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THE RECAPITULATION THEORY
AND HUMAN INFANCY

BY
PERCY E. DAVIDSON, Pa.D.

ASSOCIATE PROFESSOR OF EDUCATION, LELAND STANFORD JUNIOR UNIVERSITY

TEACHERS COLLEGE, COLUMBIA UNIVERSITY
CONTRIBUTIONS TO EDUCATION, NO. 65

PUBLISHED BY
Teachers Gallege, Columbia University
NEW YORK CITY
1914

Copyright, 1914, By
Percy E. Davipson

ACKNOWLEDGMENTS

This paper was presented to the Division of Philosophy of
Columbia University as a doctoral dissertation. It was written
under the direction of Professor John Angus MacVannel, of
Teachers College, to whom is made grateful acknowledgment
of kind encouragement and valued suggestions. The writer
welcomes the opportunity of expressing his sense of an indebt-
edness of a fundamental character to the teachings and gen-
erosity of Professor John Dewey. Thanks are due also to
Professor J. Perrin Smith, of the Department of Geology in

Stanford Unversity, for his courtesy in reading the manuscript.
P.E. D.

ul

CONTENTS

CHAPTER I Paqe
INTRODUCTION x: 20.4 cen ar aNd noose Pus Reine ae eae GEE 1
CHAPTER II
Tae RecaPiroLaTIon Tazeory In Biotoay: A Sxetcu oF its History
Sec. 1. Other Names for the Theory............... cece eeeeeeeee 5
“2. Anticipations of the Recapitulation Idea.................... 5
33. “The “Theory of Ty pea) ick tensa dibs Sanens sha ceaw sh eares 5 7
>“ 4. Von Baer’s Law: The Law of Embryonic Resemblance....... 8
“5. The Correspondence Stated as Between Developmental Stages
of Existing Animals and the Succession of Adult Forms of
Extinct Representatives. Agassiz..............0-0ee sees 9
—> 6. Embryology and Darwinism..............00..ccee eee ee eens 11
BEL NTs DD AWM: od cosa g Gd allgneh 255 eae wate Coe os oa I HON Ea OE 11
«8. The Developmental-ancestral Correspondence Clearly Enunci-
ated: Fritz Miiller..... 0.2... ccc cee eee eee 14
—-f +9. “Ontogeny is a Short and Rapid Recapitulation of Phylogeny”:
Hacckelaudt wicucebvnwaietts uence aiies esas same kee eS he oe 14
© 10, | Herbert: Spencers :ses22 Sintea saves vidcn che eotisw a tense horas 20
“11. The Laws of Acceleration and Retardation................ 23
—$ 12. The Facts of Recapitulation................ 0. cece eee eee 238
<—> a. Those of Palaeontology. ........ 0.0. cc ccc cece eee 29
—“*p. Those of Embryonic Resemblance..................... 33
-—™x. Those of Comparative Morphology..................- 37
~? 13. Recapitulation and the Physiology of Development........ 41
“ 14. Biological Opinion Regarding Recapitulation................ 49
“15. Review and Summary............ 0. cece cece ee eee cece eee 57
CHAPTER III
Homan Inrancy and RECAPITULATION
suo.) Human Embryogeny......... 0... ccc ccc cece teen e en eee 62
fy. "The Theory” of: Infaney2ci3), «dia oa esd ca He RRR a 64
«3. Recapitulation and Human Infancy...................... 77
«4, Cultural Recapitulation............0. 00.02 cece cee ee eens 93
a CHAPTER IV
CONCLUSION ....... seaiee ys walaudd a4 nasi ne ee ouG en Sih aeeuly Saas Eat eas 99

THE RECAPITULATION THEORY
AND HUMAN INFANCY

CHAPTER I

INTRODUCTION

The strong interest in its biological and anthropological set-
ting which attended the beginnings of the systematic study
of childhood in this country has somewhat abated. Among
other things practical considerations have drawn attention
away to urgent matters of institutional management, while
newer and more exact methods, borrowed from the nearby
sciences, have been enthusiastically resorted to in the hope
of a more immediately serviceable knowledge of childhood
than any search into its history could reasonably be expected
to yield.

Doubtless this change of emphasis is a wholesome one. Ed-
ucation has still to find its most advantageous methods, if
indeed it has not yet to delimit its field. It is only right, then,
that all the methods which have done excellent work in the
sciences should be tested and evaluated for their usefulness
in its service. It would be a mistake, however, to regard this
departure from biology and anthropology as a final one, and
to conclude that education has nothing to learn from these
sources. Man’s animal heritage is too intimate a part of him,
and his historical career too significant of his make-up, ever
to justify a neglect of these things on the part of those who
propose to mould his present condition and in some measure
to direct his future.

It may be, too, that some sense of disappointment has figured
in this willingness of students of childhood to turn in new
directions. Fruitful as it was in suggestion, the older genetic
line of approach could not, in the nature of the case, lead to

1

2 The Recapitulation Theory and Human Infancy

a scientific basis for a practical educational program. This
could come only with the aid of an exact and faithful inter-
pretation of childhood as it exists in modern societies. HEd-
ucational schemes based upon historical inferences were there-
fore necessarily precarious and could easily be found unsound
when fairly tested. More especially has the older genetic
method of study suffered from the discredit into which some
of its guiding principles have fallen. One of these principles
was embodied in the theory of recapitulation, the idea that the
child in its development rehearses the history of its ancestry,
and that in consequence its nature may be inferred from the
probable course of human evolution. Taken bodily from em-
bryology, this idea was projected upon the field of mental gen-
esis, where it became a commonplace. More recently dis-
quieting rumors from the source of its origin have been heard
to the effect that the principle was formulated without suffi-
cient warrant, and that it cannot be depended upon even as a
helpful hypothesis. Its prestige has in consequence been ser-
iously damaged and there is plainly evident great uncertainty
as to the degree of truth it may contain.

This uncertainty with regard to a principle with important
implications for the theory of infancy and psychogenesis, is
hardly excusable or necessary. For recourse to the science
from which the principle was derived is open, and no obvious
reason exists why its real standing there should not be known.
If education is to be spared the humiliation which comes in-
evitably from building on the sand, it must earnestly endeavor
solidly to ground its doctrine. Especially is this true when
this doctrine is drawn from the pure sciences, for a thorough
knowledge of these on the part of outsiders is not easy of attain-
ment and a little knowledge is a dangerous thing. Moreover,
the position of education is peculiarly difficult, for as an art

, , its practice is not only dependent upon science as such; more

than one science is implicated. Education is none the less
in duty bound either to acquaint itself with the true value of
these borrowed principles or to leave them alone.

This paper represents an effort to discover something of the
status of recapitulation in biology and to note its implications
for the period of infancy. It makes no pretensions to scholarly
exhaustiveness. Its justification is the lack of any accessible

Introduction 3

account of the history and present position of the idea to which
students of psychogenesis may refer, and its one merit is that
it stands for a conscientious attempt to understand and report
some of the more obvious aspects of the discussion. At some
future time someone with the requisite knowledge of biology,
anthropology, and psychology will do full justice to the topic
and supply us with an authoritative account of the matter.
Meanwhile we can at least clear away the superficial obstacles
and prepare ourselves for the more complete statement.
No one can justly object to a desire on the part of students
of childhood to know its biological history and its nature in con-
sequence. It is at least a legitimate object of curiosity. More
than this, no situation ever failed to become more intelligible,
and so more amenable, in the perspective yielded by its history.
On the side of possible cultural homologies in infancy and child-
hood there is the chance of a more direct usefulness. Some
years ago Professor Dewey inquired pointedly as to what good
could come from a knowledge of the historical genetic order,
when an argument from it directly to the proper treatment of
growth is not warranted. And it must be admitted that there
are positive limits to the use of principles derived from this
source. Education must be based primarily upon a knowledge
of the ontogenetic order itself. But it appears already that the
ontogenetic order is not easy of discovery. Although childish
and youthful performances can be objectively described and
in many cases measured, the true inward significance of
these performances is determined with the greatest diffi-
culty, because it is ultimately a matter of interpretation. Is
it not possible, then, that a knowledge of historical processes
may have something to offer, not as principles upon which ac-
tion shall be based, but as cues and hypotheses with which to
approach the exceedingly intricate phenomena of individual
psychogenesis? Historical processes expressed themselves slow-
ly. They were made with difficulty and became registered
step by step in objective products which lie open the world
over for sympathetic inspection. If a warrant can be found in
general terms for some degree of correspondence between in-
‘dividual psychogenesis and social or historical development,
it seems not impossible that a close study of the latter order
may yield suggestions of real value with which to approach

4 The Recapitulation Theory and Human Infancy

the difficulties of the first. At least the possibility should not
be denied in advance of a fair trial. Obviously the resources
of child psychology would be immensely amplified if they might
include those of comparative psychology and ethnology. This
hope may stand as some justification for the present effort
to clear away some part of the obscurity which gathers about.
the relations of the child and the race. If this should be in-
sufficient there still remains the interest which attaches to a
knowledge of the net result of one phase of a significant pioneer
movement in the study of childhood.

CHAPTER II

THE RECAPITULATION THEORY IN BIOLOGY: A
SKETCH OF ITS HISTORY

1. Other Names for the Theory.

“This has been named by Hatschek the ‘morphogenetic
theory,’ by Hyatt the ‘law of morphogenesis,’ by Haeckel the
‘biogenetic law,’ by Cope the ‘doctrine of parallelism,’ and by
Morgan the ‘repetition theory.’ Sometimes it has been alluded
to as the ‘law of von Baer,’ but incorrectly, for von Baer was
its severest critic.’”’?

2. Anticipations of the Recapitulation Idea.

The idea that embryos of higher forms pass through the
adult stages of the lower animals is a very old one and no one
name is associated with its origin. The first clear reference
to it appeared at the end of the eighteenth and the beginning
of the nineteenth centuries. The system of classification then
in vogue was that of Linnaeus, which placed the various groups
one above the other in a single scale or series from the lowest
to the highest. In this scale the worms held the lowest rank,
and then in order, the insects, fishes, amphibia, birds, mammals.
The allusions to the animal series in the extracts which follow
are therefore to this uniserial system.

In these early expressions embryonic or developmental
stages were naturally found to resemble the mature forms of
existing lower animals, evolution as yet being a conception
of a very few prophetic minds. One of the earliest of these
expressions, however, was that of such a prophetic mind. Lor-
enzo Oken, a speculative evolutionist and a popularizer of the
science of the time, wrote in 1805,

“Each animal ‘metamorphoses itself’ through all animal
forms. The frog appears first under the form of a mollusk in
order to pass from this stage to a higher one. The tadpole

1 Montgomery, Analysis of Racial Descent in Animals, 1906, p. 177.
5

6 The Recapitulation Theory and Human Infancy

stage is a true snail; it has gills which hang free at the sides of
the body as is the case in Unio pictorum. It has even a byssus,
as in Mytilus, in order to cling to the grass. The tail is nothing
else than the foot of the snail. The metamorphosis of an insect
is a repetition of the whole class, scolopendra, oniscus, julus,
spider, crab.’”?

Later, in 1883, Oken wrote, in reference to the same matter,

“There is no doubt that we have here a striking resemblance,
and one that justifies us in thinking that the development in
the ovum is merely a repetition of the story of the creation of
the animal groups.’

Here, plainly enough, is a statement in crude form of the idea
of recapitulation which was to have clear definition with the
advent of the doctrine of descent, and which was destined to
play so important a role in the history of that doctrine.

The other early references to be noted make comparisons
of development with the rank of existing animals. Thus, Wal-
ther, in 1808, said,

“The human foetus passes through its metamorphosis in the
cavity of the uterus in such a way that it repeats all classes of
animals, but, remaining permanently in none, develops more
and more into the innate human form. First the embryo has
the form of a worm. It reaches the insect stage just before its
metamorphosis. The origin of the liver, the appearance of the
different secretions, etc., show clearly an advance from the
class of the worm into that of the mollusk.’’

The embryologist Meckel, in 1808, 1811, and 1821, gave
greater definiteness to these comparisons:

“He held that the embryo of higher forms, before reaching
its complete development, passes through many stages that
correspond to those at which the lower animals appeared to be
checked through their whole life. In fact the embryos of higher
animals, the mammals, and especially man, correspond in the
form of their organs, in their number, position, and proportionate
size, to those of the animals standing below them. ‘The skin is
at first, and for a considerable period of embryonic life, soft,
smooth, hairless, as in the zoophytes, medusae, many worms,
mollusks, fishes, and even in the lower amphibians.’’§

2Quoted by Morgan, Evolution and Adaptation, 1903, p. 59.

3 Quoted by Bolsche, Haeckel, His Life and Works, translated by J. McCabe, p.
227.

4 Quoted by Morgan, loc. cit., p. 59.

Ibid.

The Recapitulation Theory in Biology 7

Many other instances were given by Meckel, some fantastic
and absurd, others still to be found in the text-books on em-
bryology. It was this conception that met with the opposition
of von Baer, writing in 1828. Von Baer refers to

“The accepted idea, that the embryo in higher animals passeS
through the permanent forms of the lower. . . . This idea,
which was born in a time when, besides Malpighi and Wolff,
no connected investigations had been undertaken upon the
early periods of the embryology of any animal, and was especi-
ally carried out by a man who possessed perhaps the most
knowledge upon the embryology of the higher organisms, could
not help but arouse great support, because it was based upon a
multitude of special proofs. . . . Some supporters were so
zealous that they spoke no longer of similarity, but of complete
identity, and acted as though the correspondence were proven
universally and in each particular. We read a short time ago,
in a paper upon the blood circulation of the embryo, that the
human embryo does not omit a single animal form.’’é

“That,” remarks Montgomery, “‘must indeed have been the
luscious Springtime of the theory!”
Von Baer urged against the prevailing view of recapitulation

“(1) that no adult animal ever has a yolk sac, or (2) is sur-
rounded by embryonic fluids; (3) that it is not the case that an
embryo of a higher animal in each embryonic stage corresponds
in every point with an adult of a lower species, or (4) that in
the ontogeny of a lower form structural relations do not occur
which are found in the adult of a higher; (5) that it is equally
not the case that parts which are characteristic of only the high-
est forms appear latest in the ontogeny.’’?

3. The “Theory of Types.”

Recapitulation in its next phase became intimately involved
in that scientific theory of the natural world which preceded
the evolutionary or Darwinian conception now current, and
which stubbornly contested the claims of the latter until over-
whelmed by an incontrovertible array of fact. It is known as
the “theory of types,’’ and is associated especially with the
names of Georges Cuvier, Louis Agassiz, Johannes Mueller,
and Richard Owen. The conception has been analyzed and
traced to various sources by Merz in his “History of European

6 Quoted by Montgomery, loc. cit., p. 177.
7 Ibid, p. 176.

3 The Recapitulation Theory and Human Infancy

Thought in the Nineteenth Century.’’® Only its more general
character need be noted here. It was, in brief, the logical culmi-
nation of the progress of descriptive science following the Re-
vival of Learning. From independent beginnings, embryology
and physiology, comparative anatomy, geology and geography,
and botany, had by degrees and in unrelated ways accumulated
a vast amount of unorganized knowledge which by the first
quarter of the nineteenth century invited a general and unified
formulation. The outcome was a conception constituted in
part of inductions and analogies derived from the observation
of nature, in part of the literal biblical interpretation of the
overshadowing Puritanism of the time.®

In this theory the plan of arranging the animal groups in
a single scale or series gave way to a system in which the species
were regarded as modifications of four main ‘“‘types’’ or ‘‘em-
branchements,’’ independent and equivalent “plans of struc-
ture,’’ namely, the vertebrate, articulate, radiate, and mol-
juscan. The species representing these great types were
“fixed,” in the sense that they had been separately created
as they were found to be, and were in no wise genetically related.
The study of fossils and geological formations led to the addi-
tional idea that species had suffered extinction coincident with
colossal revolutions or catastrophes in the life of the planet,
succeeded by the creation of new types. Only by the intervention
of such episodes could be explained the succession of life forms
so unequivocally indicated in these phenomena.

4. Von Baer’s Law: “The Law of Embryonic Resemblance.”

ad

Von Baer was identified with the theory of types; in fact he
seems to have had some share in its formulation, although he
did not go to the extremes of its chief exponents. His views of
the significance of embryonic development are therefore to be
understood with this theory as a background. For von Baer
did not merely criticize the prevailing ideas of Meckel and others
on this subject. A distinguished embryologist, he held original
and striking ideas of his own, which had a large place in the
subsequent history of the discussion. Von Baer’s position is
represented by the following laws, which he formulated:

8 Vol. II, Chap. IX.
9 Poulton, Essays on Evolution, pp. 56, 57.

The Recapitulation Theory in Biology 9

“(1) That the general of a large animal group expresses itself
earlier in the embryo than the special. (2) Out of the most
general of the structural relations evolves the less general, and
so forth until finally the most special appears. (3) Each em-
bryo of a particular animal form instead of passing through the
other particular forms, separates itself rather from them. (4)
In reality accordingly the embryo of a higher form is never like
to another animal form, but only to its embryo.’’!°

Morgan illustrates these laws as follows:

“For example two similar species of pigeons will follow the
same method of development ue to almost ae actical

Yossie. Ou he other hand fvo animale bong to ¢ different
feales of the same phylum wi ee Saar stages in
‘Thus, a bir bird-and-w- mammal Witt have the first stagés
: suuilan, ori identical, a and then diverge, the mammal adding the
higher characters of its group. The resemblance is between
corresponding embryonic stages and not between the embryo
of the mammal and the adult form of a lower group.
“Von Baer was also careful to compare embryos of the same
phylum with each other, and states explicitly that there are no
ounds for comparison between embryos of different groups.
In one place von Baer raises the question whether the
egg may not be a form common to all the phyla.’

The phyla alluded to are, of course, the four great groups or
types. It is important to remember that von Baer had reference
in his statements to likenesses among existing animals, and not
to ancestral relationships. Von Baer did not accept evolution
although the issue between the two theories had been well
drawn before his death. Later Herbert Spencer pointed out
that a thoroughgoing application of von Baer’s law in filial and
ancestral relationships implied the recapitulation of Oken, that
is, the idea that the embryogeny “repeated the story of the
creation of the animal groups.”

5. The Correspondence Stated as between Developmental Stages of
Existing Animals and the Succession of Adult Forms of Extinct
Representatives. Agassiz.

Von Baer’s significant contribution to the discussion did not
exert an immediate influence. It was Louis Agassiz, a pupil of
Cuvier, the principal originator of the type theory, who made

10 Quoted by Montgomery, loc. cit., p. 178.
u Loc. cit., p. 61.

10 The Recapitulation Theory and Human Infancy

recapitulation an integral element in this theory and gave it its
new form. Early in his life Agassiz entered upon elaborate
studies of living and fossil fishes and so came upon resemblances
between developmental phases of living animals and the adult
forms of their extinct representatives. As his interest broadened
to include the systematic classification of the whole animal
world, Agassiz relied more and more upon the facts of embry-
ology to make good the deficiencies of fossil remains and to pre-
vent the confusion, inevitable as he believed, from an examina-
tion of anatomical differences alone. In 1857 he wrote, ‘‘I satis- -
i myself long ago that embryology furnishes the most trust-
worthy standard to determine the relative rank among animals.”
In the system ultimately evolved by Agassiz, descriptive of
what he believed to be the natural order, there were four great
parallelisms, or systems of relationship. These were (1) a paral-
lelism between the geological succession of animals and their
relative standing or structural gradation; (2) a parallelism be-
tween the geological succession of animals and the individual
development of their living representatives; (3) a parallelism
between the relative rank or gradation of animals and their
individual development; and (4) these several series were again
related to geographical distribution. Thus

“the phenomena of animal life correspond to one another,
whether we compare their rank as determined by structural
complication with the phases of their growth, or with their suc-
cession in past geological ages; whether we compare this succes-
sion with their embryonic growth, or all these different relations.
with each other and with the geographical distribution of ani-
mals upon earth. The same series everywhere!’’”

This interlocking system of relationship constituted the ground-
work of the ‘‘plan of creation” Agassiz’s “‘Essay on Classifica-
tion” was meant to delineate, a plan very satisfying to his own
religious sentiments, if indeed it was not inspired by them.
“Shall we,” he exclaims, ‘‘by any false argumentation, allow
ourselves to deny the intervention of a Supreme Intellect in
calling into existence combinations in nature by the side of
which all human conceptions are child’s play?”

12Essay on Classification, 1857, p. 196.
38 Ibid., p. 197.

The Recapitulation Theory in Biology 11

It was the second parallelism, that between the succession in
geological time and the embryonic stages of living representa-
tives, that constituted the new phase in the history of recapitula-
tion. Of this he said more particularly,

“These relations, now they are satisfactorily known, may also
be considered as exemplifying, as it were, in the diversity of
animals of an earlier period, the pattern upon which the phases
of the development of other animals of a later period were to be
established. They appear now, like a prophecy in those earlier
times, of an order of things not possible with the earlier combina-
tions then prevailing in the animal kingdom, but exhibiting in a
later period, in a striking manner, the antecedent considerations
of every step in the gradation of animals.’’!

There is here suggested Agassiz’s well known concept of
“prophetic types,” the facts for which, as well as for his “syn-
thetic” and “progressive’’ types, were so significant to other
minds of a genetic relationship he himself refused to acknowledge.

6. Embryology and Darwinism.

This correspondence between embryonic stages and the geo-
logical succession of animal forms was destined to play an im-
portant part with the advent of Darwinism (“Origin of Species,”’
1859). It will be well to indicate at once the three allied uses
to which the facts of embryology were put in the development
of this theory. They became, in the first place, one main sup-
port to the doctrine of descent itself. This was naturally the
value attached to them chiefly by Darwin. Once the doctrine
was accepted, embryology was employed with all degrees of
assurance to determine the affinities of living animals in the
interests of a classification based upon genetic relationship.
Fritz Miiller was one of the first of a long line of students to
demonstrate their usefulness from this viewpoint. Finally, as
this classification became elaborated, it made possible the trac-
ing back of genealogies, phylogenies, or racial histories, and this
was introduced systematically by Haeckel.

7. Darwin.

By the time of the sixth edition of the “Origin of Species” in
1872, the two applications of the facts of embryology just men-
tioned had been made and had received the sympathetic notice

14 Essay on Classification, 1857, p. 156.

12 The Recapitulation Theory and Human Infancy

of Darwin. The contribution of Fritz Miller to the classifica-
tion of the Crustacea, largely by the aid of embryology, had
been of particular interest to him, and Haeckel’s work with
phylogenies was alluded to with approval.”

Darwin’s treatment of the facts under discussion is found in
Chapter XIV of the sixth edition where he deals with the mutual
affinities of organic beings. Referring to the efforts of the
“special creationists” to arrange a “natural system” in ac-
cordance with the divine plan, he urges that such a plan is mean-
ingless unless it relates to time and place and has a specific con-
tent, and that all the rules, aids, and difficulties in the then
current efforts at classification are well explained by a view of
a natural system founded on descent with modification. In
support of this contention he proceeds to submit to scrutiny the
several kinds of recognized affinities among animals, those of
embryology among them. After a citation of facts, including
some of von Baer and a direct reference to his law of embryonic
resemblance, Darwin asks,

“How then can we explain these several facts in embryology,
—namely, the very general, though not universal, difference in
structure between the embryo and the adult ;—the various parts
in the same individual embryo, which ultimately become very
unlike and serve for diverse purposes, being at an early period
of growth alike;—the common, but not invariable, resemblance
between the embryos or larvae of the most distinct species in the
same class;—the embryo often retaining whilst within the egg
or womb, structures which are of no service to it, either at that
or at a later period of life; on the other hand larvae, which have
to provide for their own wants, being perfectly adapted to the
surrounding conditions;—and lastly the fact of certain larvae
standing higher in the scale of organization than the mature
animal into which they are developed?”

The explanation is contained in the two principles, viz.,
“|. . that slight variations generally appear at a not very
early period of life and are inherited at a corresponding not.
early period.” Darwin’s illustration helps to make his meaning
plain,

“Now let us apply these two principles to species in a state

of nature. Let us take a group of birds, descended from some
ancient form and modified through natural selection for differ-

15 Origin of Species, American ed., p. 231.

The Recapitulation Theory in Biology 13

ent habits. Then, from the many slight successive variations
having supervened in the several species at a not early age, and
having been inherited at a corresponding age, the young will
have been but little modified, and they will still resemble each
other much more closely than do the adults,—just as we have
seen with the breeds of pigeons.’’6

For Darwin did not fail to verify his statements by carefully
Measuring young and old dogs, horses, and pigeons. Accord-

ingly,

“Tt is highly probable that with many animals the embryonic
or larval stages show us, more or less completely, the condition
of the progenitor of the whole group in its adult state.”

Furthermore, ‘‘we can see why ancient and extinct forms so
often resemble in their adult state the embryos of existing species
of the same class. Agassiz believes this to be a universal law of
nature; and we may hope hereafter to see the law proved true.
It can, however, be proved true only in those cases in which
the ancient state of the progenitor of the group has not been
wholly obliterated, either by successive variations having super-
vened at a very early period of growth, or by such variations
having been inherited at an earlier stage than that at which
they first appeared. It should also be borne in mind that the
law may be true, but yet, owing to the geological record not
extending far enough back in time, may remain for a long period,
or forever, incapable of demonstration. The law will not strictly
hold good in those cases in which an ancient form became adapted
in its larval state to some special line of life, and transmitted the
same larval state to a whole group of descendants; for such
larvae will not resemble any still more ancient form in its adult
state.”

These passages have a peculiar interest in the light of the
later history of the discussion. There is every intention evident
of doing full justice to the complexity of the facts and a plain
acknowledgment of a variety of cases. Nevertheless, one de-
tects an unmistakable leaning in the direction of a general state-
ment favorable to recapitulation, and in the allusion to Agassiz
an expressed sympathy for a ‘‘universal law of nature.” With
the great authority of Darwin offering this much justification,
one cannot be surprised if in the hands of less careful students
the facts should be found to warrant a much more sweeping
statement.

18 Origion of Species, American ed., pp. 245, 247, 249.
17 Ibid., pp. 252, 254.

14 The Recapitulation Theory and Human Infancy

8. The Developmental-A ncestral Correspondence Clearly Enunciated:
Fritz Miller.

It has been noted that Darwin had profited by the contribu-
tion to his theory made by Miller in his book, ‘Fir Darwin,”
published in 1864. Torn between the claims of the rival theories,
Miller determined rigidly to apply the principles of Darwin to
one group, the Crustacea, in order to discover whether lines of
descent and a genetic classification could in this manner be
determined within it. In concluding his study Miiller general-
ized upon the facts of resemblance between the developmental
history of descendants and the adult state of ancestors in a more
precise manner than Darwin had in his first edition. His con-
clusions are as follows:

“Descendants, therefore, reach a new goal, either by deviat-
ing sooner or later whilst still on the way towards the form of
their parents, or by passing along this course without deviation,
but then, instead of standing still, advance still further.

“In the second case the entire development of the progenitors
is also passed through by the descendants, and, therefore, so far
as the production of a species depends upon this second mode of
progress, the historical development of the species will be mir-
rored in its developmental history.

“The historical record preserved in developmental history is
gradually effaced as the development strikes into a constantly
straighter course from the egg to the perfect animal, and it is
frequently sophisticated by the struggle for existence which the
free-living larvae have to undergo.

“Which of the different modes of development at present
occurring in a class of animals may claim to be that approach-
ing most nearly to the original one, is easy to judge from the
above statements.’’!8

9. “Ontogeny is a Short and Rapid Recapitulation of Phylogeny:”
Haeckel. :

In the statement of principles quoted above from Fritz Miiller
it will be observed that there is no disposition to weight the cases
of recapitulation in very great disproportion to those of embry-
onic or larval deviation. Two possible courses of development
are shown, recapitulation being the second. And there is little
disposition, if any, to make the second class of cases the more
prevalent or the more characteristic in any fundamental way .

18 Facts and Arguments for Darwin, pp. 111, 112, 114.

The Recapitulation Theory in Biology 15

It was noticed, too, that Darwin hesitated to formulate a gen-
eralization distinctly in favor of recapitulation, whatever may
have been his inclination. It remained for Haeckel to raise
Miiller’s second class of cases into very great prominence at the
expense of the first, to assume that this represents the more
general, and indeed in some fashion a necessary order, and to
throw together all the cases of the first class as mere subsidiary
disturbances of the order represented by the second. Thus the
“law of recapitulation” took the form in which it is best known.
It is interesting to consider the consequences if by chance the
emphasis had been placed the other way round. Then the
“law’’ would have read somewhat as follows: Ontogeny records
the adaptations the life history of descendants has made in its
evolution and is indicative of its phylogeny in those cases only
in which embryonic or larval deviation has not occurred.

Haeckel’s great popularity as a writer gave his statement
very wide currency, in fact, made it dominant. It has happened
in consequence that the whole succeeding history of the discus-
sion, including its application to mental growth, has turned
largely upon either the possible substantiation of his “‘biogenetic
law,” or upon its possible refutation. It may be said with
justice that much of the mischief that has resulted from a care-
less use of his formula has been due to the particular form in
which the facts were thus summarized.

Haeckel was a young man beginning his career at Jena when
Darwin’s great book appeared. The circumstances of his train-
ing had been such as to prepare his mind for the new doctrine and
he became its most ardent advocate and disseminator in Ger-
many. Haeckel was not content to limit himself to a study of
the causes of descent. At once speculative and intrepid, he
carried the doctrine in every direction his system-loving mind
pointed, and ultimately built a complete natural philosophy
upon it. He would not demonstrate the kinships within one
class only, as had Fritz Miller. Nothing less than a genealogical
tree of the entire animal world became his object. Haeckel was
particularly interested in the two extremes of descent concerning
which Darwin had been less explicit, that of the ancestry com-
mon to the great phyla among the lowest forms, and that of
man. His original investigations were consequently directed
upon the lowest orders and he was able to suggest a succession of

16 The Recapitulation Theory and Human Infancy

steps by which the Metazoa had evolved from the simplest form
of living matter. This he in turn derived from the inanimate.
Haeckel was equally consistent in applying the doctrine of
descent to mankind. The groundwork of his entire system was
laid in the ‘“Generelle Morphologie,” published in 1866, his numer-
ous later publications being practically extensions of this work.

In this book Haeckel recurs to the threefold parallelism of
Agassiz between the order represented by the classification of
existing animals and those of palaeontology and of individual
development. But in place of the mystic bond of connection
between the three of Agassiz, Haeckel substitutes a ‘close casual
nexus’’ derived from the theory of descent in the two factors of
heredity and adaptation. This primary conception assists in
the understanding of his attitude toward recapitulation, for it
is the keynote to his whole system.

When one considers the situation in 1866 and the nature of
his general purpose, it is not surprising that Haeckel should have
reverted to this threefold parallelism. To his mind Darwin
had shown conclusively the truth of the doctrine of descent with
modification. Obviously the hierarchy of living forms, from
the lowest one-cell condition through the several grades of
complication to the highest, was a result of descent, and was at
least suggestive of what the historical order had been. It
would therefore correspond with the actual historical order so
far as this was indicated by the succession of fossils in the earth’s
formations. The gradual progression through development
from the ovum to the complicated adult was again suggestive
of this order in its broad outlines at least. All three of these
had served Darwin as foundations for his theory, and the least
plausible, that of development, had received a certain warrant
in fact in the writings of Darwin and Fritz Miiller, besides
having had a respectable history prior to the descent theory.
Development, indeed, presented in the concrete the only avail-
able picture of what the idealized evolution of animals through
geological time presupposed. This suggestiveness of develop-
ment has often been alluded to since Haeckel, and still is, by
biological students. If one is content wtih exceedingly broad

io“ . . die Stufenleiter des natiirlichen Systems mit den parallen Stufenleitern ;
der individuellen und der paliontologischen Entwickelung in dem engsten mechani-
schen Causalnexus steht.'’ Gen. Morph. II, XIX.

The Recapitulation Theory in Biology 17

outlines one may still hold with justice for the truth of this
threefold parallelism.2? Its recurrence with Haeckel was con-
sequently the obvious thing on the part of one who desired to
present a panoramic view of the natural world after the manner
of Humboldt and Agassiz. The imperfections of the parallel-
ism would naturally appear subsequent to its original formula-
tion.

It may have been the prestige of this parallelism in his mind,
together with the fact that he was for the time primarily a
morphologist, as the title of his book implies, that led Haeckel
to over-simplify the effects of heredity and adaptation through-
out descent, and to neglect somewhat the question of what was
required of these two factors to substantially support the paral-
lelism. This had been a matter of primary concern to Darwin
and Miller, as has been noted. Throughout his works the
ontogenetic-phylogenetic parallelism is associated especially
with the “laws’’ of hereditary transmission at correspond-
ing ages and in corresponding place relations, and with that of
abbreviated heredity suggested by Miiller.» The effect of
the first two was to repeat the parental order; the effect of the
last was to simplify and shorten this order perhaps, but not to
destroy it. This is essentially the situation in the fifth edition
of the ‘Evolution of Man,’’?? where the symbolic representation
of the two series indicates omission of ancestral stages, and some
modification of them in ontogeny without obscuring their
identity.

The appearance of novelty, or variation, was identified by
Haeckel with adaptation, or the direct modifying effect of
environment. This again would explain in part his over-em-
phasis of the conservative influence of heredity, for the ever-
recurring changes induced by germinal variations regardless

20 “*Tt is indisputable, if we only consider the most general features, that the history
of the development of an individual is a kind of rapid recapitulation of the slow phases
of the evolution of the species and of the branch.’’ Depéret,Transformations of the
Animal World, trans. 1909, p. 254.

1“ Der Parallelismus zwischen der phyletischen (paliontologischen) und de: bion-
tischen (individuellen) Entwickelung erklart sich einfach mechanisch aus den Verer-
bungs-Gesetzen und insbesondere aus den Gesetzen der gleichzeitlichen, der gleichort-
lichen und der abgeklirtzen Vererbung. Alle Erscheinungen, welche die individuelle
Entwiekelung begleiten, erklairen sich lediglich, soweit sie nicht unmittlebares Resultat
der Anpassung an neue Existenz-Bedingungen sind, aus der paliontologischen
Entwickelung der Vorfahren des Individuums.’’ Gen. Morph. II, p. 372.

22 Trans., 1910, p. 4.

18 The Recapitulation Theory and Human Infancy

of adaptation would be eliminated at one stroke. Adaptation
would effect embryonic and larval structures, as he clearly
points out, but presumably its principal effect would be to
extend the ontogeny in a linear way corresponding to a similar
linear extension of the phylogeny through geological time.
However this may be, one misses in the accounts of Haeckel
the detailed consideration of the effects of heredity, variation,
and adaptation in the life-histories of succeeding generations,
so noticeable in the treatment of Darwin and Miller. This,
perhaps, is what reasonably might have happened from a pre-
occupation with the parallelism he presupposed. The upshot
of the matter is that Haeckel greatly overestimated the con-
serving force of heredity operating through descent. This
renders intelligible his concluding formula: ‘Phylogeny is the
mechanical cause of ontogeny,” a true statement when the par-
ents and immediate ancestors are considered, only true with
respect to the remote ancestors in a phylogeny on the assump-
tion that the force of heredity has been fairly constant through-
out.

It would, however, be unfair to Haeckel to rest an inter-
pretation of his biogenetic law upon his formal summaries alone.
A consideration of the actual use to which the law was put
in elaborating phylogenies presents a somewhat different aspect.
For instance, in developing the phylogeny of man the argument
invariably proceeds from a comparison of embryonic resem-
blances to a discovery of the palingenetic, or racially older, fea-
tures by an elimination of the cenogenic, or more recent ad-
ditions. Once these older features are determined the bio-
genetic law is invoked and the ancestral reference made. In
the earlier stages the ancestral reference is to hypothetical
ancestral adult forms, as from the gastrula to the Gastraea,
or from the coelomula to the hypothetical Coelomaea, and a
sequence of such forms results, in keeping with recapitulation
in the ordinary sense of a chronological series. But in the
later and higher stages the ancestral reference is not to specific
ancestral adult characters, but to ancestors having an embry-
ogeny with similar features. This last may be _ illustrated
“We see,” he says, ‘that man entirely resembles the higher
Mammals, and most of all the apes, in embryonic development
as weil as in anatomic structure. And if we seek to understand

The Recapitulation Theory in Biology 19

this ontogenetic agreement, in the light of the biogenetic law,
we find that it proves clearly and necessarily the descent of
man, from a series of other Mammals, and proximately from
the Primates.’ From ontogenetic resemblances a common
ancestry is argued. Clearly this is not recapitulation in the
strict sense. But Haeckel is applying the biogenetic law ashe
understands it, wherefore it must be that he means by recapit-
ulation in this application only that an ontogeny presents in
its racially older features evidence of value regarding its prox-
imate or less remote ancestors. Haeckel’s formal general-
izations and their actual use thus do not appear wholly in
agreement, and if the meaning of principles lies more espec-
ially in the work they do, it must be admitted that the common
opinion of Haeckel’s conception requires some modification.
It should be noted that the notion of recapitulation conveyed
by the practice just referred to brings Haeckel close to the
position of some of the most radical critics of his theory.

Whatever the case may be in these particulars, the general
effect of Haeckel’s formal statements of the biogenetic law
was to imply a sequence in embryonic development such in gen-
eral that it was broadly descriptive of a similar sequence in
phylogeny. His qualifications of the law still did not have the
force of robbing the principal statement in the formula of
first-rate descriptive value. Moreover his language was such
as to suggest some fundamental tendency toward or necessity
for recapitulation, which might be obstructed partially so as
to “falsify” or ‘‘confuse” or “distort”? this order. All this
is declared to be misleading in its implications. Ontogeny
is subject to many factors, of which those favoring recapitula-
tion are but of equal value, or even much less than equal value,
with the rest. And they are no more natural or to be expected
or primary than those with which they associate.”

% Evolution of Man, trans., 1910, p. 307.

*% Compare this statement from Miall:

“I diverge from him [Haeckel] when he says that each animal is compelled to
discover its parentage in its own development. . . . I admit no sort of neces-
sity for the recapitulation of the events of the phylogeny in the development of the
individual. . . . Iam oon my guard when he talks of laws, for the term is mis-
leading, and ascribes to what is a mere general statement of observed facts the force
of a command. The so-called laws of nature (a phrase to be avoided) may indeed
enable us to predict what will happen in a few cases, but only when the conditions
are uniform and simple—a thing which is common in Physics, but very raie in Biol-

20 The Recapitulation Theory and Human Infancy

10. Herbert Spencer.

It is interesting to compare with the views of Haeckel the
position of another great systematist whose book appeared in
the same year with the ‘“Generelle Morphologie.” This book
is the ‘Principles of Biology” of Herbert Spencer. Spencer
makes his starting point von Baer’s law and does not widely
depart from it throughout the account of his first edition.
He however cautions his reader against accepting the general-
jzation as exact. The resemblances among related embryos
noted by von Baer “are not precise but approximate. Only
leading characteristics are the same: not all the details. . . .
each kind of organism, though having a general direction of
development like that of the others it is for a time traveling
with, shows from the first a tendency to leave the general route—
a tendency which presently becomes strongly marked.” Still
as an average truth the generalization may be regarded as be-
yond question. But, “the generalization must not be con-
founded with an erroneous semblance of it that has obtained
considerable currency. An impression has been given by those
who have popularized the statements of embryologists, that
during development each higher organism passes through
stages in which it resembles the adult forms of lower organ-
isms. . . This is not the fact.’”’ Thus Spencer repudiates
recapitulation in the form it was taking with Haeckel.*

In a later chapter where he presents with the others the
embryological arguments for evolution, Spencer is occupied
in showing that evolution explains not only the resemblances
of embryos but the lack of such resemblances as well. This
is due to the very unlike life conditions and consequent unlike
adaptations made by different groups in their evolution sub-
sequent to their departure from the common ancestor, adap-

ogy.” Report of the British Association for the Advancement of Science, 1897, p. 682.
Compare also the following from Hyatt:

“The use of terms indicating that Nature has confused o1 destioyed its own onto-
genetic records of the transmission of characters in certain cases assumes (1) that
these are exceptional cases, (2) that caenogenesis is not the normal mode of trans-
mission in certain types in which it occuis, (3) that both of these modes of trans-
mission are not affected by tachygenesis, all these implications being erroneous.

. “destruction,” ‘confusion,’ or ‘“‘falsification’’ are subjective terms inap-
plicable to the objective character of the phenomena. . . entirely out of place
in natural science.’’ Phylogeny of an Acquired Characteristic, p. 401, footnote.

28 Vol 1, lst American ed., 1898, pp. 143, 144.

The Recapitulation Theory in Biology 21

tations which are reflected in embryonic changes. As a result,
“the embryological parallelism is qualified by irregularities
that are mostly small, in many cases considerable, and occas-
ionally great.’’*

The irregularities in the law noted by Spencer may be briefly
enumerated: (1) The substitution of organs and the suppression
of organs in certain embryos as compared with others, the
first illustrated by the succession of changes in the aérating
appliances of the mammalian embryo, the second by the
suppression of the foetal teeth of whales; (2) retrograde
development, as in the loss of limbs and senses in adult par-
asites; (3) substituted modes of development, the two typical
modes being direct and indirect. In the former case the
‘development of the animal proceeds from the egg to the adult
condition without intermediate stages. In the latter a cir-
cuitous route is to be noted involving often many metamor-
phoses. The latter mode is that of the higher or more com-
plicated animals because it reflects the many changes incident
to the embryo from the long succession of unlike conditions
through which the group has passed. The direct mode is there-
fore the substituted mode among the higher animals, the cause
being a prolonged constancy of conditions inducing finally an
adjustment of all parts of the animal to the settled condition
of its life as a whole. Similar facts are to be noted among
particular organs as such.

Subsequent to the publication of the first edition of the
“Principles of Biology’’ Spencer’s views suffered a change of
emphasis. In later editions the condemnatory sentences re-
garding recapitulation are missing. He has found, in fact,
that von Baer’s law, when carried out consistently in evolu-
tionary terms, implies recapitulation.27

“This conception,” says Spencer, “of a tree, symbolizing
the relationships of types and a species derived from the same
root, has a concomitant conception. The implication is that
each organism, setting out from the simple nucleated cell, must
in the course of its development follow the line of the trunk,
some main branch, some sub-branch, some sub-sub-branch, etc.,
of this embryological tree; and so on till it reaches the ultimate

% Vol. 1, 1st American ed., 1898, p. 368.
37 See the first two laws of von Baer, p. 9.

22 The Recapitulation Theory and Human Infancy

twig representing the species of which it is a member. It must
in a general way go through the particular line of forms which
preceded it in all past times: there must be what has been aptly
called a “‘recapitulation” of the successive ancestral structures.
This, at least, is the conclusion necessitated by the generaliza-
tion we are considering under its original crude form.’

Thus in any unfolding embryo there are two sets of energies
at work, one tending toward the type of the primitive ances-
tors, the other toward the evolved terminal type, the inter-
mediate structures being influenced by their conflict. Still
other factors intervene to affect the character of development.
One is economy. A premium is placed upon any animal in a
series which can mature at a saving in vital energy. This tends.
to shorten the process. Economy again explains the entire
disappearance of intermediate forms in some cases. Economy
explains, once more, “preadaptation,” in the earlier preparation
of structures and functions of increasing size and importance
in the life of the evolving animal. A demand for more time
in the upbuilding of increasingly complicated organs may also
bring about preadaptations. Finally the lack of uniformity
in the decrease and disappearance of organs may be explained
in several ways: large organs will suffer more than small ones
from the principle of economy; decrease in unused organs may
not coincide with the evolution of more important ones; ances-
tral features may become embodied as parts of new organs;
and some disused organs may entail evil by being in the way
of the modes of living.”

Spencer’s views are interesting in that while they arrive at
an acceptance of the chronological idea of recapitulation, they
do so by inferences directly from the law of von Baer. But
recapitulation is true only to the extent that von Baer’s law
holds, and Spencer is very well aware of the variations from the
law. His statements thus escape the extreme form given to
those of Haeckel by the latter’s presupposition of a biogenetic
fundamental law. Spencer’s position is representative of an
acceptance of recapitulation more just to the complexities of

the facts, and more nearly in accord with the views of Darwin
and Miiller.

*Loc. cit., p. 453.
*Ibid., p. 458, et seq.

The Recapitulation Theory in Biology 23

11. The Laws of Acceleration and Retardation.

A notable series of investigations in which recapitulation
figured largely was inaugurated by Alpheus Hyatt in Boston
in the year 1866. MHyatt’s original study was made upon fossil
shells of certain mollusks, but his method has been used by his
pupils and followers with various groups of mollusks and other
invertebrates, and even with the vertebrates. This school of
investigators has derived so much assistance from recapitulation
that they are now to be regarded as its chief defenders. In-
deed, one member of the school has declared that ‘If the em-
bryologists had not forestalled them, the paleontologists would
have had to invent the theory.” ‘‘This,’’ observes Cumings,
“‘may be considered as a fair sample of tbe general attitude
of paleontologists of the Hyatt school. . .’*

It was suggested by Hyatt that the conditions for making
comparisons between development and the ‘‘phylocycle” by
means of fossil shells are exceptionally favorable. The shell
and its parts are highly significant of the structure of the animal,
and display in a unique way the important phases of its growth
from the later embryonic stages to old age. Moreover, the
procession through geological time is abundantly shown in
the successive geological formations not only for the adult forms
but for the corresponding immature stages in every youthful
phase as well.*1 It is therefore possible for students of these
shells to compare immature stages directly with their own adult
condition and with the immature and adult conditions of their
predecessors and descendants. These favorable circumstances
make the conclusions of this group of investigators of peculiar
value within the limits of their field of study.

In making these comparisons Hyatt found certain relations
prevailing between the development of the individual and the
ancestral series, and summarized them by means of a restate-
ment of recapitulation, along with an induction original with him,
since known as the law of acceleration. His own words for
these two generalizations are:

40 For a valuable summary of the work of this school, with bibliographies, see an
article by this writer, Paleontology and the Recapitulation Theory, in Proceedings of
the Indiana Academy of Sciences, 1908-09: pp. 305-340.

31 Phylogeny of an Acquired Characteristic, Proceedings American Philosophical
Society, 1893: p. 350.

24 The Recapitulation Theory and Human Infancy

““We have endeavored to demonstrate that a natural classifi-
cation can be made by means of a system of analysis in which
the individual is the unit of comparison, because its life in all
its phases, morphological and physiological, embryo, larva, ado-
lescent, adult, and old (ontogeny), correlates with the morpholog-
ical and physiological history of the group to which it belongs
(phylogeny).

‘All modifications and variations in progressive series tend
to appear first in the adolescent stages of growth, and then to be
inherited in successive descendants at earlier and earlier stages
according to the law of acceleration, until they either become
embryonic or are crowded out of the organization and replaced
in the development by characteristics of later origin.’

The term acceleration is not to be understood as implying neces-
sarily a quicker development. On the contrary, ‘an animal
having accelerated development of characteristics does not
necessarily have a quick development, but may grow, so far
as time is concerned, even more slowly than others of its own
group.’ The accelerated characteristic merely takes a new
relative position in the whole ontogeny by reason of the omis-
sion or suppression of the earliest or older stages and the addition
of adaptive phases at the adult end.

The evolutionary explanation of the law is as follows:

“We can fully understand the phenomena of acceleration
in development only when we begin by assuming that the char-
acteristics last introduced in the history of any type were more
suitable to the new conditions of life on the horizon of occurrence
of the species than those which characterized the same stock
in preceding horizons. These characters would then necessarily,
on account of their greater usefulness and superior adaptability,
interfere with the development of the less useful ancestral stages,.
and thus tend to replace them.’’

Two important additions to this law of acceleration were
made by the distinguished American naturalist, Cope, who
presented an independent formulation of the law itself in the
year 186635—a year significant for recapitulation, for as has
been noted, it gave expression to three original statements of
the law, namely, those of Haeckel, Hyatt, and Cope. One of

32 Genesis of the Arietidae, Smithsonian Contributions to Knowledge, 1890, pref-
ace

3Ibid., p. 40, footnote.

“Ibid., pp. 44, 45.

36 Primary Factors of Evolution, 1896, p. 9.

The Recapitulation Theory in Biology 25

these added ideas was that of unequal acceleration, concerning
which Cope makes this statement:

“The acceleration in the assumption of a character, progressing
more rapidly than the same in another character, must soon
produce, in a type whose stages were once the exact parallel
of a permanent lower form, the condition of inexact paral-
lelism. As all the more comprehensive groups present this
relation to each other, we are compelled to believe that accelera-
tion has been the principle of their successive evolution during
the long ages of geological time.”

Two other extracts from another writer will show more fully
the meaning of this principle:

‘A character useful to the immature form will have a tendency
to be inherited at an earlier age than those useful only to the
adult, and so by unequal acceleration of development the parallel
between ontogeny and phylogeny is broken”’;

and this unequal acceleration is especially to be expected

“in the larval and adolescent periods where the shortness of the
time of development causes throwing together of characters
that were not contemporaneous in the ancestors, and where
the small size and general habits prevent differentiation of organs
that in the correlative adult forms were highly developed...’

The other idea added to the law of acceleration was named by
Cope ‘‘retardation.’’

“Where characters which appear latest in embryonic history
are lost, we have simple retardation, that is, the animal in suc-
cessive generations fails to grow up to the highest point of com-
pletion, falling further and further back, thus presenting an in-
creasingly slower growth in the special direction in question.’’®

This gives rise to retrogressive series in evolving forms in
contrast with progressive series resulting from the effect of
acceleration.

The bearing of these principles of acceleration, unequal ac-
celeration, and retardation upon the theory of recapitulation
has now to be indicated. If acceleration should operate uni-
formly upon lines of descent without obstruction, plainly the

46 Origin of the Fittest, p. 142.
37 J. P. Smith, Journ. of Geology, Vol. 8, 1900, p. 417.
% Origin of the Fittest, p. 13.

26 The Recapitulation Theory and Human Infancy

ontogeny of a descendant would be a perfectly repeated se-
quence of the succession of its adult ancestors, except where
the most ancient forms would have been suppressed or omitted
from the earliest corresponding embryonic period. This is
Cope’s “exact parallelism.’ It would also have the effect
of condensing stages without confusing the ancestral order in
certain portions of the ontogeny. In case of simple retardation
the ontogeny would fail to repeat the most ancient forms, would
repeat faithfully the later forms up to the point where the re-
tardation left off, and would then fail to repeat stages which
the ancestry had recently lost by retardation or successive
failure to complete its life cycle. Unequal acceleration would
have the effect of ‘telescoping,’ or bringing together, stages
in ontogeny which had been successive in phylogeny, and to
locate later phylogenetic stages before earlier ones. It is ob-
vious that, theoretically, this last could confuse the phylogenetic
order hopelessly or could even reverse it.

The relative importance of these several principles, and the
validity of recapitulation, becomes therefore a matter of fact.
On this point we can but quote competent authority:

«... there are so many species and genera in the various
groups of invertebrates whose ontogeny is simple, progressive,
and fairly complete, and whose stages of growth are almost
exact repetitions of successive antecedent genera, that it would
be impossible to find a student of morphogeny of the brachiopods,
the marine mollusks, or the lower crustaceans, that does not
believe implicitly in the value of larval stages of these groups
as records of their family history.’

“In the Cephalapoda, Pelecypoda, Gastropoda, Brachiopoda,
Trilobita, Bryozoa, Graptolites, Echinoderms, and Corals, ex-
amples are pointed out in which there is clear and unmistak-
able evidence of recapitulation.’

Hyatt and Cope adduced certain illustrations of accelera-
tion and retardation with man and other vertebrates, but since
the more recent writers do not emphasize these, it may be as-
sumed that the case for recapitulation rests for the group of
students here referred to chiefly upon the examples among the
invertebrates.

J. P. Smith, loc. cit., p. 422.
49 Cumings, loc. cil., p. 337.

The Recapitulation Theory in Biology 27

A point of importance emphasized by Cumings deserves
notice here:

“...the Hyatt school of paleontologists have based their
phylogenies on epembryonic [i. e., larval] rather than embryonic
stages....since in the nature of the case the true embryonic
stages are scarcely ever accessible to the student of fossils. . .
There arises here a question of definition, does the biogenetic
law mean that the ontogeny is a recapitulation of the phylogeny,
or does it mean that the embryogeny is a recapitulation of the
phylogeny?” ‘In most of these cases [those listed in the second
paragraph above] it is the epembryonic and not the embryonic
stages that are the basis of comparison.’’#

In concluding this report of the bearing of acceleration and
retardation upon recapitulation, it will be well to refer to a
significant caution contained in Cope’s discussion of “inexact
parallelism.” It has been noted that Cope used this expression
in part to refer to a lack of correspondence between any ontogeny
and its own restricted line of descent. But he used it also to
cover a lack of correspondence between an ontogeny of one
line of descent and forms in parallel lines of greater or less kin-
ship by reason of ancestors at different points of remoteness
in the past. Thus,

“So soon as new subordinate characters are assumed....
the parallelism becomes “‘inexact,’’ and such is the kind of
parallelism usually observed. And it is the more inexact the
more widely removed in relationship are the forms compared.
Thus the parallelism between the embryo man with five branchial
slits, and the adult shark, it is very inexact; but that between a
true fish and a shark is much less inexact. That between a
higher and a lower shark is still more exact, and so on.” ‘As
we compare species which are more and more different the more
necessarily must we confine the assertion of parallelism to single
parts of the animals and less to the whole animal.”

It appears, therefore, that in the cases of perfect acceleration
we have just those conditions required by the logic of the theory
of recapitulation in its extreme form. They illustrate nicely
the modifications “at a not early age’’ that Darwin saw were
needed for a genetic explanation of von Baer’s law, and they
fall into Fritz Miiller’s second class of cases. The evidence

Loc. cit., pp. 306, 337.
42 Primary Factors in Evolution, 1896, pp. 200, 207.

28 The Recapitulation Theory and Human Infancy

and the authority of the writers quoted in this section leave no
question of the actuality of many examples of more or less
close recapitulation among the invertebrates, at least for shell
characteristics as such, and for whole organisms to the extent
shells are illustrative of the entire structure of the animal.‘
Just how general this recapitulation is does not appear, probab-
ly this can not be known as yet. The gist of the contentions
of the writers in this field seems to be nothing more than that
recapitulation constitutes a working principle for genetic classi-
fication of very genuine usefulness. There is no disposition to
make of it, at the present time at least, a principle of universal
application. It is plain that generalizations carried over from
this rather circumscribed field of fact to the vertebrate or
human territory, and more especially to the human nervous
system or mind, can be the sheerest hypothetical possibilities,
in view of the complexity of the facts upon this field of their
clearest embodiment and of the possible and probable very un-
like conditions that have surrounded the evolution of the high-
er vertebrate forms.

12. The Facts of Recapitulation.

The sketch of the history of the idea of recapitulation thus
far drawn shows that speculation and deduction have had no
small part in its formulation. The purpose of the present
section is to refer somewhat independently to the facts that
have been adduced in its support at different times and by
various writers. These facts are found to fall into three classes:
(a) those derived from a comparison of known ontogenetic
and palaeontological data; (b) those of embryonic resemblance
among existing types; (c) thoseof stages or features in ontogeny

esemblance x features_so common to lower
allied living groups as to raise the question of an an ancestral re-—
_Jationship. The facts of the first group “are “unequivocal in
“their significance. Either the parallel exists or does not exist
when ontogeny and phylogeny are known and accurately com-
pared. The other two types of fact are open to alternative
explanations, and give ground for controversy, as we shall see.

4“ The Mollusks would seem, at first sight, bound to supply us with exact phylo-
genetic documents by reason of the abundance of their calcerous shells in all geological

strata. But. . . the shell isa moiphological organ of little importance.’’ Depéret,
toc. cit., p. 48.

The Recapitulation Theory in Biology 29

(a) The Facts of Palaeontology.

In the discussion of the views of Darwin reference was made
to his expressed sympathy for the belief of Agassiz in the
embryonic character of extinct forms. As late as the year
1872 Darwin said, ‘‘We may hope hereafter to see this law
proved true.” Commenting on this point an eminent Eng-
lish embryologist, Sedgwick, says, ‘‘But as Huxley has shown
and as the whole course of palaeontological investigation has
demonstrated, no such statement can be made. The extinct
forms of life are very similar to those now existing and there
is ‘Js nothing specially embryonic about them. So that the facts,
as we know them, lend no support to theory.”“ The reference
to Huxley in this quotation is made to papers written in the
years 1855 and 1862. In the second paper Huxley wrote “An
impartial survey of positively ascertained truth then negatives
the common doctrines of progressive modification, or a neces-
sary progress from more or less embryonic forms. . . . it
either shows us no evidence of any such modification or demon-
strates it to have been very slight.’’45

Passing the question as to whether Huxley’s views may have
undergone a change of emphasis later with the accession of new
facts, we may compare with the statement of Sedgwick the
opinions of a distinguished German palaeontologist. Zittel,
writing on Palaeontology and the Biogenetic Law, in 1895, says,
after referring to the immense advantages that would accrue
to palaeontology if this law could be strictly used,

“If we consult palaeontology, it shows that these surmises
are by no means confirmed. There are, indeed, a great number
of fossil genera which retain throughout life the embryonic, or,
rather, the youthful characters of their existing allies, but it is
only among the mammals, and to some extent among the rep-
tiles, that I could name a complete series of forms following one
another in time and belonging to the same line of development.
The Eocene, Oligocene, and, in part also, even the Miocene
Mammalia stand to their now existing allies, for the most part,
in the relation of youthful forms, while they, almost without
exception, exhibit at least some characters which are quickly
passed through by their geologically younger successors in the
embryonic or youthful stage. The ontogeny of organisms now

#In Darwin and Modern Science, 1909, p. 174.
4’ Scientific Memoirs, Vo]. II, p. 528.

30 The Recapitulation Theory and Human Infancy

living would, for the rest, afford but an unsafe basis for the
reconstruction of ancient faunas and floras, since experience
teaches that the biogenetic law is frequently veiled or completely
obscured owing to various causes.”
Concluding a series of illustrations of the absurdities to follow
from an unchecked use of the law this authority remarks that
these few instances ‘‘may suffice to show how trivial are the
discoveries concerning existence in earlier periods of earth-
history that can follow from ontogenetic researches alone.’’#s
Cope and others were interested in collecting particular in-
stances of recapitulation and these appear in the text-books.
They are conveniently presented by Woodward in the follow-
ing paragraph: ;

‘‘There_is no doubt, for example, that in the course of the

aodisidual dj reloument the homocercal tail of a.modern_bony
ish passes through the same stages as those successively--ex-

he majority of the-adult-fishes. at_the different geo-
logical epochs. is aso evident thet the family of deet (Cet-
Vidae) has gradually acquired” complex antlers in precisely the
same.manner as~-every-modern stag acquires them during the
course of its individual lifé” Again the “‘cloven foot” of the
existing ruminant appears-in the embryo with separated meta-
podial bones, like those of the adult ancestral ruminants. It is
also tolerably certain (though fossils have not yet provided
absolute demonstration) that the rudimentary teeth and hind
limbs of the existing whale bone whales (Mystacoceti) are in-

herited from functionally toothed quadrupedal ancestors. ’’47

In Osborn’s “Evolution of Mammalian Molar Teeth’’ this
example of recapitulation_is to be found, ars

“In the lower molar teeth the order of calcification is precisely
the_or volution.....So we find that the order of embryonic’
“development exactly repeats the order of historical development
...-But this. ...is_not. exactly the case in the upper molars.
Nevertheless, out_of eight cusps in the upper and lower molars
“considered together, six cusps calcify in the order in which they

‘were successively added to the single reptilian cone.’

ae

And from the same authority—this note,

“The recent discovery of the modes of origin of the horns in
the titanotheres, a perissodactyl group remotely related to

4s Natural Science, Vol. 6, 1895: pp. 308, 309.
47 Outlines of Vertebrate Palaeontology, 1898, p. xxiii.
@p. 65.

The Recapitulation Theory in Biology 31

horses, tapirs, and rhinoceroses, permits of a comparison of
phylogenesis with the ontogenesis of the horns in bovine mam-
mals—the conclusion is that ontogeny closely recapitulates
phylogeny, that the genesis is gradual or continuous, that the
horns arise definitely and determinately.’’*

As is well known the ancestry of the horse is one of the few
vertebrate ancestries that have been reconstructed on palaeon-
tological evidence, and it is therefore of peculiar interest to
note the results of a comparison of the embryogeny af the horse
with its racial history. This comparison has been made in part
by Ewart, who, in the course of his report, raises and answers
this question, :

““What evidence is afforded by the horse in favour of the re-
capitulation theory?... .

Evidently if the reservations made on the plea of abbreviation
in development, etc., are almost unlimited, a very remote re-
semblance in an embryo to a supposed ancestor might be con-
sidered sufficient evidence of recapitulation....There must,
however, be some limit to the use of the word recapitulation... .
Recapitulation, if it means anything at all, must be held to mean
that, say in the case of the horse, the embryo should after a time
not only resemble the unknown embryos of its extinct ancestors,
but that it should resemble the fully-developed ancestors. This
implies that during its ontogeny the horse should not only ad-
vance in a zigzag fashion along the trunk of the animal tree, but
also when it reached its own particular branch that it should
during its onward course make deflections in the direction of
Hyracotherium, Mesohippus, etc., until having, at a respectful
distance, done hurried homage to its ancestors, it at last reaches
its final goal, and presents its true characters....It is impos-
sible with any degree of accuracy, either to speak of a Hyraco-
thertum or a Mesohippus stage, or even of a Hipparion stage.
If, on the other hand, all that is meant by recapitulation is that
the developmental record of any given form is represented by
a series of zigzags or curves instead of a straight line, the
horse may be claimed as supporting it. As is to be expected
in forms that have evidently descended from the same ancestors,
there is a certain amount of agreement between horse embryos
and the so-called fossil horses; and were it possible to know the
development of these extinct forms, the points of agreement
would be doubtless increased. Further, as might also have been
expected, the points of agreement become more numerous and
more evident as Hipparion—a not very ancient form—is reached.

Science, Vol. XXXV, 1912, pp. 595, 596.

32 The Recapitulation Theory and Human Infancy

So much is this the case, now that we know the second and fourth
digits are for a time fairly well developed, we might speak of a
Hipparion stage in the ontogeny of the horse. To admit that
the horse, before assuming its own specific characters, makes, as
it were, a deflection towards the not very ancient form Hipparion,
is hardly going far enough to justify the assertion that the horse
during its development assumes, one after another, the charac-
ters of its ancestors, or, in other words, except in the most limit-
ed sense, ‘climbs its own ancestral tree.’’’*°

Depéret, in the book to which reference has already been made,
not only presents an authoritative appraisement of the embry-
ological method of determining phylogenies, from the viewpoint
of palaeontology, but gives also a convenient summary of the
amount of correspondence of ontogeny with phylogeny as
determined from this same viewpoint:

“Has Palaeontology completely confirmed the conclusions
thus drawn from the embryology of existing beings? We may
approach this important question by two different methods.
The first method, which is the oldest and the one most generally
employed, consists in finding in geological strata forms which in
the adult state reproduce one of the transitory phases through
which the development of an existing animal passes. We give
to these fossil forms the name of Persistent Embryonic types.
Palaeontology is able to furnish us with a fairly large number of
examples of this. Thus the Fishes of the Primary epoch, such
as the scaly Ganoids, have a soft vertebral column in a state of
embryonic tissue or notocord, as in the existing Ganoids or Teleo-
steans....In the same way the Palaeozoic Amphibians pass, as
regards the ossification of the vertebral column, through a series
of progressive phases....These different phases are reproduced
in the development of our present Reptiles and Amphibians. In
recent and modern Ruminants the bones of the metacarpus and
of the metatarsus, separate in the embryo and the young animal,
become welded later in the adult into a cannon-bone caused by
the fusion of the two metapods. We know among the early
Ruminants genera... .in which the metacarpaland the metatarsal
bones remain distinct in the adult state.

" “We may also quote a few persistent types among the Inverte-
rates......

“But it must be clearly stated that these examples of representa-
tion in fossil adult species of the embryonic, or more correctly,
of the youthful characteristics of existing animals, cannot be

so Ewart, Journ. Anat. and Phys., Vol. XXVIII, 1893-94, pp. 348-350.

The Recapitulation Theory in Biology 33

generalized, and that they remain up till now in the state of
exceptional facts. ’’

The second mode of answering the question is that of studying
the development of fossils themselves, and this has been re-
ported in the earlier section dealing with the laws of accelera-
tion and retardation. The evidence for recapitulation there
presented belongs in character with that just cited.

With the exception of this last group of facts relating to the
shells of invertebrates the authorities quoted are in general
agreement. We must conclude that the palaeontological evi-
dence for recapitulation is not impressive. Among certain
groups of animals in some part of their history, some forms
are embryonic in a broad way, and a considerable number of
particular instances of the embryonic or youthful retention
of ancestral adult traces are noted. Apparently the conditions
favoring recapitulation in fossil shells are peculiar to such char-
acters.

(b) The Facts of Embryonic Resemblance.

The historical importance of von Baer’s law for the present
topic has been obvious enough. Darwin, Haeckel, and Spen-
cer either made it the point of departure of their arguments or
drew heavily upon it. Spencer showed clearly in the words
quoted from him that a consistent evolutionary application of
the law is equivalent to recapitulation. But the limitations
of the formula were noticed very early. Darwin alluded to the
common, but not invariable, resemblance between embryos in
the same class. Fritz Miller speaks of ‘‘developmental forms
now so totally different in the nearest allies, now so surpris-
ingly similar in members of the most distant groups.’”’® Spen-
cer regarded the generalization as an average truth only.
Haeckel and others found great difficulty in reducing to an order
consistent with the law the observed differences between com-
parable embryonic stages. The following extracts will indicate
the attitude of more recent writers toward the facts in question:

“Von Baer’s statement appears to be erroneous from a modern

point of view in the following respects. We know that in certain
large groups some forms develop in a very different way from

tipp. 254-256.
62 For Darwin, p. 97.

34 The Recapitulation Theory and Human Infancy

that followed by other members of the group....Again, it is
entirely arbitrary to assume that the group-characters are the
first to appear, and then successively those of the order, family,
genus, species. Finally....we do not find early embryos of a
group identical, for with a sufficient knowledge of the develop-
ment it is always possible to distinguish between the embryos
of different species, as well as between adults, only it is more
difficult to do so, because the embyyonic forms are simpler.”

ck put. to_test by
«making comparisons between embryos of closely-allied. animals

ad embryos of animale remotf
did not substantiate the law‘

ment is as follows:

ick’s more recent state-

“The law asserts that embryos of different species of animals
of the same group are more alike than the adults and that, the
younger the embryo, the greater are the resemblances. If this
law could be established it would undoubtedly be a strong argu-
ment in favor of the ‘‘recapitulation’”’ explanation of the facts
of embryology. But its truth has been seriously disputed. If
it were true we should expect to find that the embryos of closely
similar species would be indistinguishable from one another,
but this is notoriously not the case. It is more difficult to meet the
assertion when it is made in the form given above, for here we
are dealing with matters of opinion. For instance, no one would
deny that the embryo of a dogfish is different from the embryo
of a rabbit, but there is room for difference of opinion when it is
asserted that the difference is less than the difference between
an adult dogfish and an adult rabbit. It would be perfectly
true to say that the differences between the embryos concern
other organs more than do the differences between the adults,
but who is prepared to affirm that the presence of a cephalic
coelom and of cranial segments, of external gills, of six gill slits,
of the kidney tubes opening into the muscle-plate coelom, of an
enormous yolk-sack, of a neurenteric canal, and the absence of
any trace of an amnion, of an allantois, and of a primitive streak
are not morphological facts of as high an import as those implied
by the differences between the adults? The generalization
undoubtedly had its origin in the fact that there is what may be
called a family resemblance between embryos and larvae, but.
this resemblance, which is by no means exact, is largely superfi-
cial and does not extend to anatomical detail.’’5§

From these authoritative statements it appears that the
facts of embryonic resemblances fail to support recapitulation

ss Morgan, loc. cit., pp. 74, 75.
%4 Quart. Journ. of Micros. Sci. Vol. 36, N. S., 1894, pp. 35-52.
65 Darwin and Modern Science, p. 175.

The Recapitulation Theory in Biology _ 85
in all three of its main implications. The order of appearance
of characters is not uniformly, or even commonly, that required
by recapitulation, which is first those representative of the
order, and then in succession, of the family, genus, species.
In she second place, embryonic resemblance in comparable
stages does not vary directly with remoteness of kinship, but
shows often very great divergence from this rule, indicating
unlike careers in lines of descent in the same group and there-
fore great diversity in the appearance of variation during de-
velopment, at any period, and not only at the adolescent or
adult end of ontogeny. Finally, where resemblance does ex-
ist, it is not identity, nor even close, implying that the effect
of variation upon the same ancestral structure has not been
the same in allied lines of descent, but has been productive of
new structures, suggesting perhaps in broad outlines the an-
cestral structure, but still variant in every case, and essenti-
ally so. ¢

What is left for von Baer’s law is the ‘family resemblance.”
But family resemblance does not imply recapitulation. It
means at most a common ancestor.*¢ This common ancestor
may have had his ontogeny determined in any way, recapit-
watory or other. That this family resemblance may often be
striking without implying recapitulation is well shown in a
recent statement. The Nauplius larva is common to many
Crustacea. ‘‘But it is not in the least justifiable to deduce,
as some have attempted, that the Nauplius larva represents
the adult ancestral form from which the Crustacea as a whole
have sprung.” *” The Zoaea larva is similarly characteristic of
many widely separated Crustacean groups, nevertheless ‘“‘it
cannot possibly be looked upon as representing the adult an-
cestral type of these animals.” *

Again, ‘‘A larval form, yet more widely spread than either of
the Crustacean larvae mentioned, is the Trochosphere larva,
characteristic of Annelids of all kinds and curiously enough of
some Mollusks. . . . which in the adult state are entirely

66 ‘* When we recognize a larval or embryonal form as characteristic for a whole
animal group, we may not conclude therefrom that necessarily a similar phylogenetie
stage is represented by the same. We are justified only in the conclusion that the
ancestral form of this animal group had possessed that characteristic developmental
stage.’’ Hatschek, quoted by Montgomery, loc. cit., p. 185.

87 Smith, Primitive Animals, 1912, p. 64.

8 Ibid., p. 65.

36 The Recapitulation Theory and Human Infancy

different in their whole organization from worms of any de-
scriptive. This fact implies that the Trochosphere is an ex-
ceedingly ancient type of larva, which must have been possessed at
some period by the common ancestor of the Annelids and Mol-

lusks . . . There is however nothing to support the view
that the Trochosphere in any way represents the common an-
cestor of the Annelids and Mollusks. . .’’#

“We cannot however press the argument too far and say
that no larval form ever represents an adult ancestral form.
Every case must be judged on its own merits after taking into
account all the available evidence to be derived from the com-
parative study of related forms. Thus it seems indubitable
that the so-called Mysis larva, a stage assumed by [many mem-
bers of a group of Crustaceans] after the Zoaea. . . . does
very closely represent an adult ancestral form, the actual ex-
istence of which is nearly realized by the primitive Anaspides
and Schizopod shrimps. Here we are dealing with a late
larval form just before the adult structure is attained, and it
would appear not to have had time to have been profoundly
modified in accordance with larval existence. It would seem,
therefore, that we are more likely to meet with actual adult
ancestral types in the late larval or developmental stages of
fairly closely related animals, which have not had time to be
secondarily modified, than in the very early stages of more
remotely related forms, although these, in accordance with
von Baer’s law, may show many points of resemblance which
are lost in the adults.”’®

The writer from whom these sentences are taken is able to
accept von Baer’s law by a loose construction of it: “his [von
Baer’s] statement was that in any two or more related animals
the further back we go in their developmental history from the
egg the more do they resemble one another. In this form
it must be admitted that von Baer’s law holds good with very
few exceptions.....’’%

This statement may be compared with those of the author-
ities already quoted. It appears that even on this loose con-
struction of the meaning of von Baer’s formulae there is no
settled unanimity of opinion among biologists. These dis-
crepancies, however, do not affect the essential significance
of the law for recapitulation, for as to this all the writers quoted
agree in that embryonic likenesses do not of themselves imply

59 Smith, Primitive Animals, 1912, pp. 68, 70.
60 Ibid., pp. 66-68.
© Ibid., p. 58.

The Recapitulation Theory in Biology 37

a law of recapitulation, but at most only the retention of ances-
tral forms. Whether these are to be regarded as embryonic
or adult forms is a matter for study in each case.

(c) The Facts of Comparative Morphology.

The third type of evidence for recapitulation, that involving
a ee with forms common to “To
er__existing groups, may I now be referred to. There are, first,

Hee phases in the very early embryonic development of Met-
azoa suggestive of a progression from the unicellular condition,
and in the development of Chordata, from the simple metazoon
form to the chordate and vertebrate condition. The case for
recapitulation on these lines is well stated by Dendy in his
recent text-book.

“We have already referred....to some of the earlier stages
in the development of that primitive fish-like animal Amphioxus.
Let us next enquire how these stages may be interpreted in accor-
dance with the recapitulation hypothesis. The unicellular
ovum obviously represents the remote protozoon ancestors which
were common to the whole animal kingdom, and which are also
represented at the present day by independent unicellular or-
ganisms such as the Amoeba. The segmentation of the ovum
into primitive embryonic cells or blastomeres represents the
transition from the condition of the simple protozoon to that of
the protozoon colony, in which the individual cells, instead of
separating, as in the dividing Amoeba, remain together, but still
without undergoing any marked differentiation and division of
labor. The arrangement of the blastomeres in the form of a
hollow sphere, the blastula or blastosphere, with a single layer
of cells surrounding a central cavity, represents the formation
of such a protozoon colony as we see in the existing Volvox or
Sphaerozoum. The process of gastrulation, whereby the single-
layered blastula is converted into a two-layered gastrula, with
primitive digestive cavity (enteron) and primitive mouth (blas-
topore) represents the transition from the protozoon colony to
the coelenterate stage of evolution, the latter being still repre-
sented at the present day by such forms as Hydra, Obelia, the
jelly-fish, the corals, and all their numerous relations, which
retain in their organization all the essential features of the gastru-
la, though generally complicated by the development of tentacles,
skeleton, etc. The development of the coelomic pouches as
outgrowths of the primitive digestive cavity, and the conversion
of these into mesoblastic somites, arranged serially or metameri-
cally down each side of the body, mark the transition from the
unsegmented and coelenterate condition to the metamerically

38 The Recapitulation Theory and Human Infancy

segmented and coelomate condition. The cavities of the coelo-
mic pouches form the coelom or body cavity, which is at first
transversely sub-divided into compartments, as it still is in the
adult earthworm, while their walls form the third germ-layer
or meso-blast, lying between the epiblast which covers the sur-
face of the body and the hypoblast which lines the digestive
cavity. Along the mid-dorsal line of the body a strip of epi-
blast sinks down and becomes folded into the form of a tube, the
rudiment of the central nervous system (brain and spinal cord)
and beneath this tube a long strip of hypoblast becomes nipped
off from the roof of the gut, forming the notocord or axial skele-.
tal rod—the foundation around which in higher types the verte-
bral column is built up. A little later the front part of the gut
becomes pierced by gill-slits for purposes of respiration and the
primitive chordate condition is thus fully attained.

Amphioxus does not progress much beyond this stage in its
development. ...Amphioxus is a chordate animal but it is not a
true vertebrate. It probably, however, represents fairly close-
ly a stage of evolution through which the ancestors of the verte-
brates have passed, though it becomes somewhat modified by
secondary features in the later stages of its development.’ ®

In the case of man Haeckel carried the series beyond that
represented by Amphioxus through three stages, the cyclostoma,
the ichthyoda, and the amniote, making ten stages in all re-
presenting an ontogenetic-phylogenetic correspondence.* But
as suggested above in the account of Haeckel’s part in the for-
mulation of the theory of recapitulation, the ancestral refer-
ence in the higher stages is often to ontogenetic conditions in
lower forms, making the adult phylogenetic equivalence in such
stages indirect, to say the least.

It is significant, by the way, that'the chief exponent of recap-
itulation is able to present an ontogenetic-phylogenetic cor-
respondence of ten stages only. When it is considered that on
the phylogenetic side the sequence occupied millions of years
and proceeded through an almost indefinite number of special
forms, the limitations of a conception of ontogeny as illus-
trative of the chronological sequence of ancestors become fairly
obvious.

It is almost impossible to report biological opinion as to the
significance of the kind of fact now referred to, so various are
the views held regarding it. One can merely set the outside.

* Outlines of Evolutionary Biology, 1912, pp. 265-267.
62 Evolution of Man (5th ed. trans.), pp. 547-550.

The Recapitulation Theory in Biology 39

limits within which it ranges. These are represented at one
end by the views of Dendy and Haeckel, as indicated, and those
of the palaeontologist, Depéret, at the other. The latter re-
fers to Haeckel’s hypothetical ancestors as “visions of the
mind” because no fossil evidence can be offered for them.
It is probably true that most naturalists and embryologists
do not wholly discount the phylogenetic significance of the
series of early embryonic stages among the Metazoa, and are
willing to admit that it may possibly represent in a very gen-
eralized fashion what actually happened in the early evolution
of organic forms. It may be well, however, to report here a
recent conservative statement apparently aimed directly at
the type of discussion illustrated in the quotation from Dendy
just given:

if3

....In the present state of knowledge we are able to separate
the various components of the animal kingdom into a certain
number of divergent groups or phyla; and that within the limits
of these phyla, although we are far from knowing even approxi-
mately in every case the course evolution has followed, yet we
are safe in concluding that all the diverse ramifications have
originated in the remote past from one common source, or type.
But when we attempt to go behind the phyla and discover their
origin and inter-relationships, we leave the firm ground alto-
gether and wander in a slippery and nebulous region of specula-
tion.

It is true that certain hypotheses of a plausible character have
been suggested which have satisfied uncritical minds, and which
we often hear advanced as a part of ascertained science and
accepted in an otiose spirit. We are urged to believe that life
“originated”’ in certain chemical compounds which on attaining
a certain degree of complexity began to exhibit the fundamental
properties of life; and from these comparatively structureless
masses the nucleated cell was evolved and the unicellular animals
and plants, the Protozoa and Protophyta, made their appearance;
that these gave rise to cell colonies, the Metaphyta on the one
hand, and the Metazoa on the other. The Coelenterate type
of organization is presented to us as the form in which the early
Metazoa had their being, and from this by the addition of the
mesoderm we arrive at the Platyhelmia, and from them by the
addition of a coelom and of metameric segmentation at the seg-
mented Annelid. And so by the addition and subtraction of
their characteristic qualities we may pass in imagination from
one fundamental type to another; but what is there of reality
in these speculations? They rest not on any objective evidence

40 The Recapitulation Theory and Human Infancy

but upon the tendency of the mind to pass from the apparently
simple to the manifestly complex, and to regard the former as.
primitive and ancestral and the latter as secondary and deriva-
tive.’

Another class of facts representing this third type of evidence
for recapitulation is made up of certain profound metamor-
phoses observable in the development of certain groups possess--
ing larvae which recall in a rather striking way the ancient
forms from which groups in question are believed to be descend-
ed. These facts bear unmistakable evidence to a course of
evolution in parts of some lines of descent, in which variations.
or mutations leading to the higher form have supervened em--
phatically at the adult end of the ontogeny. Ordinarily these
larvae have been adapted in important ways to the special
conditions of their life as larvae, but not so seriously as to wholly
obscure the ancient structures upon which the adaptations
took place. These larval forms are untrue to the ancient
pattern also by virtue of the fact that they are transient, con-
stantly progressing in the direction of the adult condition,
and their organization is therefore disposed in part with refer-
ence to the demands of the future. The customary example
is the familiar metamorphosis of the common frog. Similar
cases are found among the ascidians, the crustaceans, the in-
sects, the flat fishes. The only way in which the ancestral
reference in these cases is denied is by so minimizing the resem-
blance to the ancient form that the recapitulation is said to be-
wholly superficial and lacking in real significance. This has
been done by a few extreme critics of the recapitulation theory.
Currect opinion of this class of facts is reported below.

Finally these are those rudiments and isolated special char-
acters in the embryos of higher vertebrates which recall sim-
ilar characters and conditions in the adults of lower vertebrate
forms. These are referred to by Sedgwick as follows:

“...the embryos of the higher vertebrate possess in the struc-
ture of the pharynx and of the heart and vascular system cer-
tain features—namely, paired pharyngeal apertures, a simple
tubular heart, and a single ventral aorta giving off right and left

«4 Smith, Primitive Animals, pp. 14 et seg.

For an elaborate hypothesis regarding the evolution of animal forms largely on
the type of evidence now under discussion, see Bernard, Some Neglected Factors in
Evolution, 1911.

The Recapitulation Theory in Biology 41

a number of branches which pass between the pharyngeal aper-
tures—which permanently characterize these organs in fishes.
The skeleton, largely bony in the adult, passes through a stage
in which it is entirely without bone, and consists mainly of carti-
lage—the form which it permanently possesses in certain fishes.
Further, the vertebrate embryo possesses for a time a notocord, a
segmented muscular system, a continuity between the pericar-
dium and the posterior part of the perivisceral cavity—all
features which characterize certain groups of Pisces in the adult
state. Instances of this kind might be multiplied for the work
of anatomists and embryologists has of late years been largely
devoted to adding to them.’’®

There is no disposition evident on the part of biological stu-
dents to deny the ancestral reference of this class of facts. Opin-
ion differs as to the sense in which they are to be regarded as
ancestral. These differences of opinion are reported in the
second section following. But it is important to note that
such facts coexist with other embryonic conditions for which
no ancestral reference is found. For instance,

“Examples of embryonic characters which are not found in
the adults of other vertebrates are the following: At a certain
stage of development the central nervous system has the form
of a groove in the skin, there is a communication at the hind
end of the body between the neural and alimentary canals, the
mouth aperture at the first has the form of an elongated slit,
the growing end of the Wolffian duct is in some groups continuous
with the ectoderm, and the retina is at one stage a portion of
the wall of the medullary canal. In the embryos of the lower
Vertebrates many other instances of the same interesting char-
acter might be mentioned.’’*

13. Recapitulation and the Physiology of Development.

The later history of recapitulation has been seriously affected
by two lines of thought which combined to unsettle some of
its primary assumptions. These followed upon the gradual

6’ Encyclopaedia Britannica, 11th edition, art. Embryology, p. 322.

% Ibid.,

For a statement of the evidence favorable to recapitulation, see Marshall, Lectures
on the Darwinian Theory, 1894, and Biological Lectures and Addresses, 1894, by the same
author. Miall’s comment on the presentation of Marshall is, ‘‘ Development tells
us something, I admit, and that something is welcome, but it gives no answer at alt
to most of the questions we put. . . . The best facts of the Recapitulationist
are striking and valuable, but they are much rarer than the thoroughgoing Recapitu-
lationist admits; he has picked out all the big strawberries and put them at the top
of the basket.’’ Brit. Assoc. for the Adv. of Science, 1897, p. 682.

42 The Recapitulation Theory and Human Infancy

depreciation of the inheritance of acquired characters which
took place in the latter part of the last century, and the appli-
cation of experimental methods to the facts of growth and de-
velopment (Experimental Zoology, Experimental Embryology,
The Mechanics of Development, Experimental Morphology).
The inheritance of acquired characters favored a conception
of variation at the adult end of ontogeny in response to the
direct action of the environment. It was one of the chief in-
terests of Hyatt to show how these latest acquisitions in devel-
opment became successively inherited in such fashion that
they left in the ontogeny a true record of the changes in descent,
and it is well known that the three men whose authority gave
the greatest prestige to recapitulation, Darwin,’ Haeckel,
and Spencer, all acknowledged the direct action of the environ-
ment as a source of variation.

With the progress of the study of development the complex-
ity of the whole matter of growth and differentiation of struc-
ture became apparent, and the implications for the dominant
idea of recapitulation were pointed out. Wilhelm His, in 1874,
in ‘“Unserer Korperform,” gave expression to his dissatisfac-
tion with Haeckel’s view of phylogeny as the mechanical cause
of ontogeny, and introduced the idea of forces inherent in the
process of growth itself to account for its changes of form. His
words are as follows:

“In the entire series of forms which a developing organism
runs through, each form is the necessary antecedent step of the
following. If the embryo is to reach the complicated end-forms,
it must pass, step by step, through the simpler ones. Each
step of the series is the physiological consequence of the preceding
stage and the necessary condition of the following. Jumps, or
short cuts, of the development process, are unknown in the
physiological process of development. If embryonic forms are
the inevitable precedents of the mature forms, because the more
complicated forms must pass through the simpler, we can under-
stand the fact that paleontological forms are so often like the

embryonic forms of today. The paleontological forms are
embryonal, because they have remained at the lower stage of

61‘ Whatever influence long-continued use or disuse may have had in modifying
the limbs or other parts of any species, this will chiefly or solely have effected it
when nearly mature, when it was compelled to use its full powers to gain its own liv-
ing; and the effects thus produced will have been transmitted to the offspring at a
corresponding nearly mature age.’’ Origin of Species, II, 6th ed., London, 1902,
Pp. 613.

The Recapitulation Theory in Biology 43

development, and the present embryos must pass also through
lower stages in order to reach the higher. But it is by no means
necessary for the later, higher forms to pass through embryonal
forms because their ancestors have once existed in this condition’’®

Haeckel’s phylogenetic method is therefore ‘‘a mere by-path,”’
and is “not necessary at all for the explanation of the facts of
embryology.”

The implications of the germinal origin of variations were indi-
cated by Hatschek in these sentences:

““When one premises (as Haeckel does) that the modifications
which the developed individual inherits directly through outer
influences become hereditary in its descendants, then the ex-
planation shapes itself very simply. The new acquisitions of
the adults bring about immediately a prolongation, in the single
generation very insignificant, in the course of generations in-
creasing, of the ontogenetic row of forms in the descendants.
But when one holds fast to the view that only those newly oc-
curring characters become inherited, which have arisen through
variation of the reproductive cells. ...another explanation seems
necessary. One must presuppose ‘overstepping varieties.’ With
this name I would call such varieties as consist in a prolongation
of the ontogenetic row of forms.”®

From this conception another seems to follow:

“We must consider it as a general law, derivable from the
principle of causality, that with the phylogenetic modification
of the animal form (individual cycle) never only the end stage
becomes changed, but always the whole row from egg cell to
the end stage. Each modification of the end stage necessitates
a change of the egg cell itself.’’7°

In view of the truth contained in the last sentence, we must
believe that through the course of descent from the unicellular
condition to the existing higher species, the germ cell has under-
gone an evolution from simple to complicated conditions, cor-
responding to the difference in organic complication suggested
by a comparison of existing protozoon and highly differentiated
adult animals. In what sense, then, can the ovum of a higher
vertebrate be said to correspond with the ancestral Amoeboid?

68 Quoted by Morgan, Evolution and Adaptation, p. 71.

® Quoted by Montgomery, Analysis of Racial Descent, p. 184, from Lehrbuch der
Zoologie, 1888.

70 Quoted by Montgomery, loc. cit.

44 The Recapitulation Theory and Human Infancy

“Our doctrine is, that the species-cell, even as the adult,
many-celled representative of the species, has passed through
@ progressive, and, indeed, in general a corresponding develop-
ment in the course of phylogeny. This view appears to stand
in contradiction to the biogenetic law....We must drop the
expression ‘repetition of the form of extinct forefathers’, and
put in its place the repetition of forms which are necessary for
organic development, and lead from the simple to the complex. . .
The egg-cell of the present time, and its one-celled predecessor
in the phylogenetic history, the amoeba, are only comparable
in so far as they fall under the common definition of the cell,
but beyond this they are extraordinarily different from each
other. ...Undoubtedly there exists in a certain sense a parallel
between the phylogenetic, and the ontogenetic, development....
Ontogenetic studies give us therefore only greatly changed copies
of phylogenetic stages. The two correspond not according to
their actual contents but only as to their form.’”’7!

This is the argument and conclusion of the embryologist, O.
Hertwig (1898). Hertwig’s concluding idea that the embryo
repeats the ancestral stage in its form only does not commend
itself to Morgan as a model of clear thinking: ‘Can we be asked
to believe for instance that a young chick repeats the ancestral
adult fish form but not the contents of the fish?’’”

Montgomery was so greatly impressed by these physiological
considerations that he was compelled to repudiate recapitula-
tion in toto.

“...@ new racial character is not something, like dead

ballast, passively transported by the germ plasm; it is a
change in the living processes....The egg of a Mammal is as
dissimilar from that of a Fish as their adult stages, no matter
whether the differences are as perceptible or not. This was the
idea of the great old-master von Baer; the egg is as much a
bird as is the hen.....The earlier the ontogenetic stage the
more the individual may seem to be like its simple ancestors;
but in reality it is just as unlike them in those earlier stages
as in its matured condition. For degree of difference must not
be adjudged in this case from visible differences alone, but rather
equally well from differences in growth energies and ultra-ob-
servational structural bases, which, though not perceptible, are
nevertheless just as clearly proven to exist....Therefore we
can only conclude that the embryogeny does not furnish any

71 Quoted by Morgan, Evolution and Adaptation, pp. 78, 79, 80, 82.
7 Ibid., p. 83.

The Recapitulation Theory in Biology 45

recapitulation of the phylogeny, not even a recapitulation
marred at occasional points by secondary change.’

According to Cumings the error latent in the views of Montgom-
ery is the confusion of morphology with physiology.

“The confusion arising from this source colors all the argument
of Montgomery, in which he endeavors to prove that new specific
characters must have some representation in the ovum—a view
which we must certainly agree with—and that therefore ‘the
whole row’ of cells from the ovum to the adult must be different.
We grant that the ‘whole row’ is different in some way, different
in the play of energies; but it may conceivably be morphologi-
cally identical up to the very point where the new character
is added. It is just as easy to conceive that the energy, or what-
ever we choose to call it, that is at a certain stage of development
to produce a certain rib or spine or color-band on the shell of a
gastropod, may be handed through the row of cells reaching up
to the given stage, without producing a single recognizable
morphological change in the row, as compared with the individual
that is not to possess the new character, as it is to conceive the
opposite. The argument for the one view is just as a priori
as the argument for the other view. It is also perfectly conceiv-
able that the morphology of the individual cells in the row might
differ after the acquisition of the new character (in so far as this
assumption is required by recent cytological studies), and yet
not a single organ or part of the organism be different up to the
stage in ontogeny when the new character appears. Unless,
therefore, a change in the energies of the cells inevitably neces-
sitates a change in the morphology of all the cells or all the organs
which they compose, the argument of Montgomery proves
nothing.” 74

The argument between Montgomery and Cumings apparent-
ly labors with difficulties of a logical character as well as with
issues of fact, and suggests the desirability of clear concep-
tions of the business of intelligence in the presence of the truly
genetic phenomenaof development. By carrying back in thought
to the germ cell all the derivative complexities of the adult,
Montgomery succeeds in imputing to it and to all the interven-
ing stages a correlative complexity out of keeping with the ob-
vious simpler conditions of the earlier ontogenetic stages. By a
similar logical extreme Cumings conceives a segregation of the
physiological ‘energies’ from the objective morphological

7 Analysis of Racial Descent, pp. 191, 192.
7% Indiana Acad. of Science, 1908-09, pp. 310, 311.

46 The Recapitulation Theory and Human Infancy

changes up to the point in development when the new variation
appears, when, presumably, the hitherto unrelated ‘“energies’’
are suddenly connected up with the morphological sequence
of events.

It has been clearly pointed out by the students of genetic
logic that in dealing with a genetic series of events the intel-
ligence works under constraints which do not hamper it in non-
genetic phenomena. A primary obligation laid upon thought
in such circumstances is that it shall deal fairly and accurately
with the phenomena of any one stage without reading into it
what the stage in question may ultimately lead to or what it
has proceeded from, except as evidences of these things are
actually exhibited in the phenomena.7®

With these restrictions in mind we may recur to the facts
of development as they have been presented by the experi-
mental students of the subject. It is worthy of notice that
one of the many names applied to the experimental study of
development is Experimental Morphology, and it seems evi-
dent that in so far as the term ‘‘energies,’’ in Cumings’s usage,
is necessitated by the observed facts it is required in explan-
ation of morphological changes, minute and gross, that is, changes
of form. A primary dynamic expression, “‘induction,’’ employ-
ed by Driesch, and by Jenkinson after him, is thus defined by
the latter: ‘‘An ‘induction’ is simply an effect produced upon
the parts that are developing by other parts, or possibly by some
factor in the external environment.’’7* Perhaps, then, a juster
statement of the case would be that inasmuch as latent ‘“en-
ergies’’ are known only as they express themselves in the struc-
ture and behavior of cells and their aggregates, resemblances
and differences in the latter will be the only available index
to the resemblances and differences of the ‘‘energies’’ which
lie within. Ontogenetic-phylogenetic resemblances, when they
have been truly described, therefore, must be regarded as real
and not factitious. Moreover, although it must be admitted
that the living substance has been greatly modified and differ-
entiated through descent, does it follow that it has been utterly
made over? If homologies do not refer to essential resemblances,
to what can they refer?

7 See Dewey, Studies in Logical Theory, Ch. I; Baldwin, Development and Evolu-
tion, Ch. X1X.
78 Experimental Embryology, 1909, p. 2.

The Recapitulation Theory in Biology 47

The question thus becomes one of accurate description, of
the greatest difficulty necessarily, in view of the peculiar nature
of the facts upon which all inferences as to ontogenetic-ancestral
comparisons rest. In the following extract from Minot is pre-
sented an illustration of a somewhat closer approach to the
comparison than is customary:

“One of the first things which will impress itself upon the
student of vertebrate embryology is, that, though he may find
at the proper stage in the embryo the organs of the body clearly
developed, yet, owing to the fact that they consist of relatively
undifferentiated cells, they are incapable in large part, of per-
forming functions which they are ultimately to assume, and the
performance of which is the very object of their development.
This change in histological structure brings about a marked
unlikeness of the embryo to the assumed ancestral type.’’?7

The main point of difference between Montgomery and Cum-
ings, is, however, not one of logical form merely, but turns upon
a significant question of fact. This has to do with the manner
in which the specific differences, which by general consent reside
n the germ-cell, affect the subsequent course of development.
Do these differences express themselves equally upon all periods
of ontogeny, and so disturb “the whole row’’ of stages, as
Montgomery implies, or can they be regarded as relatively
unimportant in certain phases and highly important in others,
as suggested by Cumings? Does a variation affect the entire
ontogeny uniformly, or does it exhibit itself at a given period
when the conditions are favorable? In short, how much liberty
has any phase of growth to evolve by itself without markedly
disturbing other phases?

The facts, as reported by the investigators, seem to favor the
suggestion of Cumings. Thus in the language of Driesch,

“|. .the actual fate of a part need not be identical with its
possible fate, at least in many cases;....There are more morpho-
genetic possibilities contained in each embryonic part than are
actually realized in a special morphogenetic case.’’78

That is to say, the fate of a part is determined in some degree
in the course of its subsequent history. A complementary
thought is embodied in these words of Morgan:

71 Laboratory Text Book in Embryology, 2d ed., 1910, p. 14.
78 The Science and Philosophy of the Organism, Vol. 1, 1909, p. 77.

48 The Recapitulation Theory and Human Infancy

“There is certainly no evidence in favor of the view that the
organization of the egg need be anything like the organization
of the embryo that comes from the egg, although the organiza-
tion of the egg may be perfectly definite in its character.”’”?

The several “factors’’ contributing to the differentiation of
structure are thus summarized by Jenkinson:

“Experimental investigation, as far as experiment has at
present gone, has shown, first, that a certain complexity of the
physical and chemical environment is a necessary condition
of normal development; that complexity may, it is true, vary
within certain limits, but those limits can only be transgressed
under pain of abnormality or death. In the second place, it
has been demonstrated that the initial structure of the germ,
and the mutual interactions of the parts as they develop are
both indispensable factors. ’’8°

We are thus encouraged to believe that development is neith-
er an independent process of self-realization of the germ-cell on
the one hand, nor a differentiating effect of a regulative environ-
iment upon a neutral protoplasm on the other, but rather an
intricate and puzzling interaction or mutual interrelationship
of specific external influences and internal conditions. The
authoritative primacy of the germ-cell thus becomes greatly re-
duced. ‘To recall the usage of von Baer, the egg, the chick, and
the hen, the entire ontogeny in fact, is really the bird. The two
important ideas for the present discussion of ontogenetic-ances-
tral resemblances, to be derived from these considerations,
are these: the fate of any embryogeny is in part determined
in the course of ontogenetic history, and the succession of
events in this history permits a new organization in each phase.
This conception of development receives empirical support
from the circuitous and indirect course taken by many animals
from the germ-cell to the terminal or adult condition. If then
the caterpillar is found to have certain describable resemblances
to a worm, or a tadpole to a fish, the fact that the subsequent

79 Regeneration, 1901.

80 Experimental Embryology, 1909, p. 279.

For a summary of the results of experimental study of the effect of environmental
differences upon the life cycle, see Morgan, Experimental Zoology, 1910, Chaps.
XIX-XXIII.

A recent significant discussion of the effective relationship of environment to or-
ganic existence, is to be found in Henderson, Fitness of the Environment, 1913.
A summary statement from this book is the following: ‘‘. . . . somehow, be-

neath adaptations, peculiar and unsuspected relationships exist between the proper-
ties of matter and the phenomena of life."

ae a ae

The Recapitulation Theory in Biology 49

development leads to a butterfly or a frog need not necessarily
be held to discredit these resemblances, and the force of Cumings’
contention receives a certain justification.

That this position has limitations appears from one other
aspect of the study of development. Apparently it is possible
to over-emphasize the isolation of phases in ontogeny. For
although, as Morgan suggests, the organization of one period
need not be like the organization of another, still we are told
the essential unity of an animal is the central fact of the in-
ternal condition of its differentiation of structure, rather than
any mere interaction of the parts. This feature of development
has led to radical differences of opinion as to its import, and has
been interpreted in both vitalistic and mechanical terms. Aside
from the matter of interpretation the fact is admitted. The
following quotation from Morgan presents the situation as
viewed by one student of the facts:

“The central problem for embryology is the determination
of what is the cause, or causes of differentiation. Our analysis
leads us to answer that it is the outcome of the organization;
but what is the organization?’’®

The organization....is a structure or arrangement of the
material basis of the organism, and to it are to be referred all
the fundamental changes in form, and perhaps of function as
well....We know this organization at present from only a few
attributes that we ascribe to it, and are not in a position even
to picture to ourselves the arrangement that we suppose to
exist. ’’82

The whole discussion of the section is thus shown to be full
of difficulty. We must conclude that the resemblances between
ontogenetic stages and ancestral forms are real and not factitious;
still they are resemblances that show themselves among en-
tities in some fashion unique in every case. But this seems to
be true of all resemblances among organic beings.

14. Biological Opinion Regarding Recapitulation.

The situation in biology with reference to recapitulation
may be summed up as follows:

1. Recapitulation as a record of phylogeny is denied in foto.

2. The traditional view is still upheld.

81 Regeneration, p. 258.
82 Ibid., p. 288.

50 The Recapitulation Theory and Human Infancy

3. The facts are regarded as indicating resemblances between
present ontogenies and ancestral ontogenies.

4. The third view is held, but cases of recapitulation are
admitted.

(1) Montgomery’s general denial of recapitulation on phys-
iological grounds has been noted and discussed in the section pre-
ceding. In an article written in 1897, Hurst takes an equally
radical position.

‘.... ontogeny is not an epitome, is not a record, either perfect
or imperfect, of past history, is not a recapitulation of the course
of evolution.”

Hurst’s argument runs as follows:

“Tn order that any structure of the adult which varies, and
hence ceases to exist as an adult structure at all, may become an
ontogenetic record of that adult structure, it is necessary that
variation should occur in a way utterly unlike the way in which
it does actually occur. The more the adult structure comes to
be unlike the adult structure of the ancestors, the more do the
late stages of development undergo a modification of the same
kind. This is not mere dogma, but is a simple paraphrase of
von Baer’s law....

“In order to produce a ‘record’ it isnecessary that new chapters
be added at the end of the pre-existing record. It is necessary,
in fact, that as the adult structure varies in one direction, the
late stages in development shall vary in another, so as to become,
not more like the new adult structure than they were before,
but more like the old ones. 88

In an article in reply to Hurst, in the same year, Bather makes
the following comment upon the former’s argument:

“This is hardly a fair statement of the case. It is not correct
to say that the late stages of development must vary in another
direction; for it surely is the case, in any series of parents and
offspring, which are varying in a given direction, and which we
may denote Al, A2, A3, An, that A6 is nearer to A7 than A5 is.
Consequently, if the latest stage of development of the form A7
resembles A6, it is necessarily more like A7 than a stage that
resembles A5. That is to say, on the Recapitulation Theory,
the stages of development vary in the same direction as the
adults.’’ ™

Bather substitutes for Hurst’s method of variation that of
the Hyatt school, with which we are familiar, and then says,

88 Natural Science, Vol. II, 1893, pp. 197, 198.
% Natural Science, Vol. II, p. 278.

The Recapitulation Theory in Biology 51

“Although the adherents of the Recapitulation Theory will
doubtless accept the above as, in the main, a correct statement
of the method of development, yet not the most sanguine of
them will hope to find so perfect an epitome of phylogeny in
the majority of cases.”” It is ‘‘truly remarkable that we should
get as much recapitulation as we do.’’85

Hurst rested his argument mainly upon von Baer’s law and
the cases cited in its favor by Darwin, with a few of hisown. In
his reply Bather refers to cases which point very strongly to
an actual retention of adult characters in ontogeny, and ques-
tions Hurst’s use of von Baer’s law. This law was meant to
refer to existing groups.

‘« _..there is all the difference in the world between filial and
fraternal relationship, and although von Baer’s law is undoubt-
edly true of the latter, there are many objections to supposing
that it is equally true of the former.”

(2) In the section on acceleration and retardation it was shown
that many palaeontologists strongly uphold the theory of reca-
pitulation and present many illustrative cases especially among
invertebrate fossils. That recapitulation in practically the form
given it by Haeckel still has advocates appears from the fol-
lowing extract of a recent text-book.

“Tn short, the embryological investigation of both animal and
vegetable organisms leaves no doubt as to the general truth of
the recapitulation hypothesis, and must convince any unbiased
observer that, however much modified it may be by abbreviation
and by the superposition of secondary features, the life-history
of the individual is essentially a condensed epitome of the ances-
tral history of the race. The law of recapitulation, indeed, may
be regarded simply as a logical extension of the law of heredity,
for every organism tends to inherit the characters not only of
its immediate progenitors but of all its ancestors, and these
characters appear in the individual life-history in the same order
as that in which they first appeared in the ancestral history—
in other words, ontogeny is a repetition of phylogeny and can
only be explained in terms of organic evolution.’’®¢

Perhaps the following quotation from a recent text-book of
embryology is more representative of the views of those who
still accept recapitulation. It will be noticed that the histor-

86 Natural Science, Vol. II, p. 278.
8¢ Dendy, Outlines of Evolutionary Biology, 1912, p. 281.

52 The Recapitulation Theory and Human Infancy

ical reference is a general one and not to a series of ancestral
forms.

“This repetition is seldom particular. or detailed, never com-
plete, yet so many of the phenomena of development can be
satisfactorily interpreted from the historical point of view, seem-
ing to have this historical sign rather than an immediately adap-
tive relation, that as a general statement the law remains funda-
mentally true.’’8?

(3) The view that the facts upon which the traditional theory
of recapitulation has been based can be better explained as indi-
cating resemblances between ontogenies of descendants and
ontogenies of ancestors has the support of Hurst, Morgan,
Sedgwick, Cunningham, Griggs, and others. Of this view
Griggs (1909) has this to say:

“The form which has the largest number of adherents is per-
haps that proposed by Morgan (’03), who believes that animals
in their ontogeny repeat not the adult, but the embryonic stages
of their ancestors. ... Much of the evidence which the zodlogists
bring forward in favor of such a modification as against any
broader application is so conclusive, one must acknowledge
that such is a correct statement of the facts in the particular
cases cited, whatever the general law of development may be....

“The evidence presented by the kelps clearly tends to establish
the repetition theory of Morgan.’

Griggs does, however, find evidence among the kelps of the
retention of adult characters, and concludes with a statement
favorable to recapitulation.

Hurst’s application of von Baer’s law to the disparagement
of recapitulation has been given above. His constructive
statement from the same point of view follows:

“Hach transient stage in the development of any individual
is a modification of the corresponding stage of development of
its ancestors. It is in no case a modification of the adult stage
of the ancestor. The adult stage of a bird, and no other, cor-
responds to the adult stage of the fish-like ancestors (if it ever
had such ancestors.) ’’®

Morgan refers to this suggestion of Hurst with approval.
His own treatment of the subject under discussion may be

87 Kellicott, General Embryology, 1913, p. 24.
88 Kelps and the Recapitulation Theory, Amer. Naturalist, Vol. 43, 1909, p. 97.
89 Loc. cit., p. 199.

The Recapitulation Theory in Biology 53

summarized. Passing in review the most prominent of the
cases that have been offered in support of recapitulation, namely,
the gill-clefts of reptiles, birds, and mammals, the notocord in
the vertebrate series, the development of the skull, of the kid-
neys, of the heart, with some others, and noting in some de-
tail in each case the likeness of the ontogenetic formation to
the corresponding conditions and functions at different levels
in the chordate series, he is impressed by the following facts.
Certain differentiations, such as external gills in the tadpole,
do not seem to have any representation among adults in the
lower groups. Such transformations as those of the tadpole,
can only be regarded as at best analogous to ancestral transi-
tions. More especially, the gill-clefts appear as early in the
development of the mammal as in the salamander or fish, which
seems paradoxical if the appearance in the mammal is a repeti-
tion of the adult amphibian stage. The case is not greatly
different with the notocord, skull, kidneys, and heart. Again,
in the cases of rudimentary teeth in birds, whales, and other
animals, it is manifestly absurd to claim that the ancestral adult
condition is repeated when rudiments only appear. Finally,
the possible complete loss of ancestral stages is shown in the
lack of any indication in the ontogeny of the snake of the limbs
of its lizard-like ancestors. Cases of the repetition of adult
ancestral stages outside the group of vertebrates, he avers, are
often doubtful, sometimes little less than fanciful. Moreover,
the work of certain students among the invertebrates shows that
common embryonic forms are found which could not possibly
be regarded as due to the retention of adult ancestral forms.

How, then, are the apparent resemblances between the em-
bryos of higher forms and the adult of lower animals to be ex-
plained?

“The answer is that this resemblance is deceptive, and in so
far as there is a resemblance it depends on the resemblance of
the adult of the lower form to its own embryonic stages with
which we can really make a comparison. The gill-slits of the
embryo of the chick are to be compared, not with those of the
adult fish, but with those of the embryo of the fish... .It is
only the embryonic stages of the two groups that we are justified
in comparing; and their resemblances are explained on the as-
sumption that there has been an ancestral adult form having
these embryonic stages in its development and these stages

54 The Recapitulation Theory and Human Infancy

have been handed down to the divergent lines of its descend-
ants.’

In the opinion of Sedgwick the facts implying an ancestral.
reference have been much exaggerated, but a sufficient number
of unequivocal cases do exist to require explanation. His ex-
planation follows:

‘“‘A disappearing adult organ is not retained in a relatively
greater development by an organism in the earlier stages of its.
individual growth unless it is of functional importance to the
young form. In the cases in which the whole development is
embryonic this rarely happens, because the conditions of em-
bryonic life are so different from free life that functional embryon-
ic organs are usually organs sui generis, e. g., the placenta, am-
nion, etc., which cannot be traced to a modification of organs:
previously present in the adult. It does, however, appear to
have happened sometimes, as an instance of it may be mentioned
the ductus arteriosus of the Sauropsidan and Mammalian
embryo. On the other hand, when there is a considerable period
of larval life, it does appear that there is a strong case for thinking
that organs which have been lost by the adult may be retained
and made use of by the larva. The best known example that
can be given of this is the tadpole of the frog. Here we find
organs, viz., gills and gill-slits, which are universally regarded as
having been attributes of all terrestrial Vertebrata in an earlier
and aquatic condition, and we also notice that their retention
is due to their being useful on account of the supposed ancient
conditions of life having been retained. Many other instances,
more or less plausible, of a like retention of ancestral features
of larvae might be mentioned, and it must be conceded that
there are strong reasons for supposing that larvae often retain
traces, more or less complete, of ancestral stages of structure..
But this admission does not carry with it any obligation to ac-
cept the widely prevalent view that larval history can in any
way be regarded as a recapitulation of ancestral history. Far
from it, for larvae in retaining some ancestral features are in no
way different from adults; they differ only from adults in the feat-.
ures which they have retained. Both larvae and adults retain an-
cestral features, and both have been modified by an adaptation
to their respective conditions of life which has ever been becom-
ing more perfect.

The conclusion, then, has been reached, that whereas larvae
frequently retain traces of ancestral stages of adult structure,
embryos will rarely do so; and we are confronted again with
the question, How can we account for the presence in the embryo:

90 Evolution and Adaptation, pp. 73, 83.

The Recapitulation Theory in Biology 55

of numerous functionless organs which cannot be explained other-
wise than as having been inherited from a previous condition
in which they were functional? The answer is that the only
organs of this kind which have been retained are organs which
have been lost by the adult and have become in this way im-
pressed upon development. As an illustration taken from cur-
rent natural history of the manner in which larval characters
are in actual process of becoming embryonic may be mentioned
the case of the viviparous salamander (Salamander atra), in
which the gills, etc., are all developed but never used, the animal
being born without them. In other and closely allied species
of salamander there is a considerable period of larval life in which
the gills and gill-slits are functional, but in this species the larval
stage, for the existence of which there was a distinct reason, viz.,
the entirely aquatic habits of life in the young state, has become
at one stroke embryonic by its simple absorption into the em-
bryonic period. The view, then, that embryonic development
is essentially a recapitulation of ancestral history must be
given up; it contains only a few references to ancestral history,
namely, those which have been preserved probably in a much
modified form by previous larvae.’

This lengthy quotation may be brought to a point by a con-
crete application. The traces of gill-slits in the human embryo
mean that at a certain period in geological time one of the ances-
tors of man was an animal with a larva possessing functional
gills of use to it in the water. Later with the extension of the
embryonic period this functional condition was rendered use-
less by being absorbed, that is, taken into the egg or body of
the mother before birth. Its subsequent embryonic history
greatly modified it and reduced it to a rudiment.

It appears, therefore, that with reference to ancestral traces
among embryos Sedgwick agrees in the main with Hurst and
Morgan. These traces are due to the transmission of similar
embryonic forms through successive generations. But Sedgwick
differs from these writers in that he does believe there are a
few cases of the embryonic retention of functional adult char-
acters. And he differs radically in the belief that larvae often
retain adult characters in continuing in the life conditions of
their ancestors. This however does not happen in a way to
show recapitulation. Sedgwick goes beyond Morgan in sug-
gesting how the ancestral form originally got the adult char-

%1 Encyclopaedia Britannica, 11th ed., art. Embryology, p. 323.

56 The Recapitulation Theory and Human Infancy

acter which was carried down throvgh embryogeny in descent.
This, it will be recalled, Morgan did not attempt to explain.

This hypothesis of Sedgwick? was accepted and applied by
two other biologists. Cunningham carried the discussion back
to the probable ancestor of the Amniota to which the larval
condition may be assigned. It is not likely, he says, that the
case of Salamander atra is illustrative of the absorption of the
branchiate condition among mammals,

“Since viviparity even in Mammals was evidently acquired
at a later stage, and the change came about by means of the
development of an egg-shell in which the larva was contained
and protected during its development.” Moreover, ‘‘the mere
fact that they were functional originally in a free larval condi-
tion is probably not the whole explanation of the temporary
development of a complete system of gill-arches and gill-slits
in the amnoite embryo. Supposing that no functional import-
ance in embryonic life belongs to them, it is to be noted that the
embryonic branchial blood vessels are metamorphosed into the
vascular system of the adult, as they are in the metamorphosis
of the Amphibia, and a very considerable and very important
part of them persists in the adult structure. This does not ac-
count for the persistence in the embryo of open branchial clefts,
but even these do not wholly disappear in development. The
first remains as the Eustachian tube, and even the posterior
are related to the thymus gland. It seems to be a general fact
that a structure which in metamorphosis disappears completely
may easily be omitted altogether in embryonic development,
while one which is modified into something else continues to
pass more or less through its original larval condition. If the
aquatic larval condition then was ever an adult ancestral con-
dition it must have been the ancestor of Amphibian forms, and
only through these the ancestor of the Amniota.’’s

The adapted character of these larval forms which reflect in
some degree an ancient adult condition is made clear by Cunning-
ham, and is of special significance for this whole class of recapitu-
latory cases. From a comparison of the tadpole and the known
forms of fishes he concludes that

“The larva of the frog, therefore, instead of recapitulating
the ancestral condition has lost nearly everything characteristic
of a fish except the pharyngeal branchiae, which it could not

2 Cunningham notes that the same suggestion was made antecedently by Bal-
four. See Comparative Embryology, 2d ed., 1885, p. 210.
93 Science Progress, VI, 1897, p. 488.

The Recapitulation Theory in Biology 57

lose without ceasing altogether to be an aquatic larva. The
larva is therefore much more of an adaptation than a recapitu-
lation.’’%

This he finds generally true of flat fish and other animals with
such larvae, so that he feels warranted in making the statement
that “ Recapitulation does not occur... .except when the extern-
al condition to which the ancestral structure was adapted con-
tinues to act at an early period of life.’’95

Macbride, employing Sedgwick’s theory, gives many illus-
trative cases and compares the conditions of larvae and embryos.
Ancestral traces are found in the vast majority of larvae.%6

(4) We are thus led to the fourth position assumed toward
recapitulation. It is close to that of Sedgwick just described.
The greater part of the resemblance between descendants and
ancestors is, where it exists at all, between their ontogenies.
Nevertheless, cases exist, more especially among larvae, of the
ontogenetic retention of adult characters. This, it is to be
noted, agrees with the results of the Hyatt school of palaeontol-
ogists. In their impressive array of facts, as summarized by
Cumings, it was the post-embryonic and not the embryonic
stages that made the basis of comparison.%7

Grigg’s acceptance of both the view of ontogenetic repetition
and that of ontogenetic-adult repetition, has been noted. A
sentence from this writer will serve as a fitting conclusion to
this report of opinion: ‘‘In each case the evidence must be
weighed before a conclusion can be reached.”

15. Summary and Conclusions.

The history of the recapitulation theory may be briefly re-
viewed. In the early references to the idea at the beginning
of the nineteenth century, when the science of embryology
was taking form, the attention of observers was caught by re-
semblances which evoked the belief that individual develop-

% Science Progress, VI, 1897, p. 489.

96 Ibid., p. 508.

The functional character of embryonic and rudimentary embryonic structures is
illustrated and enlarged upon by Peter, Ueber die biologische Bedeutung embryonaler
und rudimentarer Organe, Arch. fiir Entwickelungsmechanik, 1910.

96 Sedgwick’s Theory of the Embryonic Phase of Ontogeny, etc., Quart. Journ.
Micros. Sci., XXXVII, 1894-95.

97 See page 27.

58 The Recapitulation Theory and Human Infancy

ment displayed in succession the forms of animals as they
ranged in a single series one above the other. In one instance
this was regarded as a rehearsal of the story of creation of these
forms (Oken). Von Baer’s suggestion that the prevailing idea
was an error and that the resemblances were between embryos
of the four great types, to be detected among animals, was for
the time disregarded, in favor of a conception of Agassiz of a
parallelism between the succession of geological forms as in-
dicated by fossils and the succession of stages in development,
a parallelism expressive of one feature of the divine plan of cre-
ation. With the advent of the theory of descent with modi-
fication the facts of the older view were invoked in support of
the theory, and Darwin, with the help of Fritz Miller, showed
how a genetic classification could be determined in large part
with the aid of embryology. Darwin’s moderate acceptance
of the theory of a developmental rehearsal or recapitulation of
racial history, was supplanted by the radical statements of
Haeckel, who, by misconceiving the effects of heredity and
adaptation through successive generations, formulated a ‘“‘bio-
genetic fundamental law,’’ which implied that by necessity on-
togenies must preserve an abbreviated and condensed record
of phylogeny. Herbert Spencer helped to extend the influ-
ence of this view by accepting it in general, while showing in
some detail its limitations. Recapitulation derived new war-
rant from a series of important investigations made by Hyatt
and his followers upon fossil shells of some invertebrates, which
showed how by the acceleration and retardation of adult char-
acters in ontogeny a record of the phylogeny was preserved.
The palaeontologists of this school to-day constitute the chief
advocates of the views of recapitulation as supplying a fairly
faithful record of phylogeny in many cases. Among the embry-
ologists the ancestral record in ontogeny was acknowledged
and employed for a considerable period until absurdities due
to its extreme application greatly impaired its prestige. At
the present time the weight of authority favors an explanation
of established ancestral traces in ontogeny as being due to
the transmission of similar embryonic and larval conditions
through successive descendants, while admitting the retention
of adult characters in ontogeny in some instances. These traces
are not such, however, as to present in any real sense a chrono-

The Recapitulation Theory in Biology 59

logical record or recapitulation of the evolution of the race
through descent. Several biologists believe that the origin of
embryonic traces of adult ancestral forms is due to an extension
of the embryonic period to include characters once functional in
larve, these characters having been retained by the larvae when
no longer needed by the modified adult. The genuineness of
ancestral resemblance has been impugned on _ physiological
grounds, but the justification for this seems questionable when
the facts are carefully described.

Conclusions Regarding Recapitulation.

The above account of the biological discussion of recapit-
ulation seems to lead to the following conclusions:

1. Ontogeny denotes the sequence of events in the life-history
of the individual beginning with the maturation and fertiliza-
tion of the egg, and progressing, under the stimulation of the
environment and the mutual relation of parts, through a series
of structures to senility and death.

2. A proper conception of an animal involves the entire life-
history and should not be based upon its adult condition alone.
There has been some kind of life-history from the beginning.
“Development and life are coextensive.’

3. Heredity denotes the persistence of characteristics through
descent, whereby the life-history tends to be preserved in its
original form.

4. But the.several phases or periods of ontogeny (embryonic,
larval, adolescent, adult, senile) are all subject to variation,
and selection (when they are such as to be affected by biolog-
ical utility) and have varied in unlike degrees, whether one
compares stages in one line of descent or homologous stages
in different lines of descent.

5. These variations, whether small or greater, have appeared
in, upon, and around old structures, so that any phase of on-
togeny undergoing revision tends to preserve in some degree
the character of the original basic structure. Because of this
fact any ontogeny is likely to give some indication of its past,
and to this extent constitutes a ‘‘record.”’

6. Resemblances between comparable ontogenetic periods
will therefore tend to be closest between descendants and im-

% Cf. Sedgwick, in Darwin and Modern Science.

60 The Recapitulation Theory and Human Infancy

mediate ancestors. They will on the whole decrease with the
widening of the interval between the ancestors and descendants
compared.

7. The millions of years occupied by any line of descent has
given opportunity for every degree of reconstruction of the life-
history to the most radical and it is surprising that a later
ontogeny should preserve any traces whatever of the life-history
of remote ancestors.

8. In many groups there are very few, if any, such traces,
the life-history showing from an early period only the features
of its present adult condition.

9. In other groups the life-history is not direct but circui-
tous, and presents forms which require an explanation other
than that of adaptation to the environmental conditions of the
adult. These forms often have some kind of ancestral refer-
ence, and have been retained probably because of some utility
either to the larvae in their independent struggle for existence,
or as structural bases for higher differentiations in case they
are found in embryos. Some are rudiments without utility
of any discernible sort.

10. In the majority of cases the ancestral reference of embry-
onic or larval stages is to embryonic and larval stages of ances-
tors. These may have originated either as larval or embryonic
conditions as such, or as adult structures which have been re-
tained in some fashion in the earlier ontogeny of descendants.

11. In the smaller number of cases where the ancestral refer-
ence of early ontogenetic stages is conclusively to adult forms
the explanation is as follows: A life-history originally direct may
have been modified at a not early age and thus left the earlier
part to resemble the adult ancestor. If this should have happen-
ed successively so that modifications each time came later than
the already acquired modifications, the later stages in the devel-
opment of descendants would indicate something of the sequence
in which the modifications were successively added in the phy-
logeny. These stages would then “recapitulate” that part of the
phylogeny during which the modifications took place in this
fashion. If the modifications had been made uniformly in this
way, then the whole ontogeny would present a ‘‘recapitulation”’
or chronological record of phylogeny, except where suppression,
consolidation, unequal acceleration, and retardation had inci-
dentally prevented.

The Recapitulation Theory in Biology 61

12. It is obvious that recapitulation in the sense of a chrono-
logical repetition of a succession of adult forms in phylogeny is
very unlikely. It may have happened in the earliest evolu-
tion of organic form as suggested by the very general
similarity in early ontogenetic development of the Metazoa,
a development which has a somewhat’ general corre-
spondence to what is believed by many to be the evolu-
tionary sequence among existing lower forms. It has happened
somewhat conspicuously among many animals with larvae,
for a certain part of the life-history, and also with particular
characteristics and organs in some degree, more noticeably in
shells and bony structures.

13. But where such recapitulation has occurred, there has
been coincidently an alteration of the ancient structures, so that
the original form of the latter is often made out with great
difficulty, the alteration having had the effect of obscuring the
older pattern to some degree, often radically. As a conse-
quence life-history has been very much more altered than it
has been extended through descent.

14. If by recapitulation is meant any traces of adult features
in early ontogeny, there is considerable evidence for it, although
not a large amount comparatively. But this is not recapitu-
lation in the proper meaning of the term. If by recapitulation
is meant any ancestral reference whatever in early ontogeny,
there is much of this, especially to more recent ancestral life-
history, but this is even a farther remove from the meaning of
the word. It is practically synonymous with heredity. If
ontogeny is a ‘“‘record’’ at all, it is more particularly a record
of antecedent ontogenies, to the degree these are not effaced
by subsequent variational or mutational changes.

CHAPTER IIT

HUMAN INFANCY AND THE RECAPITULATION
THEORY

1. Human Embryogeny.

The ancestral significance of the facts of human foetal develop-
ment was carefully considered by Duckworth in “ Morphology and
Anthropology” (1904). This author made comparisons with
respect to external features, topographical and systematic ana-
tomy, between the human foetus at birth, also at a point about
half way through embryonic development, and the human adult
and existing primates. His conclusions are briefly as follows.
With respect to the external features of the human foetus a
small number of simian characters are recognizable in both
stages studied, although the younger stage does not show these
in any greater frequency. This is practically the result of the
comparison based on topographical anatomy. Some of the
points of difference from the adult human condition constitute
resemblances to conditions obtaining among the primates. No
special primate form is indicated. The conclusions regarding
systematic anatomy are given in the words of the author. The
observations regarding the ninth month foetal stage are arranged
with respect to descent in three groups.

“First of all, there are to be noticed characters, such as the
relatively large size of the liver, of the hypogastric arteries, or
of the fontanelles, which appear to be quite irrelevant; these are
in fact, conditions associated with, and determined by the par-
ticular and peculiar mode of development in the higher Eutheria,
and, therefore, they may be expected to obtain in all these
animals alike. Secondly, there are a number of characters,
such as the great size of the head and of the cerebrum, which
are related to the specific and peculiar characters of the Homin-
idae, and which might well be expected to be so impressed in
their organization as to appear prematurely, so to speak, in his
individual development. . . . These two classes constitute
a very considerable number of characters which do not bear
upon the question of descent and must be carefully eliminated.

62

Human Infancy and the Recapitulation Theory 63

a . there remains a residue. . which may be collected

and associated in a category of pithecoid affinities. The flat-
ness of the nose, the imperfect power of opposition of the pollex
(shown by the mode of grasping in the new-born infant), the
straighter lumbar column, the flattened sacrum, the imperfectly
extensible hip and knee, the proportionately long upperlimb,
the incurved feet (and, in the female, the straighter vagina),
may be mentioned as features of this kind . . . further
: there is no reasonable doubt but that the associations
are with the Simidae rather than with their lower congeners
among the Primates.’’?

The foetus at the fifth month shows a somewhat greater
prominence of the features associated with placental development
as such, and the specific human characters are asserting them-
selves. The residue of simian characters is very small, so small
indeed, that nothing is indicated of man’s ancestry beyond the
immediately antecedent Simidae.

It will be seen from this authoritative review of the facts of
foetal development that the character of the human foetus is
determined chiefly by its particular foetal condition and by its
future as an adult human organism. The resemblances to adult
existing apes, and presumably to the adult ape-like ancestor,
are few and comparatively unimportant, and as far as we can
see, are such as might be due to an indirect likeness to this ape-
like ancestor by way of the foetus of the latter. This accords
with the view of ancestral similarities reported in the preceding
chapter as that having the greater weight of authority among
biologists. In instituting these comparisons between non-
comparable stages, that is, between the human foetus and the
adult ape, Duckworth is under the influence of the traditional
conception of recapitulation, to which he refers sympathetically
in his introductory paragraphs.

In the chapter following (VIII) the author reports the results
of a comparison of certain features in the mode of development of
man and the apes in the earlier stages. As we should now expect
when corresponding ontogenetic stages between closely allied
forms are compared, a striking resemblance isfound. And, as we
should also expect, the resemblances, though more often with
the embryogeny of the ape, are to a less degree, with other and
lower mammals. The closeness of this correspondence between

Ipp. 188, 190.

64 The Recapitulation Theory and Human Infancy

ontogenetic stages, together with the comparative lack of it
between the human foetus and the adult condition among apes,
once more tends to illustrate the fallacy of the traditional view
of recapitulation and to yield added support to the substituted
conception of ontogenetic correspondence between descendants
and immediate ancestors. A study? of the degree of likeness
of a foetal gorilla to the human foetus made by the same writer
seems to agree with this view, although the author is more
interested in indicating the distinguishing characteristics.
Human traits are quite plainly manifested in early foetal stages.*

2. The Theory of Infancy.

The life-history of the higher mammalia, like that of many
lower vertebrate and invertebrate groups, is characterized by a
period intervening between the close of embryogeny and the
full assumption of adult structures and functions. But whereas
larval forms are compelled by the necessities of their independent
life to provide themselves with food and protection during the
progress of their maturing, the corresponding period among the
higher mammalia is one in which the processes of growth and
increasing maturity are largely freed from such necessities by
the care and protection of a parent or parents.

The term infancy has been applied to this period and an ex-
planation of it in terms of biological utility has become current,
associated especially with the name of the American philosopher
and historian, John Fiske. In the address on the subject printed
in ‘Century of Science” Fiske deals reminiscently with the incep-
tion of the theory. He recalls that the impression left upon the
minds of many from the reading of Darwin’s ‘‘ Descent of Man”
in 1871 was in some ways unsatisfying. Although Darwin’s
work presented an impressive array of instances of similarity be-
tween man and the animals, still the method of the transition
to an essentially human condition was not clearly elucidated,
and there was a consequent confusion as to man’s future destiny
as determined by the Darwinian factors of species evolution.

2Studies in Anthropology, 1904.

3Ontogenetic likeness is affirmed in current statements of an ‘‘almost appalling
resemblance between man and the ape before birth,"’ a resemblance which is
asserted to be much closer than that between adult man and adult ape. See Mitchell,
Childhood of Animals, pp. 7-9; von Buttel-Reepen, Man and his Forerunners, trans.,
1913, p. 76.

Human Infancy and the Recapitulation Theory 65

A significant suggestion which was to lead to a better under-
standing of this transition, had already been made in an essay
by Wallace, Darwin’s co-discoverer of the descent theory. This
essay appeared in 1864,‘ and presented the idea that for a long
period in the history of man’s immediate ancestors natural
selection had been slowly transferring from the body to the mind,
so that by the time of the final emergence of the human species
man’s bodily evolution had been practically completed for all
time, his future evolution being destined to take place along
intellectual and moral lines. That is to say, the transition from
the ape-like to the human condition had been chiefly in the
region of mind and the nervous system.

It is in this connection that Fiske’s theory of infancy became
prominent. Fiske’s thought in this direction was taking form as
early as the year 1873, as we learn from a paper published in the
North American Review for that year. A more complete state-
ment appeared in the Cosmic Philosophy of 1875, an independent
and constructive presentation of the Spencerian philosophy for
American readers. Fiske’s views were reiterated with insigni-
ficant modifications in his later writings.®

The argument of the theory runs as follows. There is an
increase in the amount of nerve tissue of the cephalic ganglia,
and in the convolutions of the cerebral surface, paralleled by an
increase in the higher psychical powers, in the vertebrate scale
from lower to higher forms. These higher powers are associated
with the compounding and co-ordinating of already compounded
nerve connections in the lower centers. Whereas among the
lower vertebrates the uniformity and repetition of identical
responses to environment brings about a fixed and determined
reflex and instinctive organization of nerve tracts in the individu-
al, which are transmitted to descendants, the responses of higher
vertebrates are so complex, so lacking in uniformity, that repeti-
tion of any specific mode is insufficient to fasten upon the indi-
vidual and his descendants fixed modes of action. There arises
accordingly among such animals a plastic condition of the higher
nerve connections which requires time in the early years of life

‘Reprinted in Natural Selection and Tropical Nature, chap. VIII.

6 Vol. II, Chap. XVI and XXII. For later statements, see Excursions of an Evolu-
tionist, Chap. XII; Destiny of Man, 35-76. Anticipations of Fiske’s idea have been
pointed out by Butler, Armstrong, and others. See Phil. Rev., Vol. 15, p. 59.

66 The Recapitulation Theory and Human Infancy

for their exercise and adult determination, and brings with it
coincidently a corresponding amount of helplessness on the part
of the young, demanding parental care and protection. Con-
sciousness is especially associated with these complex and intri-
cate connections of the higher ganglia, and very little or not at
all with the mechanical reactions of the lower centers. Thus
arises conscious intelligence with its differentiation in emotion,
memory, perception and reasoning, and volition. In the case
of man this whole evolution has reached its acme, so that brain
tissues are largest, convolutions of the cerebral surface are most
noticeable, the highest psychic powers are manifested, the period
of infancy is longest, and parental solicitude most intense. The
process has been continued from savagery to civilization. Paren-
tal care first provided by the mother alone, is later assumed by
the father also, and as the succession of maturing young prolongs
the period of conjugal association, with its incidental fostering
of family sympathy and feelings of attachment, the family
is born, its elaboration giving rise to social as contrasted with
merely gregarious relationships. Thus the omission in Darwin’s
account of the descent of man is made good, as Fiske believed,
and the helpless babe is shown to be the instrument of man’s
peculiarly social and humane endowment.

Fiske’s later statements added little to the original one, but
other students have illustrated and elaborated certain features of
the theory, while certain contributions must be regarded as posi-
tive additions to it. The American naturalist, Marsh, had found
from a study of fossil remains evidence of a marked increase in
cerebral substance in recent mammals as compared with their re-
latives of the lower tertiary epochs. Eocene brains were small,
hardly larger than those of the reptiles in some cases. There was
a gradual increase in the size of the mammalian brain through the
tertiary period, generally in the cerebral hemispheres. The same
law holds good for birds and reptiles from the Jurassic to the
present. The brain of a vigorous progressing race was relatively
large, that of a declining race relatively small. The brain
size of young was found to be proportionately greater than that.
of adult. This brain increase was regarded by Marsh as an
important element in survival.®

6 Amer. Journ. of Sci., Vol. VIII, 1874; abstract in Nature, Vol. XXXII, p. 562.

Human Infancy and the Recapitulation Theory 67

Lankester regards the conclusions of Marsh as illustrating a
general truth, to which the case of Homo and his pithecoid rela-
tions is no exception. This authority further considers this
progression to be one from action based on instinct to action
based on ‘‘educability.”” Educability is transmitted by heredity
but its products are not. Instinct and educability are to a large
extent in opposition, the loss of the first making an opportunity
for the appearance of the latter. Lewis and Romanes are funda-
mentally wrong in imputing instinct to “lapsed intelligence.”
There is no community between the two. One can grow only
as the other diminishes.’

In a study of the causes of extinction of mammalia, Osborn
assigns to brain capacity, among a variety of causes, a primary
importance. The identification of educability with brain size
in surviving mammal forms appears clearly in the following:

- . the chief advantages of brain capacity are un-

doubtedly i in relation to adaptability of habit, resourcefulness in

times of exposure, alertness in avoiding new dangers to which

the young may be exposed, enterprise in seeking new habitat
Mg

The early insistence upon the cruelty of the natural order as
described by Darwinism, and especially the conflict between the
state of nature and that of art and humanity, so vigorously
urged by Huxley in his “Evolution and Ethics,” brought out a
series of replies calling attention to the facts of parental care and
mutual aid among animals and men. These facts had been
alluded to by naturalists incidentally but were made the principal
theme of two very widely read authors. These were Henry
Drummond in the “Ascent of Man” (1894) and P. Kropotkin
in a series of articles? in which the facts illustrative of co-opera-
tion among animal and savage societies were brought together.

In 1898, Sutherland, in the early chapters of the “Origin and
Growth of the Moral Instinct,’’ summarized the facts of parental
care among the principal vertebrate groups in terms indicative
of its historical evolution. The high fertility, rapid hatching,
and early maturity by means of which the species of the lower
groups were maintained is shown to yield to the biologically

7 Nature, Vol. LXI, 1900, p. 624.
* Amer. Naturalist, Vol. KL, 1906, p. 857.
® Reprinted in Mutual Aid as a Factor in Evolution, 1902.

68 The Recapitulation Theory and Human Infancy

more advantageous plan, incidental with the lower groups but
characteristic of the higher, in which parental care in some form
is involved. In its early organic and unconscious expressions
parental care was manifested in the safeguarding of germ-cells
in the coming together of the sexes. Subsequently the hatching
eggs were variously and increasingly protected, notably in the
brooding of birds and in the placental gestation of mammals.
The extension of parental care to the post-natal period opened
the way to the evolution of conscious parental solicitude, gradu-
ally increasing in duration and intensity. The breeding rate
is found to vary with the increasing scope and degree of care
from parents. The decrease in the number of eggs and young
is associated with a higher nervous organization expressing itself
especially in intelligence, and helplessness is made concomitant
with intelligence as its necessary condition.

The peculiar utility of parental care, according to Sutherland,
consisted in providing an opportunity for variation in the direction
of increasing intelligence. Intelligence in any large amount is nec-
essarily associated with delay in the assumption of life-saving abili-
ties. Among those animals without parental care variations favoring
intelligence, with its coincident delay of maturity, would have been
immediately rendered futile by the extinction of the immature
animal. There were therefore strict limits to any extension of
intelligence among the lower groups. It would increase only toa
degree not inconsistent with an independent struggle for existence.
With the coming of parental care the way was cleared for an
indefinite amount of variation in the direction of intelligence,
and thus it is that intelligence is peculiarly the possession of the
higher mammals.

All these contributions to the discussion of infancy and paren-
tal care showed clearly that infancy and biological superiority
are causally related without indicating just how the associated
plasticity of the nervous system was used to bring the improved
adaptation about. This last has been done by the psychologists.
In connection with his studies upon young animals, reported es-
pecially in ‘Habit and Instinct” (1896), Lloyd Morgan demon-
strated with considerable particularity how the imperfect instincts
with which the young of learning animals come into the world
are adapted to the peculiar circumstances of their existence by the

Human Infancy and the Recapitulation Theory 69

supplementations of habit. In the view of Morgan intelligence
has two functions, that of setting up an equipment of specialized
habits during immaturity, and that of the readjustment of these
habits in some degree in maturity. ‘It isin the period of youth-
ful plasticity that intelligence has its most important part to
play so far as the genesis of habit is concerned.’’9 Some intel-
ligence remains over for adult life; the higher the mental grade
and the more varied the conditions, the greater is the balance
left over. But habit formation is peculiarly the affair of infancy.
Another significant idea from this writer, taken in turn from
Hudson’s ‘Naturalist in La Plata,’’ as Morgan acknowledges,
is that of tradition, or the transmission by imitation from one
generation to another of successful acquired modes of behavior.
This fact of imitation has been greatly emphasized in human
society since by Tarde,! Baldwin,!? Royce, and Sumner."
Imitation and tradition are to be regarded as two sides of the
same fact, the one standing for the process by which the other
is brought about. More recent study of animal behavior has
tended to minimize the amount of imitation among animals in
general, but its presence among the primates is admitted, and
in the human species imitation and tradition are so impressive
as to be considered by some authorities the most significant of
all the factors of its life. It would follow logically, although
confirmation from a sufficient knowledge of the life of the higher
primates is still lacking, that in the evolution of man and espe-
cially in the progression from the ape-like to the human condi-
tion, biological well-being and success were closely identified
with the transmission of socially derived habits or tradition,
in connection with neuro-muscular plasticity. Nature’s method
of guaranteeing this transmission was through the invention of
the instinct or impulse of imitation, a special device, according
to Groos, by which modes of action not resting upon well-defined
instinctive tendencies could be taken up by the young wholesale,
so to speak. There seems to be no other way of adequately ac-

ie p. 157.

11 Laws of Imitation, 2nd. ed. trans., 1902.

122 Mental Development in the Child and the Race, 1895.
13 Outlines of Psychology, 1903.

44 Folkways, 1907.

70 The Recapitulation Theory and Human Infancy

counting for so profound a disposition as the imitative tendency
in the human animal.”

In the course of the discussion of imitation the term has been
found too inclusive, and there is a noticeable tendency among
psychologists to distinguish between instinctive imitation or
suggestion and true imitation based upon ‘‘copies” existing in
terms of related ‘‘objects.’”’ Suggestion has now an important
literature of its own, and while much of it has made slight refer-
ence to biological history and any relation to infancy, enough has
been said in these connections to make of it a somewhat distinct
factor in the transmission of social modes. Suggestion is differ-
entiated from imitation in that its excitants are simpler, sensory
rather than perceptive and relational. It is therefore found
among gregarious animals before true imitation and is illustrated
in the pseudo-imitation of schools of fish, flocks of birds, sheep,
etc. But it has been retained in human evolution in great force
and must be accorded high if not supreme importance in the
transmission of social habit. Its primacy over true imitation
can scarcely be denied when one considers the comparatively
advanced nature of the latter, and its controlling power among
primitive and less cultivated men.

Suggestion and imitation have been intimately associated
with play, the biological value of which has been authoritatively
shown by Karl Groos. With Groos “the very existence of
youth is due in part to the necessity of play; the animal does not
play because he is young, he has a period of youth because he
must play.’!6 Whether or not one should quite agree to the
form of this statement, there can be no question of the most
intimate relationship of play to infancy. Infancy is the period
during which the young animal reaches the adult level of effi-
ciency upon which the species is maintained in its struggle for

15 For the purposes of the present account imitation is referred as to a single or uni-
tary thing whereas the term of course denotes a highly intricate complex. In the mind
of the writer much confusion in the use of the term is due to an unjust distinction of it
from trial and error. Imitation is through and through a trial and error process, but
this trial and error is incited by, and in its higher forms in part guided by, the behavior
of others. The original or instinctive phase lies in the incitement to someresponse. This
response may be comparatively general to begin with but it becomes more definite by
trial and error with its resulting special habits. It is precisely in this combination of
instinctive incitement and capacity for adapted and suitable behavior that its biological
utility consists. For a specific instinctive response to the behavior of others would.
prevent the adjustment that imitation obviously provides for.

16 Play of Animals, trans. 1898, preface, p. xx, and p. 75.

Human Infancy and the Recapitulation Theory 71

survival. This degree of efficiency involves some practice in
all learning animals and in many a long continuation of it.
This indispensable practice would be fatal if left to the period
of independence. It might conceivably have been enforced by
parents, as it is to a very slight extent among animals, but this
implies a degree of intelligence and foresight beyond the capacity
of animal parents, indeed not easily assumed by civilized human
parents with all their higher resources. Self-imposed practice,
or play, was therefore the simplest biological expedient. If
the formula of Groos be understood to assert that infancy without
play is useless, its truth must be admitted, and it is fair to assume
that infancy and play evolved together. A merely docile plastic-
ity could scarcely give rise to the habits of maturity. Play is
the necessary middle term between plasticity on the one hand
and intelligence on the other.

These several additions to the ideas of Fiske are brought to-
gether in Baldwin’s “‘ Development and Evolution” (1902), per-
haps without explicit reference to their bearing upon a theory of
infancy as such. Their interrelations are, however, there shown.
The doctrine of ‘organic selection,” also reported in this book,
is not without its implications for the present topic.!’ This
theory was presented by three writers independently—Osborn,
Lloyd Morgan, and Baldwin—and has obtained a fairly general
acceptance. Its general effect is to show how plasticity has
determined in part the selection of non-plastic or fixed or-
ganic characters. It must have been noticed in the reported
statements of Fiske that the evolution of both reflex or instinc-
tive and intelligent behavior was explained in terms of use-
inheritance. This explanation was not inconsistent with the
views prevailing at the time Fiske wrote, but has come to be no
longer tenable by reason of the change of emphasis since regard-
ing the transmission of acquired characteristics. It was inevi-
table that plasticity and its effects should be made to accord
with the more acceptable doctrine of the germinal origin of
variation and mutation.

Organic selection assumes that although plasticity is physically
inherited its resulting habits are not. But these habits, because
of their effect in making adaptations more adequate, would

17 See Appendix B for the original statements with others.

72 The Recapitulation Theory and Human Infancy

often have life-saving value as such, and would therefore in the
long run preserve and select individuals in whom the fixed and
physically inherited germinal variations should increase in the
direction of better adaptations. Plasticity and its habits would
thus blaze the way along which germinal evolution could follow,
because the incidence of natural selection would fall first upon
habits and only through them upon the physical make-up of the
animal. With the rise of tradition the value of this process.
would increase, so that on higher simian levels and early human
levels the selection of hereditary strains was increasingly deter--
mined by the character of the social habits directly or indirectly
favoring survival and leaving of offspring. Infancy being es-
pecially responsible for the assumption of habits, in this manner
becomes intimately related to organic evolution to the extent.
that the theory of organic selection is true.

In the light of these later contributions, Fiske’s original state-
ment of the theory of infancy requires some amplifying. The
biological explanation of infancy assumes that with this period
is associated species preservation and success, and in the case of
man, species dominance. The advantages accruing to species
because of infancy reside in the greater adaptability of individu-
ally acquired habits over the mechanical behavior of instinct.
This is made possible by an elaboration of the central nervous
system, especially in the cerebral portions. But the accumula-
tion of habits requires time and practice and a degree of ineff-
ciency and dependence corresponding to the difference at any
time obtaining between the neuro-muscular condition of the
young and that of the adult. Among the higher primates these-
habits are in large part socially derived, calling for the psycho-
physical adjustments of suggestion and imitation on the part of
infancy to insure their transmission. The inefficiency of infancy
necessitates counterbalancing parental oversight, and the indis-.
pensable practice is obtained by imposing upon the young an
instinctive need of self-exercise or play. This spontaneous
exercise is directed not only upon well-defined tendencies char-
acteristic of the adult life of the species in need of perfecting, but
also to modes of social action resting slightly upon an instinctive
basis and more largely acquired by successive generations in re-
sponse to the changing conditions of their lives. Play is there-
fore both specific in its forms and broadly imitative and general-

Human Infancy and the Recapitulation Theory 73

ized. As to its origin, plasticity is characteristic in small degree
of animals other than the higher mammals, but mutations in
this direction with their coincident delayed maturity were futile
until accompanied by the protection of parents. Plasticity is
for this reason conspicuous with mammals. In turn the assump-
tion of valuable habits had the effect of preserving and selecting
germinal mutations in a given direction which would otherwise
have been sacrificed. Finally, the vital energy necessary to the
production of organic complexity in the higher learning animals
was made possible in some part by the saving from a lowered
birth-rate due to the increasing parental care and solicitude
given to the eggs and the immature young."

Two recent volumes from the pens of accomplished naturalists
discuss the infancy and youth of animals in a convenient and
exceedingly attractive fashion.1® In the main these books con-
firm the earlier accounts, but with important minor qualifications.
The economic value of parental care as a substitute for great
fertility in biological competition is accepted and illustrated by
both writers. Pycraft, however, refers to ‘‘some puzzling facts”
and rejects the view which finds in the mortality of young a
cause of exaggerated fertility. Rather, it should be said, fertility
encourages mortality by offering large numbers of young for food.
Fertility, like extravagance in ornament and gorgeousness of
color, is to be regarded as a specific character and not a direct
response to biological necessity. Moreover, the relation of
fertility to mortality can often be only surmised, from ignorance
of the actual natural conditions surrounding many species. It
still does not appear that Pycraft’s position need be in essential
contradiction to the older way of stating the matter, which
perhaps failed to clearly affirm that the only effect of selection
was the limitation or survival or inherent specific characters.
There seems to be small reason for doubting the broad correlation
of decreasing fertility and degree of parental care in relation to.

14 The following extract from Washburn’s Animal Mind, 1908, p. 284, should be
reported in this general connection: ‘‘ One of the most vital meanings of the long period
of helplessness and dependence constituting human infancy lies in the fact that by
relieving from the necessity of attending exclusively to external objects, it renders
possible attention to the sensations resulting from movement; and thus, by supplying
an essential condition for the revival of such sensations in idea, it opens the way for
the control of movement through the movement idea.’’ The extract should be read
with its context.

19 Mitchell, The Childhood of Animals, 1912. Pycraft, The Infancy of Animals, 1913.

74 The Recapitulation Theory and Human Infancy

mortality, provided it be understood that natural selection need
not always have produced an exact or refined adaptation.

The value of parental care as a necessary condition to the emer-
gence of organisms of the higher types and the correspondence
of youthfulness with this higher organization is also acknowl-
edged by both writers. The greater capacity of the higher ani-
mals with the prolonged infancy period is due to a more or less
extensive education to fit them for the strenuous activities of
their life. This education varies with the different groups
and conforms to the necessities of circumstances and the mode
of living. To play is attributed a large importance in the prose-
cution of this education, and it is interesting to note that on the
mooted question as to whether young animals learn directly
from their parents both authorities speak with certainty in the
affirmative. Mitchell’s description of imitation below the mon-
keys is, however, a carefully guarded one, and amounts to scarcely
more than a belief in organic predispositions to trial and error
modes of action which are in some degree encouraged and facili-
tated by the presence of similar action on the part of others.
With the apes this author holds for something akin to human
types of conscious imitation.

In view of prevailing assumptions regarding the causes of the
duration of youth Mitchell’s statement in this connection may
serve to call attention to the complexity of the facts and yet to
show the degree of truth in the assumed parallel between youth-
fulness and intelligence in the species.

“The duration of youth in all [vertebrates] is settled by no
invariable chain of organic necessity. It has no relation to the
duration of the complete cycle of life from birth to death. It is
linked with size, but only in an indirect fashion, most apparent
in animals most akin. It is linked much more closely with
complexity of organization, so that the higher forms usually
take longer to mature than their near but lower relations. It is
linked most closely with intelligence, the more intelligent ani-
mals having relatively longer youth. And as we pass down-
wards from intelligence to instinct we find that the duration of
youth shortens.’”°

Helplessness in young animals has been very generally identi-
fied with the immaturity of neuro-muscular co-ordinations con-

20 Mitchell, The Childhood of Animals, p. 54.

Human Infancy and the Recapitulation Theory 75

stitutive of intelligent or adaptive behavior. It appears from
the two accounts now under discussion that other causes may
contribute to this condition. The young of many carnivores
are thought to be born in their imperfect physical state be-
cause the agility required of the mother in catching living prey
would be seriously hindered by carrying heavy young. Among
nestlings in the less precocious birds helplessness is alleged as a
safeguard to premature hazardous beginnings in locomotion.
Thus helplessness as a condition due to unlearned adaptive
powers is to be distinguished from that induced by other biological
needs, as well as from that which may be unrelated to any utility.
The helplessness which associates with neuro-muscular plasticity
is presumably not a general condition at all, but is relative to
the learning that any species may accomplish in those special
directions characteristic of it.

With regard to recapitulation in the period of infancy Mitchell’s
statement is as follows:

ee the young of nearly allied animals are much more

alike “than. are the adults. . . . We explain this by sup-
posing that the evolution of the individual to a certain extent
repeats the evolution of the race. . . . We have to re-

member, however, that this explanation is not complete, and we
shall find many characters of young animals to which it does
not apply. The young animal owes its characters not merely
to its ancestry; as much as the adult, it has to be fitted to the
special environment in which it lives. It is not merely a stage
in development, but an independent living creature with its
own needs and its own aptitudes, presenting characters that are
neither a memory nor an anticipation, neither a relic of the
past nor a preparation for the future, but suitable for its own
purposes.’

The tenor of Pycraft’s statement is not greatly different:

“Time was when it was believed that these early-growth
stages, if carefully followed, would reveal all the mysteries of
evolution, since, it was supposed, every animal had to climb its
own genealogical tree, so to speak. But it was soon found that
such hopes were over-sanguine, for records of some of the most
important phases have been lost completely, and others blurred;
while some of the phenomena have nothing to do with ancestry,

21 Mitchell, The Childhood of Animals, p. 7.

76 The Recapitulation Theory and Human Infancy

but represent what we may call scaffolding—features which
have been introduced solely for the benefit of the individual.

The study of young mammals does, nevertheless, throw a
flood of light bearing on their ancestry. . . .’”

It must be noted that both writers, by the terms infancy
and youth, refer not only to that period of plasticity in the early
life of animals of the learning type, but to the period following
hatching whether plastic, larval, or merely precocious and essen-
tially unmodifiable, as with growing reptiles. If we limit the
application of their remarks to the period of plastic neuro-mus-
cular development, certain other statements of these authors
should be considered. Mitchell, for instance, with reference
to the mammals, the group in which the period of plastic infancy
is most conspicuous, writes as follows:

“Mammals, when they are born or very soon afterwards,
closely resemble their parents. The differences are due to
greater likeness to ancestors and to their nearest allies, to the
absence of special weapons or ornaments, or to the presence of
characters useful to the young themselves.’

One gathers that the period of youth among mammals is not
essentially recapitulatory but rather adaptive and anticipatory.
Nevertheless, both these authors present a very considerable
number of youthful characteristics which they explain as re-
tained ancestral features. From the account of Pycraft are to
be noted the following: certain cases of ‘‘milk-teeth”’; horns of
ruminants; antlers of deer; the presence of a hairy covering
which does not persist; the under-fur of one group of seals;
spines in certain Insectivora; and the familiar ape-like features
of the human infant. Pycraft concludes his list with the remark,
“We might add considerably to the number of instances of this
kind.”

In the matter of coloration the case is complicated and some
difference of opinion is expressed, yet the two authors agree in
the statement that the young of mammals very commonly
show differences in coloration when compared with adults, the
youthful coloration being regarded by both as older, the adult
as a later modification.

2 Mitchell, The Childhood of Animals, p. 40.
23 Op. cit., p. 13.

Human Infancy and the Recapitulation Theory 77

Thus the youth of mammals is not devoid of ancestral features.
These may be “‘recapitulatory” either because they resemble
features of the youthful period of the ancestor, or because they
represent the actual adult ancestral condition modified in descent.
It would be a matter for study in each case. Still, this does
not make youth essentially recapitulatory, for these features
are comparatively few when measured against the total make-
up of the young animal. They exist alongside others which
are adapted to the infantile condition as such, and in spite of
what is declared to be a close resemblance of young and adult
mammals, taking the group as a whole.

3. Recapitulation and Human Infancy.

Before undertaking a discussion of the relation of the theory
of recapitulation to human infancy—more especially to the mental
traits of infancy—it will be well to consider just what may be
properly understood by ancestral reference in this connection.
It is obvious, in the first place, that there is nothing to correspond
to palaeontological evidence, the court of last resort on the physi-
cal side,—unless something of value may be inferred from the
structure of fossil skulls. Ancestral allusions to racial mind
must be made in the main to what can be inferred legitimately
from objective behavior in the scale of living animals, and
since these animals are almost universally end-forms in a long
process of specialization away from common ancestors, it is
clear that inferences as to phyletic mentality are extremely
hazardous. If, however, a mental or physical trait peculiar
to infancy has a fairly well-defined homolog among lower animals
that may be regarded as closely related to probable ancestors,
there is ground for assuming an ancestral reference. If the case
is one of degree, there must be reasonable certainty of a greater
resemblance to the ancestral homolog than to the infant’s own
adult condition. There will be no justification for assuming
an ancestral reference simply because an infantile trait shows
some analogy to any animal trait whatever, and surely none
merely because no prospective, adult, or adaptive reference
can be made. Biological utility is no longer a category of uni-
versal application. Heredity is now known to carry much more
than the materials of organic adaptations, having laws of its

78 The Recapitulation Theory and Human Infancy

own which operate without reference to such adaptations.™
Unfortunately a very considerable number of the examples
offered for recapitulation in infancy are merely fanciful or even
wholly absurd because of a neglect of these obvious logical require-
ments. Unless these limitations are acknowledged the ancestral
doctrine of childhood becomes meaningless. For if by recapitula-
tion or ancestral reference is meant only that the organized and un-
acquired part of the mind is due to its history, without regard
to a disparity in kind or degree as between infancy and maturity,
this is simply equivalent to declaring that the hereditary part
of the human mind is inherited, a statement of little descriptive
value. That the recapitulationist has done good service in
emphasizing the racial character of mind, whether adult or youth-
ful, is not questioned. The point at issue is whether infancy is
peculiarly ancestral, that is, older than maturity.

A faithful application of the traditional idea of recapitulation
to psycho-physical behavior would mean that as the individual
develops it will rehearse in a chronological way the chief stages
of psycho-physical evolution in the phylogeny, except as this
has been disarranged by direct or cenogenic modifications.
There rests upon the advocate of this view, then, the necessity
of showing that the sequence of developmental stages is really
representative of the racial sequence, and that the constituent
phases in the progression are truly homologous with the ancient
stages and not merely analogous or convergent phenomena.

This consistent application of the biological theory has rarely
been made to infancy and mental genesis. Recapitulation has
taken the form, for instance, of the declaration that the psycho-
physical functions appear in the individual in the order of their
racial evolution. So stated the doctrine disregards the repre-
sentativeness in development of the whole phylogeny. All
existing functions may be comparatively recent and many, or
even most of them, may have been lost. Those that do appear,
however, rise in the phylogenetic order. This view of psycho-
physical recapitulation varies from that derived from embryology
in another particular, for whereas biological recapitulation
assumes that the individual passes through and leaves behind, or
radically makes over, its recapitulatory stages in the progression

* See Bateson, Problems in Genetics, 1913.

Human Infancy and the Recapitulation Theory 79

towards the specific adult form, the view in question has refer-
ence merely to the appearance of psycho-physical features, which
thereafter remain functional for life; for example, in the statement
that the emotions appear in the order of their rise in the race.

From these more or less direct applications of the biological
theory there is noticeable a grading off to a less and less chrono-
logical notion of it, as there is in embryology, until recapitulation
is supposed to be illustrated in any juvenile retention of ancestral
adult characteristics, or indeed of any ancestral traits whatever,
juvenile or adult.

However these interpretations of recapitulation may differ,
they have in common the idea that infancy is essentially retro-
spective, rather than adaptive and preparatory. This idea
therefore becomes the chief point of attack in any criticism of
the theory of recapitulation in its psycho-physical applications.

There is perhaps little profit in attempting to assign to specific
writers the different interpretations of psycho-physical recapitu-
lation just alluded to. These have not been clearly distinguished
in the literature of psycho-genesis, and since the guiding ideas
were so directly taken from embryology the history of the dis-
cussion there is the really important matter.

Romanes seems to have been the first to undertake along
inductive lines a detailed comparison of human psycho-genesis
with the history of mind as exemplified in existing animals.
A glance at the diagram at the beginning of “Mental Evolution
in Animals’ (1885) will reveal the results of his effort. A glance
will suffice also to show its essentially artificial character. The
comparison was extended with greater thoroughness in “Mental
Evolution in Man” (1889). To the mind of Romanes the dia-
gram indicates “in how strikingly quantitative, as well as quali-
tative, a manner the development of an individual human mind
follows the order of mental evolution in the animal kingdom.’’?*

As is well known, President G. Stanley Hall has had a large
part in the extension of the doctrine into the field of infancy
and mental genesis, and it is not surprising that his ‘‘ Adoles-
cence” (1904) should assume it throughout. Hall’s statements
are made with the full admission of cenogenic ‘‘distortion,”’
“‘confusion,” etc.; but the underlying adherence to the chrono-

25 Mental Evolution in Man, p. 5.

80 The Recapitulation Theory and Human Infancy

logical conception is unmistakable. One allusion among many
is the familiar one to the period of childhood from nine to eleven
years as representing ‘‘a terminal stage in human development
at some post-simian point.”’ This period is followed by adoles-
cence ‘‘which recapitulates the long pilgrimage of the soul from
its old level to a higher maturity which must have taken place
in the race in certain of its important lines long before the his-
torical period. ’’26

Statements of the kind are legion.27, Two others will serve
the present purpose. One is from the biologist Tyler, who says,
“The child is naturally successively animal, anthropoid, half-
barbarian, and then civilized.’ The other is taken from the
literature of the “‘boy problem” which is fairly saturated with
the doctrine. ‘We are by turns vertebrates, gill-breathing
vertebrates, lung-breathing vertebrates (we make the great
change at birth), little monkeys, little savages, and finally
civilized men and women.’’?

It now becomes our object to examine briefly the facts of
human infantile recapitulation. It will be impossible to cite
every allusion of the kind, for these have been made casually
in the course of numerous papers on an indefinite number of
topics. The present intention is limited to a general charac-
terization of classes of cases and to probabilities in the light of
accepted principles of general genetic psychology. The degree
of ignorance still prevailing with respect to the course of individu-
al and racial psycho-genesis prohibits more than a preliminary
survey of the topic.

In making this survey of the facts we have the advantage of
an hypothesis derived from the revision of the biological attitude
toward the ancestral facts of embryology, as summarized in the
preceding chapter, and illustrated further in the section on
human embryogeny. What is true of embryogeny may be true.
of infancy. We may keep in mind the idea that the ancestral
life-history has been transmitted from generation to generation
as a whole, and that it has been altered with each step in descent
rather than extended. In keeping with this view infancy prob-

26 Vol. Il, p. 73.

27 See Thorndike, Original Nature of Man, 1913, pp. 249-252, for an interesting collec-
tion.

2 Growth and Education, 1907, p. 53.

29 Puffer, The Boy and his Gang, 1912, p. 77.

Human Infancy and the Recapitulation Theory 81

ably has had its own evolution, having been evolved when it
was needed, and having been altered from age to age from germi-
nal mutation, and by selection as the necessities of its circumstan-
ces required. We should expect to find in infancy a compara-
tively small number of traits having an ancestral reference merely.
These traits would be scattered and not related in a chronolog-
ical sequence suggestive of phyletic recapitulation, and their
ancestral reference would be first to ancestral infancies and only
indirectly to adult characters for which the infantile condition
was preparing. Some ancestral traits would perhaps have been
made over in part to meet new conditions, and there would
likely be an insignificant number of useless rudiments.

The most important group of facts adduced in favor of mental
recapitulation are those referring to a savage human condition,
as illustrated in the behavior of lower living races of men.”
These include a large number of instinctive tendencies, especially
among boys, which are characteristically savage. Some of these
are the love of games embodying running, dodging, throwing,
hitting with a club, wrestling, boxing; a strong interest in ad-
venturous undertakings, fishing, swimming, exploits requiring
endurance, courage, self-control, daring; outdoor interests in row-
ing, sailing, climbing, exploring, the handling of animals, hunt-
ing; the instinctive grouping in “gangs,” group undertakings,
hero-worship, group loyalty, antipathy for outsiders, fighting,
with all its savage excesses, predatory excursions. The facts
are too familiar to require further illustration.

But this whole group of cases cannot be regarded as ancestral
or in any sense recapitulatory; in fact it points quite the other
way. The living races of men, to whose modes of life these
examples all refer, belong to one species. The older view of
Spencer, Galton, Fiske, and others, which held for an organic
difference between savage and civilized human nature, has
been supplanted by a conception of the essential identity in the
hereditary make-up of all races regardless of the degree of civili-
zation.*!

The differences between civilized and savage men are chiefly,
if not wholly, acquired and are due to the unlike exploitation of

20 See Chamberlain, The Child, Chap. VIII, and Swift, Mind in the Making, Chap.
Il, for convenient summaries.

a1 See Boas, Mind of Primitive Man; also, Thomas, Source Book for Social Origins,
Part II, and bibliographies.

82 The Recapitulation Theory and Human Infancy

human capacity by traditional and environmental forces. The
savage character of boyhood is thus shown to be a necessary
preparatory adaptation to the adult conditions prevailing at
the period when human nature had assumed its specific form,
conditions which are roughly pictured in the instinctive equip-
ment of the boy whether the circumstances of his later life are
still fairly true to the ancient pattern in some contemporaneous
savage society, or whether they have been radically modified
in the course of historical development. If this kind of boyhood
in some respects seems out of place in civilization, it is not because
it is rehearsing a former ancestral adult condition of life; it is
due to the fact that the traditional and socially acquired habits
have altered so much for the adult in some societies that what
the boy is by nature disposed to do is not, superficially at least,
just what is expected of him as an adult in these societies. Civili-
zation has affected boys and adults probably equally. If this
should not be admitted, and a greater resemblance be found
among the young in different culture levels, this could very well
be accounted for by the fact that the inhibition, selection, and
organizing of the inborn qualities by habit and intelligence,
have had less time to register their differentiating effects.

This last thought may be used to explain another class of
facts which has been supposed to illustrate recapitulation.
Children are thought to betray ancestral limitations in their
primitive tastes, their love of myth and of melodrama, of crude
music, dancing, the spectacular, strong colors, etc., and on the
side of conduct, in their laziness, desultoriness, dislike of work,
discontinuity of attention, stealing, lying, truancy, teasing and
bullying. But these things are not peculiar to children; they
are found equally among uncultivated adults in civilized and
uncivilized societies, and merely record the lack of cultural and
moral discipline and the coercion of civilized industry. They
manifest themselves wherever civilization is lacking, as in isolated
or unfortunate classes in modern life, or in tramps or delinquents
who for some reason have escaped its influence, and they are
not unknown in cultivated adults when the tension of civilized
habit is temporarily or suddenly removed.

i Continuing the process of elimination, we may refer to one
other group of alleged recapitulatory facts. This includes cer-
tain emotional attitudes associated with objects acting as their

Human Infancy and the Recapitulation Theory 83

excitants. These may be illustrated by the fear of snakes and
other animals, of celestial objects, of fire, darkness, eyes, teeth,
solitude, death, disease, ghosts, etc. A very large number of
similar attitudes have been cited as evidence of the recurrence
in childhood of ancient attitudes which have been inherited.
In all these cases there is evident a confusion of the inherited
and the acquired. We are indebted to McDougall’s “Introduc-
tion to Social Psychology”? (1908) for a lucid explanation of
this matter. Each of the basic instinct-emotions has its charac-
teristic ‘‘native excitants,’’ with the inherent power of rendering
it vital, or setting it up in psycho-physical behavior. Sensory
abruptness, especially of sound, has this effect with fear; inter-
ruption of normal functions is a similar excitant for anger; as is
the infant wail for parental solicitude. The various native
excitants have not as yet been satisfactorily described but the
general principle seems clear enough. It follows that certain
“objects” or acquired units of perception built around these
excitants, will often have an emotion-exciting value because they
so vividly contain the native excitants; such objects are thunder
for fear or substances of vile odor for disgust. Other objects
will have these emotion-exciting effects by association with
the original ones, and it is apparent from the observed variety
of these derived or acquired excitants that there is scarcely any
limit to their multiplication. Almost every aspect of the natural
world has been such a fear excitant, if we may believe the ethnol-
ogists, and there is probably no conceivable object which may
not have this function under appropriate suggestion. Only
native excitants, then, can have ancestral reference, and we may
safely neglect all objects connected with emotional attitudes and
confine our attention to the possible recapitulatory value of
excitants as such.

Undoubtedly native excitants are very old, but as common
experience testifies, they are not peculiar to infancy, and they
cannot therefore be regarded as recapitulatory in this sense.
It is not impossible that such native excitants may become so
embedded in complexes with more dominant emotion-exciting
excitants as to lose their original force. Such may be the case
with aesthetic or religious objects containing essentially ugly
or even essentially disgusting elements, but this does not of it-
self assign the native excitant to infancy because it works there

84 The Recapitulation Theory and Human Infancy

in simpler fashion. As to the excitants of attention, curiosity,
and their derivative ‘‘interests,’”’ it is probable that the more
conspicuous of these (such as sensory intensity, massiveness,
visible motion), are common to children and adults. The
strange-in-the-familiar as an incitement to attention and thought
apparently affects both alike. Much of the “peculiarity”
assigned to children’s interest in natural phenomena and in
the images of their minds can with practical certainty be assigned
to the unlikeness in apperceiving content due to intellectual
immaturity. The incitements to activity seem very closely
related to children’s capacities; when they find they are able to
grasp they are interested in grasping, when they discover they
can walk or climb, they take to these things with avidity, and so
on through the succession of childish, youthful, and adolescent
“activities.”” In these things childhood and youth are very
obviously preparatory. Excitants are here nicely adjusted to
disposing the young animal to undertake his own education the
moment the underlying structures are ready.

It is generally assumed that instinct represents the ancient
basic structure upon which plasticity has supervened. A natural
inference would identify the native excitant as the original cue
to the unmodifiable action which preceded the plastic or habit-
induced action in the phylogeny. This is of course not necessari-
ly the case, for the original cue may have altered in descent along
with the supervening plasticity, in accordance with the theory of
organic selection. However, it is at least likely that the native
excitant is a conservative and comparatively ancient feature
of psycho-physical organization, even if it has not remained
wholly unchanged. If this is so, the progression in the infant
from the native excitant to the ‘“‘meaning”’ which absorbs it, is.
homologous with the original phyletic progression from the
ancient sensori-motor to the percept-motor action system, and
we are apparently confronted with a genuine case of ontogenetic
rehearsal or “‘recapitulation.”

If now we turn to the motor aspect of the presumably ancient
instinctive structure we find the distinction, commonly assumed,
between its inherited and involuntary expressions and the ac-
quired habits which grow up with use and exercise. But the case
here is not the same as with excitants and meanings. Plasticity
presumably has not been merely added to instinctive muscular

iad

Human Infancy and the Recapitulation Theory 85

action; it has reduced it, permeated it, and substituted for it;
that is, essentially altered it rather than supplemented it. As
Lankester puts it, plasticity can rise only as instinct yields it
place. It is customary, therefore, to speak of the involuntary
instinctive motor expressions,—those discussed by Darwin and
other students of the emotions—as remnants of older and more
complete action systems. With what degree of justice this
assumption is made is a question, for the evolution of skill is a
comparatively neglected topic. Students of the animals have
thus far been chiefly concerned with the problems relating to
animal intelligence.

Still, there is probably no counterpart to the genetic sequence
from native excitant to meaning on the side of motor control.
In fact the situation seems just reversed. For phylogenetically
there was a progression from stereotyped behavior to less and
less fixed modes of behavior. Ontogenetically the progression
is from a few established modes to an indefinite number of adapted
voluntary habits. And these acquired habits cannot be homol-
ogous with the instinctive phylogenetic action systems, for
the very good reason that motor plasticity was evolved for the
express purpose of substituting better and different action systems
for them.

There is, however, the possibility that there may be examples
of recapitulation among the various types of inherited modes of
movement: the automatic visceral control, the involuntary
accompaniments of the emotions, (fear, joy, grief, “‘expression’’),
the random movements of early infancy, and the true reflexes.
With respect to the first two, so far as the writer is aware, there
are no essential differences between youth and maturity excep-
ting such as are induced by habit with the second, and none that
requires an ancestral explanation. Mumford*? advanced the
theory that the random movements of early infancy, associated
with the gradual ripening of the lower centers, are reminiscent in
certain cases of ancient aquatic modes of action. The suggestion
is perhaps a possible one without being at all convincing, and
surely the resemblance is not conspicuous. Besides, as Miss
Shinn notes, in commenting on the suggestion, many of the
movements such as the asymmetrical movements of the eyes,

22 Brain, Vol. XX, 1897.

86 The Recapitulation Theory and Human Infancy

grimacing, the rolling of the head, cannot be brought under the
theory at all.

The sucking and crying reflexes of the infant are obviously
adaptations. As for sneezing, yawning, coughing, and similar
reflexes, all these appear early and remain essentially unchanged
through life. Certain other reflexes and a number of physical
traits, were collected by Robinson,*4 and Buckman,?: and offered
as illustrations of recapitulation. Examples of infantile adaptive
characteristics from these writers referring to the rpithecoid
infantile condition are the clasping reflex, the supporting of the
body by the hands and arms, the thumb-like action of the big-
toe—all having to do with the necessity of holding fast to the
hair of the mother in arboreal life. The very early “hide and
seek” propensity of babies is another example of pithecoid
recapitulation. Examples of physical traits are the baby’s
snub nose, prognathism, remnant of lip furrcw, tail mark, Jong
arms, position of the legs and feet, and the plantar lines. If ¢
one should be disposed to grant a certain plausibility to these
cases of ancestral reference, there is still no necessity of assigning
them to the adult monkey or ape, where they are not obviously
infantile. They may very well resemble the adult because of the
infant ape’s resemblance to its own adult condition and they
thus become illustrative of ancestral ontogenetic resemblance.
They may be compared with the many pithecoid vestiges remain-
ing in the human adult organization, and before any assertion of
greater antiquity of infancy as such can be made it is necessary
to show that they are representative of a very much larger group
of such vestiges than can be found in adults. This is to say,
the whole human ontogeny has pithecoid vestiges. Of course
infancy has its share.

Other illustrations of recapitulation from the same source
are referred to the conditions of primitive man. The intensity
of fear in children, useless crying, shyness, the instinctive appeal
and clinging to the parent in the presence of strangers,—these
recall the dangers of the early life of man. The greediness and
selfishness of children point to a considerable degree of parental
neglect and a consequent survival of those who managed to fend

33 Notes on the Development of a Child, Vol. I, p. 397, footnote.

4 Nineteenth Century, Vol. 30, 1891; Vol. 31, 1892; North Amer. Rev., Vol. 159, 1894;

Brit. Med. Journ., Vol. 2, 1891.
35 Nineteenth Century, Vol. 36, 1894.

Human Infancy and the Recapitulation Theory 87

for themselves. The plumpness of babies as a precaution against
famine, infantile attractiveness as an evidence of primitive parep-
tal selection, the strong interest in animals, the carrying of things
to the mouth, and many other childish characteristics are given
their appropriate recapitulatory explanation. The value of this
type of evidence will doubtless vary with the sense of credulity,
but, accepting them at their face value, it is to be noted that
some of these traits may still be of value to the species in existing
savage societies, others refer to infantile adaptations in the past
and not to remote recapitulations, and once more illustrate the
familiar principle of ancestral ontogenetic resemblance. Infants
today resemble the infancies of their ancestors just as adults
today resemble ancestral adults.

As for emotional equipment, children and youth have no
characteristic attitudes of the kind which are inaccessible to the
sympathetic appreciation of adults. Like native excitants their
early character may be simpler, but they are not different in
quality. The one attitude, which by reason of its oddity ior
adults has been designated a “mania,” is that of collecting.**
One has difficulty in seeing a preparatory value in this propensity.
Perhaps it had an adaptive value in earlier infancies. Seemingly
fear is intensified with young children, and it may be the egoistic
sentiments are more powerful relatively throughout the earlier
part of immaturity. It has been noticed that Robinson saw
in these things illustrations of infantile adaptation. The two
great sources of altruism are more especially associated with
advanced stages of development,—friendship with the clannish-
ness and romantic love of the pubertal and adolescent years,
parental regard with the coming of offspring. Childhood,
although not devoid of these sentiments, does not need them in
the same way. Its major business is to practice its own individual
powers.*7

Drummond, following Romanes, asserted categorically that
the order of the appearance of the emotions in growth is the
order of their distribution on the scale of animals. As to this

26 Thorndike finds abundant evidence of this instinct among adults, op. cit., p. 267.

37 For a pungent criticism of the recapitulation theory as applied to mental genesis,
together with a clear statement of the ‘‘utility’’ theory, of which he is an advocate,
see Thorndike, op. cit., chapter XVI. For an earlier statement of this latter theory, see
King, Psychology of Child Development, 1904.

% Ascent of Man, p. 133.

88 The Recapitulation Theory and Human Infancy

it must be said that the lack of knowledge of the probable facts
in either series prohibits inferences.*

Grouping together the less propulsive and more passive in-
herited psycho-physical traits under the head of “sensibilities,”
it is to be noted that President Hall and others have called atten-
tion to possible recapitulations in this region. Certain hedonic
qualities attached to sensations of touch, smell, and taste,
especially, are thought to require an ancestral explanation,
one reason for this being the probable degeneration of these
senses and their old-time greater importance. This is not an
unreasonable attitude, for the protection afforded by the evolv-
ing higher senses might well permit the carrying down of useless
remnants of the kind. Instincts, intelligence, and modes of
action under the guidance of sight and hearing, would doubtless
be more directly subject to natural selection. There is, however,
a lack of convincing evidence of any predominance of such traits
with the young as such, and until this is forthcoming there is no
need of appealing to recapitulation for an interpretation of such
cases as may seem truly vestigial to adults.

Baldwin’s acceptance of recapitulation was due in part to his
belief in its unimpaired standing in biology as late as 1906, to
the idea that it was logically required as an effect of heredity,
and to the parallel he found between the great epochs of psycho-
physical evolution in the race and comparable epochs in individual
mental development.‘ It is true Baldwin noticed very signi-
ficant departures from a faithful psycho-physical recapitulation,
some of which have been referred to in the present discussion.
Indeed they might well seem to his reader much more impressive
than the arguments he adduced in support of the theory. Bald-
win’s first two reasons for a modified acceptance of recapitula-
tion have been sufficiently discussed. Without following his
analysis in detail we may consider briefly his empirical support
of the theory in terms of current ideas of psycho-physical evolu-
tion and development. The students of comparative psychology
have agreed fairly well upon the main outlines in the evolution
of behavior. The series of epochs in this evolution is represented
as follows: The period of the tropisms; that of the reflex and the
essentially unmodifiable instinctive behavior; that of very grad-

39 Compare Thorndike, op. cit., p. 256.
«0 Mental Development, Chap. I. Development and Evolution, Chap. I.

Human Infancy and the Recapitulation Theory 89

ually modified instinctive behavior; that of intelligence, or the
more abrupt adjustment of instinctive modes to the perception
of related ‘‘objects,” with its associated revival and desire; that
of the imitative and lower types of conceptual intelligence of the
primates; and finally the rational learning of man.‘t These
are of course not distinctly marked periods but rather points
of emphasis in a gradually changing evolution. To what extent
is the series paralleled by the development of the human individ-
ual? It is wholly beyond the scope of the present discussion
to make a careful study of the correspondence. One can here
speak of probabilities only, in view especially of our ignorance of
the course of individual development. The underlying organic
structures are of course wholly incomparable. They are as
unlike as the complicated human nervous system at birth and
undifferentiated protoplasm, to refer to the two extremes; or
as the infant human and pithecoid brain, to narrow the interval
of contrast. The point at issue is whether the rise of psycho-
physical functions in the human child follows in an homologous
fashion the course marked out by the evolution of behavior.

The nervous control of human behavior offers no ground of
comparison with the tropisms. With regard to the reflexes of
infancy, it is obviously impossible to establish genuine homologies
with the lowest animal reflex action systems. In their origin
they were undoubtedly removed from primordial phylogenetic
systems by inconceivable intervals of time, and their only common
attribute is their reflex quality. Moreover, they do not consti-
tute an “epoch” in development, in the sense that they are
succeeded by a later and different mode or organization, for
they persist throughout life. The random movements do sub-
side and give way to higher systems, but even if these be regarded
as peculiarly ancestral, they are so only as fragments of older
more complete instinctive systems and not as representative
ancient reflexes. Again, it is not at all obvious that the particu-
lar reflexes that remain in man are especially old in comparison
with his instinctive make-up. The sucking reflex has risen
with the mammals; it is probably much younger than the basic
fear structure. What is true of this reflex may be true of others.

41 8ee Hobhouse, Mind in Evolution, 1901; Morgan, Animal Behavior, 2nd. ed.
1908; Holmes, The Evolution of Animal Intelligence, 1911.

90 The Recapitulation Theory and. Human Infancy

Similarly the instincts do not constitute an epoch in human
development for they also rise early and persist through life,
speaking generally. But we have noted that the progression
from the native excitant to ‘‘meaning’” seems to represent a
phylogenetic rehearsal, and we are confronted by the very signi-
ficant fact that the sequence from assimilative through intelligent
to conceptual learning is one that has been illustrated in the
accounts of the evolution of intelligence indifferently from the
animal series and the course of the child’s intellectual progress.
Romanes, for instance, believed implicitly in the closest possible
correspondence of animal and childish modes of thought, up
to the point where human intelligence passes beyond the limit
of animal capacity.*2 And this assumption of a fundamental
likeness of childish to animal modes of learning is not confined
to older accounts but passes as a sort of commonplace in current
discussions of intelligence. It has been very generally held
since Romanes that the differences in intelligence whether ex-
hibited in animals, primitive men, or children are differences not
in kind but in degree, and there is undoubtedly implicit in these
views the thought that there exists some kind of scale or genetic
progression against which all acts of intelligence may be measured.
It has, in fact, been assumed, whether properly or not, that
intelligence in its representative character cannot differ in kind
but only in degree. For intelligence has been regarded as
yielding a direct acquaintance with the environing world, so
that a better acquaintance with this world could only mean a
more adequate relationship of the same kind. If, then, lower
animals have any intelligence they must possess some amount
of the same thing which higher animals and human beings.
possess in larger measure.** The progressive character of the

42 Mental Evolution in Man, passim.

42 That its a@ priori attractiveness has favored this assumption is probably true.
An adequate treatment of it in the light of the available facts is beyond the possi-
bilities of this account. Yet a few obvious considerations may be noted. The low
type of learning involved in the dropping of useless movement or in threading a maze
may be effective without being representative, and so escape the implication of the
assumption in question. The possession of a free prehensile organ has been noted as
of first importance in the perception of objects and their qualities, and as a probable
source of difference between human or pithecoid and lower animal intelligence (com-
pare Washburn, Animal Mind, p. 279). And the contribution of the linguistic func-
tion to intelligence must be remarked, whatever this is. That much remains to be
said for the view here referred to, despite such considerations, is apparent. See, for
instance, Morgan, Animal Behavior, pp. 332 et seq.

Human Infancy and the Recapitulation Theory 91

evolution of intelligence has derived added support from the
views currently held of the historical increase in complication
of the nervous system, especially of the cerebral portions. The
original segmental nervous system has been successively inte-
grated, first by co-ordinating centers of limited scope, and suc-
cessively by hierarchies of increasing range and inclusiveness.
This evolution has been in the main one of gradual progression
in a given direction, and those portions associated with intelli-
gence are regarded as being peculiarly illustrative of this order.
In a passage in which he characterizes the method of his work
on the evolution of mind Hobhouse speaks somewhat explicitly
of the homologies existing between human and animal modes
of intelligence. Referring to the stages in mental evolution as
summarized in Chapter XV of his book, this writer says,

“The fourfold method of correlation differing stage by stage
(a) in respect of the factors explicitly taken into account, and
(b) therewith in extent of the sphere comprehended, appears to
the writer to be realized in human consciousness as we run the
gamut from philosophical reflection down to the quasi-mechan-
ical response of habit. Whether these stages into which de-
veloped human reason can be analysed correspond to stages by
which it grew is of course another question—a question only to
be answered by a much wider knowledge of animal psychology
and of the distinct processes of human development than we at
present possess. If we accept evolution, analogy suggests that
human intelligence is a specific and higher development of a
more general form of intelligence. Hence, if we cut away the
higher development, we should come to something roughly
common to man and the higher animals. If we cut further,
we should come to something common to man and a wider
class of animals, and so forth. But there is a caution to be
borne in mind. No two species will come to a quite identical
development. No part of the physical structure of man, I
suppose, is precisely equivalent to the homologous part in
another mammal, still less in another vertebrate of a different
class. It is the same with the mental structure. We must not
expect to find any animals whose intelligence falls readily into
any classification based on the analysis of human experience.
We can only expect to find homologous developments. That
being understood, it may be said that the method of the preced-
ing chapters, so far as they relate to animals, has been to analyze
out the phases of intellectual development as distinguishable in
human experience, and to discover what homologous structures

92 The Recapitulation Theory and Human Infancy

are to be found in the animal world. In accordance with these
homologies animals are ranked in the classification.

Hobhouse here again gives expression to the pervasive idea
that has played so large a part in all ontogenetic study, namely,
that the theory of evolution implies a progressive historical
sequence that becomes registered in development. We now
know that this is not the only method in evolution. Rather, if
the evidence presented in the first chapter is representative, it
is the unusual one, the life history being so altered in the suc-
cessive stages in descent as to leave comparatively few evidences
in any one ontogeny of what took place in the phylogeny. But
it may be that in the case of intelligence there has been just
such a progression. The theoretical considerations to which
reference has just been made, and the degree of success which
has attended the work of students of mental evolution who have
assumed it, give a fair presumption of its actuality. The prin-
ciple of homologous relationships obtaining between animal
and childish modes of thought therefore remains as a valid
working hypothesis, and recapitulation may reasonably be ex-
pected to find illustration in this direction. What we already
know of the correspondence, however, forbids the acceptance of
Romanes’ belief in a close similarity. It may be, for instance,
that the phylogenetic order is not so much shown through
chronological periods of immaturity as in the progression from
ignorance to conceptual or rational control at any period of
growth. And there is the further possibility that intelligence
has been adapted not only to human interests as contrasted
with animal interests—which is obviously the case—but to par-
ticular phases of psycho-physical organization, as in connection
with the development of skilled voluntary movements. As
Hobhouse suggests, we are not yet in a position to speak with
any confidence of the real character of the correspondence, if it
exists.

This survey of the facts offered in behalf of psycho-physical
recapitulation is far from complete, but the more prominent
illustrations have been referred to, and they probably warrant
tentative conclusions. On examination the more striking cases
are found to refer not to ancestral savage conditions, but to

44 Mind in Evolution, p. 327, footnote.

Human Infancy and the Recapitulation Theory 93

traits characteristic of the human species in general which have
been differently affected by the contingencies of historical
development. The civilized societies work differently with the
same human nature and by contrast the fundamental inborn
traits seem ancestral when they are only less trained. Other
cases rest upon analogies due to a confusion of inborn and ac-
quired elements in mental organization. Assertions of a phylo-
genetic rehearsal in the order of appearance of traits have been
made without empirical warrant. In the interests and activi-
ties which more especially characterize development as such,
the preparatory nature of immaturity is obvious, and this is
well illustrated in the group of cases which have had greatest
emphasis in connection with mental recapitulation. In the
matter of intelligence certain genera] considerations, as well as a
considerable amount of inductive study, give a fair presumption
of some degree of ontogenetic-phylogenetic correspondence in
this region.

4. Cultural Recapitulation.

Cultural recapitulation, or the theory of culture epochs, has
had a curious status in educational literature. While its sep-
arate origin has been acknowledged, and its integrity as a sub-
ject of discourse has been maintained by an independent title,
as a matter of practise the discussion of biological recapitula-
tion has encroached upon its territory with impunity and ap-
parently without full knowledge of what it was doing. For it
is clear that any application of biological recapitulation to men-
tal development as a whole deals directly with the question of
how its cultural acquisitions are assumed, whether in the order
followed by the race in the historical development of its cultural
products, or in some other way. And it is a commonplace
of the literature of recapitulation based upon the biological
analogy that the transition from barbarism to civilization con-
cludes the phylogenetic sequence.

Now the doctrine of biological recapitulation had reference
to ancestral species. By the statement that ontogeny re-
hearses phylogeny was meant that ontogeny repeats the suc-
cession of steps in the biological evolution of ancestors. This
was due to the force of heredity operating in descent despite
the modifications which marked the successive stages. But
the transition from primitive to civilized man, according to pre-

94 The Recapitulation Theory and Human Infancy

vailing views, is not a biological progression. Primitive man
and civilized man represent the same species and the same men-
tality. The differences between the two are due in the main to
the unlike use of this common mentality by social and environ-
mental forces. Therefore historical development is not phylo-
genetic, but ontogenetic, i. e., has taken place in individuals of
the same species. Biological recapitulation applied to the mind
of man must be held to refer to the alleged correspondence of
the hereditary sequence of psycho-physical functions in indi-
vidual development with the succession of homologous func-
tions in the series of ancestors. It applies then to the appear-
ance of reflexes and instincts, and to psycho-physical modes;
only indirectly to habits or acquired products represented in
culture. Our treatment of these matters has just been con-
cluded in the preceding section. We address ourselves at pre-
sent to the somewhat distinct issue of cultural recapitulation.

There is no need of recounting the history of the theory of
cultural recapitulation here. This has been done elsewhere.**
The general bearing of the present discussion upon the theory
may, however, be briefly indicated. Cultural recapitulation
rests upon three distinct propositions: 1. The historical develop-
ment of culture, either as a whole or in particular lines, was
determined in some degree by the inherent nature of the human
mind which permitted this order and no other. 2. There is an
inherent and necessary order in the acquisition of culture by
the immature mind. 38. The underlying necessity in develop-
ment is identical in the two series.

Let us consider the status of each proposition. 1. The con-
ception of an inevitable order in the development of culture
was apparently a derivative and special application of the idea
of biological evolution to social phenomena when the prestige
of the new doctrine was very great and when the sciences of
anthropology and sociology were yet in their early stages. The
application is due chiefly to Spencer, Tylor, and L. H. Morgan.*®
The empirical basis of the conception consisted of similarities
which were at first found conspicuous among all races, and more
especially of parallel lines of development in culture which were

43 Vincent, Social Mind and Education, 1897, Chap. III and IV; Dewey, art. Culture
Epochs Theory, in Monroe’s Cyclopedia of Education. See also, Henderson, Princi-
ciples of Education, 1910, Chap. VI.

46 Boas, Mind of Primitive Man, Chap. VII.

Human Infancy and the Recapitulation Theory 95

considered general. Later investigation and discussion seems
to have sadly shaken the foundations of the conception. It has
been pointed out that similarities may be due to factors other
than common mentality, such as similar geographical environ-
ments, common points of radiation of culture, common tradi-
tions, and convergence from unlike sources of origin. Investi-
gation has dealt even more seriously with parallels in develop-
ment. The words of two anthropologists writing with high
authority will suggest the present situation in the science with
respect to the conceptions in question.

“The theory of parallel development, if it is to have any sig-
nificance, would require that among all branches of mankind
the steps of invention should be followed, at least approximately,
in the same order, and that no important gaps should be found.
The facts, so far as known at the present time, are entirely
contrary to this view. We are thus led to the conclusion that
the assumption of a uniform development of culture among all
the different races of man and among all tribal units is true in a
limited sense only.’’47

The different races cannot be arranged, therefore, on a scale of
culture.

“While parallelisms of a certain kind were shown [by the
older students] to occur, this does not hold for parallelisms of
any degree of complexity and duration, nor for integral historic
processes, the individuality of which seems so conspicuous that
doubt prevails in the highest quarters as to whether anything
like historic laws in the strict sense will ever become more than
a desideratum.”

“Whether the parallelisms refer to entire historical complexes
and embrace millenniums, or modestly comprise parallel develop-
ments of less extent and duration, when demonstrated they do
not constitute a solution, but a problem which has not so far
been successfully attacked.’’

It will be noticed that these writers do not wholly repudiate
parallelisms in development due presumably to common mer-
tality. Their expressions have the force of setting positive
limits to the idea of their general prevalence held by the older
anthropologists. They also may not do justice to the fact that
there exists in their science an element or school laying great
stress upon the factor of common mind. Wundt’s “ Vélker-

47 Boas, op. cit., pp. 182, 195.

« Goldenweiser, Jour. of Amer. Folklore, July-Sept., 1913, pp. 281, 283. See also,
Boas, in Thomas, Source Book of Social Origins, 313-15.

96 The Recapitulation Theory and Human Infancy

psychologie”’ represents the farthest advance in this direction,
and while this work is regarded as having the imperfections of a
pioneer effort, promise in this type of anthropological study is
not denied. As a matter of fact the sciences of anthropology
and psychology have not as yet been vitally joined in the in-
vestigation of culture, a significant thing in itself for our topic.
For the present it must be admitted that the idea of a neces-
sary order in historical development of an inclusive sort is some-
what under suspicion. The possibility, or rather the actual
existence of isolated cases of cultural parallels, seems to be
generally acknowledged.”

2. Passing to the second proposition contained in the theory
of cultural recapitulation we find an equally uncertain situation.
That there is a determined order in some part of the progressive
development of the child mind no one doubts, and serious ef-
forts have been made with a view to its description. But it
cannot justly be held that a description of this order in general
terms has as yet been agreed upon by the students of child psy-
chology. More especially, the distinction necessary to an ap-
plication of the culture-epochs theory, between deferred inborn
or original traits and those traits which are to be regarded as
the results of exercise and cultural stimulation, has not yet
been determined with clearness, and until this distinction is
made it is obviously impossible to institute comparisons between
racial modes of cultural acquirement and genetic sequences
characteristic of the learning of children. Speaking broadly,
the many existing characterizations of ‘‘ periods of development,”
of “‘interests,’’ or of “‘nascencies,”’ etc., besides being too various
for general acceptance, deal indifferently with the appearance
of original traits and the development of acquisitions. Valu-
able special studies in certain lines are not wanting, notably
in language and drawing. Recently, in connection with mental
testing, progress towards maturity has been measured, but as yet
a qualitative description of this progress has not been under-
taken. On the whole, there is no question of genetic sequences
in many aspects of mental and cultural growth. We are, how-
ever, still in the dark as to just how these sequences should
be systematically described.

~ A philosophical and critical survey of the history of human progress conceived
largely in genetic terms is that of Santayana’s Life of Reason (5 Vols., 1906).

Human Infancy and the Recapitulation Theory 97

3. Notwithstanding the insecurity of the two primary as-
sumptions underlying the theory of culture-epochs, the develop-
ment of the individual and that of the race have been found by
serious students to have much in common.” A competent
examination of any one of the many applications of the theory of
cultural recapitulation is beyond the scope of this paper. They
range from religion to mathematics, and call in each case for
very special knowledge of the history of the branches of culture
in question, as well as for a broad equipment in the psychology
of the mental processes implicated. We can deal here with
but a few logical considerations.

It would not be surprising if the theory held that mature men
in a given society were required by their inherent nature to
follow in some degree the development of the culture that had
been evolved by mature minds in the course of history, for this
would imply, apart from the differentiating effects of environ-
mental influences, only some common mentality among adults
in the same species and some common elements in their modes
of progression in any given cultural direction. We have already
noticed the difference of opinion between the anthropologists
and psychologists with reference to this possibility.

But the theory goes beyond this. It asserts that unlike
ontogenetic periods may be compared with respect to their
cultural acquisitions. The child’s mind is said to rehearse the
history of culture, which is essentially the expression of matur-
ity. Supposing, then, that a true genetic sequence had been
determined in the historical development of a given branch of
culture, based upon parallels among the different races of men,
is there a possible warrant for the assumption, made in the
culture-epochs theory, that a child’s progress in this branch of
culture may be so accelerated that he can accomplish in his
immaturity what adults in the past could with difficulty attain
to? The answer to the question could be determined of course
only by an appeal to fact, but such acceleration is not impos-
sible if certain conditions be assumed. If the underlying or-
ganic basis for the historic progression has always been the
possession of childhood, and the conditions in civilized societies

0 See the account and references of Vincent, loc. cit., also Ribot, Evolution of General
Ideas, 1899; Branford, A Study of Mathematical Education, 1908; Huey, Psychology
of Pedagogy of Reading, 1910, Part Il.; Baldwin, Thought and Things, Genetic
Logic, 1906.

98 The Recapitulation Theory and Human Infancy

are now especially favorable to its functioning, it need not be
surprising if children should exhibit achievements that were
characteristic of adult societies in past times. For adults in
these societies were, on the present assumption, in a state of
arrest. From childhood they had had the capacity for advanc-
ing beyond the point of their actual adult attainments, but their
advance was prevented by the limitations of their cultural
environment. To illustrate, if in a genetic sequence symbolized
by the series a, b, c, d, e, f, childhood or youth has the inherent.
capacity for rising to stage d, and does so in the highly favor-
able environment of civilized societies, it is easily conceivable
that adults in historical times, laboriously evolving their culture
independently, should remain life-long at points b or c. This
is no more than the equivalent of the thought that primitive
and historical men were relatively childlike, a familiar and wide-
spread idea among students of early cultural expressions. From
this it would follow that cultural recapitulation need not be
expected in any regions where organic differences between
children and adults exist. If certain branches of culture are
expressive of characteristically adolescent or mature attitudes
it will be idle to search for illustrations of their genetic rehearsal
in earlier periods. And since cultural recapitulation has to do
with acquisitions and processes of acquiring we must limit our
search for such recapitulations to the course of development
taken after the basic instinctive structures have begun their
functioning, at whatever period of growth this may be.

It is perhaps not possible as yet to characterize the disting-
uishable lines of growth within the complex field of cultural
acquisition. They are broadly represented by taste, moral
and social character, motor skill, and ideas, but these obviously
overlap. An adequate analysis of the general principles of
mental development will doubtless deal with much finer cate-
gories. It is worthy of notice that those who have done most
with the cultural recapitulation hypothesis have worked more
particularly in the field of thought and it is not impossible that
reasons may be found for regarding the plasticity represented by
thought and ideas as being available so early in life as to make
possible a genuine comparison of childish and historical pro-
cesses. And since ideas are most intimately related with every
aspect of cultural acquisition the possibility may be extended in
some degree to motor, moral, and aesthetic development.

CHAPTER IV

CONCLUSION

The history of recapitulation is an instructive one. A prin-
ciple of limited application within the field of its origin was
elevated to a position of wide generality, and so gave rise to a
conception in the main misleading. Carried into a new terri-
tory without a sufficient examination of its merits, it was ap-
plied broadly as an explanatory principle and thus distributed
its misleading influence beyond its own borders.

Disregarding the qualifications which were forced upon it by
recalcitrant facts, the conception represented a view of individual
development as successively extended in the course of evolu-
tion, in such fashion that in any ontogeny the earliest features
are oldest, the later ones in succession increasingly recent. Thus
embryogeny as a period was oldest, infancy less old, and matur-
ity the last to evolve. From this form the conception degener-
ated to a less and less chronological notion, until it came to mean
often no more than that any particular feature in development
which had an historical rather than a present reference was
illustrative of it.

A more thorough consideration of the facts has led to a view
of development essentially contradictory of this recapitulatory
one. Ontogeny represents the ancient life-cycle which as such
has been transmitted from the beginning. The chronological
sequence from egg to maturity is not a rehearsal of a like his-
torical series of events throughout the phylogeny of species; it
is but the recurrence of an order which has been repeated in the
lifetime of each individual from the beginning. In general, the
effect of the modifications induced by germinal mutations and
selection in the successive ontogenies constituting the phylo-
geny, was to alter these ontogenies, to make them over, and to
destroy the resemblance of later ones to their predecessors.

Still this alteration was not complete; neither was it regular
in its effects. Some very ancient forms are still hinted at in

99

100 The Recapitulation Theory and Human Infancy

existing ontogenies; more especially particular structures were
often retained through long periods of time with considerable
faithfulness. Because of the slowness with which modifications
occurred, any ontogeny repeats most of the features of its proxi-
mate ancestral ontogeny, and in general the record grows less
and less true of phyletic ontogenies with remoteness in descent.
Because any ontogeny thus throws some light upon earlier ones,
and particularly upon proximate ones, the facts of ontogeny
gathered together help to reconstruct the whole line of descent.
Probably this is what is often meant by the statement that on-
togeny is a record of phylogeny. The statement should read
that genetically related ontogenies when compared supply some
ground for reconstructing phylogenies.

Although the effect of mutation and selection was in general
productive of alteration of the life-cycle, evidence points to a
considerable amount of extension of the life-cycle coincidentally
with alteration. This happened at times with the form of the
organism as a whole, but more often with particular organs or
structures.

These considerations apply to the period of infancy with
qualification. Infancy was evolved from an ancient life-cycle
which did not possess such a period, presumably during and
since the Age of Mammals. We can only guess as to the nature
of its origin. It may represent a modified later part of the
ancient embryogeny set over into the post-natal period, or it
may be a remodelled part of the ancient period of precocious
maturity, or it may be both. In any case it is probably not due
to the successive extension of the mature end of old ontogenies,
and there is no need presupposing evidence within it of such
extensions.

It is, rather, probably the ancient structure of maturity,
either in process of growth or in completion, shorn of and supple-
mented by those things which plasticity presupposes. In its
most ancient features, such as the emotional phases and involun-
tary rudiments of instinct, it probably retains the characteristics
of maturity. We have seen no reason for assigning differences
between human infancy and adulthood in these respects. As
for the rest, we may tentatively bring over the classification of
features employed by Duckworth in connection with human
embryogeny, as follows:

Conclusion 101

The infantile condition as such explains many adjustments that
natural selection might have insisted upon—the early dependence,
both physical and mental, upon the mother; the later larger
degree of self-care and self-protection, through fearfulness, shy-
ness, greediness, and selfishness. Then there is the necessity of
preparing for the adult condition—the spontaneous interest in
self-practice, the close correlation of mental need and maturing
structure as exhibited in the succession of interests, followed by
the palpably preparatory conditions of puberty and adolescence.
Finally there remains the small group of vestiges and “‘recapit-
ulatory”’ cases referring to ancestral infantile necessities or
adult preparation no longer required.

The period of infancy can have then no single explanation.
Many factors have conspired to give it its peculiar character.
As time passes we may be able to speak of these with greater
assurance. For the moment we may conclude with reason-
able certainty that infancy is not as such older than maturity;
from the same starting point the two evolved together, the one
giving character to the other by reason of those improvements
which have entered upon the horizon of later evolution—those,
namely, of intelligence and sociability. Infancy is obviously
incomplete; it is older, apparently, only in the degree, yet to be
determined, in which the growth of intelligence is required to
follow a phylogenetic order.

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