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FIFTY YEARS OF
DARWINISM

MODERN ASPECTS OF EVOLUTION

CENTENNIAL ADDRESSES IN HONOR OF
CHARLES DARWIN

Before the American Association for the Advancement
of Science, Baltimore, Friday, January 1, 1909

NEW YORK
HENRY HOLT AND COMPANY
1909

Aa\553

Copyricat, 1909,

BY

HENRY HOLT AND COMPANY

Published April, 1909

THE QUINN & BODEN CO. PRESS
RAHWAY, N. J.

CONTENTS

INTRODUCTION
T. C. Caampertin, University of Chicago
FIFTY YEARS OF DARWINISM .
Epwarp B. Povutron, Oxford University
THE THEORY OF NATURAL SELECTION FROM
THE STANDPOINT OF BOTANY .
Jounxn M. Courter, University of Chicago
ISOLATION AS A FACTOR IN ORGANIC EVOLU-
TION
Davi Srarr Tenax, Stanford University
THE CELL IN RELATION TO HEREDITY AND
EVOLUTION
Epmunp B. Wison, Columbia University
THE DIRECT INFLUENCE OF ENVIRONMENT .
D. T. MacDouca1, Carnegie Institution of Wash-
ington
THE BEHAVIOR OF UNIT CHARACTERS IN
HEREDITY .
W. E. Casriz, Harvard ‘University
MUTATION Sy 6. 167 oP oe Se ae 8
Cras. B. Davenport, Carnegie Institution of
Washington
ADAPTATION :
Cart H. Eicenmann, fndiana University
DARWIN AND PALEONTOLOGY .
Henry Famrretp Ossorn, Columbia (Toivexsity
and American Museum of Natural History
EVOLUTION AND PSYCHOLOGY .
G. Stantey Haut, Clark University

iii

PAGE

57

72

92

114

209

251

PLATES

Puave To. ewe we we
Fig. 1. Leptinotarsa undecimlineata, normal form.

Fig. 2. Form derived from L. undecimlineata through
the application of the climatic conditions.

Figs. 3, 4. Normal mitosis of nuclei in cells of plant.

Figs. 5, 6, 7, 8. Irregularities of mitosis in cells of
onion roots resulting from exposure to radium.
[After Gager.]

Peavwe TT, gw ee ee

T. T. Upper and lower aspects of rosette of @nothera
biennis.

'D. D. Rosette of derivative resulting from ovarial
treatment with zine sulphate.

Prats III. A Few or rae Numerous Tyres of TEETH IN

THE CHaRACINS . . . . . . . « « 192
Pirate IV. Some Srmiranities In THE CHaRactns . . 192
UATE el oe Gl Jel. ae a. GL AR ee ea

REcTIGRADATIONS IN THE TEETH oF Eocene UNGULATES.

Tor View or Tuner Sxuris or Eocene TITaANOTHERES
ILtustRaATING BRACHYCEPHALY, MESATICEPHALY, AND
DoxicHocepHaty RESPECTIVELY.

INTRODUCTION
BY

T. C. CHAMBERLIN

THE greatness of a man is shown in what he
is, in what he does, and in what he sets a-doing.

If the long list of contributions to the ses-
sions of this Association for these fifty years
were searched for products of thought whose
stimulus sprang from the life and works of
Charles Darwin, it would reveal an impressive
testimonial to his greatness as a power in our
scientific world. If it were possible to give such
an intellectual product a material embodiment
and an appropriate form, we could raise no more
sincere monument to his memory. Even in the
less tangible form it inevitably bears, it is our
monument. .By responses, individual and col-
lective, to the marvelous suggestiveness of Dar-
win’s inquiries and interpretations, the members
of this Association during the last half century
have been paying their truest tributes. More or
less unconsciously, no doubt, but none the less
genuinely, we have thus been doing honor to one
of the greatest of intellectual leaders.

The magnitude of any moving force is meas-
ured scarcely less by the obstacles surmounted

2 INTRODUCTION

and by the inertia overcome than by the positive
momentum it generates. In the first decades of
the great Darwinian movement in biology, the
tribute of our members may not have been want-
ing in demonstrations of the force of old adhe-
sions, but even then, whether by resistance or by
codperation, we gave our testimony to the new
power that made itself felt in the scientific world.
A little later we paid the tribute of conviction—
the general tribute of willing conviction, on the
part of some of us, and the even more significant
tribute of reluctant conviction, on the part of
others; but, in one way or another, we paid a uni-
versal tribute.

If we of the older school permit ourselves to be
reminiscent, the tides of thought and feeling of
the early days of the half century we celebrate
easily surge back into consciousness. We readily
recall the stirrings in the biological field when the
great question of derivation of species arose into
a concrete and, as it seemed to some, a threaten-
ing form. But it was not among us as biolo-
gists, but among us as members of a proud race,
that emotion was deepest stirred. It was in the
humanistic atmosphere that protests were most
vibrant, for man—scientific man not excepted—
is first of all a creature who takes thought of him-
self. His anthropic pride, fostered by tradi-
tional assumptions of separateness and eminent
superiority—assumptions peculiar to no race,
nation, or religion, but the common inheritance

INTRODUCTION 3

of us all—rose up in remonstrance and put bar-
riers in the way of a candid reception of the new
interpretations. But still, with all his foibles,
man, at least man of the better sort, proclaims
adhesion to the ancient admonition, “ Know thy-
self,” and ultimately he strives to be loyal to the
intellectual precedence he assigns himself. It is
his to know the truth. Those of scientific trend
early found occasion to call into fresh activity
the maxim that it is better to accept the truth
than to think of ourselves more highly than we
ought to think. Whatever rufflings of our fond
sense of humanistic caste were felt from the new
interpretations in those first days of disturbed
equanimity, we soon came to find complacency
in the new place assigned us at the head of a
multitudinous kin, the place of leadership in the
van of a great procession of ascending tribes
striving for supreme fitness.

But the days of disturbed tranquillity, for us
of the scientific household at least, soon passed
away; and, if they linger with any still, it can only
be among those outside the wide limits of this
Association. We are yet far from knowing the
whole truth, but we are tranquil in the search for
it, welcome or unwelcome as it may prove at first
to be.

In the later decades of this memorable half
century, the tribute of our membership, indi-
vidual and collective, has lain in attempts to
extend, to amend, to qualify, and to. apply the

4: INTRODUCTION

parent thought to which Darwin gave such pro-
digious impetus. To what result we have labored
to add to, or to subtract from, his great concep-
tion, the future must decide. The effort is our
tribute to the power that has moved us.

The biological realm was indeed the center of
the great movement. Of this central movement
and of the varied lines into which it has deployed,
we shall learn through the words of those who are
entitled to speak. To these, in a moment, I
shall give place. But, though the revolution had
its origin in the biological field, it was by no
means limited to it. It soon became a radiant
influence so penetrating and so stimulating that
it has been felt in every field of thought. No
realm of the intellectual world has failed to re-
spond to the power of Darwin’s method, the can-
dor of his spirit, and the force of his clear insight
and restrained judgment.

Darwin not only gave form to the whole trend
of evolutionary inquiry, but he chastened and re-
fined the moral aspects of thought in all lines of
serious intellectual endeavor. It would be too
much to say that he was the father of the evolu-
tionary conception or the sole parent of the
chastened moral attitude of thought now felt to
be binding in the scientific world. We would do
him a dishonor most obnoxious to his candid and
truthful spirit if we were to assign him more than
historic truth amply warrants. We must not
fail to recognize that before his time the evolu-

INTRODUCTION 5

tionary conception had found place in the thought
of not a few philosophic inquirers, not the least
among whom was one of his own lineage; but yet
it was Charles Darwin, more than any other, who
gave definiteness and concreteness, who gave
method and spirit, to the doctrine of derivation,
and who thus became parental to the great move-
ment in a sense equaled by no other. Such ac-
ceptances of evolutionary conceptions as had much
currency before his day, or had much tangible
influence on research, were cosmogonic rather
than biologic. Beyond doubt these pioneer
gropings in the less biased fields prepared the
way for his great contribution, but they did not
equally encounter the central obstacle. that lay in
inherited adhesions and traditional preposses-
sions, and they did not, therefore, and could not,
equally revolutionize the spirit and the attitude
of the thinking world by touching with trans-
forming power the mainspring of bias.

But if Darwin found some measure of prep-
aration for his work in the labors of predecessors
in his own and other fields, he more than amply
repaid the debt. The stimulative influence of
Darwinism on fundamental conceptions in the
celestial and terrestrial kingdoms followed close
on those in the biological realm. Both terrestrial
and celestial history are even now in the flux of
reinterpretation. The sources of this revision of
view are indeed various, but a profound Dar-
winian influence is felt in it all. It would have

6 INTRODUCTION

been felt had Darwin left nothing but his
Origin of Swpecies and the remarkable trea-
tises that followed it, but he has added thereto
leaders of thought of his own name and lineage,
and they have carried his spirit and his breadth
of view into realms he could not himself enter.
The evolution of the earth and of the heavens
has thus felt his transmitted touch. The
concept of kinship of worlds follows eas-
ily on the concept of the kinship of organic
beings.

In the transformed attitude of the intellectual
world to-day, the mooted question of the hour—
the evolution of the atom—finds a fair field,
wherein evidence needs but to accredit itself duly
to have its place and weight freely accorded it.
If the atom shall show an authenticated pedigree,
it will easily take its place in the procession of
the derived, with the plant, the animal, the earth,
and the stars.

The contributions of Darwin to the science
which it has fallen to me to follow have been great
and various, but the greatest of them all relate
to the history of life on the globe. The geolog-
ical record, as known in his day, was at once a
foundation for his work and an obstacle to its
acceptance. It was the mission of his interpre-
tations to bring forth the added truth which made
the foundation broader and firmer, and which not
only removed the seeming obstacles in the evolu-
tionary path, but replaced them by cogent evi-

INTRODUCTION 7

dence of the continuity of life and of its successive
steps of progress.

But it does not fall to me to enter upon any of
the special fields to which Darwin made his mon-
umental contributions. Your committee has
wisely assigned the leading aspects of the theory
of evolution to those peculiarly fitted to treat
them by reason of their own high attainments.
In this introductory word on behalf of the Asso-
ciation, I have found no more fitting way to ex-
press our appreciation than to recall the tribute
we have been paying by what we have done, and
what we are trying to do, because Darwin set us
a-doing.

FIFTY YEARS OF DARWINISM
BY
EDWARD B. POULTON

On this historic occasion it is of special interest
to reflect for a few moments on the part played
by the New World in the origin and growth of
the great intellectual force which dominates the
past half century. The central doctrine of evo-
lution, quite apart from any explanation of it,
was first forced upon Darwin’s mind by his South
American observations during the voyage of the
Beagle; and we may be sure that his experience
in this same country, teeming with innumerable
and varied forms of life, confirmed and deepened
his convictions as to the importance of adaptation
and thus prepared the way for Natural Selection.
Wallace, too, at first traveled in South America;
only later in the parts of the Old World tropics
which stand next to South America in richness.

Asa Gray in the New World represented Sir
Joseph Hooker in the Old, as regards the help
given to Darwin before the appearance of the
Origin, and in strenuous and most efficient de-
fense after its appearance. Chauncey Wright
similarly represents Henry Fawcett. Fritz
Miller not only actively defended Darwin, but

8

FIFTY YEARS OF DARWINISM 9

continually assisted him by the most admirable
and original observations carried out at his Bra-
zilian home. Turning to those who in some im-
portant respects differed from Darwin, I do not
think a finer example of chivalrous controversy
can be found than that carried on between him ©
and Hyatt. The immense growth of evolution-
ary teaching, in which John Fiske played so im-
portant a part, although associated with the name
of Herbert Spencer, must not be neglected on
an occasion devoted to the memory of Darwin.

Outside the conflict which raged around the
Origin, we find Dana, the only naturalist who at
first supported Darwin in his views on the per-
sistence of ocean basins and continental areas, and
Alexander Agassiz, for many years the principal
defender of the Darwinian theory of coral islands
and atolls.

American paleontology, famed throughout the
world, has exercised a profound influence on the
growth and direction of evolutionary thought.
The scale and perfection of its splendid fossil
records have attracted the services of a large band
of the most eminent and successful laborers, of
whom I can only mention the leaders:—Leidy,
Cope, Marsh, Osborn, and Scott in the Ver-
tebrata; Hall, Hyatt, and Walcott in the Inver-
tebrate sub-kingdom. The study of American
paleontology was at first believed to support a
Neo-Lamarckian view of evolution, but this, as
well as the hypothesis. of polyphyletic origins,

10 FIFTY YEARS OF DARWINISM

was undermined by the teachings of Weismann.
Difficulties for which the Lamarckian theory had
been invoked were met by the hypothesis of
Organic Selection suggested by Baldwin and
Osborn, and in England by Lloyd Morgan.
Weismann’s contention that inherent characters
are alone transmissible by heredity has also re-
ceived strong support from the immense body of
cytological, Mendelian, and mutationist work to
which the present volume bears such eloquent tes-
timony. Finally, the flourishing school of Amer-
ican psychology, under the leadership of William
James and James Mark Baldwin, accepts, and in
accepting helps to confirm, the theory of Natural
Selection.

ERASMUS DARWIN AND LAMARCK

Professor Henry F. Osborn, in his interest-
ing work From the Greeks to Darwin, con-
cludes that Lamarck was unaware of Erasmus
Darwin’s Zoonomia, and that the parallelism of
thought is a coincidence.* The following passage
from a letter* written to Huxley probably in
1859, and published since the appearance of Pro-
fessor Osborn’s book, indicates that Charles Dar-
win suspected the French naturalist of borrowing
from his grandfather :-—

1 From the Greeks to Darwin, New York, 1894, pp. 152-55. Pro-
fessor Osborn shows that on p. 145 Erasmus Darwin made use of
the term “acquired” in the sense of “acquired characters”;
“changement acquis” is the form employed by Lamarck.

2 More Letters of Charles Darwin, I, p. 125.

FIFTY YEARS OF DARWINISM 11

“ The history of error is quite unimportant, but it is
curious to observe how exactly and accurately my
grandfather (in Zoonomia, Vol. I, p. 504, 1794) gives
Lamarck’s theory. I will quote one sentence. Speaking
of birds’ beaks, he says: ‘ All which seem to have been
gradually produced during many generations by the
perpetual endeavor of the creatures to supply the want
of food, and to have been delivered to their posterity
with constant improvement of them for the purposes
required.” Lamarck published Hist. Zoolog. in 1809.
The Zoonomia was translated into many languages.”

A careful comparison of the French transla-
tion of the Zoonomia with Lamarck’s Philosophie
Zoologique and with a preliminary statement of
‘ his views published in 1802, would probably de-
cide this interesting question.

THE INFLUENCE OF LYELL UPON CHARLES
DARWIN

The limits of space compel me to pass by the
youth of Charles Darwin, with the influence of
school, Edinburgh and Cambridge, including the
intimacy with Henslow and Sedgwick—friend-
ships leading to his voyage in the Beagle, an
event which more than any other determined his
whole career. We must also pass by his earliest
convictions on evolution, the first note-book begun
in 1837, the reading of Malthus and discovery of
Natural Selection in October, 1838, the imper-
fect sketch of 1842, the completed sketch of 1844.

It is necessary, however, to pause for a brief
consideration of the influence of Sir Charles

12 FIFTY YEARS OF DARWINISM

Lyell. Although the writings of the illustrious
geologist have always been looked upon as among
the chief of the forces brought to bear upon the
mind of Darwin, evidence derived from the later
volumes of correspondence justifies the belief
that the effect was even greater and more sig-
nificant than has been supposed.

Huxley has maintained with great force that
the way was paved for Darwin by Lyell’s Prin-
ciples of Geology far more thoroughly than by
any other work.

“| . . Consistent uniformitarianism postulates evo-

lution as much in the organic as in the inorganic
world. The origin of a new species by other than ordi-
nary agencies would be a vastly greater ‘ catastrophe’
than any of those which Lyell successfully eliminated
from sober geological speculation.” *

When the Principles first appeared Darwin
was advised by Henslow to obtain and study the
first volume, “but on no account to accept the
views therein advocated.” But a study of the
very first place at which the Beagle touched, St.
Iago, one of the Cape de Verde Islands, showed
Darwin the infinite superiority of Lyell’s teach-
ings. He wrote to L. Horner,” August 29,
1844 :—

™ «I have been lately reading with care A. d’Orbigny’s
work on South America, and I cannot say how forcibly
impressed I am with the infinite superiority of the
Lyellian school of Geology over the continental. I

1 Life and Letters of Charles Darwin, II, p. 190.
2 More Letters, II, p. 117.

FIFTY YEARS OF DARWINISM 13

always feel as if my books came half out of Lyell’s brain,
and that I never acknowledge this sufficiently; nor do I
know how I can without saying so in so many words—
for I have always thought that the great merit of the
Principles was that it altered the whole tone of one’s
mind, and therefore that, when seeing a thing never
seen by Lyell, one yet saw it partially through his eyes
—it would have been in some respects better if I had
done this less, . . . ”

This letter was written a few weeks after the
date, July 5, 1844, which marks the completion
of the finished sketch of that year. On July 5
Darwin wrote the letter to his wife begging her,
in the event of his death, to arrange for the pub-
lication of the account he had just prepared. At
this psychological moment in his career he wrote
of the influence received from Lyell, and we are
naturally led to observe how essentially Lyellian
are the three lines of argument—two based on
geographical distribution, one on the relation be-
tween the living and the dead—which first led
Darwin toward a belief in evolution! The
thoughts which shook the world arose in a mind
whose whole tone had been altered by Lyell’s
teachings. Inasmuch as the founder of modern
geology received his first inspiration from Buck-
land, Oxford may claim some share in moulding
the mind of Darwin.

“COMING EVENTS CAST THEIR SHADOWS
BEFORE ”

The characteristic feature in which Natural
Selection differs from every other attempt to

14 FIFTY YEARS OF DARWINISM

solve the problem of evolution is the account
taken of the struggle for existence, and the réle
assigned to it. This struggle is keenly appre-
ciated in Tennyson’s noble poem, In Memoriam,
the dedication of which is dated 1849, ten years
before the Origin. The poet is disquieted by:—

*“ Nature red in tooth and claw
With ravine, . . .”

and by
“, . . finding that of fifty seeds

She often brings but one to bear.”

It is interesting to note that the obvious under-
statement of this last passage is corrected in the
author’s notes published by his son a few years
ago. In these we find “for fifty” read
“myriad.” The poignant sense of the waste of
individual lives is brought into close relation in
the poem with the destruction of the type or
species :—

“So careful of the type she seems,
So careless of the single life;

* So careful of the type’? but no,
From scarpéd cliff and quarried stone
She cries ‘ A thousand types are gone:
I care for nothing, all shall go.’ ”

In this association between the struggle for
existence waged by individuals and the extinction
and succession of species we seem to approach
the central idea of Darwin and Wallace. I asked
Dr. Grove of Newport in the Isle of Wight if he

FIFTY YEARS OF DARWINISM 15

would point out the parallelism, so far as it ex-
isted, to his illustrious patient, hoping that some
light might be thrown on the source of the in-
spiration. Nor was I disappointed. “ Stay,”
said the aged poet when Dr. Grove had spoken,
“In Memoriam was published long before the
Origin of Species.’ “Oh! Then you are the
man,” replied the doctor. ‘ Yes, I am the man.”
There was silence for a time and then Tennyson
said: “ I don’t want you to go away with a wrong
impression. The fact is that long before Dar-
win’s work appeared these ideas were known and
talked about.” From this deeply interesting
conversation I think it is probable that, through
mutual friends, some echo of Darwin’s researches
and thoughts had reached the great author of
In Memoriam.

The light which has been recently thrown* upon
Philip Gosse’s remarkable book, Omphalos, indi-
cates that its appearance in 1858 was connected
with the thoughts that were to arouse the world
in the following year. The author of Omphalos
was a keen and enthusiastic naturalist held fast
in the grip of the narrowest of religious creeds.
We learn with great interest that he and others
were by Lyell’s advice prepared beforehand for
the central thoughts of the Origin. To the new
teaching all the naturalist side of his nature re-
sponded, but from it the religious side recoiled.
Religion conquered in the strife, but the natural-

1In Father and Son, London, 1907.

16 FIFTY YEARS OF DARWINISM

ist found comfort in the perfectly logical con-
clusion that :—

“ Any breach in the circular course of nature could
be conceived only on the supposition that the object
created bore false witness to past processes, which had
never taken place.” *

Thus the divergence between the literal inter-
pretation of Scripture and the conclusions of -
both geologist and evolutionist were for this re-
markable man reconciled by the conviction :—

“That there had been no gradual modification of the
surface of the earth, or slow development of organic
forms, but that when the catastrophic act of creation
took place, the world presented, instantly, the structural
appearance of a planet on which life had long existed.” ?

Philip Gosse could not but believe that the
thoughts which had brought so much comfort to
himself would prove a blessing to others also.
He offered Omphalos “ with a glowing gesture,
to atheists and Christians alike. . . . But,
alas! atheists and Christians alike looked at it
and laughed, and threw it away.”* Charles
Kingsley expressed the objection felt by the
Christian when he wrote that he could not “ be-
lieve that God had written on the rock one enor-
mous and superfluous lie.” *

About twenty years ago I was present when
precisely the same conclusion was advanced by a
high dignitary of the English Church. He
argued that even if the history of the Universe

1 Father and Son, pp. 120, 121. * L. ey p. 120.
* DL. cy p. 122. + Ibid.

FIFTY YEARS OF DARWINISM 17

were carried back to a single element such as
hydrogen, the human mind would remain unsat-
isfied and would inquire whence the hydrogen
came, and that any and every underlying form
of matter must leave the inexorable question
“whence?” still unanswered. Therefore if in
the end the question must be given up, we may
as well, he argued, admit the mystery of creation
in the later stages as in the earlier. Thus he
arrived at the belief in a world formed instanta-
neously, ready-made and complete, with its fos-
sils, marks of denudation, and evidences of evolu-
tion—a going concern. Aubrey Moore, the
- clergyman who more than any other man was
responsible for breaking down the antagonism
toward evolution then widely felt in the English
Church, replied very much as Kingsley had done,
that he was unwilling to believe that the Creator
had deliberately cheated the intellectual powers
He had made. I may add that, inasmuch as
science consists in the attempt to carry down
causation as far as possible, it is above all the
scientific side of the human intellect that is out-
raged,—no weaker term can be used,—by this
more modern development of the argument of
Omphalos.

THE PUBLICATION OF THE DARWIN-
WALLACE ESSAY

In May, 18356, Darwin, urged by Lyell, began
to prepare for publication. He had determined

18 FIFTY YEARS OF DARWINISM

to present his conclusions in a volume, for he was
unwilling to place any responsibility for his
opinions on the council of a scientific society. On
this point he was, as he told Sir Joseph Hooker,
in the only fit state for asking advice; namely,
with his mind firmly made up: then good advice
was very comforting while it was perfectly easy
to reject bad advice. The work was continued
steadily until June 18, 1858, when Wallace’s let-
ter and essay arrived from Ternate. As a result
of the anniversary held in London on July 1 last
year new light has been thrown upon the circum-
stances under which the joint essay was published
fifty years before.

In consequence of the death of the eminent
botanist, Robert Brown, Vice-President and ex-
President of the Linnean Society, the last meet-
ing of the summer session, called for June 17,
was adjourned. The by-laws required that the
vacancy on the Council should be filled up within
three months, and a special meeting was called
for July 1, for this purpose. Darwin received
Wallace’s essay on June 18, too late for the sum-
mer meetings of the Society, but in good time for
Lyell and Hooker to present it to the special
meeting. Hence, as Sir Joseph Hooker said on
July 1st last, the death of Robert Brown caused
the theory of Natural Selection to be “ given to
the world at least four months earlier than would
otherwise have been the case.” Sir Joseph
Hooker also informed us that from June 18 up

FIFTY YEARS OF DARWINISM 19

to the evening of July 1, when he met Sir Charles
Lyell at the Society, all the intercourse with
Darwin and with each other was conducted by
letter, and that no fourth person was admitted
into their confidence. The joint essay was read
by the secretary of the Society. Darwin was
not present, but both Lyell and Hooker “ said
a few words to emphasize the importance of the
subject.” Among those who were present were
Oliver, Fitton, Carpenter, Henfrey, Burchell,
and Bentham, who was elected on the Council
and nominated as Vice-President in place of
Robert Brown. I cannot resist the temptation
to reprint from the memorial volume issued by
the Linnean Society of London some passages
in the address which A. R. Wallace felt con-
strained to deliver on July 1, 1908, protesting
against the too great credit which he believed had
been assigned to himself. After describing Dar-
win’s discovery of Natural Selection and the
twenty years devoted to confirmation and patient
research, Wallace continued :—

“ How different from this long study and preparation
—this philosophic caution—this determination not to
make known his fruitful conception till he could back it
up by overwhelming proofs—was my own conduct. The
idea came to me, as it had come to Darwin, in a sudden
flash of insight: it was thought out in a few hours—
was written down with such a sketch of its various appli-
cations and developments as occurred to me at the
moment,—then copied on thin letter-paper and sent off

to Darwin—all within one week. J was then (as often
since) the ‘ young man in a hurry ’; he, the painstaking

20 FIFTY YEARS OF DARWINISM

and patient student, seeking ever the full demonstration
of the truth he had discovered, rather than to achieve
immediate personal fame.

“ Such being the actual facts of the case, I should
have had no cause for complaint if the respective shares
of Darwin and myself in regard to the elucidation of
nature’s method of organic development, had been
thenceforth estimated as being, roughly, proportional to
the time we had each bestowed upon it when it was
thus first given to the world—that is to say, as twenty
years is to one week. For, he had already made it his
own. If the persuasion of his friends had prevailed with
him, and he had published his theory after ten years’,
fifteen years’, or even eighteen years’ elaboration of it,
I should have had no part in it whatever, and he would
have been at once recognized, and should be ever recog-
nized, as the sole and undisputed discoverer and patient
investigator of the great law of ‘ Natural Selection’
in all its far-reaching consequences.

“Tt was really a singular piece of good luck that
gave me any share whatever in the discovery . . . it
was only Darwin’s extreme desire to perfect his work
that allowed me to come in, as a very bad second, in the
truly Olympian race in which all philosophical biologists,
from Buffon and Erasmus Darwin to Richard Owen and
Robert Chambers were more or less actively engaged.”

ECHOES OF THE STORM

It is impossible to do more than refer briefly
to the storm of opposition with which the Origin
was at first received. The reviewer in the Athe-
neum for November 19, 1859, left the author
“to the mercies of the Divinity Hall, the Col-
lege, the Lecture Room, and the Museum.”’*
Dr. Whewell for some years refused to allow a

+ Life and Letters, II, p. 228 n.

FIFTY YEARS OF DARWINISM 21

copy of the Origin to be placed in the library of
Trinity College, Cambridge." My predecessor,
Professor J. O. Westwood, proposed to the last
Oxford University Commission the permanent
endowment of a Reader to combat the errors of
Darwinism. “ Lyell had difficulty in preventing
[Sir William] Dawson reviewing the Origin on
hearsay, without having looked at it. No spirit
of fairness can be expected from so biased a
judge.” * And even when naturalists began to
be shaken by the force of Darwin’s reasoning,
they were often afraid to own it. Thus Darwin
wrote to H. Fawcett, on September 18, 1861:—

“ Many are so fearful of speaking out. A German
naturalist came here the other day; and he tells me that
there are many in Germany on our side, but that all
seem fearful of speaking out, and waiting for some one
to speak, and then many will follow. The naturalists
seem as timid as young ladies should be, about their
scientific reputation.” °

-Among the commonest criticisms in the early
days, and one that Darwin felt acutely,* was the
assertion that he had deserted the true method of
scientific investigation. One of the best exam-
ples of this is to be found in the letter, Decem-
ber 24, 1859, of Darwin’s old teacher in geology,
Adam Sedgwick :—

1 Life and Letters, Il, p. 261.

?From a letter written by Darwin, November 4, 1862. More
Letters, I, p. 468.

® More Letters, I, p. 196.

4 See Darwin’s letter to Henslow, May 8, 1860. More Letters,
I, pp. 149, 150.

22 FIFTY YEARS OF DARWINISM

“You have deserted—after a start in that tram-road
of all solid physical truth—the true method of induc-
tion, and started us in machinery as wild, I think, as
Bishop Wilkins’s locomotive that was to sail with us to
the moon.” 7

These wild criticisms were soon set to rest by
Henry Faweett’s article in Macmillan’s Maga-
zine in 1860 and by a paper read before the
British Association by the same author in 1861.
Referring to this defense, Fawcett wrote to Dar-
win, July 16, 1861:—

“TI was particularly anxious to point out that the
method of investigation was in every respect philosoph-
ically correct. I was spending an evening last week
with our friend Mr. John Stuart Mill, and I am sure
you will be pleased to hear that he considers your reason-
ing throughout is in the most exact accordance with
the strict principles of logic. He also says the method
on investigation you have followed is the only proper
one to such a subject. It is easy for an antagonistic
reviewer, when he finds it difficult to answer your argu-
ments, to attempt to dispose of the whole matter by
uttering some such commonplace as ‘This is not a
Baconian induction.’ ”

“ As far as I am personally concerned, I am sure I
Pp ‘y med, :
ought to be grateful to you, for since my accident
nothing has given me so much pleasure as the perusal of
your book. Such studies are now a great resource
to me.” ?

* Life and Letters, II, p. 248. See also the Quarterly Review
for July, 1860. Sedgwick’s review in the Spectator, March 24,
1860, contains the following passage: “ .. . I cannot conclude
without expressing my detestation of the theory, because of its
unflinching materialism; because it has deserted the inductive
track, the only track that leads to physical truth; because it
utterly repudiates final causes, and thereby indicates a demoralized
understanding on the part of its advocates.” Quoted in Life and
Letters, II, p. 298.

2 More Letters, I, pp. 189, 190.

FIFTY YEARS OF DARWINISM 23
To this Darwin replied:—

“You could not possibly have told me anything
which would have given me more satisfaction than what
you say about Mr. Mill’s opinion. Until your review
appeared I began to think that perhaps I did not under-
stand at all how to reason scientifically.” *

THE MATURITY OF THE ORIGIN CONTRASTED
WITH THE CRUDITY OF RIVAL INTERPRE-
TATIONS

It is remarkable to contrast the maturity, the
balance, the judgment, with which Darwin put
forward his views, with the rash and haphazard
objections and rival suggestions advanced by his
critics. It is doubtful whether so striking a con-
trast is to be found in the history of science;—
on the one side twenty years of thought and in-
vestigation pursued by the greatest of naturalists,
on the other offhand impressions upon a most
complex problem hastily studied and usually very
imperfectly understood. It is not to be won-
dered at that Darwin found the early criticisms
so entirely worthless. The following extract
from an interesting letter * to John Scott, written
on December 3, 1862, shows how well aware he
was of difficulties unnoticed by critics:—

“You speak of difficulties on Natural Selection:
there are indeed plenty; if ever you have spare time
(which is not likely, as I am sure you must be a hard
worker) I should be very glad to hear difficulties from
one who has observed so much as you have. The major-

1 More Letters, I, p. 189. ? More Letters, II, p. 311.

24 FIFTY YEARS OF DARWINISM

ity of criticisms on the Origin are, in my opinion, not
worth the paper they are printed on.”

From the very first the most extraordinarily
crude and ill-considered suggestions were put for-
ward by those who were unable to recognize the
value of the theory of Natural Selection. A
good example is to be found in Andrew Mur-
ray’s principle of a sexual selection based on con-
trast,—“ the effort of nature to preserve the typ-
ical medium of the race.” * And even in these
later years the wildest imaginings may be put
forward in all seriousness as the interpretation of
the world of living organisms. Thus in Beccari’s
interesting work on Borneo,’ the author com-
pares the infancy and growth of the organic world
with the development and education of an indi-
vidual. In youth the individual learns easily,
being unimpeded by the force of habits, while
“with age heredity acts more strongly, instincts
prevail, and adaptation to new conditions of ex-
istence and to new ideas becomes more difficult;
in a word, it is much less easy to combat hered-
itary tendencies.” Similarly in the state of ma-
turity now reached by the organic world Beccari
believes that the power of adaptation is well-nigh
non-existent. Heredity, through long accumula-
tion in the course of endless generations, has be-
come so powerful that species are now stereo-

typed and cannot undergo advantageous changes.

1 Life and Letters, II, p. 261.
* Wanderings in the Great Forests of Borneo, London, 1904,
English translation, pp. 209-16.

FIFTY YEARS OF DARWINISM 25

For the same reason acquired characters cannot
now be transmitted to offspring. Beccari imag-
ines that everything was different in early ages
when, as he supposes, life was young and heredity
weak. In this assumed “ Plasmatic Epoch ” the
environment acted strongly upon organisms,
evoking the responsive changes which have now
been rendered fixed and immovable by heredity.

Even the hypothesis proposed as a substitute
for Natural Selection by so distinguished a bot-
anist as Carl Nageli turns out to be most unsat-
isfactory the moment it is examined. The idea _
of evolution under the compulsion of an internal |
force residing in the idioplasm is in essence but ,
little removed from special creation. On the sub- °
ject of Nageli’s criticisms Darwin wrote,’ Au-
gust 10, 1869, to Lord Farrer:—

“It is to me delightful to see what appears a mere
morphological character found to be of use. It pleases
me the more as Carl Nigeli has lately been pitching into
me on this head. Hooker, with whom I discussed the
subject, maintained that uses would be found for lots
more structures, and cheered me by throwing my own
orchids into my teeth.”

DARWIN’S GREATEST FRIENDS IN THE TIME
OF STRESS

It is interesting to put side by side passages
from two letters? written by Darwin to Hooker,
one in 1845 at the beginning of their friendship,

1 More Letters, II, p. 380.
2. ¢, I, p. 39. The passages here quoted are put side by side
by the editors of this work.

26 FIFTY YEARS OF DARWINISM

the other thirty-six years later, a few months be-
fore Darwin’s death. The first shows the instant
growth of their friendship: “ Farewell! What
a good thing is community of tastes! I feel as if
I had known you for fifty years. Adios.”

The second letter expresses at the end of Dar-
win’s life the same feelings which find utterance
ever and again throughout the long years of his
friendship.

* Your letter has cheered me, and the world does not
look a quarter so black this morning as it did when
I wrote before. Your friendly words are worth their
weight in gold.”

The friendship with Asa Gray began with a
meeting at Kew some years before the publica-
tion of Natural Selection. Darwin soon began
to ask for help in the work, which was ultimately
to appear as the Origin. The following letter to
Hooker, June 10, 1855, shows what he thought
of the great American botanist :—

“JT have written him a very long letter, telling him
some of the points about which I should feel curious.
But on my life it is sublimely ridiculous, my making
suggestions to such a man.” *

The friendship ripened very quickly, so that on
July 20, 1856, Darwin gave Asa Gray an account
of his views on evolution,” and on September 5
of the following year a tolerably full description *

1 More Letters, I, p. 418. Asa Gray’s generous reply is printed
on p. 421.

2 Life and Letters, II, p. 78.

*Z. c., pp. 119, 120.

FIFTY YEARS OF DARWINISM QT

of Natural Selection. From this latter letter
Darwin chose the extracts which formed part of
his section of the joint essay published July 1,
1858.

Asa Gray’s opinion on first reading the Origin
was expressed not to Darwin but to Hooker in
a letter written January 5, 1860:—

“It is done in a masterly manner. It might well
have taken twenty years to produce it. It is crammed
full of most interesting matter—thoroughly digested—
well expressed—close, cogent, and taken as a system it
makes out a better case than I had supposed pos-
Glee es ea

After attending to Agassiz’s unfavorable
opinion of the book, he continues: “ Tell Darwin
all this. I will write to him when I get a chance.
As I have promised, he and you shall have fair
play here. . . .”* A little later, when on Jan-
uary 23, he wrote to Darwin himself, Asa Gray
concluded: “ I am free to say that I never learnt
so much from one book as I have from yours.” *

It is impossible to do justice on the present
occasion to the numerous letters in which Darwin
expressed his gratitude for the splendid manner
in which Asa Gray kept his word and “ fought
like a hero in defense.” * At a time when few |

naturalists were able to understand the drift of
| Darwin’s argument, the acute and penetrating |
(mind of Asa Gray had in a moment mastered
| every detail. Thus Darwin wrote on July 22, '

1 Life and Letters, II, p. 268.
2D. Gs p. 272, "DT. ¢, p. 310.

28 FIFTY YEARS OF DARWINISM

1860, concerning the article in the Proceedings
of the American Academy for April 10:—

“T can not resist expressing my sincere admiration
of your most clear powers of reasoning. As Hooker
lately said in a note to me, you are more than any
one else the thorough master of the subject. I declare
that you know my book as well as I do myself;
and bring to the question new lines of illustration and
argument in a manner which excites my astonishment
and almost my envy!. . . Every single word seems
weighed carefully, and tells like a 32-pound shot.” *

Some weeks later, on September 26, 1860,
Darwin again expressed the same admiration,
and stated that Asa Gray understood him more
perfectly than any other friend :—

“| . . You never touch the subject without making

it clearer. I look at it as even more extraordinary
that you never say a word or use an epithet which does
not express fully my meaning. Now Lyell, Hooker,
and others, who perfectly understand my book, yet
sometimes use expressions to which I demur.” ”

Darwin also sent* Asa Gray’s defense of the
Origin to Sir Charles Lyell, whom he was ex-
tremely anxious to convince of the truth of evolu-
tion. Asa Gray’s religious convictions pre-
vented the full acceptance of Natural Selection.
He was ever inclined to believe in the Providen-
tial guidance of the stream of variation. He also
differed from Darwin in the interpretation of
all instincts as congenital habits.*

+ Life and Letters, II, p. 326. 7D. ¢, pp. 344, 345,
* More Letters, I, p. 169.
‘ Life and Letters, III, p. 170.

FIFTY YEARS OF DARWINISM 29

The same close intimacy and mutual help be-
gun in the preparation of the Origin was con-
tinued in Darwin’s later botanical works. Thus
Darwin owed his Climbing Plants to the study
of a paper by Asa Gray, and he dedicated
his Forms of Flowers to the American botanist
“as a small tribute of respect and affection.”
Concerning some of the researches which after-
ward appeared in this book, Darwin wrote: * “ I
care more for your and Hookevr’s opinion than
that of all the rest of the world, and for Lyell’s
on geological points.”

Another great name, that of Huxley, is espe-
cially associated in our minds with the defeat of
those who would have denied that the subject was
a proper one for scientific investigation. In the
strenuous and memorable years that followed the
appearance of the Origin the mighty warrior
stands out as the man to whom more than to any
other we owe the gift of free speech and free
opinion in science,—the man so admirably de-
scribed by Sir Ray Lankester at the Linnean
celebration, “the great and beloved teacher, the
unequaled orator, the brilliant essayist, the un-
conquerable champion and literary swordsman—
Thomas Henry Huxley.”

Comparing the friendships to which Darwin
owed so much, Lyell was at first the teacher but
finally the pupil,—unwilling and unconvinced at
the outset, in the end convinced although still

1 Life and Letters, III, p. 300.

30 FIFTY YEARS OF DARWINISM

unwilling; Hooker in England and Asa Gray in
America were the two intimate friends on whom
he chiefly depended for help in writing the Origin
and for support to its arguments; Huxley was
the great general in the field where religious con-
victions, expressed or unexpressed, were the
foundation of a fierce and bitter antagonism.

THE ATTACKS OF RICHARD OWEN AND
ST. GEORGE MIVART

An unnecessary bitterness was imported into
the early controversies in England, because of
the personality of the scientific leaders in the
attacks on the Origin. Of these the chief was
the great comparative anatomist, Richard Owen.
In spite of his leading scientific position, this re-
markable man withdrew from contact with his
brother zodlogists, living in a self-imposed isola-
tion which tended towards envy and bitterness.
The same unavailing detachment had been car-
ried much further by the great naturalist W. J.
Burchell, who, as from a watch-tower, looked
upon the world he strove to avoid with an ab-
sorbed and jealous interest. Professor J. M.
Baldwin has shown how inevitable and inexorable
is the grip of the social environment: the more
we attempt to evade it the more firmly we seem
to be held in its grasp.

In the first years of the struggle Owen’s bitter
antagonism made itself felt in the part he took
as “crammer ” to the Bishop of Oxford, and in

FIFTY YEARS OF DARWINISM 31

his anonymous article in the Edinburgh Review
for April, 1860. But Owen could not bear to
remain apart from the stream of thought when
there was no doubt about the way it was flowing,
so that in a few years he was maintaining some
of the chief conclusions of the Origin, although
retracting nothing, but rather keeping up his bit-
ter attacks upon Darwin. This treatment re-
ceived from one who was all affability * when they
met was naturally resented by Darwin, whose
feelings on the subject are expressed in the fol-
lowing passage from a letter to Asa Gray,’ July
23, 1862 :—

“ By the way, one of my chief enemies (the sole one
who has annoyed me), namely Owen, I hear has been
lecturing on birds; and admits that all have descended
from one, and advances as his own idea that the oceanic
wingless birds have lost their wings by gradual disuse.
He never alludes to me, or only with bitter sneers, and
coupled with Buffon and the Vestiges.”

In the historical sketch added to the later edi-
tions of the Origin, Owen is the only writer who
is severely dealt with. In this introductory sec-
tion Darwin said that he was unable to decide
whether Owen did or did not claim to have orig-
inated the theory of Natural Selection.’

About twelve years after the appearance of
the Origin another opponent, St. George Mivart,

1“Mrs. Carlyle said that Owen’s sweetness always reminded
her of sugar of lead.” Life and Letters of T. H. Huzley,
London, II, p. 167.

2 More Letters, I, p. 203.

* Origin of Species, 6th ed., p. xviii.

32 FIFTY YEARS OF DARWINISM

produced something of the same bitterness as
Owen and for a similar reason. Thus Darwin
wrote* to Hooker, September 16, 1871, as fol-
lows :—

“You never read such strong letters Mivart wrote
to me about respect towards me, begging that I would
call on him, etc., etc.; yet in the Q. Review [July, 1871]
he shows the greatest scorn and animosity towards
me, and with uncommon cleverness says all that is most
disagreeable. He makes me the most arrogant, odious
beast that ever lived. I can not understand him; I
suppose that accursed religious bigotry is at the root
of it. Of course he is quite at liberty to scorn and
hate me, but why take such trouble to express something
more than friendship? It has mortified me a good
deal.”

On other occasions at a much later date I have
myself observed that there was something pecu-
liar about the poise of Mivart’s mind, which
seemed ever inclined to pass with abrupt transi-
tion from the extreme of an unnecessary effusive-
ness to an unnecessarily extreme antagonism.

Mivart’s attack, contained in his book The
Genesis of Species, was effectively dealt with
by Chauncey Wright in the North American
Review for July, 1871. Darwin was so pleased
with this defense that he obtained the author’s
permission for an English reprint,’ and with fur-
ther additions it was published as a pamphlet by

2 More Letters, I, p. 333. See also Life and Letters, Il,
. 147.
. ? The pamphlet was published at Darwin’s expense. For his
keenly appreciative letter to the author see Life and Letters,
III, p. 145.

FIFTY YEARS OF DARWINISM 33

John Murray in 1871. A copy presented by
Darwin to the late J. Jenner Weir and now in
the Library of the Hope Department of Oxford
University Museum contains an interesting holo-
graph letter referring to the pamphlet and bear-
ing upon the controversy that followed upon the
appearance of Mivart’s book. This letter is, by
kind permission of the Darwin family, now made
public :—
“ Down,
“ Beckenham, Kent.
“ Oct. 11, 1871.

“ My dear Sir

**T am much obliged for your kind note & invitation.
I sh? like exceedingly to accept it, but it is impossible.
I have been for some months worse than usual, & can
withstand no exertion or excitement of any kind, & in
consequence have not been able to see anyone or go
anywhere.—As long as I remain quite quiet, I can do
some work, & I am now preparing a new and cheap
Edit” of the Origin in which I shall answer Mr.
Mivart’s chief objections. Huxley will bring out a
splendid review on d° in the Contemporary R., on
November Ist.

“T am pleased that you like Ch. Wright’s article. It
seemed to me very clever for a man who is not a
naturalist. He is highly esteemed in the U. States
as a Mathematician & sound reasoner.

“TI wish I could join your party.—

“My dear Sir
“Yours very sincerely
“ Cu. Darwin.” *

Chauncey Wright speaks of presenting, in his
review of Mivart, considerations “in defense and

1 The letter is addressed to J. Jenner Weir, Esq. 6 Haddo
Villas, Blackheath, London, S. E.

34 FIFTY YEARS OF DARWINISM

illustration of the theory of Natural Selection.
My special purpose,” he continues, “ has been to
contribute to the theory by placing it in its proper
relations to philosophical inquiries in general.” *
This able critic in America and Henry Fawcett
in England represent a class of thinkers who have
taken and still take a very important part in up-
holding the theory of Natural Selection. It is not
necessary to be a biologist in order to compre-
hend the details and the bearings of this theory.
They were at the very first understood by able
thinkers who were not scientific men or who fol-
lowed some non-biological science, when natural-
ists themselves were hopelessly puzzled. And at
the present time such support is of the highest
importance when within the limits of the sciences
most nearly concerned the intense and natural
desire to try all things is not always accompanied
by the steadfast purpose to hold fast that which
is good.
LAMARCK’S HYPOTHESIS AND THE HERED-

ITARY TRANSMISSION OF ACQUIRED CHAR-
ACTERS

The greatest change in evolutionary thought
since the publication of the Origin was wrought,
after Darwin’s death, by the appearance of that
wonderful and beautiful theory of heredity,
which looks on parents as the elder brother and
sister of their children. In this theory, itself
an outcome of minute and exact observation,

1 Life and Letters, III, pp. 143, 144,

FIFTY YEARS OF DARWINISM 35

Weismann raised the question of the hereditary
transmission of acquired characters, the very
foundation of Lamarckian evolution. Darwin
accepted such transmission, and it was in order
to account for “the inherited effects of use and
disuse, &c.,” * that he thought out his marvelous
hypothesis of pangenesis. If such effects be not
transmitted pangenesis becomes unnecessary and
Weismann’s simpler, more convincing, and bet-
ter supported hypothesis of the continuity of the
germ-plasm takes its place. It is impossible on
the present occasion to speak in any detail of the
controversy which has raged intermittently dur-
ing the past twenty years on this fascinating sub-
ject. I will, however, briefly consider a single
example of the error into which, as I believe,
Darwin was led by following the Lamarckian
theory of hereditary experience. I refer to the
interpretation which he suggests for feelings of
“the sublime,” applying this term to the effect
upon the brain of a vast cathedral, a tropical for-
est, or a view from a mountain height. Thus,
writing to E. Gurney, July 8, 1876, Darwin said
on this subject:—“. . . possibly the sense of
sublimity excited by a grand cathedral may have
some connection with the vague feelings of terror
and superstition in our savage ancestors, when
they entered a great cavern or gloomy forest.”

An interesting account is given by Romanes *

1 See the letter to Huxley, July 12 (1865?), in Life and Letters,
Ill, p. 44.

2 Life and Letters, III, p. 186.

2 Ibid. pp. 54, 55. See also I, pp. 64, 65.

36 FIFTY YEARS OF DARWINISM

of Darwin’s own experience of these feelings, re-
lating how he at first thought that they were most
excited by the magnificent prospect surveyed
from one of the summits of the Cordilleras, but
afterwards came down from his bed on purpose
to correct this impression, saying that he felt
most of the sublime in the forests of Brazil.

We may first observe that the remarkable feel-
ings induced by such experiences are very far
from unpleasant, as we should expect them to be
on the theory which refers them to the apprehen-
sions and dangers of our primitive ancestors.
Thus, on May 18, 1832, when the first impres-
sions of a Brazilian forest were freshest in Dar-
win’s mind, he wrote to Henslow, telling him of
an expedition of 150 miles from Rio de Janeiro
to the R. Macao.

“ Here I first saw a tropical forest in all its sublime
grandeur—nothing but the reality can give any idea
how wonderful, how magnificent the scene is... .
I never experienced such intense delight. I formerly
admired Humboldt, I now almost adore him; he alone
gives any notion of the feelings which are raised in
my mind on first entering the tropics.” *

Furthermore, how are we to account on any
such hypothesis for the similarity of the feelings
excited by the forest, where enemies might lurk
unseen, and the mountain peak, the very spot
which offers the best facility for seeing them? It
is also difficult to understand why the terrors of
primitive man should be specially associated with

1 Life and Letters, I, pp. 236, 237,

FIFTY YEARS OF DARWINISM 37

caves or with the most magnificent forests on the
face of the earth. There is no valid reason for
believing that any less danger lurked amid trees
of ordinary size or lay in wait for him by the
riverside, in the jungle, or the rock-strewn waste.
In the midst of life he was in death in every sol-
itary place that could afford cover to an enemy;
on the mountain top probably least of all.

The feelings inspired by the interior of a cathe-
dral are especially instructive in seeking the ex-
planation of the psychological effect. We may
be sure that the result is here produced by the
unaccustomed scale of the esthetic impression.
A cathedral the size of an ordinary church would
not produce it. However intensely we may ad-
mire, the sense of the sublime is not excited or
but feebly excited by the exterior of a cathedral,
nor does it accompany the profound intellectual
interest aroused by the sight of the pyramids.
The thrill of the sublime, in the sense in which the
term is here used, is, I do not doubt, the result of
surprise and wonder raised to their highest power
—a psychological shock at the reception of an
esthetic visual experience on an unwonted scale,
—vast as if belonging to a larger world in which
the insignificance of man is forced upon him. It
is not excited by the pyramids which are in form
but symmetrical hills of stone, nor does the ex-
terior of any building afford an experience suf-
ficiently remote to produce the feeling in any high
degree.

38 FIFTY YEARS OF DARWINISM

W. J. Burchell, in one of his letters’ to Sir
William Hooker, points out that the feelings of
awe and wonder aroused in a Brazilian forest are
not to be expected in those to whom the sight is
familiar. As regards the depth and nature of
the effects produced by the experiences here re-
ferred to, it would be very interesting to com-
pare the savage with the civilized man, the uned-
ucated with the educated mind. That the results
are intimately bound up with the psychological
differences between individuals—in part inherent,
in part due to training and experience—is well
illustrated in a story told by the late Charles
Dudley Warner, who took two English friends
to see for the first time the Grand Canyon of
the Colorado. When they reached the point
where the whole prospect—boundless beyond im-
agination—is revealed in a moment of time, one
of his friends burst into tears, while the other
relieved his feelings by unbridled blasphemy.

The remarkable psychological effects of a
grandeur far transcending and far removed from
ordinary experience may be compared to the
thrill? so often felt on hearing majestic music, a
thrill we do not seek to explain as a faint, far-off
reminiscence of dread inspired by the savage war-
cry. I do not doubt that an explanation of the
sublime based on the terrors of our primitive an-

1 Preserved in the Library at Kew, but, I believe, as yet unpub-
lished.

2 Darwin spoke of his backbone shivering during the anthem
in King’s College chapel. Life and Letters, I, p. 49; see also
p. 170.

FIFTY YEARS OF DARWINISM 39

cestors is an example of the mistaken interpre-
tations into which even Darwin was led by fol-
lowing the hypothesis of Lamarck.

FRANCIS DARWIN ON THE TRANSMISSION OF
ACQUIRED CHARACTERS

One of the most recent attempts to defend the
Lamarckian doctrine of the hereditary transmis-
sion of acquired characters is contained in the
important Presidential Address of Mr. Francis
Darwin to the British Association at Dublin
(1908). In this interesting memoir the author
expresses his belief that such transmission is im-
plied by the persistence of the successive develop-
mental stages through which the individual
advances toward maturity. Following Hering
and Richard Semon he is disposed to explain the
hereditary transmission of these stages by a
process analogous to memory. It is interesting
to observe that this very analogy had been
brought before Charles Darwin, but failed to sat-
isfy him. He wrote* to G. J. Romanes, May 29,
1876 :—

*More Letters, I, p. 364. See also the following sentence in
a letter on Pangenesis, written June 3, 1868, to Fritz Miller: “It
often appears to me almost certain that the characters of the
parents are ‘photographed’ on the child, only by means of
material atoms derived from each cell in both parents, and devel-
oped in the child.” More Letters, II, p. 82. The following
passage in a letter to Sir Joseph Hooker, February 28, 1868, is
also of great interest: ‘When you or Huxley say that a single
cell of a plant, or the stump of an amputated limb, has the
‘potentiality’ of reproducing the whole or ‘diffuse an influence,’
these words give me no positive idea;—but when it is said that
the cells of a plant, or stump, include atoms derived from every
other cell of the whole organism and capable of development, I
gain a distinct idea.” Life and Letters, III, p. 81.

40 FIFTY YEARS OF DARWINISM

“T send by this post an essay by Hiackel attacking
Pan. and substituting a molecular hypothesis. If I
understand his views rightly, he would say that with
a bird which strengthened its wings by use, the forma-
tive protoplasm of the strengthened parts became
changed, and its molecular vibrations consequently
changed, and that these vibrations are transmitted
throughout the whole frame of the bird, and affect
the sexual elements in such a manner that the wings
of the offspring are developed in a like strengthened
manner. . . . He lays much stress on inheritance
being a form of unconscious memory, but how far this
is a part of his molecular vibration, I do not under-
stand. His views make nothing clearer to me; but this
may be my fault.”

Should it hereafter be proved that acquired
characters are transmitted, I can not but think
that the interpretation will be on the lines of
Charles Darwin’s hypothesis of Pangenesis. But
the probability that any such result will be estab-
lished, already shown to be extremely small, has
become even more remote in the light of the re-
cent investigations conducted by Mendelians and
mutationists.

For the transmission of all inherent qualities,
including the successive stages of individual de-
velopment, Weismann’s hypothesis of the con-
tinuity of the germ-plasm supplies a sufficient
mechanism. JI remember, more than twenty
years ago, asking this distinguished discoverer
how it was that the hypothesis arose in his mind.
He replied that when he was working upon the
germ-cells of Hydrozoa he realized that he was
dealing with material which early and late in the
history of the individual was most carefully

FIFTY YEARS OF DARWINISM 41

preserved as if of the most essential importance
for the species. If the efficient cause of the
stages of ontogeny resides in the fertilized ovum
—as we cannot doubt—Weismann’s hypothesis
satisfactorily accounts for their hereditary trans-
mission. For the portion of the ovum set aside
to form the germ-cells from which the next gen-
eration will arise is reserved with all its powers
and includes the potentiality of these stages no
less than the other inherent characteristics of the
individual.

It is, I think, unfortunate to seek for analogies
—and vague analogies they must always be—
between heredity and memory. However much
we have still to learn about it, memory is, on its
physiological side, a definite property of certain
higher cerebral tissues,—a property which has
clearly been of the utmost advantage in the strug-
gle for life and bears the stamp of adaptation.
Compare, for instance, the difficulty in remem-
bering a name with the facility in recognizing a
face. Adaptation would appear to be even more
clearly displayed in the unconscious registration
in memory and the instant recognition of another
individual as seen from behind or when partially
concealed. Such memory is quite independent
of the artistic power. Without any intelligent
appreciation of what is peculiar to another indi-
vidual, his characteristic features are stored up
unconsciously so that when seen again he is in-
stantly recognized.

42 FIFTY YEARS OF DARWINISM

One other consideration brought forward by
Mr. Francis Darwin may be briefly discussed.
It is well known that plants have the power of
adjusting themselves to their individual environ-
ment, and that such adjustment may beneficially
take the place of a rigid specialization. The
static condition of plants renders this power espe-
cially necessary for them, and the hereditary
transmission of the results of its exercise espe-
cially dangerous. Where the seed falls, there
must the plant grow. The parent was limited to
one out of many possible environments; the off-
spring may grow in any of them, and for one
that would hit off the precise conditions of the
parent and would benefit by inheriting the
parental response, numbers would have to live in
different surroundings and might be injured by
the hereditary bias.

Mr. Francis Darwin calls attention to the
leaves of the beech, which in the interior shaded
parts of the tree possess a structure different
from that exhibited in the outer parts more freely
exposed to light. The structure of the shaded
leaves resembles that apparently stereotyped in
trees permanently adapted to shade, and Mr.
Francis Darwin is inclined to regard the fixed
condition as a final result of the hereditary trans-
mission of the same response through a large
number of generations.

The development of shade foliage in the beech
is, I presume, a manifestation of a power widely

FIFTY YEARS OF DARWINISM 43

spread among animals and probably among plants
also, a power of producing a definite individual
adaptation in response to a definite stimulus.
To stereotype the result would be to convert a
benefit to the individual into an injury to the
species. The beech in a very shady place would
presumably develop the maximum of the shade
foliage. How disadvantageous would the hered-
itary bias be to its offspring that happened to!
grow in more exposed situations. But, it is
argued, in plants subject to the fixed condition
we do meet with the fixed structure, just as if
repetition had at length produced an hereditary
result.. The answer to this argument seems to
me to be complete. When conditions are uni-
form and no power of individual adaptation is
required, Natural Selection, without attaining’
the power, would produce the fixed result in the
usual way. If, however, a species already pos-
sessing the power, ultimately came to live perma-
nently in one set of conditions and thus ceased
to need it, the power itself, no longer sustained
by selection, would sooner or later be lost.

DARWIN’S VIEWS ON EVOLUTION BY
“ MUTATION ”

It is interesting to note that the term “ Muta-
tion ” appears at one time to have suggested itself
to Darwin‘ in order to express the evolution or

1This seems clear from the following passage in a letter
written February 14, 1845, to Rev. L. Blomefield (Jenyns):
“Thanks for your hint about terms of ‘mutation,’ etc.; 1 had

44 FIFTY YEARS OF DARWINISM

descent with modification of species, by no means
implying change by large and sudden steps as in
the usual modern acceptation of the term. In-
deed, the words “ mutable,” “ mutability,” and
their opposites have never been employed with
the special significance now attached to “ muta-
tion.” Every one believes in the mutability of
species, but opinions differ as to whether they
change by mutation.

It is a mistake to suppose that Darwin did not
long and carefully consider large variations, or
“ mutations,” as supplying the material for evo-
lution. Writing to Asa Gray as early as August
11, 1860, he said* of great and sudden varia-
ation :—

“TJ have, of course, no objection to this, indeed it
would be a great aid, but I did not allude to the subject,
for, after much labor, I could find nothing which satis-
fied me of the probability of such occurrences. There
seems to me in almost every case too much, too complex
and too beautiful adaptation in every structure to
believe in its sudden production.”

In the twenty years between 1860 and 1880 we
find that Darwin was continually brought back
to this subject by his correspondents, and by re-
views and criticisms of his work. Scattered over

some suspicions that it was not quite correct, and yet I do not
yet see my way to arrive at any better terms. It will be years
before I publish, so that I shall have plenty of time to think
of better words. Development would perhaps do, only it applied
to the changes of an individual during its growth.” More Letters,
I, p. 50. :

2 Thife and Letters, Il, pp. 333, 334.

FIFTY YEARS OF DARWINISM 45

this period we find numbers of letters in which he
expressed his disbelief in an evolution founded on
“sudden jumps” or “ monstrosities,” as well as
on “ large,” “extreme,” and “ great and sudden
variations.” Out of many examples I select one
more because of its peculiar interest. The Duke
of Argyll had criticised Darwin’s theory of Nat-
ural Selection as though it had been a theory
of mutation, an interpretation repudiated by
Darwin.

The Duke of Argyll in his address* to the
Royal Society of Edinburgh, December 5, 1864,
had said:—“ Strictly speaking, therefore, Mr.
Darwin’s theory is not a theory of the Origin of
Species at all, but only a theory on the causes
which lead to the relative success and failure of
such new forms as may be born into the world.”
In a letter to Lyell (January 22, 1865), Darwin
wrote concerning this argument of the Duke’s:—

“T demir . . . to the Duke’s expression of ‘new
births.” That may be a very good theory, but it is not
mine, unless he calls a bird born with a beak 1-100th of
an inch longer than usual ‘a new birth’; but this is
not the sense in which the term would usually be under-
stood. The more I work the more I feel convinced it
is by the accumulation of such extremely slight varia-
tions that new species arise.” ”

I desire again to state most emphatically that,
during the whole course of his researches and re-

flections upon evolution, Darwin was thoroughly

1 Scotsman, December 6, 1864,
2 Life and Letters, III, p. 33.

46 FIFTY YEARS OF DARWINISM

aware of the widespread large variations upon
which the mutationist relies. He had the mate-
rial before him, he formed his judgment upon it,
and on this memorable day it seems specially
appropriate to show how extraordinarily sure his
scientific instincts were wont to be. This will
be made clear by a few examples of the solution
which Darwin found for problems which at the
time had either not been attempted at all or had
been very differently interpreted.

Darwin’s explanation of coral islands and
atolls, at first generally accepted, was afterwards
called in question. Finally, the conclusive test
of a deep boring entirely confirmed the original
theory. Perhaps the most remarkable case is
that of the permanence of ocean basins and con-
tinental areas, a view which Darwin maintained
single-handed in Europe, although supported by
Dana in America, against Lyell, Forbes, Wal-
lace, Hooker, and all others who had written on
the subject. Darwin considered it mere waste
of time to speculate about the origin of life;
we might as well, he said, speculate about the
origin of matter. Nothing hitherto discovered
has shaken this opinion, which is ‘expressed al-
most in Darwin’s words in Professor Arrhenius’
recent work.” In the fascinating subject of geo-
graphical distribution we now know that Darwin
anticipated Edward Forbes in explaining the

alpine arctic forms as relics of the glacial period,
+ Worlds in the Making. English translation, London, p. 190.

FIFTY YEARS OF DARWINISM ANT

while he interpreted the poverty of Greenland
flora and the reappearance of north temperate
species in the southern part of South America as
results of the same cause. Almost as soon as the
facts were before him in Wollaston’s memoirs,
Darwin had interpreted the number of wingless
beetles in oceanic islands as due to the special
dangers of flight. He anticipated H. W. Bates’
hypothesis of mimicry, but drove it from his mind
because he did not feel confident about the geo-
graphical coincidence of model and mimic. Long
before the Origin appeared Darwin had thought
over and rejected the idea that the same species
could have more than a single origin or could
arise independently in two different countries—
a hypothesis very popular in later years, but, I
believe, now entirely abandoned.

I should wish to advance one consideration be-
fore concluding this section of my address. Cer-
tain writers on mutation seem to hold the view that
Natural Selection alone prevents large variations
from often holding the field and leading to great
and rapid changes of form. Such a view is not
supported by the history of species which inhabit
situations comparatively sheltered from the
struggle, such as fresh water, caves, certain
islands, or the depth of the ocean. Organisms
in these places tend to preserve their ancestral
structure more persistently than in the crowded
areas where Natural Selection holds more potent
sway.

48 FIFTY YEARS OF DARWINISM

EVOLUTION CONTINUOUS OR DISCONTINUOUS

Darwin fully recognized the limit to the results
which can be achieved by the artificial selection
in one direction of individual variations. ‘Thus
he wrote,, August 7, 1869, to Sir Joseph
Hooker :—

“TI am not at all surprised that Hallett has found
some varieties of wheat could not be improved in cer-
tain desirable qualities as quickly as at first. All
experience shows this with animals; but it would, I
think, be rash to assume, judging from actual experi-
ence, that a little more improvement could not be got
in the course of a century, and theoretically very
improbable that after a few thousands [of years’] rest
there would not be a start in the same line of variation.”

The conception of evolution hindered or for a
time arrested for want of the appropriate varia-
tions is far from new. The hypothesis of organic
selection was framed by Baldwin, Lloyd Mor-
gan, and Osborn to meet this very difficulty, as
expressed in the following paragraph quoted
from the present writer’s address to the Amer-
ican Association for the Advancement of Science
at the Detroit meeting, October 15, 1897 :—

“ The contention here urged is that natural selection
works upon the highest organisms in such a way that
they have become modifiable, and that this power of
purely individual adaptability in fact acts as the nurse
by whose help the species . . . can live through

1 More Letters, I, p. 314.

FIFTY YEARS OF DARWINISM 49

times in which the needed inherent variations are not
forthcoming.” ?

It has already been shown that Darwin entirely
recognized the limits which the variations now
called “ fluetuating” may set to the progress
achieved by artificial selection, and that he ad-
mitted the necessity of waiting for a fresh “ start
in the same line.” In this respect he agreed with
modern writers on mutation; but differed from
them, as has been already abundantly shown, in
the magnitude assigned to the variations form-
ing the steps of the onward march of evolution.
His observation and study of nature led him to
the conviction that large variations, although
abundant, were rarely selected, but that evolu-
tion proceeded gradually and by small steps,—
that it was “ continuous,” not “ discontinuous.”

In his presidential address * to the British As-
sociation at Cape Town in 1905, Sir George
Darwin brought forward the following argument
from analogy against the “ continuous transfor-
mation of species ” :—

“In the world of life the naturalist describes those
forms which persist as species; similarly the physicist
speaks of stable configurations or modes of motion of
matter; and the politician speaks of States. The
idea at the base of all these conceptions is that of
stability, or the power of resisting disintegration. In
other words, the degree of persistence of permanence
of a species, of a configuration of matter, or of a State

2 Development and Evolution. J. M. Baldwin, New York, 1902,
. 350.
Py Report British Association, 1905, p. 8.

50 FIFTY YEARS OF DARWINISM

depends on the perfection of its adaptation to its sur-
rounding conditions.”

After maintaining that the stability of states
rises and declines, culminating when it reaches
zero in revolution or extinction, and that the
physicist witnesses results analogous with those

studied by the politician and the historian, the
author continues :—

“These considerations lead me to express a doubt
whether the biologists have been correct in looking for
continuous transformation of species. Judging by
analogy we should rather expect to find slight con-
tinuous changes occurring during a long period of
time, followed by a somewhat sudden transformation
into a new species, or by rapid extinction.” *

I do not, of course, doubt that there is reality
in the analogy between the evolution of states
and of species, but it is not, I submit, close
enough to justify the author’s reasoning from
one to the other. The communities of the social
Hymenoptera present much closer analogies with
political states, and yet even here it would be
unjustifiable to infer that the evolution of insect
societies has been discontinuous.

+The following footnote is appended to Sir George Darwin’s
address:—“ If we may illustrate this graphically, I suggest that
the process of transformation may be represented by long lines
of gentle slope, followed by shorter lines of steeper slope. The
alternative is a continuous uniform slope of change. If the
former view is correct, it would explain why it should not be
easy to detect specific change in actual operation. Some of my
critics have erroneously thought that I advocate specific change
per saltum.”

In reply to this note it may be pointed out that “ per saltum
evolution” or “discontinuous evolution” differs from “ continu-
ous evolution” only in the steepness of the slope of change.

FIFTY YEARS OF DARWINISM 51

The analogy seems to me far looser between the
changes of configuration of matter witnessed by
the physicist and the modification of a species as
a result of the struggle with its organic environ-
ment. The essential characteristics by which the
evolutionary history of the organic world di-
verges widely from that of the inorganic is very
clearly stated in the following brief passage from
a letter* written by Charles Darwin to Sir Jo-
seph Hooker, on November 23, 1856, just three
years before the publication of the Origin:—

“ Again, the slight differences selected, by which a
race or species is at last formed, stands, as I think can
be shown (even with plants, and obviously with animals),
in a far more important relation to its associates than
to external conditions. Therefore, according to my
principles, whether right or wrong, I can not agree
with your proposition that time, and altered conditions,
and altered associates, are ‘ convertible terms.’ I look
at the first and last as far more important, time being
important only so far as giving scope to selection.”

THE FIFTIETH ANNIVERSARY OF THE ORIGIN
OF SPECIES;—A RETROSPECT

That the Origin of Species, which Darwin de-
scribed as undoubtedly the chief work of his life,’
should have been bitterly attacked and misrepre-
sented in the early years of the last half century,
is quite intelligible; but it is difficult to under-
stand the position of a recent writer who main-
tains that the book exercised a malignant influ-

+ Life and Letters, Il, p. 87.
2 Life and Letters, I, p. 86.

52 FIFTY YEARS OF DARWINISM

ence upon the interesting and important study
of species and varieties by means of hybridism.
As regards these researches its appearance, we
are told, “ was the signal for a general halt”; *
upon them Natural Selection “ descended like a
numbing spell”; ? and if we are still unsatisfied
with his fertility in metaphor the author offers a
further choice between the forty years in the wil-
derness,’ and the leading into captivity.*
Francis Galton, in his address as a recipient
of the Darwin-Wallace medal on July Ist last,
recalled the effect of the Linnean Society Essay
and the Origin. The dominant feeling, he said,
was one of freedom. This liberty was offered to
the student of hybridism as freely as to any other.
No longer brought up against the blank wall of
special creation, he could fearlessly follow his re-
searches into all their bearings upon the evolution
of species. And this had been clearly foreseen
by Darwin when, in 1837, he opened his first
note-book and set forth the grand program which
the acceptance of evolution would unfold. He
there said of his theory that “it would lead to
study of . . . heredity,” that “it would lead
to closest examination of hybridity and genera-
tion.” In the Origin itself the admirable re-
searches of Kélreuter and Gartner on these very
subjects received the utmost attention and were

‘Report British Association, 1904, p. 575.

°L. ¢., p. 576,

8 Mendel’s Principles of Heredity, W. Bateson, 1902, p. 104.
*D. c, p. 208.

FIFTY YEARS OF DARWINISM 53

brought before the world far more prominently
than they have ever been either before or since.
Furthermore, the only naturalist who can be de-
scribed as a pupil of Darwin’s was strongly ad-
vised by him to repeat some of Girtner’s experi-
ments." It is simply erroneous to explain the
neglect of such researches as a consequence of
the_appearance_of-the-Origin and the study of
adaptation. So far from acting as a “ numbing
spall ape cay other inquiry, adaptation itself
has been nearly as much neglected as hybridism,
and for the same reason—the dominant influence
upon biological teaching of the illustrious com-
parative anatomist Huxley, Darwin’s great gen-
eral in the battles that had to be fought, but not
a naturalist, far less a student of living nature.

The momentous influence of the Origin upon
the past half century, as well as that strange lack
of the historic sense which alone could render pos-
sible the comparisons I have quoted, require for
their appreciation the addition of yet another
metaphor to the series we have been so freely
offered.

The effect of the Origin upon the boundless
domain of biological thought was as though the
sun had at length dispelled the mists that had
long enshrouded a vast primeval continent. It
might then perhaps be natural for some primitive

1 Darwin’s letter of December 11, 1862, to John Scott, contains
the following words: “If you have the means to repeat Girtner’s
experiments on variations of Verbascum or on maize (see the
Origin), such experiments would be preéminently important.”

54 FIFTY YEARS OF DARWINISM

chief to complain of the strong new light that was
flooding his neighbors’ lands no less than his own,
thinking in error not inexcusable at the dawning
of the intelligence of mankind, that their loss
must be his gain.

And now in my concluding words I have done
with controversy.

Fifty years have passed away, and we may be
led to forget their deepest lesson, may be tempted
to think lightly of the follies and the narrow-
ness, as they appear to us, of the times that are
gone. ‘This in itself would be a narrow view.

The distance from which we look back on the
conflict is a help in the endeavor to realize its
meaning. Huxley’s Address on The Coming of
Age of the Origin was a pean of triumph. Tyn-
dall, his friend, further removed from the strug-
gle by the nature of his life-work, realized its
pathos when he spoke in his Belfast Address of
the pain of the illustrious American naturalist
who was forced to recognize the success of the
teachings he could not accept,—the naturalist
who dictated in the last year of his life the
unalterable conviction that these teachings were
false.

I name no names, but I think of leaders of
organic evolution in this continent and in Europe,
—sons of great men to whom the new thoughts
brought the deepest grief, men who struggled
tenaciously and indomitably against them. And
full many a household unknown to fame was the

FIFTY YEARS OF DARWINISM 55

scene of the same poignant contrast, was torn by
the same dramatic conflict.

We have passed through one of the world’s
mighty bloodless revolutions; and now, standing
on the further side, we survey the scene and are
compelled to recognize pathos as the ruling
feature.

The sublime teachings which so profoundly
transformed mankind were given by Him who
came not to bring peace on earth but a sword.
And so it is in all the ages with every high cre-
ative thought which cuts deep into “ the general
heart of human kind.” It must bring when it
comes division and pain, setting the hearts of the
fathers against the children and the children
against the fathers.

The world upon which the thoughts of Dar-
win were launched was very different from the
world to which were given the teachings of Gal-
ileo and the sublime discoveries of Newton. The
immediate effect of the first, although leading to
the bitter persecution of the great Italian, was
restricted to the leaders of the Church; the influ-
ence of the second was confined to the students of
science and mathematics, and was slow in pene-
trating even these. Nor did either of these high
achievements of the human intellect seriously
affect the religious convictions of mankind. It
was far otherwise with the teachings of the Origin
of Species; for in all the boundless realm of phi-
losophy and science no thought has brought with

56 FIFTY YEARS OF DARWINISM

it so much of pain, or in the end has led to so
full a measure of the joy which comes of intel-
lectual effort and activity as that doctrine of
Organic Evolution which will ever be associated,
first and foremost, with the name of Charles
Robert Darwin.

THE THEORY OF NATURAL SELEC-
TION FROM THE STANDPOINT
OF BOTANY

BY
JOHN M. COULTER

THE indebtedness of Botany to Charles Dar-
win extends beyond his formulation of the theory
of the origin of species by Natural Selection.
His historical position in plant physiology and
in plant ecology is one of first rank, which these
phases of Botany have often gratefully acknowl-
edged. As for the theory of Natural Selection,
its relation to’ the development of modern plant
morphology is still more fundamental. It is true
that about ten years before the appearance of
the Origin of Species, Hofmeister had given to
modern plant morphology its first great impulse
in his demonstration of the essential relationships
among higher plants; but the announcement of
the theory of Natural Selection suggested a
modus operandi for the plant phylogeny that
may be said to have been established. Among
plants, the facts and an outline of phylogeny
for the application of any theory of descent had
been secured, so that Natural Selection came to
plant morphology at the psychological moment.

It is no wonder that it was received by plant mor-
87

58 NATURAL SELECTION FROM

phologists with eagerness, and that it stimulated
tremendously the type of investigation initiated
chiefly by Hofmeister. Whether Natural Selec-
tion stands or falls as an adequate explanation of
the origin of species, there can never be any doubt
as to the breath of life it infused into the young
science of phylogenetic plant morphology.

I am in no position to state whether from the
standpoint of Botany the theory of Natural Se-
lection presents any more difficulties or probabil-
ities than it does from the standpoint of Zodlogy.
The literature of the theory in its application to
animals is so vast, and has become so special, that
no botanist can be expected to compass it intelli-
gently. The present series of papers may make
this situation clear; and yet I cannot presume to
speak for botanists in general, among whom there
is great diversity of opinion. I can only express
the opinion of an individual botanist who has had
some experience in dealing with the facts that
enter into the construction of phylogenies.

SELECTION DOES NOT ORIGINATE
CHARACTERS

When the botanist confines his attention to a
wide-ranging genus of numerous species, as the
genus Aster in North America, for example, the
origin of these species by Natural Selection
would seem to be an adequate explanation of the
situation. The variations are endless and in

THE STANDPOINT OF BOTANY 59

every direction, the intergrades are innumerable,
the habitats are exceedingly diverse, and Natural
Selection would seem to necessitate just the re-
sult observed. In fact, the greatest American
student of the genus, after a prolonged effort to
detect and define the boundaries of its species,
gave it as his private opinion that “ there are no
species in Aster.” Of course this must be under-
stood as an expression of despair rather than of
belief, but it emphasizes the situation. With the
wide-ranging genera showing this condition, it
was not difficult to imagine that the sharp differ-
ences among isolated species are to be explained
by the breaking up of their continuity; and so all
species were swept into the category of Natural
Selection.

On the other hand, when the botanist came to
enlarge the horizon of his observation, and in-
cluded the whole phylogeny of some great group
of plants, or even the phylogeny of the whole
plant kingdom, he began to have doubts as to the
adequacy of Natural Selection as an explanation
of all the changes. He has learned to regard: this
selection as a factor that perpetuates and perhaps
develops certain characters, and that eliminates
others; but he cannot discover how it can really
originate new characters. The genus Aster, for
example, is defined by a definite group of char-
acters; and the species may be regarded as the
selected variants of these same characters. The
pattern changes, as in the kaleidoscope, but noth-

60 NATURAL SELECTION FROM

ing new has entered into any combination. But
when the Aster boundary is crossed, and still
more when the boundaries of Composite and
then of Angiosperms are crossed, absolutely new
characters are met on every hand; and still the
phylogenetic connections seem convincing. For
example, perhaps no plant morphologist doubts in
these days that at least some of the Gymnosperms
are phylogenetically related to ancient ferns. The
distinguishing mark between the two groups is
the absence of seeds in the one and their presence
in the other. The seed and all that goes with it
is a new character, and how selection could have
originated it, is a question at whose answer even
scientific imagination balks. It is evident that
the ovules of Gymnosperms are related by de-
scent to the sporangia of ferns in some way, but
so extensive a change does not seem to come
within the possibilities of Natural Selection. We
have relatively primitive ovules, but they are
enormously different from fern sporangia; and
we can imagine how selection may have trans-
formed these ovules into those of more advanced
type, for this is only manipulating a structure
already in existence and is adding nothing new.
The leaves of sporophytes, the vascular system,
the root system are further illustrations of the
same kind. Absolutely unrepresented in the
lower groups, they are new, complex, and fully
functioning structures when we meet them first.
Of course lost records and an inconceivable lapse

THE STANDPOINT OF BOTANY 61

of time are the usual answers, but they do not
save us from doubt.

In brief, by the botanist who has brought to-
gether a wide range of material, natural selection
might be accepted as having variously arranged
a group of established characters, and in this
sense given rise to what we call species; but it
could not be accepted so easily as originating
such new characters as distinguish great groups.
In a certain sense, of course, there is nothing new,
or else there would be no phylogeny; but as we
use the word character, it often appears as a new
thing in passing from one great group to another
one presumably derived from it.

NON-ADAPTIVE “ ADAPTATIONS ”

To the botanist, the greatest immediate diffi-
culty with Natural Selection has probably ie
from the idea of adaptations associated with it.
For a time he was captivated with the idea, and :
much botanical literature testifies to the fact.
As he then understood it, nature selected those
forms that are best adapted to their environment,
and destroyed those that are less adapted. This
meant that the characters of the forms selected
for survival must show some fitness for the envi-
ronment, and great ingenuity was displayed in.
explaining this fitness. Then came the new sub-
ject ecology and its associate experimental mor-
phology, and the old explanations began to
vanish.

62 NATURAL SELECTION FROM

For example, the character of thorns was said
to be selected because their presence was a pro-
tection against grazing animals. Now it is
known that thorns chiefly prevail among plants
in regions peculiarly free from grazing animals;
and that even if the grazing animals are present
the thorns do not appear in the early stages of the
plant, when they are most needed. Conversely,
the plants chiefly attacked by grazing animals are
singularly free from thorns. Experimental work
has shown that many thorns are a response to
poor nutrition, and that they may or may not be-
come an established character.

The elaborate stinging hairs of the nettle rep-
resent a character that according to this view
was built up by Natural Selection, with adapta-
tion as_the principle.of selection. Now it is
known that the nettle is indifferent to their pres-
ence and gets along without them.

It is a well-known fact that many seeds, espe-
cially those of arid regions, develop a testa so
hard that it interferes with the breaking through
of the embryo. In fact, it is becoming evident
that if selection is working in these cases it is
working towards “ over-adaptation.” *

A difficulty is also presented by such structures
as the velamen of the aérial orchids, as well as
by the water-conducting vessels of the vascular
system. In both of these cases the structures do

1This situation has been developed by the recent studies of
the germination of seeds and spores by Dr. William Crocker of
the University of Chicago.

THE STANDPOINT OF BOTANY 63

not perform their very important functions until
the cells are dead. Just how a group of dead
cells, performing a mechanical function, could
have been built up by Natural Selection, is hard
to imagine; and yet, in the case of the vascular
system its presence is a fundamental distinction
between two great divisions of the plant king-
dom.

A striking illustration of the change of view
that plant structures are necessarily useful be-
cause they have been selected on account of adap-
tation has been developed by a very recent inves-
tigation of extra-floral nectaries,* which included
an examination of 100 species of plants growing
in the Botanic Gardens of Buitenzorg, Java.
The view in reference to many of these extra-
floral nectaries has been that they attract ants,
which in turn defend the host plant from its ene-
mies. Hence we have such a category of plants
as myrmecophiles, or “ ant-loving plants.” Dar-
win himself naturally believed in myrmecophiles,
and Kerner included them among his illustrations
of protection against “ unbidden guests.” Now
it appears that any such use for these remark-
able organs is untenable; and there are many
facts that suggest that they have no definite pur-
pose that could be laid hold of as an adaptation.
The secretion often begins late in the life of the
plant, so that any protection it affords is lacking

‘1 Nieuwenhuis von Uxkiill-Giildenbandt, M.: “ Extraflorale
Zuckerausscheidungen und Ameisenschutz,” dann. Jard. Bot. Bui-
tenzorg, II, 6; pp. 195-327. 1907.

64 NATURAL SELECTION FROM

when most needed! In some cases the secretion
begins at a very early stage of the plant and soon
fails, leaving the maturing and adult plants un-
protected. The nectaries secrete spasmodically
and are often dry; and the nectar of many forms
is avoided by ants and other animals. There is
no relation between: mutilated flowers, ants, and
extra-floral nectaries. Most mutilated flowers
produce as many seeds as those that are not; and
the honey-seeking ants are not combative and do
not attack other insects visiting their host. If
these extra-floral nectaries have been developed
and perpetuated by Natural Selection, it is an
illustration of the selection of harmful structures,
for they often attract insects of all kinds, which
damage the plant in various ways. The investi-
gation showed that individual plants which se-
crete little or no nectar are less harmed by insects
than are those that produce nectar.
It is such work that is playing havoc with the
“adaptations” of botanical literature, and is
_ forcing botanists to see in these various structures
‘inevitable responses to conditions that have noth-
ing to do with adaptation. It would be going
too far to say that such results destroy absolutely
all faith in the selection and development and fix-
ing of adapted structures, but they do tend to
weaken faith and to demand that every claimed
case shall be subject to rigid experimental inves-
tigation. That there must be selection no one
pretends to deny, so far as I know, but when the

e

THE STANDPOINT OF BOTANY 65

selection includes unfavorable as well as favor-
able characters, it seems to have lost its motive.

And still, behind all this uncertainty as to the
selection and perpetuation of small variations, as
to whether this kind of indiscriminate selection
can result in anything so definite as distinct spe-
cies, there is clearly evident the large fact of the
evolution of the plant kingdom, which has be-
come a more difficult problem than ever before.
To observe and explain the small results, which
are the only kind that can be brought under the
absolute control of modern investigation, seems
to result in obtaining a measuring rod too short
to apply to general phylogeny; and the more con-
fusing are our experimental results, the larger
becomes the error that is multiplied by the gen-
eral application.

So far as I am acquainted with the opinions
of botanists whose work has to do with structures
and phenomena involved in evolution, there seems
to be a general feeling that Natural Selection
does not select individual plants on the basis of
some small and better adapted variation, and so
build up a character, which with its associates
will gradually result in a closely allied new spe-
cies; but that its selection of individuals seems
to hold no relation to their useful characters. On
the other hand, there is general conviction that
Natural Selection determines what species shall
survive, simply by eliminating those that do not.
Applying this to a general phylogeny, Natural

66 NATURAL SELECTION FROM

Selection becomes a factor of enormous impor-
tance; for the species that survive determine,
within limits, the species to be produced.

NON-UTILITY IN THE EVOLUTION OF
GYMNOSPERMS

A general illustration of this point of view may
be taken from the phylogenetic relationships
among Gymnosperms. This ancient group
stands among plants as one of remarkable rigid-
ity. Land plants should be more plastic than
land animals, for they must remain fixed in a
given environment, while animals can shift their
environment when the pressure of change comes.
A striking contrast between the taxonomic char-
acters used by zodlogists and those used by bot-
anists is brought out here. Among botanists, the
taxonomic characters in most general use are
those that respond with least promptness or not
at all to changing environment; while among
zodlogists, as I am informed, the taxonomic char-
acters in most general use largely fall in the cat-
egory of so-called “adaptation” characters,
which had far better be called ‘“‘ response ” char- -
acters. For this very reason, I can easily imag-
ine that there should be more supporters of Nat-
ural Selection among zodlogists than among bot-
anists.

Be this as it may, Gymnosperms seem to be
about the least plastic of land plants, certainly
the least plastic of any great group. Even the

THE STANDPOINT OF BOTANY 67

number of chromosomes, which in some groups
of plants may vary from species to species, seems
to be practically a fixed number in the whole
assemblage. There seems to be among them lit-
tle or no visible response in nature to changing
conditions of the most extreme kinds. It would
seem that selection among these relatively inva-
riable forms can hardly be more than the accident
of crowding. Certainly one can lay hold of no
kind of variation in nature that even suggests
the coming characters of another species, much
less of another genus or family. And yet the
group as a whole shows that certain distinct evo-
lutionary tendencies have been worked out in a
progressive way. Students of the group may
differ as to the details of the phylogenetic his-
tory, but there is no difference of opinion as to
its general features. Some of these general fea-
tures may be instructive in this connection.

The plant which produces the female sex or-
gans, known as the female gametophyte, is not
only in the midst of an ovule invested by a thick
integument, but is also directly inclosed by the
heavy wall of the megaspore that produced it.
Tf any structure is shut away from the influences
of a changing environment, it would seem to be
this one. And yet, through the whole series of
Gymnosperms, this gametophyte shows a pro-
gressive transformation. In the most primitive
forms it matures as a relatively large mass of
tissue, and late in its history the female sex organs

68 NATURAL SELECTION FROM

(archegonia) appear. In the first stage of its
development it consists of a large number of free
nuclei; in the second stage walls appear and a
tissue is formed; and in the last stage this tissue
grows and finally produces the archegonia with
their egg. The constant tendency throughout
the whole group is to produce the female sex
organs earlier and earlier in the history of the
gametophyte. A series can be arranged illus-
trating the appearance of the sex organs at what
might be called the mature stage of the gameto-
phyte, at one extreme; then their appearance at
earlier and earlier stages of the tissue develop-
ment, until they appear with the first formation of
walls; and finally, at the other extreme, the eggs
appear at the stage of free nuclei, so that no sex
organs are formed. This progressive slipping
back of the egg in the ontogeny of the gameto-
phyte holds no relation to any advantage that can
be detected. Certainly it holds no relation to
any advantage in fertilization, for that is a pro-
longed process among Gymnosperms, and the
pollen tube containing the sperms may live for a
season or two in the tissues of the ovule. Taking
the group as a whole, this is not a sporadic
change, occurring here and there; but the two
extremes I have given are the two extremes of
the Gymnosperm phylum. This kind of progres-
sive change is beyond the reach of experiment,
and its explanation is beyond the reach of imagi-
nation as yet.

THE STANDPOINT OF BOTANY 69

The same kind of progressive change is shown
also in the embryo of Gymnosperms. In the
most primitive condition, the first stage of em-
bryo formation is extensive free nuclear division
within the fertilized egg; after this, walls are
formed and the egg becomes filled with tissue,
the proembryo. Throughout the Gymnosperm
series there is a steady reduction of the amount
of free nuclear division, and with it a reduction
of the amount of proembryonic tissue, so that
finally it occupies a very small portion of the fer-
tilized egg. All this change has taken place fur-
ther from outside influences than the change in
the gametophyte, for the embryo is imbedded in
the gametophyte.

It may be claimed that these are not the char-
acters that taxonomists use in distinguishing spe-
cies. This is true, but they are just the charac-
ters that distinguish great groups, and represent
the advancement of the plant kingdom as a whole.
It so happens that both of the progressive
changes noted as occurring among Gymnosperms
culminate among Angiosperms.

The male gametophyte of Gymnosperms
shows a similar progressive change, not so steady,
but none the less evident. Its few cells are con-
tained within the resistant wall of the pollen
grain which produces it. In the more primitive
condition the vegetative cells are variable in num-
ber, but evident; but there is a persistent tend-
ency to eliminate them, which reaches comple-

70 NATURAL SELECTION FROM

tion in certain Gymnosperms, and is a constant
feature of Angiosperms.

It may be said that in all these cases we are
dealing with structures that have ceased to be
useful, and therefore are being gradually elim-
inated. No one can say how useful they are, but
no one can deny that they are functional. But
there is a striking illustration of another sort
among Gymnosperms. The suspensor is a con-
spicuous organ of the embryo in this group, with
a development apparently out of all proportion
to its usefulness. In fact, it is a most exagger-
ated structure, often becoming closely coiled on
account of its extreme length. One would sup-
pose that this would be the first structure
eliminated, or at least curtailed, if usefulness de-
termines suppression. But the suspensor of
Gymnosperms shows no symptom of suppression
throughout the whole group, and still among the
heterosporous Pteridophytes below and the An-
giosperms above, where the same conditions pre-
vail, it shows no such unusual development.

Several illustrations could be taken from Gym-
nosperms, all of them fundamental in the struc-
ture and progress of the group, and none of them

‘in use by taxonomists. My claim is that it may
' be one thing to pass from species to species within
‘the limits of a small natural group; and a very
different thing to pass from one great group to
another. I do not doubt that the characters of
a genus may have been juggled in a variety of

THE STANDPOINT OF BOTANY 71

ways to form what we call its species, and that
one of these ways may have been Natural Selec-
tion, with or without adaptation. Our problem,
however, includes more than the origin of species.
All of our observation and experimental work in
this field is immensely important in demonstrat-
ing the theory of descent, and in showing how the
final diversity of species is reached; but the meth-
ods for securing this final diversity may not apply
and probably do not apply to the establishment
of the assemblages of different characters that
distinguish the great groups, and that any study
of phylogeny shows to have been wrought out
by steady and progressive change through all im-
aginable changes of environment. Species have
been likened to the individual waves that appear
on the surface of a choppy sea; if so, the deep-
seated changes to which I refer, and which phy-
logeny makes so evident, may be likened to the
great oceanic currents, whose movement and
direction proceed with no relation to the choppy
surface.

ISOLATION AS A FACTOR IN
ORGANIC EVOLUTION

BY
DAVID STARR JORDAN

By isolation, segregation or separation as a
factor in evolution, we mean the failure of a por-
tion of one group or species to interbreed freely
with the rest of its kind. Such failure is due to
the presence of some barrier which prevents free
intermingling of individuals or to some condition
or group of conditions which sets certain indi-
viduals off from the mass of their kind. Through
separations of this sort race distinctions arise,
and in time by the same means the more profound
modifications which mark what we call species.
The occasion of divergence in most cases is found
in geographical separation, the “ raiimliche Son-
derung,” on which such strong emphasis has been
justly laid by Moritz Wagner. It may again
be a separation of some other kind, as segrega-
tion, through the occupation of different tracts
within the same general area, or seasonal separa-
tion, as when flowers bloom or animals mate at
different times of the year. There are also forms
of physiological segregation. Self-fertilized
plants mate with their neighbors irregularly or
by chance, the pure species standing alongside of

72

ISOLATION IN ORGANIC EVOLUTION ‘73

hybrids or quasi-hybrids. Dr. Shull informs us
that several such cases occur in the flora of Cali-
fornia. A race or species of higher animals may
develop dislikes or infertilities with forms other-
wise nearly related. Caton tells us that this is
true of deer, which will not cross with other spe-
cies unless ‘“‘ demoralized,” or relieved of race
antipathy, by enforced association.

LAW OF GEOGRAPHICAL DISTRIBUTION

Free interbreeding tends to unify or obliterate
forms which are fertile with each other. Isola-
tion in any form tends to check this process, and
hence in negative fashion works to create new
forms based on distinctions arising through nat-
ural variation and retained through heredity.
From this fact arises the rule that closely related
forms or nascent species do not as a rule inhabit
or rather breed in the same area. This proposi-
tion has been termed by Dr. J. A. Allen “ Jor-
dan’s Law of Geographical Distribution.”

The law or generalization has been stated as
follows :—

“ Given any species (or kind) in any region, the near-
est related species (or kind) is not to be found in the
same region, nor in a remote region, but in a neigh-
boring district separated from the first by a bar-

rier of some sort, or at least by a belt of country,
the breadth of which gives the effect of a barrier.”

This law holds good as a general rule among
animals. ‘The only exceptions yet indicated are

74 ISOLATION AS A FACTOR

found among plants in which cross-fertilization
is not general, among Protozoa and other low
forms in which specific distinctions are unknown
or at least obscurely shown, in cases of isolation
other than geographical, and in a few cases which
seem to be explainable on the ground of re-
invasion. It is possible that species once thor-
oughly separated through some form of geo-
graphical segregation may later invade the terri-
tory, the one of the other, without crossing or
hybridization. This seems likely to occur among
plants, and it is possible among migratory ani-
mals also. Taking the world over, re-invasion is
probably not a rare phenomenon, although in
most cases the invading species may fail to estab-
lish itself. In the case of animals dependent on
man, we find sometimes a form of political segre-
gation, which may lead to the separation of races
without actual physical barriers. The races of
sheep in England, for example, go by counties.
The artificial boundary of a county is a barrier
to man, rather than to the sheep. In all forms
of artificial selection, a corresponding degree of
artificial segregation is always implied and, with-
out segregation, selection has no effectiveness in
race-forming. Nothing, for example, can be
done for the race improvement of fishes, unless
these can be segregated in artificial ponds, away
from the unselected mass of the species.

IN ORGANIC EVOLUTION 15

THE WAY ISOLATION WORKS

Isolation, as a factor in evolution, represents
the failure of a species to unify itself or to main-
tain a homogeneous character among its mem-
bers. Within a unified species, each member will
be fertile with any other of the opposite sex. In
time, the descendants of any one may cross with
descendants of all the others, thus bringing all
individuals to that degree of common relation-
ship implied by membership in a common species.
Wherever inter-crossing is checked along any
line, a part of the individuals will be set off from
the mass, and here divergence at once begins.
One cause of divergence may lie in the fact that
in each isolated group there is some original de-
viation from the average of the common stock,
thus giving at the start some slight difference in
heredity. But this is purely hypothetical and it
is not probable in any special case. Other and
apparently more potent causes of divergence lie
in the difference of experiences to which each
group is exposed. The stress of the struggle for
existence is never quite the same in different lo-
calities, and the nature of selection must vary
accordingly.

That notable differences obtain in time, even
in pure stocks, and when there is no visible reason
for change, is clearly shown in the experience of
stock breeders. Of this, a typical example will
suffice. Darwin tells us that the two flocks of

76 ISOLATION AS A FACTOR

Leicester sheep, those of Mr. Buckley and of Mr.
Burgess, were “ purely bred from the original
stock of Mr. Bakewell for fifty years.” There is
not a suspicion of a single instance of deviation
from the pure Bakewell Leicester breed in either
flock. Yet after fifty years the difference in the
flocks of sheep is so great that they “have the
appearance of being quite different varieties.”
In nature, as in domestication, individuals of the
same race, animals or plants, prevented from
inter-crossing for a long time, present at least the
appearance of distinct varieties or species. A
study of the weeds of the world, as they have
spread from place to place, should show this fact
in interesting fashion. It can also be shown by
a comparative study of dogs or horses. Mr.
Vernon Bailey tells me that in the pouched
gophers and other rodent groups each valley has
its individual peculiarities, those shown in the
skulls as well as in the forms or colors of the ani-
mals. All these variations, too small to justify
the use of technical names, form the beginnings
of difference in subspecies. With more perfect
isolation these characters would soon assume
greater importance. They seem to indicate the
beginning of species-forming.

So far as species in nature are concerned, we
can account for the origin of none of them, except
on the ground of the presence of some forms of
isolation. In those groups of animals or plants
which have been most studied, subspecies or vari-

IN ORGANIC EVOLUTION 77

eties are recognized only as a geographical lim-
itation can be shown.

The known facts fully justify the statement
by Dr. A. E. Ortmann that :—

“The four factors named, variation, inheritance,
selection, and separation, must work together to form
different species. It is impossible to think that one of
these should work by itself, or that one could be left
aside.”

To use a convenient analogy, the movement of
organic evolution may be compared to the course
of a stream. Isolation is the rocky ledge which
does nothing, but whose resistance must deter-
mine the direction of the river’s flow. Selection
is the force that drives the stream along, and vari-
ation and heredity lie inherent in the nature of the
stream of life itself. All of these are necessary
in bringing about the final result, whatever that
may be. With these there are doubtless other
facts, extrinsic and intrinsic, but in this world of
varied contour and of prodigal reproduction, no
organism, whatever its heredity or its variations,
can escape these limiting environmental condi-
tions. Whatever takes part in the final result
must be a factor in evolution, whether it be an
initial factor in variation or not.

In the belief of the writer, the minor differ-
ences which separate species and subspecies
among animals and plants, in so far as these are
not traits of adaptation (and most of them are
clearly not such), owe their existence to some

78 ISOLATION AS A FACTOR

form of isolation or segregation. By the effect of
some form of barrier the members of one group
are prevented from interbreeding with those of
another minor group or with the mass of the
species. As a result, from difference of parent-
age, or difference in selection, or from difference
in the trend of development, whatever its cause,
local peculiarities arise. “ Migration,” says Dr.
Coues (and by this he means the shifting of hab-
itation), “holds species true; localization lets
them slip ”; or, rather, localization leaves them in
differing conditions in the general process of av-
eraging up the mass of the species. The peculi-
arities of the parents in an isolated group become
intensified by in-breeding. These peculiarities
become modified in some continuous direction by
the selection induced by the characteristics of
the local environment. They may possibly be
changed, as some have imagined, in one way or
another, by germinal reactions induced by impact
of environment. It may be that change of envi-
ronment sometimes excites germinal variation.
In any event, a new form is sooner or later inev-
itable if the segregation is complete. This new
form is never coincident in range with the parent
species, nor with any other closely cognate or
germinate form. Neither is it likely to be found
in some remote part of the earth. The details
of its distribution will be determined by the na-
ture of the organism and by its relation to its
environment. The struggle for existence is a

IN ORGANIC EVOLUTION 79

very different matter in different parts of the
world of life. The competition with like forms,
the struggle with unlike forms, the compromise
with hard conditions of life, all these change at
every angle, and the character of Natural Selec-
tion changes with them. The individual animals
are mobile, as plants are not. They shift about
and occupy their range more perfectly, while in
plants their pollen and their seed have great ad-
vantages over animals. With a plant everything
depends on where its seed is dropped. Where
an animal is born or hatched is a matter of rela-
tive indifference. With plants, some seed is sure
to reach almost every available point within the
range of the species, while the vast majority of
seeds never have a chance to germinate. All
these, and every other point of difference, be-
tween one group of organisms and another, affect
the nature and relative value of the different fac-
tors in divergence. They tend also to obscure
the laws of distribution. But no law is invali-
dated by the occurrence of exceptions which come
under some other rule or law.

The obvious immediate factor in the splitting
apart of races or species is, therefore, in all
groups, that of isolation. Behind this lies the
primal factor of variation, continuous or discon-
tinuous. Fluctuation, saltation or mutation, all
these are one for the purposes of our present dis-
cussion. With these come the factor of heredity
and the factor of selection, to which we must

80 ISOLATION AS A FACTOR

ascribe all adaptive changes and apparently no
others. Selection alone does not produce new
species, although it may continuously modify old
ones. Usually related species become modified
in parallel fashion by selection. Through adap-
tations to special surroundings, selection may
produce convergence of characters, often of such
a character as to give a semblance of real homol-
ogy. The selection of the desert gives the horned
toad resemblance to the cactus; this deceives no
one. But it may give one cactus a deceptive
resemblance to another which is forced to adapt
itself to exactly the same conditions.

It is not often that one species is distinguished
from another by adaptive characters, or by any’
conceivable difference in fitness to the same con-
ditions in life. In this regard all are fit, and the
process of natural selection holds each one close
to its possible limit so long as conditions remain
constant.

SOME ILLUSTRATIONS OF THE RESULTS OF
ISOLATION

The formation of different breeds of sheep
through isolation and unconscious selection in the
different counties of England, as elsewhere de-
scribed by the writer, is apparently exactly par-
allel with the formation of species in nature. The
formation and fixing of new breeds or races
through conscious selection is exactly parallel
with this, except that in conscious artificial selec-

IN ORGANIC EVOLUTION 81

tion the destruction of the less fit is more drastic
than in nature and the segregation of the garden
or the flock is more perfect than is ever found in
field or forest. There are no natural barriers so
effective as those which may be reared in field or
garden.

The existence of cognate or “ geminate spe-
cies,” as I have elsewhere called them, the one
representing the other on opposite sides of some
barrier, has been long recognized by naturalists.
In a general way such species agree with each
other in all the respects which usually distinguish
species within the genus. Their differences ap-
pear in minor regards, characters of degree, or
proportion; traits which we may safely suppose
to be of more recent origin than the ordinary
characters marking off species within the group.

Illustrations of geminate species of birds,
mammals, fishes, reptiles, snails, crustaceans, in-
sects, trees, flowers, are well known to students
of these groups.

To take familiar examples, each well separated
island in the West Indies has its own form of
golden warbler. Each island in the East Indies
has its own forms of reptiles, monkeys, snails, and
fresh water fishes. ach island in Hawaii has
its own species of each genus of Drepanine birds;
each forest its own type of land snails. Each of
the three groups of rookeries in Bering Sea has
its own species of fur seal. Hach section of the
Isthmus of Panama has its geminate species of

82 ISOLATION AS A FACTOR

fishes, representing nearly every genus or sub-
genus of the shore-water of Mexico. Each floral
region of the northern hemisphere has its char-
acteristic form of most of the widespread genera
of trees or shrubs. Wherever a distinct barrier
exists, geminate species may be found on the
two sides of it, unless for one reason or another
one of these forms has failed to maintain itself
in the struggle for existence. If the barrier is
imperfect, the two species are likely to intermin-
gle, giving an intergradation of forms. The
absence of such connecting series is the only dis-
tinction between a species and a subspecies or
geographical variety which many naturalists rec-
ognize. A subspecies that lives permanently
in the same region coincident in range with the
species from which it springs is unknown in
zoology.

DARWIN’S VIEW OF THE ROLE OF ISOLATION

Assuming that this view of the relation of geo-
graphical distribution to species-forming is a cor-
rect one, it is interesting to note the attitude of
Darwin in regard to it.

It is clear that Darwin had the basal concep-
tion of the views here set forth. His own work
in South America and that of Wallace in the
East Indies yielded similar conclusions, although
with Darwin geographical studies were subordi-
nated to other forms of evidence of the transfor-
mation of species. Isolation Darwin considered

IN ORGANIC EVOLUTION 83

mainly in its static aspects, not as a necessary or
at least not a separate factor in evolution.
“Each species,” he says, “has been produced
within one area and has migrated as far as it
could.” This statement may be taken as the
central fact of our knowledge of geographical
distribution. The distribution of each species
covers the earth except in so far as it is unable to
reach distant parts through barriers, or as it has
been unable to maintain itself in regions which
it has reached—or as it has, through selection and
isolation, been changed in some part of its range
into a different species. In this case as else-
where selection and segregation must work to-
gether, the one producing adaptive divergence or
adaptive convergence, the other non-adaptive
divergence alone.

Darwin quotes from Wallace that “every spe-
cies has come into existence coincident in space
and in time with a pre-existing closely allied spe-
cies.” This coincidence is attributed, by Darwin
and Wallace, to “descent with modification.”
The language quoted is perhaps obscure, but the
meaning of Wallace is clearly a recognition of
the mutual relations of geminate species.

Darwin further states: “I do not doubt that
isolation is of considerable importance in the for-
mation of new species.” He goes on to say that:
“On the whole I am inclined to believe that large-
ness of area is of more importance, especially in
the production of species which will prove capa-

84 ISOLATION AS A FACTOR

ble of enduring for a long period and of spread-
ing widely.” But he regards past isolation as a
factor in this case also, for he says:—

“Moreover, great areas, though now continuous
owing to oscillations of level, will often have recently
existed in a broken condition so that the good effects
of isolation will generally to a certain extent have
concurred.

“Tn isolation in a small area, conditions will tend
to be uniform, so that natural selection will tend to
modify all the varying species throughout the area in
the same manner in reference to the same conditions.”

He goes on to show that in isolation, inter-
crossing with outside individuals will be pre-
vented; that individuals will be freed from outside
competition, a condition favorable or “ giving
time” for “improvement,” that is, for adaptive
divergence.

It will be noticed that Darwin uses the word
“isolation ” in its literal meaning of island-resi-
dence, and that he does not extend it to include
segregation or separation by barriers. Yet a
mountain lake or a river basin may be just as
much isolated in a biological sense for its water
animals as an island is for its land inhabitants.
Darwin makes no effort to separate two sets of
facts. The one is that a great continent or a
great sea or a great river will contain at any
point more species than a small continent, a small
sea, or a small river basin. This is because the
large area offers freer access for many different
types of organisms. Its less perfect barriers

IN ORGANIC EVOLUTION 85

favor reinvasion, and each group will have some
representatives in all available locations. The
other fact is that the forms in the small area tend
to be more sharply defined. They are better spe-
cies, from the point of view of taxonomy, and the
causes of their existence can be better traced. In
our current studies of evolution, we are of neces-
sity more analytical than Darwin. We would
view as separate factors elements which to him
were simply phases of Natural Selection. In
artificial selection, segregation or isolation was
taken by Darwin for granted. Natural Selec-
tion was to Darwin the same cause or factor re-
lated to natural processes. In his chapter on
Geographical Distribution, Darwin shows an
essentially modern grasp of the subject, though
without analysis of the reasons why variations in
distribution naturally persist.
Darwin says :—

“The preservation of favorable variations and the
rejection of injurious variations, I call Natural Selec-
tion. Variations neither useful nor injurious would be
unaffected by natural selection, and would be left a
fluctuating element.”

It is clear that the completed process of Nat-
ural Selection as here indicated implies segrega-
tion also, especially if we are to explain how those
forms bearing “ fluctuating elements” are to be
codrdinated as species. It is, moreover, certain
that in most groups, probably in all, the charac-
ters that distinguish species are these elements,.

86 ISOLATION AS A FACTOR

neither useful nor injurious. Unless we use
“Natural Selection ” to cover both processes, as
Darwin certainly would have done, we must as-
sign to selection the preservation and intensifi-
cation of adaptive characters, and to segregation
the seizing and fixing of the non-useful, usually
fluctuating, element. It is, however, a fact well
known to breeders that these indifferent or non-
useful characters are often or generally more per-
sistent in heredity than the traits which are
| plainly adaptive. The slight traits which mark the
’ races of men are in themselves, often not ob-
viously, valuable in the struggle for existence.
They are mostly ineradicable in such selective
breeding as history offers. In like manner the
dusky face, and other marks of Hampshire sheep,
persist after the adaptive traits of the original
breed have been enormously modified by selection
in the direction we regard as sheep improvement.
But fine or coarse, fat or lean, Hampshire sheep
are still Hampshires.

In Darwin’s view, isolation or segregation was
doubtless a feature of Natural Selection, not to
be set off against the latter as a separate factor
in descent. It is very plain from Darwin’s own
words, as well as from the explicit statement of
Francis Darwin, that his main contention was for
the reasonableness of the idea of the origin of spe-
cies through descent with modification. What
were the causes of modification, was to him a sec-
ondary matter. But he was convinced of the

IN ORGANIC EVOLUTION 87

existence of one such cause, and this one he set
forth in most effective fashion. Without selec-
tion, the other life-forces known in his day could
not be imagined to lead to any evolutionary re-
sults. We are to-day in the same condition. If
we exclude selection from our category of forces,
we imagine an evolution without motive force, an
evolution which would bring about no result.
But in Darwin’s mind, Natural Selection was the
cognate of artificial selection. At bottom they
were to him the same thing, and segregation a
necessary element in both.

Natural Selection was contrasted to supernat-
ural selection or special creation, a theory b
which knowable facts were referred to unknow
able causes, operations wholly unimaginable i
application to details. At present, we have
ceased to set off selection as against creation.
We agree that all processes are alike natural or
alike supernatural, if we consider them in their
philosophic aspects.

The origin of a species is as natural as the for-
mation of a snow bank, and both are resultants of
forces and conditions within the range of our ob-
jective study.

POST-DARWINIAN VIEWS

As compared with Darwin, the investigator of
to-day has more facts at his disposal; better in-
struments of precision; less need to heed the
opposition of ignorance and bigotry; and greater

88 ISOLATION AS A FACTOR

need for analysis of scientific conceptions. Under
these conditions, while not departing in essentials
from the position of Darwin, we are forced to
bring forward isolation as one of the separate
factors in the origin of species, and the factor on
which the great and growing science of animal
and plant geography mainly depends.

Nearly a decade after the publication of the
Origin of Species, Dr. Moritz Wagner set forth
the factor of isolation, and showed in convincing
fashion its fundamental relation to the problem
of the origin of species.

Wagner showed plainly that in the study of
the evolution of any form we need to know where
it lived, what it did, how it was bounded, and
what was its relation to other forms, geographic-
ally as well as morphologically. ‘‘ For me,” he
says, “it is the chorology of organisms, the study
of all the important phenomena embraced in the
geography of animals and plants, which is the
surest guide to the knowledge of the real phases
in the process of the formation of species.”

The work of Wagner, a most necessary sup-
plement to that of Darwin, has never received the
attention it deserves. This is due in part to the
fact that most of our investigators do not travel.
They know little of animal or plant geography at
first hand. They have had nothing to do with
species as living, varying, reproducing, adapting,
and spreading groups of organisms. Another
reason lies in Wagner’s own attitude of opposi-

IN ORGANIC EVOLUTION 89

tion to Darwinism. He substituted separation,
“ratimliche Sonderung,” for Natural Selection
itself, and denied the potency of the latter factor.
The two became in his philosophy competing, not
codperating, elements, and this threw on isolation |
the impossible task of accounting for all the phe-'!
nomena of adaptation. We may not ascribe’
to Natural Selection the “ Allmacht,” or limit-
less power, which some Neo-Darwinians have
ascribed to it, but on the other hand, those who
reject it as a factor in organic evolution can

vive no rational explanation of the universality

f adaptive organs and adaptive traits; no clue

o the most universal characters of organic nature
as it is.

Certain writers urge that neither selection
nor isolation are factors in evolution, but rather
elements in speciation or species-forming, a proc-
ess defined as something distinct from evolution.
Selection and isolation, as obstacles in the stream
of life, help to split the on-moving group of or-
ganisms into different categories or species; but
the impulse of the forward movement is internal,
and the changes of evolution proper affect groups
as a whole, and are not concerned with splitting
them up into species.

This view may be questioned in two ways. It
may be untrue as to fact, or it may be a matter
of words only. As a matter of fact, we know
nothing of evolution in vacuo, of progress in life
without relation to environment. All forms of

90 ISOLATION AS A FACTOR

life, we know, are split up into species, with
adaptation to external conditions traceable in
every structure. We know of no way in which,
organisms can become adapted to special condi-
tions except by the progressive failures of those
not adaptable. Hence we know of no organism
which has escaped or can escape from the influ-
ence of selection. In like manner, as the world
is covered with physical barriers, no organism
can escape the form of evolutionary friction
which prevents uniformity in breeding. There
must be some degree of “ réumliche Sonderung,”
even in a drop of water.

To admit these facts, and yet to say that selec-
tion and isolation are not factors in evolution,
would appear to make the matter a mere question
of words. If by evolution we mean the theoret-
ical progress of life, in vacuo, the effects solely
of forces intrinsic in organisms, then extrinsic
forces or extrinsic obstacles are of course not fac-
tors in such evolution. If we mean by evolution,
the actual life movements of actual organisms, on
this actual earth, then forces and obstacles are
alike factors in modifying change, and both spe-
ciation and adaptation as well necessary parts of
the process.

We admit the primary necessity of variation
and of heredity, but we can conceive of no case
of actual animal or plant in the forming of which
selection and isolation have not played each a
large and persistent part. Among the factors

IN ORGANIC EVOLUTION 91

everywhere and inevitably connected with the
course of descent of any species, variation, hered-
ity, selection, and isolation must appear; the first
two innate, part of the definition of organic life,
the last two extrinsic, arising from the necessities
of environment, and not one of these can find
leverage without the presence of each of the
others. Isolation as the factor longest over-
looked, though to the field naturalist the most
conspicuous of the four, must be advanced to the
post of honor beside the others, not instead of
any of them.

THE CELL IN RELATION TO HERED-
ITY AND EVOLUTION

BY
EDMUND B. WILSON

I trust that my colleagues in this symposium
will not suspect me of any intention disrespectful
to them if I speak of my own small contribution
to it as the voice of one crying in the wilderness.
I do not mean to imply by the Scriptural phrase
that the cytologist has to announce the coming of
a new gospel of heredity or of evolution. He is,
to say the least, as much in need of light as are
others. I wish only to suggest the somewhat iso-
lated position of the subject assigned to me, deal-
ing, as it mainly must, with matters with which
Darwin’s own work was not very directly con-
cerned, and which in their detailed aspects belong
mainly to the post-Darwinian period. With the
notable exception of the provisional hypothesis
of pangenesis Darwin made no systematic at-
tempt to correlate his own conclusions with those
towards which cell-research was already tending
in his day; and pangenesis was rather a specula-
tive construction than an induction from known
cytological facts. Nevertheless my intrusion
into this circle may perhaps be justified on two
grounds. One is the keen interest in the inter-

92

HEREDITY AND EVOLUTION 93

nal mechanism of heredity everywhere shown by
Darwin in his remarkable chapter on pangenesis
and attested by many passages in his private let-
ters. The other is the now general admission
that the mechanism over which Darwin so long
pondered is to be sought in the organization of
the germ-cells.

PANGENESIS AND THE PRINCIPLE OF GENETIC
CELLULAR CONTINUITY

Of the original hypothesis of pangenesis I shall
say but a few words. Darwin says in one of his
letters that he had considered it for upwards of
five-and-twenty years. It is easily the most ab-
stract and speculative portion of all his writings.
It was published against the advice of his trusted
friend and counselor, Huxley, who had himself
many years earlier written one of the first and
ablest reviews of the cell-theory that appeared in
our language. Darwin predicted that pangene-
sis would be called a mad dream; and on its pub-
lication the hypothesis was, in fact, received for
the most part with hostile criticism or scanty ap-
preciation. In its original form it has been gen-
erally abandoned; though one of its principal
postulates, remodeled by De Vries to form the
hypothesis of “intracellular pangenesis,” is still
accepted by some biological thinkers. It is none
the less deeply significant that so great and saga-
cious a naturalist, one whose life was so largely
given to the study of the external aspects of

94 THE CELL IN RELATION TO

heredity and evolution, should have found him-
self irresistibly driven to look below the surface
of these phenomena and should have made so
carefully wrought an attempt to picture their
physical foundations to his mental vision. His
deep-seated conviction that sooner or later the
phenomena would have to be attacked from this
side is revealed in a letter written to Sir Joseph
Hooker, in 1868, where he declares, “TI feel sure
that if pangenesis is stillborn it will, thank God,
at some future time reappear, begotten by some
other father and christened by some other name.”
That this prediction still awaits fulfilment need
not here concern us. What is significant is the
attitude towards the general problem that it re-
veals. And the modern cytologist, therefore, de-
spite his failure to find support for Darwin’s par-
ticular conception, has a right to feel that his
efforts to analyze the cellular mechanism of
heredity would be viewed with sympathetic inter-
est by the great naturalist could he follow their
progress at the present time.

Pangenesis was put forward many years after
Virchow had pronounced his celebrated apho-
rism “ Omnis cellula e cellula” (which Darwin
quotes), and a full decade after the eminent Ger-
man pathologist had insisted on the “eternal
law ” of genetic continuity by cell-division. Dar-
win nevertheless admitted this law unreservedly
only in the case of plants, and went no further
than to recognize its wide prevalence among ani-

HEREDITY AND EVOLUTION 95

mals. In both cases he assumed that in addition
to the powers of division cells multiply by means
of minute germs or “ gemmules,”’ which are
thrown off by the somatic cells, collected from all
parts of the body to form the sexual elements, and
are “ultimately developed into units” (cells)
like those from which they were originally de-
rived.* Pangenesis thus comprised two princi-
pal postulates, both of which had been in a meas-
ure foreshadowed by the speculations of Bonnet,
Buffon, and even earlier writers. One is the
particulate or meristic assumption that particular
hereditary traits are represented in the germ-cell
by discrete and specifically organized particles,
the “ gemmules ” or “ pangens,” that are capable
of self-perpetuation by growth and division with-
out loss of their specific character. The second
assumption is that the gemmules are cell-germs
originally produced by the somatic cells; and by
this Darwin sought to explain the transmission
of somatogenic or acquired characters. How
have these two assumptions fared with the prog-
ress of modern studies on the cells?

1 The development of the gemmules was supposed to depend on
their “union with other partially developed or nascent cells, which
precede them in the regular course of growth.” Darwin does
not make it quite clear whether he assumed that the gemmules
actually grow into new cells. Many passages (like the one placed
in quotation marks in the text above) seem open to no other
interpretation; but in the case of plants, accepting the universality
of division in them, he concluded that “the gemmules derived
from the foreign pollen do not become developed into new and
separate cells, but penetrate and modify the nascent cells of
the mother plant.” This process, he says, is almost identical with
a fertilization of the cells of the mother plant by gemmules
derived from the foreign pollen.

96 THE CELL IN RELATION TO

The first has been accepted by many acute bio-
logical thinkers as almost a logical necessity, and
has been developed, especially by Weismann, into
one of the most ingenious and elaborate specula-
tive constructions to be found in the whole his-
tory of biology. Its logical grounds need not
here be analyzed. I will only emphasize the fact
that the conception did not grow out of actual
studies on the cell, but was an imaginative con-
struction, based on the facts of variation and
heredity. It may be true; but for the present we

_can only regard it as a kind of symbolism, anal-

‘ogous in some respects to the molecular-atomic
symbolism of physical science, but of far more
doubtful validity. Those who find such a sym-

bolism useful will encounter no positive obstacle
in the known cytological facts—they may even
find in them a certain amount of indirect support
—but the assumption remains unverified, and is
probably unverifiable.

The second postulate of pangenesis is wholly
unsupported by either experimental or cytolog-
ical evidence. There is not a particle of evidence
to show that in the higher forms of life cells pro-
duce gemmules or that the germ-cells are built
up by the aggregation of such bodies derived
from the somatic cells. The most fundamental
contribution of cell-research to the theory of he-

-redity is the law of genetic continuity by cell-

division. Cells arise only by the division of pre-
existing cells. And the stream of growth and

HEREDITY AND EVOLUTION 97

division by which the continuity of organization
is maintained seems clearly enough to be genetic-
ally irreversible. It flows forward from germ-
cell to germ-cell in endless succession. It is peri--
odically diverted from the germ-stream to form
the bodies of successive generations of individ-
uals. These are made of the same stuff as'the
stream from which they flow. In each genera-
tion the germinal stuff runs through the same:
series of transformations; hence that reappear-
ance of the same traits in successive generations
that we call heredity.

This conclusion loses nothing of its force by
reason of the fact that in {sexual reproduction
or regeneration the whole body may be repro-
duced from a fragment, from a small group of
cells, or even from a single cell, of the soma.
These cells, too, have arisen by division in un-
broken descent from the germ-cell; they, too,
have been made from the same original stuff ; and
they, too, hand on by division to their descendants
the specific tradition of their lmeage. It is true
that these cells and the germ-cells alike grow by
the intussusception of matter from without, that
the cell-substance is built ‘from, and its activities
modified and controlled by, materials that have
been elaborated by other cells. But the whole
force of the evidence goes to show that their fun-
damental basis is determined by genetic contin-
uity with that of their predecessors, that some-
thing is handed on by division which holds

98 THE CELL IN RELATION TO

the cell true to its specific type and builds the
incoming food-stuffs into the characteristic fabric
of the species. I need not dwell on a conception
with which we are all so familiar. Some of the
specific applications of the doctrine may have
proved unacceptable, but the advances in our
knowledge of the cell are ever adding weight to
the fundamental principle of germinal continuity
for which so many eminent investigators, from
Remak and Virchow to Nussbaum and Weis-
mann, have contended. And this principle ob-
viously affords the true standpoint from which
the phenomena of heredity and development
must be viewed.

From this standpoint we are confronted with
four principal questions, which I shall in the
briefest possible way attempt to consider. (1)
What is the physical basis of heredity? (2) How
is it transmitted from cell to cell? ‘ (3) In what
way does it play its part in the determination of
the hereditary characters? (4) How may it be
so modified as to give rise to new heritable char-
acters?

THE PHYSICAL BASIS OF HEREDITY

It is now universally admitted that the physical
basis of heredity is contained in the germ-cell.
Is this basis formed by the entire living energid,
or may we distinguish in the cell a particular
species-substance or idioplasm, that is at least
theoretically separable from the other cell-con-

HEREDITY AND EVOLUTION 99

stituents? This question has not yet been an-
swered with certainty. The cell-system forms
an enormously complex moving equilibrium,
which must in one way be regarded as a single
and indivisible unit. From this point of view it
may justly be maintained that the basis of hered-
ity and of the vital activities generally is repre-
sented by the cell-system in its totality. But
such a position, philosophically correct though it
may be, cuts us off from the possibilities of exact
analysis. We have every right to inquire in what
way the energies of cell-life are distributed in the
system and how they are related; and the ques-
tion whether certain elements of the system may
possess an especial and primary significance for
the determination of the cell-activities forms a
legitimate part of this inquiry.

I stand with those who have followed Oscar
Hertwig and Strasburger in assigning a special
significance to the nucleus in heredity, and who
have recognized in the chromatin a substance that
may in a certain sense be regarded as the idio-
plasm. This view is based upon no single or
demonstrative proof. It rests upon circumstan-
tial and cumulative evidence, derived from many
sources. The irresistible appeal which it makes
to the mind results from the manner in which it
brings together under one point of view a multi-
tude of facts that otherwise remain disconnected
and unintelligible. What arrests the attention
when the facts are broadly viewed is the unmis-

100 THE CELL IN RELATION TO

takable parallel between the course of heredity
and the history of the chromatin-substance in the
whole cycle of its transformation. In respect to
some of the most important phenomena of hered-
ity it is only in the chromatin that such a par-
allel can be accurately traced. It is this sub-
stance, in the form of chromosomes, that shows
the association of exactly equivalent maternal
and paternal elements in the fertilization of the
egg. Init alone do we clearly see the equal dis-
tribution of these elements to every part of the
body of the offspring. In the perverted forms
of development that result from double fertili-
zation of the egg and the like it is only in the
abnormal distribution of the chromatin-substance
by multipolar division that we see a physical coun-
terpart of the derangement of development.
Only in the chromatin-substance, again, do we
see in the course of the maturation of the germ-
cells a redistribution of elements that shows a
parallel to the astonishing disjunction and redis-
tribution of the factors of heredity that are dis-
played in the Mendelian phenomenon.

These are perhaps the most striking of a mul-
titude of faets that point towards the chromatin
as the embodiment of specific primordia of deter-
mination. We may be sure that the microscope
reveals to us but part of the story; but that which
we see is not for this reason less significant. Ex-
periment has taught us, it is true, that the rdle of
the nucleus in determination cannot be regarded

HEREDITY AND EVOLUTION 101

as an exclusive one. It is certain that specific
factors of determination also exist in the proto-
plasm of the egg; it is possible that the same may
be true of the spermatozoon. Experiment has
demonstrated in the clearest manner that many.
features of the early development, among them
some of the most important, are immediately de-
termined by conditions in the egg-protoplasm
without direct action of the nucleus. But this’
fact can be rightly estimated only when the whole |
genesis of the egg has been taken into account. |
The researches of recent years have proved that
the egg undergoes a long process of development
during its ovarian history and in the process of
maturation, in the course of which the greater
part of its protoplasmic substances are formed
and ultimately segregated in a particular config-
uration. It has thus become more than probable |
that some at least of the determinative conditions
in the protoplasm of the fertilized egg are of sec-
ondary origin—that they are the outcome of an |
antecedent development in which the nucleus has |
played its part. Important formative protoplas-
mic materials are known to be of nuclear origin.
It is possible that all may have such an origin.
But even if we do not go so far as this, even if we
admit that the determinative factors of the nu-
cleus constitute but one element in an activity
that properly belongs to the living energid as a
whole, we still can not close our eyes to the plain
record that is written in the history of the nuclear

102 THE CELL IN RELATION TO

substance. I doubt whether any one holds the
‘view, which some of the opponents of the chro-
‘matin hypothesis have endeavored to force upon
its adherents, that the nucleus enjoys a complete
“monopoly of heredity.” To what extent the
chromatin embodies primary factors of deter-
mination remains to be shown by further re-
search. We are still too ignorant of the physio-
logical relations of the nucleus and cytoplasm to
be justified in any attitude of dogmatism on this
question. But as a matter of evidence the con-
clusion that chromatin does embody such factors
seems at least a probable one. As a means of
practical inquiry it is, I believe, a good working
hypothesis, without which we should be deprived
of one of our most effective instruments for the
analysis of the mechanism of heredity. And re-
cent research has, I think, clearly shown that, far
from being exhausted as some of its critics would
have us believe, this hypothesis is steadily open-
ing new possibilities of inquiry. .

CELL-DIVISION

Accepting the idioplasm hypothesis, in the
sense I have indicated, what do we know of its
mode of transmission? We may answer with
assurance that it is transmitted from cell to cell
by division; and we may still safely assume, I
think, in most cases by mitotic or karyokinetic
division, though the direct or amitotic process may
play a larger rdle than was formerly supposed.

HEREDITY AND EVOLUTION 103

We can but glance at one or two of the most
significant features of karyokinetie division. The
most striking and telling of these is the contrast
so often shown between the distribution of the
nuclear and of the protoplasmic elements. With
certain exceptions in the phenomena of matura-
tion, which only bring fresh support to the general
principle, nuclear division is both quantitatively
and qualitatively exactly equal. Protoplasmic
division is often both quantitatively and qualita-
tively unequal, separating substances that have
been proved by precise experiment to be of dif-
ferent physiological value. But more than this,
the formation and division of chromosomes effect
not merely a mass-division of the chromatin but
an equal meristic division of its whole substance;
and as Wilhelm Roux first urged, we can find no
meaning in the whole elaborate process if the
chromatin be not composed of qualitatively dif-
ferent elements that require equality of distribu-
tion. That such is really the constitution of the
chromatin can no longer be doubted by any who
are familiar with the evidence. If the chromo-
somes be not actually persistent individuals, as |
Rabl and Boveri have maintained, they must at:
least be regarded as genetic homologues that are
connected by some definite bond of individual
continuity from generation to generation of
cells. And the evidence has steadily accumulated’
to show that the chromosomes exhibit definite
qualitative differences. In many animals and

104 THE CELL IN RELATION TO

plants constant differences of size, in some cases
also of form, are shown among the chromosomes.
Specifically different classes of chromosomes can
in some cases be distinguished, which show con-
stant and characteristic peculiarities of behavior
in respect to some of the most important opera-
‘tions of the cell. The probability is increasing
‘that individual chromosomes possess a particu-
Jar significance for the development of particular
‘characters. It has become probable that sexual
dimorphism in general is determined by a differ-
ence of nuclear constitution between the sexes.
In some groups of animals the sexes differ in
respect to one or more particular chromosomes.
In a more general way, Boveri’s experiments
have proved that abnormal combinations of chro-
mosomes lead to falsified forms of development;
and these observations give the strongest reason
to believe that normal development is dependent
upon the normal combination of the chromo-
somes.

All these facts are pointing in the same direc-
‘tion. They render the conclusion almost irre-
sistible, not only that the chromatin-substance is
involved in heredity, but that the chromosomes
are composed of specifically different materials,
the ensemble of which is essential to normal devel-
opment. It is obvious that the beautiful mechan-
ism of karyokinesis is perfectly adapted for the
meristic division and equal distribution of these
materials. The energies that lie behind the for-

HEREDITY AND EVOLUTION 105

mation and action of the karyokinetic figure con-
stitute a puzzle for which, as it seems to me, no
adequate solution has yet been found. But the
effect of its action gives us good reason to regard
it as the most important instrument by which the
nuclear substance is handed on with its integrity
unimpaired from generation to generation of
cells.

DIFFERENTIATION

Our third question involves the problem of dif-
ferentiation, which is inseparable from that_of
cell-metabolism in general, since it involves the
mode of interaction of nucleus and protoplasm.
It is a significant fact that visible structural dif-
ferentiation affects the protoplasmic substance in
far greater degree than the nuclear. Both in
their structure and in their modes of activity the
most important characteristics of different kinds
of cells are found in the protoplasm. To some
extent, no doubt, the nuclei of different tissues .
show certain characteristic peculiarities, and these
can in a measure be correlated with the function
of the cells. It is nevertheless obvious that the
most characteristic features of the muscle-cell,
the nerve-cell, or the gland-cell are displayed in
the protoplasmic rather than the nuclear sub-'
stances. And this again falls into line with the
view that the nucleus is the main conservative
element of the cell-system, the protoplasm the
plastic element through the modifications of

106 THE CELL IN RELATION TO

which the cell adapts itself to the performance of
the varied special conditions of cell-life.

In considering the problem of differentiation
we are therefore led to inquire in what manner
the nucleus may be conceived to operate in the
determination of specific modes of protoplasmic
change. De Vries and many of his followers
have supposed that control of the cell is effected
by an actual migration of organized gemmules or
pangens from nucleus to protoplasm. But do
we really need to employ the pangen symbolism
in the consideration of this question? It seems a
sufficient basis for our practical attack on the
problem to assume that the control of the cell-
activities is at bottom a chemical one and is
effected by soluble substances that may pass from
nucleus to protoplasm or from protoplasm to
nucleus. Certainly it is to such a view that very
many of the chemical and physiological studies
in this field are now unmistakably pointing. The
opinion is gaining ground that the control of de-
velopment is fundamentally analogous, perhaps
closely similar, to the control of specific forms of
physiological action by soluble ferments or en-
zymes. Experiment has established the fact that
certain forms of development are thus controlled
by substances, the “ hormones,” that may be ex-
tracted from the cells that produce them, and
upon injection into the body call forth their char-
acteristic results. Such an effect, for instance,
is the development of the cock’s comb in the hen

HEREDITY AND EVOLUTION 107

upon injection of testic-extract and its recession
to the characteristic female condition upon cessa-
tion of the injections, as recently described by
Walker. Analogous phenomena are seen in the
well-known effects of thyroid extracts, or in the
effect upon the mammary glands of injection of
extracts of the fetus, as described by Starling
and Lane-Claypole.

We are thus led to something more than a sus- |

picion that the factors of determination, and
therefore of heredity, are at bottom of chemical

nature. It is a well-known fact that correspond-:

ing tissues of different species often show char-
acteristic chemical differences; and to some extent
the same is known to be true of the germ-cells.
The conclusion thus becomes highly probable that
the characteristic differences of metabolism be-
tween different species, including those involved
in development, are traceable to initial chemical
differences in the germ-cells. In so far as the
chromatin theory expresses the truth, the pri-
mary basis of these differences may be sought
in the nuclear substance. There is good reason
to believe that some at least of the enzymes are
of nuclear origin. It seems a promising hypoth-
esis that the chromosomes may be regarded as
self-perpetuating magazines of specific sub-
stances, similar in nature to the enzymes or their
chemical antecedents, that play an essential réle
in the determination of the cell-activities, includ-
ing those involved in development. From this

108 THE CELL IN RELATION TO

point of view the fertilization of the egg might
‘almost be compared to an intracellular injection
of enzymes.

The apparent simplicity of such an hypothesis
should not delude us into the belief that it touches
the root of the matter. It presupposes a specific
“ organization ” of the chromosomes of which we
know nothing, and upon which must depend the
perpetuation of their characteristic chemical con-
stituents. In this direction we are thrown back
upon purely speculative constructions which it
would be unprofitable to follow out here. But
so far as the hypothesis goes it seems to offer a
really practical point of attack for the chemical
study of differentiation and heredity. In the
Mendelian phenomenon we see a synthesis, split-
ting apart, and recombination of determinative
factors that is singularly like that of chemical ele-

ments or radicals. In the Mendelian heredity
of color, for instance, the orderly resolution by
the germ-cells of compound pigment-producing
factors into simpler ones, their recombination to
form new compounds, the intensification or dilu-
tion of color by specific and separable factors, the
production of particular colors by mixing to-
gether factors which are singly incapable of pro-
ducing color—in all this we see a series of oper-
ations that show an astonishing similarity to the
procedure of the chemist in his laboratory. That
such things are possible in the case of relatively
simple characters, such as colors, gives strong

HEREDITY AND EVOLUTION 109

ground for the belief that similar operations are
concerned in the production of more complex
characters. Those who hesitate to draw such a
conclusion may well reflect upon the remarkable
effects of the “internal secretions” of the en-
zymes and hormones, and upon the extreme sus-
ceptibility of the developing embryo to even very
slight chemical changes in the surrounding me-
dium. It is my belief that in the direction here |
indicated lie the greatest possibilities of future |
investigations upon the cell, and that in the union |
of cytology and biochemistry lies our greatest ;
hope of future advance.

HEREDITY AND EVOLUTION

Lastly, if we accept the working hypothesis
that the primordia of determination are chemical
in nature, how may we conceive them to be so
modified as to produce new characters? It seems
to me that this question may well be reversed; for
the wonder is, not that the idioplasm changes, but
that it adheres so stubbornly to its type. It may —
as well be admitted that both our cytological and
our chemical knowledge in this direction is prac-
tically nil. It is well, further, to speak a word
of caution at this point. We must not forget
that some of the most acute and thoughtful of
naturalists have in recent years expressed the
conviction that the ultimate control of develop-
ment is not to be sought in the physico-chemical
properties of the germ-cells, but in an indwelling

110 THE CELL IN RELATION TO

“entelechy ” or “ élan de la vie,” a power of un-
known nature, that may, in the last analysis, be
psychical in nature. But, profoundly interest-
ing as some of these vitalistic speculations are, we
are bound to hold fast to the physico-chemical and
mechanistic hypothesis of heredity until the pos-
sibilities of observation and experiment in this
direction have been exhausted. If there be a
physico-chemical basis of heredity we should ex-
pect to find it capable of modification by physico-
chemical agencies; and so much, at least, is known
to be the fact. It has been abundantly demon-
strated that both the body-cells and the germ-
cells react to changes of the environment by def-
inite physiological and morphological changes.
Many experimenters have demonstrated the ex-
treme susceptibility of the discharged eggs or
spermatozoa to even very slight chemical and
physical stimuli. We can not doubt that they are
equally sensitive to stimuli while still within the
body, and at every stage of their development.
The almost unique experiments of MacDougal
on the higher plants seem to show that direct
chemical treatment of the germ-cells may pro-
duce definite and irreversible effects upon the off-
spring. Those of Tower on the insects, though
less direct, are hardly less convincing.

Though we may not fully understand the man-
ner in which the germ-cells are modified, there is
no inherent improbability or difficulty in the con-
ception that such modifications will produce blas-

HEREDITY AND EVOLUTION 111

togenic variations or mutations that are inherited,
permanently or temporarily. We can readily |
understand that the constitutional effects of tem-
perature, food, moisture, and similar general |
agencies of the environment may manifest them- |
selves in definite changes that reappear in follow-:
ing generations because the germ-cells have been |
directly affected in the same way as the somatic
cells. It is natural to suppose that the idioplasm /
possesses a slight instability of chemical or molec- ;
ular composition that results in corresponding,
fluctuations or indefinite variations of the adult, ;
which may or may not be inherited. We find st
difficulty in the conception that the idioplasm
may undergo considerable, sudden, and irre-
versible changes which produce mutations of
greater or less degree. We can comprehend how
particular constituents of the idioplasm may
change without affecting others, thus giving rise
to mutations in respect to only a single character
or a particular group of characters. We can con-
ceive the idioplasm as undergoing a slow secular
change that results in continual divergence in
many directions or in a definite orthogenetic line
of transformation. But in respect to the trans- |
mission of acquired characters the old difficulty
confronts us to-day as formidable as when it was
first fairly revealed to us through the argument
of Weismann. What is really difficult to com-
prehend, what I think we can not really conceive
if pangenesis be discarded, is how the idioplasm,

112 THE CELL IN RELATION TO

or the germ-cell as a whole, can be a storehouse of
specific and detailed somatic impressions which
cause the reappearance of similar somatic effects
in generations to come.

Darwin’s ingenious attempt to picture such a
process was a legitimate speculation, worked out
with a power and insight that should stir enthu-

_ Siasm in even the most skeptical of critics. More
' than this, it still remains, as I think, the only in-

telligible hypothesis of the transmission of ac-

quired characters, as Darwin understood the
phrase. But it finds to-day little or no real sup-
‘port in the results of observation and experiment.

Attempts have been made to substitute for Dar-
win’s migrating gemmules soluble internal secre-
tions—hormones or other substances—that are
produced by the various organs and transmitted
to the reproductive organs through the fluids of
the body. Heredity has been compared, and
with justice, to an “ organic memory ”’; and this
has been assumed to be a property of the organ-
ism as a whole, irrespective of the distinction be-
tween germ-cells and soma. It has been urged
that the heredity of acquired characters is more
readily conceivable if the increments of change
be small and extended through long periods of
time. Any or all of these things are possible;
but let us not deceive ourselves. Does any of
these assumptions really lessen the difficulty or
give us a clear mental picture of what must occur
if the heredity of acquired characters be a fact?

HEREDITY AND EVOLUTION 113.

I do not see how. Inability to form a clear
a priori conception of the process has in itself no |
validity as an argument against the fact, if fact | |
it be. The progress of biological discovery has
repeatedly transformed apparent a priori impos-
sibilities into everyday realities. And if exper-|
iment shall really demonstrate the transmission’
of somatogenic modifications the cytologist has
no fundamental obstacle to interpose. The
mechanism that his studies have revealed will ac-
count for the transmission of all forms of ger-
minal modifications, however they may be caused.
The question involved is not of the transmission’
of the idioplasm or of the germ-cell, but of its |
interaction with the soma; and this is not an’

a priori question, but one of fact. Let us_admit

sumed may ‘be a real and potent fi actor. in. = ened:

ity, t though it gives no hint of its existence in in the
visible ‘apparatus of the cell. In the “present
defective state of our knowledge we may well
grant that there may be many a thing between
germ-cell and body that is not yet dreamed of in
our biological philosophy. But has the trans-
mission of acquired characters, in the strict and
proper sense of that much abused phrase, been
demonstrated? If in closing I venture to ques-
tion this, I pray that my sins be not visited upon
the study of the cells, but upon a failure to dis-
cover the demonstration in other fields of inquiry.

THE DIRECT INFLUENCE OF
ENVIRONMENT

BY
D. T. MacDOUGAL

ANY serious consideration of the diversity of
organisms, of the complexity of the qualities they
bear, of the relationships they sustain, and of the
character of the stresses under which they exist
with relation to the environmental setting, leads
inevitably to the conclusion that their evolution-
ary development must have been affected by
many modifying agencies; that the origination,
or activation of their qualities or characters may
not be ascribed to any single causal force or guid-
ing factor; and that the course of heredity from
generation to generation has been determined
by many things beside the simple inertia of prim-
itive initial qualities of protoplasm.

When we join in the accepted generalization
that the qualities and forms of organisms now
existent are the net result of the action of envi-
ronic forces upon ancestral structures, selective
as well as initiatory, we implicate a much larger
group of conceptions than that embodied in the
present thesis, since it is the intention to confine
discussion to the possibilities that arise when liv-

114

DIRECT INFLUENCE OF ENVIRONMENT 115

ing or self-generating matter transmits its spe-
cialized characters from one generation to an-
other in the germ-cell, and displays its periodic
somatic expansions in ontogeny.

Within this definite and restricted field, exact-
ness and clearness of comprehension of the rela-
tions involved will depend directly upon the thor-
oughness with which we may be able to connect
our conceptions with the physico-chemical proc-
esses of organisms.

The more important external, direct, or phys-

ical factors, the influence of which induces adjust-

ments and engages the activities of protoplasm,
include radiant energy in its various phases, and
the chemical structure of the medium, substratum
or substances coming into contact with the living
matter and included with its intake and output.
These agents interlock intimately with the parts
of the self-generating protoplasmic machine, fur-
nishing building material, energy in various
forms, catalysts, and control reactions in a man-
ner so intimate that it is impossible to think of
living matter free from its environic setting.
Nowif we set about the calibration of the quan-
titative relation of any of these factors to living
matter, or attempt an estimation of the qualita-
tive effect, we will find that, with respect to any
given strain of organisms or any individual, the
constellation of specific activities, processes or
functions, grouped in the plant are adjusted in
such manner that they proceed at the most advan-

116 THE DIRECT INFLUENCE

tageous rate with relation to each other within,
for example, some narrow range of temperature.
In our easy acceptance of the obvious, we are apt
to assume that these optimal conditions are fur-
nished by the native habitats of plants, or in other
words, the place they happen to occupy in their
movements about the world when they are called
to our attention. Now, on the one hand, plants
simply are found in areas they have been able to
reach, and “ native habitats”” may by no means
offer the optimal conditions, a condition of affairs
of which more than a hint is furnished by the
irruption of weeds, followed by a development
of a vigor unknown within the previous range of
the species. On the other, the reminder is neces-
sary that no one habitat may furnish the optima
for the accomplishment of all of the processes
involved in the ontogeny and reproduction of the
individual, and all environic relations include
groups of compromises and of adjustments that
put the capacity of the living matter to the ut-
most stresses it may bear.

Two main considerations arise when attention
is directed to the behavior of the organism as it
encounters the external factors in unusual inten-
sities, an experience which has been countlessly
repeated and which is one of the eliminating fac-
tors in selection. The first concerns the mechan-
ism of the adjustment of the individual to alter-
ing environment, and the second, the possibilities
of transmission of the effects of the adjustment

OF ENVIRONMENT 117

to the progeny, both in functional capacity and
accompanying structure.

ADJUSTMENT OF THE INDIVIDUAL TO ALTER-
ING ENVIRONMENTS

Let us take, for example, a plant standing in
the open in a habitat in which it is firmly estab-
lished, and introduce some modifications of wide
range of the insolation, which may or may not
register with anything previously encountered by
this individual. The primary or direct effect of
the change will undoubtedly be a modification of
the reaction-velocities of some of the chemical
processes so that metabolism and all of the life-
phenomena dependent upon it will undergo alter-
ations in rate, cell-division, chromosomatic invo-
lution, catalyptic action involving respiration,
intake and excretion, and finally growth also.
A secondary effect accompanying these changes
will be due to the irritability of the living matter
by which sudden changes in almost any external |
factor will exercise a releasing or unloosing ac-
tion: Outward manifestations of such action are
seen in the various thermotropic and heliotropic
movement of leaves, and while there seems to be
a disposition on the part of some physiologists to
eliminate metabolic activities from the realm of
irritable reactions, yet it does not seem justifiable
upon present evidence.

Whether an irritational phase intervenes or
not, when an environmental factor undergoes

118 THE DIRECT INFLUENCE

rapid alteration, the activities affected soon as-
sume a fairly steady rate, determined directly by
the reaction velocities of the substances con-
cerned, and the change goes no further than that
of a purely physiological, or, strictly speaking,
physico-chemical, accommodation. If the change
in question is introduced in the developmental
period of the individual, the members and organs
not fully mature may take on unusual structures
and assume aberrant or variant forms, while if
the resting seed or spore is germinated under
altered conditions, all purely irritational re-
sponses are eliminated and the entire individual
may show a more or less atypic ontogenetic pro-
cedure.

This somatic variability in response to environ-
ment is a matter of common observation, but de-
viations of this character are of but little impor-
tance in heredity unless they or their effects are
repeated in successive generations. This trans-
mission of somatogenically induced characters is
the cause of our confusion and the source of our
doubts, constituting as it does the essence of the
controversy as to the “ heredity of acquired char-
acters.” On the one hand Weismannists predi-
cate an isolated current of heredity coursing from
germ-cell to germ-cell, yielding qualities that
direct ontogeny, but receiving nothing in return
except nutrition and continuance, while on the
other hand a by no means voiceless constituency
presses for the acceptance of the conclusion that

OF ENVIRONMENT 119

every wave of variability and every impress of
the environment upon the soma are communi-
cated from it to the germ-plasm upon which it
becomes forever indelibly engraved. When to
this claim there is added the assumption that while
the effect of a single external impression may be
very slight, its repetition, rhythmically or other-
wise, would finally cumulate to produce appre-
ciable and lasting effects, we have a conception
difficult to prove or disprove, especially since it
is a well-established fact that repetition of stimu-
lation does give cumulative effects in both irrito-
motility and variability. The whole question,
however, resolves itself into the comparatively
simple inquiry as to the physiological connections
and correlations of the soma and germ-plasm.

It is well known that not all of the various
organs or tracts of tissue are directly affected
alike by any external factor, a result due to the
essential differences of the cells composing them.
Thus an arid atmosphere or intense insolation
would affect leaf activities chiefly, while unusual
soil concentrations would influence roots only.
The various members of the root and shoot are
in close correlation, however, and the activity,
growth, and mode of development of organs not
directly acted upon by the factors mentioned may
be profoundly influenced by the altered products
of the organs that are affected. Thus the wound-
ing of a root is reflected by changes in the shoot,
the removal of one of the parts of a compound

120 THE DIRECT INFLUENCE

leaf causes adjustments in the remaining ones,
and instances might be multiplied almost indef-
initely to show that effects produced in one part
are quickly and forcefully transmitted to other
parts of the soma. It matters not for the pres-
ent whether the means of communication be spe-
cial tracts, nervous mechanisms, chains of cata-
lytic reactions, or what other method of com-
munication.

THE ACTION OF SOMA UPON GERM-PLASM

Similar communications between the egg and
soma are to be encountered. In some of the car-
potropic and gametropic movements of seed-
plants, the accomplishments of definite stages in
the development of the embryo-sac and fertiliza-
tion, result in impulses to stems and peduncles
several centimeters distant, producing move-
ments and morphogenic alterations of a very
striking character. Without further enlarge-
ment on this theme it is to be said that the securest
foundation is laid for the conclusion that well-
defined correlations exist in the plant by which
secondary effects of the action of external factors,
or of morphogenic or embryonic procedure,
may be freely communicated from one part of
the soma to another, and from the egg to the
soma.

With such a substantial substratum of estab-
lished facts, we now turn to the problem as to
the communication of effects from the soma to the

OF ENVIRONMENT 121

egg or sperm, in such manner that these effects
would be transmitted to succeeding generations.

The most obvious and the most primal relation
between the soma and the egg is the nutritive one,
and a review of the evidence offered by Pictet
and others leads to the conclusion that the char-
acter of the building material supplied to the egg
as varied by environmental influences may work
changes that pass from one generation to an-
other, so that it is indubitably established that the
egg is not isolated and possessed of such highly
developed selective power that it may avoid the
intrusion of unusual substances.

The experiments of Oscar Riddle, S. H. and
S. P. Gage,* in which it was shown that Sudan
III, a dye, fed to a hen, results in the coloration
of the yolk of her eggs, and that the chicks
hatched from such eggs take up the dye from the
yolk, which finds a lodgment in their own fatty:
tissues, are of special interest in this connection.

Actual available evidence does not warrant us
in predicating any other form of influence of in-
ternal region upon the germ-plasm as it takes
form and special activity in the egg and sperm,
beyond that of physio-chemical processes orig-
inating in the soma. Alterations in these proc-
esses which might affect the egg and be registered
in its hereditary activities might occur at any
stage of the ontogeny without direct reference to
the time intervening between the reception of the

1 Science, 28: 494. 1908.

122 THE DIRECT INFLUENCE

stimulus and the reception of a possible impress
by the egg.

Concerning the results from repetition of
stimuli in a series of generations, about the only
facts at hand are those obtained from a study
of variability as affected by nutrition, in which
it is found that more favorable conditions of nu-
trition increase the range, and that further in-
creases accumulate with the continuance or repe-
tition of the optimal conditions with relation to
successive generations. The foregoing may be
taken as a fair representation of the physiolog-
ical basis of the possibilities by which alterations
in the soma might be impressed upon the germ-
plasm and transmitted to successive generations,
and a description of the authenticated observa-
tions and well-ordered experiments which have
been made by skilled workers in dealing with this
subject during the last few decades would form
no mean record. It would entail a historical re-
view far too voluminous for the present occasion.
However, among other general features it appears
that plants moved to habitats and to cultivated
fields to the northward and southward have been
seen to take on a seasonal rhythm in accordance
with the new climatic conditions encountered.
Unusual temperatures and foods have caused
marked alterations in structure, markings, com-
position of the body, periodicity of reproduction
and range of adjustment and endurance in both
plants and animals, but in all of these cases the

OF ENVIRONMENT 123

alteration gradually disappeared when the induc-
ing conditions were removed, except in a few
instances in which it could not be demonstrated
that the germ-plasm had not been directly
affected.

Butterflies, moths, fishes, crustaceans, birds,
guinea pigs, rabbits, trees, fungi, cereals, and
bulbous plants have all been drawn into the ex-
perimental field with a remarkable unanimity of
negation in so far as the somatogenic induction
of characters was solely concerned, which might
be fully transmissible to successive generations
not under the influence of the exciting factors.
Temperature, light, food, and composition of the
medium or substratum all have been tested in
their various effects. Only when the germ-plasm
has been acted upon simultaneously with the
soma has any well-defined reappearance of in-
duced characters in succeeding generations been
noted, and of the earlier results those of Stand-
fuss and Fischer seem most notable, sinee in ex-
periments with Vanessa and Arctia the applica-
tion of special temperatures or the modification
of nutritive conditions induced the formation of
aberrant characters in some of the offspring. The
new qualities were displayed in varying degree,
and maintained their distinctive appearance in
the products of hybridization with the parental
strain. There seems to be some doubt among
zodlogists acquainted with these forms as to the
significance of these results. It is not clear as

124 THE DIRECT INFLUENCE

to the manner in which the formation of the new
characters was induced. The experimental agen-
cies employed affected both the soma and the
germ-plasm segregated in the reproductive ele-
ments, and no interpretation of the facts would
justify the conclusion that the aberrant qualities
were somatogenically acquired.

While failure has attended all efforts to dem-
onstrate the continued inheritance of impressions
received by the body alone, a number of arrange-
ments are found in nature which seem to demand
such action for their explanation. Among these
certain rudimentary organs, and also co-adapta-
tions in which simultaneous specialization occur-
ring in two or more members of the body has
made for increased fitness, are difficult of inter-
pretation without the interposition of somatic
induction.

DIRECT STIMULATION OF THE GERM-PLASM
IN BEETLES

Meanwhile the possibility of influencing hered-
ity by agencies acting directly upon the germ-
cells has awakened the keenest interest among
biologists. The relations of soma and germ-
plasm make it difficult to induce changes in the
body without affecting the reproductive elements,
while it is possible to devise experimental meth-
ods by which the egg or sperm alone may be sub-
jected to modifying agencies. This has been
done with such success that some very important

PLATE I.

Fig. 1. Leptinotarsa undecimlineata, normal form.

Fig. 2. Form derived from L. undecimlineata through the application of the
climatic conditions. For convenience this form has been called angustovittata be-
cause it most closely resembles a species described by Jacoby, but it differs from
angustovittata in many characters considered important by the eystematists,
[From Plate 16, Investigation of Evolution in Chrysomelid Beetles of the genus
Leptinotarsa. Carnegie Institution, Publication No. 48, 1905. After Tower.]

Fies. 3,4. Normal mitosis of nuclei in cells of plant.

Fras. 5,6,7, 8. Irregularities of mitosis in cells of onion roots resulting from
exposure to radium. [After Gager.j

OF ENVIRONMENT 125

conclusions may be founded upon the evidence
obtained. The results of the work by Tower, in
which beetles of the genus Leptinotarsa were
subjected to various combinations and alterations
in climatic conditions in a series of experiments
carried on for a period of more than twelve years,
have recently been available and far surpass in
importance anything previously obtained from
animals. The value of the evidence is greatly
enhanced by its repetition, by the fact that pedi-
greed cultures were used and conditions so regu-
lated that an accurate analysis of the effects of
the various climatic factors could be made.
Professor Tower finds that :—

“Not only members of the genus Leptinotarsa, but
also of allied genera can be directly modified by the
application of intense environmental stimuli to the
germinal material. The use of temperature and
moisture in unusual degrees of intensity has given rise
to a number of forms and modified characters. Some
notion of the extent of these modifications is gained
from the two following illustrations. In Plate I,
Figure 1, is shown the normal form of L. wndecimline-
ata, and in Figure 2, a race derived from it by the
application of low temperature and low relative humid-
ity. This new form resembles in some respects Jacoby’s
species L. angustovittata, and breeds true. Jt matters
not whether this new form is a species, race, elementary
species, or a nightmare to the systematist, the important
point is, that as the result of subjecting the germinal
material to certain conditions at a fixed point in its
development, that the eggs thus treated, when fertilized
by normal male germs, gave the form shown, which
breeds true without subsequent segregation of charac-

126 THE DIRECT INFLUENCE

ters. In this case both structural and color char-
acters are modified.

“Many other illustrations might be given of the
entire change in the coloration of body, both in larve
or adult, of the modifications of parts and of particular
portions of the body or of individual color marks. These
arise, some from the treatment of the male germinal ma-
terial, some from treatment of the female germinal sub-
stance, others from a treatment of both germinal ma-
terials to the conditions of experiment. In some of
the modifications thus induced, the full expression of
the change is attained at once in the individuals that
develop from the treated germs, and in others it
requires one, two, three or more generations to attain
the full expression of the modified attribute. It does
not make any difference whether the full development of
the modification is attained at once, or after the lapse
of several generations, the behavior is the same, in that
there is no regression or reversion to the parental con-
dition.

“In my published work I have given some of the
results derived from the application of external factors
at one stage of the germ cells. Eggs that have been
subjected to the conditions of experiment immediately
before the maturation period, have given the results
now in print and it was from eggs so treated that the
race illustrated in this statement came. Analysis of
the results from these experiments shows a number of
interesting points.

“First: Not all of the germ-cells are modified, but
only a varying proportion of them, which may indicate
one of two things; either that there are differences
between the eggs in their capacity for modification, or
that only certain eggs were in the proper stage for
modification, at the time of the application of the experi-
mental conditions. Second: The results are sometimes
modifications all in one direction, at others they are in
many directions, two, three or more different forms
arising from the same experiment. Third: The mod-

OF ENVIRONMENT 127

ifications in some characters stand apart from the condi-
tion of the parents without intergrades, at other times
the same modifications have intergrades; some charac-
ters, as far as known, never have intergrades and some
always show them, and there is no place where one can
draw a line and say that on one side all are discontinu-
ous variations and on the other side they are continuous.
Fourth: The modifications produced never, as far as
known, segregate the characters in subsequent genera-
tions, indicating a condition different from hybrids. In
this respect my results are like those of MacDougal
with plants.”

Obviously the subjection of an entire organism
to the influence of an enveloping factor implies
also its action upon the soma as well as upon the
germ, and while necessarily the possibility of
some secondary or parallel inductions are not
entirely eliminated, yet an examination of the
detail of the experiments points unerringly to
the conclusion that the major effect is due to the
action of the external agency on the egg or sperm.
The soma is indeed the most immediate environ-
ment and medium of the germ-plasm, and its
activities must interlock most intricately with
those of the egg and sperm, in what manner has
already been suggested.

EFFECT OF RADIATIONS ON GERM-PLASM

Somewhat easier of analysis are the effects
produced by such forms of energy as radiation
of known character and measured wave-length
as illustrated by the results secured by the use of
X-rays, Roentgen rays, and radium emanations.

128 THE DIRECT INFLUENCE

In general it may be said that such forms of
energy retard growth and compel an incomplete
differentiation of tissues when applied to an indi-
vidual before maturity, producing serious delete-
rious effects if applied afterward. When eggs
or sperm are treated by these agents, the most
profound disturbances may ensue in the primary
divisions, and the ontogeny of individuals aris-
ing from a fertilization, either component in
which has been subject to such action, shows a
destruction of correlations and great disturbances
in symmetry, according to the most recent tests
of MacGregor with frogs. In most of these
cases the disturbances were so great that the indi-
viduals concerned were incapable of reprodue-
tion, and nothing further concerning their effect
on heredity was possible. The fact that the re-
sults were of the same general character, whether
the egg or sperm was subjected to the action of
the experimental agency, whether held in the re-
productive tracts of the animal or wholly free, is
a matter of some importance, since it eliminated
the intervention of the soma as a possible source
of modification of the results.

Recently Dr. C. S. Gager has completed an
extensive study of the influence of radium on
plants so applied that the elements subjected to
its action survived and were capable of reproduc-
tion. An examination of the effects on the nu-
cleus as well as the structure of the soma was
made with some highly interesting results.

OF ENVIRONMENT 129

When the root tips of the onion (Allium cepa)
were exposed for different periods of time to rays
from radium bromide of various degrees of activ-
ity, profound alterations were induced in the
mitoses of the cells. In nearly all cases the
passage of the chromosomes to the poles of the
spindle proceeded with great irregularity. Fre-
quently one or two chromosomes would remain
behind near the equator of the spindle, failing
completely to take part in the organization of the
daughter nuclei (Plate I, Fig. 6). At times
several chromosomes or portions of chromosomes
would remain at one side of the spindle, or be
carried beyond the poles (Fig. 8), or again be
drawn out as if subjected to considerable tension
(Fig. 5). In one instance, after the main cell-
division was nearly completed, a small secondary
spindle, in tardy telephase, was observed at one
side of the cell (Fig. 7).

From these results it was seen that the radium
treatment afforded a method by which chromatin
elements might be eliminated from reproductive
cells, and if these are the carriers of certain spe-
cific characters, as indicated by the researches of
Wilson, then a ready means of suppression or
substitution of characters would be afforded. In
addition to these distinctly radical effects, the
chromatin might be modified so as to form the
basis of characters not hitherto expressed by
the organism.

Proceeding on this basis, Gager exposed to

130 THE DIRECT INFLUENCE

radium rays the egg and sperm-cells of carefully
pedigreed Onagra biennis at various periods of
their development, both before and during fertil-
ization. Plants grown from the seeds produced
under this influence varied profoundly from their
parents. Old characters disappeared, and new
ones became evident. The treatment followed
by heritable alterations was one in which the pol-
len grains were exposed for twenty-four hours to
rays from radium of 1,500,000 activity, con-
tained in a sealed glass tube. Thus only the
X-rays and possibly the more penetrating of the
Beta-rays were effective. The three individuals
with thick, leathery leaves, which resulted from
this treatment of the pollen, have already pro-
duced a second generation in which the new char-
acters are seen to be reproduced, and, while await-
ing the continuance of this work, it may be as-
sumed with fair certainty that the atypic strain
will continue its development parallel to the pa-
rental one.

Other striking departures in ontogeny were
secured by exposure of the pollen and the ovary
before and after fertilization, and also by treat-
ment of maturing seeds, which were not transmis-
sible. Some slight modification of the technique
might well secure more extensive results and also
permit an analysis of the difference, if any, be-
tween somatogenic and odgenic inductions and
also illuminate the matter of the appearance of
bud-sports.

OF ENVIRONMENT 131

EFFECT OF SOLUTIONS ON GERM-PLASM

The idea that solutions of various kinds might
be introduced into the plant, and that modifica-
tions of the ontogenetic procedure might be thus
brought about, has been in the minds of many
workers in the laboratory. Developing inflor-
escences have been excised and set in vessels con-
taining salt solutions, and in other cases sub-
stances were applied to cut surfaces of the vege-
tative parts of the reproductive organs without
result.

This in part was suggested to Darwin by vege-
table galls, and in the first chapter of the Origin
of Species (page 7) we find him saying :—

“Such facts as the complex and extraordinary out-
growths which invariably follow from the insertion of
a minute drop of poison by a gall-producing insect,
show us what singular modification might result in the
case of plants from a chemical change in the nature of
the sap.”

That his interest in this matter was continued
is evidenced by the following from Life and
Letters :—

“Shortly before his death, my father began to
experimentise on the possibility of producing galls arti-
ficially. A letter to Sir J. D. Hooker (November 3,
1880) shows the interest he felt in the question :—

“¢] was delighted with Paget’s Essay.* I hear

* Disease in Plants, by Sir James Paget. Gardeners’ Chronicle,
1880.

182 THE DIRECT INFLUENCE

that he has occasionally attended to this subject from his
youth. . . . I am very glad he has called attention to
galls: this has always seemed to me a profoundly in-
teresting subject ; and if I had been younger would take
it up.’

“ His interest in this subject was connected with his
ever-present wish to learn something of the causes of
variation. He imagined to himself wonderful galls
caused to appear on the ovaries of plants, and by these
means he thought it possible that the seed might be
influenced, and thus new varieties arise. He made a
considerable number of experiments by injecting
various reagents into the tissues of leaves, and with some
slight indications of success.” *

In response to a request for a more detailed
account of work that may have been done on this
subject by the elder Darwin, Professor Francis
Darwin writes under date of November 27,
1908 :—

“JT am sorry that I can give you no further informa-
tion about the experiments on galls. My recollection
is that we tried only injections with leaves and stems,
and that no actual experiments were made on ovaries.
I have never looked at his notes and do not know where
they are at this moment, but I feel pretty sure that no

definite results were obtained. I think acetic or formic
acid was used in the experiments.”

In the course of my extensive cultures dealing
with mutations, the theoretical conclusions of
De Vries as to the pre-mutation period came up
for serious consideration, and in order to obtain
some evidence upon this point, as well as to test
the assumption that the actual changes upon

1 Life and Letters of Charles Darwin, by F. Darwin, II, p. 517,
1905. New York.

PLATE II.

T. T. Upper and lower aspects of rosette of Qinothera bennis.
D. D. Rosette of derivative resulting from ovarial treatment with zinc sulphate.

OF ENVIRONMENT 133

which mutation rests ensue previous to the reduc-

tion divisions leading to the formation of the
reproductive nuclei, some new methods of experi-

mentation were developed. Among other opera-

tions, solutions of sugar, calcium, potassium, and

zine were injected by the use of hypodermic

syringes into the developing ovaries of Raiman-

nia, one of the evening primroses, early in 1905,

with the result that out of the several hundreds”
of seeds borne by the treated ovaries sixteen in-

dividuals were found to be notably atypic, among

other characters lacking the trichomes which are

so conspicuous with the parental form. These

reproduced themselves in the second and third

generations, coming true to the newly assumed

characters.

The same method was tried with Oenothera
biennis (Plate II), the common evening prim-
rose of waste lands in eastern United States, with
the result that two individuals were found among
the seedlings which were different from the par-
ents in a series of characters so distributed
through the ontogenetic period that the deriva-
tives * could be recognized by the first two leaves,
while the cotyledons were still waxing. This
form is now being cultivated at the Desert Lab-
oratory in the fifth generation, and is being
thrown against the climatic selective factors in
the mountain plantations at various altitudes.

1The derivatives, lettered D in Plate II, are to be “compared
with the typical young plants, lettered T.

134 THE DIRECT INFLUENCE

These two successes had been scored by the use
of crude instruments, entire lack of information

we N s
SESE ett,
Ae

i,
sere pena
2
x

pd
(0
A a.

‘Mare

Suits
SROs ae
we,

Schematic section of ovule showing action of reagent, intro-
duced into ovary. mi, micropyle, P, egg, a, antipodal nuclei, i,
inner integument. The reagent is taken up by the micropylar
cells, and also follows the stream of nutritive material around
the inner integument to the neighborhood of the antipodal cells.

OF ENVIRONMENT 135

as to the mechanical action of the reagents, and
with plants offering an ovarial structure most
difficult to deal with. In the development of the
method, non-corrosive syringes of glass with gold
needles and an extended list of substances were
employed, while a selection of species was made
in which the reagents could be brought into con-
tact with the egg apparatus with proportionately
least damage to its somatic structures. The sub-
stitution of dyes for the substances to be used
was found useful in making out the mechanical
results of an injection. Since these operations
inevitably resulted in the destruction of a large
number of ovules, it was found most convenient
to work with forms which are characterized by
many-seeded ovaries. By this development of
technique, more important results capable of def-
inite analysis were secured and a fair basis for a
theoretical explanation gained.

Many progenies representing genera in widely
separated families are now under observation, but
announcement of results beyond those of a year
ago will be confined to Penstemon.

Penstemon wrightii is a species well marked
and readily separable from its nearest relatives,
which alone of the genus inhabits the slopes
around the Desert Laboratory. It is, therefore,
growing under perfectly undisturbed conditions.
Various injections of zinc, calcium, and iodine
into the young ovaries were made when these
structures were not more than 3 mm. long and

136 THE DIRECT INFLUENCE

two-thirds of that diameter. A large number of
the ovaries were killed by this treatment, but
many matured. The percentage of germination
in the species has been found to be low, however,
and of the few hundreds of seeds sown, not more
than a fifth germinated, and a few were killed by
drought. Eighty individuals grew to make ma-
ture rosettes during 1908. Sixty of these pro-
gressed so far as to bloom during the season, and
of these, twenty offered such material departures
from the parental form as to be readily distin-
guishable by visitors who had not critically ex-
amined any member of the genus, or, indeed, had
but little knowledge of plants. These twenty
derivatives showed eight distinct types, one of
which was represented by five individuals, one by
four, two by three, one by two, and three by one.
One type resulted from treatments with iodine,
calcium, and zinc; four types came from a treat-
ment of two reagents, two from iodine alone, and
two from calcium alone. The revolution of the
corolla segments, the absence of the stiff clump
of trichomes from the lower lip, increase in vis-
cidity, mottling of the flower, and adhesion of leaf
bases resulting in perfoliation, are some of the
distinguishing marks of the new forms. Of these
characters some are already displayed by other
members of the genus, while some of the progres-
sive and retrogressive changes seem to be taken
before any relative had moved in the same direc-
tion.

OF ENVIRONMENT 137

Briefly summarizing the results of the investi-
gations cited it may be taken as safely established
that individually acquired or induced characters
or modifications of existing qualities may be
transmitted from one generation to another prac-
tically unchanged. The assumption that organ-
isms may make direct fitting or adaptive re-
sponses of the soma to environmental factors,
which may be impressed on the germ-plasm and
transmitted to successive generations, has not
been confirmed by actual observation or experi-
mental tests.

This tentative conclusion that somatogenic
characters are not transmitted is one with which
the following facts must always be taken into
account: A4—the physiological mechanism of or-
ganisms, particularly of the seed-plants, is one
which offers direct means of communication be-
tween the soma and the germ-plasm in the form
of reproductive elements, and which might per-
mit the making of enduring impressions on
embryonic tissues during ontogeny, or their
effective communication to the egg, or sperm;
B—the experimental and cultural test of the
effect of repetition of the action of external agen-
cies upon the soma in inducing hereditary alter-
ation has not yet been seriously attempted, and
may indeed include the crucial requisite of the
whole matter; C—a great number of structures
and functions sustain the closest adaptive relation
to environic forces, and important correlations

138 THE DIRECT INFLUENCE

are found among or between organs in a manner
difficult of explanation upon any ground except
that of simultaneous somatogenic induction.

MECHANISM OF THE INHERITED CHANGE

The modification of heredity brought about by
the direct action of various agencies upon the
germ-plasm is now safely established, and the
available results are sufficient to justify some few
generalizations as to the mechanism of the
change. The most important evidence as to the
nature of the disturbances which may ensue in
reproductive elements comes from the work of
Gager, who found that the action of radium
might eliminate definite chromatin elements dur-
ing the mitoses of the egg and pollen, and, fur-
thermore, that some of the eggs fertilized by
pollen subjected to such irradiation produced a
progeny in which qualities different from those of
the parental strain were exhibited. It is not
proven, of course, that the atypic strain was de-
rived from a fertilization into which one less or
one more chromosome entered, and possible dis-
turbances of the autolytic action of the cell might
well be as important as the departures from nor-
mal mitotic procedure. The well-known influ-
ence of temperatures upon these processes and
also the readiness with which unusual substances
might be thrown into the cytoplasm in the ordi-
nary course of nutrition, suggests that the plant

OF ENVIRONMENT 139

would be susceptible to modification in the stage
between the reduction divisions and fertilization.

This conclusion is borne out by my own results
in which solutions were introduced into the ovary
during this stage. The extent of the treatments,
together with the diversity of results, makes pos-
sible an analysis of other features. Thus the in-
duction of more than one form by the use of a
single reagent suggests either that different chro-
matin elements were affected in the separate
ovular reactions, or that unlike parts of the chains
of catalytic action were interrupted or disturbed
by the introduced substances. Some of the com-
pounds used are inimical to enzymatic action, or
may be capable of a negatively catalytic effect,
or might indeed set up unusual splitting proc-
esses, a state of affairs distinctly favorable to the
last named alternative.

Not only may irradiation and the introduction
of unusual substances occur naturally to the mod-
ification of heredity in plants, but the climatic
factors may, as in Tower’s experiments, exercise
an influence upon the reaction velocities of va-
rious parts of the metabolic series, or by varia-
tions in humidity, regulate the excretion or reten-
tion of active substances. All of these possibilities
must be taken into account in attempts at expla-
nation of bud-sports or bud-mutations in plants.
It is to be seen that either egg or sperm may be
affected by experimental agencies, and that the
results do not differ in quality or degree. Gager’s

140 THE DIRECT INFLUENCE

atypic forms were obtained by the treatment of
pollen; my own from ovarial injections which
might have acted upon the egg, or sperm, and
Tower’s work was with both.

The new forms of beetles and plants which
have thus been called into existence sustain the
following general relations to their environ-
ment and to the strains from which they were
derived:

1. Some of the species dealt with were growing
in the open, and domesticated forms were not in-
cluded in the experiments.

2. The newly arisen or modified characters
maintained their distinctive appearance when
crossed with the parental strains; in some no re-
versions have yet been shown.

8. Discontinuous departures induced by ova-
rial treatments in plants were full and constant
within the limits of fluctuability with the first
generation. Similar abruptness of divergence is
exhibited by beetles in some cases, while in others
more than one generation, after removal from
experimental conditions, was necessary to secure
full expression.

4, Many aberrations induced by irradiation in
plants and by climatic effects in beetles were of
the nature of closely continuous variations, the
range of which was widened by the exciting
agent. Some of the derivatives of Penstemon
may prove to be of this character. The single
derivative of Oenothera biennis obtained by ova-

OF ENVIRONMENT 141

rial treatment with zinc sulphate is distinctly
discontinuous with the parent.

5. Some of the modifications may be regarded
as an increase of capacities already present; some
imply the loss of characters or structures, and
some are acquisitions; in more than one instance
qualities new to the genus have been taken on.
Changes such as the mottling of a solidly col-
ored flower may be regarded as a loss of a por-
tion of a design, the total effect of which was a
shaded or a self color, or it may be taken as a
differentiation in advance.

6. The behavior of the newly derived forms
when subjected to natural conditions, competi-
tion, and possibility of hybridization with paren-
tal forms, has been extremely diverse. Some of
the beetles have been swamped by hybridization
with the parental form; others have displayed
some power of endurance. The plant deriva-
tives induced by ovarial treatments were weaker
than the parent in some localities, and more en-
during in others. The derivative of Oenothera
biennis induced by a zinc sulphate ovarial treat-
ment is less adapted to xerophytic conditions
than the parent, does not readily hybridize with
it when grown in contact, and its earlier char-
acters appear to be dominant when crosses are
made artificially.

7%. The departures obtained by the experi-
mental manipulation of external exciting agen-
cies bear a general similarity to the initiatory

142 THE INFLUENCE OF ENVIRONMENT

and modificational phenomena exhibited by or-
ganisms in a state of nature, and it seems justi-
fiable to conclude that the processes disturbed or
set in motion are identical with some of those
concerned in the main evolutionary development
of organisms.

THE BEHAVIOR OF UNIT CHARAC-
TERS IN HEREDITY

BY
W. E. CASTLE

_ No one recognizes more frankly and joyously
than would Darwin, were he here to-day, the
great advance which has been made in our knowl-
edge of heredity since his time. His work and
writings have pointed the way to that advance,
and it is largely owing to a return to the experi-
mental method of testing hypotheses, which Dar-
win used so successfully, that the remarkable
progress of the last decade has been made pos-
sible. We do, therefore, the greatest honor to
Darwin if we pause to consider what superstruc-
ture of knowledge has been built on the founda-
tions which he laid. This superstructure is, in-
deed, still in the building, and it is not easy in
all cases to distinguish between the solid structure
of proved fact and the scaffolding of hypothesis.
Still, the attempt should be made, and it will
give us encouragement to discover that, notwith-
standing the considerable amount of rubbish
lying about, there is, nevertheless, good con-
structive work going on here which gives prom-

ise of permanency.
148

144 THE BEHAVIOR OF UNIT

The particular topic which I have been asked
to discuss is the behavior of unit characters in
heredity.

The subject of heredity units is one to which
Darwin gave much thought. With characteristic
thoroughness and patience he assembled the facts
of inheritance, reversion, bud variation, regenera-
tion, and related subjects, which in his opinion
had a common underlying cause, and with delib-
eration framed a tentative hypothesis to explain
them. This hypothesis, which he called pangen-
esis, was itself short-lived, but has left a numer-
ous progeny. ‘The most important are the idio-
plasm theories of Weismann and Nageli, and the
theory of intracellular pangenesis of De Vries.
Darwin’s hypothesis was useful because it set
people to thinking, observing, and experiment-
ing. The theories of Weismann, Nageli, and
De Vries were attempts to bring Darwin’s fun-
damental idea into harmony with facts subse-
quently discovered. All these theories were
scaffolding, not masonry.

MENDEL’S LAW

A conception of unit characters fundamen-
tally different from Darwin’s, one which
antedates slightly the pangenesis theory, but
which suffered total eclipse by it, is to-day
known as Mendel’s law. It accords so fully
with a variety of biological facts discovered

CHARACTERS IN HEREDITY 145

since Darwin’s time, that we are coming to re-
gard it as the cornerstone of our knowledge of
heredity.

The romantic story of Gregor Mendel is
known to you, how toiling long years in obscurity
hybridizing garden-peas, he made a great dis-
covery only to see it scarce noticed and soon
forgotten. He himself, meanwhile, called to ad-
minister the affairs of an ecclesiastical establish-
ment, was forced to relinquish his favorite pur-
suit of scientific investigation, and was thus
unable to follow up his great discovery and force
it upon the attention of scientists. So he died
unhonored by his fellow-scientists and all but
unknown to them.

The story of how, a generation later, Mendel’s
law was rediscovered thrice over is scarcely less
romantic. That the rediscoverers, having first
established the law independently and then hav-
ing discovered Mendel, should assign the honor
unreservedly to the obscure and forgotten Abbot
of Briinn, is a circumstance which should cause
us long to remember and honor the names of De
Vries, Correns, and Tschermak.

According to Darwin’s pangenesis theory, the
reproductive cell is made up of minute units de-
rived from and representing each part or organ
of the entire body. A few critical experiments
instituted by Galton showed this theory to be
untenable, and they seem to have involved in
public esteem an adverse decision against all less

146 THE BEHAVIOR OF UNIT

well-known theories in which the existence of
units in heredity was assumed. Such was the
fate deservedly of the highly speculative theories
of Nageli, and undeservedly of the generalization
reached by Gregor Mendel, a scientific protégé
of Nageli.

Mendel did not frame any complete theory of
heredity, but observed, as the result of experi-
ment, that certain characters of plants are, in
crosses, inherited by definite proportions of the
offspring. He framed in general terms a state-
ment of what those proportions are and advanced
a simple hypothesis to account for them. Men-
del’s generalization we know to-day as Mendel’s
law, and his hypothesis as the theory of unit
characters.

By a unit character in the sense of Mendel’s
law, we mean any quality or part of an organism,
or assemblage of qualities or parts, which can be
shown to be transmitted in heredity as a whole
and independently of other qualities or parts.
Thus Mendel found that the starchy char-
acter of the seed of some varieties of garden-
peas, which makes the seeds round and smooth
when dried, is a quality which may by suitable
crosses be replaced by a sugary character, causing
wrinkling of the seed on drying. This change of
the seed character through crossing may be
brought about without essential modification of
the other parts of the plant. Round and wrin-
kled seed forms in peas, Mendel accordingly con-

CHARACTERS IN HEREDITY 147

sidered to be alternative and interchangeable unit
characters.

Similarly yellow color of the cotyledons in the
seed of peas was found to be a unit character
alternative with green color. In animals we find
similar simple unit characters to exist. Thus in
mammals black pigmentation is due to the pres-
ence of a unit character which may be replaced
by another changing the pigmentation to brown.
Among horned ruminants, such as cattle and
sheep, development of the horns depends upon
the presence of a unit character which may be
replaced by (or perhaps become associated with)
another, in the presence of which horns fail to
develop.

RECENT EXTENSIONS OF THE THEORY OF
HEREDITARY UNITS

In cases less simple than these, a unit character
may have more than a single manifestation, as
where a plant having flowers of a certain color
has also a similar but fainter coloration of the
stem, or a mammal with black hair-pigment has
also black skin-pigment, while one with brown
hair-pigment has also brown skin-pigment. In
still other cases, two or more independent unit
characters must be present together to produce
a single visible effect. This fact was unknown
to Mendel. Its discovery constitutes one of the
most recent and important advances made in our

148 THE BEHAVIOR OF UNIT

knowledge of heredity, and merits further con-
sideration.

Mendel conceived of unit characters as exist-
ing always in pairs, one of which might be sub-
stituted for the other by suitable crosses. We
are now coming to realize that this is an inade-
quate statement of the matter. What is paired
is not the unit character alone, but the entire or-
ganism. All its characters and parts have their
basis in paired structures in the protoplasm of
the individual, one member of each pair being
derived from the mother of the individual, one
from the father. The cytologist has visible evi-
dence of this fact in the doubling of the number
of chromosomes at fertilization, and their subse-
quent reduction when the reproductive cells
ripen; the experimental breeder has evidence of
this duality equally convincing as regards many
hereditary characters, but the evidence is clearest
in the case of characters which occasionally are
lost. It is only in such cases that we can with
certainty identify unit characters. By compar-
ing an individual which has a certain character
with another individual which does not have it,
we learn how much that character includes, and
we can learn this in no other way. Experimen-
tal breeding will show whether the character is
simple, is really a unit, or is an aggregate of in-
dependent units. Thus if we cross a black
guinea-pig with one which lacks black—say a
brown one—we obtain only black offspring, but

CHARACTERS IN HEREDITY 149

these bred inter se produce both black offspring
and brown ones, in the proportion three black
to one brown. We thus learn that black is a
unit character. It was contributed by one par-
ent to the cross, but not by the other, and trans-
mitted by the cross-bred individual to half its
offspring, but not to the other half. This is
Mendel’s explanation of the 3:1 ratio, now fa-
miliar to every biologist.

But if we cross the same black parent in the
foregoing case, not with a brown individual, but
with a white one or with a yellow one, we may
obtain not black offspring, but wild-colored
“ agouti” ones, which bred inter se will produce
agouti, black, white (or else yellow) young, with
perhaps those of other new classes in addition.
Such a result as this puzzled Darwin, and would
naturally puzzle any one, but in the light of Men-
del’s law becomes capable of ready explanation.
The production of black pigment is a process in
which more than one unit character is concerned;
the production of a gray coat involves more units
still; how many, can in part be determined by a
study of the number of classes of individuals
occurring in the second generation from the
cross, and the numerical proportions in which the
individuals occur in these classes. The point
may be made clearer by following through
a particular case, to which Darwin makes
reference. }

150 THE BEHAVIOR OF UNIT

Primary color-varieties
of rabbits Constitutent factors

Vell we cakes eae ae ee ed ets A—C—B—R

If rabbits of various colors are turned loose
together in a warren, the population is likely to
revert more or less completely to the gray color-
ation of wild rabbits. The foregoing is in sub-
stance the statement of Darwin; and its correct-
ness is fully established.

THE FACTOR HYPOTHESIS IN RABBIT
BREEDING

Before going further it may be well to describe
the color varieties of rabbits. These are exceed-

CHARACTERS IN HEREDITY 151

ingly numerous, but for our purpose may be
reduced to four fundamental color types in addi-
tion to the albino or uncolored type. These four
are gray, black, yellow, and sooty yellow. The
last I shall for simplicity call sooty. Gray is the
original or wild type from which the others have
been derived. The gray fur contains both black
and yellow pigments, but so disposed as to pro-
duce a pattern on the individual hair, viz., a dark
base and tip and in between them a band of yel-
low. The lower surfaces of the body also are
whitish. In the black variety the hair pattern is
wanting, and the black pigment occurs through-
out the length of each hair and all over the body.
In the yellow variety black pigment is largely
wanting throughout the coat, though present in
the eye and, in very small quantities, in the hair.
The presence of the hair-pattern is nevertheless
suggested by whitish under surfaces, as in the
gray type. The sooty type closely resembles the
yellow, but has colored under surfaces, instead of
white ones. Yellow and sooty correspond with
gray and black respectively, but with a greatly
reduced amount of black pigment in the fur, so
that yellow predominates there.

Let us now consider the relation of these four
types one to the other. Gray crossed with any
other type produces only gray offspring. Black
crossed with yellow produces gray, but crossed
with sooty produces black. Yellow crossed with
sooty produces only yellow. Sooty disappears

152 THE BEHAVIOR OF UNIT

in crosses with any other type; it is recessive in
the Mendelian sense with reference to all the
others.

Darwin explained the reversion of feral rab-
bits to the gray type on two grounds: (1) “a
tendency in all crossed animals to revert to their
primordial state,” and (2) the action of a more
“natural” environment when the animals are
free than when they are in captivity. In reality
neither of these conjectured reasons has anything
to do with the case. Some varieties will under no
circumstances give reversion, if crossed with each
other; but reversion may be obtained as readily
in captivity as anywhere. Reversion is due solely
to the bringing together of certain unit char-
acters, whose joint action is necessary to produce
the observed result.

In producing the gray coat characteristic of
wild rabbits at least eight independent unit char-
acters are involved. Other color varieties of the
rabbit have arisen by regressive variation, i.e. by
loss, more or less complete, of one or more of
these unit characters.

To illustrate the matter, let us consider the
result of a particular experiment. Black rab-
bits were crossed with light yellow (cream)
ones, and produced wild-colored gray offspring.
These bred inter se produced young of a variety
of colors, but among them grays again predom-
inated. All the first generation grays seemed
to breed alike, producing young of various colors,

CHARACTERS IN HEREDITY 153

but not so those of the second generation (F.).
Among these thirty-two different classes may be
recognized, that is, thirty-two sorts which, though
all looking alike, produce each a different assort-
ment of young. These assortments are:—

Gray only.

Gray, and black.

Gray, and white.

Gray, black, and white.

Gray, and yellow.

Gray, black, yellow, and sooty.
Gray, yellow, and white. ©

Gray, black, yellow, sooty, and white.

St Se SUE ices

Eight other varieties produce the same sorts of
young as these eight respectively, but in addition
produce dilute pigmented ones of the same color
types, t.e. blue-grays as well as grays, blue as
well as black, cream as well as yellow, and pale
sooty as well as sooty. Sixteen other varieties
produce the same assortments of young as these
sixteen, but in addition produce animals spotted
with white in each of the several color types.

The facts briefly stated are now before us.
We can distinguish among the second generation
gray rabbits thirty-two different kinds, all look-
ing alike but all breeding differently. Out of
this apparent chaos the Mendelian theory of unit
characters brings law and order; no other ex-
planation has been offered which makes anything
but chaos out of the situation. The number of
distinguishable classes, thirty-two, shows that

154 THE BEHAVIOR OF UNIT

five independently variable characters are in-
volved; the proportions in which the several sorts
of young are produced by each class of gray
parent confirms this conclusion. If the number
of independent unit characters concerned were
one greater, as it is in guinea-pigs, the total num-
ber of classes of parents would be doubled to
sixty-four; if it were one less, the number of
classes of parents would be reduced one-half, to
sixteen.

What now are the five variable unit characters
concerned in producing the gray .coat of a rab-
bit and what are their relations one to another?
In answering this question it will be necessary
to mention a sixth unit character which contrib-
utes to the result, though not itself variable. It
will be convenient also to designate each sep-
arate unit character by a letter or symbol. The
six unit characters to which reference has been
made are :—

1. C, a general color factor, something necessary to
the production of all pigment, wanting only in albinos.

2. B, a factor for black, some substance, which acting
upon C, produces black pigment; this is in rabbits an
unvarying factor, though in other mammals it is often
variable.

The four remaining factors modify the action of
one or the other of these two; they are:—

3. A, a pattern-factor governing the distribution of
black on the individual hair, so that it converts black
into gray, blue into blue-gray, and sooty into yellow.

CHARACTERS IN HEREDITY 155

4. E, a factor governing the extension of black over
the body generally; in its most extended distribution,
black occurs on all hairs of the body, in its most
restricted distribution (R) it scarcely extends beyond
the eye, and the skin of the extremities, the hair being
practically devoid of black pigment and appearing yel-
low; that this factor is distinct from B, is shown by the
fact that it can, in guinea-pigs, be dissociated from B
and become associated with brown pigmentation.

5. U, a factor governing the distribution of C over
the body ; if C covers the whole body (condition U), the
whole body is pigmented; if C covers part of the coat
only (condition S), the rest is occupied by spots of
white. That this unit is distinct from C is shown by
the fact that it is transmissible through animals which
lack C, that is, through albinos.

6. I, a factor governing the intensity of the pig-
mentation. It is a modifier of C, for it affects all pig-
ments alike, yellow and brown as well as black, all of
which pigments have their common basis in C; but I is
distinct from C, for it is transmissible through albinos,
which lack C. When I is present all the pigments are
intense; when I is absent, or rather weakened to the
condition D, the pigmentation is dilute, as in blue and
cream, the dilute conditions of black and yellow
respectively.

It is clear from what has just been said that
these various factors, though separately variable,
are not entirely independent of each other. Some
produce no visible effects unless others are pres-
ent. Thus if C alone is wanting, none of the
others is visible. To aid in expressing the inter-
relationship of the factors I think it useful to
imitate the organic chemist and employ dia-
grams. Thus a diagram might be constructed as
follows to express the relations of the six factors

156 THE BEHAVIOR OF UNIT

in a reproductive cell transmitting the color char-
acters of a gray rabbit:—

A—C—B—E

It is possible that in protoplasm we have or-
ganic molecules built up in some such way, and
that regressive variations arise by dropping off
the constituent parts of the molecule one by one.
Certainly it is loss or extreme modification of
factors that produces the ordinary color varia-
tions. If A drops out, we have a black rabbit
instead of a gray; if E is replaced by R, a yellow
one is produced; if both these changes occur, a
sooty one; if U is replaced by S, we have a
spotted gray rabbit; if both U is replaced by S,
and A is lost, a spotted black rabbit results; if
C is lost, we have an albino, whose breeding ca-
pacity varies with the number of other invisible
factors which remain.

The list of known color factors is not ex-
hausted by those which I have enumerated. One
other, a factor for brown pigmentation, Br, has
been revealed in ae case of the guinea-pig, the
mouse, and the dog, by loss of factor B. Brown
pigmentation then everywhere replaces black.
This factor bears the same relation as does B to
both C and E. Some time doubtless we shall see

CHARACTERS IN HEREDITY 157

brown and cinnamon-gray rabbits produced by
the same mutation, loss of factor B, which has
produced brown and cinnamon-agouti varieties
among mice and guinea-pigs. Again there must
be in all rodents a factor Y which, acting in the
presence of C, produces yellow pigment, but Y
has not unmistakably revealed itself by getting
lost. It is always present, if C is, and may rep-
resent possibly a step on the road to the produc-
tion of black and brown. Certainly, however,
its distribution on the body of the rabbit is inde-
pendent of the factor E, though subject to U.
In the diagram, therefore, Y and Br will prob-
ably fall into the positions shown herewith for
the guinea-pig :-—

U B
| awe
A—C—Y E
ie A
I Br

This diagram would express the interrelations
of the color factors, as we now understand the
matter, in a reproductive cell or gamete trans-
mitting the wild type of coat. But such a
gamete might be formed by some sixty-four dif-
ferent kinds of wild-coated individuals. The
only differences, however, between these sixty-
four kinds of individuals would lie in whether
they contained a single or a double dose of each
of the factors enumerated. I therefore propose

158 THE BEHAVIOR OF UNIT

further to imitate the organic chemist by placing
a subscript, :, after each factor doubly represented
in the individual, i.e. after every factor in which
the individual is homozygous, while elsewhere
omitting it. We shall thus have a zygotic for-
mula which will look like a chemical formula, and
which will serve the same useful purpose of ex-
pressing many facts clearly and in small com-
pass.

The zygotic formula of the pure gray rabbit
will then be B2 EK: A» C2 I. U2; the gray rabbit
which also gives black young will be single in A,
but otherwise identical in formula with the fore-
going, viz., B. KE, A C: I. U2, and so on through
the list.

The question will naturally suggest itself, how
common are unit characters? Are all the quali-
ties and parts of organisms due to them, or only
certain kinds of qualities or parts? Such ques-
tions can not at present be answered satisfac-
torily. It may be pointed out, however, that we
are already acquainted with a considerable va-
riety of Mendelizing characters. These include
in plants both structural and physiological char-
acters of stem, leaf, flower, and seed. In ani-
mals, where a less extensive study has as yet been
made and where the organization is much more
complex, the unit characters thus far identified
relate chiefly to superficial characters, pigmenta-
tion, hair-structure, and the like. Certain pecu-
liar variations of the skeleton, digital variations,

CHARACTERS IN HEREDITY 159

and the like, have, however, been shown to Men-
delize, and further study will undoubtedly reveal
the existence of additional unit characters. We
should also bear in mind that we have no means
of identifying unit characters except as they drop
out of existence in certain individuals. Many
unit characters are probably of such vital impor-
tance to the organism that they cannot be dis-
pensed with, for when they are lost the organism
ceases to exist. In such cases the existence of
unit characters, however probable, can not be
unmistakably demonstrated by any method now
known to us. Fragmentary as our present
knowledge is, it is doubtful whether any category
of organs, quantities, or parts can be mentioned
which is not subject to Mendelian inheritance.
If we could only discover some means of sup-
pressing particular unit characters, what an in-
strument for unraveling the mysteries of inheri-
tance would be ours!

Time does not suffice to discuss the mutability
or immutability of the unit characters, the pos-
sibility of new characters arising de novo, and
other interesting but disputed questions. These
are matters with which the second fifty years
after Darwin will have to deal.

MUTATION
BY

CHARLES B. DAVENPORT

FortTy-THREE years after the Origin of Spe-
cies there appeared the first part of a book by the
Dutch naturalist, Hugo de Vries, entitled Die
Mutationstheorie. Many other theories of evo-
_lution have been propounded and defended in the
last half-century, but hardly any other has
commanded such immediate consideration and
received such widespread acceptance. The muta-
tion theory must therefore contain certain evi-
dent elements of truth. Let us consider its
scope and some of the evidence on which it rests.

MUTATION DEFINED

First of all it is necessary to define mutation
in De Vries’ sense and to show its relation to
other evolutionary principles. Mutation in any

‘strain is a change in the unhybridized germ-
_ plasm of that strain which is characterized by the
acquisition or loss of one or more unit charac-
ters. There has already been presented to you
the evidence for unit characters, a conception
first clearly elucidated by Darwin. I think it
may fairly be said that the mutation theory rests

on the doctrine of unit characters and applies
160

MUTATION 161

only so far as that doctrine applies. As even the
most extreme neo-Darwinian school recognizes
such units with their representatives (determin-
ants of Weismann) in the egg, and as in evolu-
tion there must be the acquisition or loss of at
least some one character, it might be expected
that the idea of mutation as defined above would
find universal acceptance. But it has not done
so. The difference of opinion relates to the gra-
dient of the transition by which a new unit char-
acter is introduced or an old one disappears.
Mutation in De Vries’ sense implies the sudden
appearance, complete in the first generation, of
the new unit character and its germinal repre-
sentative, the pangene or determinant. Muta-
tion is regarded by many who call themselves
Darwinians as an innovation and as opposed to
Darwin’s fundamental assumptions. For the
neo-Darwinian conceives the determinant as
gradually changing in evolution and exhibiting
in the adult forms of successive generations the
same continuous series that an organ shows in its
ontogenetic development. The view of neo-
Darwinians is well indicated in the following
quotation from Weismann *:—

“If I mistake not we may say at least so much that
all variations are, in ultimate instances, quantitative, and
that they depend on the increase or decrease of the vital
particles, or their constituents, the molecules. .
What appears to us a qualitative variation is, in reality,

nothing more than a greater or less, a different mingling
of the constituents which make up a higher unit, an

The Evolution Theory, Vol. II, p. 151.

162 MUTATION

unequal increase or decrease of these constituents, the
lower units. We speak of the simple growth of a cell
when its mass increases without any alteration in its
composition . . . but the cell changes its constitution
when this proportion is disturbed, when, for instance,
the red pigment granules which were formerly present
but scarcely visible increase so that the cell looks red. If
there had previously been no red granules present, they
might have arisen through the breaking up of certain
particles—of protoplasm, for instance,—in the course
of metabolism so that, among other substances, red
granules of uric acid or some other red stuff were pro-
duced. In this case, also, the qualitative change would
depend on an increase or decrease of certain simpler
molecules and atoms constituting the protoplasm-mole-
cule. Thus, in ultimate instance, all variations depend
upon quantitative changes of the constituents of which
the varying part is composed.”

So far Weismann. With his accustomed thor-
oughness he has followed the consequences of his
stand that quantitative changes alone are suf-
ficient to account for the processes of evolution,
although to do so he has been forced to take the
position that the loss of certain atoms from a
molecule is merely a quantitative change, and
that the appearance of a new quality is quantita-
tive because merely of the order of a change from
zero to one! Weismann’s argument here degen-
erates to a mere play of words. Just as good an
argument could be made to support the assertion
that all changes are qualitative—that 96 is qual-
itatively unlike 97. But if the ideas are both
to be retained, then it must be admitted that a
loss of atoms from a molecule, the appearance of

MUTATION 163

a new kind of molecule, the appearance of red
pigment where none was, are all qualitative
changes. Weismann’s admission that red gran-
ules may arise de novo in consequence of a molec-
ular change in the germ-plasm is an admission
that an organism may undergo a qualitative va-
riation, and this is a mutation. Recalling, then,
in recapitulation, that every character of an or-
ganism has a chemical basis, that a new character
implies one or more new kinds of molecules and
that molecular change is essentially qualitative
and discontinuous, the conclusion seems safe that
variations involving new characters are essen-
tially discontinuous, and consequently of the
order of mutations.

DARWINIAN VARIATIONS

At this time the Weismannian view and that
of the neo-Darwinists in general is of less interest
than that of Darwin himself. What was Dar-
win’s attitude on the question whether variations
that play a part in evolution are of the qualita-
tive or the quantitative order? The answer
seems to be simple; the question did not present
itself to him—our formulation of the matter is
a comparatively recent product of scientific anal-
ysis. Darwin did recognize saltation as opposed
to ordinary variability, and remarks: “ It is dif-
ficult to drawn any distinct line between a vari-
ation and a monstrosity.” In his Variation of
Animals and Plants under Domestication, Dar-

164 MUTATION

win cites cases of characteristics that he believes
to have arisen suddenly, such as the blackness of
the japanned peacock, jaw appendages of pigs,
short upper jaw and hornlessness in cattle, short-
leggedness in sheep and dogs, elongated wool in
merinos, and downless fruit in peaches. These
instances sufficiently indicate Darwin’s recogni-
tion of saltation, and if he was led to reject it as
the usual mode of modification of species, he did
so because the doctrine had a crude form and car-
ried with it the connotation of something terato-
logical or pathological. But is there sufficient
evidence that, in rejecting saltation, he regarded
evolutionary changes in unit characters to pro-
ceed always by the fourth place of decimals?
On the contrary, his examples of variations are
very unlike the raw material of the biometric
school. This is a sample of his idea of variation
in poultry :—

“The tarsi are often feathered. The feet in many
breeds are furnished with additional toes. Golden

spangled Polish fowls are said to have the skin between
the toes well developed.”

In the short section labeled “ Remarkable va-
riations of Goats,” Darwin refers to the great
ears of goats of the Island of Mauritius, to the
various forms of mamme, to throat appendages,
hornlessness, and presence or absence of toe
glands. The entire work on Variation under
Domestication demonstrates that Darwin fre-
quently, if not usually, meant by Variation the

MUTATION 165

acquisition or loss of unit characters. Darwin’s
position has been sadly misrepresented by those
neo-Darwinians who have insisted that Natural
Selection operates only upon variations of the
quantitative order. In the Origin of Species,
Darwin was arguing for continuity and natural
law, and accepted the principle “ natura non facit
saltum ”’ as in accord with the new view. Con-
tinuity in nature was his great argument against
creation. ‘“ Why,” he asks, “ should all the parts
and organs of many independent beings, each
supposed to have been separately created for its
special place in nature, be so invariably linked
together by gradated steps?” Fifty years ago,
we must remember, it was the battle of continu-
ity against special creation that was being fought
and not the gradual as opposed to the sudden
appearance of a unit character.

Recognizing, then, that the mutation theory,
far from being opposed to Darwin’s theory of
the origin of species, would have been welcomed
by him, we pass with more satisfaction, on the
occasion of this celebration, to a detailed consid-
eration of some of the facts of mutation.

MUTATIONS IN NATURE

The classical case of mutation is that of the
evening primrose, named after Lamarck, but
henceforth to be no less closely linked with the
name of his-evolutionary successor, De Vries.

166 MUTATION

Here is a plant of characteristic form and flower
which regularly produces a small percentage of
offspring of strikingly different forms—sparsely
branched instead of profusely, with brittle leaves
instead of smooth, of stunted size and small flow-
ers, with strap-shaped or with ovoidal leaves in
place of lanceolate. The unit characters that
appear in these peculiar progeny of lamarckiana
do not intergrade with the corresponding charac-
ters of the parents, and, on self-fertilization, are
reproduced in successive generations.

While the particular kind of mutation exhib-
ited by Lamarck’s primrose is rare, it is common
to find species in which an organ appears, in dif-
ferent individuals, in a number of distinct forms
constituting the so-called “elementary species ”
—a term that seems justified since, bred to their
like, these forms are reproduced in successive
generations. Striking examples of this sort have
been found in wild violets by Doctor Ezra Brain-
erd, and in the shepherd’s purse by Doctors
Lotsy and Shull. Animals have been less care-
fully scrutinized for elementary species; but we
are not without instances. The true bugs and
the straight-winged insects often show both long-
winged and short-winged forms, without inter-
grades. Some tiger beetles, of both sexes, appear
either in a brown or a blue-green dress. Wheeler
has collected over a score of pink katydids discov-
ered in the United States within recent years, and
has noted cases of pink forms of green hemip-

MUTATION 167

tera. The same green species sometimes have a
brown form, too. In these cases the new char-
acters of pinkness and of brownness have un-
doubtedly arisen suddenly and no intergrades are
known. Of the common May beetle, I am in-
formed by Professor Forbes, no less than forty-
two forms are known from Illinois alone, several
of them difficult to distinguish by superficial
characters, all of them readily separated by ref-
erence to the copulatory structures, which are dif-
ferent in the various species and in the two sexes.
“These structures are so constant,” writes Pro-
fessor Forbes, “that one of my assistants who
has handled over ten thousand specimens of one
species for determination, says that they are all
like castings from the same mold.” There are
features of this case that certainly look like mu-
tation; particularly the large number of species
in a small area separated by non-intergrading
differences in one variable organ. But, as Pro-
fessor Forbes suggests, there is one difficulty in
the way of seeing how the differences could have
arisen by mutation: the copulating organs in each
species are mechanically adapted to each other;
and this requires that a coincident and coadaptive
mutation occur in the two sexes. But this is a
true difficulty only so long as we conceive the
entire organ to be a single unit character. There
is, however, as little reason for so conceiving it
as for regarding the human hand as one unit
character instead of many units. The evolu-

168 MUTATION

tion of mutually adapted sex organs may be ,
readily conceived as. follows: Let a new species
differ from its ancestor by a character m; then,
in accordance with the familiar fact of sex dimor-
phism in unit characters this takes in the two
sexes the forms m’ and m”. If the two sex-forms
are incompatible the new species will come to
nought; but if not incompatible the two modi-
fied sexes may interbreed and be prevented from
breeding with the parent species. By the addition
of a series of new unit characters, n, 0, p, etc.—
each of which must stand the test of compatibility
in the two sexes—a complex dimorphic organ may
be built up by mutation. It were wearisome to
attempt to catalogue the mutant-like variations
that have been recorded among insects and other
animals. The great work of Bateson, Materials
for the Study of Variation, is full of instances,
and the entomological and conchological jour-
nals are full of many more. Everywhere we find,
along with the universal quantitative variation,
cases of qualitative, discontinuous variation in-
volving entire unit characters; and these new
characters are, probably, judging from our expe-
rience with domesticated animals, inheritable.

MUTATIONS UNDER DOMESTICATION

When we study a group of domesticated or-
ganisms, such as poultry, we find the races dis-
tinguished by characters that do not intergrade

MUTATION 169

and can not be made to intergrade by crossing.
An instance will show how these characters be-
have. When a black fowl is crossed with an
albino, of the Silky race, the offspring are black
with a trace of red in the males. When the hy-
brids are mated together they yield albinos, solid
blacks, blacks marked with red, and typically
colored red-and-black Games. If you keep on
crossing together the red-ticked blacks you
always get albinos, solid blacks, red-ticked blacks
and Games, and nothing else. Such an experi-
ence makes clear, better than any argument, the
meaning of unit character, discontinuity, and mu-
tation. Further analysis of this case shows that
the black fowl has a unit character—melanic
super-pigmentation—that has been added to the
primitive Game coloration; and the albino lacks
a unit character—the pigment forming enzyme
—found in the ancestral plumage. Neither of
these unit characters blends in the crossing. If
now these unit characters of normal plumage
color, excessive melanism, and albinism are to-
day non-blending, essentially unalterable char-
acters, it is probable that they have always been
so and were so in their origin. But we have
direct evidence as to this matter. In discussing
the case of the black-shouldered peacock, Darwin
concludes: “The case is the most remarkable
one ever recorded of the abrupt appearance of
a new form.” If the black peacock arose sud-
denly, so probably did the first black Mediterra-

170 MUTATION

nean fowl, at a time long before records were
kept. Again we find that human albinos appear
suddenly, complete, and breed true like real spe-
cies. We have other cases of semi-albinos of
which the history is known. The blue-green
Australian parakeets were first brought to Eu-
rope in 1831. In 1872 an expert records seeing
a single yellow specimen, and by 1877 they had
become relatively common in Germany, since
they breed true, and now they may be found in
most bird-stores of our cities. This yellow par-
akeet has lost the power of forming black pig-
ment, and the new character appeared suddenly
and completely. ‘There is every reason for be-
lieving that the yellow canary was thus derived
from the green canary, the white Java sparrow
from the gray form, and the albino fowl from a
pigmented ancestor. The sudden origin of color
changes is generally admitted by breeders and
field naturalists; and many more cases of sud-
denly appearing characters might be cited, such
as hornlessness in cattle, sheep, and goats; tail-
lessness in cats, dogs, and poultry; hairlessness in
horses, cows, and dogs; spinelessness and _hair-
lessness in vegetative organs and fruits; fascia-
tion of the stem and pelorism of the leaves and
petals of many plants, and extra digits in poul-
try, swine, horses, and man. These are examples, _
merely, for since man first began to domesticate
plants and animals hundreds of new characters
have appeared suddenly and completely and ca-

MUTATION 171

pable of vigorous transmission. The frequency
of such mutations depends on the number of
individuals studied.

Now, during the past four years I have bred,
handled, and described over ten thousand poul-
try of known ancestry. Of striking new char-
acters I have observed many, some incompatible
with normal existence; others in no way unfit-
ting the individual for continued life. In the
egg, unhatched, I have obtained Siamese. twins,
anteriorly duplex individuals with shortened
upper jaw (like that of the niata cattle, pug
dogs, and some carp), and chicks with thigh
bones absent. There have been reared chicks
with toes grown together by a web, without toe-
nail or with two toe-nails on one toe; with five
toes, six toes, seven toes, or three toes; with one
wing lacking or both absent; with two pair of
spurs; without oil-gland or tail (though from
tailed ancestry); with neck nearly devoid of
feathers; with cerebral hernia and a great crest;
with feather shaft curved; with barbs twisted and
dicotomously branched, or lacking altogether.
Of the comb alone I have a score of forms: single,
double, triple, quintuple, and walnut, V-shaped,
cup-shaped, comprising two horns or four or six,
absent posteriorly, absent anteriorly, and absent
altogether. All of these conditions have been
offered me without.the least effort or conscious
selection on my part, and each appeared in the
first generation as well developed peculiarities,

172 MUTATION

and in so far as their inheritance was witnessed
each refused to blend when mated with a dissim-
ilar form. For example, the pea X single gives a
pea comb which in the next generation yields sin-
gle and pea; cerebral hernia and no hernia give
no hernia in the first generation, but hernia again
in the second; taillessness may follow the Men-
delian formula, polydactylism approaches it, and
the color varieties illustrate it strikingly. In a
word, while quantitative variations are never ab-
sent in poultry, the sudden appearance and dis-
appearance of full-fledged characters is most
striking. Mutation as thus defined presents to
the breeder as a common phenomenon. But, say
the neo-Darwinists, your mutations are of a
teratological sort and have nothing to do with
species as we find them in nature. In reply I
admit, first, that under domestication many mu-
tations are preserved by man that would perish
in nature. It is quite likely that mutations occur
almost as frequently in nature as under domesti-
cation, but the unfavorable new forms are apt
to suffer early elimination. There remains, how-
ever, a host of characters that are not detrimental
to the individual, and such are, not necessarily
eliminated. They are teratological only in the
sense that they are novel to the species, but they
are of the same order as many of the specific dif-
ferentie of feral species. Take, for instance, the
passerine birds—what are some of their striking
qualitative characters? We find crossed bill

MUTATION 173

(Loxia), crest (cardinal bird and jay), greatly
elongated tail (widah bird), bare throat (bell
bird), wattle (huia bird of New Zealand), barb-
less feather shaft (paradise birds), barbs with-
out barbules (emu-wren), twisted feathers (Chi-
rocylla). The plumage may be glossy black,
snowy white, or of broken colors. Since such
characters have arisen suddenly, by mutation,
in poultry it is fair to conclude that they have
probably done so in other birds. Of course there
are many characters found in wild birds that are
not found in poultry, but where we have evidence
_ that many characters have arisen suddenly, dis-
continuously, it seems probable that many others,
of the same general sort, whose origin can not
possibly be known have arisen in the same way.
The experimental demonstration of the mutative
origin of many characters makes probable such
an origin for characters beyond the pale of ex-
perimentation.

MUTATION VS. SUMMATION OF FLUCTUATIONS

There are many who are quite willing to admit
that mutations do occur, but hold that the part
they play must always be regarded as relatively
less important than the summation of fluctua-
tions. From this view the mutationist can ap-
peal to the results of experiment. Does the
breeder actually introduce new characters into
the organic world by summating fluctuations?
De Vries insists that the improvement that fol-

174 MUTATION

lows selection nearly or wholly ceases after four
or five generations, and if selection be abandoned
the race rapidly returns to its primitive condi-
tion. Such has been the experience of breeders
of maize, sugar beets, and other crops, and of
poultrymen who have sought to increase the egg
yield of fowl. Permanent improvement, wher-
ever made, has been effected either by hybridiza-
tion with a wild form possessing the desired char-
acter or by preserving a fortunate sport—a
“ Shakespeare,” as Professor Hansen puts it.
Such a sport is a new center from which further
progress may start. Recognizing the futility of .
selecting merely those individuals having the old
characters best developed, the most advanced
breeders (as at Svalof in Sweden), have system-
atized the search for single mutations in the
midst of extensive seed plats. This law of im-
provement holds for animals likewise. Four
years ago I started several series of experiments
to create, in poultry, new breeds by quantitative
selection. In one of these I sought to re-create
a uniform buff bird like the buffs that arose in
China two thousand years ago and are the par-
ents of all known uniformly red or buff breeds.
A bird with a red-and-black plumage coloration
of the Jungle fowl was crossed with a White
Leghorn. The hybrids were white with red on
the wings and breast. I then planned to breed
together the reddest of these birds and the red-
dest of their descendants until I should have

MUTATION 175

gained uniformly red birds. The second genera-
tion of the hybrids did show more red than the
first, but during the last two years no advance
has been made. Again, a cock having a high
single comb was crossed with a hen having a typ-
ical low pea comb; the hybrid offspring had high
combs with papille placed high up on each side.
An effort to establish by quantitative selection
a high pea comb has failed. Dr. Castle tells me
that his continued attempts to modify color types
of rats by quantitative selection have of late been
inefficacious, since regression is very strong to-
ward the original types. The evolution of the
American trotter is often cited as a clear case of
the results of quantitative selection. Yet is it
not true that the advances in recent years have
been quite as much determined by the evolution
of the sulky and certain technical improvements
in handling the trotter and training him? The
running record, the result of a larger selection,
has, I understand, stood quite still for the last
twenty years. Thus even race horses form no
exception to the rule that selection, within given
characters, soon reaches a period, and improve-
ment must wait on the appearance of a new char-
acter by mutation.

This conclusion, far from being opposed to
Darwin, would doubtless have been cordially ac-
cepted by him, as certain passages in his writings
indicate. After describing the early improve-
ment of the gooseberry, he says :—

1 Compare the instance given at p. 48.

176 MUTATION

“‘ The ‘ London’ gooseberry (which, in 1852, had al-
together gained 333 prizes) has, up to the present year
of 1875, never reached a greater weight than that at-
tained in 1852. Perhaps the fruit of the gooseberry
has now reached the greatest possible weight, unless, in
the course of time, some new and distinct variety shall
arise.”

“

De Vries could not have put it better.

MUTATION AND NATURAL SELECTION

But, it is objected, the origin of characters by
mutation can not account for adaptation as well
as quantitative selection; and adaptation is the
preéminent fact in nature. There is no good
reason for drawing such a contrast. For the
theory of mutation is nowhere incompatible with
that of Natural Selection; there may just as well
be, there just as truly is, a selection among dis-
continuous variations as among quantitative va-
riations. In the modern classification of varia-
tions selection has come to be associated with
quantitative variations; but Darwin did not al-
ways so associate it, as I have tried to show. Any
variation, of any kind or degree, must stand the
test of fitness to survive. If it can not meet the
test it must be eliminated. In a field I had 300
young fowl, of which twenty per cent were of
mixed colors, and eighty per cent were either
white or black. Twenty-four of these birds were
killed by crows, and all the dead were either
white or black excepting one spotted white and
buff. The solid colors are mutants; being con-

MUTATION 177

spicuous on the grass they were relatively unfit
to survive, and so they were eliminated. Again
the elevation of the tail feathers by the hen is
essential to successful coupling with the male;
but this is impossible in rumpless hens, and they
must all be infertile except for an operation.
The wingless cock could successfully couple only
with bantam hens, as without wings he could not
balance himself while treading larger hens.
These examples suffice to show how unadaptive
mutations tend quickly to be eliminated. On
the other hand, the split spur, the extra toe, the
varied forms of comb, the frizzled and silky
forms of plumage, even the absence of the oil-
gland seem, under the conditions of the poultry
yard, to offer no important impediment to sur-
vival and propagation. We may conclude, con-
sequently, that selection will act on mutations as
well as on graduated variations, eliminating the
unfit and letting survive favorable mutations or
such as are merely neutral. But, granted that |
the unfit mutations are eliminated, can such a
case of close adaptation as is exhibited by the
leaf butterflies (Kallima and the rest) result from
a series of mutations? Does not the very per-
fection of the adaptation indicate that the final
touches have been of the quantitative order?
Not at all. The perfection of the result may be
due to a combination of adaptive unit characters.
Bateson,.who examined thirty-eight individuals
from one locality, finds that they fall into four

178 MUTATION

discontinuous groups with respect to the colora-
tion of the under side of the wings, a, “leaf-
veinings ” absent or nearly so, ground nearly
plain; b, ground without veins but with promi-
nent black speckled spots; c, veins strong, no
blotches; d, with blotches, with or without veins.
Here at least three unit characters appear; dark
lines (veins), black speckled spots, and blotches;
but one or all may be absent from a given wing.
Between presence and absence of the character
no intergrades occur except possibly in the case
of “nearly absent” veins. There is reason for
concluding that even in Kallima new characters
arise fully formed, and that these are numerous
enough to affect all the detail of the pattern. If
the combination of pattern characters is pro-
tective, no doubt it will preserve many individ-
uals from elimination.

There is, moreover, still another way in which
mutations may become adaptive; and that is by
their possessor selecting a habitat that fits its
organization. At the risk of encroaching on the
subject of adaptation, assigned to another, I may
give an illustration. The whole surface of the
earth is scattered over with spores and seeds of
plants and the resistant eggs and gemmules of
various lower animals. Only if conditions are
propitious will they hatch or germinate. Some
years ago a dam broke at Cold Spring Harbor
in February and drained a lake of eighty years’
standing. In the Spring a luxurious terrestial

Sah at See

MUTATION 179

vegetation sprang up on the lake bottom from
seeds lying dormant there. One Winter a ditch
was dug through a salt marsh, where the only
higher plant was a species of marsh grass—
Spartina. The black peat cut from the ditch
was piled in a ridge by its side so high that it was
no longer covered by the tide. In the Spring
various roadside weeds sprang up along the
ridges, forming striking lines of vegetation run-
ning athwart the marsh. In these cases the
germs were present, but failed to germinate until
conditions suitable to their organization inter-
vened. So, in general, there are abundant means
of dissemination, and for almost every character
there is a situation for which it is best suited. In
that situation the new character will prove itself
adapted to its environment.

THE MUTATION THEORY A KEY TO
DIFFICULTIES

The notion of mutation, when fully grasped,
solves two difficulties which formerly confronted
evolutionists. The first difficulty is the swamp-
ing effect of intercrossing. If the usual result
of crossing a new character with its absence were
a blend of the two conditions, then the difficulty
would be a real one. But even in wild species
any unit character typically fails to blend when
crossed with its absence. The unit characters of
violets, shepherd’s purse, and spots of beetles are
experimentally tested instances. The characters

180 MUTATION

of domesticated organisms behave in the same
way, as illustrated by poultry. Unit characters,
then, in so far as they refuse to blend, will not
be swamped by intercrossing, but will reappear
intact in a predictable proportion in successive
generations.

The second difficulty which the mutation doc-
trine solves is discontinuity between species.
Species differ in the presence or absence of cer-
tain unit characters. These unit characters are
typically discontinuous in their origin. Hence
it is futile to look for intergrades; as well might
one look for intergrades between carbon monox-
ide and carbon dioxide. Species are discontin-
uous because specific characters are discontin-
uous; and specific characters, in so far as they are
unit characters, are discontinuous because the
molecular changes upon which they depend are
discontinuous.

It is rash at the threshold of any. new science
to accept any one hypothesis to the exclusion of
others. The president of our Association has
taught us our duty toward multiple hypotheses.
As in the newer chemistry transitions between
molecules are becoming a recognized possibility,
so it can not be denied that some unit characters
may arise gradually; or, as a result of repeated
crossing, show true blending and intergrading
conditions. Many characters are indeed less or
more because they have an ontogeny, and the
adults stop at different points in the ontogeny,

MUTATION 181

as seems to be the case with human hair color.
In many instances of geographic variation a gra-
dation of climatic conditions causes a gradation
in the development of a unit character all the
way from invisibility to strong expression.
Doubtless many important discoveries are about
to be made in the field of graduated characters.
But from henceforth we must, I think, start in
our studies of unit characters from the stand-
point of their normal discontinuity. While we
remember the services of De Vries in insisting
on the normal discontinuity of unit characters,
we shall, in considering the idea of the unit char-
acter, recognize more clearly how great is the
debt of biological science to the insight of Charles
Darwin.

ADAPTATION
BY

CARL H. EIGENMANN
I. DEFINITIONS

Tue chief object in the life of any animal is
to leave another like it in its place when it dies.
To this end we find numerous adjustments and
compromises, adaptations in animals or plants,
to place them in harmony with the elements of
their physical or biological environment, or to
codrdinate the different parts of the same animal
or plant.

We have major adaptations, such as those of
birds, mammals, etc., for aérial respiration, and
those of fishes for aquatic. We have also minor
adaptations for a particular combination of tem-
perature, light, heat, and the other elements of
the physical environment. And, finally, we have
adaptations fitting the animal to cope with other
animals for a mate and a home, to secure food
and to avoid being food.

Aside from adaptations an organism consists
of vestiges, and frequently of other characters,
that are not adaptations.

Vestiges, we know, are the remnants of past
adaptations. Specific characters which are not

182

ADAPTATION 183

vestiges and are not now adaptations may also
be past adaptations, or possibly they may be-
come such in the future; it is only certain that
they now do not particularly fit the species for
survival. Some characters, while undoubtedly
adaptive, give the impression that they are over-
done. The antlers of the deer, the fang of the
saber-tooth, the power of continuous growth of
the incisors of rodents, are all adaptations that
have in some instances proved to be too much of
a good thing.

II. QUESTIONS

In the words of Weismann, the most ardent of
the Darwinians, ‘“ Adaptations arise whenever
needed if they are at all possible.”

Adaptations have usually been looked upon
as adjustments in the organism to its environ-
ment. The suggestion has more recently been
made that adapted environments and habits are
selected by animals adjusted to them.

Is a man healthy and strong because he prac-
tises athletics, or is he practising athletics because
his strength inclines him to athletic sports? We
have all been modified by our environment and
by our activities. It is at least suggestive that
some of us have never taken to pole-vaulting and
should not have made a record if we had. Evi-
dently there is a difference between the questions
of the origin of adaptations in the individual and
the origin of an adapted fauna.

184 ADAPTATION

The latter is a comparatively simple question.
No one, for a moment, would claim that the
entire fauna of any particular area of land, or
river, or ocean arose where it resides,—became
adapted in its present habitat. Adapted faunas
are only in small part autochthonous; in large
part they are made up by selective migration.

III. ORIGIN OF ADAPTED FAUNAS

For a consideration of the origin of adapted
faunas I would invite attention to the fresh water
and cave fish-faunas.

The major conditions distinguishing fresh
waters from the ocean as an environment for
fishes are these: (1) The fresh water contains a
very much smaller per cent of salts in solution
than sea water. (2) It is, with few exceptions,
in continuous locomotion in one direction. (3)
It contains sediment. Minor characters distin-
guishing fresh water differ in different localities.

Fresh-water fishes are not a group different
from salt-water fishes. Many salt-water fishes
can enter fresh water, and we may for present
purposes assume that all candidates for fresh-
water existence are adapted or readily adaptable
to the fresh water. Adaptations to the second
and third of the fresh-water conditions imply pe-
culiarities in habit or structure not possessed by
all fishes, and these must, in the main, have been
acquired by the marine fishes before they could
enter and maintain themselves in fresh water.

ADAPTATION 185

“

The downward current and sediment, if the lat-
ter is not too abundant, are not obstacles suf-
ficient to keep an adult fish from entering fresh
waters. The eggs and young furnish the point
of attack. Among oceanic fishes we have many
that have pelagic eggs, others that have adhesive
eggs, others that have heavy cohesive eggs, others
that have filaments for the attachment of eggs,
while others harbor their eggs.

Currents would naturally tend to carry pelagic
eggs into the. ocean, and as far as I know only
one fish with pelagic eggs has succeeded in estab-
lishing itself in fresh water, and it, the eel, to the
present day, descends to the sea to deposit its
eggs!

The other types of eggs of marine fishes are
all found in fresh waters, and it is certain that
in many cases the possession of eggs of one or
another of these sorts has enabled the fish to
establish itself in fresh water. Thus the major
adaptations were acquired by the ancestors of
fresh-water fishes before they were eligible to a
fresh-water existence. Innumerable minor adap-
tations to the peculiar combinations of heat, sed-
iment, light, etc., found in each selected locality,
have no doubt arisen in such localities.

When a new water area arises, selective migra-
tion is the method of origin of the adapted fauna.
The vast territory containing our North Amer-
ican lakes and streams north of the southern line
of glaciation, the area from the Arctic south to

186 ADAPTATION

near the Ohio River, was covered a few thousand
years ago with a sheet of ice. It contained no
environment suitable for fishes. The entire
fauna and flora of this area, including the fish-
fauna, are composed of immigrants that moved
in as the ice moved out, and selected the places
adapted to each species. While a few of them
have become modified since their advent into this
area, their fundamental and even their minor
adaptations were acquired elsewhere than in their
present home. Their adaptation is due to the
selection of an adapted environment.’ The entire
area is unsuitable as a place for the study of the
origin of all but a few minor adaptations.

The check by cold has not been placed on any
individual migration or set limits to the adult.
Rhinichthys dulcis living in glacial waters and
warm springs and the many species adapted to
the great range of variation in the temperature
in any of our temperate lakes show this. The
temperature factor determining distribution is
set rather by the adaptation of the eggs to warm
or cold water. Our trout, salmon, and white
fishes breed largely in winter when the tempera-
ture is low. The rate of development of their
eggs, like that of all cold-water eggs, is slow.

*Of the 152 species of fishes of the Great Lake basin, only
26 species and varieties, 17 per cent of the total, are peculiar to
the area. Five of these are but varieties of more southern species,
and the other 21 more than represent the extent to which the
fauna has become adapted in this area, for eight salmonids and
eight cottids are cold water species that may have been crowded
out of the region to the south of the basin, by the encroaching
heat after the passing of the last glacial epoch.

ADAPTATION 187

The warm-water species are warm-water species
not because their individuals are incapable of
entering cold water, for they do, but because
their eggs will not develop in anything but water
much warmer than that in which the eggs of cold-
water species develop. Their eggs are quickly
developed, they are adjusted to fluctuations in
temperature, and they respond to such fluctua-
tions in temperature by hastening or slowing
their rate of development.

The origin and modification of the cave fauna
give a concrete example of the change of loca-
tion resulting from predestined major adapta-
tions and subsequent minor adjustments. Caves,
at the present time, are being colonized by immi-
gration of salamanders of the genus Spelerpes
and other animals that have become adapted to
a cave existence while living in the dark under
rocks, bark, and in other similar places. The
adaptation to the conditions of cave existence in
this case determines the change of location when-
ever a cave presents itself.

That minor adaptations occur in these after
they have become exclusively cave forms is shown
by the structure of the permanent cave salaman-
ders of Missouri and Texas. These have, in
large measure, lost their color, and have degen-
erate eyes.

Not infrequently where we have extreme adap-
tations to a particular and a peculiar environ-
ment, such as are found in the blind fishes to the

188 ADAPTATION

caves, or the ability of ichneumon flies to detect
and lay their eggs in deeply hidden grubs, we do
not really need to account for the extreme adap-
tation to the extreme environment. The envi-
ronment and the adaptation may have developed
together, as armor-piercing projectiles and armor
have so developed together. An illustration is
found in the origin of the cave fishes of Ken-
tucky, and still more of those of Cuba.

The cave fauna of Kentucky, so highly
adapted it would be hopelessly lost if removed
from its peculiar environment, is the result of
‘selective emigration, immigration, and _ local
adaptation. It has become adjusted with the
development of the environment it inhabits. At
Horse Cave, Ky., a wide valley extends north
and south. Tributary valleys come from the
east and west. The hills bordering these valleys
are limestone capped with sandstone. The
north-and-south valley was formed by the Horse
Cave River, which originally flowed over sand-
stone like that capping the bordering hills. No
doubt it had a fauna as varied as that of any
surface stream. The stream first cut through
the sandstone, then into the limestone, in which
it gradually dissolved an underground channel.
To-day not a sign can be seen on the surface of
the streams that are responsible for the valleys
about Horse Cave. At least one of them rushes
through lofty chambers one hundred and eighty-
five feet beneath the streets of Horse Cave.

ADAPTATION 189

With this change in the environment, with the
disappearance of Horse Cave River from the
surface, its inhabitants were compelled to mi-
grate. They moved in two directions to adapted
environments. The shore-fishes, channel-fishes,
ete., depending on light to find their food and
mates, moved out to the Green River, where their
descendants live to the present day. The fishes
negatively heliotropic, nocturnal, or stereotropic,
moved into the holes dissolved in the bottom of
the river, followed its subterranean development,
and their descendants live to-day in the stream
which now flows entirely below the valley. They
are colorless and all but eyeless, and have, no
doubt, acquired this exaggerated adaptation to
their present abode since their immigration. The
major adaptation to the cave existence, the power
of finding their food and mates without the use
of light, they possessed before the formation of
the caves, and it is responsible for their present
habitat.

Primarily blind fishes do not have degenerate
eyes because they live in caves, but they live in
caves because their ancestors were adjusted to do
without the use of eyes. The degeneration and
disappearance of their eyes form another matter.

Wherever in the past environments arose lack-
ing light, they became, and still are, the gather-
ing place of those not dependent upon light.

The Cuban blind fishes offer another example
of the concomitant development of a peculiar

190 ADAPTATION

and complex environment and its peculiar fauna.
The blind fishes of Cuba are members of a
family of marine fishes, but live in fresh water in
caves of central and western Cuba. They have
undoubtedly arisen with the environment in which
they now live. The caves are enlargements of
rifts in coral reefs. They can be traced from
the hills near Matanzas to the shore of Cuba.
One of the cracks is seen in the naked coral beach
near the Carboneria at the mouth of Matanzas
Bay. Another can be traced a little way inland,
but a few feet above sea level. The former must
contain salt water—the latter certainly’ contains
fresh water. In places similar to the former
the nearest marine relatives of the cave blind
fishes are found, with eyes. In the latter cave
blind fishes are abundant. Evidently the ances-
tors of the cave blind fishes have always lived in
the crevices in which they now live. When these
crevices were below the ocean’s surface they con-
tained salt water. As the land arose the salt
water was gradually replaced by fresh water, to
which the fishes as gradually became adapted.
The fishes have literally grown up with the
country.

Selective migration, the migration to adapted
locations, is the chief factor contributing to the
origin of adapted faunas. This factor “ change
of location” is to the origin of adapted faunas
what the “ change of function ” is to the origin of
adaptive structures. ,

ADAPTATION 19]

IV. ORIGIN OF ADAPTATIONS

A. Tuer Prostem. The question of the ori-
gin of the adaptations themselves is much more
difficult. If comparatively few or no new adap-
tations have arisen in any one neighborhood,
nevertheless all these modifications must have
arisen somewhere and should be accounted for.
Many explanations have been offered. The sup-
porters of some of the explanations adhere to
them with the fanaticism of religious belief. But
it is necessary to have been reared in the faith
to see all that is claimed for them.

Hereditary succession may follow a horizontal
line or one that swerves up or down. In other
words, successive generations may be alike, in
which case the species remain in statu quo, or
subsequent generations may deviate from their
parents in one or more points.

All deviations from the horizontal must start
in the germ, or must become located in the germ.
The question of the origin of adaptive deviations
is the question of how and why adaptive ger-
minal modifications arise, or how adaptive so-
matic modifications are transferred to the germ.
In either case it is the question of how the straight
line of exact hereditary repetition may be caused
to swerve in a definite direction to reach an
adaptive point. This is the question of the pres-
ent generation, perhaps of the entire twentieth
century.

192 ADAPTATION

To be effective the deviation must be pre-
served, but it is not necessary to enter into any
discussion of Natural Selection. This very occa-
sion bears evidence of the all but universal ac-
ceptance of the principle. It forms part of
nearly every theory of the origin of adaptation.

B. Tue Marteriat. In discussing the origin
of adaptations I shall confine myself mostly to
the brief examination of some of the adaptations
in the American Characins, to determine, if pos-
sible, to what extent different factors of evolu-
tion have contributed to their origin.

The Characins are fresh-water fishes now in
their prime in tropical Africa and in tropical
America.

I hope I need not apologize for confining my-
self to a bit of the wealth of that continent,
South America, which has been the training
ground of Darwin, Wallace, Bates, Miiller, and
so many of their supporters.

In America there are known about six hun-
dred species ranging from the borders of the
United States to Patagonia. Different mem-
bers are adapted to nearly all possible fish envi-
ronments, both physical and biological. There
are mud-eaters without teeth, flesh-eaters with
teeth like a mowing-machine, and others with
long fang-like canines projecting through the
upper jaw when the mouth is closed. In the Es-
sequibo River I caught over forty species in one
day. Some of these minute translucent species

PLATE III.

A Few or THE Numerous Typsés OF TEETH IN THE CHARACINS.

(From photographs by the author )

Raphiodon vulpinus Spix.

Astyanax bimaculatus brevoortii Gill.

Serrasalmo humeralis Cuv. & Val.

Henochilus wheatlandi Garman

Acestrorhynchus falcatus Bloch.

Hoplerythrinus uniteniatus Spix. (Head resembles that of Amia.)
Leporinus conirostris Steindachner.

Prochilodus scrofa Steindachner.

Aphiocharax dentatus Eigenmann & Kennedy.

Reg Rewn

PLATE IY.

SoME SIMILARITIES IN THE CHARACINS.
(All figures after Steindachner.)

Luciocharax insculptus, a Garpike-like Characin.
Salminus affinis, a Salmon-like Characin.

Prochilodus longirostris, a Sucker-like Characin.
Chalcinus magdalene, a fresh water Herring-like Characin.
Gasteropelecus maculatus, a flying Characin.

Myleus knerii, a Pompano-like Characin.

Nannostomus unifasciatus, a Cyprinodont-like Characin.

ADAPTATION 193

burrow in the sand in the bottom of the river,
others fly with wing strokes through the air above
the river, and others occupy all possible spaces
between. In appearance they parallel our gar-
fish, our pickerel, our top minnows, our pom-
pano, our trout, our minnows, our suckers, our
darters, our fresh-water herrings and shad; and
besides these there are a variety of shapes and
sizes and adaptations not to be found in other
fishes. Chief of these is the series ending in a
true flying fish, i.e. a fish with wing-like pecto-
rals, large muscles to move them, and the ability
to propel itself with wing strokes along the sur-
face of the water for forty or more feet, and to
continue its flight for five or more feet in the air.

C. Causes or ADAPTATIONS. The causes lead-
ing to new adaptations may be intrinsic or ex-
trinsic. The theories of Nageli, Weismann, and,
in part, of Darwin and De Vries, are based on
intrinsic causes; those of Buffon, Lamarck, Gu-
lick on extrinsic.

D. Ortsocenesis. Nageli, and in a modified
form Eimer, Waagen, Osborn, Whitman, and
others, have shown that lines of evolution are
orthogenic, predetermined in definite directions.
According to Nageli direction is maintained by
the make-up of the protoplasm of the individual.
According to Weismann direction is given by the
process of germinal selection, helped out by per-
sonal selection. By Osborn and others it is recog-
nized but not explained.

194 ADAPTATION

The Characins offer us the very best imagi-
nable proof, both for orthogenesis and against its
universality. The fact that lines of evolution
radiate in so many directions in this family is ab-
solutely conclusive proof that there are many
possibilities, that evolution to adaptive points
may not only take place along one line or par-
allel lines, but along very many diverging lines.
On the other hand, the fact that there are lines
with but few breaks leading from the general-
ized central type to such aberrant forms as the
minute sand-burrowing Characins, duplicating
our sand darters, or to the death-dealing Serra-
salmo, or the flying Gasteropelecus, shows that, a
path of adaptive modification once entered upon
by these fishes, evolution along that line may
take place, even beyond the point of highest ad-
vantage. These lines are not parallel and can
not therefore have been the result of the inherent
make-up of the family.* They have in some way
been determined and are being followed to the
limit.

E. Mutations. The possibility of divergence
in many directions has been experimentally
demonstrated by De Vries, who, with others, has
claimed that the line of adaptive modification is
broken, not bent. Waiving the question of
whether the difference between the bend and

break is one of kind or degree, permit me again

1 Similar characters like a pair of canines or ctenoid scales
have appeared in very diverse genera both in Africa and in
South America.

ADAPTATION i

to point out instances of both in the Characins.
I do this fully aware of the fact that some of our
experimentalists have claimed that evidence in
favor of mutation would not be noted by the sys-
tematic zoologist. It is, however, quite certain
that evidence for mutation can not be obtained
by experiment only. I have several times found
evidence in favor of it in the Characins.

In the Tetragonopterine there are parallel
genera or subgenera, as we care to look at them.
One series has a complete lateral line; the other
series has pores developed on but a few scales.
No doubt one has been derived from the other—
not once but several times. One species, Hemi-
grammus inconstans, is evidently mutating.
Two of the four specimens known have a com-
plete lateral line, in the others it is quite short.

Among hundreds of specimens of another spe-
cies with an incomplete lateral line a single mu-
tation has been found with a complete line.
Moenkhausia australe by mutation is producing,
or has produced Hemigrammus. In such cases
we have, if a bull is permitted, individuals that
are specifically alike but generically different.

While we have many undoubted cases of muta-
tion, there are many reasons why we should not
jump to the conclusion that all adaptations have
so arisen.

One example of continuous variation leading
to an adaptive point is found in some localities
of Nicaragua. Here the species of Astyanax

196 ADAPTATION

eneus, elsewhere with two maxillary teeth, is
varying in the old-fashioned way towards a form
whose entire maxillary is covered with teeth, i.e.
it is varying to become a Hemibrycon. Of
thirty-five specimens there are nine with two
teeth, two with three teeth, five with four teeth,
five with five teeth, five with six teeth, five with
seven teeth, three with eight teeth, and one with
nine teeth in the maxillary. No doubt there are
some who will claim that these are really muta-
tions, not variations, and I am perfectly willing
that they should put this balm upon their preju-
dices.

The nature of the progressive degeneration of
the eyes of blind fishes argues also against the uni-
versality of the origin of adaptations by muta-
tion. The degeneration of the eyes of such fishes
is a continuous process. The eyes of individuals
during their lifetime undergo a continuous de-
generative modification leading sometimes to the
entire elimination of the eye in the old. The
retrogressive changes begin in ever earlier stages
of the ontogeny. The differences between indi-
viduals are so slight as to exclude the possibility
of personal selection, without which either muta-
tion or Natural Selection is incapable of produc-
ing results.

There is no evidence that mutation has had
any more to do with the production of degener-
ate eyes than special creation, and we can not
even imagine how the degenerate eyes might have

ADAPTATION 197

arisen by mutation. Their degeneration is due
to orthogenesis or to use-transmission.

F. ENviroNMENTAL ADAPTATION May BE
Intrinsic or Extrinsic. 1. Geographical va-
riation or divergence. The facts of geographical
distribution make it certain that adaptations
have not arisen through intrinsic causes only.’
In fact, they make us doubt at times whether
intrinsic causes have had anything whatever to
do with the origin of adaptations. If all forms
were the result of mutation, due to intrinsic
causes, there is no reason why a large river such
as the Rio San Francisco should not contain all
the modifications possible to the genera inhabit-
ing it, for Shull has shown that new forms may
arise in a restricted area. But it does not. Of
equal sized streams belonging to different sized
river systems the one belonging to the larger sys-
tem harbors a larger number of species of any
genus.” And other things equal, the wider the
distribution of any genus the more species com-

1 Tower: Evolution in Chrysomelid Beetles, p. 314, says: “. . . All
evidence showing them (mutants) to be most rigorously extermi-
nated by natural selection. On the other hand, the study of geo-
graphical distribution and variation gives the strongest of
circumstantial evidences for direct and rapid transformation in
response to environmental stimuli as to the result of dispersion
... according to the method of trial and error, with
natural selection acting as the conservator of the race by limiting
the variation to a narrow range of possibilities.”

? Bean Blossom Creek of Monroe County, Indiana, draining an
area of about 250 square miles, is known to harbor in two miles
of its course 44 species of fishes. The Colorado, draining an area
nearly 1,000 times as large, contains but 33 species of fishes. But
Bean Blossom is part of the Mississippi basin that far exceeds

the Colorado basin in size and harbors at least 200 species. The
still larger Amazon basin harbors at least 700 species.

198 ADAPTATION

pose it. In nearly all cases where a species is
distributed over a wide, discontinuous unit of
environment, i.e. an area broken up into isolated
parts, the parts contain forms that are meas-
urably different from each other.

A. most instructive example is furnished by
the Characins. Astyanax fasciatus is found
from Patagonia to Mexico, except at Panama
and the Rio Parahyba. It differs in different
localities, and in the Rio Parahyba, near Rio de
Janeiro, and at Panama the differences have be-
come of specific value. The species is continued
in southern Mexico as Astyanax eneus, and in
northern Mexico as Astyanav argentatus. In
other words, in those cases where the divergence
has gone far enough we call the divergents spe-
cies, in those cases where they are diverging, vari-
eties. These geographical varieties are species
in the making, just as truly as the elementary
species of De Vries.*

Isolation is not always accompanied by differ-
entiation. Some species of Galaxias in Patago-
nia and Australia are identical, while those in
different parts of Patagonia are different. Geo-
graphical isolation must lead to differentiation
if the isolation forces the individuals to live in
places on the whole different from their original
home. A species (Astyanax fasciatus) may be
all but identical even if isolated in different rivers

+The different diverging lines will be fully considered in my
monograph on the Characins, now in preparation.

ADAPTATION 199

from Mexico to Patagonia, provided it may oc-
cupy the same sort of environment in each
stream. ‘There is more environmental differ-
ence in the different parts of a cross-section of a
river in the Amazon region, or in a mile of the
length of a small brook, than there is in the
pelagic region of streams from Mexico to Pata-
gonia.

2. Geographical convergence. Fach river is
made up of many different wnits of environment.
The pelagic area is but one of these. Muddy
bottom, weedy bottom, stagnant water, swiftly
flowing water, are other units. Each has its
peculiarly adapted fauna. Different members
of the same family may belong to different eco-
logical series, and different ecological groups are
made up of members of different families. In
shallow, swift water over gravel, in a small
stream, the adaptations required are a heavy
body, strong pectorals and ventrals, on which the
fish sits and which are held in readiness for sud-
den springs. The conditions and adaptations
are the same whether the stream be in North
America, in Cuba, or in South America. Fishes
are adapted to the conditions in each locality, but
the adapted faunas in the three areas are not re-
lated. In North America, darters, or diminu-
tive perches, are adapted to this niche; in Cuba
it is members of the marine Gobies, and in South
America members of the versatile Characins and
catfishes. Shape and many other things count

200 ADAPTATION

for little among fishes. All shapes occur at
nearly all times and nearly all places.

Similarly, blind fishes adapted to caves or
other dark places have arisen in many places, but
are not necessarily related to each other. The
blind fishes of Point Loma are Gobies, and have
their nearest relatives in neighboring waters.
Those of the Mississippi valley belong to the
Amblyopside, some of which live in the terranean
streams of that valley. The caves of Cuba de-
rived their blind fishes from the cracks of the
coral reefs in which caves were formed. In
South America their nearest relatives are the
nocturnal catfishes of Brazil and the blind fishes
of Pennsylvania have their nearest relatives in
the nocturnal catfishes of Pennsylvania.

The burrowing lizards of Florida living as
earthworms do, look so much like earthworms
that the very chickens do not discriminate against
them.

3. Geological convergence or parallelism. Geo-
logical records of the simultaneous and similar
changes in the form in the mass of species of any
area during changing physical conditions are not
wanting. For instance, Scott says:—

“ The steps of modernization, which may be observed
in following out the history of many different groups
of mammals, are seen to keep curiously parallel, as may
be noticed, for example, in the series of skulls figured by
Kowalevsky, where we find similar changes occurring in
such families as the pigs, deer, antelopes, horses, ele-

ADAPTATION 201

phants, etc. Indeed, one may speak with propriety of a
Puerco, or Wasatch, or White River type of skull, which
will be found exemplified in widely separate orders.”

One adaptation has not arisen once but many
times." To repeat, “ Adaptations arise when-
ever needed, if they are at all possible.”

4. Origin of geographical and geological di-
vergence and convergence. All these facts tend
to show that adaptations have arisen as the result
of the peculiarity of the environment. How?

It has been demonstrated many times that the
individual is modified by his physical environ-
ment. It is claimed on the one hand that the
deviation is maintained by its transmission to the
germ-plasm, and thus the next generation; and,
on the other, that the environment, in some cases
at least, directly affects the germ-plasm.

There is a third possibility. In some localities
the individuals of certain species are very dark,
in others they are practically without color. If
the latter individuals are examined closely it is
found that they are abundantly supplied with
chromatophores, and only the needed environ-
mental stimulus is lacking to bring out the strong
color. This is not a matter of the simple expan-
sion or contraction of the pigment, which may
take place in a few moments, but the develop-

+ Among characters that have appeared several times inde-
pendently in the Characins may be mentioned: The incomplete
lateral line, the scaled caudal, three series of teeth in the pre-
maxillary, a pair of canines in the lower jaw, ctenoid scales,
incisor-like teeth.

202 ADAPTATION

ment of an excess of color under the necessary
conditions. =

It is possible that other nascent intrinsic adap-
tations are present in different individuals, unno-
ticed and inconspicuous until the requisite envi-
ronment causes them to reach the limit of their
individual power, that they are environmental
adaptations only in appearance. On the other
hand, it is certain that in cave animals there is a
gradual bleaching with the removal from the
light. It is at first purely ontogenic. But no
scheme of selection* will account for the pro-
gressive reduction in the pigment in successive
generations. Nevertheless the color becomes less
in each generation. And in the final establish-
ment of the bleached condition in hereditary suc-
cession even in the light we have an instance of
the transmission of an environmental adaptation.

Where environmental adaptation is the result
of a struggle with the physical environment, the
struggle is entirely independent of the rate of re-
production. The individual must adapt himself
to heat and cold whether alone or not. Temper-
ature and other elements of the physical environ-
ment affect many individuals at one and the same
time. For this reason the physical environment,
when it makes its presence felt, operates in a
dramatic way. It attacks the mass, sometimes
killing thousands of the non-adapted at one
stroke. As long as it does not kill all, the kill-

1 Mutation is ruled out without selection.

ADAPTATION 2038

ing must be selective and preserve both those
ontogenetically and those innately adapted. The
attack being on the mass of species and individ-
uals, it tends to preserve those that are alike."

G. Functionat Apaprations. The whales
living like sharks look like them. Osborn re-
marks: “ If a primate begins to imitate the hab-
its of an ungulate by becoming herbivorous, it
also begins to acquire the dental cusps of an un-
gulate in about the same order as these cusps
would arise in an ungulate.”

I could paraphrase Osborn’s words for the
Characins many times. The Characins have
taken on the habits of many fishes and have par-
alleled them while they diverged from each other.
A certain habit and habitat in fishes carries with
it a certain regulative adaptation. Living as a
sand-darter does, carries with it a sand-darter
shape. The question that confronts us first is
not, why does the sand-darter habit carry with it
a certain form, but what caused Characins to
adopt the darter habit?

What caused Osborn’s primate to begin to imi-
tate the habits of an ungulate? What caused
different Characins to begin to eat mud, crusta-
ceans, plants, plankton, and each other?

Overproduction of individuals leading to
crowding, the struggle with the biological envi-
ronment for food (or light in the case of plants) ,

1 No more striking example is found than in the old but uniform
deciduous habit of plants of the temperate region.

204 ADAPTATION

causes all accessible places to become inhabited.
Food itself is dependent on other food, and this
ultimately on light, heat, depth, nature of bot-
tom, current, and other elements of the physical
environment. The habitat once selected, the
effect of the changed physical environment will
cause the changes already discussed, and the
changed biological environment will cause an
animal to adopt a changed mode of existence.

It is again possible either that innate charac-
ters in certain individuals of a crowded com-
munity cause them to migrate in certain direc-
tions, or that chance individuals migrate, and that
intrinsic or accidental extrinsic causes then start
new activities. It is certain that new activities
once adopted the result is individual modifica-
tions.’ It has long been claimed and as vigor-
ously denied that these adaptive individual devia-
tions are transmitted.

The factors of both Buffon and Lamarck
hinge on the possibility that somatic modifica-
tions are transmissible to the reproductive cells.
We have not been able to imagine how somatic
changes could so influence the reproductive cells
that they could, in their turn, produce individuals

+ We can imagine that this process of overproduction and con-
sequent adoption of different areas may take place in a small
basin, but certainly the larger the basin the greater the diversity
of conditions, the greater chance of comparative isolation in dif-
ferent sorts of environments, and the greater the number of
species.

No small stream long isolated contains many species of a given
genus. Notable exceptions are Orestias in Lake ‘Liticaca, and
Chirostoma in the Lerma. What applies to the species of a genus
applies with equal force to the genera of a family.

ADAPTATION 205

possessing in a measure the same characters.
Nevertheless, the transmission of individual en-
vironmental adaptations has been established.

No cases of the transmission of functional
adaptations as unquestionable as those of envi-
ronmental adaptations are on record.

It has seemed difficult indeed to devise experi-
ments which would prove that the small somatic
changes possible during a lifetime are transmit-
ted. We were not sanguine enough to suppose
that in one generation modifications could be
effected and transmitted that would surpass nat-
ural variability, and which could, therefore, be
recognized as transmitted characters. I have
long been convinced that the progressive degen-
eration of the eyes of cave vertebrates, coupled
with the differential degeneration of different
parts, is due and can be due to nothing but the
transmission of functional adaptation. I can
not altogether regret that this evidence does not
seem to have convinced many others.

The possibility of the transmission of somatic
characters to the reproductive cells has been
shown by the transplantation of ovaries in chicks
by Guthrie. He found that a black hen con-
taining an ovary transplanted from a white hen,
mated with a white male, did not give white
chicks exclusively, as the non-transmissibility of
somatic characters would require, but that more
than half of the chicks were spotted with black.
Also that a white hen containing an ovary trans-

206 ADAPTATION

planted from a black hen and mated with a black
male gave young all of which were spotted.
These results, if based on rigorously selected
material, ought to convince all but a packed
jury that somatic characters are transmissible to
the reproductive cells. If any one knows of de-
fects in Guthrie’s material it is incumbent on him
to furnish or define material free from all objec-
tions on which his experiments may be repeated;
for the method promises a final answer to this
much debated question.

H. Concriusions. We are forced to the in-
evitable conclusions that adaptations are not
chargeable to one factor, but that sometimes there
has been one, sometimes another, and more fre-
quently several factors have codperated to bring
about the adaptations in any one animal.

It is but justice to Darwin to say that he did
not pin his faith to the theory of Natural Selec-
tion exclusively. Darwinism is broader than
neo-Darwinism, whose insufficiency to account
for all adaptations becomes daily more apparent.

After fifty years of study of the origin of
adaptations a single sentence from Darwin’s
Origin of Species approaches closely to the gen-
eral conclusions of to-day, and, “ lest we forget,”
it should be emblazoned on the walls of every
Biological Laboratory: “'These laws, taken in
the largest sense, (are) growth, with reproduc-
tion; inheritance, which is almost implied by re-
production; variability, from the indirect and

ADAPTATION 207

direct action of the external conditions of life,
and from use and disuse; a rate of increase so
high as to lead to a struggle for life, and as a
consequence Natural Selection entailing diver-
gence of characters and the extinction of less
improved forms.”

I. A PLEA For THE Naturauist. I can not
close this paper without a plea for the naturalist
and systematic zoologist. “ Analysis,” says Rus-
kin, “is an abominable business. I am quite
sure that people who work out subjects thor-
oughly are disagreeable wretches. One only feels
as one should when one doesn’t know much about
the matter.”

The systematic zoologist is liable to lose sight
of the woods on account of the trees, and follow
the example of Jean Paul Richter’s Quintus
Fixlein, who collected a vast number of typo-
graphical errors, assured the public that valuable
conclusions could be drawn from them, and left
it to some one to draw them.

The imagination is in Biology as elsewhere the
guiding spirit. The trouble is our imaginations
are sometimes too heavily loaded with statistics
and at other times they fly without the balancing
kite’s tail of facts. The Paleontologists have
contributed so much to speculative zodlogy be-
cause their imaginations have been kept alive by
bridging their numerous gaps and because they
have not been hampered by too great a wealth
of material.

208 ADAPTATION

Whether we amputate eyes and legs to see
them regenerate, determine the chromosomic dif-
ferences between related species, centrifuge eggs,
or invent new plants, potato beetles, guinea-pigs,
or poultry, match butterflies, count scales, or
measure fossils, we are all at work on the prob-
lem of problems, ‘‘ The origin of adaptations.”

Experiment is the watchword of the day; but
while we are experimenting in our back yards we
should not lose sight of the beauty and the impor-
tance of the experiments in landscape gardening
and zoological gardening, that are and have been
going on in our front yards that extend from
here to Cape Horn.

DARWIN AND PALEONTOLOGY
BY
HENRY FAIRFIELD OSBORN

On March 4, 1860, Charles Darwin wrote’ to
Joseph Leidy of Philadelphia :—

“Your note has pleased me more than you could
readily believe; for I have during ‘a long time heard all
good judges speak of your paleontological labours in
terms of the highest respect. Most paleontologists
(with some few good exceptions) entirely despise my
work, consequently approbation from you has gratified
me much; all the older geologists with the one exception
of Lyell, whom I look at as a host in himself, are even
more vehement against the modification of species than
are even the paleontologists. I have, however, been
equally surprised and pleased at finding that several of
the younger geologists, who are now doing such good
work in our own geological survey go with me and are
as strong as I can be on the imperfections of geological
record.

“Your sentence that you have some interesting facts
‘in support of the doctrine of selection, which I shall

1 Darwin’s letter to Dr. Leidy is under date of March 4, 1860, in
reply, as he states, to Leidy’s letter of December 10, 1859.

On March 27, 1860, upon the recommendation of Isaac C. Lea
and Dr. Joseph Leidy, Darwin was elected a corresponding
member of the Philadelphia Academy of Natural Sciences. It is
probable that to the Philadelphia Academy belongs the honor of
having been the first foreign society to accord this great work
official recognition. This recognition was appreciated by Darwin,
as is shown by his reference to it in a letter to Sir Charles Lyell,
dated May 8, 1860.

The original letter is in the collection of Dr. Joseph Leidy of
Philadelphia, nephew of the great anatomist.

209

210 DARWIN AND PALEONTOLOGY

report at a favourable opportunity,’ has delighted me
even more than the rest of your note. I feel convinced
that, though as long as I have strength I shall go on
working on this subject, the sole way of getting my
views partially accepted will be by sound workers show-
ing that they partially accept them. I say ‘ partially,’
for I have never for a moment doubted that, though
I can not see my errors, much in my book will be proved
erroneous.”

Fifty years ago paleontology was an embry-
onic science so far as natural philosophy is con-
cerned; beyond the grand outlines of change in
the world of extinct mammals and reptiles Dar-
win knew little of its processes or results. In the
letter cited above he is encouraged by Leidy’s
promise of paleontological support for the gen-
eral doctrine of evolution; he is even more grat-
ified with the passage relating to Selection. In
other words, in this characteristically candid let-
ter Darwin appeals for evidence from paleontol-
ogy in support of evolution; he hopes that sound
workers will partially accept his views regarding
Selection; he does not for a moment doubt that
much of his views regarding Selection will prove
to be erroneous. ‘

A year later, April 26, 1861, Darwin writes to
L. Davidson, the great authority on brachiopods,
asking him to undertake a piece of work which
would test the doctrine of evolution.

“| . . in that book [the Origin] I have made the
remark, which I apprehend will be universally admitted,
that as a whole, the fauna of any formation is interme-

DARWIN AND PALEONTOLOGY Q11

diate in character between that of the formations above
and below. But several really good judges have re-
marked to me how desirable it would be that this should
be exemplified and worked out in some detail and with
some single group of beings. Now. every one will
admit that no one in the world could do this better
than you with Brachiopods. The result might turn
out very unfavourable to the views which I hold; if so,
so much the better for those who are opposed to me.

. I know it is highly probable that you may not
have leisure, or not care for, or dislike the subject, but
I trust to your kindness to forgive me for making this
suggestion.” *

I shall show that the sanguine as well as the
questioning prophecies of these epistles of 1860
and of 1861 have been fulfilled to the very letter
by paleontology; but in order to place the whole
matter in its true perspective, and brighten rather
than dim the grandeur of Darwin’s fame, let me
first briefly picture paleontology as it was in
1859 and as Darwin himself knew it even up to
the time of his death in 1882.

It is true that modern, or Darwinian, paleon-
tology, as distinguished from the older, or Cuvie-
rian paleontology, dates from a decade after the
publication of the Origin, or from 1868, when
Waagen”® first exactly and minutely described
the mutations which occur in a descent or phy-
letic series of ammonites, and it is true that this
epochal work was followed by others; so that the

1 Life and Letters, II, pp. 366, 367.

? Waagen, Wilhelm Heinrich: “ Die Formenreihe des Ammonites
subradiatus,” Benecke’s Geognostische Paléontologische Beitrage,
II, 1868, pp. 185-86.

212 DARWIN AND PALEONTOLOGY

new paleontology of evolution, as distinguished
from the old paleontology of special creation,
reached vast proportions before Darwin’s death.
But all this remained a terra incognita to Dar-
win. Absorbed in his observations on living
things, in his vast anthropological, psychological,
zoological, and botanical researches in his revision
of the Origin and other works, Darwin never
found time or opportunity to grasp the meaning
of the Darwinian paleontology. He attempted
but failed to understand the work of Alpheus
Hyatt, which was directly along the lines of that
of Waagen, but unfortunately rendered unneces-
sarily mysterious and difficult to comprehend
through the inveterate American love of word-
making. If Hyatt’s work had been expressed
in Darwin’s simple language, as it might have
been, then Darwin would certainly have grasped
the Waagen principle of mutation, and we should
have had the benefit of his marvelous insight into
. its significance. As it was, like Moses, Darwin
‘ led his paleontological followers to the Promised
_ Land, but he did not live to enter it; he gave the
impulse to search for phyla, or close continuous
lines of descent of animals and plants, but he
himself never observed a single phylum.

This simple fact is of vast importance in our
estimate of the weight to be attached to Dar-
win’s opinions. In contrast with Herbert Spen-
cer he was essentially a deductive-inductive
worker; that is, he pursued a trial hypothesis

DARWIN AND PALEONTOLOGY 213

along the strictest lines of observation, he was
less interested in how nature might, should, or
would work than in how nature does work. Of
his trial hypotheses that of adaptation through
selection of minute favorable variations he can-
didly tested by all the facts he could bring to-
gether; among these, however, were none of the
facts observable only in close phyletic series of
fossils. This is a fair way to estimate Darwin
and to be influenced by him, namely, by his strict
inductive methods and in his times, not in ad-
vance of his times.

In the last half century thousands of fossil or-
ganisms of all kinds have been exactly studied
and compared, more or less complete descent
series of vertebrates and invertebrates have been
garnered, facts and principles entirely unknown
to Darwin, and foreign to the logical mind of
Huxley as well, have been revealed; in short, the
data of induction as to how nature does work
in the origin of certain new characters have to-
tally changed in paleontology perhaps more than
in any other biological field of observation.

Two grand lines of observation have been fol-
lowed in paleontology quite independently of
each other: first, the minute changes in phyla of
invertebrates observed in fossil shells by Waagen,
Hyatt, Hilgendorf, Neumayr, and many others;
second, minute changes in phyla of fossil mam-
mals observed by Osborn, Scott, Depéret, Mat-
thew, and many others. It is obvious that the

214 DARWIN AND PALEONTOLOGY

hard shells of molluscs and the enameled teeth
and other parts of mammals are entirely inde-
pendent parts of entirely different organisms,
and that if similar laws have been discovered in
such widely distinct fields of observation they
tend to show that these laws were of force or of
wide potency in living organisms in general.

We are, therefore, now enjoying an entirely
new vintage of facts and principles. How far
can this new wine be put into the old bottles of
Darwin’s beliefs? What would Darwin him-
self say if with his incomparable candor and his
incomparable power of generalization he were
to examine these facts discovered in close phyletic
series of vertebrates and invertebrates, and were
to test the conclusions which appear to be in-
ductively derived from them?

Thus two great questions arise on this anni-
versary day in connection with the two words,
Darwin and Paleontology: first, what has Dar-
win done for paleontology; second, what has pa-
leontology done for Darwin or for the sum and
detail of Darwin’s teachings?

DARWIN THE SECOND FOUNDER OF
PALEONTOLOGY

The former question is readily answered; as
Cuvier was the first, so Darwin was the second
founder of paleontology. His contributions to
the principles of the science were prepared for

DARWIN AND PALEONTOLOGY 215

by his familiarity through Lyell with the work
of the great Frenchmen Buffon, Lamarck, and
Cuvier. These principles were stimulated and
made his own by his observations during the voy-
age of the Beagle, and his survey of the extinct
life of South America. His comments on what
he saw exhibit a close observer of nature, the
geologist and biologist, the ideal paleontologist
except only in the technical field of anatomy.
He himself knew few or no lines of descent, but
he felt they must be found, and he set the whole
world in search for them. These principles of
paleontology were given full expression in the
Origin of Species. There are in that great work
innumerable allusions to what may now be called
the working method of paleontology, the method
which Huxley formulated and expressed in clear
terms in 1880. Darwin believed that the breaks
in the geological record caused the interruptions
in the hypothetical phyla, and his fond confidence
that they would be overcome has been more than
vindicated. The impulse which he gave to ver-
tebrate paleontology was immediate and un-
bounded. It found expression especially in the
writings of Huxley in England, of Gaudry in
France, of Kowalevsky in Russia, of Cope and
Marsh in America. These works swept aside
the dry fossil lore which had been accumulating
since the passing of Cuvier’s influence, and
breathed the new spirit of search for the princi-
ples of fitness, of descent, of survival, and of ex-

216 DARWIN AND PALEONTOLOGY

tinction. Thus Darwin gave a new birth to pa-
leontology, as to every other branch of biology.

The second question, what has paleontology
done for Darwin, calls not for one but for a series
of answers. In some ways it has vastly strength-
ened him as a natural philosopher or as the seeker
of natural causes; it affords more convincing
proof than any other branch of biology of the
truth of Darwin’s grandest contribution to our
knowledge of the universe, namely, his complete
demonstration, which others had attempted and
failed to give, of the law of evolution with all its
consequences. In this way it has shown him to
be quite infallible; in other ways it has under-
mined his position and shown him quite as fallible
as other great men.

It seems therefore that the most important
part which a paleontologist can play in this dis-
cussion is to state exactly and clearly what pale-
ontology has to say for and against the special
hypotheses set forth by Darwin as well as what
it has to say that is entirely new since Darwin’s
time.

SELECTION

Darwin’s own hypotheses of the causes of evo-
lution through Natural Selection are concentric
or in ever narrowing circles; they center around
the broad survival of the best fitted groups of
organisms of all degrees, of orders, families,
genera, species, varieties, of the best fitted single

DARWIN AND PALEONTOLOGY Q17

organs, of the best fitted variations in these, and
finally come down to the focal point that the
causes of adaptation and the origin of species
ultimately center around constant variability and
the survival or selection of minute variations.
From his exhaustive knowledge of Darwin’s
work Professor Poulton holds that the great phi-
losopher had in mind as the material for Natural
Selection small variations, congenital and inher-
itable; he knew well that the material included
“great and sudden variations,’ but he did not
believe that they were selected. His variations
had no power of developing in definite direction.
Direction was given by Selection. That is, it
remained for selection to give direction by choos-
ing from all variations those which happened to
be in an adaptive direction.

It is obvious that as we pass from the broad
to the minute the theoretic demand upon the
selection hypothesis becomes more and more in-
tense, but the tendency of our time is to waive
aside theoretic considerations and come down to
actual observations and facts and see how far
they support the Darwinian and other hypoth-
eses, and how far they call for new hypotheses
and interpretations.

Thus the question of the hour is to see what
parts of this entire hypothetical system of selec-
tion within selection, until we reach the minute,
are in accord with modern paleontological evi-
dence.

218 DARWIN AND PALEONTOLOGY

Let us begin with the broad and proceed to
the minute.

Selection of entire animals and parts of ani-
mals through elimination. Paleontology not
only sustains Darwin’s broad induction of evolu-
tion, but in an equally convincing manner it sus-
tains his broad induction that Natural Selection
is and always has been one of the dominant prin-
ciples of change in the aspect of the living world.
Because of the thousands of facts which he mar-
shaled from every branch of natural history in
support of this factor he is entitled to be regarded
as the founder although not as the originator of
the law of the survival of the fittest. In study-
ing the causes of the extinction of the mammals
throughout Cenozoic times,* I have been struck
by the fact that there is hardly an hypothesis of
extinction suggested by more recent research
which escaped the more or less serious attention
of Darwin. My general survey of the economy
of extinction in this great class of animals cer-
tainly establishes the existence of a very great
variety of causes of elimination, some of which
are internal, some external in origin, while all
operate under the broad principle of selection.
I believe I have found fresh proofs of the con-
tinuous operation of selection on all organs, be-
cause some new and brilliant instances in addi-
tion to those gathered by Kowalevsky and Marsh

2“The Causes of Extinction of Mammalia,” American
Naturalist, Vol. XL, No. 479, December, 1906, pp. 769-95; No.
480, November, 1906, pp. 829-59.

DARWIN AND PALEONTOLOGY 219

are adduced not only in support of the broad in-
duction that the fittest survive, but also in proof
of the more specific principle of Darwin that cer-
tain single organs, such as certain types of tooth
structure, or of foot structure, have been favor-
able or fatal to their possessors. This is now
capable of statistical demonstration and no
longer a matter of highly probable inference, as
Darwin left it. The most readily comprehended
case is that during the Upper Oligocene and
Lower Miocene periods, a large number of en-
tirely unrelated quadrupeds possessed a closely
similar pattern * in their grinding teeth; it was
the one character which they possessed in common
and certainly was the one character which led
them all alike to extinction.

Selection of the larger variations of propor-
tion. When we approach the further applica-
tion of the selection principle, however, as more
novel with Darwin and more intimately asso-
ciated with his personal views, namely, his doc-
trine of the selection of larger variations of pro-
portion, as, for example, in the classic case of the
elongation of the neck of the giraffe, we are
forced to admit that paleontology neither posi-
tively sustains nor destroys this working hypoth-
esis, although the evidence which it presents is
rather favorable than unfavorable.

By exclusion of other hypotheses, paleontol-

1] allude to the grinding teeth technically known as bunosele-
nodont, that is, with a rounded crown (bumos) on the inner side of
the grinders, and crescentic (selene) ridges on the outer side.

220 DARWIN AND PALEONTOLOGY

ogy may however be said to lend support to this
hypothesis. Changes of proportion in long
periods of time, that is, in millions of years, play
an enormous part in evolution, as seen by the fol-
lowing contrasts in certain well-known structures,
among herbivorous quadrupeds :—

Short-toothed and long-toothed=short-lived and long-
lived.

Short-toothed and long-toothed=browsers and grazers.

Short-footed and long-footed =short rangers and
long rangers.

Short-headed and long-headed =browsers and grazers.

Short-necked and long-necked =near feeders and far
feeders.

Among the horses these very changes of pro-
portion in four important organs, the teeth, the
feet, the head, and the neck, constitute a very
large percentage of the total evolutionary
changes, and result finally in certain phyla of
horses becoming long-lived animals, capable of
traveling long distances, capable of grazing on
the harder kinds of food, and capable of reach-
ing food at a considerable distance from the
body. This joint action of heredity, ontogeny,
environment, and selection of congenital varia-
tions of proportion, appears to best explain the
transformation of round-headed or brachyceph-
alic into the long-headed or dolichocephalic forms
of the horses as well as of other herbivora, in re-
lation to the browsing or grazing habit respect-
ively. The only explanation which has as yet

DARWIN AND PALEONTOLOGY 221

been offered for such changes of proportion is
that of the selection of hereditary quantitative
variations.*

I am therefore myself inclined to regard long-
headedness or short-headedness in the vertebrates
generally as well as the similar phenomena of
long-footedness (dolichopody) or short-footed-
ness (brachypody) as in many cases caused by
the selection of changes of proportion; yet I
freely admit that we can not prove or demonstrate
this Darwinian hypothesis through paleontology.

One direct paleontological reason may, how-
ever, be adduced in favor of the hypothesis of
selection of variations of proportion, namely,
changes of proportion do not fall under what I
call the law of ancestral control of variation.
Head proportions or foot proportions, or, in
fact, any other change of proportion can not be
regarded as controlled by ancestral affinity, be-
cause descendants of the same ancestors soon give
rise to very different results. For example, a
primitive intermediate (or mesaticephalic) form
of skull does not at all control the form of skull
which may be derived from it; the animal is free,
as it were, to evolve into one of many different
kinds of head forms. The point is that hered-
itary predetermination does not appear in the
evolution of proportion and of form as I shall

show that it does appear in the evolution of cer-

1The fact that this throws little light on the origin of dolicho-
cephaly or brachycephaly in the human species appears to throw
the selection hypothesis again into doubt.

222 DARWIN AND PALEONTOLOGY

tain other new characters, except in so far as
an evolutionary tendency once established in the
direction of brachycephaly or dolichocephaly is
apt to be pursued to its very limits or extremes.
Selection of minute variations. Not only is
paleontology not positively conclusive on the hy-
pothesis of selection of large variations, it has
nothing positive, but rather something negative
to say on the still more intimate or focal feature
of the Darwinian hypothesis that minute varia-
tions without direction in certain specific organs
are of survival or of elimination value. Certainly
appeal must be made to some other branch of
biology on this particular problem, if indeed it
is ever capable either of verification or of dis-
proof. Through paleontology we can neither
say that Darwin was right or wrong, because we
meet with certain peculiar barriers or limitations
of paleontological observation. Slight changes
of geological level may mark long periods of
time. The limitations are not solely due to rela-
tive rarity of contemporaneous or synchronous
material, because among invertebrates vast num-
bers of synchronous forms are sometimes brought
together so that minute variations may be read-
ily measured, but it is quite another matter to
prove through paleontology that such variations
are selected. It was Waagen’s view that it is
not the variations but the less conspicuous muta-
tions which reappear in the next generation.
This question of the selection of minute varia-

DARWIN AND PALEONTOLOGY 223

tions is probably par excellence a field of research
for the biometrician and the experimentalist
rather than for the paleontologist.

ORIGIN OF NEW CHARACTERS

We now reach a turning point and pass from
differences of proportion, of development, and
of degeneration, to the origin of new characters.

Origin of new characters not by selection of
the fit from the fortuitous. When, however, this
focal point of the selection of minute variations
is pressed home as an hypothesis of the origin of
all new adaptive characters, then paleontology
ceases to be either neutral, silent, or inconclusive,
and gives to Darwinism a most emphatic nega-
tive. In all the research since 1869 on the trans-
formations observed in closely successive phyletic
series no evidence whatever, to my knowledge,
has been brought forward by any paleontologist,
either of the vertebrated or invertebrated ani-
mals, that the fit originates by selection from the
fortuitous.

Lest the statement be made that this is truly
the sanctum sanctorwm of Darwin’s theory of
adaptation, let me recall the historical fact * that
fitness for twenty-five centuries had been the
stumbling block of those who sought a natural-
istic interpretation of nature; that Kant’ had

1 Osborn, H. F.: From the Greeks to Darwin. An Outline of
the Development of the Evolution Idea, Vol. 1 of the Columbia
University Biological Series, 8vo, Macmillan, 3rd ed., p. 248.

* Ibid, p. 100.

224 DARWIN AND PALEONTOLOGY

wondered if any one could ever give an explana-
tion of the origin of fitness in a blade of grass;
that fitness had become the teleological citadel of
the supernaturalists. Darwin was believed by
many, but not by all, to have solved this problem
of the ages. Let me quote the very recent lan-
guage of our most profound American philo-
sophical thinker, William James *:—

“It is strange, considering how unanimously our
ancestors felt the force of this argument [that is, the
teleological], to see how little it counts for since the
triumph of the Darwinian theory. Darwin opened our
minds to the power of chance-happenings to bring forth
‘fit’ results, if only they have time to add themselves
together. He showed the enormous waste of nature in
producing results that get destroyed because of their
unfitness.”

I repeat: paleontology is not silent, but pre-
sents a solid array of evidence against what was
never more than an ingenious working hypoth-
esis of Darwin; one he fathered and loved, it is
true, but which met little favor in the sturdy and
logical mind of Huxley, predisposed as he was
to Darwinism. It is now no longer a question

1 James, William: Pragmatism. 8vo, Longmans, Green &
Co., New York, 1907, pp. 110, 111. Professor William Bateson
gives a similar definition. “ Darwin’s Solution. Darwin, without
suggesting causes of Variation, points out that since (1) Varia-
tions occur—which they are known to do—and since (2) some
of the Variations are in the direction of adaptation and others
are not—which is a necessity—it will result from the conditions
of the Struggle for Existence that those better adapted will on
the whole persist and the less adapted will on the whole be lost.”
Materials for the Study of Variation, Treated with Especial
Regard to Discontinuity in the Origin of Species, 8vo, London,
1894, p. 5.

DARWIN AND PALEONTOLOGY 225

of logic but of fact. Does paleontology sup-
port this focal hypothesis of fortuity or absence
of direction in the minute variations leading to
adaptation, or does it destroy it?

The answer is in no uncertain sound. While
fortifying all the outworks, paleontology under-
mines the hypothesis of adaptation through the
selection of the directed from the variations with-
out direction by eliminating the occurrence of the
variations without direction in many important
organs. Fortuitous variations as material for
advance should certainly be found, if anywhere,
in closely successive phyletic series; they have not
been found. At the same time this evidence
does not leave a vacuum, but replaces the law
of chance by another law, namely, that as in the
domain of inorganic nature, so in the domain of
organic nature fortuity is wanting, and the fit
originates in many hard parts of the body
through laws which are in the main similar to
growth,—laws the modes of which we see and
measure, the causes of which we do not and may
never understand, but nevertheless laws and not
fortuities or chance happenings.

Now let us inquire how it comes that paleon-
tologists, far in advance of other biologists, have
reached this profoundly important principle as
to the origin of certain new characters.

The paleontologist observes origins. Having
already disclaimed certain powers for paleontol-
ogy as regards evidence on the evolution factors,

226 DARWIN AND PALEONTOLOGY

and having still others to disclaim, I may now
claim for paleontology as its transcendent power
that it alone of the biological sciences can pro-
duce evidence of the reign of definiteness, of
order, of law in the origin and early history of
certain adaptive characters, because in the hard
parts of animals it alone is in with organs before
their beginnings and from their beginnings to
their finalities. The beginning of new charac-
ters is at once the central problem and the most
mysterious problem of evolution. In using the
word “beginnings” or “origins” we do not
imply causes but simply appearances in order of
time. It is of unique advantage to the paleon-
tologist as an observer of the origin of new char-
acters that concentrating his attention on single
characters entirely irrespective of the species
question, which is wholly a by-question, he may
trace new characters from the period before their
origin, through their first adumbrations, through
the stages which may be denominated as origins,
through their every subsequent change, through
their entire history, in fact. In this long-lived
sense as an observer the paleontologist is immor-
tal in contrast with those mortal observers, the
zodlogists and experimentalists.

Second, in successive series of animals such as
horses, rhinoceroses, or the related titanotheres,
the paleontologist may observe the behavior of a
very large number of characters at the same time
and through long periods of time, some rising,

DARWIN AND PALEONTOLOGY 227

some falling, one structure taking a rounded
form, the structure next it taking a crescentic
form, every single element evolving independ-
ently in some way. The theory of the simulta-
neous operation of several factors on different
groups of characters and on different kinds of
group characters could only suggest itself to a
paleontologist working on a very complex ani-
mal like one of these big quadrupeds in which
countless numbers of characters are simulta-
neously evolving.

Third, the paleontologist has this further
unique advantage: he is in a position to judge
which new characters are important and which
are unimportant; he is, therefore, in a peculiarly
favored judicial position. By contrast neither
the zodlogist nor the botanist is in a position to
know whether a new character which he believes
to be important is going to persist or not. The
difficulty under which the zodlogist labors in this
lack of judicial discernment is illustrated, for
instance, in Bateson’s Materials for the Study of
Variation, in which he attempts to prove the law
of discontinuity from a review of a very large
assemblage of characters, the greater number of
which the paleontologist would recognize at once
as wholly unimportant and non-significant. The
only way zodlogy and botany could overcome
this disadvantage, as regards the origin of new
characters, would be through a series of relay
observations extended by successive observers

228 DARWIN AND PALEONTOLOGY

over long periods of time or through a series of
lifetimes. The mortality of the zodlogist, the
experimentalist, the botanist, is a fatal handicap,
for the reason that they are alike too short-lived
to observe and measure those changes in the hard
parts (if they exist) which are so excessively slow
as to be invisible and immeasurable by mortal
eye; while the paleontologist alone is in a posi-
tion to demonstrate the existence and importance
of such slow origins. With his short-time vision
is not the zodlogist and botanist more prone to
fall into the error of “ exclusive hypotheses,” and
conclude that visible, measurable changes, such
as saltations, discontinuities, mutations of De
Vries are the most important if not the only
changes which are going on in organisms? Thus
the paleontologist listens serenely to the fanfare
of trumpets of exclusive hypotheses; he knows
that time and time alone will show whether these
will with other fashions fade.

Sudden origins demonstrable by zodlogy and
botany, but not by paleontology. As regards
the soft parts of animals and even as regards pro-
portions, changes which occur geographically or
in space can be measured by the zoologist, but
this does not apply to origins. The first point
as to origin, namely, the question of rate or speed
of origin, finds paleontology at a disadvantage
as a sphere of research. The law of sudden or
discontinuous principles has repeatedly been
demonstrated in zodlogy and in botany. It

DARWIN AND PALEONTOLOGY 229

reaches the climax in De Vries’ work, where mu-
tation is regarded as an exclusive principle, but
discontinuity can never be either demonstrated
or disproved by paleontology, since this is the
most unfavorable of all the biological fields for
the recognition of sudden changes of character,
through absence of that abundance of synchro-
nous and contemporaneous material for com-
parison on which alone it is safe to establish the
existence of a mutation. Despite this obvious
shortcoming of paleontology, it is noteworthy
that the saltatory hypothesis has been—illogically
I believe—fathered by a series of paleontologists,
by St. Hilaire in 1830, by Cope, and more re-
cently by Dollo and Smith Woodward. It
should be borne in mind constantly that wherever
a new animal suddenly appears or a new char-
acter suddenly arises in a fossil horizon, such ap-
pearance may be attributable to the non-discovery
of the greater or more minute transitional links
with older forms or to the sudden migration of a
new type provided with a new organ or organs
which have gradually evolved elsewhere. More-
over, the doctrine of sudden appearances is di-
rectly the reverse of Waagen’s law of mutation.
The point, however, is that as a sphere of evidence
paleontology neither approves nor disproves the
law of discontinuity.

Slow origins demonstrable by paleontology,
but not by botany or zoélogy. Paleontology, on
the other hand, affords the most favored field for

230 DARWIN AND PALEONTOLOGY

the observation of slow origins of new characters.
It is well known that Darwin was a firm advo-
cate of the hypothesis of slow origins; this was,
indeed, consistent with his doctrine of evolution
by the adding up of favorable fluctuations. The
law of gradual appearance or origin of many new
characters in definite or determinate directions
from the very beginning I regard as the grandest
contribution which paleontology has made to
evolution. This law of gradual change in the
origin and development of single characters,
measurable only at long intervals of time, has
now come to rest on a vast number of observa-
tions; it is the working basis of the science. Ver-
tebrate and invertebrate paleontologists search-
ing independently of each other on wholly differ-
ent kinds of animals have reached entirely sim-
ilar opinions.

Mutations of Waagen. The first, I believe,
to express from observation the law of gradual
change was Waagen in 1868. The mutations
of Waagen* were originally distinguished by
him from the often more conspicuous contempo-
rary fluctuations by the fact that, although seen in
minute features, they are very constant and can
always be recognized again, but only in success-
ive geological levels, that is, at intervals of many
geologic years. Such gradations are observed

1 Waagen, Wilhelm Heinrich: “Die Formenreihe des Ammonites
subradiatus,” Benecke’s Geognostische Paldontologische Beitrige,
II, 1868, pp. 185-86.

DARWIN AND PALEONTOLOGY 231

in single characters; they are the nuances, or
shades of difference, which are the more gradual
the more finely we dissect the geologic column;
bit by bit the Waagen mutations are added to
each other in different single characters until the
sum or degree of mutations is reached which no
zo0logist would hesitate to assign specific or ge-
neric rank. The essence of Waagen’s mutation
is orthogenesis or variation in determinate direc-
tions, as distinguished from the indefinite varia-
tion implied in Darwin’s theory.* This law re-
ceived the powerful support of our countryman
Hyatt, of the Austrian paleontologist Neumayr,
and many others.

In 1889 Osborn,’ in observing the teeth of large
numbers of Eocene mammals, chiefly of the
smaller monkeys, horses, tapirs, and other forms,
first noticed that new elements here also arise def-
initely and can only be measured after long in-
tervals of time. He first applied (1890) the
term “ definite variations ” * to these characters,
but many years later, on observing that many
such characters were destined to become adaptive,
he gave the same elements the name “ rectigrada-

1 Professor Poulton maintains that determinate variation is
precisely what Natural Selection would show, namely direction
through the accumulation of favorable variations.

2 Osborn, H. F.: “ The Paleontological Evidence for the Trans-
mission of Acquired Characters,” British Association Reports,
Newcastle-upon-Tyne meeting, September, 1889. London, 1890.

*“ Are Acquired Variations Inherited? Opening a Discussion
upon the Lamarckian Principle in Evolution.” American Society
of Naturalists, Boston, December 31, 1890. American Naturalist,
Vol. XXV, No. 291, March, 1891, pp. 191-216.

232 DARWIN AND. PALEONTOLOGY

1

tions.”* It appears probable, but it is not yet
demonstrated, that the rectigradations of Osborn
are of the same nature as the mutations of
Waagen. Scott’ in 1894 was the first vertebrate
paleontologist to call the attention of his co-
workers to Waagen’s law among the inverte-
brates. This principle of rectigradation in the
origin of many new characters in the mammals
cuts both ways; it demonstrates the absence of
the chance happenings without direction, which
form the basis of Darwin’s hypothesis of the
origin of adaptations, and positively shows that
certain new adaptive characters appear definitely
and assume adaptive direction from their very
minutest beginnings.

To sum up, the law of gradual change in cer-
tain determinate, definite, and at least in some
cases adaptive directions, through very long
periods of time, and the absence of chance or non-
direction in the origin of a large number of
adaptive and other new characters, is the com-
mon working principle both in vertebrate and
invertebrate paleontology.

It is thus that the characters which the older
paleontological observers, such as Owen, Leidy,
Cope, and Marsh, designated as specific and even
as generic are gradually built up. We thus wit-

1“ Homoplasy as a Law of Latent or Potential Homology,”
American Naturalist, Vol. XXXVI, April, 1902, pp. 259-
71.

2 Scott, W. B.: “On Variations and Mutations,” American
Journal of Science, Vol. XLVIII, 1894, pp. 355-74,

DARWIN AND PALEONTOLOGY 233

ness the origin of what naturalists have been des-
ignating as species.

In a lower horizon a cusp of one of the teeth,
for example, is adumbrated in shadowy form; in
a slightly higher horizon it is visible; in a still
higher horizon it is fully grown, and all paleon-
tologists have hitherto agreed to honor this final
stage by assigning to the animal which bears it
a new specific name. In the face of these con-
tinuous series of changes revealed by paleontol-
ogy the species and genera of Linneus break up
into the continuous chain of the “ mutations of
Waagen,” and for such progressive changes
Depéret has proposed the term “ ascending mu-
tation.”

No theoretical conflict between the mutations
of Waagen and of De Vries. Tt will be shown
presently that a very considerable number, if not
all, of these slow origins are of a kind which arise
from internal causes (intrinsic causes, Williams),
that is, in heredity. It is evident that if there do
exist hereditary predispositions to mutate in def-
inite directions, such predispositions may mani-
fest themselves very gradually, as in the “ muta-
tions of Waagen,” or under certain circum-
stances very suddenly, as in the lesser saltations
or “mutations of De Vries.” Theoretically, at
least, there thus ceases to be any inherent conflict
between the hypotheses of “continuity” and
“ discontinuity ”; the latter may represent an in-
tensified or accelerated state of the former.

234 DARWIN AND PALEONTOLOGY

ADAPTATION

Adaptive nature of certain new origins. Dar-
win’s hypothesis of the selection of variations
lacking direction is essentially a law of chance.
Origins of many kinds and in many places
should be observed; the principle of trial and
error should be seen in operation; paleontology
should be an especially favorable field for such
observation. Yet, as noted above, the mutation
law of Waagen and the identical or similar rec-
tigradation law of Osborn is essentially a prin-
ciple of definiteness and determinateness from the
beginning.

Definiteness is not necessarily adaptiveness.
The novel feature of Osborn’s observations in
1889 on the cusps of the teeth appears to consist
in the demonstration of this element of adaptive-
ness;* the new element is not merely determi-
nate, but it is leading directly to utility, and will
at a later stage be useful. Thus vertebrate pale-
ontology enables us to establish the law that cer-
tain origins are adaptive in direction from the
beginning; namely, the law of rectigradation.

Such origins of new characters are chiefly
numerical; something is added to the organ or
to the organism which did not exist before in vis-

+“Certain Principles of Progressively Adaptive Variation
Observed in Fossil Series.” Biological Section of the British Asso-
ciation for the Advancement of Science, British Association
Reports, 1894, p. 643 (title); Nature, Vol. 50, No. 1296, August,
30, 1894, p. 435,

DARWIN AND PALEONTOLOGY 235

ible form, such as the beginning of a cusp or of
a horn. The origin of horns has always been a
famous problem, because horns are eminently in
the nature of new characters. In the great quad-
rupeds known as titanotheres rudiments of horns
first arise independently at certain definite parts
of the skull; they arise at first alike in both sexes,
or asexually; then they become sexual, or chiefly
characteristic of males; then they rapidly evolve
in the males while being arrested in development
in the females; finally they become in some of
these animals dominant characters to which all
others bend.

The form, the proportion, the modeling, both
of the cusps and of the horns, accord with the
proportions of the teeth or of the skulls in which
they appear; they are thus correlated in form
with other organs. The cusps of the grinding
teeth of mammals form a peculiarly advanta-
geous field of observation because they do not
depend either upon ontogeny or environment for
their perfection; they are born complete and per-
fect, use and environment destroy rather than
perfect them. They thus contrast with the
bones, muscles, and many other tissues of the
body which depend upon ontogeny for their per-
fection.

Failure of attempted explanation of adaptive
origins by transmission of acquired characters.
In seeking explanation of this definiteness or
adaptiveness of direction in the origin of certain

236 DARWIN AND PALEONTOLOGY

new parts, it was natural to first have recourse to
the doctrine of the transmission of acquired char-
acters, because it is a well-known principle that
certain organs are definitely directed or guided
along adaptive lines by use. By reference to my
papers of 1889 and 1890, it will be seen that it
was in seeking an explanation of direction, I was
led to support the Lamarckian principle. I do
‘not propose to discuss this enormous question
here. Cope concentrated his whole energy on
trying to demonstrate Lamarckianism from pa-
leontology, but ended in a logical failure, or non
sequitur, because the explanation will not apply
to all cases. Here again I believe that experi-
mental zodlogy rather than paleontology is the
best field of research, and that the Lamarckian
principle should not be finally abandoned until
it is tested by a prolonged series of experiments
extending over many years. It is well known
that Darwin, for the very reason that he thought
he saw in it a working explanation of a directing
influence on heredity, finally adopted the La-
marckian principle and proposed his hypothesis
of pangenesis. This was also the ground of my
first conclusion of 1889, yet owing in the first
instance to a trenchant criticism by Poulton, I
have for the time abandoned this Lamarckian
interpretation, since quite apart from the difficul-
ties in the field of heredity, paleontology appears
to offer many objections to it. The objections
are simply these: that a very large number of

DARWIN AND PALEONTOLOGY 237

new, definite, orthogenetic characters which could
not have been acquired in ontogeny arise at birth,
among them the cusps of the teeth. Since the
Lamarckian doctrine either fails or need not be
invoked to explain these definite adaptive origins
in the teeth, and apparently also in the horns,
why invoke it for other adaptive phenomena?
This does not preclude the constant operation of
the law of organic selection* or the “ selection
of coincident variations ” advocated by Morgan,
Baldwin, and myself, which I still regard as a
useful supplementary hypothesis to Natural Se-
lection, explaining many of the alleged instances
of the inheritance of acquired characters.
Unknown causes of certain adaptive origins.
In 1890 I pointed out that, since the Lamarckian
principle gave us a working hypothesis of direc-
tion in these adaptive origins, in abandoning the
Lamarckian principle we would be left without
any explanation, and in developing this idea I
came to the conclusion in 1895’ that we must
appeal to the existence of some unknown factor

1Qsborn H. F.: “A Mode of Evolution Requiring Neither
Natural Selection nor the Inheritance of Acquired Characters
(Organic Selection),” Trans. N. Y. Acad. Sci., March and April,
1896, pp. 141-48.

See also: “Ontogenic and Phylogenic Variation,” Science,
Vol. IV, 1896, November 27, pp. 786-90; “Organic Selection,”
Science, N. S. Vol. VI, No. 146, October 15, 1897, pp. 583-87;
“The Limits of Organic Selection,” American Naturalist, Vol.
XXI, November, 1897, pp. 944-51; “ Modification and Variation,
and the Limits of Organic Selection: A Joint Discussion with
Professor Edward B. Poulton of Oxford University,” Proc. Amer.
Assoc. Adv. Science, Vol. 46, 1897, p. 239.

2“‘The Hereditary Mechanism and the Search for the Unknown
Factors of Evolution,” Biol. Lect. Marine Biol. Lab. 1894, Ginn &
Co., Boston, 1895.

238 DARWIN AND PALEONTOLOGY

or factors of evolution. Subsequent research
has convinced me that in these phenomena of the
internal origin first of certain determinate char-
acters, and second of certain adaptive charac-
ters, we are dealing with the unknown if not with
the unknowable, although the latter despairing
attitude should not be hastily adopted. The
immediate causes are internal, that is, they lie in
the domain of heredity rather than of ontogeny,
environment, or selection; but lest I might be
mistaken on this point, I have devoted several
years of thought to the development of a circle
of causes, so to speak, which I have finally formu-
lated * in the law called the four inseparable fac-
tors of evolution. According to this law I re-
gard heredity not as something inseparable, al-
though extraordinarily stable; on the contrary I
have recently expressed the relations of heredity
to the other factors as follows:—

The life and evolution of organisms contin-
uously center around the processes which we
term heredity, ontogeny, environment, and se-
lection; these have been inseparable and inter-
acting from the beginning; a change introduced
or initiated through any one of these factors
causes a change in all. First, that while insep-
arable from the others, each process may in cer-

*The Four Inseparable Factors of Evolution. Theory of
Their Distinct and Combined Action in the Transformation of
the Titanotheres, an Extinct Family of Hoofed Animals in the
Order Perissodactyla,” Science, N. S. Vol. XXVII, No. 682,
January 24, 1908, pp. 148-50.

DARWIN AND PALEONTOLOGY 239

tain conditions become an initiative or leading
factor; second, that in complex organisms one
factor may at the same time be initiative to an-
other group of characters, the inseparable action
bringing about a continuously harmonious result.

This inseparableness of internal processes (he-
redity and ontogeny) and external processes
(selection and environment) is not surprising
when we reflect that it must have existed from
the very beginnings of the organic world.

Thus hypothetically the origins of certain new.
characters in heredity may find expression not
spontaneously, or irrespective of conditions, or
from self-operating internal mechanical causes,
but through some unknown and at present en-
tirely inconceivable relation between heredity
(the germ-cells), ontogeny or habit and use (the
somatic cells), environment or external condi-
tions, and selection. This does not preclude
spontaneous origins.

Prolonged analysis and synthesis of the evolu-
tion processes of the various kinds which led to
the enunciation of the above law only served to
convince me that certain adaptive origins are im-
mediately matters of heredity whatever their in-
itiation may be in the circle of ontogenetic or
environmental causes. We have to do with a
potential of similar mutations or rectigradations
independently.

Here we find ourselves expanding a principle
which was clearly foreshadowed by Darwin, and

240 DARWIN AND PALEONTOLOGY

which, had he pursued it to its logical sequence,
would have brought him to orthogenesis, namely,
that variations may not be without direction, but
that law may lie among the hidden recesses of the
nature of the organism; in other words, Darwin
himself frequently professed ignorance of the laws
of variation as well as the belief that such laws
might be discovered. Paleontology has revealed
certain laws of variation, and it is quite con-
sistent with the principle that the ancestral nature
of the organism limits and conditions variation
that I have to record the following interpretation
or hypothesis * announced in 1902, namely, that
the adaptive origins ‘of certain characters are
predetermined by hereditary kinship. This pre-
determination may be due to a similarity of
hereditary potential in evolution, that is, ani-
mals of similar kinship transmit similar poten-
tialities in the origin of. new characters. There
is an ordinal kinship, a family kinship, a generic
kinship, etc. This first renders possible the oc-
currence of certain new characters, and second,
conditions or limits these new characters when
they do occur. For example, in a certain inde-
pendent series of extinct animals derived from
common ancestors, we can predict where a new
cusp or a new horn rudiment will show itself be-

1 Osborn, H. F.: “ Homoplasy as a Law of Latent or Potential
Homology,” American Naturalist, Vol. XXXVI, April, 1902, pp.
259-71.

The term Homoplasy was wrongly employed in this paper under
a misapprehension as to the significance which its author, Pro-
fessor E. Ray Lankester, intended to apply to it.

DARWIN AND PALEONTOLOGY Q41

fore the actual occurrence of either. It is only
through some such restraining or limiting law of
hereditary kinship and potential that we can
explain the marvelous uniformity which exists,
for example, in the fundamental structure of the
grinding teeth of the mammalia.

Hypothetical interpretation. This is not to be
understood as an internal perfecting tendency.
Such an interpretation may be abandoned at once
so far as it applies to the independence of these
hereditary origins from other causes. While a
phenomenon of heredity, the definite origin of
adaptive structures is, in a manner which is en-
tirely incomprehensible to us, related to ontogeny
and environment, to new habits and new condi-
tions of life, there is a marvelous nexus be-
tween the internal and the external. Thus, for
example, if a monkey or lemur begins to imitate
the habits of the hoofed animals by becoming
herbivorous, it also begins to acquire the dental
cusps of the herbivorous hoofed animals in ap-
proximately the same order. This principle of
the relation of the internal and the external lies
at the basis of many of the phenomena of par-
allelism. For example, some of the Eocene
monkeys so closely parallel the Eocene hoofed
mammals in dental structure that they were first
placed in the same taxonomic order. Some un-
known relation between external and internal
causes appears to evoke the potential of similar
development. Thus there appear to be accelera-

242 DARWIN AND PALEONTOLOGY

tions and retardations of characters in heredity
which remind us of the well understood laws of
acceleration and retardation in individual de-
velopment.

Degrees of kinship also affect to a certain ex-
tent, but not absolutely, the time of appearance
or the time of origin of new characters as well as
the rate of their development. Thus four lines
of Eocene quadrupeds (Titanotheres) branched
off independently from one stock; in all the
branches we observe similar new cusps arising on
the premolar grinding teeth, and similar new
horn rudiments rising on the forehead above the
eyes, both independently evolved. Neither the
new cusps nor the new hornlets appear at just
the same moment of geological time; some phyla
hasten forward these rectigradations, other phyla
retard them.

The independence of single characters and
multiplicity of origins. The independence of
single characters reminds us of the independence
of the “unit characters” as known to the stu-
dents of Mendelism and of De Vries’ mutation,
yet the single characters we have in mind are not
unit characters in the Mendelian sense because
they do not mendelize; they appear in every indi-
vidual. The independence of single characters
in the “ Waagen mutations” or the “ Osborn
rectigradations ” is shown by the fact that a con-
siderable number of characters evolve in a per-
fectly regular and lawful succession. Each char-

DARWIN AND PALEONTOLOGY 243

acter is a law unto itself, yet all subserve the gen-
eral good. For example, a new horn rudiment
arising on a brachycephalic skull will be broad
or rounded; if it arises on a dolichocephalic skull
it will be elongate or oval. Thus in a large quad-
ruped like a horse, a tapir, a titanothere, or a
rhinoceros each horn, each tooth, each bone of
the skull and skeleton, and by inference all
the hard parts as well as all the soft parts of
these animals in each phylum, have two sets of
relations:

I. In the origin of new characters each phylum
will evolve, like other phyla, hypothetically
through inherited predispositions. Thus from
forty to forty-eight new characters will similarly
arise in a number of phyla in the grinding teeth
alone.

II. In changes of proportion and in rate of
evolution each phylum will evolve unlike other
phyla, through freedom from hereditary predis-
position in matters of form, proportion, and rate
of evolution.

These are the conclusions which I have reached
after twenty-two years of very precise work on
the evolution of the mammals. Besides exactly
observing primates, horses, rhinoceroses, during
the past seven years I have devoted myself to
still more precise monographic work on the group
of titanotheres, bringing together great quanti-
ties of material, and with the assistance of Mr.
W. K. Gregory making thousands of exact ob-

244 DARWIN AND PALEONTOLOGY

servations and measurements. Thus the evo-
lution of the group has been traced from a small,
hornless animal, of the size of a sheep, to a
gigantic horned quadruped little inferior to an
elephant. I have realized that the origin of all
changes which are discovered in the skeleton must
be credited to one of the four factors which take
part in evolution, namely :—

Herepiry.
ONTOGENY.
ENVIRONMENT.
SELECTION.

Thus new characters which can not be credited
immediately to selection, to ontogeny, to environ-
ment, must by exclusion be attributed to heredity,
these are the mutations or rectigradations.

METHOD OF EVOLUTION (TITANOTHERZS)

An interpretation of the evolution of a family.
In picturing the evolution of this great famliy
of quadrupeds, the titanotheres, through a long
period of time and with an unique sequence of
material, may we not interpret the facts by imag-
ining a continuous interoperation of the four
chief factors, and analyze what we see somewhat
as follows?

First, these animals are all of the titanothere
kinship and of the larger perissodactyl kinship.
The ordinal kinship and the family consanguinity

PLATE VY.

RECTIGRADATIONS IN THE TEETH OF EoceNE UNGULATES.
A. A-primitive Equid, Orohippus sp.
B. A primitive Titanothere, Palwosyops paludosus.

From specimens in the American Museum of Natural History. Internal view
of lower teeth.

The circles mark the cusps which appear independently in the different phyla ;
they are at first barely visible but increase in size in successive geological levels.

Tor View oF THREE SKULLS OF EocENE TITANOTHERES ILLUSTRATING
BRACHYCEPHALY, MESATICEPHALY, AND Do.icHoceruALy ReEspecr-
IVELY.

(From specimens in the American Museum of Natural History.)

A. Palwosyops major, brachycephalic. ;
B. Manteocer as manteocer as, mesaticephalic,
C. Dolichorhinus cornutus, dolichocephalic.

DARWIN AND PALEONTOLOGY 245

(different from that of the tapirs, rhinoceroses,
or horses) apparently tincture and condition
many things which happen in the evolution of
this group. There are forty-four grinding teeth
altogether; twelve of these teeth (the molars)
early attain their final form, but are destined
through family kinship to lose certain characters
and to change their proportions through generic
kinship; twelve others (the premolars) have not
attained their final form, but gradually do so
through the origin of from forty to forty-eight
new characters, each of which appears to arise
through an unknown law of hereditary predispo-
sition, which operates alike, through ordinal kin-
ship, not only in the titanotheres but in all other
odd-toed or perissodactyl mammals to which the
titanotheres are related. Changes of proportion
in the skull, whether toward breadth (brachy-
cephaly), or toward length (dolichocephaly), af-
fect the form of the grinders as a whole and thus
the birth-form of each of these new cusps. The
immediate cause of changes of proportion is not
interpreted as due to hereditary predisposition,
because in teeth, in skull, in foot and limb, and
even in horns each generic branch or phylum from
the original stem forms of titanotheres acquires
its own proportions. Thus changes of proportion
are interpreted rather as immediately affected by
ontogeny, by the mechanics of use and disuse, by,
an environment which favors some rather than
other proportions, but especially by the selection

246 DARWIN AND PALEONTOLOGY

of variations in proportion which coincide with
the needs of the phylum.*

No abrupt variations (mutations) have been
observed in the evolution of the titanotheres, but
this in no way renders it inconceivable that skel-
etal mutations in the De Vries sense have pro-
duced new races in certain phyla. The addition
or loss of a vertebra in the sacral region, which
appears to distinguish certain titanothere phyla,
may be a case of such sudden inheritable muta-
tions.

Independently in four or five Eocene branches
of the titanothere stock the horn rudiments very
gradually arise, apparently through hereditary
predisposition or family kinship, as rectigrada-
tions, at the junction of the nasal and frontal
bones. As in the case of the cusps, the shape of
these horn rudiments is from the first conditioned
by the respective breadth (brachycephaly) or
length (dolichocephaly) of the skull.

The branches or sub-phyla become more and
more sharply distinguished from each other
by increasing brachycephaly or dolichocephaly,
brachypody or dolichopody, apparently through
congenital variations of proportion accumulated
by selection and guided by ontogeny through
“organic selection.” The animals belonging to

11t is important to note, on the authority of Professor Castle,
that proportions of the skeleton and probably of the teeth are not
inherited as distinct “unit characters.” Inheritance of bone size
and shape seems to be as a rule regularly blended by interbreed-
ing and without subsequent Mendelian splitting.

DARWIN AND PALEONTOLOGY Q47

these branches appear to have chosen their own
local environments, whether in localities favor-
able to grazing or to browsing, and in turn con-
genital changes of proportion would be favored
by selection if in the right direction. The trans-
formation into brachycephaly and dolichocephaly
is brought about through independent changes of
proportion in every bone of the skull, as ascer-
tained by exact comparative measurements. A
trend once established in either direction seems to
constitute a sort of “ hereditary momentum ” or
predisposition, which leads to great extremes of
brachycephaly, on the one hand, or dolichoceph-
aly on the other, as shown in the accompanying
cut. The rudimentary horns, at first barely no-
ticeable as the faintest convexities of the skull
invariably appearing at the junction of the
frontals and nasals, and produced by a thicken-
ing of the cellular spaces, are first observed of
equal size in the males and females; later they
become more prominent in the males than in the
females; finally they assume vast proportions in
the males and present an arrested development
in the females. At the summit of the Eocene
the extreme dolichocephalic and brachycephalic
phyla die out, and in the Oligocene a new series
of phyla arise. Among these the long-horned
forms appear through selection to develop the
horns at the expense of other characters, the
males with the longest horns probably securing
the most females and becoming the chief breed-

248 DARWIN AND PALEONTOLOGY

ers. It is especially noteworthy that in these
long-horned phyla the main incidence of selection
seems to be diverted to the horns from the teeth
which appear to be dwarfed or arrested in evolu-
tion. In the short-horned phyla, on the other
hand, including one series at least, protected by
more slender limbs and more rapid movements,
the teeth are constantly sharpened and improved;
this may be interpreted as caused by the selection
of changes of proportion in the teeth.

The teeth, however, of all these phyla of
titanotheres are of a mechanical type which does
not admit of further evolution; they have reached
a stage which is a cul-de-sac," beyond which no
progress is possible. The change of environment
and of flora, therefore, finds these animals inca-
pable of further mechanical betterment either
through heredity or through the selection of vari-
ations of proportion. All the titanotheres be-
come suddenly extinct, and it is noteworthy that
all other herbivorous quadrupeds having this cul-
de-sac type of grinding tooth also became extinct
in North America and in Europe either during
the Oligocene or Miocene periods.

This is an outline of the only theoretical inter-
pretation which can be offered at present. In it
heredity, ontogeny, environment, and selection
are supposed to be in continuous interaction or

1 Osborn, H. F.: “Rise of the Mammalia in North America.”
Vice-Presidential Address before the American Association for

the Advancement of Science. Section of Zodlogy. Madison,
Wis., August 7, 1893.

DARWIN AND PALEONTOLOGY 249

interplay. One feature has been omitted: that
is, that all the branches of all the phyla, with one
exception, show a continuous and progressive in-
crease in size. This increase in size is, however,
itself interpreted not only as a response to favor-
able environment, but also to the selection of he-
reditary variations in size due to the fact that
the larger quadrupeds are better able to stand
off the attacks of their carnivorous enemies.

CONCLUSION

This interpretation, finally, is seen to include
the codperation of factors recognized by Buffon,
by Lamarck, and by Darwin, except as to the
transmission of acquired characters, which is left
in doubt. There is, however, a new principle in
the “ mutation of Waagen ” or “ rectigradations
of Osborn,” unknown to Darwin and due to
causes entirely unknown to us at the present time,
and perhaps, as already intimated, unknowable.
In this connection it is interesting to recall the
comment of Aristotle* on the survival-of-the-
fittest theory (the bracketed insertions [ ] and
italics are our own) :—

“What, then, hinders but that the parts in Nature
may also thus arise [namely, according to law]. For
instance, that the teeth should arise from necessity, the
front teeth sharp and adapted to divide food, the
grinders broad and adapted to breaking the food into
pieces.

» Osborn, H. F.: From the Greeks to Darwin, 8vo, Macmillan
& Co., 1894, p. 55.

250 DARWIN AND PALEONTOLOGY

‘‘ [Another explanation may be offered.] Yet, it may
be said, that they were not made for this purpose [i.e.
for this adaptation], but that this [adaptive] purposive
arrangement came about by chance; and the same
reasoning is applied to other parts of the body in which
existence for some purpose is apparent. And, i is
argued, that where all things happened as if they were
made for some purpose, being aptly [adaptively] united
by chance, these were preserved, but such as were not
aptly [adaptively] made, these were lost and still perish,
according to what Empedocles says concerning the bull
species with human heads. This, therefore, and sim-
ilar reasoning, may lead some to doubt on this subject.

“It is, however, impossible that these [adaptive]
parts should subsist [arise] in this manner; for these
parts, and everything which is produced in Nature, are
either always, or, for the most part, thus [#. ¢., adapt-
ively] produced; and this is not the case with anything
which is produced by fortune or chance, even as it does
not appear to be fortune or chance that it frequently
rains in winter. . . . If these things appear to be
either by chance, or to be for some purpose, and we
have shown that they can not be by chance, then it
follows that they must be for some purpose. There is,
therefore, a purpose in things which are produced by,
and exist from, Nature.”

Paleontology at present seems to support the
philosophical contention of Aristotle, that when
we come to the minute slowly progressing in-
ternal changes, the fittest originates in law.

EVOLUTION AND PSYCHOLOGY
BY
G. STANLEY HALL

DARWIN’S CONTRIBUTION TO PSYCHOLOGY

Tue contributions of Darwin to psychology.
have not been adequately recognized. Not only
in his famous seventh chapter on “ Instinct ” in
the Origin of Species; in the second and third in
the Descent of Man, comparing the psychic pow-
ers of men and animals; in his Ewpressions of
Emotions, and in Domestication, but sometimes
in other works, he not only showed a depth of in-
sight into, but laid anew the foundations of,
genetic as well as comparative psychology. These
should, and I believe will, eventually make him
regarded as hardly less the founder of a new
departure in this field than in that of classifica-
tion, form, and structure. For him the soul of
man is no whit less the offspring of that of ani-
-.mals than is his body. Our psychic powers are
new dispensations of theirs. The ascending
series of gradations is no more broken for the
psyche than for the soma. The gaps are no
wider or more numerous from the lowest to the
highest in the one than in the other. The affini-

ties and analogies are as close, and the soul in-
251

252 EVOLUTION AND PSYCHOLOGY

herits as much from our venerable, brute for-
bears as does the body. The rudiments are as
numerous and, to those who can rightly interpret
them, as significant. From the higher anthro-
poids, we need to go down the evolutionary stage
but a little way to span an interval quite as great
as that separating even the existing great apes
from the lowest savages.

But Darwin’s method is always and every-
where objective and observational, never sub-
jective or introspective. ( Few who have ever
written about the mind of man know or say so
little about consciousness, which has spun its
Merlin spell of enchantment about our craft and
allits works and ways. His language is the con-
crete facts of life and mind, and not the categories
and intuitions that an ingrowing intellect loves
to manipulate. The brute soul explains that of
man, rather more than man explains the brute;
the unconscious explains the conscious and not
conversely. He posits a natural history rather
than a philosophy of mind. As Steinthal said
language could be studied only historically—
“* Sie ist was sie geworden ”—so for Darwin the
true, ultimate knowledge of our psyche is the de-
scription of all developmental stages from the
amoeba up; and those move most surely among
the altitudes who have most carefully explored
the depths in which the highest human powers
originate. Emotions are best studied in their
outward expressions in gesture, will is investi-

EVOLUTION AND PSYCHOLOGY 253

gated by the study of behavior, intelligence by
massed instances of sagacity, and not by analysis
under old rubrics. While he would have wel-
comed all the illuminating experiments and tests
under controlled conditions, which have lately
given us such a wealth of insight, he would prob-
ably have preferred careful observations of ani-
mals afield in their accustomed habitat. Let us
psychologists find in this celebration motivation
to re-read his masterful contributions to our sci-
ence, for nothing in our perhaps all too copious
literature so grows upon the mind by frequent
reperusal; and thus only shall we profit to the
full, as we have been tardier than the biologists
in doing, by the method, direction, and inspira-
tion he so abundantly offers us.

GENETIC SYNTHESIS THE NEED OF MODERN
PSYCHOLOGY

Probably most psychologists in our day accept
evolution in a general way and have only praise
for Darwin; yet I can think of but very few
whose interest in the studies of the soul is pre-
dominately evolutionary or very much influenced
even by Herbert Spencer. Students of instinct
have profited most here, although many of their
studies are made under artificial and highly-
specialized aspects, with too little reference to
life history and habits of the species in the state
of nature. The human mind is, for the most
part, now studied introspectively, not only by the

254 EVOLUTION AND PSYCHOLOGY

literary psychologists but in the laboratory,
which is more and more regarded as a method
and microscope of subjective analysis. Even
Wundt approached psychology from the stand-
point of physics and physiology, and his great
text-book would have been but very little differ-
ent had Darwin never lived. The doctrine of
apperception and even of feeling, with its recent,
labored, introspective discussions of peripheral
versus central origin and tri-dimensional theories,
very rarely considers any developmental aspects;
and this is one reason why, as has lately been so
ably pointed out, neither Wundt nor the other
standard text-books offer any aid to the student
of abnormal psychology or of instinct.
Meanwhile, our science has had a prodigious
and sudden horizontal expansion far beyond the
old themes and limits. We have a psychology
of religion, with a more special literature on such
subjects as conversion, atonement, faith, posses-
sion, holy spirit, inspiration, immortality, proph-
ecy, prayer, Sabbath, and even the process of
dying, sin, and demonology. Then there is the
new psychology of crime, under its special ru-
brics, murder, theft, arson, rape, suicide, fraud,
and swindling, with traits of the chief classes of
criminals. Hypnotism and suggestion, not to
mention ghosts and telepathy, have opened an-
other field. Then we have the psychology of
sex in its normal and morbid manifestations,
psychic differences, eugenics, and moral prophy-

EVOLUTION AND PSYCHOLOGY 255

laxis. There is the psychology of language, ges-
ture, music, imitation, social instincts, truthful-
ness, infancy, childhood, adolescence, pedagogy,
property, play, genius, and prodigies, sleight-of-
hand, advertising, war, second breath, leader-
ship, provincialism, business and panic, psy-
chic epidemics, and many more, not to speak
of the long list of admirable studies of excep-
tional individuals from Helen Keller to Miss
Beauchamp, Flournoy’s Mlle. Smith, Beers,
Monod, and Mrs. Piper. Instead of restricting
himself to the classic, old themes of memory, as-
sociation, logic, freedom of the will, conscience,
in more or less academic seclusion and aloofness,
the modern psychologist is often consulted by
parents, pedagogues, lawyers, legislative com-
mittees; lectures before popular audiences; or
writes books and articles in a catchy, impression-
istic style, with great attention to phrase-making.
( Thus, present themes are so absorbing, so many
and so new, that if we are not beginning to
lose sight of each other, we have lacked time and
incentive to keep posted and interested all over
the field, until now the task has grown beyond the
ability of any one less gifted than Darwin to mas-
ter details, see perspective, and mosaic items into
true, evolutionary order which can alone bring
unity into this teeming but now chaotic domain.
The material for perhaps the most majestic struc-
ture yet reared by science is already quarried.
The need of and call for a master builder in this

256 EVOLUTION AND PSYCHOLOGY

field must, ere long, produce the man. Some of
us are already convinced that the human soul in
all its power is just as much a product of evolu-
tion as the body; but our faith needs to add the
knowledge that can only come when all the au-
thentic data are properly grouped. That the
impending synthesis must be genetic, not in the
prolix and platitudinous sense of Spencer, but
with concrete facts as warp and woof, is inevita-
ble if the psychology of the future is to correlate
the facts of instinct, of daily human life with all
its hot and intense impulses and all its morbid
manifestations, and so become the Bible of the
soul of man, in a sense our current, fragmentary
systems do not dream of—this seems to me to be
self-evident.

RUDIMENTARY PSYCHOSES

The signs and foregleams of such a recon-
struction and transvolution are already many.
In abnormal psychology, devolution is a rubric
of increasing dominance. The Jacksonian the-
ory of epilepsy brings in the genetic perspective
in its conceptions of higher and lower levels.
The studies of sex perversions are replete with
references to the past history of the race, and
some of them can be explained only as reversions,
as in the case of the impulsions to nudity and ex-
hibitionism. Many of the psychic facts in hu-
man courtship point directly to that of animals.
Some of the laws of the long-circuiting of the

EVOLUTION AND PSYCHOLOGY = 257

genesic instinct into secondary sex qualities are
the same for brute and man. The more we know
of this instinct the more orderly and unbroken
becomes the progression upward and the closer
the parallel. Even the differences are more and
more explicable. The same is true of the care
of the young, where the basal phenomena are
common to all the higher mammals, and some of
them to all viviparous creatures. Again, the cor-
respondences between adolescence and senescence
are, in some cardinal points, strangely comple-
mentary. Here, too, should be mentioned the
striking morphological, pathological, and psychic
indications from the study of childhood that
puberty once came much earlier in our forbears,
the autogenetic inferences in this direction, how-
ever, being as yet too slightly supported by phy-
letic facts, on account of the necessary imperfec-
tions of the record. Perhaps best of all as an il-
lustration is the new psychology of crime and
criminals, who are so shot through, body and
soul, with atavisms that only the early history of
the race can explain them.

Again, if we eliminate from the later studies
of mental diseases, all the evolutionary elements
and suggestions, they would be robbed of no lit-
tle value. I refer especially to psychasthenic and
dissolutive states, to certain of the phobias, fuges,
imperative ideas, to various eruptive or fulminat-
ing phenomena and psycholeptic crises, and to the
formation of the more or less subconscious con-

258 EVOLUTION AND PSYCHOLOGY

stellations of psychic elements, which may act
like foreign bodies in the soul, and some of which
are peculiarly suggestive of atavistic or outgrown
states. Here, too, belong many phenomena of
hypnoidization with more or less psychic decapi-
tation—Verdichtung—(which probably repre-
sents a type of psychoses that are peculiarly
characteristic of prehistoric man, who ejected
his subjective states much as Freud thinks that
dreamers are doing, to say nothing of the latest
studies of phonisms, photisms, and coenesthesias.
It is studies in this field, it may also be men-
tioned, that have led acute minds, like Bleuler,
to violent polemics against consciousness as the
muse of modern psychology, some of them insist-
ing that but little of the experience that has made
the mind in its human form has been connected
with either consciousness, apperception, or even
attention. The view is unquestionably gaining
ground that consciousness is an epiphenomenon
of mind, and that its function is essentially no
less remedial or cathartic than the church has
held confession to be, though in a somewhat dif-
ferent way. There is no better test of a psycho-
logical system than its applicability to psychi-
atry; and it is here that Wundt so signally fails,
for his fundamental assumption is that conscious-
ness is the condition of all psychic experience,
and he defines even feeling as a “ subjective reac-
tion of consciousness.” In fact, on the contrary,
there are incessant and manifold affective and

EVOLUTION AND PSYCHOLOGY 259

other processes going on in us that lack conscious-
ness, although they often resemble it in them-
selves and in their influence upon us, and which
can not be ignored because they often dominate
psychopathic symptoms and also our normal
lives. These are processes which become con-
scious only when associated with the ego-com-
plex. Many sudden choices, movements, feelings
of anger and fear, and many other experiences
Sometimes lack all intellectual motivation as
much as do melodic haunts. It is such states and
activities, possibly mediated by sub-cortical areas,
that irresistibly suggest past evolutionary stages
of mentation, and it is also this group of under-
lying processes that may put on and off suc-
cessive, conscious personalities as garments. It
is these deep yet dominant complexes that love,
hate, shape many currents of conduct, before con-
Sciousness is aware of it, and which are constantly
reinforcing and approving or censuring what con-
sciousness does. They suffer or rejoice sometimes
with, sometimes without, consciousness, which is
only their very imperfect instrument. Per-
haps nothing is ever fully conscious, while much
that takes place in us may be wholly unconscious.
To say with Raimann that “there is no uncon-
scious knowledge ”’; or with Hellpach that “ psy-
chology deals only with consciousness,” and that
“the unconscious can not be an object of knowl-
edge,” is a form of psycho-physic parallelism that
amounts to obscurantism; while to urge, as we

260 EVOLUTION AND PSYCHOLOGY

must, that even attention may be unconscious
would shock even an alienist so speculative as
Ziehen, who persistently identifies the psychic
with the conscious.

PSYCHIC “ RECAPITULATION ”

( Hardly less than animal instinct, child psy-
chology, as Darwin in his famous observations
on infancy, although not the first was perhaps the
third to see, can only be explained on an evolu-
tionary basis.} The child, uncivilized and to some
extent even savage, is precociously thrust into
an environment saturated with adult influences
because of language and accumulated grown-up
customs, traditions, and ideas; and for this rea-
son as well as because of its intense, imitative pro-
pensities tends to be very early stripped of many
of its psychic rudiments and _ recapitulatory
traces. Yet the more we know the child, the
more clearly do we see the germs of many ata-
vistic tendencies nipped in the bud, though many
of them have so long been. There can no longer
be any doubt that the human infant not only
tends to but occasionally does develop real words
that are its own original creation, products of the
rudiment of the same instinct in which language
took its first rise. This vestige is thus not com-
pletely eliminated by the early, mimetic adoption
of the speech of the environment. I have col-
lected from the literature over two score of these

EVOLUTION AND PSYCHOLOGY 261

words which, I believe, can not possibly be ex-
plained as imitations, and which have been used
consistently by the child for some time and occa-
sionally for a number of years. So in infantile
drawing we have undoubted, though dwindling,
traces of what Verworn calls the physioplastic
stage of paleolithic man, before the idioplastic
stage of the neolith, who ceased to draw directly
from the object itself but rather copied his own
mental image of it. Here, again, a well-recog-
nized phyletic stage has dwindled to little more
than a filmy vestige in the modern infant, but is
as recognizable as the rudimentary gill-slits in
the embryo. The swimming, paddling move-
ments, too, by new-born infants if supported in
tepid water; the wonderful power to cling and
support the weight for a minute or two during
the first few weeks after birth, a power soon lost
but reminscent of arboreal life; the phobias of
infants of a few weeks or months seen often in
nervous shudders at the first impressions of fur,
big teeth and eyes; the joy experienced by toss-
ing and other levitation movements, creeping,
and the processes of assuming the erect position;
the very intricate and interesting stages of the
progressive acquirement of the complex sense of
self; the loud cry of the human infant from birth
on as contrasted with the silence of the new-born
of other animals, so eloquent of the early power
of the parent to protect; and for older children
fetishisms galore, gangs corresponding to the

|

262 EVOLUTION AND PSYCHOLOGY

primitive tribes, propensity for hunting, killing,
striking with clubs, pounding, stealing, etc., the
sense of the power of the point, edge, string, and
many forms of plays and toys, the nascent sense
of death, and other items far too numerous to
even catalogue here—all show that the child is
vastly more ancient than the man, and that adult-
hood is comparatively a novel structure built
upon very antique foundations. The child is
not so much the father of the man as his very
venerable and, in his early stages, half-anthropoid
ancestor. There can no longer be any question
that its rudimentary psychic organs are no whit
less numerous than the half-score of anatomical
rudiments that Wiedersheim enumerates. Per-
haps, in general, the traces of the psychic reca-
pitulation of the history of the race are most
traceable and most unbroken, faint as some of
the traces are. Psycho-genesis, like embryology,
shows many rudiments preserved and developed
by being diverted to other than their original
uses, although of very few psychic traits or func-
tions have there been adequate material methods
of record and preservation as structural details
are preserved; nevertheless, they follow the same
lapidary law and speak a language which, when
it is set down and interpreted, is no less clear and
certain.

In general, nearly every act, sensation, feel-
ing, will, and thought of the young child tends
to be paleopsychic just in proportion as the child

EVOLUTION AND PSYCHOLOGY 263

is let alone or isolated from the influence of
grown-ups, whose presence always tends to the
elimination of these archaic elements, and in all
cases makes havoc with them, over-repressing
some that should have their brief fling, if only
on the principle of the Aristotelian catharsis, to
give early immunity from the hypertrophy of
bestial traits by awakening the next higher pow-
ers that repress them in their nascent period; but
which, in some environments, are left to grow into
faults and then into juvenile crimes, which they
are prone to do just in proportion as the order of
their nascency is perverted. Thus the problem
of a true mentally, esthetically and morally or-
thopedic education still gropes in the trial and
error stage, although not without some progress
toward a scientific basis for pedagogy which, if
it ever comes, can rest on no other foundation
than a well-established embryology of the soul,
all the way from eugenics and the psychic states
and regimen of pregnancy on to the fully ma-
tured nubility of the offspring. Thus, from one
point of view, infancy, childhood, and youth are
three bunches of keys to unlock the past history
of the race. Many of the keys, especially those
which belong to the oldest bunch, are lost and
others are in all stages of rust and decay. Many
of the phyletic locks which they fit are also lost
or broken; both locks and keys are often dis-
torted and, to change the figure, the sequences
which the race followed are often inverted in the

264 EVOLUTION AND PSYCHOLOGY

autogenetic processional of growth; but, if the
goal is still dim and far, it is unmistakable, and
as we slowly and surely approach it, the genetic
psychologist feels it beckoning, calling, and in-
spiring, almost like a new muse. This has intro-
duced a temporal perspective or new dimension
into a field where most preceding and even pres-
ent studies have all been in the flat surface of the
present state of adult consciousness. This is sup-
ported by, though still but very imperfectly cor-
related with, the studies of animal instinct on the
one hand, and with those of the myth, custom, and
belief of primitive races on the other. It already
suggests to the many laboratory studies of the
affective life (based on the method of controlling
the conditions of very slight variations of emo-
tional tone exigously made and based only ona few
adult experts), a more excellent way, which would
tend to bring psychology back to the study of
human life as it is lived out, where it is hottest,
most intense and passional with love, anger, fear,
hate, jealousy, grim and dour struggles with sin,
wrought out with sweat, blood, and supreme
effort, with perhaps the life and death of the indi-
vidual or even the race at stake. Here, rather
than in the isolation of the laboratory or the
study, lies the heart of a psychology that touches
life and that really avails and has worth and
value, because it is in line with the eternal pow-
ers and is, in a word, a true, natural history of
the soul, and can make “ philosophy ” again, as

EVOLUTION AND PSYCHOLOGY 265

the motto of one of our best-known culture fra-
ternities has it, “ the guide of life.”

THE PSYCHOLOGY OF THE FUTURE

Finally, education, now perhaps the most uni-
versal and uniform of all the social institutions,
is now looking to psychology for guidance as
never before, and we are at present able to meet
this call in only a halting and partial way. Re-
ligion seems of late to be becoming strangely
docile to all the too little we have to teach it.
Psychiatry, to which we should have at least
given a science of normal psychic life, is now in
danger of finding our texts of little avail in solv-
ing its problems, is building new foundations of
its own, and growing weary of our sophistic sub-
tleties concerning parallelism and interaction and
the nature of feeling, conscience, etc. Few, even
of our recent experimental results, are available
for determining or influencing normality or ab-
normality; our discussions of freedom, necessity,
or responsibility are too academic for use in crim-
inology. The great newly discovered continent
of the unconscious is still regarded by many mem-
bers of our guild as mystical, perhaps superlim-
inal, and its phenomena are used to cast augu-
ries as to whether the soul is independent of or
survives the body. The unconscious is really
like the submerged eight-ninths of an iceberg,
which is impelled by deeper currents in a denser
medium, and which the glittering summits that

266 EVOLUTION AND PSYCHOLOGY

emerge above the tide and are impelled by only
atmospheric pressure have little control over.
And once more, just as psychiatry is now chang-
ing its emphasis from a predominantly somatic
and neurological basis, which has been so fruitful
under the old slogan of Virchow, “ Ubi est mor-
bus,” to a more psychic, pathological viewpoint,
so perhaps even the doctrine of heredity is com-
ing our way by changing the terms applied to its
elements from the mystic, pathological ids and
determinations of Weismann to Semon’s no less
mystic but psychological postulates of mnemes
and engrams. Here, too, we are hardly ready to
meet the new demands or utilize the new princi-
ples, because our department is still, despite its
great, recent progress, only half scientific and is
not unlike Milton’s new-born tawny lion pawing
to get away from the metaphysical and theolog-
ical soil from which it sprang. We have too
long yielded to the seductions of the heterai of
the ancient, speculative problems that have ob-
sessed us and not yet definitely broken with those
in our midst who still urge that psychology
should be developed in the closest rapport with,
if not under the influence of, a speculative phi-
losophy.

Finally, as Darwin freed biology from the in-
veterate dominance of the ideas of fixed and
divinely created species, conceptions directly in-
herited from Plato’s ideas and Aristotle’s cate-
gories, so everything in the present psychological

EVOLUTION AND PSYCHOLOGY 267

situation cries out for a new Darwin of the mind,
who shall break the persistent spell of theoretical
problems incapable of scientific solution, the ideal
of a logical and methodical exactness greater
than our subject in its present stage permits of,
which Aristotle well dubbed pedantry, and re-
mand the haunting problem of the ultimate
nature of consciousness and the final goal of the
psyche to the same limbo, by suspending convic-
tions, as those of the constitution or cause of
energy and the nature of reality and objectivity.
Only by so doing can we again get up against the
essential facts of life as it is lived out by the toil-
ing, struggling men, women, and children, nor-
mal and defective, of our day. If this rough
diagnosis of the present situation is correct, only
a pessimist can doubt that the need will, ere long,
bring the man or the men to meet it in the only
way it can be met, viz., by a comprehensive evo-
lutionary synthesis in the psychological domain,
which by every token seems at present to impend.

INDEX

Acquired characters, inheritance
of, 34-43, 111, 112, 120-124,
137, 204-206

Adaptation, 41, 61-66, 213; ab-
sence of, 61-66, 85; in muta-
tions, 178; address on, 1892-
208; functional, 203

Adapted environments, 183, 186

Adapted faunas, 184

Adjustment, self-, 42; to en-
vironment, 116

Acassiz, Alexander, theory of
coral islands, 9

Acassiz, Louis, unfavorable to
Darwin, 27

Albinism, 155, 169

ARGYLL, Duke of, views of, 45

ARISTOTLE, quoted, 249

ARRHENIUS, on origin of mat-
ter, 46

Artificial selection, 74; isolation
in, 85

Aster, evolution of genus, 58, 59

Atheneum, review of Origin in,
20

Barter, on pouched gophers, 76

Batpwin, J. M., organic selec-
tion, 10, 48; effect of social
environment, 30

Barriers in species formation,
81, 84

Bates, H. W., hypothesis of
mimicry, 47

Bateson, W., variation in Kal-
lima, 178; variation, 224-227

Beagle, voyage of the, 8, 11, 12,
192, 215

Beccari, theory of evolution,

3

Beetles, experiments upon, 124

Bentuam, 19

Blind fishes, 189, 190, 200

Bromerrexp, L., word “ muta-~
tion,” 43

Bowwner, C., forerunner of pan-
genesis, 95

Botany, debt to Darwin, 57

Boveri, T., chromosome theory,
103, 104

Brachiopoda, 210, 211

Bratnerp, E., violets, 166

Brown, R., 18

Bud-sports, 130

Burron, 31, 215, 249; adapta-
tion, 193, 204; evolution, 20;
pangenesis, 95

BourcHetr, W. J., 19; feelings
in forest, 38; isolation, 30

Cartyte, Mrs. on Owen, 31

CarrEenTER, 19

Castie, W. E., address by, 143-
159

Catfishes, 200

Cathedrals as awe inspirers, 36,
37

Cave faunas, 184, 186-190

Cell, in heredity and evolution,
92-113

Cuamperiin, T. C., address by,

Cuampers, R., evolution doc-
trine, 20

Characters, acquired (see: Ac-
quired characters); new, 58-
61, 223-233; origin of, 58-61;
unit (see: Unit character)

Characins, 192-196, 203

Chemical nature of heredity,
107, 163, 180

Chromatin, 99-104

Chromosomes, in fertilization,
100, 103; radium on, 129, 138;
réle of, 107

Climbing plants, debt to Asa
Gray, 29

Cognate species, 81

Coleoptera, experiments with, 12

Color, mendelian phenomena in,
108, 152, 153

269

270

Combs of cocks, 127, 171

Continuity of germ-plasm, 35

Continuous evolution, 48-50

Corr, E. D., 9, 215, 229, 232

Coral islands, Darwin’s theory
of, 46

Correns, C., rediscoverer of
Mendelism, 145

Covers, E., quoted, 78

Covtter, J. M., address by, 57-
vel

Crime and evolution, 256

Crocker, W., work on seeds, 62

Cuvier, G., 215

Cytoplasm in heredity, 101

Dana, theory of coral islands, 9
Darwin, C., 249; influence, 1;
early life, 11; first attention
to evolution, 7; first sketch of
Origin, 13; prepares for pub-
lication, 18; maturity of the
Origin, 23; thrilled by anthem,
38; on Leicester sheep, 76; on
isolation, 87; on mutation,
43-45, 163-165; work on galls,
131, 1382; on black peacock,
169; adaptation, 193; rela-
tion to paleontology, 212;
psychology, 251-254, 260; let-
ters: Huxley, 10; Owen, 31;

Wright, 32; Leidy, 209;
Davidson, 210
Darwin, Erasmus, Zoonomia,

10; evolution, 20

Darwin, Francis, on acquired
characters, 39; presidential
address, 39; letter about galls,
132

Davenrort, C. B., address by,
166-181

Davinson, L., letter from Dar-
win, 210

Definite variations, 231

De Vas, H., 242; intercellu-
lar pangenesis, 93, 106, 144;
premutation period, 132; re-
discoverer of Mendelism, 145;
mutation theory, 160, 229;
cessation of selection, 174;
adaptation, 193

Differentiation and cytology,
105

Directed variation, 236

INDEX

Discontinuous evolution, 48,
140, 180, 227, 228
Dotzo, L., 229

Ecology, 61

Edinburgh Review, article by
Owen, 31

Education and evolution, 263,
265

Effect of Origin, 54, 55

Eicenmann, C. H.,
182-208

Ermer, T., orthogenesis, 193

Elementary species, 166

Elimination, 176, 177

Emotions and evolution, 251

Entelechy, 110

Environment, adjustment to,
117; factor in evolution, 244

Enzymes in heredity 106-109

Evening primrose, 130, 133, 165-
166

Evolution first brought to Dar-
win’s attention, 8; of Gymno-
sperms, 66-70; isolation in,
72-91; cell in relation to, 92-
113; réle of environment in,
114-142; and psychology, 251-
266

Experimental morphology, 61

Extra-floral nectaries, 63

External factors, 115, 126, 197-
207, 238, 239

address,

Factors of evolution, 238

Factor hypothesis in heredity,
108, 115, 150-158

Farrer, Lord, letter of Dar-
win to, 25

Fawcett, H., defense of Dar-
win, 8; letter to, from Dar-
win, 21, 22; review of Origin,
22, 34

Ferments in heredity, 106

Fertilization of egg, 108

Fiscuer, E., experiments, 123

Fiske, J., evolutionary teaching,
9

Firron, 19

Fluctuation, limit to, 49, 173-
176; in isolation, 85, 173

Forses, E., coral reefs, 46;
views on arctic relics antici-
pated by Darwin, 46

INDEX

Forses, S. A., quoted, 167

Forests, excite feeling, 36

Forms of Flowers, dedicated
to Asa Gray, 29

Fortuitous variation, 226

Freshwater fishes, 184

Frevp, 258

Gacz, S. H. and S. P., experi-
ments, 121

Gacer, C. S., experiments with
radium, 128, 138

Gauitz0, effect of teaching, 55

Galls, vegetable, 131

Gatton, F., effect of Origin,
52; experiments on pangen-
esis, 145

G&rtner, hybridization, 52, 53

Gaunry, 215

Geminate species, 81

Gemmules, 95, 96

“Genesis of Species,” 32

Genetic synthesis in psychology,
253

Geographic convergence, 199,
201; distribution, 73; varia-
tion, 181, 196-198

Geologic convergence, 200, 201

Germ-plasm, continuity of, 35,
40; influence of soma on, 120

Goats, 164

Gooseberry, cessation of varia-
tion, 176

Gosse, P., Omphalos, 15, 16

Graduated tharacters, 127

Gray, A., defense of Darwin,
8; friendship with Darwin,
26-29; Darwin’s opinion of,
26; correspondence with Dar-
win, 31, 44

Grecory, W. K., 243

Grove, Dr., interviews Tenny-
son, 15

Guinea-pig, 148, 149

Guuick, J. T., 193

Gurney, E., letter of Darwin
to, 35

Gurnrim, C. C., experiments,
205

Gymnosperms, phylogeny, 60;
evolution without utility, 66

Haxcxet, E., on pangenesis, 40
Hair, 151, 170

271

Hatt, G. Stantey, address by,
251-267

Hat, James, the fossil record, 9

Hatter, cessation of improve-
ment in wheat, 48

Hetipacnu, 259

Henrrey, 19

Henstow, J. S., friendship with
Darwin, 11; opinion of Lyell’s
Geology, 12; letter of Darwin
to, 36

Heredity (see also Inheritance),
chemical nature of, 110; and
memory, 112; determination
of, 114; unit characters in,
143-159; of mutations, 171;
factor of evolution, 244

Henrine, on heredity, 39

Hertwic, O., the nucleus in
heredity, 99

Hiutcenporr, work of, 214

Hormeister, on plant relation-
ships, 57

Hooxer, Sir Josern, defense of
Darwin, 8; advice asked by
Darwin, 18; presents papers
of Darwin and Wallace, 18,
19; utility, 25; friendship with
Darwin, 25, 26; letter of Dar-
win to, about Mivart, 32;
about pangenesis, 39; about
limits to artificial selection,
48; coral reefs, 46; letters
from Darwin, 51, 94, 131

Hooxer, Sir Wittr1am, letter
from Burchell to, 38

Hormones, 106, 109, 112

Horns, 147, 164, 170, 240, 247

Horner, L., letter to, 12

Horse, 175

Humsotpt, Darwin on, 36

Hoxtey, T. H., 215, 224; letter
of Darwin to, 10; friendship
with Darwin, 29; reviews
Origin, 33; effect on study
of biology, 53; on coming of
age of the Origin, 54; op-
posed to pangenesis, 93

Hyatt, <A. controversy with
Darwin, 9; the fossil record,
9; work of, 212, 213, 231

Hybridity, and selection, 52;
characters swamped by; 141,
179

272

Idioplasm, 99

Inheritance of acquired char-
acters (see Acquired char-
acters)

Intelligence and evolution, 253

Intercrossing, checked by isola-
tion, 75

Internal secretions, 109, 112

Intercellular pangenesis, 93

Island faunas, 81

Isolation in evolution, 72-91;
réle of, 75-80; and differenti-
ation, 198

James, W., leader of American
psychology, 10; quoted, 224
Jorpan, Davin Srarr, address

by, 71-91

Kallima, 177

Karyokinetic division and he-
redity, 103, 104

Kinestry, C., quoted, 16

Korrevrter, hybridism, 52

Kowatevsxy, 200, 215

Lamarck, 215, 249; debt to
Erasmus Darwin, 10; hy-
pothesis, 34, 35; adaptation,
193, 204

Lane-Ciaypote, effect of fetus
extract, 107

Lanxesten, E. Ray, quoted, 29;
“homoplasy,” 240

Leaf-butterfly, 177

Lewy, J., 232; fossil record, 9;
correspondence with Darwin,
209

Lepidoptera, experiments upon,
123

Linnean Society, meeting for
Natural Selection papers, 18

Lizards, 200

Lorsy, J. P., 166

Lye.tt, Cuartes, influence on
Darwin, 12, 13, 29; presents
the papers of Darwin and
Wallace, 18, 19; prevents
Dawson’s review, 21; letter
of Darwin to, 45; coral reefs,
46

INDEX

MacDoveat, D. T., chemical
treatment of germ-cells, 110;
address by, 114

MacGrecor, experiments, 128

Mattuts, influence on Darwin,

11

Mammals, fossil, 213

Mammary glands, stimulated by
fetus extract, 107

Marsu, O. C., 9, 215, 218, 232

Marruews, a13

Maturation, 103

May beetles, 167

Memory in heredity, 41, 112

Menor, G., 145

Mendelism, 10, 144, 242; and
pangenesis, 40; and heredity,
100, 108, 152, 153

Metabolic activities, irritable re-
actions, 117

Mut, J. S., opinion of Origin,
22, 23

Mitotic division
102

Mivart, Sr. Georce, opposition
to Darwin, 31-33

Moore, Ausrey, quoted, 17

Morcan, Luoyn, organic selec-
tion, 10, 48

Mutter, Frrrz, defense of Dar-
win, 8; letter of Darwin to, 39

Morray, Anprew, crude theory
of, 24

Mutation, 202; bearing on pan-
genesis, 40; Darwin’s views
on, 43-46; origin, 111; ad-
dress on, 160-181; and adap-
tation, 194

Myrmecophiles, 63

in heredity,

Nice, theory of evolution, 25;
idioplasm, 144, 146; adapta-
tion, 193

Natural selection, 206; theory
of, 10; discovery of, 11; pecu-
liarities of, 14; opponents of,
24; claimed by Owen, 31; in
relation to mutation, 47; to
hybridism, 52; to botany, 57-
71; implies segregation, 85;
not opposed to isolation
theory, 89; and mutation,
176; and adaptation, 192, 196

Neo-Darwinism, 161-163

INDEX

Neo-Lamarckism and paleontol-
ogy, 9, 237

Neumayer, 213, 231

Newton, effect of teachings, 55

er ue in heredity, 99, 105,

Nousssaum, M., 98

p’Orsieny, A., 12
Otiver, 19
CEERI factor of evolution,

Organic selection, 10, 48, 237

Origin of life, not a subject
for speculation, 46

Origin of Species, reception of,
2, 20-23; influence, 6; attacks
on, 51

Orthogenesis, 111, 197, 234-240

Orrmann, quoted, 77

Oszorn, H. F., 11, 213, 231;
fossil record, 9; theory of
organic selection, 10, 48; or-
thogenesis, 193; address by,
209-250

Owen, R., 31; evolution doc-
trine, 20; attack on Darwin-
ism, 30; characters of fossils,
232

Oxrorp, bishop of, attacks on
Darwinism, 30

Oxford University, 13, 33

Paleontology, address, 209-250

Pangenesis, 35, 39, 40, 92-97,
106, 144, 236

Parallel adaptations, 80

Peacock, black-shouldered, 169

Peas, 146

Pedagogy and evolution, 146

Penstemon, 135

Permanence of ocean basins, 46

Philosophie zoologique of La-
marck, 11

Picret, nutrition of egg, 121

Pigment, 147

Polyphyletic origins, hypothesis
of, 9

Poutron, E. B., 236; address
by, 8-56; Darwin’s views on
variation, 217

Poultry, 168-174

Psychical nature of develop-
ment, 109

273

Psychiatry, 265
Psychology and evolution, 251
Pterydophytes, 70

Rabbit, 149-159

Rast, C., 103

Radium, effect on germ-plasm,
127-130

Raimmann, 259

Recapitulation in psychology,
260

Rectigradation, 231, 234, 239,
242

Regeneration, Darwin on, 39, 97

Religion, 265

Remax, germinal continuity, 98

Repetition of stimuli, 122

Reversion, 151, 152

Ruwozz, O., experiments, 121

Rodents, variation of, 76

Roentcen’s rays, experiments
with, on germ-plasm, 127

Romanes, G. J., Darwin’s con-
scientiousness, 36

Rovx, W., significance of mi-
tosis, 103

Sarnt-Hinarre, 229

Saltation, Darwin on, 165

Scorr, J., letter from Darwin
to, 53 y

Scorr, W. B., fossil record, 9;
quoted, 200, 213

Secretions, internal, 112

Sevewicx, A., friendship with
Darwin, 11; criticises Dar-
win, 21

Seeds, origin of, 60; unadaptive
characters in, 62

Segregation, types of, 72; neces-
sity of, 87

Selection, 216-223, 244; artifi-
cial selection, limits to, 48;
role of, 59-61; cessation of,
48, 174

Selective migration, 185, 190

Self-adjustment, 42

Semon, R., on heredity, 39, 266

Sex, 104

Shade foliage and heredity, 42

Sheep, isolation and develop-
ment of races, 74-76, 86

Snot, G. H., 166, 197

Skull, 221

274

Solutions, effect on germ-plasm,
131-137

Spencer, H., 212, 253, 256;
evolutionary teaching, 9

Sporophytes, origin of, 60

Sranpruss, M., experiments, 123

Sraruine, injection of fetus ex-
tract, 107

Srraspurcer, nucleus in hered-
ity, 99

Struggle for existence, 203

Sublime, feelings of, 35, 38

Swamping effects of intercross-
ing, 179

Teeth, 219, 232-234, 241,242, 248

Temperature, check on migra-
tion, 186

Tennyson, A., the struggle for
existence, 14-15

Teratological characters, 173

Testic extract, effect of, in-
jected, 107

Thyroid extract, effect of, 107

Titanotheres, 242-249

Tower, W. L., modification of
germ-cells, 110, 125-127, 197

TscHERMAK, E. v., rediscoverer
of Mendelism, 145

Tynpatt, J., effect of Origin,
54

Unit characters, 143-159; and
mutation, 160, 161

Use and disuse, inheritance of,
35

Variability, somatic, in response
to environment, 118

Variations, small, 217, 220, 222;
large, 217

Vestiges of Creation, 31

Verworn, M., 261

Vincuow, R., germinal continu-
ity, 98

Waacen, W., 249; orthogenesis,
193; mutation, 211, 229-233,
242; fossil series, 213

INDEX

Waener, M., on isolation, 72, 88,
89

Watcorr, C. O., the fossil rec-
ord, 9

Watxer, effect of testic extract,
107

Wattace, A. R., in New World,
7%; natural selection, 18; ad-
dress at Linnean Society’s
Anniversary, 19; coral reefs,
46; on isolation, 83

Warner, C. D., feeling of awe,
38

Weir, J. J., letter of Darwin
to, 33

Wesrwoop, J. O., proposes read-
er to combat Darwinism, 21

Weismann, A., 35, 40; under-
mined Lamarckism, 10; non-
transmissibility of acquired
characters, 10, 11; idioplasm,
144; quoted, 161, 162, 183;
adaptation, 193

Weismannism, 118

Wheat, limits to improvement,
118

Wueeter, W. M., insect mu-
tants, 166

Wuewett, Dr., excludes Origin
from college library, 21

Wurrman, C. O., orthogenesis,
193

WieversHerm, R., 261

Will, method of investigating
the, 252

Witson, E. B., address by, 92-
113; on chromosomes, 129

Wattaston, on wingless oceanic
beetles, 47

Woopwanrp, S., 229

Waricnt, C., defense of Darwin,
8; review of Mivart, 32-34

Wonprt, 254

X-rays, experiments with, on
germ-plasm, 127

ZIEHEN, 259
Zoonomia,
marck, 10

influence on La-

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