the reaction of the weakened muscles on the
bones" (pp. 297-8). " Nathusius has shown that, with the improved races
of the pig, the shortened legs and snout, the form of the articular condyles of
the occiput, and the position of the jaws with the upper canine teeth pro
jecting in a most anomalous manner in front of the lower canines, may be
attributed to these parts not having been fully exercised. . . . These modi
fications of structure, which are all strictly inherited, characterise several
improved breeds, so that they cannot have been derived from any single
domestic or wild stock. With respect to cattle, Professor Tanner has
remarked that the lungs and liver in the improved breeds ' are found to be
considerably reduced in size when compared with those possessed by animals
having perfect liberty ;' . . . The cause of the reduced lungs in highly-bred
animals which take little exercise is obvious" (pp. 299-300). [And on pp.
301, 302 and 303, he gives facts showing the effects of use and disuse in
changing, among domestic animals, the characters of the ears, the lengths
of the intestines, and, in various ways, the natures of the instincts.]

But Mr. Darwin's admission, or rather his assertion,
that the inheritance of functionally-produced modifications
has been a factor in organic evolution, is made clear not
by these passages alone and by kindred ones. It is made
clearer still by a passage in the preface to the second edition
of his Descent of Man. He there protests against that
current version of his views in which this factor makes no
appearance. The passage is as follows.

\\

r

32 THE FACTORS OF ORGANIC EVOLUTION.

" I may take this opportunity of remarking that my critics frequently
assume that I attribute all changes of corporeal structure and mental power
exclusively to the natural selection of such variations as are often called
spontaneous ; whereas, even in the first edition of the ' Origin of Species,' I
distinctly stated that great weight must be attributed to the inherited effects
of use and disuse, with respect both to the body and mind."

Nor is this all. There is evidence that Mr. Darwin's
belief in the efficiency of this factor, became stronger as he
grew older and accumulated more evidence. The first of
the extracts above given, taken from the sixth edition of the
Origin of Species, runs thus : —

"I think there can be no doubt that use in our domestic animals bas
strengthened and enlarged certain parts, and disuse diminished them ; and
that such modifications are inherited."

Now on turning to the first edition, p. 134, it will be
found that instead of the words — " I think there can be no
doubt," the words originally used were — "I think there
can be little doubt." That this deliberate erasure of
a qualifying word and substitution of a word implying
unqualified belief, was due to a more decided recognition of
a factor originally under-estimated, is clearly implied by the
wording of the above-quoted passage from 'the preface to
the Descent of Han ; where he says that " even in the first
edition of the ' Origin of Species/ " &c. : the implication
being that much more in subsequent editions, and subsequent
works, had he insisted on this factor. The change thus
indicated is especially significant as having occurred at
a time of life when the natural tendency is towards fixity
of opinion.

During that earlier period when he was discovering the
multitudinous cases in which his own hypothesis afforded
solutions, and simultaneously observing how utterly futile
in these multitudinous cases was the hypothesis pro
pounded by his grandfather and Lamarck, Mr. Darwin
was, not unnaturally, almost betrayed into the belief that
the one is all-sufficient and the other inoperative. But
in the mind of one so candid and ever open to more
evidence, there naturally came a reaction. The inheritance

THE FACTORS OF ORGANIC EVOLUTION. 33

of functionally-produced modifications, which, judging by
the passage quoted above concerning the views of these
earlier enquirers, would seem to 'have been at one time
denied, but which as we have seen was always to some'!
extent recognized, came to be recognized more and more, )
and deliberately included as a factor of importance.

Of this reaction displayed in the later writings of Mr.
Darwin, let us now ask — Has it not to be carried further ?
Was the share in organic evolution which Mr. Darwin
latterly assigned to the transmission of modifications caused
by use and disuse, its due share ? Consideration of the
groups of evidences given above, will, I think, lead us
to believe that its share has been much larger than he
supposed even in his later days.

There is first the implication yielded by extensive
classes of phenomena which remain inexplicable in tho
absence of this factor. If, as we see, co-operative parts do
not vary together, even when few and close together, and
may not therefore be assumed to do so when many and
remote, we cannot account for those innumerable changes
in organization which are implied when, for advantageous
use of some modified part, many other parts which join it
in action have to be modified.

Further, as increasing complexity of structure, accom
panying increasing complexity of life, implies increasing
number of faculties, of which each one conduces to preserva
tion of self or descendants ; and as the various individuals
of a species, severally requiring something like the normal
amounts of all these, may individually profit, here by an
unusual amount of one_,_and jthere by an unusual amount of
another^ it f ollows~ikat as the number of faculties becomes
greater, it becomes more difficult for any one to be further
developed by natural selection. Only where increase of
some one is predominantly advantageous does the means
seem adequate to the end. Especially in the case of

34 THE FACTORS OP ORGANIC EVOLUTION.

powers which do not subserve self-preservation in appreci
able degrees, does development by natural selection appear
impracticable.

It is a fact recognized by Mr. Darwin, that where, by
selection through successive generations, a part has been
increased or decreased, its reaction upon other parts
entails changes in them. This reaction is effected through
the changes of function involved. If the changes of
structure produced by such changes of function, are
inheritable, then the re-adjustment of parts throughout the
organism, taking place generation after generation, main
tains an approximate balance ; but if not, then generation
after generation the organism must get more and more out
of gear, and tend to become unworkable.

Further, as it is proved that change in the balance of
functions registers its effects on the reproductive elements,
we have to choose between the alternatives that the regis
tered effects are irrelevant to the particular modifications
which the organism has undergone, or that they are such
as tend to produce repetitions of these modifications. The
last of these alternatives makes the facts comprehensible ;
but the first of them not only leaves us with several
unsolved problems, but is incongruous with the general
truth that by reproduction, ancestral traits, down to minute
details, are transmitted.

Though, in the absence of pecuniary interests and the
interests in hobbies, no such special experiments as those
which have established the inheritance of fortuitous varia
tions have been made to ascertain whether functionally-
produced modifications are inherited ; yet certain apparent
instances of such inheritance have forced themselves on
observation without being sought for. In addition to
ether indications of a less conspicuous kind, is the one I
have given above — the fact that the apparatus for tearing
and mastication has decreased with decrease of its function,
alike in civilized man and in some varieties of dogs which

THE FACTORS OF ORGANIC EVOLUTION. 35

lead protected and pampered lives. Of the numerous cases
named by Mr. Darwin, it is observable that they are
yielded not by one class of parts only, but by most if not
all classes — by the dermal system, the muscular system, the
osseous system, the nervous system, the viscera ; and that
among parts liable to be functionally modified, the most
numerous observed cases of inheritance are furnished by
those which admit of preservation and easy comparison —
the bones : these cases, moreover, being specially signifi
cant as showing how, in sundry unallied species, parallel
changes of structure have occurred along with parallel
changes of habit.

What, then, shall we say of the general implication ?
Are we to stop short with the admission that inheritance
of functionally-produced modifications takes place only in
cases in which there is evidence of it ? May we properly
assume that these many instances of changes of structure
caused by changes of function, occurring in various tissues
and various organs, are merely special and exceptional
instances having no general significance ? Shall wTe
suppose that though the evidence which already exists
has come to light without aid from a body of inquirers,
there would be no great increase were due attention
devoted to the collection of evidence ? This is, I think,
not a reasonable supposition. To me the ensemble of the
facts suggests the belief, scarcely to be resisted, that the
. / inheritance of functionally-produced modifications takes
place [universally. Looking at physiological phenomena as
conforming to physical principles, it is difficult to conceive
that a changed play of organic forces which in many
cases of different kinds produces an inherited change of
atrnfitnrftj dnpa not fin f/hjs in all oases. The implication,
very strong I think, is that the action of every organ
produces on it a reaction which, usually not altering its
rate of nutrition, sometimes leaves it with diminished
nutrition consequent on diminished action, and at other

86 THE FACTORS OP ORGANIC EVOLUTION.

times increases its nutrition in proportion to its increased
action ; that while generating a modified consensus of
functions and of structures, the activities are at the same
time impressing this modified consensus on the sperm-cells
and germ-cells whence future individuals are to be pro
duced ; and that in ways mostly too small to be identified,
but occasionally in more conspicuous ways and in the
course of generations, the resulting modifications of one or
other kind show themselves. Further, it seems to me that
as there are certain extensive classes of phenomena which
are inexplicable if we assume the inheritance of fortuitous
variations to be the sole factor, but which become at once
explicable if we admit the inheritance of functionally-pro
duced changes, we are justified in concluding that this
inheritance of functionally-produced changes has been not
simply a co-operating factor in organic evolution, but has
been a co-operating factor without which organic evolu
tion, in its higher forms at any rate, could never have
taken place.

Be this or be it not a warrantable conclusion, there is,
I think, good reason for a provisional acceptance of the
hypothesis that the effects of use and disuse are inheritable j
and for a methodic pursuit of inquiries with the view of either
establishing it or disproving it. It seems scarcely reasonable
to accept without clear demonstration, the belief that while
a trivial difference of structure arising spontaneously is
transmissible, a massive difference of structure, main
tained generation after generation by change of function,
leaves no trace in posterity. Considering that unquestionably
the modification of structure by function is a vera causa,
in so far as concerns the individual ; and considering
the number of facts which so competent an observer as
Mr. Darwin regarded as evidence that transmission of
such modifications takes place in particular cases ; the
hypothesis that such transmission takes place in con
formity with a general law, holding of all active structures,

THE FACTORS OF ORGANIC EVOLUTION. 37

should, I think, be regarded as at least a good working
hypothesis.

But now supposing the broad conclusion above drawn to
be granted — supposing all to agree that from the beginning,
along with inheritance of useful variations fortuitously
arising, there has been inheritance of effects produced by
use and disuse; do there remain no classes of organic
phenomena unaccounted for ? To this question I think it
must be replied that there do remain classes of organic
phenomena unaccounted for. It may, I believe, be shown
that certain cardinal traits of animals and plants at large
are still unexplained; and that a further factor must
be recognized. To show this, however, will require
another paper.

II.

Ask a plumber who is repairing your pump, how the
water is raised in it, and he replies — " By suction." Recall
ing the ability which he has to suck up water into his
mouth through a tube, he is certain that he understands
the pump's action. To inquire what he means by suction,
seems to him absurd. He says you know as well as he
does, what he means ; and he cannot see that there is any
need for asking how it happens that the water rises in the
tube when he strains his mouth in a particular way. To
the question why the pump, acting by suction, will not
make the water rise above 32 feet, and practically not so
much, he can give no answer; but this does not shake his
confidence in his explanation.

On the other hand an inquirer who insists on knowing
what suction is, may obtain from the physicist answers
which give him clear ideas, not only about it but about
many other things. He learns that on ourselves and all

88 THE FACTORS OF ORGANIC EVOLUTION.

things around, there is an atmospheric pressure amounting
to about 15 pounds on the square inch : 15 pounds being
the average weight of a column of air having a square inch
for its base and extending upwards from the sea-level to
the limit of the Earth's atmosphere. He is made to observe
that when he puts one end of a tube into water and the
other end into his mouth, and then draws back his tongue,
so leaving a vacant space, two things happen. One is that
the pressure of air outside his cheeks, no longer balanced
by an equal pressure of air inside, thrusts his cheeks
inwards; and the other is that the pressure of air on
the surface of the water, no longer balanced by an equal
pressure of air within the tube and his mouth (into which
part of the air from the tube has gone) the water is forced
up the tube in consequence of the unequal pressure. Once
understanding thus the nature of the so-called suction,
he sees how it happens that when the plunger of the pump
is raised and relieves from atmospheric pressure the water
below it, the atmospheric pressure on the water in the well,
not being balanced by that on the water in the tube, forces
the water higher up the tube, so that it follows the plunger.
And now he sees why the water cannot be raised beyond
the theoretic limit of 32 feet: a limit made much lower
in practice by imperfections in the apparatus. For if,
simplifying the conception, he supposes the tube of the
pump to be a square inch in section, then the atmospheric
pressure of 15 pounds per square inch on the water in the
well, can raise the water in the tube to such height only
that the entire column of it weighs 15 pounds. Having
been thus enlightened about the pump's action, the action
of a barometer becomes intelligible. He perceives how,
under the conditions established, the weight of the column
of mercury balances that of an atmospheric column of
equal diameter ; and how, as the weight of the atmospheric
column varies, there is a corresponding variation in the
weight of the mercurial column, — shown by change of

THE FACTORS OP OKGANIC EVOLUTION. 39

height. Moreover, having previously supposed that he
understood the ascent of a balloon when he ascribed it to
relative lightness, he now sees that he did not truly under
stand it. For he did not recognize it as a result of that
upward pressure caused by the difference between the
weight of the mass formed by the gas in the balloon phis
the cylindrical column of air extending above it to the limit
of the atmosphere, and the weight of a similar cylindrical
column of air extending down to the under surface of the
balloon : this difference of weight causing an equivalent
upward pressure on the under surface.

Why do I introduce these familiar truths so entirely irre
levant to my subject ? I do it to show, in the first place,
the contrast between a vague conception of a cause and a
distinct conception of it; or rather, the contrast between
that conception of a cause which results when it is simply
classed with some other or others which familiarity makes
us think we understand, and that conception of a cause
which results when it is represented in terms of definite
physical forces admitting of measurement. And I do it to
show, in the second place, that when we insist on resolving
a verbally-intelligible cause into its actual factors, we
get not only a clear solution of the problem before us, but
we find that the way is opened to solutions of sundry other
problems. While we rest satisfied with unanalyzed causes,
we may be sure both that we do not rightly comprehend the
production of the particular effects ascribed to them, and
that we overlook other effects which would be revealed
to us by contemplation of the causes as analyzed? Espe
cially must this be so where the causation is complex.
Hence we may infer that the phenomena presented by
the development of species, are not likely to be truly
conceived unless we keep in view the concrete agencies;) at
work. Let us look closely at the facts to be dealt with.

The growth of a thing is effected by the joint operation

40 THE FACTORS OP ORGANIC EVOLUTION.

of certain forces on certain materials ; and when it dwindles,
there is either a lack of some materials, or the forces co
operate in a way different from that which produces growth.
If a structure has varied, the implication is that the processes
which built it up were made unlike the parallel processes
in other cases, by the greater or less amount of some one or
more of the matters or actions concerned. Where there
is unusual fertility, the play of vital activities is thereby
shown to have deviated from the ordinary play of vital
activities ; and conversely, if there is infertility. If the
germs, or ova, or seed, or offspring partially developed,
survive more or survive less, it is either because their
molar or molecular structures are unlike the average ones,
or because they are affected in unlike ways by surrounding
agencies. When life is prolonged, the fact implies that
the combination of actions, visible and invisible, consti
tuting life, retains its equilibrium longer than usual in
presence of environing forces which tend to destroy its
equilibrium. That is to say, growth, variation, survival,
death, if they are to be reduced to the forms in which
physical science can recognize them, must be expressed
as effects of agencies definitely conceived — mechanical
forces, light, heat, chemical affinity, &c.

This general conclusion brings with it the thought that
the phrases employed in discussing organic evolution,
though convenient and indeed needful, are liable to mislead
us by veiling the actual agencies. That which really goes
on in every organism is the working together of component
parts in ways conducing to the continuance of their com
bined actions, in presence of things and actions outside ;
some of which tend to subserve, and others to destroy, the
combination. The matters and forces in these two groups,
are the sole causes properly so called. The words "natu
ral selection," do not express a cause in thefphysical sense/1
They express a mode of co-operation among causes— or
rather, to speak strictly, they express an effect of this>'

THE FACTORS OP ORGANIC EVOLUTION. 41

mode of co-operation. The idea they convey seems perfectly
intelligible. Natural selection having been compared with
artificial selection, and the analogy pointed out,, there
apparently remains no indefmiteness : the inconvenience
being, however, that the definiteness is of a wrong kind.
The tacitly implied Nature which selects, is not an em
bodied agency analogous to the man who selects artificially ;
and the selection is not the picking out of an individual
fixed on, but the overthrowing of many individuals by
agencies which one successfully resists, and hence con
tinues to live and multiply. Mr. Darwin was conscious
of these misleading implications. In the introduction to his
Animals and Plants under Domestication (p. 6) he says : —
" For brevity sake I sometimes speak of natural selection as an intelligent
power ; . . . I have, also, often personified the word Nature ; for I have
found it difficult to avoid this ambiguity ; but I mean by nature only the
aggregate action and product of many natural laws, — and by laws only the
ascertained sequence of events."

But while he thus clearly saw, and distinctly asserted,
that the factors of organic evolution are the concrete
actions, inner and outer, to which every organism is
subject, Mr. Darwin, by habitually using the convenient
figure of speech, was, I think, prevented from recognizing
so fully as he would otherwise have done, certain funda
mental consequences of these actions.

Though it does not personalize the cause, and does not
assimilate its mode of working to a human mode of wrork-
ing, kindred objections may be urged against the expression
to which I was led when seeking to present the phenomena
in literal terms rather than metaphorical terms — the sur-
vival of the fittest;* for in a vague way the first word,
and in a clear way the second word, calls up an anthro-

* Though Mr. Darwin approved of this expression and occasionally
employed it, he did not adopt it for general use ; contending, very truly,
that the expression Natural Selection is in some cases more convenient.
See Animals and Plants under Domestication (first edition) Vol. i, p. G ; and
Origin of Species (sixth edition) p. 49.

THE FACTOKS OP ORGANIC EVOLUTION.

pocentric idea. The thought of survival inevitably suggests
the human view of certain sets of phenomena, rather than
that character which they have simply as groups of
changes. If, asking what we really know of a plant, we
exclude all the ideas associated with the words life and
death, we find that the sole facts known to us are that
there go on in the plant certain inter-dependent processes,
in presence of certain aiding and hindering influences out
side of it ; and that in some cases a difference of structure
or a favourable set of circumstances, allows these inter
dependent processes to go on for longer periods than in
other cases. Again, in the working together of those many
actions, internal and external, which determine the lives
or deaths of organisms, we see nothing to which the words
fitness and unfitness are applicable in the physical sense.
If a key fits a lock, or a glove a hand, the relation of the
things to one another is presentable to the perceptions.
No approach to fitness of this kind is made by an organism
which continues to live under certain conditions. Neither
the organic structures themselves, nor their individual
movements, nor those combined movements of certain
among them which constitute conduct, are related in any
analogous way to the things and actions in the environ
ment. Evidently the word fittest, as thus used, is a figure
of speech; suggesting the fact that amid surrounding
actions, an organism characterized by the word has either
a greater ability than others of its kind to maintain the
equilibrium of its vital activities, or else has so much
greater a power of multiplication that though not longer
lived than they, it continues to live in posterity more
persistently. And indeed, as we here see, the word fittest
has to cover cases in which there may be less ability than
usual to survive individually, but in which the defect is
more than made good by higher degrees of fertility.

I have elaborated this criticism with the intention of
emphasizing the need for studying the gfagflges)which have

THE FACTOES OF ORGANIC EVOLUTION. 43

gone on, and are ever going on, in organic bodies, from an
^sij^ly^phjsical^ poin t_pf.jdew. On contemplating the
facts from this point of view, we become aware that,
besides those special effects of the co-operating forces
which eventuate in the longer survival of one individual
than of others, and in the consequent increase through
generations, of some trait which furthered its survival,
many other effects are being wrought on each and all
of the individuals. Bodies of every class and quality,
inorganic as well as organic, are from instant to instant
subject to the influences in their environments; are
from instant to instant being changed by these in ways
that are mostly inconspicuous; and are in course of time
changed by them in conspicuous ways. Living things in
common with dead things, are, I say, being thus perpetu
ally acted upon and modified; and the changes hence
resulting, constitute an all-important part of those under
gone in the course of organic evolution. I do not mean to
imply that changes of this class pass entirely unrecognized ;
for, as we shall see, Mr. Darwin takes cognizance of certain
secondary and special ones. But the effects which are not
taken into account, are those primary and universal effects
which give certain fundamental characters to all organisms.
Contemplation of an analogy will best prepare the way for
appreciation of them, and of the relation they bear to those
which at present monopolize attention.

An observant rambler along shores, will, here and there,
note places where the sea has deposited things more or less
similar, and separated them from dissimilar things — will
see shingle parted from sand; larger stones sorted from
smaller stones; and will occasionally discover deposits of
shells more or less worn by being tolled about. Sometimes
the pebbles or boulders composing the shingle at one end
of a bay, he will find much larger than those at the
other : intermediate sizes, having small average differences,

occupying the space between the extremes. An example
5

44 THE FACTORS OP ORGANIC EVOLUTION.

occurs, if I remember rightly, some mile or two to the
west of Tenby ; but the most remarkable and well-known
example is that afforded by the Chesil bank. Here, along
a shore some sixteen miles long, there is a gradual in
crease in the sizes of the stones; which, being at one end
but mere pebbles, are at the other end immense boulders.
In this case, then, the breakers and the undertow have
effected a selection — have at each place left behind those
"tones which were too large to be readily moved, while
taking away others small enough to be moved easily. But
now, if we contemplate exclusively this selective action of
the sea, we overlook certain important effects which the
sea simultaneously works. While the stones have been
differently acted upon in so far that some have been left
here and some carried there; they have been similarly
acted upon in two allied, but distinguishable, ways. By
perpetually rolling them about and knocking them one
against another, the waves have so broken off their most
prominent parts as to produce in all of them more or less
rounded forms; and then, further, the mutual friction
of the stones simultaneously caused, has smoothed their
surfaces. That is to say in general terms, the actions of
environing agencies, so far as they have operated indiscri
minately, have produced in the stones a certain unity of
character; at the same time that they have, by their
differential effects, separated them : the Jarger ones having
withstood certain violent actions which the smaller ones
could not withstand.

Similarly with other assemblages of objects which are
alike in their primary traits but unlike in their secondary
traits. When simultaneously exposed to the same set of
actions, some of these actions, rising to a certain intensity,
may be expected to work on particular members of the
assemblage changes which they cannot work in those which
are markedly unlike ; while others of the actions will work
in all of them similar changes, because of the uniform

THE FACTORS OF OEQANIC EVOLUTION. 45

relations between these actions and certain attributes
common to all members of the assemblage. Hence it is
inferable that on living organisms, which form an assem
blage of this kind, and are unceasingly exposed in common
to the agencies composing their inorganic environments,
there must be wrought two such sets of effects. There
will result a universal likeness among them consequent on
the likeness of their respective relations to the matters
and forces around ; and there will result, in some cases, the
differences due to the differential effects of these matters
and forces, and in other cases, the changes which, being
life-sustaining or life-destroying, eventuate in certain
natural selections.

I have, above, made a passing reference to the fact that
Mr. Darwin did not fail to take account of some among
f these effects directly produced on organisms by surrounding
C inorganic agencies. Here are extracts from the sixth
edition of the Origin of Species showing this.
" It is very difficult to decide how far changed conditions, such as of
climate, food, &c., have acted in a definite manner. There is reason to
believe that in the course of time the effects have been greater than can be
proved by clear evidence. . . . Mr. Gould believes that birds of the same
species are more brightly coloured under a clear atmosphere, than when
living near the coast or on islands ; and Wollaston is convinced that
residence near the sea affects the colours of insects. Moquin-Tandon
gives a list of plants which, when growing near the sea-shore, have their
leaves in some degree fleshy, though not elsewhere fleshy " (pp. 106-7).
" Some observers are convinced that a damp climate affects the growth of
the hair, and that with the hair the horns are correlated" (p. 159).

In his subsequent work, Animals and Plants under
Domestic ationj Mr. Darwin still more clearly recognizes
< these causes of change in organization. A chapter is
devoted to the subject. After premising that " the direct
action of the conditions of life, whether leading to definite
or indefinite results, is a totally distinct consideration
from the effects of natural selection;" he goes on to say
that changed conditions of life "have acted so definitely
and powerfully on the organisation of our domesticated

46 THE FACTORS OF ORGANIC EVOLUTION.

productions, that they have sufficed to form new sub-
I varieties or races, without the aid of selection by man or
( of natural selection." Of his examples here are two.

" I have given in detail in the ninth chapter the most remarkable case
known to me, namely, that in Germany several varieties of maize brought
from the hotter parts of America were transformed in the course of only
two or three generations." (Vol. ii, p. 277.) [And in this ninth chapter
concerning these and other such instances he says " some of the foregoing
differences would certainly be considered of specific value with plants in a
state of nature." (Vol. i, p. 321.)] " Mr. Meehan, in a remarkable paper,
compares twenty-nine kinds of American trees, belonging to various orders,
with their nearest European allies, all grown in close proximity in the
Bame garden and under as nearly as possible the same conditions." And
then enumerating six traits in which the American forms all of them differ
in like ways from their allied European forms, Mr. Darwin thinks there is
no choice but to conclude that these " have been definitely caused by the
long-continued action of the different climate of the two continents on the
trees." (Vol. ii, pp. 281-2.)

But the fact we have to note is that while Mr. Darwin
thus took account of special effects due to special amounts
and combinations of agencies in the environment, he did
not take account of the far more important effects due to
the general and constant operation of these agencies.* If
a difference between the quantities of a force which acts
on two organisms, otherwise alike and otherwise similarly
conditioned, produces some difference between them; then,
by implication, this force produces in both of them effects

* It is true that while not deliberately admitted by Mr. Darwin, these
effects are not denied by him. In his Animals and Plants under Domesti
cation (vol. ii, 281), he refers to certain chapters in the Principles of
Biology, in which I have discussed this general inter-action of the medium
and the organism, and ascribed certain most general traits to it. But
though, by his expressions, he implies a sympathetic attention to the
argument, he does not in such way adopt the conclusion as to assign
to this factor any share in the genesis of organic structures— much less
that large share which I believe it has had. I did not myself at that
time, nor indeed until quite recently, see how extensive and profound have
been the influences on organization which, as we shall presently see, are
traceable to the early results of this fundamental relation between organism
and medium. I may add that it is in an essay on " Transcendental
Physiology," first published in 1857, that the line of thought here followed
out in its wider bearings, was first entered upon.

THE FACTOKS OF ORGANIC EVOLUTION. 47

which they show in common. The inequality between two
things cannot have a value unless the things themselves
have values. Similarly if, in two cases, some unlikeness of
proportion among the surrounding inorganic agencies to
which two plants or two animals are exposed, is followed
by some unlikeness in the changes wrought on them; then
it follows that these several agencies taken separately, work
changes in both of them. Hence we must infer that
organisms have certain structural characters in common,
which are consequent on the action of the medium in
which they exist : using the word medium in a compre
hensive sense, as including all physical forces falling upon
them as well as matters bathing them. And we may con
clude that from the primary characters thus produced there
must result secondary characters.

Before going on to observe those general traits of
organisms due to the general action of the inorganic
environment upon them, I feel tempted to enlarge on
the effects produced by each of the several matters and
forces constituting the environment. I should like to do
this not only to give a clear preliminary conception of
the ways in which all organisms are affected by these
universally-present agents, but also to show that, in the
first place, these agents modify inorganic bodies as well
as organic bodies, and that, in the second place, the organic
are far more modifiable by them than the inorganic. But
to avoid undue suspension of the argument, I content
myself with saying that when the respective effects of
gravitation, heat, light, &c., are studied, as well as the
respective effects, physical and chemical, of the matters
forming the media, water and air, it will be found that
while more or less operative on all bodies, each modifies
organic bodies to an extent immensely greater than the
extent to which it modifies inorganic bodies.
i/

Here, not discriminating among the special effects which

48 THE FACTORS OF ORGANIC EVOLUTION.

these various forces and matters in the environment
produce on both classes of bodies, let us consider their
combined effects, and ask — What is the most general trait
of such effects ?

Obviously the most general trait is the greater amount
of change wrought on the outer surface than on the inner
mass. In so far as the matters of which the medium is
composed come into play, the unavoidable implication is
that they act more on the parts directly exposed to them
than on the parts sheltered from them. And in so far as
the forces pervading the medium come into play, it is
manifest that, excluding gravity, which affects outer and
inner parts indiscriminately, the outer parts have to bear
larger shares of their actions. If it is a question of heat,
then the exterior must lose it or gain it faster than the
interior; and in a medium which is now warmer and now
colder, the two must habitually differ in temperature to
some extent — at least where the size is considerable. If
it is a question of light, then in all but absolutely trans
parent masses, the outer parts must undergo more of any
change producible by it than the inner parts — supposing
other things equal ; by which I mean, supposing the case
is not complicated by any such convexities of the outer
surface as produce internal concentrations of rays. Hence
then, speaking generally, the necessity is that the primary
and almost universal effect of the converse between the
body and its medium, is to differentiate its outside from its
inside. I say almost universal, because where the body is
both mechanically and chemically stable, like, for instance,
a quartz crystal, the medium may fail to work either inner
or outer change.

Of illustrations among inorganic bodies, a convenient
one is supplied by an old cannon-ball that has been long
lying exposed. A coating of rust, formed of flakes within
flakes, incloses it ; and this thickens year by year, until,
perhaps, it reaches a stage at which its exterior loses as

THE FACTOES OP ORGANIC EVOLUTION. 49

much by rain and wind as its interior gains by further
oxidation of the iron. Most mineral masses — pebbles,
boulders, rocks — if they show any effect of the environment
at all, show it only by that disintegration of surface
which follows .the freezing of absorbed water : an effect
which, though mechanical rather than chemical, equally
illustrates the general truth. Occasionally a " rocking-
stone " is thus produced. There are formed successive
layers relatively friable in texture, each of which, thickest
at the most exposed parts, and being presently lost by
weathering, leaves the contained mass in a shape more
rounded than before; until, resting on its convex under-
surface, it is easily moved. But of all instances perhaps
the most remarkable is one to be seen on the west bank of
the Nile at Philae, where a ridge of granite 100 feet high,
has had its outer parts reduced in course of time to a
collection of boulder-shaped masses, varying from say a
yard in diameter to six or eight feet, each one of which
shows in progress an exfoliation of successively-formed
shells of decomposed granite : most of the masses having
portions of such shells partially detached.

If, now, inorganic masses, relatively so stable in com
position, thus have their outer parts differentiated from
their inner parts, what must we say of organic masses,
f characterized by such extreme chemical instability ? —
instability so great that their essential material is named
protein, to indicate the readiness with which it passes
from one isomeric form to another. Clearly the necessary
inference is that this effect of the medium must be
wrought inevitably and promptly, wherever the relation
of outer and inner has become settled : a qualification for
which the need will be seen hereafter.

Beginning with the earliest and most minute kinds
of living things, we necessarily encounter difficulties in
getting direct evidence; since, of the countless species

50 THE FACTORS OF ORGANIC EVOLUTION.

now existing, all 1 a/"e been subject during millions upon
millions of years to the Evolutionary process, and have had
their primary traits complicated and obscured by those
endless secondary traits which the natural selection of
favourable variations has produced. Among protophytes
it needs but to think of the multitudinous varieties of
diatoms and desmids, with their elaborately-constructed
coverings ; or of the definite methods of growth and
multiplication among such simple Algse as the Conjugate ;
to see that most of their distinctive characters are due to
inherited constitutions, which have been slowly moulded by
survival of the fittest to this or that mode of life. To
disentangle such parts of their developmental changes as
are due to the action of the medium, is therefore hardly
possible. We can hope only to get a general conception of
it by contemplating the totality of the facts. ^

The first cardinal fact is that all protophytes are cellular^J
— all show us this contrast between outside and inside.
Supposing the multitudinous specialities of the envelope
in different orders and genera of protophytes to be set
against one another, and mutually cancelled, there remains
as a trait common to them — an envelope unlike that which
it envelopes. The second cardinal fact is that this simple
trait is the earliest trait displayed in germs, or spores,
or other parts from which new individuals are to arise;
and that, consequently, this trait must be regarded as
having been primordial. For it is an established truth of
organic evolution that embryos show us, in general ways,
the forms of remote ancestors ; and that the first changes
undergone, indicate, more or less clearly, the first changes
which took place in the series of forms through which the
existing form has been reached. Describing, in successive
groups of plants, the early transformations of these primi
tive units, Sachs* says of the lowest Algss that "the con-

* Text-Book of Botany, d-c. by Julius Sachs. Translated by A. W. Bennett
and W. T. T. Dyer.

THE FACTORS OP ORGANIC EVOLUTION. 51

jugated protoplasmic body clothes itself with a cell-wall "
(p. 10) -, that in " the spores of Mosses and Vascular Crypto
gams " and in " the pollen of Phanerogams " . . . " the
protoplasmic body of the mother-cell breaks up into four
lumps, which quickly round themselves off and contract, and
become enveloped by a cell-membrane only after complete
separation" (p. 13); that in the Equisetaceze "the young
spores, when first separated, are still naked, but they soon
become surrounded by a cell-membrane " (p. 14) ; and that
in higher plants, as in the pollen of many Dicotyledons,
"the contracting daughter-cells secrete cellulose even
during their separation" (p. 14). Here, then, in whatever
way we interpret it, the fact is that there quickly arises an
outer layer different from the contained matter. But the
most significant evidence is furnished by "the masses of
protoplasm that escape into water from the injured sacs
of Vaucheria, which often instantly become rounded into
globular bodies," and of which the "hyaline protoplasm
envelopes the whole as a skin" (p. 41) which "is denser than
the inner and more watery substance " (p. 42). As in this
case the protoplasm is but a fragment, and as it is removed
from the influence of the parent-cell, this differentiating
process can scarcely be regarded as anything more than
the effect of physico-chemical actions : a conclusion which
is supported by the statement of Sachs that "not only
every vacuole in a solid protoplasmic body, but also every
thread of protoplasm which penetrates the sap-cavity, and
finally the inner side of the protoplasm-sac which encloses
the sap-cavity, is also bounded by a skin" (p. 42). If
then " every portion of a protoplasmic body immediately
surrounds itself, when it becomes isolated, with such a
skin," which is shown in all cases to arise at the surface of
contact with sap or water, this primary differentiation of
outer from inner must be ascribed to the direct action of
the medium. Whether the coating thus initiated is secreted
by the protoplasm, or whether, as seems more likely, it

52 THE FACTOES OP ORGANIC EVOLUTION.

results from transformation of it, matters not to the argu
ment. Either way the action of the medium causes its
formation ; and either way the many varied and complex
differentiations which developed cell-walls display, must be
considered as originating from those variations of this
physically-generated covering which natural selection has
taken advantage of.

The contained protoplasm of a vegetal cell, which has
self - mobility and when liberated sometimes performs
amoeba-like motions for a time, may be regarded as an
imprisoned amoeba ; and when we pass from it to a free
amoeba, which is one of the simplest types of first animals,
or Protozoa, we naturally meet with kindred phenomena.
The general trait which here concerns us, is that while
its plastic or semi-fluid sarcode goes on protruding, in
irregular ways, now this and now that part of its peri
phery, and again withdrawing into its interior first one
and then another of these temporary processes, perhaps
with some small portion of food attached, there is but
an indistinct differentiation of outer from inner (a fact
shown by the frequent coalescence of the pseudopodia in
Rhizopods) ; but that when it eventually becomes quiescent,
the surface becomes differentiated from the contents : the
passing into an encysted state, doubtless in large measure
due to inherited proclivity, being furthered, and having
probably been once initiated, "fyy the action of the medium.
The connexion between constancy of relative position among
the parts of the sarcode, and the rise of a contrast between
superficial and central parts, is perhaps best shown in the
minutest and simplest Infusoria, the Mojiadlnse. The genus
Monas is described by Kent as "plastic and unstable in form,
possessing no distinct cuticular investment ; . . . the food-
substances incepted at all parts of the periphery ";* and
the genus Scytomonas he says " differs from Monas only in

* A Manual of the Infusoria, by W. Saville Kent. Vol. i, p. 232.

THE FACTOES OP OEGANIC EVOLUTION. 53

its persistent shape and accompanying greater rigidity of
the peripheral or ectoplasmic layer." * Describing generally
such low forms, some of which are said to have neither
nucleus nor vacuole, he remarks that in types somewhat
higher " the outer or peripheral border of the protoplasmic
mass, while not assuming the character of a distinct cell-
wall or so-called cuticle, presents, as compared with the
inner substance of that mass, a slightly more solid type of
composition." t And it is added that these forms having so
slightly differentiated an exterior, " while usually exhibiting
a more or less characteristic normal outline, can revert at
will to a pseud-amoeboid and repent state." J Here, then,
we have several indications of the truth that the permanent
externality of a certain part of the substance, is followed
by transformation of it into a coating unlike the substance
it contains. Indefinite and structureless in the simplest of
these forms, as instance again the Gregarina,§ the limiting
membrane becomes, in higher Infusoria, definite and often
complex: showing that the selection of favourable varia
tions has had largely to do with its formation. In such
types as the Foraminifera, which, almost structureless
internally though they are, secrete calcareous shells, it is
clear that the nature of this outer layer is determined by
inherited constitution. But recognition of this consists
with the belief that the action of the medium initiated the
outer layer, specialized though it now is ; and that even
still, contact with the medium excites secretion of it.

A remarkable analogy remains to be named. When
we study the action of the medium in an inorganic mass,
we are led to see that between the outer changed layer
and the inner unchanged mass, comes a surface where
active change is going on. Here we have to note that, alike
in the plant-cell and in the animal-cell, there is a similar
relation of parts. Immediately inside the envelope comes

* 16. Vol. i, p. 241. f Kent, Vol. i, p. 56. i Ib. Vol. i, p. 57.

§ The Elements of Comparative Anatomy, by T. H. Huxley, pp. 7-9.

54 THE FACTORS OF OEGANIC EVOLUTION.

the primordial utricle in the one case, and in the other
case the layer of active sarcode. In either case the
living protoplasm, placed in the position of a lining to the
cuticle of the cell, is shielded from the direct action of the
medium, and yet is not beyond the reach of its influences.

Limited, as thus far drawn, to a certain common trait of
those minute organisms which are mostly below the reach
of unaided vision, the foregoing conclusion appears trivial
enough. But it ceases to appear trivial on passing into
a wider field, and observing the implications, direct and
indirect, as they concern plants and animals of sensible sizes.

Popular expositions of science have so far familiarized
many readers with a certain fundamental trait of living
things around, that they have ceased to perceive how
marvellous a trait it is, and, until interpreted by the Theory
of Evolution, how utterly mysterious. In past times, the
conception of an ordinary plant or animal which prevailed,
not throughout the world at large only but among the
most instructed, was that it is a single continuous entity.
One of these livings things was unhesitatingly regarded as
being in all respects a unit. Parts it might have, various
in their sizes, forms, and compositions ; but these were
components of a whole which had been from the beginning
in its original nature a whole. Even to naturalists fifty
years ago, the assertion that a cabbage or a cow, though
in one sense a whole, is in another sense a vast society
of minute individuals, severally living in greater or less
degrees, and some of them maintaining their independent
lives unrestrained, would have seemed an absurdity. But
this truth which, like so many of the truths established by
science, is contrary to that common sense in which most
people have so much confidence, has been gradually
growing clear since the days when Leeuwenhoeck and his
contemporaries began to examine through lenses the
minute structures of common plants and animals. Each

THE FACTORS OF OKGANIC EVOLUTION. 55

improvement in the microscope, while it has widened our
knowledge of those minute forms of life described above,
has revealed further evidence of the fact that all the
larger forms of life consist of units severally allied in
their fundamental traits to these minute forms of life.
Though, as formulated by Schwann and Schleiden, the
cell-doctrine has undergone qualifications of statement;
yet the qualifications have not been such as to militate
against the general proposition that organisms visible to
the naked eye, are severally compounded of invisible
organisms — using that word in its most comprehensive
sense. And then, when the development of any animal
is traced, it is found that having been primarily a nucleated
cell, and having afterwards become by spontaneous fission
a cluster of nucleated cells, it goes on through successive
stages to form out of such cells, ever multiplying and
modifying in various ways, the several tissues and organs
composing the adult.

On the hypothesis of evolution this universal trait has to
be accepted not as a fact that is strange but unmeaning.
It has to be accepted as evidence that all the visible forms
of life have arisen by union of the invisible forms ; which,'
instead of flying apart when they divided, remained
together. Various intermediate stages are known. Among
plants, those of the Volvox type show' us the component pro-
tophytes so feebly combined that they severally carry on
their lives with no appreciable subordination to the life of
the group. And among animals, a parallel relation between
the lives of the units and the life of the group is shown
us in Uroglena and Syncrypta. From these first stages
upwards, may be traced through successively higher types,
an increasing subordination of the units to the aggregate;
though still a subordination leaving to them conspicuous
amounts of individual activity. Joining which facts with
the phenomena presented by the cell-multiplication and

aggregation of every unfolding germ, naturalists are now
6

5G THE FACTORS OP ORGANIC EVOLUTION.

accepting the conclusion that by this process of composition
from Protozoa, were formed all classes of the Metazoa* — (as
animals formed by this compounding are now called) ; and
that in a similar way from Protophyta,were formed all classes
of what I suppose will be called Metaphyta, though the
" word does not yet seem to have become current.

And now what is the general meaning of these truths,
taken in connexion with tin conclusion reached in the
last section. It is that this universal trait of the Metazoa
and Metapkyta, must be ascribed to the primitive action
and re-action between the organism and its medium. The
operation of those forces which produced the primary
differentiation of outer from inner in early minute masses
of protoplasm, pre-determined this universal cell-structure
of all embryos, plant and animal, and the consequent cell-
composition of adult forms arising from them. How
unavoidable is this implication, will be seen on carrying
further an illustration already used — that of the shingle-
covered shore, the pebbles on which, while being in some
cases selected, have been in all cases rounded and smoothed.
Suppose a bed of such shingle to be, as we often see
it, solidified, along with interfused material, into a con
glomerate. What in such case must be considered as the
chief trait of such conglomerate; or rather — what must we
regard as the chief cause of its distinctive characters ?
Evidently the action of the sea. Without the breakers, no
pebbles ; without the pebbles, no conglomerate. Similarly
then, in the absence of that action of the medium by which
was effected the differentiation of outer from inner in those
microscopic portions of protoplasm constituting the earliest
and simplest animals and plants, there could not have
existed this cardinal trait of composition which all the
higher animals and plants show us.

So that, active as has been the part played by natural
selection, alike in modifying and moulding the original
* A Treatise on Comparative Embryology, by F. M. Balfour, Vol. ii, chap. xiii.

THE FACTORS OP OEGANIC EVOLUTION. 57

units — largely as survival of the fittest has been instru
mental in furthering and controlling the combination of
these units into visible organisms, and eventually into large
ones ; yet we must ascribe to the direct effect of the medium
on the first forms of life, that character of which this
every where- operative factor has taken advantage.

Let us turn now to another and more obvious attribute of
higher organisms, for which also there is this same general
cause. Let us observe how, on a higher platform, there
recurs this differentiation of outer from inner — how this
primary trait in the living units with which life commences,
re-appears as a primary trait in those aggregates of such
units which constitute visible organisms.

In its simplest and most unmistakable form, we see this
in the early changes of an unfolding ovum of primitive
type. The original fertilized single cell, having by spon
taneous fission multiplied into a cluster of such cells, there
begins to show itself a contrast between periphery and
centre ; and presently there is formed a sphere consisting
of a superficial layer unlike its contents. The first change,
then, is the rise of a difference between that outer part
which holds direct converse with the surrounding medium,
and that inclosed part which does not. This primary
differentiation in these compound embryos of higher
animals, parallels the primary differentiation undergone by
the simplest living things.

Leaving, for the present, succeeding changes of the
compound embryo, the significance of which we shall have
to consider by-and-by, let us pass now to the adult forms
of visible plants and animals. In them we find cardinal
traits which, after what we have seen above, will further
impress us with the importance of the effects wrought on
the organism by its medium.

From the thallus of a sea-weed up to the leaf of a highly
developed phaenogam, we find, at all stages, a contrast

58 THE FACTORS OF ORGANIC EVOLUTION.

between the inner and outer parts of these flattened masses
of tissue. In the higher Algse " the outermost layers con
sist of smaller and firmer cells, while the inner cells are
often very large, and sometimes extremely long ; "* and in
the leaves of trees the epidermal layer, besides differing in
the sizes and shapes of its component cells from the paren
chyma forming the inner substance of the leaf, is itself
differentiated by having a continuous cuticle, and by having
the outer walls of its cells unlike the inner walls.t
Especially significant is the structure of such intermediate
types as the Liverworts. Beyond the differentiation of the
covering cells from the contained cells, and the contrast
between upper surface and under surface, the frond of Mar-
chantia polymorpha clearly shows us the direct effect of
incident forces ; and shows us, too, how it is involved with
the effect of inherited proclivities. The frond grows from a
flat disc-shaped gemma, the two sides of which are alike.
Either side may fall uppermost; and then of the develop
ing shoot, the side exposed to the light " is under all
circumstances the upper side which forms stomata, the
dark side becomes the under side which produces root-hairs
and leafy processes."! So that while we have undeniable
proof that the contrasted influences of the medium on the two
sides, initiate the differentiation, we have also proof that the
completion of it is determined by the transmitted structure of
the type ; since it is impossible to ascribe the development of
stomata to the direct action of air and light. On turning
from foliar expansions, to stems and roots, facts of like
meaning meet us. Speaking generally of epidermal tissue
and inner tissue, Sachs remarks that " the contrast of the
two is the plainer the more the part of the plant concerned
is exposed to air and light."§ Elsewhere, in correspondence
with this, it is said that in roots the cells of the epidermis,
though distinguished by bearing hairs, "are otherwise similar

* Sachs, p. 210. f Ibid, pp. 83-4. J Rid. p. 185.

§ Rid. 80.

THE FACTOKS OF OKGANIC EVOLUTION. 59

to those of the fundamental tissue" which they clothe,* while
the cuticular covering is relatively thin ; whereas in stems
the epidermis (often further differentiated) is composed of
layers of cells which are smaller and thicker- walled : a
stronger contrast of structure corresponding to a stronger
contrast of conditions. By way of meeting the suggestion
that these respective differences are wholly due to the
natural selection of favourable variations, it will suffice if
I draw attention to the unlikeness between imbedded roots
and exposed roots. While in darkness, and surrounded by
moist earth, the outermost protective coats, even of large
roots, are comparatively thin ; but when the accidents of
growth entail permanent exposure to light and air, roots
acquire coverings allied in character to the coverings of
branches. That the action of the medium causes these
and converse changes, cannot be doubted when we find, on
the one hand, that " roots can become directly transformed
into leaf-bearing shoots," and, on the other hand, that in
some plants certain " apparent roots are only underground
shoots," and that nevertheless "they are similar to true
roots in function and in the formation of tissue, but have
no root-cap, and, when they come to the light above
ground, continue to grow in the manner of ordinary leaf-
shoots, "t If, then, in highly developed plants inheriting
pronounced structures, this differentiating influence of the
medium is so marked, it must have been all-important at
the outset while types were undetermined.

As with plants so with animals, we find good reason for
inferring that while the specialities of the tegumentary
parts must be ascribed to the natural selection of favourable
variations, their most general traits are due to the direct
action of surrounding agencies. Here we come upon the
border of those changes which are ascribable to use and
disuse. But from this class of changes we may fitly
exclude those in which the parts concerned are wholly or
* Sachs, p. 83. f Ibid. p. 147.

60 THE FACTORS OP ORGANIC EVOLUTION.

mainly passive. A corn and a blister will conveniently
serve to illustrate the way in which certain outer actions
initiate in the superficial tissues, effects of very marked
kinds, which are related neither to the needs of the organ
ism nor to its normal structure. They are neither adaptive
changes nor changes towards completion of the type.
After noting them we may pass to allied, but still more
instructive, changes. Continuous pressure on any portion of
the surface causes absorption, while intermittent pressure
causes growth : the one impeding circulation and the
passage of plasma from the capillaries into the tissues, and
the other aiding both. There are yet further mechanically-
produced effects. That the general character of the ribbed
skin on the under surfaces of the feet and insides of the
hands is directly due to friction and intermittent pressure,
we have the proofs : — first, that the tracts most exposed to
rough usage are the most ribbed ; second, that the insides
of hands subject to unusual amounts of rough usage, as
those of sailors, are strongly ribbed all over ; and third, that
in hands which are very little used, the parts commonly
ribbed become quite smooth. These several kinds of evi
dence, however, full of meaning as they are, I give simply
to prepare the way for evidence of a much more conclu
sive kind.

Where a wide ulcer has eaten away the deep-seated layer
out of which the epidermis grows, or where this layer has
been destroyed by an extensive burn, the process of healing
is very significant. From the subjacent tissues, which in the
normal order have no concern with outward growth, there
is produced a new skin, or rather a pro-skin; for this
substituted outward-growing layer contains no hair-follicles
or other specialities of the original one. Nevertheless, it
is like the original one in so far that it is a continually
renewed protective covering. Doubtless it may be con
tended that this make-shift skin results from the inherited
proclivity of the type — the tendency to complete afresh

THE FACTORS OP ORGANIC EVOLUTION. 61

the structure of the species when injured. We cannot,
however, ignore the immediate influence of the medium, on
recalling the facts above named, or on remembering the
further fact that an inflamed surface of skin, when not
sheltered from the air, will throw out a film of coagulable
lymph. But that the direct action of the medium is a chief
factor we are clearly shown by another case. Accident or
disease occasionally causes permanent eversion, or protru
sion, of mucous membrane. After a period of irritability,
great at first but decreasing as the change advances, this
membrane assumes the general character of ordinary skin.
Nor is this all : its microscopic structure changes. Where
it is a mucous membrane of the kind covered by cylinder^
epithelium, the cylinders gradually shorten, becoming finally
flat, and there results a squamous epithelium : there is a
near approach in minute composition to epidermis. Here a
tendency towards completion of the type cannot be alleged ;
for there is, contrariwise, divergence from the type. The
effect of the medium is so great that, in a short time, it
overcomes the inherited proclivity and produces a struc
ture of opposite kind to the normal one.

With but little break we come here upon a significant
analogy, parallel to an analogy already described. As
was pointed out, an inorganic body that is modifiable by
its medium, acquires, after a time, an outer coat which
has already undergone such change as surrounding agencies
can effect; has a contained mass which is as yet unchanged,
because unreached; and has a surface between the two
where change is going on — a region of activity. And we
saw that alike in the vegetal cell and the animal cell there
exist analogous distributions : of course with the difference
that the innermost part is not inert. Now we have to note
that in those aggregates of cells constituting the Metaphyta
and Metazoa, analogous distributions also exist. In plants
they are of course not to be looked for in leaves and other
deciduous portions, but only in portions of long duration—

62 THE FACTORS OP ORGANIC EVOLUTION.

stems and brandies. Naturally, too, we need not expect
them in plants having modes of growth which early produce
an outer practically dead part, that effectually shields the
inner actively living part of the stem from the influence
of the medium — long-lived acrogens such as tree-ferns and
long-lived endogens such as palms. But in the highest
plants, exogens, which have the actively living part of
their stems within reach of environing agencies, we find
this part, — the cambium layer, — is one from which there
is a growth inwards forming wood, and a growth outwards
forming bark : there is an increasingly thick covering (where
it does not scale off) of tissue changed by the medium,
and inside this a film of highest vitality. In so far as
concerns the present argument, it is the same with the
Metazoa, or at least all of them which have developed
organizations. The outer skin grows up from a limiting
plane, or layer, a little distance below the surface — a place
of predominant vital activity. Here perpetually arise new
cells, which, as they develop, are thrust outwards and
form the epidermis : flattening and drying up as they
approach the surface, whence, having for a time served
to shield the parts below, they finally scale off and leave
younger ones to take their places. This still undifferentia-
ted tissue forming the base of the epidermis, and existing
also as a source of renewal in internal organs, is the
essentially living substance ; and facts above given imply
that it was the action of the medium on this essentially
living substance, which, during early stages in the organiza
tion of the Metazoa, initiated that protective envelope which
presently became an inherited structure — a structure which,
though now mainly inherited, still continues to be modifi
able by its initiator.

Fully to perceive the way in which these evidences
compel us to recognize the influence of the medium as a
primordial factor, we need but conceive them as interpreted
without it. Suppose, for instance, we say that the structure

THE FACTORS OF ORGANIC EVOLUTION. 63

of the epidermis is wholly determined by the natural selec
tion of favourable variations ; what must be the position
taken in presence of the fact above named, that when
mucous membrane is exposed to the air its cell-structure
changes into the cell-structure of skin ? The position taken
must be this : — Though mucous membrane in a highly-
evolved individual organism, thus shows the powerful effect
of the medium on its surface ; yet we must not suppose that
the medium had the effect of producing such a cell-struc
ture on the surfaces of primitive forms, undifferentiated
though they were; or, if we suppose that such an effect
was produced on them, we must not suppose that it was
inheritable. Contrariwise, we must suppose that such effect
of the medium either was not wrought at all, or that it
was evanescent : though repeated through millions upon
millions of generations it left no traces. And we must
conclude that this skin-structure arose only in conse
quence of spontaneous variations not physically initiated
(though like those physically initiated) which natural selec
tion laid hold of and increased. Does any one think this a
tenable position?

And now we approach the last and chief series of
morphological phenomena which must be ascribed to the
direct action of environing matters and forces. These are
presented to us when we study the early stages in the
development of the embryos of the Metazoa in general.

We will set out with the fact already noted in passing,
that after repeated spontaneous fissions have changed the
original fertilized germ-cell into that cluster of cells which
forms a gemmule or a primitive ovum, the first contrast which
arises is between the peripheral parts and the central parts.
Where, as with lower creatures which do not lay up large
stores of nutriment with the germs of their offspring, the
inner mass is inconsiderable, the outer layer of cells, which
are presently made quite small by repeated subdivisions,

64 THE FACTORS OP ORGANIC EVOLUTION.

forms a membrane extending over the whole surface — the
blastoderm. The next stage of development, which ends
in this covering layer becoming double, is reached in two
ways — by invagination and by delamination; but which is the
original way and which the abridged way, is not quite cer
tain. Of invagination, multitudinously exemplified in the
lowest types, Mr. Balfour says : — " On purely a priori grounds
there is in my opinion more to be said for invagination
than for any other view";* and, for present purposes, it
will suffice if we limit ourselves to this : making its nature
clear to the general reader by a simple illustration.

Take a small india-rubber ball — not of the inflated kind,
nor of the solid kind, but of the kind about an inch or so
in diameter with a small hole through which, under pressure,
the air escapes. Suppose that instead of consisting of india-
rubber its wall consists of small cells made polyhedral in
form by mutual pressure, and united together. This will
represent the blastoderm. Now with the finger, thrust in
one side of the ball until it touches the other : so making a
cup. This action will stand for the process of invagination.
Imagine that by continuance of it, the hemispherical cup
becomes very much deepened and the opening narrowed,
until the cup becomes a sac, of which the introverted wall
is everywhere in contact with the outer wall. This will
represent the two -layered "gastrula" — the simplest
ancestral form of the Metazoa: a form which is permanently
represented in some of the lowest types ; for it needs but
tentacles round the mouth of the sac, to produce a common
hydra. Here the fact which it chiefly concerns us to
remark, is that of these two layers the outer, called in
embryological language the epiblast, continues to carry on
direct converse with the forces and matters in the environ
ment ; while the inner, called the hypoblast, comes in contact

• A Treatise on Comparative Embryology. By Fiaucis M. Balfour, LL.D,
r.ir.s. Vol. ii, p. 313 (second edition).

THE FACTORS OP ORGANIC EVOLUTION. 65

with such only of these matters as are put into the food-
cavity which it lines. We have further to note that in the
embryos of Metazoa at all advanced in organization, there
arises between these two layers a third — the mesoblast.
The origin of this is seen in types where the developmental
process is not obscured by the presence of a large food-
yolk. While the above-described introversion is taking
place, and before the inner surfaces of the resulting epiblast
and hypoblast have come into contact, cells, or amoeboid
units equivalent to them, are budded off from one or both
of these inner surfaces, or some part'of one or other ; and
these form a layer which eventually lies between the other
two — a layer which, as this mode of formation implies,
never has any converse with the surrounding medium and
its contents, or with the nutritive bodies taken in from it.
The striking facts to which this description is a necessary
introduction, may now be stated. From the outer layer, or
epiblast, are developed the permanent epidermis and its
out-growths, the nervous system, and the organs of sense.
From the introverted layer, or hypoblast, are developed
the alimentary canal and those parts of its appended
organs, liver, pancreas, &c., which are concerned in deliver
ing their secretions into the alimentary canal, as well as the
linings of those ramifying tubes in the lungs which convey
air to the places where gaseous exchange is effected. And
from the mesoblast originate the bones, the muscles, the
heart and blood-vessels, and the lymphatics, together with
such parts of various internal organs as are most remotely
concerned with the outer world. Minor qualifications being
admitted, there remain the broad general facts, that out of
that part of the external layer which remains permanently
external, are developed all the structures which carry on
intercourse with the medium and its contents, active and
passive ; out of the introverted part of this external layer,
are developed the structures which carry on intercourse
with the quasi-external substances that are taken into the

6(3 TEE FACTORS OF ORGANIC EVOLUTION.

interior — solid food, water, and air; while out of the
mesoblast are developed structures which have never had,
from first to last, any intercourse with the environment.
Let us contemplate these general facts.

Who would have imagined that the nervous system is a
modified portion of the primitive epidermis ? In the absence
of proofs furnished by the concurrent testimony of embryo-
logists during the last thirty or forty years, who would
have believed that the brain arises from an infolded
tract of the outer skin, which, sinking down beneath the
surface, becomes imbedded in other tissues and eventually
surrounded by a bony case ? Yet the human nervous
system in common with the nervous systems of lower
animals is thus originated. In the words of Mr. Balfour,
early embryological changes imply that —

" the functions of the central nervous system, which were originally taken
by the whole skin, became gradually concentrated in a special part of the
skin which was step by step removed from the surface, and has finally
become in the higher types a well-defined organ imbedded in the subdermal
tissues. . . . The embryological evidence shows that the ganglion-cells of
the central part of the nervous system are originally derived from the simple
undiJerentiated epithelial cells of the surface of the body."*
Less startling perhaps, though still startling enough, is the
fact that the eye is evolved out of a portion of the skin;
and that while the crystalline lens and its surroundings
thus originate, the " percipient portions of the organs
of special sense, especially of optic organs, are often
formed from the same part of the primitive epidermis"
which forms the central nervous system, t Similarly is it
with the organs for smelling and hearing. These, too,
begin as sacs formed by infoldings of the epidermis; and
while their parts are developing they are joined fromt
within by nervous structures which were themselves epi
dermic in origin. How are we to interpret these strange
transformations ? Observing, as we pass, how absurd from
the point of view of the special-creationist, would appear

* Balfour, I.e. Vol. ii, 400-1. f Balfour, I.e. Vol. ii, p. 401.

THE FACTOKS OF OKGANIC EVOLUTION. 67

such a filiation of structures, and such a round-about
mode of embryonic development., we have here to remark
that the process is not one to have been anticipated as
a result of natural selection. After numbers of spontaneous
variations had occurred, as the hypothesis implies, in
useless ways, the variation which primarily initiated a
nervous centre might reasonably have . been expected to
occur in some internal part where it would be fitly
located. Its initiation in a dangerous place and subsequent
migration to a safe place, would be incomprehensible. Not
so if we bear in mind the cardinal truth above set forth,
that the structures for holding converse with the medium
and its contents, arise in that completely superficial part
which is directly affected by the medium and its contents ;
and if we draw the inference that the external actions
themselves initiate the structures. These once commenced,
and furthered by natural selection where favourable to life,
would form the first term of a series ending in developed
sense organs and a developed nervous system.*"

Though it would enforce the argument, I must, for
brevity's sake, pass over the analogous evolution of that
introverted layer, or hypoblast, out of which the alimentary
canal and attached organs arise. It will suffice to emphasize
the fact that having been originally external, this layer
continues in its developed form to have a quasi-externality,
alike in its digesting part and in its respiratory part; since
it continues to deal with matters alien to the organism.
I must also refrain from dwelling at length on the fact
already adverted to, that the intermediate derived layer,
or mesoblast, which was at the outset completely internal,
originates those structures which ever remain completely
internal, and have no communication with the environment
save through the structures developed from the other two:
an antithesis which has great significance.

* For a general delineation of the changes by which the development
is effected, see Balfour, I.e. Vol. ii, pp. 401-4.
7

03 THE FACTORS OF ORGANIC EVOLUTION.

Here, instead of dwelling on these details, it will bo
better to draw attention to the most general aspect of the
facts. Whatever may be the course of subsequent changes,
the first change is the formation of a superficial layer or
blastoderm ; and by whatever series of transformations
the adult structure is reached, it is from the blastoderm
that all the organs forming the adult originate. Why this
marvellous fact ?

Meaning is given to it if we go back to the first stage in
which Protozoa, having by repeated fissions formed a clus
ter, then arranged themselves into a hollow sphere, as do
the protophytes forming a Volvox. Originally alike all over
its surface, the hollow sphere of ciliated units thus formed,
would, if not quite spherical, assume a constant attitude
when moving through the water ; and hence one part of
the spheroid would more frequently than the rest come in
contact with nutritive matters to be taken in. A division
of labour resulting from such a variation being advanta
geous, and tending therefore to increase in descendants;
would end in a differentiation like that shown in the gem-
mules of various low types of Metazoa, which, ovate in shape,
are ciliated over one part of the surface only. There would
arise a form in which the cilium-bearing units effected loco
motion and aeration; while on the others, assuming an
amoeba-like character, devolved the function of absorbing
food : a primordial specialization variously indicated by
evidence.* Just noting that an ancestral origin of this
kind is implied by the fact that in low types of Metazoa
a hollow sphere of cells is the form first assumed by the
unfolding embryo, I draw attention to the point here of chief
interest; namely that the primary differentiation of this
hollow sphere is in such case determined by a difference
in the converse of its parts with the medium and its
contents ; and that the subsequent invagination arises by a
continuance of this differential converse.

* See Balfour, Vol. i, 149 and Vol. ii, 313-4.

THE FACTORS OP ORGANIC EVOLUTION. 69

Even neglecting this first stage and commencing with the
next, in which a " gastrula " has been produced by the per
manent introversion of one portion of the surface of the
hollow sphere, it will suffice if we consider what must there
after have happened. That which continued to be the outer
surface was the part which from time to time touched
quiescent masses and occasionally received the collisions
consequent on its own motions or the motions of other
things. It was the part to receive the sound-vibrations
occasionally propagated through the water ; the part to be
affected more strongly than any other by those variations
in the amounts of light caused by the passing of small
bodies close to it ; and the part which met those diffused
molecules constituting odours. That is to say, from the
beginning the surface was the part on which there fell the
various influences pervading the environment, the part by
which there was received those impressions from the en
vironment serving for the guidance of actions, and the part
which had to bear the mechanical re-actions consequent
upon such actions. Necessarily, therefore, the surface was
the part in which were initiated the various instrumentali
ties for carrying on intercourse with the environment. To
suppose otherwise is to suppose that such instrumentalities
arose internally where they could neither be operated on by
surrounding agencies nor operate on them, — where the
differentiating forces did not come into play, and the differ
entiated structures had nothing to do ; and it is to suppose
that meanwhile the parts directly exposed to the differentia
ting forces remained unchanged. Clearly, then, organization
could not but begin on the surface; and having thus begun,
its subsequent course could not but be determined by its
superficial origin. And hence these remarkable facts show
ing us that individual evolution is accomplished by succes
sive in-foldings and in-growings. Doubtless natural selection
soon came into action, as, for example, in the removal of the
rudimentary nervous centres from the surface ; since an

70 THE FACTORS OF ORGANIC EVOLUTION.

individual in which they were a little more deeply seated
would be less likely to be incapacitated by injury of them.
And so in multitudinous other ways. But nevertheless, as
we here see, natural selection could operate only under
subjection. It could do no more than take advantage of
those structural changes which the medium and its con
tents initiated.

See, then, how large has been the part played by this
primordial factor. Had it done no more than give to
Protozoa and Protopliyta that cell-form which characterizes
them — had it done no more than entail the cellular com
position which is so remarkable a trait of Metazoa and
Metaphyta — had it done no more than cause the repetition
in all visible animals and plants of that primary differen
tiation of outer from inner which it first wrought in
animals and plants invisible to the naked eye; it would
have done much towards giving to organisms of all kinds
certain leading traits. But it has done more than this.
By causing the first differentiations of those clusters of
units out of which visible animals in general arose, it
fixed the starting place for organization, and therefore
determined the course of organization; and, doing this, gave
indelible traits to embryonic transformations and to adult
structures.

Though mainly carried on after the inductive method, the
argument at the close of the foregoing section has passed
into the deductive. Here let us follow for a space the
deductive method pure and simple. Doubtless in biology
a priori reasoning is dangerous; but there can be no
danger in considering whether its results coincide with
those reached by reasoning a posteriori.

Biologists in general agree that in the present state of
the world, no such thing happens as the rise of a living
creature out of non-living matter. They do not deny,
however, that at a remote period in the past, when the

THE PACTOKS OP ORGANIC EVOLUTION. 71

temperature of the Earth's surface was much higher than
at present, and other physical conditions were unlike those
we know, inorganic matter, through successive complica
tions, gave origin to organic matter. So many substances
once supposed to belong exclusively to living bodies, have
now been formed artificially, that men of science scarcely
question the conclusion that there are conditions under
which, by yet another step of composition, quaternary com
pounds of lower types pass into those of highest types.
That there once took place gradual divergence of the
organic from the inorganic, is, indeed, a necessary implica
tion of the hypothesis of Evolution, taken as a whole ; and
if we accept it as a whole, we must put to ourselves the
question — What were the early stages of progress which
followed, after the most complex form of matter had arisen
out of forms of matter a degree less complex ?

At first, protoplasm could have had no proclivities to one
or other arrangement of parts; unless, indeed, a purely
mechanical proclivity towards a spherical form when
suspended in a liquid. At the outset it must have been
passive. In respect of its passivity, primitive organic
matter must have been like inorganic matter. No such
thing as spontaneous variation could have occurred in
it; for variation implies some habitual course of change
from which it is a divergence, and is therefore excluded
where there is no habitual course of change. In the
absence of that cyclical series of metamorphoses which
even the simplest living thing now shows us, as a result of
its inherited constitution, there could be no point d'appui for
natural selection. How, then, did organic evolution begin ?

If a primitive mass of organic matter was like a mass
of inorganic matter in respect of its passivity, and differed
only in respect of its greater changeableness ; then we
must infer that its first changes conformed to the same
general law as do the changes of an inorganic mass.
The instability of the homogeneous is a universal principle.

7'2 THE FACTORS OF ORGANIC EVOLUTION.

In all cases the homogeneous tends to pass into the hetero
geneous, and the less heterogeneous into the more hetero
geneous. In the primordial units of protoplasm, then, the
step with which evolution commenced must have been the
passage from a state of complete likeness throughout the
mass to a state in which there existed some unlikeness.
Further, the cause of this step in one of these portions of
organic matter, as in any portion of inorganic matter, must
have been the different exposure of its parts to incident
forces. What incident forces ? Those of its medium or
environment. "Which were the parts thus differently
exposed ? Necessarily the outside and the inside. In
evitably, then, alike in the organic aggregate and the
inorganic aggregate (supposing it to have coherence enough
to maintain constant relative positions among its parts), the
first fall from homogeneity to heterogeneity must always
have been the differentiation of the external surface from
the internal contents. No matter whether the modifica
tion was physical or chemical, one of composition or of
decomposition, it comes within the same generalization.
The direct action of the medium was the primordial factor
of organic evolution.

And now, finally, let us look at the factors in their
ensemble, and consider the respective parts they play:
observing, especially, the ways in which, at successive
stages, they severally give place one to another in degree of
importance.

Acting alone, the primordial factor must have initiated
the primary differentiation in all units of protoplasm alike.
I say alike, but I must forthwith qualify the word. For
since surrounding influences, physical and chemical, could
not be absolutely the same in all places, especially when
the first rudiments of living things had spread over a
considerable area, there necessarily arose small contrasts
between the degrees and kinds of superficial differentiation

THE FACTOES OF ORGANIC EVOLUTION. 73

effected. As soon as these became decided, natural selec
tion came into play; for inevitably the uiilikenesses
produced among the units had effects on their lives : there
was survival of some among the modified forms rather
than others. Utterly in the dark though we are respect
ing the causes which set up that process of fission
everywhere occurring among the minutest forms of life,
we must infer that, when established, it furthered the
spread of those which were most favourably differentiated
by the medium. Though natural selection must have
become increasingly active when once it had got a start ;
yet the differentiating action of the medium never ceased
to be a co-operator in the development of these first
animals and plants. Again taking the lead as there arose
the composite forms of animals and plants, and again
losing the lead with that advancing differentiation of
these higher types which gave more scope to natural
selection, it nevertheless continued, and must ever con
tinue, to be a cause, both direct and indirect, of
modifications in structure.

Along with that remarkable process which, beginning in
minute forms with what is called conjugation, developed
into sexual generation, there came into play causes of
frequent and marked fortuitous variations. The mixtures
of constitutional proclivities made more or less unlike by
unlikenesses of physical conditions, inevitably led to occa
sional concurrences of forces producing deviations of
structure. These were of course mostly suppressed, but
sometimes increased, by survival of the fittest. When, along
with the growing multiplication in forms of life, conflict
and competition became continually more active, fortuitous
variations of structure of no account in the converse with
the medium, became of much account in the struggle with
enemies and competitors ; and natural selection of such
variations became the predominant factor. Especially
throughout the plant- world its action appears to have

74 THE FACTOES OF ORGANIC EVOLUTION.

been immensely the most important ; and throughout that
large part of the animal world characterized by relative
inactivity, the survival of individuals that had varied in
favourable ways, must all along have been the chief cause
of the divergence of species and the occasional production
of higher ones.

But gradually with that increase of activity which we
see on ascending to successively higher grades of animals,
and especially with that increased complexity of life
which we also see, there came more and more into play as
a factor, the inheritance of those modifications of structure
caused by modifications of function. Eventually, among
creatures of high organization, this factor became an
important one; and I think there is reason to conclude
that, in the case of the highest of creatures, civilized men,
among whom the kinds of variation which affect survival
are too multitudinous to permit easy selection of any one,
and among whom survival of the fittest is greatly inter
fered with, it has become the chief factor : such aid as
survival of the fittest gives, being usually limited to the pre
servation of those in whom the totality of the faculties has
been most favourably moulded by functional changes.

Of course this sketch of the relations among the factors
must be taken as in large measure a speculation. We are
now too far removed from the beginnings of life to obtain
data for anything more than tentative conclusions respecting
its earliest stages ; especially in the absence of any clue to
the mode in which multiplication, first agamogenetic and
then gamogenetic, was initiated. But it has seemed to me
not amiss to present this general conception, by way of
showing how the deductive interpretation harmonizes with
the several inferences reached by induction.

In his article on Evolution in the Encyclopedia Lritan-
nica, Professor Huxley writes as follows : —

" How far ' natural selection ' suffices for the production of species

THE FACTOES OF ORGANIC EVOLUTION. 75

remains to be seen. Few can doubt that, if not the ^vhole cause, it is a very
important factor in that operation . . .

On the evidence of palaeontology, the evolution of many existing forms of
animal life from their predecessors is no longer an hypothesis, but an
historical fact ; it is only the nature of the physiological factors to which
that evolution is due which is still open to discussion."

With, these passages I may fitly join a remark made
in the admirable address Prof. Huxley delivered before
unveiling the statue of Mr. Darwin in the Museum at
South Kensington. Deprecating the supposition that an
authoritative sanction was given by the ceremony to the
current ideas concerning organic evolution, he said that
" science commits suicide when it adopts a creed."

Along with larger motives, one motive which has joined
in prompting the foregoing articles, has been the desire to
point out that already among biologists, the beliefs con
cerning the origin of species hare assumed too much the
character of a creed ; and that while becoming settled they
have been narrowed. So far from further broadening
that broader view which Mr. Darwin reached as he grew
older, his followers appear to have retrograded towards a
more restricted view than he ever expressed. Thus there
seems occasion for recognizing the warning uttered by
Prof. Huxley, as not uncalled for.

Whatever may be thought of the arguments and conclu
sions set forth in this article and the preceding one, they
will perhaps serve to show that it is as yet far too soon to
close the inquiry concerning the causes of organic evolution.

NOTE.

After the above articles were published, I received from
Dr. Downes a copy of a paper " On the Influence of Light
on Protoplasm," written by himself and Mr. T. P. Blunt,
M.A., which was communicated to the Eoyal Society in

76 THE FACTORS OP ORGANIC EVOLUTION.

1878. It was a continuation of a preceding paper which,
referring chiefly to Bacteria, contended that —

"Light is inimical to, and under favourable conditions may wholly prevent,
the development of these organisms."

This supplementary paper goes on to show that the injurious
effect of light upon protoplasm results only in presence of
oxygen. Taking first a comparatively simple type of molecule
which enters into the composition of organic matter, the
authors say, after detailing experiments : —

" It was evident, therefore, that oxyyen was the agent of destruction under
the influence of sunlight."

And accounts of experiments upon minute organisms are
followed by the sentence —

" It seemed, therefore, that in absence of an atmosphere, light failed
entirely to produce any effect on such organisms as were able to appear."
They sum up the results of their experiments in the
paragraph—

" We conclude, therefore, both from analogy and from direct experiment,
that the observed action on these organisms is not dependent on light per set
but that the presence of free oxygen is necessary ; light and oxygen
together accomplishing what neither can do alone : and the inference
seems irresistible that the effect produced is a gradual oxidation of the
constituent protoplasm of these organisms, and that, in this respect,
protoplasm, although living, is not exempt from laws which appear to
govern the relations of light and oxygen to forms of matter less highly
endowed. A force which is indirectly absolutely essential to life as we know
it, and matter in the absence of which life has not yet been proved to exist,
here unite for its destruction."

What is the obvious implication ? If oxygen in presence
of light destroys one of these minutest portions of protoplasm,
what will be its effect on a larger portion of protoplasm ?
It will work an effect on the surface instead of on the whole
mass. Not like the minutest mass made inert all through,
the larger mass will be made inert only on its outside;
and, indeed, the like will happen with the minutest mass if
the light or the oxygen is very small in quantity. Hence
there will result an envelope of changed matter, inclosing
and protecting the unchanged protoplasm — there will
result a rudimentary cell-wall.

THE SYNTHETIC PHILOSOPHY

OF

HERBERT SPENCER.

FIRST PRINCIPLES.

1 vol. $2.00.
CONTENTS.

PART I. — THE UNKNOWABLE.

1. Religion and Science. 4. The Relativity of all KnowL

2. Ultimate Religious Ideas. edge.

3. Ultimate Scientific Ideas. 5. The Reconciliation.

PART II.— THE KNOWABLE.

1. Philosophy defined. 13. Simple and Compound Evolu-

2. The Data of Philosophy. tion.

3. Space, Time, Matter, Motion, 14. The Law of Evolution.

and Force. 15. The Law of Evolution (con-

4. The Indestructibility of Matter. tinued).

5. The Continuity of Motion. 16. The Law of Evolution (con-

6. The Persistence of Force. tinued).

7. The Persistence of Relations 17. The Law of Evolution (con-

among Forces. eluded).

8. The Transformation and Equiv- 18. The Interpretation of Evolution.

alence of Forces. 19. The Instability of the Homoge-

9. The Direction of Motion. neous.

10. The Rhythm of Motion. 20. The Multiplication of Effects.

11. Recapitulation, Criticism, and 21. Segregation.

Recommencement. 22. Equilibration.

12. Evolution and Dissolution. 23. Dissolution.

24. Summary and Conclusion.

THE PRINCIPLES OF BIOLOGY.

2 vols. $4.00.
CONTENTS OF VOL. I.

PART I. — THE DATA OF BIOLOGY.

1. Organic Matter. 4. Proximate Definition of Life.

2. The Action of Forces on Or- 5. The Correspondence between

ganic Matter. Life and its Circumstances.

3. The Reactions of Organic Mat- 6. The Degree of Life varies as the

ter on Forces. Degree of Correspondence.

7. The Scope of Biology.

SPENCER 8 SYNTHETIC PHILOSOPHY.

PART II. — THE INDUCTIONS OF BIOLOGY.

1. Growth.

2. Development.

3. Function.

4. Waste and Repair.
6. Adaptation.

6. Individuality.

7. Genesis.

8. Heredity.

9. Variation.

10. Genesis, Heredity, and Varia

tion.

11. Classification.
12. Distribution.

PART III. — THE EVOLUTION OF LIFE.

1. Preliminary.

2. General Aspects of the Special-

Creation Hypothesis.

3. General Aspects of the Evolu

tion Hypothesis.

4. The Arguments from Classifica

tion.

6. The Arguments from Embryol
ogy.

6. The Arguments from Morphol
ogy-

7. The Arguments from Distribu

tion.

8. How is Organic Evolution

caused ?

9. External Factors.

10. Internal Factors.

11. Direct Equilibration.

12. Indirect Equilibration.

13. The Cooperation of the Factors.

14. The Convergence of the Evi

dences.

CONTENTS OF VOL. II.
PART IV. — MORPHOLOGICAL DEVELOPMENT.

1. The Problems of Morphology.

2. The Morphological Composition

of Plants.

3. The Morphological Composition

of Plants (continued).

4. The Morphological Composition

of Animals.

6. The Morphological Composition
of Animals (continued).

6. Morphological Differentiation in

Plants.

7. The General Shapes of Plants.

8. The Shapes of Branches.

9. The Shapes of Leaves.

10. The Shapes of Flowers.

11. The Shapes of Vegetal Cells.

12. Changes of Shape otherwise

caused.

13. Morphological Differentiation in

Animals.

14. The General Shapes of Animals.

15. The Shapes of Vertebrate Skele

tons.

16. The Shapes of Animal Cells.

17. Summary of Morphological De

velopment.

PART V. — PHYSIOLOGICAL DEVELOPMENT.

1. The Problems of Physiology.

2. Differentiations among the Out

er and Inner Tissues of Plants.

8. Differentiations among the Out
er Tissues of Plants.

4. Differentiations among the In
ner Tissues of Plants.

6. Physiological Integration in
Plants.

6. Differentiations between the

Outer and Inner Tissues of
Animals.

7. Differentiations among the Out

er Tissues of Animals.

8. Differentiations among the In

ner Tissues of Animals.

9. Physiological Integration in Ani*

mals.

10. Summary of Physiological Development.

SPENCER'S SYNTHETIC PHILOSOPHY. 3

PART VI. — LAWS OF MULTIPLICATION.

1. The Factors. 8. Antagonism between Expendi-

2. A priori Principle. ture and Genesis.

3. Obverso a pfi ion Principle. 9. Coincidence between High Nu-

4. Difficulties of Inductive Verifi- trition and Genesis.

cation. 10. Specialties of these Rela-
6. Antagonism between Growth tions.

and Asexual Genesis. 11. Interpretation and Qualifica-

6. Antagonism between Growth tion.

and Sexual Genesis. 12. Multiplication of the Human

7. Antagonism between Develop- Race.

ment and Genesis, Asexual 13. Human Evolution in the Fu-
and Sexual. ture.

APPENDIX.

A Criticism on Professor Owen's The- On Circulation and the Formation
ory of the Vertebrate Skeleton. of Wood in Plants.

THE PRINCIPLES OF PSYCHOLOGY.

2 vols. $4.00.
CONTENTS OF VOL. I,
PART I. — THE DATA OF PSYCHOLOGY.

1. The Nervous System. 4. The Conditions essential to Ner-

2. The Structure of the Nervous vous Action.

System. 5. Nervous Stimulation and Ner-

3. The Functions of the Nervous vous Discharge.

System. 6. ^Estho-Physiology.

PART II. — THE INDUCTIONS OF PSYCHOLOGY.

1. The Substance of Mind. 6. The Revivability of Relations

2. The Composition of Mind. between Feelings.

3. The Relativity of Feelings. 7. The Associability of Feelings.

4. The Relativity of Relations be- 8. The Associability of Relations

tween Feelings. between Feelings.

6. The Revivability of Feelings. 9. Pleasures and Pains.

PART III. — GENERAL SYNTHESIS.

1. Life and Mind as Correspon- 6. The Correspondence as increas-

dence. ing in Specialty.

2. The Correspondence as Direct 7. The Correspondence as increas-

and Homogeneous. ing in Generality.

3. The Correspondence as Direct 8. The Correspondence as increas-

but Heterogeneous. ing in Complexity.

4. The Correspondence as extend- 9. The Coordination of Correspon-

ing in Space. dences.

5. The Correspondence as extend- 10. The Integration of Correspon-

ing in Time. dences.

11. The Correspondences in their Totality.

8PENCEK S SYNTHETIC PHILOSOPHY.

PART IV. — SPECIAL SYNTHESIS.
1. The Nature of Intelligence. 5. Instinct.

2. The Law of Intelligence.

3. The Growth of Intelligence.

4. Reflex Action.

9. The Will.

6. Memory.

7. Reason.

8. The Feelings.

1. A Further Interpretation need-

ed.

2. The Genesis of Nerves.

3. The Genesis of Simple Nervous

Systems.

4. The Genesis of Compound Ner-

vous Systems.

6. The Genesis of Doubly Com-
pound Nervous Systems.

PART V. — PHYSICAL SYNTHESIS.

6. Functions as related w tuco*

Structures.

7. Physical Laws as thus inter.

preted.

8. Evidence from Normal Varia-

tions.

9. Evidence from Abnormal Va.

nations.
10. Results.

APPENDIX.
On the Action of Anaesthetics and Narcotics.

CONTENTS OF VOL. II.
PART VI. — SPECIAL ANALYSIS.

1. Limitation of the Subject.

2. Compound Quantitative Reason

ing.

3. Compound Quantitative Reason

ing (continued).

4. Imperfect and Simple Quantita

tive Reasoning.

5. Quantitative Reasoning in gen

eral.

6. Perfect Qualitative Reasoning.
7 Imperfect Qualitative Reason
ing.

8. Reasoning in general.
9 Classification, Naming, and Rec
ognition.

10 The Perception of Special Ob
jects.

11. The Perception of Body as pre

senting Dynamical, Statico-
Dynamical, and Statical Attri
butes.

12. The Perception of Body as pre

senting Statico- Dynamical and
Statical Attributes.

13. The Perception of Body as

presenting Statical Attri
butes.

14. The Perception of Space.

15. The Perception of Time.

16. The Perception of Motion.

17. The Perception of Resist

ance.

18. Perception in general.

19. The Relations of Similarity and

Dissimilarity.

20. The Relations of Cointension

and Non-Cointension.

21. The Relations of Coextension

and Non-Coextension.

22. The Relations of Coexistence

and Non-Coexistence.

23. The Relations of Connature and

Non-Connature.

24. The Relations of Likeness and

Unlikeness.

25. The Relation of Sequence.

26. Consciousness in general.

27. Results.

SPENCER'S SYNTHETIC PHILOSOPHY.

PART VII. — GENERAL ANALYSIS.

1. The Final Question.

2. The Assumption of Metaphysi

cians.

3. The Words of Metaphysicians.

4. The Reasonings of Metaphysi

cians, [ism.

6. Negative Justification of Real-

6. The Argument from Priority.

7. The Argument from Simplicity.

8. The Argument from Distinct-

9. A Criterion wanted. [ness.
10. Propositions qualitatively dis
tinguished.

11. The Universal Postulate.

12. The Test of Relative Validity.

13. Its Corollaries.

14. Positive Justification of Real-

ism.

15. The Dynamics of Consciousness.

16. Partial Differentiation of Sub

ject and Object.

17. Completed Differentiation of

Subject and Object.

18. Developed Conception of the

Object.

19. Transfigured Realism.

PART VIII. — COROLLARIES.

1. Special Psychology. 5. Sociality and Sympathy.

2. Classification. 6. Egoistic Sentiments.

3. Development of Conceptions. 7. Ego- Altruistic Sentiments.

4. Language of the Emotions. 8. Altruistic Sentiments.

9. Esthetic Sentiments.

THE PRINCIPLES OF SOCIOLOGY.

Vol. I. $2.00.

CONTENTS.

PART I. — THE DATA OF SOCIOLOGY.

1. Super-Organic Evolution.

2. The Factors of Social Phenom

ena.

8. Original External Factors.
4. Original Internal Factors.
6. The Primitive Man — Physical.

6. The Primitive Man — Emotional.

7. The Primitive Man — Intellect

ual.

8. Primitive Ideas.

9. The Ideas of the Animate and

the Inanimate.

10. The Ideas of Sleep and Dreams.

11. The Ideas of Swoon, Apoplexy,

Catalepsy, Ecstasy, and other
Forms of Insensibility.

12. The Ideas of Death and Resur

rection.

13. The Ideas of Souls, Ghosts,

Spirits, Demons.

14. The Ideas of Another Life.

15. The Ideas of Another World.

16. The Ideas of Supernatural

Agents.

17. Supernatural Agents as causing

Epilepsy and Convulsive Ac
tions, Delirium and Insanity.
Disease and Death.

18. Inspiration, Divination, Exor

cism, and Sorcery.

19. Sacred Places, Temples, and

Altars ; Sacrifice, Fasting, and
Propitiation ; Praise, Prayer.

20. Ancestor- Worship in general.

21. Idol- Worship and Fetich- Wor.

ship.

22. Animal-Worship.

23. Plant-Worship.

24. Nature- Worship.

25. Deities.

26. The Primitive Theory of Things.

27. The Scopo of Sociology.

6 SPENCER'S SYNTHETIC PHILOSOPHY.

PART II. — THE INDUCTIONS OF SOCIOLOGY.

1. What is a Society? 7. The Sustaining System.

2. A Society is an Organism. 8. The Distributing System.

3. Social Growth. 9. The Regulating System.

4. Social Structures. 10. Social Types and Constitutions.
6. Social Functions. 11. Social Metamorphoses.

6. Systems of Organs. 12. Qualifications and Summary.

PART III. — THE DOMESTIC RELATIONS.

1. The Maintenance of Species. 6. Polyandry.

2. The Diverse Interests of the 7. Polygyny.

Species, of the Parents, and 8. Monogamy,

of the Offspring. 9. The Family.

3. Primitive Relations of the Sexes. 10. The Status of Women.

4. Exogamy and Endogamy. 11. The Status of Children.

6. Promiscuity. 12. Domestic Retrospect and Proa

pect.

Vol. II.

PART IV. — CEREMONIAL INSTITUTIONS. $1.25.
CONTENTS.

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2. Trophies. 8. Titles.

3. Mutilations. 9. Badges and Costumes.

4. Presents. 10. Further Class-Distinctions.

5. Visits. 11. Fashion.

6. Obeisances. 12. Ceremonial Retrospect and

Prospect.

Vol. II.

PART V. — POLITICAL INSTITUTIONS. $1.50.
CONTENTS.

1. Preliminary. 10. Ministries.

2. Political Organization in gen- 11. Local Governing Agencies.

eral. 12. Military Systems.

3. Political Integration. 13. Judicial and Executive Systems.

4. Political Differentiation. 14. Laws.

5. Political Forms and Forces. 15. Property.

6. Political Heads— Chiefs, Kings, 16. Revenue.

etc. 17. The Militant Type of Society.

7. Compound Political Heads. 18. The Industrial Type of Society.

8. Consultative Bodies. 19. Political Retrospect and Pros-

9. Representative Bodies. pect.

PARTS IV AND V IN ONE VOLUME.
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SPENCER S SYNTHETIC PHILOSOPHY. 7

Vol. II.

PART VI. — ECCLESIASTIC INSTITUTIONS. $1.25.
CONTENTS.

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2. Medicine-Men and Priests. Priests.

8. Priestly Duties of Descendants. 11. The Civil Functions of Priests.

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Quasi-Priests. 13. Nonconformity.

6. The Ruler as Priest. 14. The Moral Influences of Pricst-

6. The Rise of a Priesthood. hoods.

7. Polytheistic and Monotheistic 15. Ecclesiastical Retrospect and

Priesthoods. Prospect.

8. Ecclesiastical Hierarchies. 16. Religious Retrospect and Pros-
tt. An Ecclesiastical System as a pect.

Social Bond.

PART VII. — PROFESSIONAL INSTITUTIONS. |

? In preparation.
PART VIII. — INDUSTRIAL INSTITUTIONS. )

Vol. III. — In preparation.

THE PRINCIPLES OF MORALITY.
Vol. I.

PART I.— THE DATA OF ETHICS. $1.25.
CONTENTS.

1. Conduct in general. 10. The Relativity of Pains and

2. The Evolution of Conduct. Pleasures.

8. Good and Bad Conduct. 11. Egoism versus Altruism.

4. Ways of judging Conduct. 12. Altruism versus Egoism.

5. The Physical View. 13. Trial and Compromise.

6. The Biological View. 14. Conciliation.

7. The Psychological View. 15. Absolute Ethics and Relative

8. The Sociological View. Ethics.

9. Criticisms and Explanations. 16. The Scope of Ethics.

PART II. — In preparation.
Vol. II. — In preparation.

"Mr. Spencer is one of the most vigorous as well as boldest thinkers
that English speculation has yet produced." — JOHN STUART MILL.

New York: D. APPLETON" & CO., 1, 3, & 6 Bond Street.

THE MISCELLANEOUS WORKS

HERBERT SPENCER

EDUCATION:

INTELLECTUAL, MORAL, AND PHYSICAL.

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CONTENTS.

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SOCIAL STATICS;

OR,

THE CONDITIONS ESSENTIAL TO HUMAN HAPPINESS SPECL
FIED, AND THE FIRST OF THEM DEVELOPED.

1 vol. $2.00.

CONTENTS.

INTRODUCTION.

The Doctrine of Expediency. Lemma I.
The Doctrine of the Moral Sense. Lemma II.

PART I.

1. Definition of Morality. 3. The Divine Idea, and the Con-

2. The Evanescence of Evil. ditions of its Realization.

PART II.

4. Derivation of a First Principle. 10. The Right of Property.

5. Secondary Derivation of a First 11. The Right of Property in Ideas.

Principle. 12. The Right of Property in Char-

6. First Principle. [ciple. acter.

7. Application of this First Prin- 13. The Right of Exchange.

8. The Rights of Life and Per- 14. The Right of Free Speech.

sonal Liberty. 15. Further Rights.

9. The Right to the Use of the 16. The Rights of Women.

Earth. 17. The Rights of Children.

PART III.

18. Political Rights. 24. Religious Establishment.

19. The Right to ignore the State. 25. Poor-Laws.

20. The Constitution of the State. 26. National Education.

21. The Duty of the State. 27. Government Colonization.

22. The Limit of State-Duty. 28. Sanitary Supervision. [etc.

23. The Regulation of Commerce. 29. Currency, Postal Arrangementsv

PART IV.

30. General Considerations. 31. Summary.

32. Conclusion.

THE STUDY OF SOCIOLOGY.

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5. Objective Difficulties. 12. The Theological Bias.

6. Subjective Difficulties — Intel- 13. Discipline.

lectual. 14. Preparation in Biology.

7. Subjective Difficulties — Emo- 15. Preparation in Psychology.

tionaL 16. Conclusion.

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geography are made to confirm one another. The book is illustrated with wood
cuts', which will prove both interesting and instructive. It tells of living mam
malia, pigs, hippopotami, camels, deer, antelopes, oxen, rhinoceroses, horses,
elephants, sea-cows, whales, dogs, seals, insect-eaters, rodents, bats, semi apes,
apes and their ancestors, and the man of the future.'1— Syracuse (N. Y.) Herald.

ANTHROPOID APES. By ROBERT HARTMANN, Professor in the
University of Berlin. With 63 Illustrations. 12mo. Cloth, $1.75.

"The anthropoid, or manlike or tailless, apes include the gorilla and chimpanzee
of tropical Africa, the orang of Borneo and Sumatra, and the gibbons of the East
Indies, India, and some other parts of Asia. The author of the present work has
given much attention to the group. Like m ost living zoologists he is an evolutionist,
and holds that man can not have descended from any of the fossil species which have
hitherto come under our notice, nor yet from any of the species now extant ; it is
more probable that both types have been produced from a common ground-form
which has become extinct1' — The Nation.

" It will be found, by those who follow the author's exegesis with the heed and
candor it deserves, that the simian ancestry of man does not as y«t rest upon such
solid and perfected proofs as to warrant the assumption of absolute certainty in which
materialists indulge." — New York Sun.

"The work is necessarily less complete than Huxley's monograph on 'The Cray
fish,' or Mivart's on 'The Cat,' but it is a worthy companion of those brilliant works'
and in saying this we bestow praise equally high and deserved."— Boston Gazette.

New York: D. APPLETOX & CO., 1, 3, & 5 Bond Street

D, APPLE TON & CO.'S PUBLICATIONS,

PHYSICAL EXPRESSION! Its Modes and Principles. By

FRANCIS WARNER, M. D., Assistant Physician, and Lecturer on Bot
any, to the London Hospital, etc. With 51 Illustrations. 12mo.
Cloth, $1.75.

"In the terra ' Physical Expression,1 Dr. Warner included all those changes of form
and feature occurring in the body which may be interpreted as evidences of mental
action. At first thought it would seem that facial expression is the most important
of these outward signs of inner processes; but a little observation will convince one
that the posture assumed by the body— the poise of the head and the position of the
hands— as well as the many alternations of color and of general nutrition, are just as
striking evidences of the course of thought. The subject thus developed by the au
thor becomes quite extensive, and is exceedingly interesting. The work is fully up
to the standard maintained in ' The International Scientific Series.1 "—Science.

u Among those, besides physicians, dentists, and oculists, to whom Dr. Warner's
book will be of benefit are actors and artists. The art of gesticulation and of postures
is dealt with clearly from the scientific student's point of view. In the chapters con
cerning expression in the head, expression in the face, expression in the eyes, and in
that on art criticism, the reader may find many new suggestions." — Philadelphia

COMMON SENSE OF THE EXACT SCIENCES. By the

late WILLIAM KINGDON CLIFFORD. With 100 Figures. 12ino.
Cloth, $1.50.

"This is one of the volumes of 'The International Scientific Series,1 and wan origi
nally planned by Mr. Clifford; but upon his death in 1879 the revision and completion
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purpose, and the book had to be finished by a third person. It is divided into five
chapters, treating number, space, quantity, position, and motion, respectively. Each
of these chapters is subdivided into sections, explaining in detail the principles under
lying each. Tlie whole volume is written in a masterful, scholarly manner, and the
theories are illustrated by one hundred carefully prepared figures. To teachers espe
cially is this volume valuable; and it is worthy of the most careful study." — New York
School Journal.

JELLY-FISH, STAR-FISH, AND SEA-URCHINS. Being
a Research on Primitive Nervous Systems. By G. J. ROMANES,
F. R. S., author of "Mental Evolution in Animals," etc. 12mo.
Cloth, $1.75.

" A profound research into the laws of primitive nervous systems conducted by one
of the ablest English investigators. Mr. Romanes set up a tent on the beach and ex
amined his beautiful pets for six summers in succession. Such patient and loving
work has borne its fruits in a monograph which leaves nothing to be said about jelly
fish, star-fish, and sea-urchins. Every one who has studied the lowest forms of life on
the sea-shore admires th.-se objects. " But few have any idea of the exquisite delicacy
of their structure and their nice adaptation to their place in nature. Mr. Romanes
brings out the subtile beauties of the rudimentary organisms, and shows the resem
blances they bear to the higher types of creation. His explanations are made more
clear by a large number of illustrations. While the book is well adapted for popular
reading, it is of special value to working physiologists." — New York Journal Q/
Commerce.

" A most admirable treatise on primitive nervous systems. The snhject-matter is
full of original investigations and experiments upon the animals mentioned as types
01' the lowest nervous developments.11— Boston Commercial Bulletin.

New York : D. APPLETOX & CO., 1, 3, & 5 Bond Street

r

^—i^^

QH Spencer, Herbert

366 The factors of organic

S74 evolution

BioMed

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