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THE EVOLUTION OF MAN

Fig. 1. Above, skull from La Chapelle-aux-Saints represent-
ing Neandertal man. Restored by McGregor. R, portion re-
stored. Below, skull from Grotte des Enfants, representing
Cro-Magnon man. After Verneau. Reproduced by courtesy of
Professors J. H. McGregor and W. K. Gregory.

The Evolution of Man

^ Series of Lectures T)elivered before the

Yale Chapter of the Sigma Xi during the

Academic Tear 1921-1922

By

Richard Swann Lull

Harry Burr Ferris

Qeorge Howard barker

fames Rowland Angell

<tAlbert Galloway Keller

Sdwin Qrant Gonklin

edited by Qeorge Alfred "Baitsell

JP

NEW HAVEN
YALE UNIVERSITY PRESS

London : Humphrey Mi If or d : Oxford University "Press
MDCCCCXXII

\ •

COPYRIGHT, 1922, BY
YALE UNIVERSITY PRESS

First published, October, 1922
Second printing, December, 1922

]^-w( Wa'

PREFACE

The contents of this book have as their basis a series of lec-
tures bearing the same title which were given at Yale Univer-
sity, during the academic year 1921-1922, under the auspices of
the Society of the Sigma Xi. As President of the Yale Chapter
for that year it became my duty to arrange the program for
the Society, and after considerable thought I came to the con-
clusion that the previous successful series of Sigma Xi lectures,
which were given in 1916-1917, and later published by the
Yale University Press, on "The Evolution of the Earth and
Its Inhabitants," could be continued with interest and profit by
another series in which specific consideration was given to the
question of the evolution of man. Accordingly a series of
lectures was arranged as follows :

THE EVOLUTION OF MAN

Lecture I. The Antiquity of Man, December 2, 192 1, Pro-
fessor Richard Swann Lull.

Lecture II. The Natural History of Man, January 20, 1922,
Professor Harry Burr Ferris.

Lecture III. The Evolution of the Nervous System of Man,
February 10, 1922, Professor George Howard Parker.

Lecture IV. The Evolution of Intelligence, April 11, 1922,
President James Rowland Angell.

Lecture V. Societal Evolution, March 10, 1922, Professor
Albert Galloway Keller.

Lecture VI. The Trend of Evolution, March 22, 1922,
Professor Edwin Grant Conklin.

The first lecture, by Professor Lull, sets forth the paleonto-
logical evidence for the evolution of man. In the second,
Professor Ferris gives in detail, largely from the anatomi-
cal and embryological standpoints, some of the important

vi PREFACE

evidence for evolution which Is to be found In the development
and structure of present-day man. The third and fourth lec-
tures, by Professor Parker and President Angell respectively,
constitute a unit In which the evolution of the highly special-
ized and preeminent nervous system of man together with the
development of Intelligence are given consideration. Pro-
fessor Keller, In the fifth chapter, presents the question of evo-
lution In the various institutions of human society, and, finally.
Professor Conklin sets forth his views with regard to the trend,
or future, of evolution. The large attendance at each of the
lectures is sufficient evidence of the extreme interest In the
question of the evolution of man, and It Is hoped that the pub-
lication of this book will stimulate an even greater Interest
in this very important subject. It is believed that the main
scientific facts which bear upon the question are here presented
from a modern viewpoint in an interesting as well as authori-
tative manner.

In conclusion, as President of the Society and editor of this
volume, I desire to express my deep gratitude to the authors
for their willingness to take the time and energy to prepare the
lectures and to arrange their manuscripts for publication; to
the officers, committees, and members of the Yale Chapter of
Sigma Xi who by their enthusiastic cooperation made It pos-
sible to carry through the year's program successfully; to my
colleagues in the Department of Zoology and elsewhere in the
University, who have shown their active Interest in the project
in many ways, and, finally, to the Yale University Press for
the splendid attitude they have shown in all matters connected
with the publication of this volume.

GEORGE A. BAITSELL,

President, Yale Chapter, Sigma Xi,

1921-1922.
Oshorn Zoological Laboratory,

Yale University, July, ig22.

CONTENTS

PAGE

Preface

GEORGE ALFRED BAITSELL

v

Chapter

I.

The Antiquity of Man . Richard swann lull

1

Chapter

II.

The Natural History of Man

HARRY BURR FERRIS

39

Chapter

III.

The Evolution of the Nervous System of Man

GEORGE HOWARD PARKER

80

Chapter

IV.

The Evolution of Intelligence

JAMES ROWLAND ANGELL

103

Chapter

V.

Societal Evolution . albert galloway keller

126

Chapter

VI.

The Trend of Evolution edwin grant conklin

152

Bibliography

185

Index

191

ILLUSTRATIONS

Fig. 1. Skulls from La Chapelle-aux-Salnts, representing
Neandertal man, and Grotte des Enfants, representing
Cro-Magnon man Frontispiece

Fig. 2. Map to illustrate the broader lines of dispersal of the

principal races of man. After Matthew .... 6

Fig. 3. Pithecanthropus erectus. Skull and face .... 15

Fig. 4. Homo {P ale anthr opus) heidelbergensis. Mandible
compared with that of a modern European. After
Schoetensack 17

Fig. 5. Eoanthropus dawsoni {VAtdown Tn2in) . Skull and face 21

Fig. 6. Skeleton of Neandertal man compared with that of

Cro-Magnon man 25

Fig. 7. Homo {Pale anthr opus) neandertalensis. Skull and

face 27

Homo rhodesiensis. Skull and face 29

Homo sapiens (Cro-Magnon man). Skull and face . 33
Provisional phylogeny of man and the anthropoids . 36

Fertilization of the ovum 41

Four diagrams of early human embryos . facing page 42
Human embryo of 1.54 mm. (von Spee). X 23.

Dorsal view facing page 44

Human embryo of 4.2 mm., in lateral view (His).

X15 facing page 44

Developing brain from a human embryo of 7 mm.

facing page 46
The pallium and cerebellum in the brains of various

vertebrates facing page 48

The individual and evolutionary development of the
nerve cell 49

Fig.

8.

Fig.

9.

Fig.

10.

Fig.

11.

Fig.

12.

Fig.

13.

Fig.

14.

Fig.

15.

Fig.

16.

Fig.

17,

X ILLUSTRATIONS

Fig. 18. Section through the spinal cord showing the early de-
velopment of a spinal nerve .... facing page 50

Fig. 19. Organs developing from the rudimentary alimentary

canal 52

Fig. 20. The development of the human heart 54

Fig. 21. The development of the face of a human embryo (His)

facing page 56

Fig. 22. The relation of the fetal to the maternal blood in the

human placenta facing page 58

Fig. 23. Comparison of the embryos of various mammals at

corresponding stages of development . facing page 62

Fig. 24. Changes in proportion during growth 66

Fig. 25. Growth curves for increase in weight and stature in

both sexes 68

Fig. 26. The caecum and vermiform appendix in various mam-
mals 74

Fig. 27. Supernumerary nipples of man 77

CHAPTER I
THE ANTIQUITY OF MAN

RICHARD SWANN LULL

PROFESSOR OF VERTEBRATE PALEONTOLOGY, YALE UNIVERSITY

The Mosaic account of the creation, which has been and is
yet of wide acceptance, would give us a very recent date for
man's advent on this planet. The strictest interpretation of
this account is that of Doctor John Lightfoot, a profound
Biblical scholar, vice-chancellor of Cambridge University in
1654, who is often quoted because of the exactness of his
findings. As a result of careful searching of the Scripture,
Doctor Lightfoot was led to declare that "Heaven and earth,
centre and circumference were made in the same instance of
time, and clouds full of water, and man was created by the
Trinity on the 26th of October 4004 B. c. at 9 o'clock in the
morning."

One questions, however, not the Scriptural account but the
exactness of its Interpretation. The researches of oriental
scholars are bringing more and more Into evidence the his-
torical truth of the Old Testament narratives, and are estab-
lishing from other lines of evidence the historical character of
Abraham, Isaac, Jacob, and the other Hebrew patriarchs, but
they are also tracing back Into a more and more remote
period the history of the Near Eastern peoples, as the result
of the extensive excavations, with their treasure trove, which
are being carried forward in these venerable abiding places of
mankind.

2 THE EVOLUTION OF MAN

Among the most interesting of these finds has been the
bringing to light of several tablets, one of which is preserved
in the Yale Babylonian Collection, and which constitute the
oldest human documents thus far discovered. These several
tablets are of black stone, of no very great size, but bear en-
graven on their surfaces characters which give to us a message
out of the past, the time of which antedates that of Christ by
some 5,500 to 6,000 years; in other words, a thousand or more
years before Doctor Lightfoot's date. Nor is this all, for the
inscriptions are no longer in the so-called picture writing or
ideographs, but in a form of writing undoubtedly derived from
this. They have progressed so far along an evolutionary path-
way that the original pictures cannot in some instances be even
guessed at. This, it would seem, implies a centuries-long de-
velopmental period before the beginning of inscriptive writ-
ings, and the inference is also justifiable that the protoscript
could not have been invented but by peoples of considerable
intellectual powers who had long since emerged from savagery
and were vastly further yet removed from their ultimate
beginnings.

The third line of evidence is cultural, based not on inscrip-
tions or documents of any sort, but upon the implements and
weapons of vanished peoples, with their varying degrees of
refinement. Historic times, as is well known, are often spoken
of as the Age of Iron, and perhaps the Age of Bronze, while
the prehistoric is called the Age of Stone. But the Stone Age
again has its subdivisions into, first, the New Stone Age or
Neolithic period, in which the distinctive characteristic of the
implements is that some of them at least were rubbed smooth
or pohshed after the preliminary fashioning was completed.
Back of this period lies the Paleolithic, varying immensely in
the degree of perfection of use and workmanship, so that
archeologists are agreed upon a number of cultures (see
table, infra) , based upon distinctions some of which are evident

THE ANTIQUITY OF MAN 3

to the most casual observer, while others are discernible
largely to the expert only. Back of the Paleolithic lies the
Eollthic, or Dawn Stone implement period, the definition of
which originally implied that the stone implements of that
time were not artifacts in the sense of purposeful manufacture,
but that they were merely pieces of stone of convenient size
which showed the effect of use. Later authorities admit of the
presence of certain retouching on the margins of implements
they still call eoliths, although just where they would draw the
line between eoliths on the one hand and paleoliths of crudest
workmanship on the other is not clear. Yet other authority
would disclaim any human association with these eoliths, either
of use or manufacture, and invoke the physical forces of
nature to account for their seeming. But our purpose is not
to tell again the arguments, but merely to establish, if possible,
on the basis of such evidence, a further criterion for the test-
ing of man's antiquity. It becomes at once evident, however,
that all races of mankind are by no means in the same degree
of cultural advancement at a given time, and that for ages of
human history the relatively static and the highly advanced
peoples must have dwelt contemporaneously in divers portions '^
of the earth, just as, for instance, the native Tasmanians, of
whom the last survivor died in 1877, were in a state of culture
which some have called Eolithic and others a rather early stage
of the Paleolithic, perhaps Mousterian (Osborn). It becomes
necessary therefore to confine ourselves to some definite region
which has been the home of mankind from remote ages, in
order to establish a chronological series. There is no doubt
in my mind that in the course of time certain portions of Asia
will provide us with a chronology of great interest and amaz-
ing antiquity, but thus far our knowledge of European cultures
is at once the most detailed and the most accurately dated, and
the one with the fewest omissions in the series. There are
readily applied checks on the European chronology, for it has

4 THE EVOLUTION OF MAN

been synchronized very accurately with the successive advances
and retreats of the Ice In the Pleistocene glacial epoch, as well
as with the recorded changes In the faunae of these several
stages. Hence the European cultural chronology has become
the standard for the world, and as It Is further possible to
synchronize the periods of glaclatlon In the Old World and in
the New, a comparative chronology for the latter may some
day be established.

The appended table is based upon the highest authority,
the American Osborn and the Belgian Rutot. Osborn feels
convinced that Pliocene man is established by the Cromer
flints (see page 36), which he says are not Eolithlc but Paleo-

CHRONOLOGICAL TABLE

CHRONOLOGY

INDUSTRIES

RACES OF MAN

Postglacial time

Magdalenian ) Upper
Aurignacian ) Paleolithic

Cro-Magnon
Grimaldi
? Rhodesian

1

1

1

Of

4th Glacial time

Mousterian ) Lower
Acheulian ) Paleolithic

Neandertal

3d Interglacial time

3d Glacial time

Chellean

? Piltdown

2d Interglacial time

2d Glacial time

Heidelberg

1st Interglacial time

1st Glacial time

Cromerian

.r

a

Upper Pliocene

Foxhallian-Red Crag
Pre-Crag

? Pithecanthropus

THE ANTIQUITY OF MAN 5

lithic In that they show the mark of fabrication; and to the
Cromer beds Is assigned a conservative age estimate of more
than half a million years.

But Europe is not supposed to have been the original evolu-
tionary center of mankind; Its small size seems to preclude
that. Rather is it a place to which, as In historic times, mi-
grating hordes came from time to time when force of circum-
stances drove them out of Asia and perhaps more rarely from
Africa. That Asia is the birthplace of mankind is seemingly
established, the following being some of the evidences for this
belief.

Asia possesses great size, and hence varying life conditions,
together with a central location contiguous to all other land
masses, even, as the north polar projection shows (Fig. 2),
to North America. From Asia, as from no other of the
continents of the world, is communication so easy and the
migratory routes so clearly discernible. Asia is the home of the
highest and best of the higher organic life and is with few
exceptions the place whence man has derived his dependents
and allies, the domestic animals and plants. Asia is the seat
of the oldest civilizations, many indications of which, though
visible as sand-drifted ruins, have outlived the vaguest tradi-
tions concerning their origins. Finally, the physical and cli-
matic conditions of Asia in the Tertiary era were such as the
scientist must postulate In his Imaginings of the modus operandi
of human origin from his prehuman forebears, i.e., such as
would enforce descent from the trees and terrestrial adapta-
tion.^ The fact that the most primitive peoples to-day —
African pygmies and Australian blackfellows — are not Asiatic
does not tend to controvert but rather to strengthen this belief,

1 See Lull, in "Evolution of the earth and its inhabitants," Yale University
Press, 1918, pp. 142-143; and Joseph Barrell "Probable relations of climatic
change to the origin of the Tertiary ape-man," Scientific Monthly, January,
1917, pp. 16-26.

2

THE ANTIQUITY OF MAN 7

for as the first formed ripples of the widening circle caused by
a stone dropped into a pool are the outermost, so the descend-
ants of the earliest migrants should to-day be found farthest
from the center of origin. The fact that the most ancient
human remains in point of time thus far discovered are Java-
nese and therefore nearer the focal point is yet another bit
of evidence.

It is with great confidence, therefore, that one looks to
Asia, which is now for the first time being systematically ex-
plored by the American Museum of Natural History, to solve
by actual findings this age-old problem of human origin.

Fossil Man

Our final and, to the paleontologist, most convincing line
of evidence for man's antiquity lies in the discovery of actual
remains of human beings which a fortunate combination of
circumstances of burial, conservation, and subsequent discovery
have brought before us. That these are rare is self-evident,
for even under the most favorable conditions for fossilization,
those of shallow-water marine deposits, it has been estimated
that but 1,044 out of each 100,000 different forms that lived
are known to us. Can we expect, therefore, that the record of
what were evidently largely forest-dwelling creatures whose
remains are but rarely preserved and who in this instance un-
doubtedly had methods of disposing of the dead by burning,
possibly by consumption as an article of diet, or by merely cast-
ing out to be devoured by beasts and birds of prey, could
possibly be as perfect as that of the marine forms? One
marvels, not that the missing links in our chain of evidence are
many, but rather that we possess any chain at all.

Conditions of preservation. There are but two conditions
under which the remains of man are ever found: one, the
older and rarer, in the valley sediments of rivers which deposit
and scour away and deposit again in time of flood or of tran-

8 THE EVOLUTION OF MAN

quil flowing, and occasionally catch and drown the unwary,
as they do to-day, to bury their remains under tons of sedi-
ments which are subsequently removed and their contents
exposed either by natural or by human agencies. The other
more fruitful source Is the underground caverns of Europe —
abandoned subterranean river beds which are always to be
found in limestone countries and which, when opened to the
air through the eroding away of overlying materials by rain,
frost, and snow, formed an inviting retreat from inclement
weather and the assaults of savage beasts. These caverns thus
became the place of abode and often of sepulture of prehistoric
man, but were evidently not available for his tenancy until com-
paratively late in time (Mousterian, see table, page 4).

Means of determining antiquity. The criteria for establish-
ing the antiquity of human remains are three. First, the
geological age of the strata wherein the remains lie; secondly,
the associated animals or artifacts or both; and third, actual
somatological distinctions from existing man. The first must
be most carefully weighed, and in general such is the very
natural scepticism even among scientists that it is well to have
corroborative evidence by unimpeachable witnesses both of the
discovery and the exhumation. It is further necessary very
carefully to distinguish between natural deposition of remains
and intrusive burial, such as is often practiced by mankind,
which places the subject among objects which may far ante-
date it in time. A scattered skeleton and one overlaid by abso-
lutely undisturbed deposits are both good criteria of contem-
poraneity, but chance often makes strange bedfellows. Thus
the finding by the writer of a glass bottle, bearing all the
marks of extremely recent manufacture, beneath the hip bone
of an extinct horse in an apparently undisturbed Pleistocene
deposit in Texas was a little disconcerting until the looseness
of the surrounding sand betrayed a filled-in animal burrow
into which the bottle had undoubtedly been thrust. The asso-

THE ANTIQUITY OF MAN 9

ciatlon therefore with extinct animals and even an apparently
like degree of fossilization are not entirely trustworthy when
taken alone. Associated artifacts when implying ceremonial
burial are fairly safe criteria and have been given high value
in European age determination.

The final criterion, that of anatomical distinction, is of
course highly valuable, but has led to difficulties, as, for in-
stance, when a modern type, such as all the American ones
prove to be, shows other indications of great antiquity. It was
formerly supposed that there was but a single line of phyletic
descent to modern man, but the belief is gaining ground that,
as in the evolution of horses, the story is not so simple as was
at first supposed, but that there were several lines of descent
all of which may be of ancient origin, so that what have been
called modern types of mankind might well be found con-
temporaneous with, or even antecedent to, the remains of more
primitive races. This will be discussed in greater detail below
(page 35)-

Record of Discovery

New World, A brief resume of the discoveries of the
actual osseous remains of prehistoric man which have thus far
come to light emphasizes the antiquity of his world-wide dis-
tribution, but we are not yet in position to date with finality
the earlier men of the New World. Of these. North America
has produced a number of specimens, the oldest of which in
time of discovery is the so-called Calaveras skull, found, to-
gether with certain implements, stone mortars and pestles,
spearheads and hammer stones, embedded in Californian gold-
bearing gravels of undoubted Pliocene age. How this ma-
terial came there is a mystery, but at present the Calaveras
man is not supposed to have been contemporaneous with the
gravels but to represent a man both physically and culturally
of much later date.

lo THE EVOLUTION OF MAN

Again and again such specimens have come to light, as in
the Trenton gravels which date from the final retreat of the
ice, the Nebraska loess man near Omaha, the Lansing man,
and that of Vero, Florida, where the remains of like degree
of fossilization with their animal associates were found en-
tombed with creatures of undoubted Pleistocene affinities. Still
other finds are those at Rancho La Brea in the Pleistocene
asphalt of California, and lastly at Dallas, Texas, in the
Lagow sand pit, associated with a Pleistocene fauna recently
described by the writer. Not one of these, despite their ful-
filment of every other prerequisite to antiquity — burial in older
strata, animal association, like degree of fossilization, and
so forth — meets the requirements of the physical anthropolo-
gist, for none shows somatological characters which are not
possessed by the modern American Indians. This leads
Doctor Hrdlicka to doubt their antiquity, but a growing con-
viction in the author's mind, stimulated by so high an authority
as Sir Arthur Keith, of the Royal College of Surgeons, Lon-
don, is that, on the other hand, they may in part be of genuine
Pleistocene age and hence point to the high antiquity of the
Indian type.

The South American record is comparable. Florentino
Ameghino (19 12) described supposedly human forms under
the names of Tetraprothomo and Diprothomo, based upon
remains which in at least one instance owed their peculiarity to
the fact that they were not even human. But in no event were
these so-called men as old or as primitive structurally as
Ameghino would have us believe, and his thesis that South
America may have been the radiation center of the human
stock seems untenable.

If none of the New World men are of archaic cast, their
association with extinct forms, as for instance with the masto-
don in the north and with living ground sloths in the south,
seems to bear the mark of authenticity. The most authentic

THE ANTIQUITY OF MAN ii

northern Instance is that described by Doctor J. M. Clarke, of
the association In Attica, New York, of mastodon remains

ith charcoal and pottery. Four feet below the surface, in a
black muck, Clarke found the bones of the mastodon, and
twelve Inches below this. In undisturbed clay, pieces of pottery
and thirty pieces of charcoal. The association of the mastodon
with the charcoal is not so significant, as It Is conceivable that
charcoal may have been formed by natural means, but not
the pottery. The Issue of the magazine Natural History for
November-December, 192 1, figures what seems to be the crude
outline of a mastodon on a piece of bone from Jacob's cavern,
Plnevllle, Missouri, in a way comparable to the Upper Paleo-
lithic engravings of Europe.

In South America, again, the association of man and the
ground sloth, Grypotherium, in a cavern at Lost Hope Inlet,
Patagonia, seems definitely established. The fresh-looking
remains, shreds of skin which show indications of having been
cut with primitive knives, the presence of apparently cut grass,
all point to the cherishing by man of what were probably the
last of these creatures, either In the role of domestic animals
or of those sacred to some deity as was the Egyptian bull
Apis.

Keith is greatly impressed with the diversity of American
languages and the high development of pre-Columbian civiliza-
tions in the New World, and feels that they point to an an-
tiquity far beyond that commonly accepted by the ethnologist.
On the other hand, all indigenous New World men are of
essentially the same general racial type, the Mongoloid, nor
have they been here long enough to establish racial differentia-
tion comparable to that of the Old World.

Old World. Africa has been productive of but two osseous
specimens of man of marked antiquity. One, found at Oldo-
way ravine, Tanganyika Territory, in the early days of the
Great War, Is impressive neither for its apparent age nor

12 THE EVOLUTION OF MAN

its somatologlcal peculiarities. The latest find, however, from
Broken Hill mine in northern Rhodesia, has aroused a great
deal of interest, because, while not very decisively dated and
associated with a recent fauna all of which are either now
alive or were so at the coming of white men, the skull itself is
of a most peculiar and interesting type, clearly not that of
modern man. And the finding of a second specimen which,
while fragmentary, serves nevertheless to show community of
type with the first, seems to establish the remains as repre-
sentatives of a race and not due to individual peculiarities.

Arguments such as those recently offered by Churchward^
striving to prove the ancestral character of the African Bush-
men and the fact that Africa may be the primal home of man-
kind are not yet established theses. Northern Africa in the
Barbary States has produced cavern murals comparable to
those in southern Europe, and Sollas has made much of Bush-
man affinities in all of these artistic remains, but these are late
in time (Upper Paleolithic, Magdalenian) and do not aid us
in our establishment of high antiquity for African man. Un-
doubtedly Africa is an old, old home of mankind — all signs
point to that conclusion — but the actual skeletal remains of
types anterior to our own species are, as we have shown, but
a single find. This is undoubtedly due largely to paucity of
discovery rather than to lack of occurrence.

Of Asia, a similar tale is told. Pithecanthropus, found in
1 89 1 in Trinil, Java, being still unique, although one looks
daily for the announcement of further finds as the outcome of
the American Museum's Asiatic expedition now in the field.
Again, we simply do not know the country paleontologically.

At Darling Downs, Australia, a human skull has been found,
apparently in association with extinct Pleistocene Mammalia.

The European finds, on the other hand, are relatively so

2 A. Churchward, "The origin and evolution of the human race," New York
and London (Macmillan), 1922.

THE ANTIQUITY OF MAN 13

numerous that as we have established our cultural chronology
upon European discovery, so we must base our conception of
human antiquity and evolutionary lines largely upon European
material. For Europe is small, accessible, and the home of an
enthusiastic band of workers whose efforts have been untiring
and whose results are already at hand, although much will
come to light in the future.

I Prehistoric Human Species

Pithecanthropus erectus
Taken in order of chronological sequence, the Asiatic Pithe-
canthropus stands first, as it does in most respects in the char-
acteristics which it betrays. Found in 1891 in the deposits of
the Bengawan River, near Trinil, on the island of Java, these
fragments of humanity are most meager, but such as they are,
they throw a flood of light on human origins. It is to be re-
gretted, however, that their owner. Doctor Dubois, a Dutch
army surgeon, now professor of physical geography in the
University of Amsterdam, will not permit their further study
by his colleagues. Our knowledge therefore is based on Du-
bois's own admirable researches, together with the wide-
spread replicas of the external aspect of the calvarium, which
have enabled some independent conclusions to be drawn. The
remains include the skull-cap, three teeth (M^ left, M^ right,
P2 left) , and a left femur, the last bearing an exostosis indica-
tive of injury or disease. These probably pertain to a single
individual, although they were found scattered through some
twenty yards of space and were not all discovered at the same
time. This scattering precludes the possibility of intrusive
burial, however. The most careful search has failed to reveal
any further fragments, although a special expedition under
Madame Selenka, which brought to light the third tooth,
carried on extensive excavations. So much has been written

14 THE EVOLUTION OF MAN

concerning this type of man that the summary of conclusions,
which, however, lack the finality of finished research, is all
that need be given here.

The skull-cap is dolichocephalic, estimates of the cranial
capacity varying from 710 to 1,060 c.c. as compared with 930
to 2,000 c.c. for modern man. The brain, while human in some
respects, is subhuman in others, especially in that area in which
the memories of past impressions derived from the higher
senses are recorded. Whether or not speech was actually used
is questioned, but the possibility of it seems clear.

The straightness of the thigh as compared with that of
Neandertal man (see infra, page 24) is marked, so that in
Pithecanthropus the posture must have been as fully erect as in
modern man. In this he is in no sense a transitional form but
in skull characters he is, for the shape of the thigh is corre-
lated with that of other parts, the vertebral column with its
curves, the pelvis, and the poise of the skull, all of which, one
may infer, were distinctly human.

The teeth of the Java man are also of a distinctly human
type, showing no shortening of the roots or development of
the pulp cavity, to which Keith has applied the term "tauro-
dont" (ox-tooth), as in the Heidelberg and Neandertal races
to be described later. The alternative type of teeth he calls
"cynodont" (dog-tooth), such as those of modern man and
the apes, adapted to a more varied and less harsh diet. Pithe-
canthropus had teeth of the latter type. The tooth crowns are
wider than long, the reverse of simian dimensions, and al-
though they do show certain minor ape-like characters, they
also show certain degenerative features.

Gregory (1920, page 690) thus sums up the status of Pithe-
canthropus:

The association of gibbon-like skull-top, modernized hu-
man femur and subhuman upper molars with reduced pos-
terior moiety, if correctly assigned to one animal, may perhaps

THE ANTIQUITY OF MAN 15

define Pithecanthropus as an early side branch of the Homini-
dae, which had already been driven southward away from
the primitive center of dispersal in Central Asia, by pressure
of higher races. But whatever its more precise systematic
and phylogenetic position, Pithecanthropus, or even its con-
stituent parts, the skull-top, the femur and the molars, sever-
ally and collectively testify to the close relationship of the late
Tertiary anthropoids with the Pleistocene Hominidae.

^

Fig. 3. Pithecanthropus erectus. Skull and face. Adapted from McGregor.
Portion beneath irregular line restored. Two fifths natural size.

Of restorations of Pithecanthropus , several have been at-
tempted. The skull completion here shown (Fig. 3) is derived
from the studies of Dubois and McGregor. The latter has

1 6 THE EVOLUTION OF MAN

done an admirable bust based on the most careful detailed

study.^

Pithecanthropus was found associated with twenty-four or
more species of mammals, all of which are now extinct and
whose affiliations are distinctly Pliocene. Gregory (1921,
page 691, Fig. 270) shows this ancient relic as of upper Siwalik
age (Pliocene). Dubois considered its assignment to late
Pliocene and therefore equivalent to the Cromer forest beds
of England (see infra). Keith describes its geologic occur-
rence as follows: under the fossiliferous bed is a stratum of
conglomerate, then a layer of clay laid down in quiet muddy
water, under the clay a marine deposit containing early Plio-
cene fossil shells corresponding to the "Crag" of East Anglia.
Over the fossil beds containing Pithecanthropus are stratified
deposits forty-five feet in thickness, recalling the Mauer sands
(see page 17). In terms of years, a conservative estimate
would give to Pithecanthropus an age of 400,000 to 500,000,
or in round numbers approximately half a million years.

Heidelberg Man {Homo {P ale anthr opus) heidelbergensis)

The jaw upon which this species is based bears the unique
distinction of having caused no controversy whatever among
anthropologists, for the absolute perfection of the specimen,
the stratigraphic position, and the circumstances of its dis-
covery leave no ground at all for doubt or dispute. It came
to its fortunate discoverer. Doctor Otto Schoetensack, as the
just reward of some twenty years of patient scrutiny and
expectation. It was found at Mauer in southern Germany in
1907. This little village lies in the valley of the Elsenz, a trib-
utary of the more famous Neckar, and at a distance of ten

3 See Lull "Organic evolution," Macmillan, 1917, PI. XXX, Fig. A. Mc-
Gregor's restorations, and those of Rutot, are reproduced in Osborn's "Men of
the Old Stone Age." Rutot's are also to be found in "Prehistoric man and his
story," by G. F. Scott Elliot, Seeley, Service & Co., 1915.

THE ANTIQUITY OF MAN 17

kilometers southeast from the city of Heidelberg, famed for
being one of the oldest seats of scientific learning in central
Europe. The Mauer sands are river valley deposits, the upper
portion of which is regarded by Schoetensack as upper, the
rest as lower. Pleistocene. From this locality has come a
fauna of mammals which compares with that of the pre-Glacial
forest beds of Norfolk, England. The jaw itself was found
in the lower portion, about seventy-nine feet below the summit
of the deposits.

Fig. 4. Homo {Paleanthropus) heidelbergensis. Mandible compared with
that of a modern European (broken line). After Schoetensack. Two thirds
natural size.

The lower jaw is complete to the last detail, although the
teeth of the left side, which adhered to a limestone pebble,
were broken off upon the removal of the latter. They are,
however, carefully preserved, and the accident brought to light
yet other characteristics not otherwise visible.

The jaw is very primitive, heavy, and massive. It lacks
entirely the chin prominence so characteristic of modern man,
as the front profile of the jaw slopes away as does that of a

1 8 THE EVOLUTION OF MAN

gorilla. Within the jaw at the symphysis there is the genial
pit for the attachment of the tongue muscles as in the anthro-
poids, and, like them, the bone encroaches on the floor of the
mouth. In both these respects the jaw is more simian than
human but not sufficiently so to preclude the possibility of rudi-
mentary speech. The body of the jaw is not unlike that of
the successor of Heidelberg man, the Neandertal race, but the
ascending branch which gave attachment for the masticating
muscles differs in shape, being gibbon-like, and is much greater,
as great in fact as that of a female orang. The teeth, while
actually large, are relatively small, and the taurodontism is
developed in a marked degree, as shown by the enlarged pulp
cavity, dilated crowns, and abbreviated roots. The teeth are
regularly placed and the canines are not in any way bestial in
their development, less so, indeed, than in some modern men.
Without the teeth, the Heidelberg jaw might well be con-
sidered as that of an ape, but the teeth affirm its human affini-
ties although in their development and in the form of the
dental arch they are prophetic of Neandertal, not of modern,
man. Keith does not believe that either Heidelberg or Nean-
derthal man lies in the direct line of modern descent, but that
the taurodont dentition implies a specialization for a rough
herbivorous diet and that in this respect both races show a
departure from the more simian dentition and implied feeding
habits of the main line of descent into Homo sapiens.

While the skull of Heidelberg man is yet unknown. Doctor
McGregor has nevertheless attempted its reconstruction, for
of course many dimensions, as well as the character of the
upper teeth, can be learned from the lower jaw, while the re-
mainder of the skull was studied from Its Neandertal succes-
sor. The result Is a pre-Neandertal skull, elongated, with a
low forehead, prominent brow-ridges, and a rounded dental
arch, and there Is reason to believe that this reconstruction will
prove prophetic when the actual cranium is revealed to us by

THE ANTIQUITY OF MAN 19

discovery, unless the latter shows certain unique and entirely
unexpected features.

The probable contemporaneity of the associated fauna with
that of the pre-Glacial forest beds has already been men-
tioned. Osborn in 19 15 considered both the fauna and the
jaw to pertain to the Second Interglacial time, but Schoeten-
sack, Geikie, and others would assign them to the First Inter-
glacial (Lower Pleistocene). Gregory says (1921, page
126):

If of Lower Pleistocene age, the Heidelberg jaw shows
that the most important diagnostic characters of the dentition
of the Hominidae had already been acquired at the beginning
of the Pleistocene epoch and indicates that prehuman transi-
tional conditions must be sought in earlier geological ages.
If, on the other hand, the Heidelberg jaw dates only from the
Middle Pleistocene, then transitional conditions may be looked
for as late as the Lower Pleistocene or Upper Pliocene.

The age of this venerable relic read in terms of years is at
least 400,000, and the associated flints are Eolithic in culture.

The Dawn Man of Piltdown {Eoanthropus dawsoni)

This is by far the most ancient English human relic thus far
discovered, although there is some question as to the precise
dating and, owing to the fragmentary character of the ma-
terial when it came into scientific hands, it has aroused a great
deal of controversy, in marked contrast with the unhesitating
acceptance of the jaw of Heidelberg. The specimen was
found at Piltdown, on the Ouse, Sussex, in a shallow stratum
of gravel, less than four feet in thickness at the point of dis-
covery. This gravel rests on a bed-rock of Mesozoic age, the
Hastings beds. From the lowest six-inch layer of the Pilt-
down gravels, where everything is stained a deep brown, came
the skull, together with certain crude (Eolithic) implements
and the remains of several animals, long since extinct. This

20 THE EVOLUTION OF MAN

pit has been worked for some time for road-mending flints
and thither occasionally came Mr. Charles Dawson, a local
lawyer and antiquarian, to secure the flint implements which
from time to time came to light. One day a workman gave
Mr. Dawson a fragment of the skull parietal. This started a
long search, ultimately resulting in the finding of other char-
acteristic portions of the cranium, a ramus of the jaw with
several molars in situ, a canine tooth, and two nasal bones.
These fragments, which represented what was at first an entire
skull unwittingly shattered by a workman's pick, were sub-
mitted to Doctor Arthur Smith Woodward of the British
Museum, who began the laborious process of reconstruction
of a complete skull from the several isolated pieces. It is but
natural that among the several workers who essayed the same
task, Smith Woodward, Keith, and McGregor, there should
be some difference of opinion, which is manifest principally in
a little variation as to the estimate of skull capacity. But in
the main there is agreement as to the general form. The
cranium is extremely thick-walled, averaging four tenths of
an inch, with a rather steep, though contracted and ape-like
forehead, and one that lacks the prominent brow-ridges of
Neandertal man. The skull was nicely balanced on the neck as
in ourselves, implying an erect posture in further contrast to
the men of Neandertal. The brain-cast was submitted to the
high authority of Professor Elliot Smith, who pronounced it
the "most primitive and most simian human brain thus far
recorded."

The jaw has proved to be a veritable bone of contention.
Everything pointed to community of origin with the cranium,
except its remarkably primitive character. One American
authority, G. S. Miller, Jr., who studied, not the original but
a cast, came to the conclusion that the jaw and skull could not
possibly pertain to the same individual or even the same genus,
but that the former was that of a fossil chimpanzee, to which

THE ANTIQUITY OF MAN

21

Fig. 5. Eoanthropus daivsoni (Piltdown man). Skull and face. Adapted
from McGregor. Two fifths natural size.

the technical name of Pan vetus was given, despite the fact that
fossil anthropoids were heretofore unknown in England. In
this conclusion Mr. Miller has had quite a large American fol-
lowing. The matter has, however, been settled beyond ques-
tion by the finding of a second specimen of the Piltdown man
some two miles distant, consisting of diagnostic cranial frag-
ments associated again with a lower molar of precisely similar
character to those in the first jaw, a happening which could

22 THE EVOLUTION OF MAN

hardly occur, according to the law of probabilities, in both of
the only known instances if the jaw and skull were not those
of the same form.

The jaw is indeed peculiar, as the symphysis is distinctly
simian, while according to Keith, the rear part is as distinctly
human. The whole, taken together with the canine tooth,
points to a man of bestial visage, united with a rather modern-
looking cranium, a combination which excludes him from our
species and genus, and to which the name Eoanthropus daW'
soni is most aptly applied, no one, as Keith says, having ever
anticipated the discovery of one of man's progenitors showing
such a remarkable mixture of human and simian characters.
Chief among the peculiarities of the jaw is, therefore, the
symphysis, which is even more simian than that of Heidelberg
in that there is no rudiment or suggestion of the forming chin.
The ape-like genial pit is present, together with the encroach-
ment of bone on the floor of the mouth. The anterior teeth,
so far as known, are also simian, while the molars are human,
although, as Gregory says, extremely like those of a chimpan-
zee, but these, in turn, are closely related in pattern to primi-
tive human molars.

As has been said, very primitive eoliths, stained brown, were
found actually associated with the skull; in the gravel above,
however, the flints are a brilliant colored iron red and of such
degree of workmanship that Dawson considers them as Chel-
lean or at the earliest pre-Chellean in age. The man, however,
as has been said, was not buried down into the older strata
but contemporaneous therewith, possibly the result of a drown-
ing accident. The British authorities, Lewis Abbott and
J. Reid Moir, both refer the older gravels to the Pliocene, but
the more widely accepted belief is that the Piltdown man is
Lower Pleistocene, of Second or Third Interglacial time, so
that in terms of years his age is from 200,000 to 300,000
years.

THE ANTIQUITY OF MAN 23

These remains occurred so near the present land surface
that had they not shown evidence of great structural antiquity,
their authenticity would be greatly in doubt. As it is, they are
conceded to be ancient, the chief discussion being as to how
ancient and whether or not the jaw pertained, whether the
canine tooth was upper or lower, and finally as to the cubic
contents of the skull. (See Fig. 5.)

Neandertal or Mousterian man {Homo neandertalensis or

primigenius)

This is now a well-established race with considerable range
of variation within it, for of it there have been found rela-
tively numerous individuals of greater or less degree of per-
fection. Of these, the first in chronological order, and the
most ancient in point of time, is the Gibraltar skull discovered
in 1848, but unappreciated scientifically for so many years that
its position in the series has been subordinate instead of at the
head. It is now preserved in the Museum of the Royal Col-
lege of Surgeons.

The most famous skeleton, which gave its name to the
race, is that found at the mouth of a cave in the Neandertal
gorge of the valley of the Dussel, a German tributary of the
Rhine. While apparently nearly perfect at the time of dis-
covery, but little of the skeleton is now preserved in the Pro-
vincial Museum at Bonn. A skull-cap, ribs, part of a right
scapula, clavicle, humeri, ulnae, femora, right radius, tibia, and
a portion of the left pelvic bone are the chief parts remaining,
and, as might well be supposed, the publication of the find
gave rise to much contention as to whether it represented a
type of man or was merely the relic of some poor waif of
humanity, diseased or otherwise, the result of abnormal
growth. It was not until the further discovery of two other
individuals at Spy in Belgium in 1886, which again bore the

24 THE EVOLUTION OF MAN

distinguishing features of Neandertal man, that it was fully
conceded that they represented a race, and that the character-
istics which they exhibited were diagnostic. Later finds,
though not in chronological order, have been made at the
following places :

Le Moustier, La Chapelle-aux-Saints, La Ferrassie, La
Quina, and Pech de I'Aze, France; Banolas, Spain; La Nau-
lette in the Lesse Valley, Belgium; Ehringsdorf near Weimar,
Germany; Krapina, Austria.

The anatomical features of the Neandertal race are now
very well known, largely through the very detailed studies of
Professor Marcelin Boule on the material from La Chapelle-
aux-Saints in the Paris Museum. Homo neandertalensis was
of low stature, hardly exceeding five feet three inches for the
males and less for the females. The posture was not fully
erect, as shown by the curved thigh bones, the absence of the
cervical flexure of the spine, and the position of the foramen
magnum of the skull. The head was borne on the immensely
muscular neck in such a way that the face was thrust forward
in an ape-like manner, thus lacking the delicate poise which it
would possess were the carriage fully erect.

The skeleton of Neandertal man is peculiar, not alone in
the lack of the fourth flexure of the vertebral column and in
the presence of curvature in the thigh, but in the enlarged
articulation of the limbs, with knee and hip joints somewhat
bent, and in the peculiarly rounded ribs, all of which point to
a clumsy, shuffling, loose-jointed being of great muscular
power. The distal segments of the limbs are relatively short,
in marked contrast with those of the great man of Cro-
Magnon described below, and the thumbs could not be so
freely opposed to the other digits, with a resultant lack of hand
skill.

The skull of Neandertal man is very large, with a cranial
capacity of i,6oo c.c. (La Chapelle) as against an average

THE ANTIQUITY OF MAN

25

o>

Fig. 6. Skeleton of Neandertal man (left) compared with that
of Cro-Magnon man. From Lull, after Boule and Verneau.

26 THE EVOLUTION OF MAN

modern cubic content of about 1,400 c.c. The skull is long, as
are all prehistoric crania, but the vault is low and the hinder
part curiously depressed and broadened out, "bun-shaped,"
as Keith expresses it, which, together with the great apparent
musculature of the neck, must have increased the peculiarity of
his appearance. Anteriorly, the supra-orbital ridges or tori
are greatly developed and are confluent across the forehead,
not divided into two parts by a median depression as with
modern man. The nasal bridge is depressed and the upper
jaw very deep, indicating a long upper lip. The lower jaw is
not unlike that of Heidelberg, nevertheless it shows a distinct
advance over the latter in that, while the chin prominence is
yet lacking, there is indication that dental reduction, already
in evidence, is beginning to cause a recession of the tooth-line
to a position more nearly above the chin, giving the latter a
greater relief. The lower border of the mandible is not so
much broadened out to give play to the tongue muscles as in
modern man, hence potential speech is less developed. (See
Fig. I (Frontispiece) and Fig. 7.)

The teeth are of the taurodont character defined above,
large of pulp capacity and short of root, again an adaptation,
according to Keith, to a coarse vegetative diet. In teeth and
palate form, Neandertal man shows a greater degree of spe-
cialization than does our own race and this in a form in other
respects more primitive.

The brain of this man was not as yet sufficiently advanced
to learn to substitute other and more effective devices for
various needs, so that the jaws still had varied uses in contrast
with their very restricted function to-day.

The brain itself shows a certain specialization in its size,
but the relative development of those parts wherein lay the
higher mental functions was not great. Nevertheless, Nean-
dertal man was a skilled worker in flints, had harnessed fire,
and by the reverential burial of his dead surrounded by beau-

THE ANTIQUITY OF MAN

27

r

Fig. 7. Homo {Paleanthropus) neandertalensis. Skull and face. Adapted
from McGregor and Boule. Two fifths natural size.

tifully wrought objects whose surrender implied a very real
sacrifice on the part of the survivors, together with apparent
food, had in greatest probability a belief of some sort in
immortality.

It is in the form of the cranial cavity and of the supra-
orbital ridges that the Neandertal skull departs most widely
from that of modern man, and it is in these two points that the

28 THE EVOLUTION OF MAN

resemblance with the anthropoids Is most pronounced. They
are both, however, in part at least, explicable as a response to
great muscular development of neck and jaw. As Keith says
of him, certain peculiarities of his were distinctly simian, but
not all of them, as he possessed other traits distinctly his own.

The following ideas have been advanced concerning the
status of this interesting race: that he was the product of
disease; that he was ancestral to modern man, representing
the Pleistocene stage in human evolution; that he was merely
an extreme variant of modern man himself, who had retained
an unusual share of ape-like traits. The present opinion, how-
ever, looks upon him as '*a separate and peculiar species of
man which died out during or soon after the Mousterian
period" (Keith).

Modern representatives of Neandertal man. As a race,
Homo neandertalensts is surely extinct. Whether or not his
blood has entirely vanished from the earth is not known, for in
diverse people, as, for instance, a certain Holland strain, the
so-called Old Black breed of the Shetland Islands, and again in
the west of Ireland, we find certain Neandertal characters still
prevalent, but not all of them. The same thing is also true
of the Australian natives, whose physiognomy is often very
suggestive of the Neandertals, so much so that they have been
held by certain authors to be persistent representatives of that
race. But while many individuals show one or more of the
distinctive characters, no one individual ever possesses all.

Rhodesian Man {Homo rhodesiensis)

The exact place of the interesting relic from Broken Hill
mine, northern Rhodesia (see supra, page 12), is yet to be
established, both from the standpoint of antiquity and the
position that it holds in its human relationship. The preserved
remains, probably complete when found, by the workmen, con-

THE ANTIQUITY OF MAN

Fig. 8. Homo rhodesiensis. Skull and face. Adapted in part from Wood-
ward. Two fifths natural size.

sist of a skull with a part of the lower jaw, both so perfect that
no questionable reconstruction of either cranium or facial
bones need be made. Certain other skeletal elements are also
present, such as the tibia and both ends of the femur, the
collar bone, part of the scapula and of the pelvis. Part of the
upper jaw of a second individual was found, thus establishing
the existence of a race or tribe as against an aberrant indi-
vidual.

30 THE EVOLUTION OF MAN

The skull is not fossilized, except that its animal matter has
been lost, and the associated animals are all recent, so that two
of our criteria of age fail us in attempting to fix other than
late Pleistocene or even the Recent period for the time when
this man lived. The position of the remains in a cavern is not
so trustworthy as usual, for while buried under tons of
mineralized bones, they may well have been intruded by means
of a shaft-like cave.

The cranium itself is not remarkable, either for its form or
estimated content, which, as Keith tells us, falls between a
modern English and an ancient French (La Chapelle) skull.
This is as yet an estimate, as the matrix had not been removed
from the interior of the skull at the time of the latest pub-
lished description. We are therefore at present ignorant of
any especial features which a brain-cast may reveal. Judging
from the position of the foramen magnum, the head was well
balanced on the neck, and this, together wth the straight shin
and the character of the ends of the thigh bone, imply a fully
erect posture in no sense Neandertaloid.

The facial region, however, departs radically from what we
have seen in that it shows a very primitive character in con-
trast with the more advanced cranium. The brows are im-
mensely prominent, so much so that they dwarf the forehead
above and give it a flattened look that closer scrutiny does not
bear out. The nose was broad and flattened but human, and
the palate so broad and rounded that it is less ape-like than in
the modern negro. The lower jaw must have been of enor-
mous strength and size to offset it. Smith Woodward tried
the Heidelberg jaw on the skull but found it too short and
narrow. The Piltdown jaw, on the other hand, he found too
large, and to be further excluded from comparison by the
prominent canines which in the Rhodesian man are not dis-
tinctively developed. The teeth as a whole are strongly
rooted, although badly worn, and subjected to caries, a disease

THE ANTIQUITY OF MAN 31

never before observed in a prehistoric skull and almost un-
known among Englishmen before the Roman invasion. The
third molar or wisdom tooth is undergoing reduction as in
modern man.

As one views the Rhodesian skull, he is certainly strongly
impressed with its Neandertal-like appearance, but this, as
has been emphasized, applies to the face, for the laterally
compressed instead of depressed cranium, together with the
implied erect posture, are departures in the more modern
direction. It would seem therefore as though no close rela-
tionship is indicated between the two and that in most respects
Rhodesian man is much more advanced. Certain community
of food adaptation or use of the jaw instead of other means
in accomplishing necessary work, may account for the facial
similarities which in the Rhodesian man, as in that of Pilt-
down, may well have lagged behind the evolution of the rest of
the skull.

Culturally, Rhodesian man must have been very primitive,
for the only associated implements are certain rounded pieces
of limestone of doubtful utility, although the crushed skull of
a lion-like creature found in association is indicative of a cer-
tain defensive value.

Homo sapiens

Upper Paleolithic man. The most notable of the several
races of our own species found in prehistoric Europe is that
of Cro-Magnon, in almost all respects the most perfect man
physically that has come within our knowledge. The first
record of the existence of this race was found at Gower, Wales,
where seventeen skeletons were discovered in 1852. These,
however, were lost to science through subsequent burial in the
village cemetery. Four years later others were discovered at
Cro-Magnon, France, and these may yet be seen in the great
Museum of the Jardin des Plantes in Paris. In all there were

32 THE EVOLUTION OF MAN

five skeletons, an old man, a woman, a child, and two young
men, and these specimens are now looked upon as the types of
the race.

The most impressive thing about Cro-Magnon man is the
majestic height, which averages six feet one and five tenths
inches in the young men, while the old man was six feet four
and five tenths inches. The women, on the other hand, had an
average height of only five feet five inches, but little above
that of to-day. The limb proportions and the great chest are
suggestive of negroes, but not the skull, which is decidedly
more Asiatic than African in implied affinities.

The skull is very large, even the female brain exceeding
that of the average male of to-day. This is perhaps the more
significant, since, as Keith says, the size of the body has a
direct influence on the size of the brain. The Cro-Magnon
skull, while long and narrow, is entirely modern, lacking as it
does the great brow-ridges of his predecessors. Nor is the
brain in any way distinctive from that of existing man. The
face, on the other hand, is broad, especially across the cheek
bones, giving, according to Osborn, a disharmony of face and
cranium. The facial angle is equal to that of the highest
modern man. (See Fig. i (Frontispiece) and Fig. 9.)

The jaw is strong and the chin, though prominent, is narrow
when seen from in front. The palate is also narrow and the
dental arch and teeth are of a relatively high type.

In Obercassel, near Bonn, Germany, there is an extinct race
resembling very closely the Cro-Magnons except for a short
stature.

Culturally, these late Paleolithic men stood very high, not
only in their production of flint implements of Aurignacian
type (see table, page 4), but because it was in representa-
tives of this race that primitive art found so high and so very
remarkable an expression. This art — sculpture, engraving,
and painting — has been found in great abundance in and upon

THE ANTIQUITY OF MAN

33

Fig. 9. Homo sapiens (Cro-Magnon man). Skull and face. Adapted in
part from McGregor. Two fifths natural size.

the walls of caverns in the Dordogne region and in the Bas
Pyrenees, and on the northern coast of Spain. A detailed
description of it is beyond the scope of this essay, and the
reader is referred to the elaborately illustrated works by

34 THE EVOLUTION OF MAN

TAbbe Breuil,* Osborn, and others. The significance of this
work, whether religious or merely a manifestation of an artis-
tic impulse, is not at all clear. That the great bulk of the
representations were of animals has perhaps some bearing on
the question; at all events, they give us an insight into the
psychic development of a race 25,000 years ago fully in accord
with their magnificent physique.

Among other types of Homo sapiens, more or less con-
temporaneous with Cro-Magnon man, is that of Grimaldi,
of which the typical skeletons come from the famous Grotte
des Enfants near Mentone in southern France. The indi-
viduals, a woman and a boy, were apparently laid on the floor
of the cavern and protected by stone blocks over which in the
subsequently accumulated cave earth there was buried a typical
Cro-Magnon man. The Grimaldi individuals show several
features which have been interpreted as negroid, — long nar-
row crania, flattened nose with typical nasal gutters at the
base, protruding teeth and slightly retreating chin, and palate
and teeth like those of the Australians. Although the lower
limbs are disproportionately long, the stature was low.

Sollas makes much of this occurrence, together with the
finding of steatopygous figurines in adjacent Mentone caverns
suggestive in their conformation of characteristic bodily curva-
tures of the modern Bushmen. He therefore, on these and
other data, concludes that "Mentone was inhabited at the
beginning of the Aurignacian age by a race allied to the Bush-
men." One is very loath, however much the resemblances
may point to it, to attribute the glories of Aurignacian art to
a negroid race, in the presence of the splendid Cro-Magnons.
The Grimaldi men may have been representatives of a wave
of invasion from northern Africa which spread for a while
into Europe, to retreat once more before the advance of the

* References to the works of Breuil may be found in the bibliography of
Osborn's "Men of the Old Stone Age."

THE ANTIQUITY OF MAN 3s

more vigorous Asiatics. The Cro-Magnon race has also
ceased to exist as such, although in the Dordogne region,
within the limits of their ancient home, there dwell individuals
which possess many of the physical traits of their probable
Aurignacian ancestors. We have to go to Asia to the region
north and south of the Himalayas to find peoples whose facial
characteristics best resemble those of Cro-Magnon man, while
the stature and bodily build are best displayed in the Sikhs.
The decline of the Cro-Magnons, Osborn says (19 16, page

450).

may have been due partly to environmental causes and the
abandonment of their vigorous nomadic mode of life, or it
may be that they had reached the end of a long cycle of psychic
development. . . . We know as a parallel that in the history
of many civilized races a period of great artistic and indus-
trial development may be followed by a period of stagnation
and decline without any apparent environmental causes.

There are yet a number of remains pertaining apparently
to Homo sapiens. These are the Galley Hill skull in the
Thames gravels, and the remains from Dartford, Clichy,
Moulin Quignon, Crenelle, Denise, Olmo, and Castenedolo.
All of these have been in dispute as to their antiquity, prin-
cipally because of their very modern character. But Keith
groups them collectively under the head of pre-Mousterian
man, accepting Galley Hill, Clichy, and Olmo as certainties,
and believes that they may well be cited to prove the great
antiquity of our own species. Other competent authorities,
however, consider the above cited as "impossible and not
proven." Keith's contention is that Homo sapiens appeared
at a remote time, flourished for a while, and disappeared, to
be replaced by the more primitive but not ancestral Neandertal
man of Mousterian time. This last was in turn deposed from
human dominance and replaced by the higher race again in the
character of Cro-Magnon man. He feels, therefore, that the

36

THE EVOLUTION OF MAN

RECENT

PLEISTOCENE

PLIOCENE

MIOCENE

OLIGOCENE

EOCENE

Oranq
{Simia)

HOMINID/E
Man
Homo
sapiens

t
H sapiens

5IMIID/E {also Simia)

Gorilla
(0 on I la)

Chimpanzee Gibbon
(Pan) {Hylobafes)

Eoanthropus
dawsoni

Pithecanthropus

t

Pa/eosimia

H.neanderthalensis
H heidelbergensis

PJiopithecus

Dryopithecus

5/MUN/E

i

HYLOBATIN/E

Propliopilhecus

{!' Structural" ancestor)

Fig. 10. Provisional phylogeny of man and the anthropoids.
W. K. Gregory 1920 (1916).

Modified from

divergence of the primitive stock into the Neandertal, Pilt-
down, and sapiens stems occurred early in the Pliocene, and
that the differentiation of H. sapiens himself into the four
great ethnic groups, African, Australian, Mongolian, and
European, occurred before the beginning of the Pleistocene.
On this account he is perfectly able to accept a Pleistocene age
at least for the men of the New World. Back of the Heidel-
berg man, the European record is blank, unless indeed Pilt-
down and Castenedolo be older. The last particularly Keith
doubts.

Tertiary man. Professor Osborn in a recent number of the
magazine. Natural History, describes at some length beliefs
which he holds as the result of a visit to East Anglia last

THE ANTIQUITY OF MAN 37

summer. That visit led to a very firm conviction of the pres-
ence of Upper Pliocene or Tertiary man in England, as shown
by his cultures. These are three, two of which ( i ) the pre-
Crag industry (rostro-carinate flints) of Ipswich, and (2) the
Foxhall flints of Ipswich, are placed in the Upper Pliocene,
while (3) the giant flints of Cromer are considered of Lower
Pleistocene age.

Supposedly associated with the Foxhall flints was found a
human jaw which unfortunately cannot now be located. If
it could be found and the certainty of association determined,
it would far antedate both that of Piltdown and of Heidelberg.
The figure which Osborn published of this jaw, from the
original by Collyer in 1867, is remarkable in that it is the jaw
of H. sapiens, if correctly drawn, and not primitive at all I
But this is exactly what Keith's arguments would lead us to
expect. With the apparent insufficiency of evidence, however,
judgment as to the antiquity of our own species should be for
the present withheld.

Summary

The recorded physical changes in prehistoric man are :

Increasing cranial capacity, with perfection of the brain,
especially in that portion which is concerned with the higher
intellectual faculties and with speech.

Change in skull conformation, heightening forehead, and
lessening brow-ridges.

Reduction of jaw power and of dental arch, which results
in the formation of the chin prominence.

Changes in the teeth, such as reduction of canines and loss
of diastemata.

Stature increasing and becoming more erect, although the
earliest known hominid. Pithecanthropus, was fully upright,
pointing to great antiquity for this characteristic.

38 THE EVOLUTION OF MAN

As yet there is no actual connection with ape-like forms
ancestral to both the modern apes and man, but the table here
reproduced (Fig. lo) gives a tentative view of implied rela-
tionships. Exploration in Asia now being carried forward
under the auspices of the American Museum of Natural His-
tory will, it is hoped, yield additional light on the problem of
human origins, for all of our evidence points to central Asia
as the birthplace of mankind, and to the Miocene, 1,000,000
to 2,000,000 years ago, as the time of his origin.

The antiquity of man has thus been made known by direct
evidence in the form of human relics, the greatest age of which
can hardly be less than half a million years. Corroborative
evidence lies in the great variation, not alone between the
several species of prehistoric man, but also among the many
races of Homo sapiens himself, of which Gregory recognizes
twenty-six, with a number of sub-races. And that the major
divisions are very old is attested by ancient murals and other
documents of the Egyptians and other oriental peoples.

Man's distribution is world-wide. In these days of easy
travel, this is not so significant as it was in the ancient days
when dispersal meant slow tribal migrations sometimes cover-
ing generations of time.

The intelligence of man so far surpasses that of his nearest
competitors, the anthropoids, that the mental gulf between
them is immeasurable, while the moral and spiritual attributes
of mankind were also long in the making.

Communal Hfe, as contrasted with the much more common
herding instinct of the gregarious, has been attained but twice,
among the social insects and among men. A long period of
time is again necessary for this attainment.

Finally, man's remains, or the products of his industry, are
found associated with numerous extinct creatures, of which he
alone survives.

CHAPTER II
THE NATURAL HISTORY OF MAN

HARRY BURR FERRIS

E. K. HUNT PROFESSOR OF ANATOMY, YALE UNIVERSITY

The fundamental structural unit in man and other organ-
isms is a microscopic mass, called a cell, which varies consider-
ably in shape and size, and possesses a central spherical body,
termed the nucleus. Animals composed of a single cell are
called protozoa, those made of many cells, metazoa. Man is
a metazoan and it has been estimated that his body is com-
posed of more than twenty-six trillion cells. Animals without
a longitudinal, dorsal body axis are called invertebrates while
those with such an axis are known as vertebrates. Man has
such an axis and also possesses other characters common to
the vertebrates, such as a bony cavity, dorsal to the body axis,
for the hollow central nervous system, and also an internal,
segmented skeleton as shown in the serial repetition of ribs
and vertebrae. Man is also a mammal in that he possesses
mammary glands and hair and has the thoracic cavity, contain-
ing the heart and lungs, separated from the abdominal cavity
by a complete diaphragm. Because of structural similarities
he belongs to the order of primates together with the lemurs,
monkeys, and apes.

Structurally man differs from his nearest relatives, the an-
thropoid apes, by differences of degree rather than of kind
such as the better adaptation of his feet and vertebral column
to the upright position, the non-opposability of the great toe,

40 THE EVOLUTION OF MAN

the greater size of the cranium and the brain, the relatively
smaller and less projecting face, and the relatively and abso-
lutely longer lower extremities. Man does not differ much
more from the tailless apes, like the gorilla, than they differ
from the old-world tailed apes.

Anthropologists generally agree that living man is repre-
sented by one genus Homo and a single species sapiens, and
that the various races are merely varieties of Homo sapiens.
Fossil remains of man have been found, as has been explained
in the previous chapter, which represent several other species
and which show marked ape-like characters. It is not certainly
known whether present man has evolved through these fossil
forms or whether they rather represent collateral lines now
extinct.

The races differ notably in many parts of their bodies. The
most important differences are shown in the size and form of
the head, in the skeletal and physiognomic characters, in the
color of the skin, the form and color of the hair, and the body
proportions. There are also differences in the susceptibility
to disease and, although less marked, psychic differences
in the races, particularly as exhibited in the temperament.
The soft tissues likewise show racial differences although little
in regard to them is known. This subject offers a large field
for further investigation. It is possible also that the races
differ in protein reactions and hormones, as held by some au-
thorities, a subject as yet quite unexplored.

Blumenbach's classification of the races is as satisfactory
as any, although the use of a single criterion of race distinc-
tion, namely, skin color, is open to objection. Blumenbach
classifies the races as follows : ( i ) Caucasian, having a white
skin, (2) Mongolian, having an olive skin, (3) Ethiopian,
having a black skin, (4) American, having a dark skin with
more or less of a red tint, (5) Malay, having a brown or
tawny skin. Some classifications include the Australians as a

I

THE NATURAL HISTORY OF MAN 41

separate race. Additional Interest Is given to this classification
of the races as It corresponds In a general way to their geo-
graphic distribution as shown in Fig. 2.

B

Fig. 11. Diagram showing the fertilization of the ovum. A, the mature
ovum with a central nucleus, or, as it is termed, female pronucleus (e),
containing the reduced number of chromosomes; the others have been given
off into the first and second polar bodies (a a'). A single sperm (b) is
entering the ovum. B, later stage in which the male pronucleus (d), with
the two paternal chromosomes, has formed from the sperm. The sperm
also brings to the ovum the centrosome (c) which is regarded as the dynamic
division center. C, still later stage in which the male and female pronuclei
are uniting to form, in stage D, the segmentation nucleus (e') which contains
an equal amount of maternal and paternal chromatin. Following this the
fertilized egg cell will divide by the complicated process of mitosis which
insures the equal division of the chromatin material among the daughter
cells, a, first polar body (divided into two parts); a', second polar body;
b, sperm entering the ovum; c, centrosome (later divides); d, male pro-
nucleus; f, cell wall; g, body of cell. Redrawn from Cunningham, Anatomy.

42 THE EVOLUTION OF MAN

Early Prenatal Development

Reproduction is started by the union of the germinal cells
of the two sexes (Fig. ii). These cells are differentiated in
development before the sixth week of prenatal life and set
aside in special organs, the gonads, for the perpetuation of
the race. Even at this early period the sex of the germinal
cells of the embryo is structurally indicated. The female cell,
or ovum, is spheroidal in shape and although it is one of the
largest cells of the body yet it is sa small as to be hardly
visible to the naked eye. The male cell, or sperm, is very
much smaller even than the ovum and is elongated and
specialized for active motility. Both the sperm cells and the
ova during their development go through a series of changes
which result in the reduction to one half of the chromatin
material contained in the nucleus. This is an important fact
as the chromatin is regarded as the carrier of the hereditary
qualities, and the fusion of these two cells at the time of fertili-
zation, each with one half the normal amount of chromatin,
produces again a complete cell with the typical amount of
chromatin and having an equal proportion of maternal and
paternal hereditary substance. As a result of fertilization the
egg cell has the power of almost indefinite multiplication and
the still more marvelous power of differentiation so that its
descendants are not all alike, but some form nerve cells, others
gland cells, still others muscle cells, et cetera. This differentia-
tion in structure is accompanied also by a corresponding func-
tional differentiation. It may be possible to explain many of
the processes of life on the mechanistic, or physico-chemical
basis, but it is difficult at present to explain reproduction on
this theory.

After fertilization, the repeated multiplication of the egg
cell quickly produces a solid spherical mass of similar cells,
still almost microscopic in size, called the morula. Some of the
cells soon become massed on one side and in this region two

I

B

Ectoderm

Amniotic cavity

Ccelom
Trophectoderm
Archenterofi'
Entoderm

Mesoderm

..•.»;:•••

Ectoderm of embryo

Ectoderm of amnion

Allantois

D

Body stalk

imniotic cavity

Trophectoderm

Yolk sac
Entoderm

Splanchnic
fuesoderm
Extra-embry-
onic ccelom

Chorionic meso-
derm
Trophoderm

Ectoderm of embryo
Cavity of amnion
Mesoderm of
amnion
Ectoderm of
chorion
Cavity of yolk
sac
Entoderm of
yolk sac
Mesoderm
of yolk sac
Extra-embry-
onic ccelom

Mesoderm,
of chorion

Chorionic villi

Fig. 12. Four diagrams of early human embryos (based on figures of Robinson and
Minot). A, Hypothetical Stage; B, Bryce-Teacher Embryo (modified); C, Peter's
Embryo; D, Graf Spee's Embryo. From Prentiss and Arey, Embryology. By permission
of W. B. Saunders and Co.

THE NATURAL HISTORY OF MAN 43

cavities develop (Fig. 12), one becomes the amniotic cavity
and ultimately surrounds the embryo, and the other forms the
yolk sac, part of which eventually becomes the alimentary
canal. Some of the cells of the two sacs, which lie adjacent
and are destined to develop the embryo, form two layers,
known as the ectoderm and endoderm, or the external and
internal membranes. This structural arrangement represents
the earliest stage known in man's development, the previous
stages described above being hypothetical and based on obser-
vations made on the developing eggs of other mammals.
Later, through the multiplication of the ectoderm cells an
elongated area, known as the primitive streak, is formed and
this indicates the anteroposterior axis of the embryo.

Along this primitive streak, between the outer ectoderm and
the inner endoderm layers, a third layer is produced, known
as the mesoderm. We now have in the region where the em-
bryo is developing, known as the embryonic area, three
layers of cells, each having its own distinctive characteristics.
These are known as the primary germ layers, and from them
all the organs and parts of the body are later derived. In the
human embryo all of the organs are formed by the third month
of development. From the outer layer, or ectoderm, are
formed the outer layer of the skin, or epidermis, including its
various appendages such as the hair and sweat glands, the cells
lining the mouth, the enamel of the teeth, and the entire
nervous system including the sensory portions of the sense
organs. From the middle layer, or mesoderm, are formed the
skeleton and other supporting tissues and the muscles, the
vascular system, and the sex cells. From the innermost layer,
or endoderm, are developed the cells lining the alimentary
canal and the essential secreting cells of the various organs
which develop as outgrowths from it, such as the thyroid
gland in the neck, the lungs, the liver, and the pancreas. In
general it may be said that the endoderm supplies the all-

44 THE EVOLUTION OF MAN

mentary system; the mesoderm, the locomotor apparatus, and
the sex cells for the preservation of the race; and the ecto-
derm, the nervous system which is placed in control of the
body and puts man in touch with his environment. This
method of development is essentially similar in other animals.

Up to this point the embryo appears as a rather simple
multicellular animal of the invertebrate type. The first indi-
cation that it is to become a vertebrate is the development of
a dorsal, longitudinal, rod-like axis, called the notochord,
which eventually extends posteriorly from the base of the
brain through the length of the body. In the lowest forms of
aquatic vertebrates this is the only longitudinal supporting
axis the body ever possesses, but in the higher fishes and the
terrestrial vertebrates, where a more stable axis is necessary,
the notochord is replaced by a more rigid, segmented, bony
structure, the vertebral column.

The rudiment of the nervous system now appears, anterior
to the primitive streak and dorsal to the notochord, as a longi-
tudinal groove, known as the neural groove (Fig. 13), in the
dorsal surface of the thickened ectoderm. The lateral edges
of the groove become elevated and meet and fuse above it
in the mid-dorsal line and thus form a hollow, ectodermal tube,
called the neural tube. Practically the entire nervous system is
developed from the cellular walls of this structure. Shortly
afterwards a part of the yolk sac lying under the embryo is
folded of{ and this process results eventually in the formation
of an endodermal tube under the notochord which is the rudi-
ment of the alimentary canal (Fig. 12 D).

Also the mesoderm, which at this stage is to be found lying
along each side of the neural canal, becomes cleft transversely,
beginning first just behind the brain, and this results in the
formation of a linear series of segments, or myotomes (Fig.
14), extending the length of the body of the embryo. This
primitive segmentation persists in a modified form in adult

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THE NATURAL HISTORY OF MAN 45

man in the serial arrangement of the vertebrae, the ribs, and
the spinal nerves. In the lateral mesoderm a cavity develops
which is the beginning of the body cavity, or coelom, and
later contains the heart, lungs, and viscera of the abdomen.
This cavity splits the mesoderm into two layers. The outer
layer joins with the ectoderm to form the body wall, and the
inner layer with the endoderm to form the wall of the ali-
mentary canal which in time becomes entirely enclosed by the
mesoderm and ectoderm of the body wall. The human
embryo at this stage has acquired the characteristics of a typi-
cal vertebrate.

Later Prenatal Development
The Nervous System. The hollow neural tube early ex-
pands at its anterior end into three sacs (Fig. 15), the primary
cerebral vesicles, or as they are often called the fore-, mid-,
and hind-brain, and later the first and third sacs partially sub-
divide making altogether ^Yt enlargements. From the walls
of these five sacs and from the remainder of the neural tube
are developed all parts of the brain and spinal cord and nearly
all parts of the cranial and spinal nerves which run to the
peripheral regions of the head and body. The developing
brain increases in length rapidly and bends in three places, the
cervical flexure remaining permanently. A small sac grows
out on each side of the hollow anterior brain vesicle and ulti-
mately forms the retina of the eye (Fig. 15), which is thus a
part of the brain projected to the surface of the head so the
light can reach it. By thickenings, thinnings, and outgrowths,
in different parts of the walls of the cerebral sacs, and by the
development of myriads of nerve cells and fibers growing in
many directions, the various parts of the brain are ultimately
formed. Another sac grows out from each side of the fore-
brain in front of the developing retina which (Fig. 15), in
man especially, possesses the power of extensive growth. This
sac expands in all directions but especially backward, spreading

46 THE EVOLUTION OF MAN

over the rest of the brain tube, and ultimately forming the cere-
brum, which is so large in man in comparison with the lower
animals. All of this sac, except the lower part, as well as the
parts of the adult brain formed from it, is known as the mantle,
or pallium (Fig. i6), the olfactory portion of which is the
archipallium since in evolution it is the oldest part of the brain,
while the rest, being a more recent addition, is called the neo-
pallium. The latter is most extensively developed in man
and forms the major part of the cerebrum.

The early condition of the neopallium in man represents
about the extent of the pallium in the adult fish (Fig. i6).
As it grows further backward it represents first the extent of
the pallium in the next higher class of vertebrates, the amphib-
ians, and later the extent in reptiles. Finally, as it begins to
cover the cerebellum, we have the extent of the pallium as
found in lower mammals and when it covers the cerebellum
completely we have the human pallium. Thus we see that the
pallium in its development in man passes through successively
the various stages represented in the adult forms of the dif-
ferent vertebrates, starting with the fish and terminating with
the mammalian type (Fig. i6). Similarly the structural unit
of the nervous system, the nerve cell, or neurone (Fig. 17),
passes in its development in man from the very simple neurone
of the fish through the increasingly complex forms of the vari-
ous vertebrates to its greatest complexity in man.

The sensory nerves ( Fig. 18), which connect the skin and
the various peripheral sense organs to the central nervous sys-
tem, develop by a separation of serial groups of cells from the
dorsal portion of the neural folds. From each of the cells in
these groups two processes grow out. One grows into the
central nervous system and the other pushes its way among
the cells of the embryo until it reaches the sensory structures
at the periphery. The motor nerves (Fig. 18) which control
the muscles, on the contrary, grow out from cells situated in

Diencephalon

Mesencephalon

Cephalic
flexure

B

Thalamus

Optic
cup
Pontine flexure

Myelencephalon

Pallium

Mesencephalon

Meten-
cephalon
Corpus striatum
Optic recess

Hypothalamus

Medulla oblongata

Fig. 15. Developing brain from a 7 mm. human embryo showing the vesicles.
A, lateral view; B, median sagittal section. The fore-brain consists of the telen-
cephalon (region labelled pallium) and diencephalon; the mid-brain consists of the
mesencephalon, and the hind-brain of the metencephalon (cerebellum) and
myelencephalon (medulla oblongata). The portion of the fore-brain which
becomes the retina of the eye is indicated in A as the optic cup. From Prentiss and
Arey, Embryology. By permission of W. B. Saunders and Co,

THE NATURAL HISTORY OF MAN 47

the anterior part of the spinal cord and thread their way
among the embryonic cells till they reach the proper muscle,
where they break up Into fine fibrils which become embedded In
its fibers. Nerve fibers, therefore, are merely the very elon-
gated processes of nerve cells. How these fibers are directed
to their proper terminations among the myriads of cells,
whether by chemical attraction or other force, and so seldom
go astray, has never been determined.

Before the nerves function they become surrounded by a
translucent covering, called the myelin sheath, which Is as-
sumed at different periods during development. In the various
parts of the spinal cord and brain. In general the myelin
sheaths are assumed first by the peripheral sensory and motor
nerves, thereby completing the reflex mechanism which In man
occurs at about the sixth month of prenatal life. Following
this the different groups of cells in the spinal cord are asso-
ciated by the development of the myelin sheaths on the con-
necting nerves, thus arranging for association of the reflex
actions. Still later the nerves connecting the spinal cord with
the cerebellum myelinate, thus completing the mechanism for
coordination of movements. Then the afferent nerves, which
connect the spinal cord with the brain, assume their myelin
sheaths, thus preparing the pathway for sensory impressions.
Not until after birth, however, are the efferent tracts connect-
ing the cerebrum and spinal cord myelinated, thus placing the
cerebrum In control of the parts below and completing the
motor pathway. This late completion of the motor tracts in
man explains the great helplessness of the human Infant at
birth, a condition which is in striking contrast to that In many
of the lower animals. It Is believed that the assumption of the
myelin sheaths in the various association tracts of the cerebrum
continues during the period of growth and perhaps until forty
years of age. As no brain cells are ever formed after birth,
the increasing myellnation of the nerve fibers is the chief struc-

48 THE EVOLUTION OF MAN

tural change in the brain that can be correlated with the educa-
tional process.

The Eye. The eye develops from three sources. The
retina, as noted above, is a direct outgrowth from the fore-
brain on the side of the head. The lens is an ingrowth from
the ectoderm, and the sclerotic and choroid membranes, which
form protective coverings enclosing the retina, are mostly dif-
ferentiated from the mesoderm. Up to the sixth month of
prenatal life a membrane stretches across the pupil of the eye
which sometimes fails to disappear and thus causes blindness.
Also the eyelids are grown together until about the same
period, but in man, unlike the condition in certain other
animals, such as kittens, a separation of the lids occurs before
birth.

The Ear. The Internal ear forms as a saccular ingrowth
from the ectoderm on the side of the head. This invaginated
sac becomes greatly modified but eventually forms the semicir-
cular canals, which preside over the function of equilibrium,
and the highly developed cochlea which is concerned with hear-
ing. The internal ear is regarded as a specialization of a part
of the lateral line sensory organs of the lower vertebrates,
which in the fish is concerned with balancing and movement
only. The added cochlea, which is present in terrestrial
animals, forms the organ of hearing.

Alimentary Canal. The alimentary canal, as stated above,
is early folded off from the yolk sac as a tube lying under the
notochord of the embryo. Both ends of the tube are closed for
a time, but long before birth an anterior and posterior connec-
tion with the external surface of the embryo has been made.
At the anterior end of the body on each side of the neck, four
crevices (Fig. 14) appear in the early embryo which, in the
lower vertebrates such as the fish, open directly into the
pharyngeal region of the alimentary canal and form the gill
clefts. In man, however, these crevices never go on to the

£: 6IR0

Fig. 16. The pallium and cerebellum, in the brains of various vertebrates. The cerebellum
is in black. After Edinger. From Bailey and Miller, Embryology. By permission of William
Wood and Co.

THE NATURAL HISTORY OF MAN 49

formation of gill clefts but soon disappear. Their presence,
however, is indicative of a fish stage in his development. The
lungs, which are the permanent respiratory organs (Fig. 19)
of man, are developed from the upper end of the alimentary
canal by the formation of a single hollow sac. This later

Han

Frog

L/^at^c^

Rat

Ei/o/utior)
of ^he
net'v'e ce//

Oeyv/o/omenf
of net^ye ce//

Fig. 17. The individual and evolutionary development of the nerve cell.
After Cajal. Redrawn from Donaldson, The Groivth of the Brain.

bifurcates to form the rudiments of the right and left lungs and
these by repeated branching develop the highly ramified, tubu-
lar structure of the adult lungs. The early simple, sac-like
lung of the human embryo Is similar in structure to the per-
manent, saccular lung of the adult amphibians.

From the neck region of the alimentary tube, three other
organs develop as branching outgrowths, all of which finally
form organs of internal secretion, namely the thyroid, the

so THE EVOLUTION OF MAN

parathyroid, and the thymus glands (Fig. 19). Another im-
portant endocrine organ, the pituitary body, or hypophysis,
has a double origin In that a portion of It develops as an
upgrowth from the ectoderm which lines the extreme anterior
end of the alimentary canal, or buccal cavity, and another por-
tion, which fuses with the former, develops as a downgrowth
from the brain. These glands, through their Internal secre-
tions, or hormones. Influence development In various ways.
All of them ultimately lose their connection with the ali-
mentary canal. The thyroid gland moving down the ventral
side of the neck stops just above the thorax. The thymus,
which in the calf is commonly called the sweetbread, descends
into the thorax until it lies just above the heart. Early In pre-
natal life the glandular structure of the thymus disappears and
a lymphoid tissue, such as we find In the tonsils, takes Its place.
This organ continues to grow until the child is about two years
of age and then gradually diminishes in size, disappearing at
about twenty years of age. This same remarkable history of
the thymus is found in other mammals as well as in man. Little
is known definitely with regard to the function of this organ.

Lower down the ahmentary canal, just below the spindle-
shaped enlargement which represents the developing stomach,
two other organs grow out and, by repeated branching, form
the liver and pancreas (Fig. 19) . These always remain In con-
nection with the alimentary canal by ducts which carry their
secretions. The pancreas develops as two outgrowths which
fuse. Usually only one of the ducts persists. Occasionally
it is found In man that both persist and the pancreas pours its
secretion into the intestine by two ducts Instead of one. The
explanation of such cases undoubtedly lies In the double origin.

The Vascular System. The heart differentiates from a por-
tion of the mesoderm lying underneath the pharynx in the head
region of the embryo. Two straight tubes are first formed
(Fig. 20). These quickly fuse for part of their length form-

Fig. 18. Transverse section through the
spinal cord of a 76-hour chick embryo
showing the early development of a spinal
nerve. After Cajal. A, motor root; B,
sensory root; C, bifurcation of fibers of
sensory root, a, b, c, d, neurones in various
stages of differentiation. From Bailey and
Miller, Embryology. By permission of
William Wood and Co.

THE NATURAL HISTORY OF MAN 51

ing a single tube which is bifurcated at each end. At this stage
of development, the human heart resembles that found in the
adult of the lowest vertebrates. Later the single tube of the
developing heart partially subdivides into two cavities, the
auricle and the ventricle, and it now resembles the heart of
the adult of the next higher vertebrates, the fish. The auricle
IS then subdivided Into two cavities, and the human heart of
three cavities resembles the fully developed heart of the next
higher vertebrate, the amphibian. Later the ventricle Is sub-
divided and the 'human heart contains four cavities, which is
characteristic of the adult heart of the highest vertebrates.
Thus It Is evident that the human heart In Its development
passes through stages representing the different adult stages
of the various ascending vertebrate classes. This again is an
illustration of the so-called Law of Recapitulation, which holds
in essence that man in his individual development repeats the
evolutionary history of the race, or that "ontogeny repeats
phylogeny.'^

The blood vessels, consisting of the arteries, capillaries, and
veins, are tubes which differentiate from the mesoderm cells
in all parts of the body and become connected with the heart.
The blood cells, which are present In countless numbers In the
blood, likewise are derived from mesoderm cells, and we find
that the red blood cells of the human embryo when first formed
are large and nucleated. In this stage they resemble those
of the fishes and amphibians; later their structure is similar to
those of the reptiles. Finally, before birth, they become In
man, as In all mammals, non-nucleated and biconcave.

The complete natural history of the human red blood cor-
puscles has never been learned. It Is known that they are con-
stantly formed In the adult from the cells of the red marrow
In the ends of the long bones and that they are nucleated at
first but lose their nuclei before they enter the circulation.
Although it is believed that the corpuscles are constantly being

52 THE EVOLUTION OF MAN

destroyed, little is known as to where or how the destructive
process occurs. Sometimes they seem to be destroyed much
faster than they are formed and this results in a great reduc-
tion of the number of the red blood cells of the body from

Middle lobe

of thyroid gland.

Thymus gland.
Lateral lobe

of thyroid gland.

Trachea.
Lung.

Right lobe of liver.

Vitelline duct.

Pharyngeal
pouches.

Stomach.

Pancreas.

Left lobe of liver.

Small intestine.

Large intestine.

Fig. 19. Organs developing from the rudi-
mentary alimentary canal. After Bonnet.
From Heisler, Embryology. By permission
of W. B. Saunders and Co.

5,000,000 to perhaps 1,000,000 per cubic millimeter, together
with the appearance also of a certain number of the embry-
onic type of nucleated red cells in the blood stream. Evidently
the immature cells are drawn into the blood stream in the
endeavor to make good the excessive loss. This is the condi-
tion which exists in that quite fatal disease, pernicious anaemia.

THE NATURAL HISTORY OF MAN 53

Reproductive System. The gonads, in which the germinal
cells form, are developed in the body cavity just at the lower
end of the kidneys, probably from mesodermal cells, and early
begin to move downward in the abdomen. In the female they
go as far as the pelvic cavity where they remain. In the male
they pass through a canal in the lower part of the abdominal
wall, called the inguinal canal, to the exterior of the body.
Similar migrations of the gonads occur in most mammals. The
reasons for these migrations are not known, but the inguinal
canal remains as a weak spot in the abdominal wall and under
special stress may permit loops of the intestines to pass
through, thus forming a hernia. This is the penalty man is
still paying for the lack of structural adjustment to the upright
position.

The external genital organs develop in a similar way in
both sexes and no structural distinction is to be observed until
near the beginning of the third month of fetal life. At this
time the indifferent sex condition begins to develop into one
sex or the other by the greater growth of some parts and the
partial suppression of others, depending upon the sex to be
formed. In rare cases the indifferent condition of the sex
organs may persist permanently in either sex, a condition
known as spurious hermaphroditism, which has particular in-
terest to criminologists and sociologists. The urinary system
develops in close relationship to the genital system and, before
the permanent adult condition is reached, passes through a
remarkable series of changes, many of which are typical of the
permanent adult condition in the lower vertebrates.

The Muscles. As noted above, the mesoderm, which lies
along each side of the developing spinal cord, becomes trans-
versely divided into a linear series of segments (Fig. 14).
This process begins when the embryo is about two weeks old
and continues until a total of thirty-eight segments are formed
which extend the entire length of the embryo. From these

54 THE EVOLUTION OF MAN

segments are developed all the muscles of the body, the axial
part of the skeleton, and the membranes surrounding the
brain and spinal cord. Although the muscles are at first

Fig. 20. Diagram showing the development of the human heart and the
changes of form and external appearance at different stages. Modified from
His's models. Figs. Ill B and IV B are side views; the others are front views.
a, primitive ventral aorta; b, bulbus cordis; c, ventricle; c', left ventricle; d,
auricle ; d', left auricle ; e, sinus venosus ; f, atrio-ventricular canal ; g, position
of orifice of atrio-ventricular canal ; h, vitelline vein. Redrawn from Cunning-
ham, Anatomy,

THE NATURAL HISTORY OF MAN 55

separate masses, by a process of fusion of the segments and
then a later splitting, either lengthwise or tangentlally, the
long, flat muscles In the front and back of the body are formed.
Also many muscles shift from their early positions to some
quite distant place. This Is the case, for example, with the
muscular diaphragm, which forms in the neck and is supplied
by a nerve from this region but which, during development,
moves posteriorly dragging its nerve with It, until in the final
position it separates the thorax from the abdomen. All of
this differentiation and shifting of muscles has been com-
pleted some time before the child is born and therefore is not
produced by any functional necessities after birth, but is due
to heredity.

The Limbs. Until the beginning of the fourth week of de-
velopment, man is a limbless vertebrate (Fig. 23). The rudi-
ments of the limbs then grow out as buds from the side of
the body and, as they elongate, five projections appear at the
end of each of the buds which represent the developing fingers
and toes. This peripheral cleavage into five parts perhaps
is representative of the five main segments of the body from
which the limb projects. Inasmuch as the five-fingered, or
pentadactyl, limb is the common vertebrate type it is believed
that polydactylism, or an extra number of fingers or toes. Is
not a reversion to an ancestral form but is due to an unknown
cause.

The Skeleton. The skeleton is preceded In very early pre-
natal life by two kinds of material, cartilage and membrane.
While most of the bones of the skeleton are ossified from car-
tilage, the bones of the cranium are largely developed from
membrane. The cranial bones begin ossification at their
centers near the end of the second month of prenatal life, the
growth of the cranium being due chiefly to additions at the
edges of the bones. In the long bones, like the femur and
humerus, which are mapped out in cartilage, the centers of

S6 THE EVOLUTION OF MAN

ossification appear about the eighth week of prenatal life in
the center of the shaft, and, at birth, while the shaft is bone,
both extremities are still cartilaginous.

The Skin. The outside portion of the skin, or epidermis, is
derived from the ectoderm, while the deeper portion, or
dermis, is developed from the mesoderm. The human skin
at the end of the second prenatal month is translucent and has
many points in common with that of fishes and amphibians.
In the third month a delicate, superficial, horny stratum ap-
pears, a stage which has been held to represent the evolution
from an aquatic to a terrestrial form of life.

Hairs are outgrowths from the epidermis and are developed
in groups and lines. Their arrangement can best be explained
on the supposition that originally the skin was covered by
scales and that the hair grew out in groups at their tessellated
junctions as is found In certain of the edentates. The skin of
man, in comparison with that of the other primates. Is com-
paratively hairless, which is probably a recently acquired
character. At the seventh month of prenatal life the chim-
panzee and gorilla have well-developed hair on the scalp, eye-
brows, and lips, while the rest of the body Is covered with fine
hair. This Is also the condition of the human fetus at a corre-
sponding period. The hair slopes In man are also very similar
to those of the apes. Some hairs, such as those present in the
eyebrows, perhaps originally had a sensory function and. In
general, hair appears to be a modification of certain glandu-
lar and sensory structures found in the skin of the amphibians.
Evidence has accumulated which shows that the development
of the hair is regulated, at least to some degree, by an internal
secretion of the thyroid and sex glands.

Face and Nose. The face is developed from a series of
paired processes surrounding the primitive mouth (Fig. 21).
These grow In from the sides toward the mid-ventral line
where they normally fuse by the third prenatal month, by a

Fig. 21. The development of the face of a human embryo
(His). From Prentiss and Arey, Embryology. By permission
of W. B. Saunders and Co.

THE NATURAL HISTORY OF MAN 57

method somewhat akin to the healing of wounds, to form the
nose and lips. A failure of proper fusion of these processes
results in harelip and various other facial deformities.

In the development of the human nasal cavity a recapitula-
tion of the conditions present in the various classes of verte-
brates is to be noted. At the end of the third week of fetal
life the rudiments of the olfactory organ appear as two thick-
ened plates of ectoderm which are in contact with the under
surface of the fore-brain. A week later these plates become
depressed and are found at the bottom of the olfactory pits.
This condition is similar to that found in fishes. Two weeks
later the depression has deepened and a nasal cavity is formed
which is somewhat similar in structure to that found in the
air-breathing or lung fishes. By the seventh week this primi-
tive nasal cavity has rapidly enlarged and a communication
has been made with the mouth as in amphibians. The mam-
malian condition is reached by the third month. At this time
the roof of the mouth is completed by the growth to the center
and fusion of two lateral shelves. A failure of these shelves
to unite produces cleft palate.

The teeth are formed by local outgrowths of the ectoderm
and mesoderm lining the mouth, the enamel being formed
from the ectoderm, and the dentine and pulp from the meso-
derm. The human molars with their several cusps have
evolved from the simple conical teeth of fishes and reptiles
either by a process of partial fusion or by an outgrowth of
cusps from the conical tooth.

The Prenatal Nourishment of the Embryo. During pre-
natal life the fetus is enclosed in a fluid-filled sac, the wall of
which is composed of two membranes, the inner called the
amnion and the outer the chorion, which serve for protection
and nutrition (Fig. 12). The development of an embryo in
utero is dependent upon its ability to secure nourishment and
to eliminate certain wastes. In order to do this it must get

58 THE EVOLUTION OF MAN

into contact with the maternal blood supply in the walls of
the uterus. It appears that, in this early stage, the outer layer
of embryonic cells is able to secrete a ferment, or enzyme,
which actually eats away, or digests, a portion of the uterine
wall with which it is in contact. This process furnishes the
embryo with a temporary supply of food which can be ab-
sorbed by the cells and also enables it to imbed itself com-
pletely in the uterine wall where it is surrounded with extra-
vascular blood, the result of the erosion of maternal blood
vessels. In a short time a certain region of the outer layer
of cells together with the underlying chorion becomes modified
to form a highly specialized structure, the placenta, through
which an interchange of materials between the mother and
embryo can take place. The fetal placental tissues become
actually fused with the uterine wall (Fig. 22), and the under-
lying tissue of the latter is gradually eroded to such an extent
that the finger-like processes, or villi, of the fetal tissues of
the placenta, which project into the maternal tissue, are sur-
rounded by intervillous spaces of considerable size which are
filled with the maternal blood (Fig. 22). Although the pla-
cental villi are richly suppHed with fetal blood vessels there is
never any direct connection between the maternal and fetal
blood vessels in the placenta, and no nerves pass from the
mother to the child. The interchange of materials, oxygen
and food from the maternal to the fetal circulation, and carbon
dioxide and hquid metabolic wastes from the fetal to the
maternal, all takes place by osmosis and specific selection.
The structure of the placenta in the different mammals shows
considerable variation. That found in the anthropoid apes
is very similar to the human type.

The maternal and fetal blood streams are separated by the
embryonic tissue of the placental villi (Fig. 22) . This separa-
tion can be proved by the microscopic examination of the con-
tents of the fetal vessels in the placental villi and the maternal

Fig. 22. The relation of the fetal to maternal blood in the placenta.
Arrows indicate the supply and exhaust of the maternal blood in the
large intervillous spaces, a, sinus of uterine vein; b, muscle tissue of
uterine wall; c, uterine vein; d, uterine artery; e, sinus of uterine
vein; f, decidua basalis; g, uterine artery; h, intervillous space filled
with maternal blood; i, syncytium; j, villus; k, umbilical vein (fetal) ;
1, umbilical artery (fetal) ; m, uterine artery. From Prentiss and
Arey, Embryology. By permission of W. B. Saunders and Co.

THE NATURAL HISTORY OF MAN 59

blood in the placental sinuses in the early stages of develop-
ment. Many nucleated red corpuscles which are found only
in the blood of the fetus will be seen in the vessels of the
placental villi but there are none in the placental sinuses.
Further, the vessels in the placental villi can be injected from
the fetal but not from the maternal blood vessels.

That gases can be transmitted from the maternal to the
fetal circulation is shown by the fact that the blood in the um-
bilical vein, which carries blood from the placenta to the fetus,
is redder and contains more oxygen than the darker blood of
the umbilical artery, which carries blood from the child to the
placenta. Also ether or chloroform administered to the
mother can be demonstrated in the blood of the child.

Substances in solution also can pass from the maternal to
the fetal blood. This is indicated by the fact that the child
grows. Also it has been experimentally demonstrated in the
case of many drugs that when they are administered to the
mother they will be found in the blood of the child. Among
these drugs are bromide of potassium, arsenic, strychnine,
quinine, and morphine.

The work of recent observers seems to show that fats and
proteins are not passed unchanged through the walls of the
placental villi from maternal to fetal blood, but are broken
down into simpler compounds and later recombined, thus mak-
ing the process of absorption in the placenta somewhat analo-
gous to that occurring in the intestine. The placental tissue
apparently has not only the power to change some substances
but also the power of specific absorption. Proteolytic, lipo-
lytic, and glycolytic ferments have been demonstrated in the
placental villi, also a ferment which changes certain of the
amino acids into ammonia.

Observers now generally agree that, while the placenta
usually acts as an efficient filter against bacteria, occasionally
bacteria may be transmitted from mother to child as has been

6o THE EVOLUTION OF MAN

known to occur in some cases of typhoid fever and, in rare
instances, of tuberculosis. On the contrary, it has been demon-
strated that the toxins and antitoxins of diphtheria, tetanus,
and typhoid fever readily pass from the maternal to the fetal
blood stream in the placenta. Furthermore, biologists agree
that there is no foundation for the more or less general belief
that maternal impressions are responsible for malformations
of a child. It can be understood, however, that a general dis-
turbance of the fundamental metabolic processes in the mother
may result in similar disturbances in the fetus and thus may
interfere with the normal developmental processes.

Birth. It has been seen that the human embryo is a para-
site which engrafts itself on the maternal tissues and by the
remarkable and highly specialized organ, the placenta, is
supplied with nourishment and relieved of its wastes. This
connection is normally retained for a period of approximately
nine months, at which time the 'host,' for reasons largely un-
known, refuses longer to support the 'parasite.' Rhythmic
contractions begin in the walls of the uterus. These increase
in strength and frequency and finally result in the birth of the
child. In separating the placenta and tearing the large ma-
ternal vessels of the uterus, without causing an excessive
hemorrhage, nature performs a wonderful surgical operation.
The moment the child breathes and the lungs expand, the
course of the circulation is changed. This change is due to
the expansion of the lungs and the consequent large flow of
blood to them. As the result of this, the opening between the
two auricles (foramen ovale) closes, the course of the circula-
tion in the heart is also changed and the blood, which was
formerly aerated in the placenta, is now aerated in the lungs.
Sometimes this interauricular opening fails to close in the
proper manner and this permits a mixture of venous with
arterial blood which causes a dark color in the skin and, there-
fore, what is commonly known as a 'blue baby.'

THE NATURAL HISTORY OF MAN 6i

In the prenatal condition the child needs to produce very
little heat because so little is radiated and the mother supplies
all of the necessary food and oxygen and removes all the
wastes. After birth the radiation of heat is greater and the
child is obliged to produce much more in order to maintain its
body temperature. The alimentary canal must take in and
digest its own food; through its lungs the child must obtain
oxygen and free itself of carbon dioxide, and its excretory
organs must remove its own wastes. It is evident, from the
above, that there is a great contrast between the prenatal
and postnatal environment, and the fundamental changes in
circulation, nutrition, and excretion which occur at the time of
birth make this period a very critical one for the child.

At birth the child weighs about seven pounds, and is twenty
inches in height. Its upper extremities are relatively long, and
the lower extremities short. The legs are partly flexed, the
great toe abducted and the soles of the feet turned in. The
latter is believed to be indicative of a persistence of the climb-
ing position which existed in arboreal man. Additional evi-
dence along this line is to be found also in the remarkable
power of the hand grip of the child during the first month of
its life. At this time the infant is able to hold its weight sus-
pended by its hands, a power which is later lost. When the
body proportions of the newly born child are compared with
those of the adult it is found that the child is four times its
head height while the adult is eight times ; that the upper and
lower extremities of the infant are equal In length while in the
adult the lower extremities are longer than the upper. The
long arms, short legs, flat nose, inverted feet, and lack of
cervical and lumbar curves in the spinal column of a newly
born infant constitute a remarkable series of structural re-
semblances to the ape which later disappear as the adult condi-
tion is reached. The child at birth can feel, see, taste, and
suffer pain but It is deaf for about twenty-four hours. Its

62 THE EVOLUTION OF MAN

most striking characteristics, In contrast to the lower animals,
are its helplessness and educabllity. Its helplessness has un-
doubtedly been an important factor in the development of the
family, while the long period of growth before maturity is
reached has exerted a great influence in the development of
man's psychic powers, which distinguish him so markedly from
all other animals.

Statistics of various animals show that the proportion of
male and female births is approximately equal; the ratio in
man being about io6 males to lOO females. Multiple births
are the usual rule in most of the lower mammals but not in the
primates. Occasionally, however, it occurs and in man even
sextuplets have been recorded. There have been some 500
theories proposed as to the cause of sex determination and
as to methods for controlling it, but the accumulated evidence
of the last few years clearly shows that sex is determined at
the time of fertilization, just as are all somatic characters,
and that it cannot later be changed by any means. Inasmuch
as the ossification of the bones of a female embryo precedes
slightly that of the male embryo, a radiograph may perhaps
aid in ascertaining the sex of the child before birth.

If we summarize the facts regarding man's early develop-
ment, which are given above, it is evident that he starts his
development as a unicellular animal, becomes a metazoan of
the Invertebrate type, develops the structure of a vertebrate,
and ultimately becomes a mammal. Many of the structures
of his body pass through temporary stages which are typical of
the adult condition in various classes of the vertebrates and,
in general, his organs are developed in a manner similar to
that in other animals. Man's development, however, parallels
that of the anthropoid apes for a longer time than that of
other mammals and at birth the child has ape-like characters
that later disappear. These facts of human development
associate man closely with the anthropoid apes and give evi-

PIG

RABBIT

MONKEY

MAN

Fig. 23. Comparison of the embryos of the Pig, Rabbit, Monkey, and Man
at corresponding stages of development. The embryos of each animal are
arranged in the vertical columns according to age, beginning with the youngest
stage at the top. Stage A of the human embryo is fully labelled and the cor-
responding structures in the other embryos can be noted, a, head region; b,
eye; c, ear; d, gill slits; e, heart; f, fore limb; g, primitive muscle segments;
h, hind limb; i, tail region. Slightly modified from K. Guenther, after Keibel.

THE NATURAL HISTORY OF MAN 63

dence that the latter reproduce, in many respects, a compara-
tively recent phase in the history of human evolution.

Postnatal Development

In the final analysis, growth in any living organism is the
result of the division of a cell into two daughter cells each of
which, when first formed, is half the size of the original cell.
The daughter cells very soon, by the process of intussuscep-
tion which undoubtedly involves complex physico-chemical
processes, grow to the size of the original cell and then the
process can be repeated. In prenatal life, the embryonic cells,
in general, divide comparatively rapidly and, as a rule, are not
as large as in postnatal development. The increase in size
after birth is believed to be due primarily to a general increase
in the size of the cells of the body rather than to the formation,
by cell division, of additional cells. Development is therefore
accomplished by cell division, cell enlargement, and cell differ-
entiation.

The ultimate size of an animal depends both upon the rate
and the duration of growth. Minot has shown that man
becomes larger than the rabbit, not because of a more rapid
growth, but because he grows for a longer period of time.
The rabbit, on the other hand, becomes larger than the guinea
pig because of a more rapid rate of growth. Large animals,
with few exceptions, continue to grow during a longer period
and live longer than do small animals. Statistical studies show
that the rate of growth is most rapid in early prenatal life and
steadily diminishes until birth. During the prenatal period
of the human embryo the weight increases more than 5,000,-
000 times, while after birth the increase is only 20.6
times. As the rate of growth is a constantly decreasing
one, its cessation seems to be the final term of a diminishing
series. During the most rapid period of growth the cells have
large nuclei but, with advancing age, the cytoplasm relatively

64 THE EVOLUTION OF MAN

increases and this change in the relative size of nucleus and
cytoplasm constitutes the chief structural difference between
the cells of the young and of the old. A decreasing rate of
growth is also accompanied by a diminution in the water
content of the body, as is shown by the fact that in the first
month of prenatal life the percentage of water in the body
is 97.5 per cent, at birth it has become 74.7 per cent, and at
maturity 58.5 per cent.

While man and the higher vertebrates have a definite period
of growth some fishes and amphibians continue to grow
throughout life. The forces which stimulate or inhibit growth
are largely unknown. Evidence is accumulating to show that
certain of the internal secretions, notably those given off by
the thyroid and pituitary glands, play a large part in the con-
trol of growth. It is believed that too much secretion of the
latter may increase the growth of local areas of the body such
as the hands and face. This condition is to be seen in the rare
disease known as acromegaly. On the other hand, a dimin-
ished secretion of the thyroid results in a failure of growth of
the entire body as well as a lack of mental development, a
condition known as cretinism. Various factors such as un-
favorable climatic conditions, poor food, lack of proper pro-
teins and vitamines, and severe illness retard growth.

However, these factors do not offer any explanation as to
why most animals stop growing after reaching the size of the
species. A mouse never grows to the size of an elephant, nor
does an elephant remain as small as a mouse. It is apparent
that there is a fundamental hereditary factor involved which in
some way, possibly through the internal secretions, controls
growth. That this hereditary influence has not always re-
mained constant is shown in the size variation of the same
species in different geologic ages. This is notably shown in
the evolution of the horse. The question of growth is closely
associated with the power of regeneration, that is, the abilii

THE NATURAL HISTORY OF MAN 6$

of an animal to replace lost parts. The power of regeneration
In an animal, In general, Is found to be In Inverse ratio to the
degree of specialization, or differentiation, which it exhibits.
For example, among the lower vertebrates, the amphibia are
able to regenerate entire limbs, whereas In the more highly
specialized animals such as man this power of regeneration
is present only in certain tissues, notably the connective and
epithelial, by the agency of which wounds are healed. Cancer
is generally regarded as a localized lawless and unrestrained
growth of epithelium, the cells having become parasites and
attacked the host. The only cure thus far discovered is an
early destruction or removal of the abnormal parasitic cells.
The causation of cancer apparently lies In the disturbed bal-
ance of the forces stimulating and restraining growth in the
affected cells and is probably essentially a faulty cellular
chemistry.

The child sits up by the sixth month, creeps by the tenth
month, and walks by the fifteenth month, thus passing from a
quadrupedal gait to the erect position in a few months, an
accomplishment which in evolution may have occupied ages.
All parts of the child do not grow at the same rate and, as
a result, the body proportions continually change during
growth (Fig. 24). Even the shaping of the features is due to
the different rates of growth of the various parts of the face.
Comparing the condition at birth with that of maturity it is
found that while the head doubles in height, the body increases
three times, the upper limbs four times, and the lower limbs
five times. These changes In the body proportions are well
shown If, with the adult proportions, we compare the pro-
portions of the child when expanded to the height of the adult.
Such a comparison will show, as has been previously noted,
that the head of the adult Is relatively smaller, the arms
shorter, and the legs longer (Fig. 24) .

Likewise It Is known that various organs grow at different

66 THE EVOLUTION OF MAN

rates with the result that they bear a different ratio to the total
body weight at different ages. Here is a field that needs much
further study inasmuch as this changing relationship in size
may have an important bearing on the incidence of disease at
different ages. The studies which have been made on the

2 mo. (fetal)

5 mo.

Newborn

2yrs.

6 yrs.

12 yrs.

25 yrs.

Fig. 24. Changes in proportion during prenatal and postnatal growth.
After Stratz. From Morris's Human Anatomy. By permission of P. Blakis-
ton's Son & Co.

relative growth of the different organs show that the same
proportionate weight of the skeleton, fat, and skin, which is
about 39 per cent of the total weight of the new-born, persists
in the adult; that the relative weight of the organs of circula-
tion, respiration, and alimentation is about twice as large in the
new-born as in the adult; that the weight of the muscles of the
new-born is relatively one half as large as in the adult, and,
that the central nervous system of the new-born is relatively
eight times as large as in the adult. It is possible that the very
rapid growth of the brain in early childhood accounts in part,
at least, for the nervous instability of that period.

Considerable data have accumulated with regard to the
growth of bone. Membrane bones, such as the bones of the

THE NATURAL HISTORY OF MAN 67

cranium, grow by additions along their edges which form the
sutures. Beginning at about forty years of age, when the brain
stops growing, the cranial sutures disappear. In the long limb
bones in early postnatal life, one or more centers of ossifica-
tion appear in the terminal cartilages and form caps of bone.
The growth in length occurs in the cartilage under the bony
caps. This was shown experimentally many years ago by
John Hunter, who inserted shot in the shaft and in the end
cap of a femur in a young animal, and later found that the dis-
tance between them had increased. Usually by the twenty-first
year these caps have joined to the shaft thus making any
further growth In length impossible. The growth in the cir-
cumference of a bone takes place by additions under the outer
fibrous membrane, known as the periosteum. This has been
shown experimentally by feeding growing animals with madder,
which gives a yellowish stain to the new bone.

The child, like the young of all mammals, is born without
teeth. The first set, twenty in number, begins to erupt about
the sixth month after birth and is completed when the child is
nearly two and one half years of age. During the next few
years the permanent teeth, thirty-two in number, are forming
beneath the temporary teeth and also behind them, and, by the
absorption of their roots, replace them. The first permanent
tooth to erupt is the first molar which appears behind all the
temporary teeth at the sixth year. By thirteen years of age
all of the permanent teeth have erupted except the third
molars, or wisdom teeth, which appear about the seventeenth
year. The latter may be small in size, be abnormally placed,
appear late, or even fail entirely to appear.

A study of the growth curves for height and weight (Fig.
25), which have been plotted by averaging the results obtained
from weighing and measuring many children at various ages,
but mostly over five years of age, shows a general agreement
of results. There is a loss of weight for the first few days

68 THE EVOLUTION OF MAN

after birth, the postnatal retardation. During the first year,

growth in both weight and height is rapid — the boy increasing

YEARS
eO 25

140

Fig. 25. Growth curves for increase in weight and stature
for both sexes. From Donaldson, after Roberts.

THE NATURAL HISTORY OF MAN 69

more rapidly than the girl — then the rate of growth goes on
more slowly up to seven years of age. This is followed by a
more rapid Increase In growth rate up to about seventeen years
in the boy and sixteen years In the girl, with a prepubertal
acceleration present in both sexes. The growth rate then de-
creases to twenty-five years of age, at which time growth prac-
tically ceases.

During the early years the boy is slightly taller and heavier
than the girl but, owing to an earlier prepubertal acceleration
in the girl, the two sexes are equal in height at twelve years of
age and for the next three years the girl Is the taller. Simi-
larly, at thirteen years of age, the two sexes are of equal weight
and for the next three years, the girl Is the heavier. After
fifteen years of age the boy surpasses the girl In height and
after sixteen years In weight. The average height for the
people In the United States Is about five feet and eight Inches
for men, and ^vq feet and four inches for women. On the
other hand some of the dwarf races of central Africa scarcely
attain four and one half feet In height. The average weight
of the male Is 150 pounds and of the female 125 pounds.

Puberty. At puberty certain marked physical and psychic
characters, known as the secondary sexual characters, develop
which quite clearly distinguish the sexes. These changes, as
experimental work on the lower animals has shown, are
brought about by the Internal secretions of the sex glands and
can be prevented by their early removal. Also some of the
sexual characters In the human female may be modified to
somewhat resemble the male after the climacteric when the
internal secretions of the sex glands diminish or cease. In the
male the growth in weight and height Is usually greater, the
brain and face grow larger, the vocal cords elongate rapidly,
which causes the pitch of the voice to drop an octave, the beard
develops, the muscles become larger, giving a more angular
appearance to the surface of the body in marked contrast to

70 THE EVOLUTION OF MAN

the curves of the female, the waist is broader, the pelvis
smaller, the shoulders less sloping, and the hands and feet
larger.

Senescence

The normal life cycle has three phases, development, ma-
turity, and decline. Each of the first two phases lasts about
thirty years and the third should be at least of equal length.
But this may be greatly exceeded as shown, for example, by
the longest life yet recorded in modern times; that of Thomas
Parr of England who was one hundred fifty-two years and nine
months old when he died. Old age in itself is a physiological
condition which results from a state of lessened vitality and
activity of the various organs. The essential factor in grow-
ing old is a progressive degeneration of the tissues, as a result
of changes in the cells which compose them, thereby bringing
about a gradually diminishing functional capacity of the
various organs until, finally, the activity of some vital organ or
organs ceases and physiological death results. Certain visible
external structural changes in the body are increasingly in
evidence as old age comes on, all of which are due funda-
mentally to degenerative changes in the individual cells of the
various tissues. The hair turns gray, the skin loses its elas-
ticity and becomes wrinkled. Extensive changes occur in the
jaws which are due to a loss of the teeth, with a consequent
absorption of that part of the jaw which held them, resulting
in a return to the infantile type of jaw. The walls of the
arteries harden (arteriosclerosis) and the blood pressure in-
creases. There is a progressive loss of strength and elasticity
in the muscles. Some of the cartilages may calcify, the bones
become more fragile, the cranial sutures disappear, and there
Is a decrease in the stature. The near point of vision recedes,
due to a loss in elasticity of the mechanism of accommodation.
Changes also take place in the nervous system. These are

THE NATURAL HISTORY OF MAN 71

associated with a shrinkage of the brain, due essentially to the
atrophy of nerve cells in the cerebral cortex, and bring about
a loss in muscular coordination and in memory, and a lack of
acuteness in the senses. Normally, physical decadence occurs
earlier than mental.

It is very difficult to distinguish between normal senile de-
generative changes and those due to disease. For example, it
seems impossible at present to tell whether the hardening of
the arteries is to be considered normal or abnormal in old age.
Also we know very little of the chemical alterations in the
body which are associated with advancing age, except that a
relative increase in the salt content has been found. In fact,
the whole subject of senescence needs renewed investigation
to determine what constitutes normal senile changes. The
striking experiments of Steinach and others have shown, in
the case of both the lower animals and man, that at least a
temporary rejuvenescence can be produced in the old by en-
grafting the gonads or, in the male, by ligating the vas
deferens.

There are three principal theories with regard to the bio-
logical significance of old age and natural death. The first
theory is that old age is a pathological condition due to lack
of internal adjustment to external environment. Metchnikoff
was an advocate of this and held that there is a constant con-
flict between certain cells of the body, some trying to destroy
the others which are essential to life. This they may accom-
plish if the cells acquire a lessened resistance as a result of
the absorption of toxins released by certain bacteria in the
intestines. Hence another species of bacteria. Bacillus hul-
garicus, by interfering with the growth of the toxin-producing
bacteria, becomes, according to Metchnikoff, a "fountain of
youth." According to the second theory, which was advocated
by Weismann, the higher organisms have acquired senility and
natural death through natural selection as a character which

72 THE EVOLUTION OF MAN

is of advantage to the existence of the species. The third
theory, which was advocated by Maupas and Minot, holds
that, at fertilization, a stimulus is supplied to the developing
organism which is gradually dissipated, during the later growth
and differentiation, until finally none is left and the organism
dies of old age. As the phenomenon of old age is a common
one to all metazoan animals it would seem that the third
theory is more in accord with the facts.

Biologists have estimated that an animal should live from
five to seven times the period of growth. This means that
man should live to be from one hundred to one hundred and
forty years old. The facts in regard to different animals, how-
ever, do not seem to support this view. Rubner has estimated
that man requires about four times as many food calories for
the period from the cessation of growth till the end of life as
other mammals and he interprets this as meaning that the hu-
man cells have a much greater total capacity for obtaining
energy from foodstuffs than those of other mammals. The
cells seem to be able to make only a limited number of chemical
transformations, after which physiological death ensues. Rub-
ner believes that the cells in man can make a greater number
of such transformations than those of most other mammals.

Vestigial Structures

The normal life cycle of man having now been considered,
attention should be given to another valuable line of evidence
as to man's origin, namely, certain structural features known
as the vestigial organs which, although practically functionless
in man at the present time, are believed to be the remains of
well-developed, functional organs in the past. A few typical
examples may be noted.

At the inner corner of the eye is a fold of the conjunctiva,
the mucous membrane covering the front of the eyeball, called

THE NATURAL HISTORY OF MAN 73

the plica semilunaris, which is relatively larger during prenatal
life. It is believed to be a reduced third eyelid, such as is
regularly found in amphibia and birds, by which the eye is
closed.

Man possesses muscles which are arranged to move the ear
either as a whole or in part, but he has entirely lost the con-
trol of them or only exceptionally retains partial control.
Probably when man assumed the erect posture with eyes look-
ing forward the head became more movable and rendered
unnecessary the mobility of the ear with the resulting loss of
function In its muscles. At one period during prenatal de-
velopment the human ear is pointed and resembles the ear of
certain monkeys. This point persists in many people as a
projection on the rolled or unrolled rim (helix) of the ear.
It is known as Darwin's tubercle and is the vestigial remains of
man's ancestral ear point.

Near the junction of the large and small intestine in man
(Fig. 26) there is a narrow, blind process, about three and a
half inches in length, known as the vermiform appendix. The
appendix in man is a vestigial structure and represents the func-
tionless, shriveled, terminal remains of the caecum, the blind
beginning of the large intestine. In an herbivorous animal,
the caecum is a large, nutritive organ of great Importance. In
carnivorous animals, the caecum is reduced. The reduction of
the terminal portion of the caecum to form an appendix occurs
only in man (Fig. 26), the anthropoid apes, and some rodents.
The frequent pathological condition of the appendix in man
has given rise to the aphorism "that vestigial structures are
particularly prone to disease."

There are various structures in the body which, although
not vestigial, give evidence of a retrogression. Such a condi-
tion Is to be noted in certain of the sense organs. The olfac-
tory organ, for example, which is of the greatest importance
to the lower mammals and other classes of the vertebrates.

74 THE EVOLUTION OF MAN

has become very much reduced in man and is represented only
by a small part of the nasal mucous membrane. In corre-
spondence with this the olfactory portion of the brain is also
very much reduced.
"•^Other structures showing signs of retrogression are the

faecum...

A/ojoe-f^cZ/x.

.Caecctm

Fig. 26. The caecum and vermiform appendix in various
mammals. 1, Horse; 2, Kangaroo; 3, Cat; 4, Lemur; 5,
Orang; 6, Man, fetal; 7, Man, adult. Redrawn from Stratz,
Naturgescliichte des Menschen. By permission of Ferdinand
Ecke.

teeth. This is indicated by the tendency for the teeth and
jaws to become ^mailer and is very evident when these struc-
tures in civilized man are compared with those of the primitive
races and with fossil man. Additional evidence is to be noted
in the occurrence of misplaced and irregular teeth which, in

J

THE NATURAL HISTORY OF MAN 75

general, signify that the jaw is too small. Likewise the fact
that the third molars and lateral incisors are variable in de-
velopment and frequently fail to appear indicates a tendency
to a reduction in the number of the teeth. A comparison of
man's dentition with that of a typical mammal having forty-
four teeth, shows that man has probably already lost twelve
teeth during his long period of evolution. The projecting chin
which man alone of all animals possesses is the result of the
shrinkage of the tooth-containing part of the jaw. This can
be well illustrated by a comparison of the fossil jaw of the
Heidelberg or Neandertal man with that of modern man.
iTooth decay also is not found so extensively in the primitive
'races as in the civilized and is apparently absent in the fossil
races, with the notable exception of the Rhodesia man recently
found in the Broken Hill mine. It is clear that the usual
prophylaxis against tooth decay is merely temporizing with
the real problem. Since the present civilization apparently
carries a distinct threat to the teeth, a radical change in diet
and habits is necessary to preserve them. What such change
should be we are awaiting our nutrition experts to show us.

Anatomical Variations

Finally, further evidence as to the ancestral history of man
can be obtained from a study of structural variations. No
two people are exactly alike in bones, muscles, or vessels, and
even the nerves, the least variable structures in the body, show
differences. Some of these variations are probably fortuitous,
others are to be considered as a reversion to an ancestral form,
and still others progressive.

Ordinarily man has twelve pairs of ribs but occasionally a
thirteenth rib appears. This is known as a cervical rib and is
located in the neck just above the thorax. It is generally
reduced in length but may be long enough to reach the sternum.

76 THE EVOLUTION OF MAN

It may be that at some time in man's ancestral history this rib
regularly existed but now it occurs only occasionally as a re-
version to an ancestral type. Its disappearance may perhaps
be associated with the assumption of the upright gait, with the
resulting dragging down of the viscera by gravity. A tendency
to the loss of more ribs is seen occasionally in the partial
deficiency of the first rib and in the absence of the twelfth.

Rarely a fourth molar tooth occurs in man, who regularly
has only three. Some of the lower mammals have four such
teeth. It is possible that the fourth molar in man, when it ap-
pears, is a reversion to the former condition. This tooth is
more likely to occur in the primitive races and presumably
occurred still more frequently in those prehistoric races which
are known only by their fossil bones.

In about four per cent of persons a small muscle exists in the
front of the thorax, parallel with the sternum, known as the
sternalis. Anatomists have been much puzzled for an explana-
tion of the occasional presence of this muscle. One theory is
that it is part of the pectoral muscle which in some unknown
way has become twisted through ninety degrees. That this
may sometimes be the proper explanation is indicated by its
receiving a branch of the same nerve which supplies the pec-
toral muscle. A second theory is that the sternalis is a recur-
rence of part of the subtegumentary muscle which moves the
skin, and which is still present in many mammals but has been
largely lost in man. A third explanation is as follows : in the
amphibians a longitudinal muscle runs from the pelvis along
the front of the entire body. Although the abdominal part of
this is present in man as the rectus muscle, the thoracic part is
absent, having been crowded out of existence, we believe, by
the enlargement of the pectoral muscles following the in-
creased use of the upper extremities for prehension. Some
authorities hold that the sternalis, when present, is the thoracic
portion of the rectus. An occasional nerve supply from the

THE NATURAL HISTORY OF MAN 77

intercostals favors this explanation and indicates the possible
reversionary character of this muscle.

On the inner side of the lower end of the humerus in the
fore limb of man there is occasionally an opening, known as
the supracondylar foramen, which is regularly found in some
of the lower animals, such as the cat, transmitting a large
nerve. The occasional appearance of this foramen in man is
believed to be a reversion.

At an early period of prenatal life a pointed projection of
the vertebral column as a tail (Fig. 23) is quite evident.
During later development this projection is gradually incor-
porated within the body so that the terminal part of the verte-

srt

Fig. 27. Supernumerary nipples of man. n, normal nipple;
sn, supernumerary nipple. Redrawn from Wiedersheim, after
Ammon.

78 THE EVOLUTION OF MAN

bral column, the coccyx, which represents the tail vertebrae of
the lower animals, no longer projects. Very rare cases are
known in which the coccyx has remained elongated and pro-
jecting in man, thus constituting a true tail. In the anthro-
poid apes this region is even more reduced than in man.

Small supernumerary mammary glands (Fig. 27), which are
not infrequently found in man, are reversionary structures. It
is found that in early embryonic life, two rows of mammary
glands begin to develop but, unlike the case of the lower
mammals, all except two of these disappear. Also, at the
sixth month of prenatal life, the body is almost entirely covered
with fine hair, called the lanugo. This is largely shed before
birth but, in some cases, it may persist and develop in the adult
to form a complete hairy covering for the body, which seems
to be a reversion to man's ancestral hairy condition such as
persists in the anthropoid apes.

Thus man's close kinship with the anthropoid apes is
strongly suggested not only by the fossil forms but also by his
natural history. Furthermore, a 'blood relationship' is indi-
cated both by the susceptibility of the apes to human diseases
and by their reaction to various blood tests, developed in the
past few years, which render it possible to distinguish between
human blood and the blood of all other animals except the an-
thropoid apes. It is pretty well agreed that the anthropoid apes
and man came from a common ancestor, and he in turn from
some primitive, broad-nosed ape. Some believe that the mam-
mals were evolved from a primitive reptilian form. Others say
they came from the amphibians, which in turn evolved from a
fish form, the .latter from an invertebrate, and so on down to
the protozoa. Evolution must likewise assume that under
some favorable condition the earliest living forms were evolved
from the inorganic world. Whether such a process is going
on at present no one knows. However, the facts of man's
development, structure, and variations, which have been given

THE NATURAL HISTORY OF MAN 79

above, certainly can be best explained on the basis of man's
descent from lower forms, and human fossils, as far as they
go, as is clearly shown in the previous chapter, definitely lead
back toward a form from which both apes and man may have
descended.

CHAPTER III

THE EVOLUTION OF THE NERVOUS SYSTEM OF

MAN

GEORGE HOWARD PARKER

PROFESSOR OF ZOOLOGY, HARVARD UNIVERSITY

The body of man, like that of the other higher animals,
carries a full complement of organs. These organs are usually-
arranged by anatomists under some ten heads, the so-called
organ systems, and are familiar to you as the skeleton, the
muscular system, the circulatory system, the nervous system,
and so forth. Although physicians have been telling us that
we normally live so long as our blood vessels last, it is never-
theless true that our daily life is dependent not upon a single
system of organs strictly but upon the interaction of all the
systems that we possess. No one system can be eliminated
without serious consequences. True we may have our tonsils
taken out, our appendix removed, we may lose an arm or a leg,
a kidney, or even a lung, but no one will give up with impunity
both kidneys, or both lungs, or shed his whole digestive tract.
Death would be the inevitable and immediate result. Our
systems of organs are so interrelated that they form a unified
whole which justifies the biological conception of an organic
individual. The integrity and continued existence of such an
individual is dependent upon the presence of at least the essen-
tial members of each system. Thus the organism as a whole,
to use a current expression, is more than an assemblage of
parts; it is an integrated unit.

EVOLUTION OF NERVOUS SYSTEM 8i

The Nervous System and Personality

Yet when we examine our systems of organs, we find them
quite differently related to our daily activities; the musician
trains his ear, the artist his eye, and the athlete his muscles.
In this way each one develops a certain individuality or what
is commonly spoken of as a personality, to use that term in its
more modern connotation. In this sense personality implies
an outline of the self, a resume of that body of characteristics
that makes up an individual in contradistinction to other indi-
viduals. Personality has commonly been regarded as an attri-
bute of the body as a whole and yet when it is closely scruti-
nized, it is seen to depend chiefly, if not entirely, upon our
nervous organization.

That personality has its seat in the nervous system is in the
main a relatively modern view. The ancients for the most
part believed that it permeated the whole human frame, and
they located what may be called the attributes of personality
in the most diverse parts. Thus Aristotle declared the heart
to be the sensorium commune of the body and, though he was
an unusually acute observer, he was unable to make out any
nervous function whatever for the brain. Galen believed the
brain to be the seat of the rational soul, but apparently he also
accepted the popular belief that the heart was the seat of
courage and anger, and the liver that of love. Views of this
kind were the prevailing opinions among the ancient writers
and show that what we regard nowadays as personality had
for them a most broad and general relation to the body as a
whole.

Vesalius, the great anatomist of the sixteenth century, may
be regarded as the founder of the modern belief that per-
sonality is of strictly nervous origin. In dealing with the
nervous system he declares that just as the heart is concerned
with the vital spirit, and the liver with the natural spirit, so

82 THE EVOLUTION OF MAN

is the brain with the animal spirit. By the animal spirit, as
the context shows, he meant the capacity to think, to re-
member, to reason, and to imagine. All these functions, how-
ever, are functions of the brain, and that body of reactions,
instincts, and habits that characterizes each individual whereby
he may be described as honest or dishonest, cheery or somber,
kindly or malevolent, are from this standpoint products of the
nervous system. Although this view has been again and again
assailed, it has maintained itself to the present time and bids
well to remain one of the fundamental facts of biological
knowledge. •

Yet to the man on the street personality and all that per-
tains thereto remains much as in pre-Vesalian days, a vague
general characteristic of the body as a whole and not a
feature of one system of its organs. To attempt to persuade
him otherwise is more likely to arouse his suspicions than to
advance his knowledge. This is particularly true of so simple
a matter as sensation. When you prick your skin with a pin
nothing seems more natural than to locate the sensation of
pain where the pin abraded the skin and yet we know that the
sensation of pain is in the cerebral cortex of the brain and not
in the skin. The evidence that this sensation is resident in
the cortex comes from several sources. First, it is known that
if a nerve is cut, the part of the body supplied by that nerve
loses sensibility. When a nerve going to a part of the hand is
accidentally severed, a pin may be thrust into that part without
producing the least sensation whatever, showing that the hand
in itself is not endowed with pain. Not until the restoration
of the nerve months after the accident does the sensation of
the afflicted part return. Not only are there circumstances
under which a part may be present though without sensation,
but there may be sensations without the presence of any part.
This condition is well seen in the so-called phantasmal extremi-

EVOLUTION OF NERVOUS SYSTEM 83

ties. Persons who have recently lost an arm or a leg often
suffer from very intense pains apparently in the missing part.
So real are these sensations and so definitely do they seem to
be located in the lost member that it is often difficult to per-
suade the patient that the pains are not connected with the lost
part and that some attention to that part is needed. Yet the
surgeon knows perfectly well that these sensations are caused
by small tumors on the cut ends of the nerves that formerly
went to the lost extremity. On removing these tumors the
sensations disappear. Both these lines of evidence show that
painful sensations though commonly referred to the skin are
really not situated there. They are functions of a more
deeply located part. When the central end of the system in
the cerebral cortex suffers destruction either by disease or acci-
dent, sensation disappears absolutely and completely, a condi-
tion that shows that the real seat of this phenomenon is not in
the peripheral parts of the body, as commonly assumed, but in
a deep portion of the central nervous system.

This is but one example of many that go to show that per-
sonality, not only from its sensational side but from all other
aspects of its nature, is a function of the nervous system. It
is not a quality that penetrates the human frame as a whole.
Yet notwithstanding the correctness of the modern view as
to the seat of personality, the ancient idea of its diffuse nature
appears in many of our daily habits and permeates our lan-
guage. It would be impossible to replace successfully the
heart on the February valentine by the true organ of affection,
the cerebral cortex, even though the convolutions of the cortex
might be shown to afford a much more subtile means of send-
ing the hidden message than the smooth surface of the heart.
Human nature cHngs to the past and the discarded theories of
the physicians of antiquity hold their place with tenacity in the
language of to-day.

84 THE EVOLUTION OF MAN

The Nervous System of Man and Other Higher

Animals

The nervous system of man is without doubt one of the
most intricate structures in the animal kingdom. It is com-
posed of a most compHcated mechanism of end-stations and
of intercommunicating hnes which far outruns in intricacy the
telephone system of such a place as Chicago or New York.
It is made of nerve cells, or neurones, whose processes, the
nerve fibers, stretch like telephone wires for relatively pro-
digious distances through the body. When these neurones are
studied individually they are seen to fall into three classes.
One of these classes is composed of elements that reach from
the skin and other outlying parts, such as the organs of smell,
taste, hearing, and the like, to the central organs. These
neurones are called sensory or afferent neurones. Other
neurones, commonly called motor or, better, efferent, stretch
from the central apparatus to the muscles and other organs
activated by the nerves. These form the second class. The
third class, the internuncial neurones, connect one part of the
central nervous system with another; they consequently lie
entirely within the limits of the central organ and may be in
accordance with their connections either functionally afferent
or efferent. These three classes of neurones make up the whole
of the real nervous substance of the human body and col-
lectively they constitute a system by means of which many of
the bodily activities are controlled and in which take place such
remarkable operations as sensation, memory, volition, and
the host of other performances which together constitute per-
sonality.

When we survey the organization of the nervous system
and its appended parts we find that, though it is made up of
neurones, the boundaries of its organs do not confori^i to the
limits of the neurones, but have a topography of their own.

EVOLUTION OF NERVOUS SYSTEM 85

Thus a whole group of peripheral parts, often the peripheral
ends of afferent neurones, are concerned with receiving such
environmental changes as are likely to excite activity in the
organism. Thus the eye is receptive for light, the ear for
sound, the organs of touch for changes of pressure and the
like. These organs, commonly designated as sense organs,
but more appropriately called receptors, constitute the first
large class of parts in the neuromuscular mechanism. The
second class includes the central apparatus proper, composed
of the central ends of the afferent neurones, the internuncial
neurones, and the central ends of the efferent elements. This is
the portion of the system, corresponding to a central telephone
station, in which the nervous impulses arriving from the re-
ceptors are directed toward the appropriate channels of re-
sponse and in which are stored those records of past experi-
ence that modify or otherwise qualify the subsequent responses.
This second portion is represented in man by the brain, and the
spinal cord, and by the sympathetic system and may be desig-
nated from one of its chief functions as the adjustor mecha-
nism. Finally there is to be mentioned the third group of parts,
not truly nervous themselves, but under the control of the
nervous system, the muscles, the electric organs, the glands,
the luminous organs and the like, all of which enable the
animal to act in some particular way on the environment.
These have been appropriately spoken of as effectors and com-
plete the list of necessary parts in the neuromuscular mecha-
nism.

A nervous system composed of the three types of neurones
already mentioned and organized into receptors, adjusters,
and effectors is characteristic of most of the higher animals.
It is found not only in the vertebrates from man to the fishes,
but also in the mollusks, in the arthropods, and in the higher
worms such as the annelids. Even such a lowly organized
creature as an earthworm has a nervous system developed

86 THE EVOLUTION OF MAN

upon this plan. The so-called brain of this animal is a small
mass of nervous material lodged in the dorsal part of its
anterior end. Connected with this brain is a long segmental
chain of ganglionic enlargements extending along the ventral
midline of the worm. These parts collectively constitute the
central nervous apparatus, or adjustor, for which the skin is
the chief receptor and the muscles the main effectors. In
neuronic composition the three types of elements already de-
scribed are abundantly represented. Afferent neurones reach
from the skin of the worm to its central organs from which
efferent neurones pass out to its muscles. Internuncial neurones
are also present, but in relatively small numbers as compared
with the conditions found, for instance, in the vertebrates.
Here many parts, like the cerebral hemispheres, to take only
one example, are made exclusively of internuncial neurones
whereas in the earthworm there is probably not a single im-
portant nerve center that is not entered by sensory neurones
or which does not give rise directly to efferent neurones.
With this difference, however, the neuromuscular mechanism
of the earthworm is based on the same principles of construc-
tion as those met with in the higher vertebrates including man
himself.

The Nervous Organization of Sea-Anemones

To gain some idea of the evolutionary steps by which such
a nervous system as that just described has been arrived at, it
is plainly necessary to examine the types of nervous organiza-
tion found among the lowest of the multicellular animals. As
a good example of these lowly organisms the sea-anemones
may be selected. Sea-anemones are sac-like animals attached
to rocks or stones, and provided with a single aperture which
leads from the exterior into their large central cavity in which
digestion goes on and from which the undigested residue is

EVOLUTION OF NERVOUS SYSTEM 87

discharged to the exterior through the single aperture already
mentioned which serves thus both as mouth and anus. This
aperture In almost all sea-anemones Is surrounded by one or
more circles of tentacles.

When an expanded sea-anemone is stimulated by being
touched or otherwise excited to action, It commonly responds
by a quick general contraction, whereby the seawater contained
in its digestive cavity Is discharged through Its mouth and the
whole volume of the animal is greatly reduced. This general
contraction may be called forth from almost any point on the
surface of the animal, showing that the muscles that lie within
the walls of the creature and are responsible for the contrac-
tion, are collectively accessible to nervous Impulses from al-
most every point on the surface. This accessibility is* insured
through the presence of a nerve-net which spreads throughout
the living substance of the animal and which brings its surface
into connection with almost its whole musculature. This
nerve-net nowhere shows a special concentration but extends
rather uniformly throughout the body and thus affords an easy
path over which Impulses may spread from the surface of the
animal to Its musculature. A nervous system of this type is
commonly called a diffuse nervous system as contrasted with a
centralized one and Is characterized by the absence of a cen-
tral organ, or adjustor, through which all Impulses must pass
on their way from the receptors to the effectors.

The characteristics by which a diffuse nervous system may
be distinguished from a centralized one are well shown in a
number of activities exhibited by sea-anemones. When small
fragments of meat or other bits of food are placed on the
tentacles of a sea-anemone, these organs wind around the bits
of food and, by bending in the appropriate direction, deliver
them to the mouth. If, now, a distending tentacle on a quiet
and expanded sea-anemone is suddenly seized at its base by
forceps, cut off and held in position so that its original rela-

88 THE EVOLUTION OF MAN

tions to the animal as a whole can be kept clearly In mind, the
tentacle will still be found to respond to food brought In con-
tact with it and will eventually turn toward that side which
was originally toward the mouth. Thus the tentacle has within
itself a complete neuromuscular mechanism for its own re-
sponses and it is unnecessary that it should be connected with
any general nervous center in order to carry out Its char-
acteristic movements. Its share of the diffuse nervous system
is sufficient for its own needs. How different this type of
organization is as compared with the centralized type is seen
when we contrast the activity of the tentacle with that of the
leg of a dog or the claw of a lobster when severed from the
animal's body. These parts when thus cut off are quite in-
capable of coordinated movement and show no evidence what-
ever of the type of response that characterizes them as a part
of the whole organism.

Another activity of the sea-anemone that illustrates the na-
ture of the diffuse nervous system is creeping. This operation
is accomplished by the so-called pedal disc, that portion of the
animal by which it attaches itself to the substrate. By means
of muscular waves that pass across this disc the sea-anemone
may creep slowly like a snail from spot to spot. If a sea-
anemone is cut crosswise in two and the upper half of the
animal carrying the mouth and tentacles is thus removed, the
lower half with the pedal disc intact will pucker up the
wounded surface and soon creep about with as much success
as the whole animal did. Here again the part concerned
carries within its own bounds a neuromuscular mechanism
complete for its needs.

Again if a sea-anemone is fed from one side of its mouth,
it will take in by means of the tentacles on that side one frag-
ment of food after another. If, now, bits of meat be alter-
nated with bits of filter paper soaked in meat juice, the two
materials will be accepted indiscriminately for some eight on

EVOLUTION OF NERVOUS SYSTEM 89

ten trials after which only the meat will be taken and the filter
paper will be discharged into the seawater without being
brought to the mouth. If, after having developed this state
of affairs on one side of the mouth, the experiment is now
transferred to the opposite side, both the filter paper and the
meat will again be taken in till this side has also been brought
to a state of discriminating. Thus the experience of one part
of the animal has no perceptible Influence on another in the
sense that there is no common nervous center where the experi-
ence of a given part may be put to the service of the rest. It is
as though we had to burn each finger in turn before we discover
that fire is bad for the hand. These examples bring into
strong contrast the types of reaction characteristic of the
higher and the lower multicellular animals and serve to illus-
trate the difference between the centralized and the diffuse
nervous system.

In a diffuse nervous system, such as that possessed by a sea-
anemone, the external surfaces of the animal serve as recep-
tors and these communicate directly with the subjacent muscu-
lature. The nerve-net serves to spread the impulses throughout
the body but without Involving any central organ. Thus the
sea-anemone may be said to possess receptors and effectors
without an adjustor or central nervous organ properly so
called. This central organ is, therefore, a feature of the
higher animals and in comparison with receptors and effectors
it must be looked upon as a more recent evolutionary acquisi-
tion. Our sense organs did not develop in consequence of a
central nervous system but our central nervous organs devel-
oped because our very early ancestors had already acquired
receptors and muscles.

If lowly organized animals, such as sea-anemones, possess
nothing worthy of the name of a central nervous organ, it
follows that their so-called sense organs must differ consider-
ably in function from those of the higher animals. In highly

90 THE EVOLUTION OF MAN

differentiated types the sense organs, the eye, the ear, the
organs of touch, of taste, and of smell, are concerned with
supplying the central apparatus with those elements out of
which the intellectual life is built. This function must be en-
tirely superfluous in such an animal as a sea-anemone where
no central organ exists. Here the sense organs are not con-
cerned with sensations; they merely excite muscles to action,
a function which they also exercise in the higher animals.
They are receptors for a multitude of external changes and
when thus excited they serve as triggers, so to speak, to set
off the subjacent muscles. Since they are not concerned with
sensations they are more appropriately designated as receptors
than as sense Organs and hence the term receptor, which is the
more inclusive of the two, is the better one to employ. Sea-
anemones, therefore, represent a more primitive type of neuro-
muscular mechanism than the higher animals do, one in which
of the three organs, receptor, adjustor, and effector, only the
first and last are present, the adjustor, or central organ, being
a later acquisition.

Sponges

If receptors and effectors were developed before adjustors,
it is natural to ask whether of these two parts one preceded the
other or did they both evolve simultaneously? Among the
multicellular animals lower than the sea-anemones, the sponges
throw light on this question. A single sponge is a goblet-shaped
or finger-shaped animal attached to the sea-bed. Its outer
surface is covered with pores which lead into a system of
canals provided with lash-cells by which the water is moved
through the canals to a large space in the middle of the sponge
from which this fluid escapes by a conspicuous opening at the
unattached end. From the current of water thus passing
through the sponge the animal extracts its nourishment and th

EVOLUTION OF NERVOUS SYSTEM 91

production and control of this current is one of its essential
activities.

Many sponges, like the ordinary bath sponge, are colonial
animals and consist of a number of sponge individuals more or
less fused together. In the bath sponge, which in its commer-
cial form is represented merely by its horny skeleton, the num-
ber of individuals can be judged by the number of very large
openings that penetrate from the outside to its interior. These
are usually four, five, or more in number and represent the
outlets for the water currents in the living sponge. In quite
a number of the colonial sponges the component individuals
are much more separated than in the bath sponge and rise
from a common base as so many separate fingers. Such
fingered sponges are very convenient for study and are com-
monly of such a size as to admit of easy experimental treat-
ment.

Sponges are for the most part extremely inert and aside
from a slight contraction and consequent bending of the body
as a whole they show very few activities except the opening
and closing of their pores and other apertures. In this way
sponges control their water currents and they accomplish
this partly by the formation of protoplasmic membranes by
which the pores are closed and partly by the action of rings of
simple muscle cells that surround the pores, especially the out-
let openings.

The control of a given outlet cannot be accomplished from
an adjacent finger nor can it be brought about by stimulating
the finger at the end of which the outlet lies except when the
stimulus is directed to the immediate neighborhood of the
outlet itself. In fact there is not only no experimental evi-
dence to show that one finger is connected nervously with
another, but there is no reason to suppose that parts of the
same finger are thus connected. In other words, nervous

92 THE EVOLUTION OF MAN

transmission, such as is abundantly seen in sea-anemones, seems
to be completely absent from sponges. When this fact is
coupled with the inability of histologists to discover any trace
of nervous tissue in sponges, it seems safe to conclude that
these animals are devoid of nervous elements and that their
muscles are set in operation by direct stimulation rather than
by anything that may be described as a nervous impulse. From
this standpoint, therefore, sponges may be regarded as
animals provided with muscles but devoid of nervous tissue.
They possess effectors but no receptors and their condition
suggests that in the evolution of the neuromuscular mecha-
nism, muscle appeared first and nervous tissue later, develop-
ing probably in close proximity to the previously formed
muscle as a device for exciting the muscle to action.

If this conclusion is true, the evolution of the neuromuscular
system must have begun with the appearance of muscle as an
independent effector, after which receptors, or nervous ele-
ments to serve as triggers for setting off the muscles, were
added. Finally, between the receptors and the effectors a
central nervous organ, or adjustor, grew up as the third ele-
ment and thus completed the neuromuscular system as exempli-
fied in the higher animals. So important has this central organ
become in the life of these animals that we scarcely realize
that it is the latest addition to our nervous equipment and yet
such seems to be the case. In its first appearance it must have
been chiefly an organ of transmission and intercommunication,
a specialized outgrowth of the more diffuse nerve-net. Later
it doubtless took on the function of modifying the animal's
responses in relation to its past and thus became a storehouse
of experience and the seat of the intellectual life. As such it
has reached its highest point of development in the verte-
brates where as the brain of man it is without doubt the most
remarkable structure ever evolved.

EVOLUTION OF NERVOUS SYSTEM 93

The Nervous System in Vertebrates

The central nervous organ of the vertebrate, using this term
in the most limited sense, consists of the spinal cord and the
brain. The spinal cord throughout the vertebrate series is a
relatively uniform structure, but the brain exhibits a strikingly
progressive development. This is seen especially in two of its
parts, the cerebellum and the cerebral hemispheres. Both, but
particularly the cerebral hemispheres, grow immensely in size
and complication as we proceed from the fishes to man. In
the lower vertebrates the cerebral hemispheres are concerned
almost entirely with the sense of smell and their cortex, or outer
covering, is spoken of as the olfactory cortex, or archipallium.
In the mammals, however, the hemispheres have reflected
upon them, in addition to olfaction, practically all the sensory
activities of the body as well as the mechanism for the volun-
tary control of the musculature. These added parts constitute
the neopallium which shoves the olfactory archipallium Into
the background. Thus the neopallium comes to be the great
central organ of the higher animals. It receives almost the
whole of the sensory Inflow; it stores the impressions of the
past; and from It emanate those impulses that excite what we
call our volitions.

It is a remarkable fact that in man the cerebral cortex con-
sists of layers of nerve cells so regularly arranged that a rough
estimate of their number may be made. This Is believed to be
approximately 9,200,000,000. This prodigious number of
cells is estimated to weigh a little over thirteen grams and to
occupy the space of less than a cubic inch. When it Is re-
membered that every human being develops from an egg cell
of approximately one fifth of a millimeter in diameter and that
this cell begins growth by dividing Into two, and these two each
Into two thus making four, and then into eight, sixteen, thirty-
two, and so forth, it will be seen what a stupendous process

94 THE EVOLUTION OF MAN

development is even from the standpoint of simple numbers,
for from this one egg cell by division must come not simply
the nine billion and more cells of the cortex, but all the other
countless billions of cells that go to make up the rest of the
body. Nor is this process of cell multiplication, prodigious
as its results show it to be, the only remarkable feature in
development, for it is also equally striking that when the
requisite number of cells have been produced, the operation of
cell division stops. At least this is true of the cortex, for here,
as in a few other parts of the body, the neurones change very
little in number after birth. The brain cells with which the
babe is born last for the most part without renewal through
mature life to old age and death. What brings the operation
of cell multiplication to an end at the appropriate moment is
as little understood by embryologists as is the exciting cause of
the initial increase.

When it is recalled that the 9,200,000,000 cells in the hu-
man cerebral cortex are the nervous elements of this organ and
that they collectively constitute rather less than a cubic inch
of protoplasm, it seems almost incredible that they should
serve us as they do. They are the materials whose activities
represent all human mental states, sensations, memories, voli-
tions, emotions, affections, the highest flights of poetry, the
most profound thoughts of philosophy, the most far-reaching
theories of science, and, w^hen their action goes astray, the
ravings of insanity. It is this small amount of protoplasm in
each of us that our whole educational system is concerned with
training and that serves us through a lifetime in the growth of
personality.

The Nervous System and Sex

The great importance of the nervous system for all that
pertains to the higher life of man cannot be denied and yet this

EVOLUTION OF NERVOUS SYSTEM 95

system after all is only one of our numerous systems of organs
and lies embedded with the rest as part and parcel of our
bodies. Notwithstanding its unique character, the nervous
system is profoundly influenced by its organic environment and
reflects in much that comes from it the characteristics of the
body in which it lies. This is nowhere more clearly seen than
in the effects which hormones have upon it. Hormones, as you
already know, are substances produced in the bodies of the
higher animals by the ductless glands, or endocrine organs as
they are now called, and circulated by the blood. They are
powerful activators for many bodily reactions and are of first
importance in many organic activities. Certain hormones have
a profound effect upon the nervous system and consequently
upon personality. In this respect they are like the supposed
humors of the physicians of antiquity. These humors were
believed to be four in number, blood, phlegm, yellow bile, and
black bile, and an excess of any one of these gave a corre-
sponding temperament, sanguinary, phlegmatic, choleric, or
melancholic as the case might be. This idea of the humors is
really a forerunner of the well-established theory of the hor-
mones, which, however, not only has to do with temperament
but with many other functions of the body. That materials
introduced into the circulation have a profound influence on
our moods and other mental states is well known and is the
basis of the use and abuse of many substances, such as nar-
cotics, alcohol, coffee, tea, tobacco, and so forth. It is, how-
ever, only within the last few years that the immense impor-
tance of hormones in relation to the nervous system has begun
to be seen. The hormones concerned are those that have to
do with the sexual traits.

The great majority of animals are either male or female
and when we seek for a definition of these states we are driven
in the end to make it turn upon the kind of reproductive cells
that the individual produces. Males produce sperm cells;

96 THE EVOLUTION OF MAN

females egg cells. These are the primary sexual characteris-
tics. But the sex of the great majority of higher animals can
also be determined by many features other than those of the
kind of reproductive cell discharged. Thus in man the male
as compared with the female is usually larger in stature and
more robust, has hair upon the face, a deeper voice, and many
other features all of which go to mark the sex as clearly and as
indubitably as the primary sexual character itself. These more
superficial and obvious distinctions are spoken of collectively
as the secondary sexual characters and serve, as has just been
intimated, with almost perfect certainty as an indication of sex.
If, however, there is any ambiguity in this respect, the final
resort in a decision is always to the primary sexual characters,
the kind of reproductive cells produced by the given individual.

For a long time much interest has been expressed as to the
way in which the secondary sexual characters arise and it is
from this standpoint that hormones have come into much
prominence. Very remarkable experiments in this direction
have been recently carried out by Steinach on guinea pigs and
rats. The original object of this hne of work was to ascertain
the influence of the sexual glands on the secondary sexual char-
acters, but the outcome of it was the discovery of a means of
influencing in a most profound way the sexual life of an
individual, in fact, so far as secondary sexual characters are
concerned, of converting a male into a female and vice versa.

Steinach removed the male reproductive glands, the testes,
from young guinea pigs and, after they had recovered from
this operation, he implanted in their bodies by means of a
second operation the female gland or ovary from a young
female. The animal destined by nature to be a male but thus
harboring within its body the opposite sex gland was allowed
to mature, whereat a most remarkable transformation was
observed. It developed the bodily proportions of the female
in skeleton, hair coat, and other particulars, its mammary

EVOLUTION OF NERVOUS SYSTEM 97

glands enlarged and even gave milk, but what is perhaps more
remarkable was that its whole nervous constitution gradually
assumed the female role. It became rather timid and retreat-
ing, mothered the young of other females and in practically all
respects exhibited the traits of the female of its kind. Or-
ganically it displayed practically the full range of secondary
female characteristics though it was an animal destined by
nature to have been a male.

Steinach also undertook the conversion of females into
males and though this from the operative standpoint proved
to be a more difficult problem, in that testes had to be repeat-
edly introduced, he nevertheless also succeeded in this en-
deavor and individuals were produced that though destined
by nature to be female had the physical and psychical traits
of males. Such individuals were aggressive and quarrelsome,
and attempted, though ineffectually of course, to copulate with
females.

Thus the presence of a particular sex gland during adoles-
cence seems to be the necessary factor in determining the type
of secondary sexual characters that a given individual will
show. When the sex glands that had been transplanted in
these experiments and that had sojourned in their new habita-
tion for a considerable time were studied histologically,
they were found to be considerably modified. The sexual cells
proper had often largely disappeared and the cells that filled
the spaces between the groups of sex cells, the so-called inter-
stitial cells, had often greatly increased. It is these cells rather
than the sex cells which produce the hormones that determine
the secondary sexual characters, and the sex glands must, there-
fore, be looked upon as double in nature. They produce, first,
the sexual elements, the sperm cells or the egg cells, and
secondly, from another source, the hormones necessary for the
development of the secondary sexual characters. They are at
once sex glands and puberty glands.

98 THE EVOLUTION OF MAN

When the full import of these experiments is clearly recog-
nized, it must be admitted at once that the sex glands not only
control such secondary sexual characteristics as are of a physi-
cal nature, such as bodily proportions and the like, but also
those more subtile features, the reactions, responses, and in-
stincts, which are equally significant in defining a given sex.
These features collectively have their origin in the nervous
system and since they are now known, from the experiments of
Steinach, to depend for their development upon the sex glands,
it follows that the nervous system of an immature animal must
be looked upon as neither male nor female but indifferent and
yet capable of developing in either one or the other direction
in accordance with its organic environment.

That the conclusions to be drawn from Steinach's experi-
ment apply with full force to human beings is now commonly
admitted. The striking influence of the sex glands on person-
ality as well as on the more physical aspects of the individual
is well known to every surgeon and is a cardinal point in his
practice. Yet the relation of this simple fact to human society
often goes unheeded. Few elements lie deeper in the nature
of man than sex. As the center around which the family is
built up, it initiates the first step in the structure of society.
From this soil have sprung the affections, chivalry, the poetry
of love, and all that vast array of literary and artistic ac-
complishment that has as its theme man and woman. And yet
when the physical background of this immense pageant is
sought for, it appears to depend upon the action of the inter-
stitial secretions of the sex glands on plastic nervous organs.
It is this plasticity that is both novel and important, for it may
have far-reaching consequences in the reconstruction of society.
Through it personality may be profoundly affected, abnormal
states may be reached and corrected, and fundamental re-
generations accomplished. As an avenue of entrance it leads
to a most important field for the psychiatrist and the social

EVOLUTION OF NERVOUS SYSTEM 99

reformer. Thus the hormones, to return to our original thesis,
illustrate how profoundly the nervous system is under the in-
fluence of its immediate organic environment.

The Nervous System and Organization

If, now, we picture to ourselves the evolution of the nervous
system of man, we must imagine the formation of the chemi-
cal elements from the electrons of the stellar laboratories, the
combination of certain of these elements into organic aggre-
gates and the formation of unicellular organisms, the develop-
ment of multicellular types in whose organization muscles ap-
pear, then receptors, and finally adjustors or central nervous
organs culminating in the brain of man.

Such a series forms, superficially, a seemingly natural and
smooth sequence and yet when it is examined closely, it proves
to be a succession of breaks and contradictions. The carbon,
hydrogen, oxygen, nitrogen, and other elements of our bodies
act in a radically different way in the hands of the chemist
from what they do as an organized part of our nervous proto-
plasm. The invariable nature of the chemical reaction is in
strong contrast with the fluctuating uncertainty of volitional
activity. True, on repeating what are intended to be exactly
the same processes, the chemist never gets exactly the same
results, but he knows that the slight differences he meets with in
his work are errors of manipiilation and observation and not
evidences of wilfulness or disobedience on the part of the
material he deals with. Yet the activities of these same chemi-
cal elements when organized into the children of his family
are regarded in a very different light and under the head of
personality he subjects them to censure and approval with the
view of lasting change and improvement. How profoundly
different is the conception of the activities of the isolated ele-
ments of our bodies and of these same elements organized into

100 THE EVOLUTION OF MAN

parts of ourselves ! No one now entertains seriously the view
once put forward by Haeckel in the heyday of the evolution-
ary movement that since human beings have souls every atom
of their bodies must have part of such a soul. The circum-
scribed nature of ordinary chemical action and the freedom of
human volition, notwithstanding its elemental background, are
two different things.

If the peculiarities of volitional action are not to be dis-
covered in the chemical elements that make up the substance
in which it occurs, they must be ascribed to the organization
of this substance, that is, to the way in which the elements of
this substance are put together and interact amongst them-
selves. From this standpoint certain chemical elements or-
ganized as nervous protoplasm have a greater degree of free-
dom in their action than when the same elements are organized
in the form of lifeless molecules. This condition may be
illustrated by a simple mathematical relation. The ordinary
and invariable type of chemical reaction might be likened to
what would take place in a mathematical world made of blocks
of fives to which we put the question. What constitutes ten?
To this there is only one answer, namely, two blocks of five.
The type of reaction that is possible in nervous protoplasm is
like that in a world made of the digits to which the answ^ers as
to what make ten may be nine and one, or three and seven, or
any other of numerous combinations all equally true. This
world has in it a degree of freedom comparable to that in
nervous protoplasm as compared with the limitations of the
ordinary chemical reaction. From this standpoint, then, nerv-
ous protoplasm, and probably most other protoplasm, when
considered from the point of view of its chemical activities has
a greater degree of freedom that that seen in the ordinary
chemical reaction and in this characteristic is to be found the
possibility of all volitional performance. That the properties
and activities of materials change with changes in organization

EVOLUTION OF NERVOUS Srs¥EM loi

is as well known to the student of the lifeless phases of nature
as to those who concern themselves with the so-called organ-
isms. The qualities and activities of water are no more novel
or different from those of its component elements, hydrogen
and oxygen, than are the qualities and activities of nervous
protoplasm as compared with the organic molecules that make
it up. Water is organized hydrogen and oxygen and in con-
sequence of its peculiar type of organization it exhibits prop-
erties quite unlike those of its constituent elements. Thus
water, like protoplasm, differs from its elements in conse-
quence of its organization.

It is sometimes assumed that man is absolutely untrammeled
and free and that his inner life is without restriction, but such
is not the case. A good example of how we are held in abey-
ance is seen in our mental furniture. This consists of elements,
our sensations, that reach us from the outer world through our
sense organs. These elements come to us from the environ-
ment and from nowhere else. We never invent them nor in
any other way develop them within ourselves. The mind is
strictly limited to what in this respect is supplied it from its
exterior. What may be done by way of freedom and origi-
nality is to set these elements in novel and unusual combina-
tions and it is in this way that the highly imaginative and
perhaps the insane mind works. But in all instances the ele-
ments themselves are those of the primitive sensations and to
such we appear to be absolutely limited.

Not only is the mind thus limited in its materials, but its
processes often show striking restrictions. This is illustrated
by the magician's receipt for turning stone into gold. Put a
clean stone into a pot of boiling water and watch it ten minutes
during which time, if you do not once think "hippopotamus,"
the stone will turn into gold. Needless to say that no one by
this means has ever enriched himself. The mind of man even
in working toward its desires is never absolutely free, but is

102 THE EVOLUTION OF MAN

subject to restrictions which continually recall the material

background on which it rests.

In the evolution of the nervous system of man as presented
in this brief outline we see a succession of steps rather than a
gradual ascent and at each step a fundamental change suddenly
appears, mutation-like in its character, to borrow a term from
the geneticists. Each step is a new phase in organization, but
not necessarily a change in the kind of elementary materials
involved, and with these changes in organization come changes
in the degrees of freedom of reaction which enable us to bridge
over the gulf that lies between the relatively circumscribed
activity in ordinary chemical operations and the greater free-
dom seen in the voluntary and responsible acts of human
beings. Something of this view of the nature and the possi-
bilities of living protoplasm has been put forward by Haldane
under the name of organicism, but with perhaps less reliance
on the material side of the problem than has been suggested
in this lecture. Yet interesting and important as it is to push,
to the extreme, speculation as to the relation of our mental life
to the materials of our body, it nevertheless must be remem-
bered that, with all our progress, we are still not far from the
position described by Vesalius in 1543 when he wrote, "How
the brain performs its functions in imagination, in reasoning,
in thinking, and in memory, I can form no opinion whatever."

CHAPTER IV
THE EVOLUTION OF INTELLIGENCE

JAMES ROWLAND ANGELL

PRESIDENT OF YALE UNIVERSITY

It may be assumed without argument that evolution has
actually occurred within the field of intelligence, as it has
within the field of organic structure, and I shall proceed at
once to examine the major features of the process. It will be
convenient to distinguish in such an analysis between the de-
velopment of intelligence in animals and the corresponding
development in man. This distinction is not for a moment
intended to postulate any fundamental difference between hu-
man and animal intelligence, for this is one of the questions
which can only be confidently answered, if at all, after adequate
examination of the available data. It is simply a device for
expediting access to two great groups of facts which present
certain practical distinctions.

In the field of cosmic and stellar evolution, we have such
facts as are disclosed to us through telescopic and spectro-
scopic examination of the heavenly bodies, with their convinc-
ing indications of evolutionary processes extending over un-
imaginable epochs of time and over equally abysmal areas of
space. In the case of the crust of our own earth, geology
similarly brings to our knowledge evidence of slow, age-long
changes, as a result of which the present superficial character-
istics of the earth's surface have been produced, together with
its climatic and other peculiarities. Again, there is convincing

104 THE EVOLUTION OF MAN

evidence of change and development, of rise and fall, in the
tide of animal life, in its geographical range, in its anatomical
organization, and in its adjustability to the major features of
environment. One of the lectures in this series has in particu-
lar been devoted to evidence of this character as it applies to
the changes brought about in the nervous system of various
forms of animal life. The development of man himself and of
the society within which he lives has also been passed in review
and convincing demonstration has been offered of the extensive
changes which have, throughout the ages, come to pass in both.
Evolution having been thus convincingly exhibited in a number
of important fields, it behooves us, in discussing the present
problem, to secure impressions as clear as possible of the char-
acter of the evidence upon which we are to base our inferences
and conclusions regarding the development of intelligence.

Animal Intelligence

In the case of animal life, the only available information is
to be gained by the direct observation of animal behavior as
that Is found among the creatures surviving in our age of the
world. Whether there may have been creatures In the past
possessing forms of Intelligence substantially different from
that of any animals now living can neither be denied nor as-
serted with absolute confidence. But such evidence as we have
Is at least all against the inference that animals superior to
those now living have ever been developed. So great is the
similarity of existing forms to such extinct forms as are known
to us, that it seems highly Improbable there should have oc-
curred developments of Intelligence widely different from those
represented In the animal life of to-day. This inference,
to be sure, rests upon the hypothesis which most scientists re-
gard as conclusively established, to wit, that intelligence is

THE EVOLUTION OF INTELLIGENCE 105

essentially a function of the nervous system and that Its char-
acteristics vary with the development of the latter.

Turning, therefore, for our clew to the behavior of living
organisms, we find this ranging all the way from the very simple
series of movements executed by the unicellular organisms like
amoeba, which Is quite devoid of a specialized nervous system,
up to the complicated behavior of the primates and the phe-
nomenal intellectual achievements of man himself. At once
we are confronted with a distinction which, much transformed
in modern times, goes back to the period of the earliest specu-
lations upon mind and behavior. All the early writers known
to us stress the distinction between instinct and reason, ac-
crediting to the animals Instinctive behavior of a far more
highly developed type than that disclosed in the behavior of
man, and assigning to man powers of reasoning either wholly
or largely denied to animals. Modern scientific analysis has
been disposed greatly to qualify the rigidity of this distinction.
Man certainly has a very definite equipment of Instincts and
some of the operations of animals contain in them the begin-
nings at least of rational conduct.

Broadly speaking, actions are designated Intelligent when
they disclose the ability to adjust quickly and successfully to
new and variable conditions. They are judged unintelligent
or mechanical when the same action is elicited again and again
regardless of changes in the situation which calls it forth, or
of the possibly disastrous nature of the reaction itself. From
this point of view, the great group of actions, known as tro-
pisms, must be regarded as non-intelligent, even though they
may at times benefit their possessors. Here, for example, is a
group of organisms which at once seek the darkest corner of
any area within which they are confined. Here is another
group which seeks the lightest place. Again, here is a group
which, if possible, takes up a position where the body may
press, or be pressed upon by, surrounding objects. In the case

io6 THE EVOLUTION OF MAN

of such organisms these tropistlc tendencies are ordinarily
responded to no matter how untoward the consequences. The
moth seeking the flame is a common exemplar of this kind of
reaction. And the biologically undesirable consequences are
plainly exhibited in the demise of the performer.

The group of reactions called reflex exhibit a similar organic
invariability which, while generally beneficial, is not infre-
quently disadvantageous. In the human being sneezing, cough-
ing, weeping, are familiar examples of actions of this character.
They are largely outside the range of voluntary control and the
more extreme forms, such as those of digestion, are completely
independent of such control.

Instincts shade off into reflex and tropistic reactions by
gradations, which makes it difficult without being arbitrary to
draw any hard and fast lines ; but they are in the higher organ-
isms much less rigid and fixed than the tropisms and reflexes
and they are more complicated than the latter because they
involve a series of muscular movements, instead of the single
movement to which we apply the term reflex.

All this group of activities, however, have in common their
hereditary and innate character. No one of the group is ever
in any proper sense learned or acquired. They are executed
either at birth, or at some later stage of the creature's de-
velopment, with a high degree of perfection and in the lower
animals they are generally quite rigid and devoid of any sug-
gestion of intelligent adaptation. They certainly represent
hereditary pathways through the nervous system over which
stimulations travel to the muscles and glands. In the higher
animals, the instincts are more or less plastic and susceptible
of modification, this modification in some cases going so far
as to result in the complete suppression of the instinct by
unfavorable environmental conditions. Most of the instincts
have a reasonably obvious biological utility, in that they con-
tribute to the maintenance of the life of the individual or the

THE EVOLUTION OF INTELLIGENCE 107

species, and the same thing is true of the reflexes and, pre-
sumably, of the tropisms.

Among the various theories of the origin of this group of
instinctive and reflex actions, two have been most frequently
urged. The one derives its chief support from an examination
of the supposed facts in the case of human beings. It assumes
that the expression of life in its original forms was sponta-
neous and indefinitely variable. It further assumes that some-
thing comparable with volition is present in these primitive
spontaneous expressions and that this volition is intrinsically
intelligent, so that among the various spontaneous, or random,
forms of movement which may be indulged there is presently
a selection of those which are most useful and a suppression or
elimination of those which are harmful. Whereupon it is
further assumed that these beneficial spontaneous reactions^
become embedded as fixed habits which presently are trans-
mitted by heredity to succeeding generations. They constitute
on this theory a sort of frozen intelligence. Although this
view has been held in times past by scientific men of eminence,
it is certainly not looked upon with favor by any considerable
number of contemporary scientists. It makes assumptions
about inheritance which are almost certainly incorrect and
assumptions about primitive intelligence which are highly im-
probable. Over against it is the view that, behavior being
essentially a function of structure, reflexes, instincts, and
tropisms simply represent accidental variations which have sur-
vived, just as the variations of form have survived, because
they were, on the one hand, positively useful, or, on the other
hand, sufficiently harmless to permit their continuation, if only
they chanced to be combined with other reactions of a pre-
servative kind. Both theories admit that, as things now
stand, acts of reflex and instinctive character, whatever their
evolutionary history, are as such intrinsically non-intelligent,

io8 THE EVOLUTION OF MAN

non-adaptive to variation in environment. This is as true of
man as of animals.

Again broadly speaking, it must be recognized that the
range and complexity of animal instincts bears some relation
to the organization of the central nervous system, but the rela-
tion is a highly complicated one. Certain arthropods, for
example, like the ant, the bee, the spider, the wasp, have amaz-
ingly elaborate instincts, although the pattern of the nervous
system is relatively simple. On the other hand, certain of the
mammals whose nervous system simulates that of man himself
are equipped with instincts of a seemingly less complicated and
remarkable character. Unequivocal tropisms, as might be
expected, are generally more striking and presumably more
frequent in creatures of simpler type than in those higher up
the scale. As is natural, instincts tend to follow patterns ap-
propriate to the particular environment in which the animal
thrives. Birds thus develop nesting instincts, which are quite
different in form from any correlative instincts of fishes. The
latter, on the other hand, develop spawning instincts, which
vary in some essential particulars from the reproductive in-
stincts of the birds and mammals. In discussing intelligence
it is highly essential to keep constantly in mind these inherited
forms of behavior and to distinguish them sharply from acts
acquired by the creature of its own initiative.

With this brief background of general impressions regard-
ing instinctive and reflex endowment of animals, we may turn
attention to their more strictly intelligent behavior. At this
point we are thrown back on two types of evidence whose
relative value is estimated quite differently by different scien-
tists. We have, on the one hand, the observations of the out-
door naturalist, who undertakes to describe the behavior of
animals as seen under the typical conditions of nature. On
the other hand, we have the experimental school, which has
attempted to study and analyze the behavior of animals under

THE EVOLUTION OF INTELLIGENCE 109

laboratory conditions of control, or at least under conditions
of a somewhat artificial character. Evidence of the first type
tends to be anecdotal in character and, in the nature of the
case, is rarely able to present any trustworthy account of the
life history of the individual creature whose behavior is under
discussion, or indeed of the immediate antecedents of the par-
ticular episode under consideration. It would be at once
unjust and ungracious to deny substantial value to much of
the Information emanating from such sources. Indeed, with
the case of the instincts nearly all of our knowledge derives
from this source. But on the other hand, evidence of this
character may be subjected to the most searching scrutiny, for
to It attaches not only more than the usual dangers of inaccu-
rate observation, but also the all but inevitable tendency to
anthropomorphic interpretation. This is the happy hunting
ground of the nature faker and of the manufacturers of
Arabian Nights tales and Baron Miinchhausen legends of
animal life and behavior. None but a hopeless ingrate could
recall Mowgli and his friends without a sentiment of deep and
lasting gratitude; but, if taken as more than literary romance,
the accounts of Kaa, of Shere Khan and the Banderlog, to
mention no other instances, can only result in profound mis-
apprehension.

On the other hand, the laboratory school suffers from the
charge of subjecting animals to abnormal conditions, under
which their reactions are distorted and in which it is impos-
sible to expect normal expressions of their Intrinsic intelligence.
As regards the larger undomesticated animals, there is doubt-
less some force in this type of criticism, and indeed when it
comes to certain forms of procedure, to be mentioned in an
instant, it may be alleged with some show of proof, that the
very conditions under which the observations are made tend
to defeat their own purposes. For example, it is a not un-
common procedure in animal experimentation to create in-

no THE EVOLUTION OF MAN

centives to the solution of simple problems, either by creating
strong hunger, or by the use of somewhat severe punishment.
In either case, it is alleged that the animal is thrown into an ab-
normal emotional condition highly prejudicial to the exercise
of such powers of intelligence as it may possess. Objections
of this character are all appreciably less significant when urged
against the milder and less unnatural forms of experimental
procedure employed, let us say, in the case of simple marine
animals, to whom can be given, under laboratory conditions,
surroundings so closely simulating their native habitat as pre-
sumably to rob them of any real abnormality. Moreover,
after every criticism has been recorded, it still remains true
that, when affirmative evidence of intelligent behavior is
secured under conditions of experimental control, whether
inside or outside a laboratory, the validity of such evidence is
likely to be forever exempt from the uncertainty which almost
inevitably attaches to the incidental observations of animals in
nature.

It is necessary to direct attention to these two main lines of
attack upon animal intelligence, for the reason that observa-
tions which have been reported from these two sources have
often varied fundamentally. The works of the outdoor
naturalist, for example, are full of records of animal be-
havior alleged to afford the most unequivocal evidence of
reasoning processes approximating those of man himself,
whereas the experimentalists have generally failed to discern
anything of this kind and in its place have reported literally
thousands of instances of behavior wholly devoid of the char-
acteristic features of human thinking.

It will be readily understood that no observation of animal
behavior is likely to be trustworthy, unless based upon a wide
and exact knowledge of the animal's usual habits of life.
Otherwise one is exposed to the error of interpreting as a

THE EVOLUTION OF INTELLIGENCE iii

rational process a piece of behavior which may be partly or
wholly instinctive, or which may have been acquired by wholly
unknown means at some earlier period of the animal's life.

When due allowance is made for such modifications as have
been already suggested, the general upshot of the observations
of the experimentalist may perhaps be summarized in this
way. The very simple forms, like the low marine orders,
exhibit a relatively limited group of reactions, some of them
troplstic in character, others, however, seemingly somewhat
variable, but few of them suggesting any exercise of intelligent
discrimination. A little further up the scale, animal forms are
encountered which are equipped with fairly definite instincts
and which evince the ability to learn to accommodate them-
selves to changes of environment, but only by the slowest and
most tedious processes, giving practically no indication of any
trait which one would naturally designate intelligent. Thus
the frog, for example, by earlier observers supposed to be
entirely incapable of taking on any modified reactions by the
process of learning, has now, through the most patient obser-
vations, been found to be capable, after many, many trials, of
slightly improving his reactions. Granted, for example, two
pathways, one of which always leads to food and the other
not, he can, if the patience of the experimenter is sufficient,
ultimately learn to choose the correct pathway. Still further
up the scale, as will be illustrated in some of the lower mam-
malian forms, we get more positive evidence of the beginnings
of real memory and of a more definite ability to modify re-
actions in a beneficial manner, although this capacity with
some of the mammals, such as the guinea pig, is almost at the
zero point. With others, however, and particularly with the
primates, there is much greater adaptability, and in a few
seemingly well-authenticated Instances there is evidence for
something at least suggesting the human forms of inference

112 THE EVOLUTION OF MAN

and thinking. This amounts to saying that there is in the
animal kingdom, as we know it, the widest range of behavior
extending from that which at one end of the line is almost, if
not wholly, stereotyped and mechanical to forms which at the
other extreme represent not only a rich life of plastic instinct,
but also highly variable forms of behavior, some of which
definitely suggest the possession of rudimentary intelligent
powers. There is, then, conclusive evidence of a real evolu-
tionary process, if one assume, as all scientists now do, that
the more complex organisms, in which behavior is most
elaborate and intelligent, have arisen from simpler and his-
torically antecedent forms. That is to say, there is no question
whatever regarding the wide variety of the present modes of
behavior extending from the reflex and tropistic type up to
the variable intelligent type, and, on the basis of the evolution-
ary conception of organic structures, there can be no question
that these differences in behavior represent historic evolution
of the more complex out of the simpler.

Intelligence and Consciousness

This is perhaps a convenient point at which to mention an
issue often much magnified in discussions of mental evolution,
to wit: Are all animals conscious, or Is consciousness a phe-
nomenon which appears only at a certain stage of evolutionary
development?

Disregarding earlier historic theories, there have been
three distinct positions represented by contemporary scientific
opinion. One of these holds that all animals are conscious,
even an amoeba. Indeed, the defenders of this extreme view
have sometimes gone further in maintaining not only that ail
life, plant as well as animal, enjoys at least a rudimentary form
of consciousness, but also that the whole physical universe Is
but one aspect of a reality, which seen in its entirety presents

THE EVOLUTION OF INTELLIGENCE 113

a corresponding conscious phase. Needless to say, we must
eschew for present purposes any discussion of this larger issue.

There is, second, the view that consciousness appears in the
evolution of the nervous system at that point at which there is
demonstrable evidence that creatures can learn to improve
their reactions on the basis of experience. From this point of
view, the frog, among the more familiar of our animals,
would represent perhaps the stage at which the first gleams of
intelligence are discernible. Practically, this test is a very diffi-
cult one to apply, because it would be precarious to allege with
confidence that, granted sufficient repetitions of a given situa-
tion, any animals would fail to show some modification in
response. But purely physical and chemical reactions, for
example the formation of crystals in minerals, exhibit a similar
slow modification. And yet, in this case, one would hardly be
disposed to allege the presence of consciousness. Furthermore,
where animals low in the scale apparently display adaptive
reactions, it is difficult to be certain that the chemical and
physical stimuli affecting them are all under control, so that
the seeming adaptation may be accepted as bona fide.

A third view holds that no animals are conscious, but that
all their reactions are essentially of the mechanical and tropistic
type. One must, of course, admit that we have no direct access
to animal consciousness, if such exists, but the same thing is
true of the consciousness of one's human neighbor.

It has seemed to me desirable to eliminate this whole issue
from the present discussion, because we are primarily con-
cerned with the demonstrable evidence of actions such as we
can properly designate intelligent without regard to any par-
ticular psychic mould in which they may be cast. This is not
because the question is devoid of interest — far from it — but
because it does not lend itself to profitable discussion within
the limits of this article, if we are also to make headway on
the general problem of the evolution of intelligence.

114 THE EVOLUTION OF MAN

Human Intelligence

How far the Intelligence of modern man has developed
beyond the stages of the prehistoric man, whose skeletons have
in recent years come to light, It Is practically Impossible to
state. Certain of these earliest remains Indicate a cranial
formation somewhat smaller than that of contemporary man
and, although the evidence Is precarious, there Is perhaps some
ground for thinking that the cerebral portion of the nervous
system was less highly developed than now and that presum-
ably the level of native Intelligence was therefore lower.
Nevertheless, this would be merely an hypothesis. If we turn
to contemporary man, we find extreme variation In the culture
and civilization of different races, and a widespread belief In
equally marked differences in native intelligence. Thus the
Occidental white man unhesitatingly puts himself at the head
of the list, with the Asiatic ranking next, American Indians
perhaps next, the African next, and at the bottom possibly the
Bushmen of Australia. This list, of course, omits a number of
important groups, but may serve to give some indication of a
common type of arrangement. It is perhaps needless to say
that the Asiatic in making out his list would accord a different
position to his own group. Nor Is any great racial stock dis-
posed to accept an inferior status.

The question which Is immediately raised by the most super-
ficial inspection of these racial differences of culture and civili-
zation has to do with the problem whether the European white
man, for example, has by virtue of superior native endowment
passed by evolutionary processes through stages of culture and
civilization comparable with some or all of those now reflected
in the several racial groups mentioned, or whether he has had
an altogether different history. Have the civilized races, in
general, evolved through superior Intrinsic talent out of the
conditions represented by savage races? The problem is

THE EVOLUTION OF INTELLIGENCE 115

greatly complicated by the difficulty of separating out those
factors which are indicative of sheer intellectual capacity and
those which have to do with the accidental advantages of cli-
matic or geographic habitat and the equally accidental develop-
ments of particular technical or social practices. It is easy to
assume that more elaborate forms of civilization necessarily
Imply higher intellectual powers and this is perhaps not wholly
true. So far as we can judge by the evidence in historic times,
there is no reason whatever to suppose that the native intel-
lectual abilities of the average American citizen are in any
way superior to those of the Egyptians four thousand years
before Christ, or the Homeric Greeks, or to others of the
peoples of that general period in the Mediterranean basin,
records of whose civilization have come more or less com-
pletely to our knowledge. It would certainly be a bold protago-
nist who should assert that modern European civilization
has produced, in sheer intellectual power, men superior to
Democrltus, or Plato, or Aristotle, or Alexander, or Julius
Caesar, to say nothing of great Orientals like Confucius. In
other words, since the period of historic records there is no
convincing evidence of marked development in human intelli-
gence, despite the enormous advances made in the parapher-
nalia of civilization; but, on the other hand, there is fairly
definite evidence that extant human races differ appreciably in
their native intelligence and those which are living most nearly
in the state of nature which we believe to have characterized
the early history of our own racial stock are, generally speak-
ing, marked by apparently lower general average intelligence
and by relatively fewer intellects of high grade. It seems
therefore a reasonable inference that the forefathers of our
own particular racial stock, could we but penetrate far enough
into past history, would be found, like the more primitive
races to-day, In possession of somewhat lower degrees of in-
tellectual capacity. How many thousands of years we might

ii6 THE EVOLUTION OF MAN

be obliged to go back to find demonstrable changes it is impos-
sible to say. We know that the major anatomical character-
istics of man have not materially shifted for the last twenty
or thirty thousand years.

There is a very common popular belief that, although
civilized man may be the superior of his uncivilized contem-
porary in certain forms of purely intellectual activities, he is
his inferior in keenness of sense perception and in his response
to many of the aspects of nature. Such evidence as we have
tends on the whole rather to discredit both of the Inferences
involved in this assertion if they be made too sweeping. It is
surely open to question whether all races of nature people now
living are radically inferior to the more civilized groups in
natural powers of intelligence. Certainly there are some
striking individual instances of high intellectual achievement
attained by representatives of some of these more primitive
racial groups; and, on the other hand, there is good evidence
for the statement that at least occasional representatives of
civilized races are quite as keen in their vision and hearing —
taking these two examples — as any of the primitive peoples
with whom they may be compared. The North American
Indian and the white frontiersman may illustrate the point.
There are not a few instances of Indians who have exhibited
intellectual capacities of a very high order, and the keenness
of vision and hearing of some of the scouts of frontier history
rival anything reported of their savage contemporaries.
Training and discipline are perhaps in both cases the clew to
achievement quite as much as deep-seated and indisputable
difference of natural capacity — a statement which in turn must
not be understood as implying that there are no significant
differences between the lowest tribes of savages and the highest
exemplars of civilization.

If, as a clever writer on these subjects has suggested, we
may consider existing tribes of savages as in some sense our

THE EVOLUTION OF INTELLIGENCE 117

contemporary ancestors, it is convincingly clear that, what-
ever is to be said of sheer native intellectual capacity, civilized
man has developed a technique so superior to that of primitive
peoples that his intelligence enjoys enormous advantages at
almost every stage. It is peculiarly difficult for us to dissociate
mere intellectual power from the cultural surroundings under
which it is exercised. It may be, for example, that the in-
ventor of the bow and arrow accomplished quite as great a
feat in the intellectual world of his day as the inventor of
printing in his, or the inventor of the steam engine, or the
inventor of the electric light. Similarly, the inventor of the
fishhook and the line, as a method of extracting food from
the sea, may have enjoyed powers of native intelligence entirely
comparable with those of our great modern inventors. All of
which is but another way of saying that the evidences of the
evolution of civilization and culture are far more striking and
far more demonstrable than those which suggest, in historic
times at least, any real progress in the intrinsic fabric of human
thought. Moreover, in all comparisons of racial groups one
must remember the astonishing variation of natural capacity
in any large number of people. The psychological tests em-
ployed in the American army during the war exhibited the
amazing range of capacity in a cross section of our population.
Certain of the recruits in the army exhibited an intelligence
capacity which marked them as morons and accordingly com-
parable with the most backward races. One is always tempted
when comparing one's own racial group with another to take
as the standard one of its very intelligent members. This is
entirely unfair and sure to result in fallacious conclusions unless
one is in a position to select from the group under comparison
an equally exceptional representative.

But, after all allowances are made, it would appear that, if
we compare the normal civilized man of any of the more ad-
vanced races with those savages lowest in the human scale, the

ii8 THE EVOLUTION OF MAN

former is distinctly superior in the power of sustained attention
and thought, in the range of things which interest him, and
in his powers of analysis, abstraction, and inference. It used
to be alleged that savages controlled their emotions less
perfectly than civilized man. Inasmuch as emotional life is
closely knit up with instinct and with the more primitive and
ancient part of our nature, it would not be strange were this
belief true. But when consideration is given to the different
conditions eliciting emotion, it may be doubted whether this
conception is in any unqualified way correct.

That portion of the history of man marked by any of the
evidences of civilization is so extremely brief, compared with
the vaster period of animal barbarism through which he must
have passed, that we may well find it difficult to secure wholly
conclusive evidence of evolutionary change in his mental
powers. But such evidence as there is all points to a great
practical improvement in the use of his native abilities.

When we contrast the conditions of savage man with those
of any of the animals, even the highest primates, the differences
in apparent intelligence are very marked. It would hardly be
a safe statement that animals make no use of gestures, whether
vocal or otherwise, to serve the purposes of a rude language.
But such use as has been reliably demonstrated is so crude, so
largely a mere expression of emotional excitement, that com-
pared with developed human speech (which presumably de-
veloped out of emotional expressions) it is a hopelessly im-
perfect tool. Primitive man as we know him, although often
carrying on his affairs with an extremely limited vocabulary,
nevertheless is able, through his language devices — to say
nothing of others — to mark off and deal with abstract and gen-
eral relations and in so far he enjoys a technical superiority to
the animals which, in effect, is a difference in kind as well as a
difference in degree. Moreover, broadly speaking, animals
make no use whatever of tools. The occasional instance of

THE EVOLUTION OF INTELLIGENCE 119

the elephant brushing off flies with a branch held in his trunk,
or the alleged instances of monkeys using stones to crack nuts,
are but sporadic examples of probably accidental achievements
which in no case lead on to any general ability to make use of
utensils in a discriminating way. One must not, in this con-
nection, confuse with intelligent actions the remarkable in-
stinctive manipulations which many animals are capable of,
nor the tricks which they may have been taught by long and
painful effort. The elaborate nests which many birds build are
amazing instances of utilizing the most varied materials in
highly complicated forms. Similarly, the beavers accomplish
the most astonishing results with the materials which they
employ and there are abundant reports of their adaptability
to changing conditions which, if well established, are certainly
suggestive of highly intelligent reactions. Here again, how-
ever, the experimental zoologist who has studied most care-
fully the instinctive activities of animals will be most hesitant
to ascribe individual intelligence comparable to that of man
in interpretation of these animal reactions. Certain it is that,
generally speaking, the primates are much more skillful than
other animals in adapting themselves to shifting conditions
and that, even among them, the evidence of anything compa-
rable with a human process of inference, or a process of ab-
stracting, or of generahzing, is very, very slight. In any case,
the issue which is raised here again must be clearly understood,
to wit, that beyond the adjustments which are innate, inherited,
and unlearned by the individual are those which represent his
Individual acquirement independent of such inherited tend-
encies. The latter is the field of individual intelligence.

As was indicated earlier in this paper, there is a wide gen-
eral correspondence between the degree of intelligence mani-
fested by animal forms and the structure of the nervous system.
In particular, intelligence in its narrower and more specific
sense, as distinguished from instinct, appears to be rather a

120 THE EVOLUTION OF MAN

function of the cerebrum and particularly of the cortex. If
animals are arranged in the order of the development of this
organ in the nervous system, the relative size and complexity
of it will be found standing roughly in parallel with the variety
and adjustability of the reaction patterns. That is to say, an
animal that has a well-developed cerebral cortex will have a
richer type of behavior, being less completely dependent upon
instincts and reflexes and being capable of carrying out a larger
range of activities than can an animal with less fully developed
cerebral structures.

Man has, as the great differentiation of his own brain from
that of most other animals, a very much more delicate internal
structure in the cortex and relatively very much larger parts of
the cortex devoted to the interconnecting and interrelating of
the various parts of that organ with itself. The frontal areas
and the so-called association areas are relatively very large.
Some of these differences are demonstrable only under the
microscope; others, however, are obvious even in the gross
anatomy. But despite these differences which are real, no one
could ever have inferred from them such marked differences in
the expressions of intelligence as do in point of fact distinguish
man from even the most highly developed animal. The gen-
eral pattern of the human nervous system is, broadly speaking,
exactly that of wide ranges of the mammals and more particu-
larly of the primates. Nevertheless, the behavior of man is
certainly very different (even though the difference be thought
of as merely quantitative and not as qualitative), especially on
the levels of memory, imagination, thought, and reflection.
On the whole, man's development and control over language is
unquestionably the greatest single achievement which his in-
telligence has compassed, and whether one thinks of it as cause
or effect, its presence, more than any other one factor, is re-
sponsible for his enormous superiority to his animal neighbors.
It has enabled him to achieve social cooperation and the fixa-

THE EVOLUTION OF INTELLIGENCE 121

tion of institutions, to preserve tradition and modify its
coercive influence by rational discussion, and incidentally it has
afforded him the most powerful single tool for creative indi-
vidual thinking.

The striking character of the difference between typical
human processes of inference and those by which animals ac-
quire wholly new reactions may be illustrated by a single
example. Here is a dog shut up in a cage with his food just
outside the door. To open the door and satisfy his hunger
involves pulling a cord which lifts a latch. No matter how
obvious the arrangement to human vision, the dog may thrash
about for a long time in the neighborhood of the cord, biting
and clawing the various parts of the cage, until by accident he
may seize the cord in his teeth and forthwith escape. A human
being having once found a single act which would thus open
the door would ordinarily require no second experience in-
stantly to repeat the success. But the animal may need many
such trials before establishing the correct response, showing
that there is very slow discernment, or possibly none, of the
real relation of the cord to the opening of the door.

Now human beings do many things quite similar to the ran-
dom activities of the animal in the cage. Many a child at-
tempting to solve a mathematical problem does exactly the
same thing and comes upon the correct result, if at all, quite
accidentally and as the outcome of a kind of mental fumbling.
Indeed, all elaborate thought processes inevitably have in them
much of this more or less haphazard experimental venturing.
But the point is that once the human being clearly sees the rela-
tion involved, he can Immediately repeat successfully the pro-
cess and generally carry over the principle to other similar but
not identical problems. It Is doubtful if animals ever do just
this thing. Even their powers of imitation are far less than is
commonly supposed.

So, despite the structural similarity of the brain of man and

122 THE EVOLUTION OF MAN

the brain of the higher mammals, the differences in intelligent
behavior are very marked. The most intelligent animal is
probably in the mental condition of the young baby or the very
low grade moron, and this despite the possession of instincts
which often enable the most astonishing adjustments to en-
vironment.

Future Development of Human Intelligence

One of the speakers in this course raised a question, which
has enjoyed a good deal of attention, and to which a further
word may perhaps be added in this connection. Is the evo-
lutionary process at an end so far as concerns the human brain
and human intelligence? In the nature of the case no dog-
matic reply can be offered with confidence and one must fall
back upon the probabilities of the case. I cannot altogether
sympathize with the somewhat definite negative opinion occa-
sionally advanced, for such negation has its chief justification
in the vast extent of time throughout which little or no demon-
strable advance has occurred in the organization of the human
brain and therefore presumably in human intelligence. One
cannot challenge the fact that for many thousands of years
there has been little or no such change ; but, on the other hand,
the period of time for which we have such evidence, twenty or
thirty thousand years, is so trifling compared to the total life
of the race and the total duration of life itself on this planet,
that a prediction based on such a relatively insignificant seg-
ment of man's history seems highly precarious. Assuming
some extra-mundane observer of the primeval slime out of
which organic life has come, it would certainly have seemed
to such an one grotesque to predict such changes as have actu-
ally come to pass, and particularly as regards intelligence.
Similarly it is entirely impossible to surmise at what point
progress beyond present human capacities may occur, but to

I

THE EVOLUTION OF INTELLIGENCE 123

conclude with any certainty that such further progress will not
occur, much more that it cannot occur, seems hardly warranted.
Whether this view regarding the further evolution of in-
trinsic human capacities is right or wrong, there would appear
to be no practical limit to the changes which man can hope to
bring about in the conditions of his life by the further appli-
cation of the same technique which has produced the highest
forms of modern civilization, has produced our fine arts, and,
particularly, has produced our modern science. Conceivably
we shall never have greater epic poetry than that of Homer,
greater sculpture than that of Phidias, greater architecture
than that of the Parthenon, greater drama than that of Shake-
speare, greater painting than that of Raphael and Titian,
greater symphonic music than that of Beethoven. There is,
however, nothing to prevent advance upon such achievements
and in the range of the natural sciences at least, thanks largely
to the perfection of experimental technique and the utilization
of mathematics, there seems to be literally no limit in sight to
the further mastery which man may achieve over the forces of
nature and consequently no limit to the alterations which he
may be able to introduce to the enrichment of civilization.
Even in the field of religion, where obvious evolution has
occurred since primitive times, the modern mind has intro-
duced modifications of the teachings of the founders of the
great world religions designed to adapt them more nearly to
the conditions of contemporary life. The doctrines of Chris-
tianity itself, while based as truly as ever upon the life and
teachings of Jesus, are undergoing constant development and
transformation designed to accommodate them to the needs of
the life and thought of our time. Strangely enough, the scien-
tific mastery of the facts of man's own nature and the laws
which control society linger far behind the corresponding in-
sight into the nature of the processes of the physical world.
But surely it is only a matter of time when these social sciences.

124 THE EVOLUTION OF MAN

so-called, will also have perfected a technique enabUng man to
secure mastery over himself and his social relations compa-
rable with that which has begun in the control of physical
nature.

In modern times, to mention but a single point, our knowl-
edge has been rapidly growing in regard to the extent to
which the mental life of the individual human being is subject
to influences which rarely or never show themselves above the
level of his conscious life, and, even upon these infrequent
occasions, come so screened and shrouded that their real
origin is seldom understood or appreciated. It has thus been
made particularly clear in the last century that man is in his
instinctive life close cousin to the brutes. But he has also in
his nature the deep grounded tendencies of hundreds of thou-
sands of generations of savage human ancestors. Further-
more, he carries into his adult life many prejudices, fears,
likes, and dislikes, which trace back to his own infantile and
childhood experiences. Any of these tendencies may well up
at a moment's notice to affect the attitude which he takes
toward any issue that may present itself in his hfe. He may
make a decision which, with a not unnatural self-flattery, he
calls a carefully reasoned choice. But to a sufficiently informed
observer it would frequently be revealed that this reasoned
choice represented an attempt to justify on rational grounds
an impulsive preference arising from some of these hidden
springs in human history, rather than a wholly disinterested
and unbiased analysis of a given situation. Moreover, man
at birth finds himself instantly surrounded with all the tradi-
tions and practices of his own time, race, and social group,
which from the very beginning hem in his spontaneous activi-
ties, furnish the stage upon which his instinctive and impulsive
life must be played, and, in general, set boundaries which, how-
ever independent, he can hardly cross. In point of fact, the
average individual is Intensely conservative, indisposed to the

THE EVOLUTION OF INTELLIGENCE 125

labor and the hazard of independent thinking, a creature of
habit, most content when most easily able to run along in the
fixed grooves of daily life without friction or annoyance.

Nevertheless, while the average individual may be intrin-
sically indisposed to encourage change, except in those circum-
stances which occasion him personally acute discomfort, the
more active and progressive minds find through the accumu-
lated knowledge of the race, now for a few centuries available
in permanent written form, and through the amazingly rapid
development In the technique of the sciences, the tools at hand
for a literally unlimited evolution In the actual conditions of
human life. From this practical point of view, therefore, the
evolution of intelligence may be considered as close to its
beginnings rather than in any sense drawing near to its close.

CHAPTER V
SOCIETAL EVOLUTION

ALBERT GALLOWAY KELLER

PROFESSOR OF THE SCIENCE OF SOCIETY, YALE UNIVERSITY

The essence of evolution is the development of form out of
form, in a connected series, with survival of the fitter forms
in adjustment to environment. The outcome of evolution is
adjustment of life to life-conditions. No informed person
feels any longer the need of arguing the truth of the theory;
interest now centers in the extension and correction of knowl-
edge as to the details of the process, and in the applications
of the truths discovered. In the Darwinian theory of adjust-
ment we have one of those widely orienting factors which array
knowledge in orderly vistas and lead mankind to believe that
there is some sense in earthly existence.

If there is any one place rather than another where man-
kind would like to find sense and order, it is in the field of
human social relations. No one can read the vivid pages of
Henry Adams's Education without a deeper appreciation
of the darkness and deviousness of the ways along which all
of us are traveling, though most of us are not so conscious and
concerned about our gropings as was that anxious and rueful
searcher after enlightenment. Adams, an evolutionist believes,
was after too much. He wanted to find some norm of prog-
ress in human history, and seems to have renounced high hopes
of Darwinism when he found that it offered no such norm.

It is one of the common misconceptions about evolution, and

SOCIETAL EVOLUTION 127

one Into which Adams fell, that it means progress. It means
adjustment only. Such adjustment seems to be progressive if
it leads in a direction which we choose to call forward; but it
may appear also to be retrogressive If its runs counter to that
direction. To us the change from the flint-lock to the per-
cussion-cap musket seems a progressive adjustment, and the
return from the latter to the former, in hot and damp regions,
where the cap deteriorated while the Imperishable flint did
not, appears to be retrogression. Both were expedient ad-
justments to life-conditions.

We ought not to be dismayed at the sight of forces operat-
ing In what seem to us opposite ways, at one and the same time.
We should not bemoan the failure of evolution because motion
is not always visibly In the direction we like or expect, any
more than we should despair of gravitation because it causes
both the stone to fall and the balloon to rise. The fact is that
the terms progress and retrogression, as their etymology indi-
cates, imply that the user of them has selected some center of
operations from which he can infallibly adjudge what is "pro''
and what is "retro." He Is at liberty, in free countries, to do
this for himself and to try to persuade others that he is right ;
and sometimes whole groups can agree on what is progress
and what is not; but it Is generally impossible to get extended
unanimity as to the identity of "forward" and "backward."
Especially Is this the case when It comes to the appraisal of
social relations. Institutions, and policies.

But this whole difficulty Is escaped, in the case of evolution,
If we consent to view that process as It is, and do not, in our
straining after the assessment of things as progressive or
retrogressive, hug to ourselves the misconception that evolu-
tion and progress are synonymous. If we simply ask, concern-
ing any organic or social form, whether It is an adjustment,
past, present, or pending, we shall all find ourselves in a sub-
stantial agreement that will permit of our going along farther

128 THE EVOLUTION OF MAN

together. I myself think the protective tariff to be a case of
retrogression, but that does not prevent me from agreeing with
its many ardent and even candid sponsors that it is an im-
portant adjustment to life-conditions. I regard the League of
Nations as the only practical and working proposition in the
field of international relations; others think it a fooHsh and
retrogressive measure; but all of us could agree that it is a
widely accepted adjustment, now under test. Slavery was once
an adjustment that everyone believed in. The time came when
conditions changed and there arose a difference of opinion as
to whether it was good or bad, progressive or retrogressive.
Now it has come to be regarded as a maladjustment. But,
whatever the judgment upon it at various times, anyone can
see that it has been one of the ways into which men naturally
fell in meeting the conditions of life as presented.

I have used, perhaps, a disproportionate amount of space
in seeking to enforce this point; but I have done so de-
liberately, because there is no other range in which people are
so wont to set up private and local standards, upon which
they then assess all things, as they are in the range of social
life. If many are disposed, petulantly or dismally, to despair
of organic evolution because it does not support their ideas of
progress — which it never set out to do, any more than it adver-
tised to explain the origin of life — how much more darkly
would they despair of a social evolution that lays no claim to
be progressive. Man's dearest Interests are vitally involved
in his social life; in fact, what discouraged Adams and others
with Darwinism was not its givings in the organic field, but
its fallings-short, in promise, of their hopes in the social field —
into which it was speedily and incontinently dragged by the
almost Instinctive tendency to ^'reason from analogy."

I cannot go into this last matter — of how conclusions were
drawn concerning the nature and life of human society from
the nature and life of organisms. It was partly Darwin's fault

SOCIETAL EVOLUTION 129

for embarking upon the discussion of social and moral matters,
in the Descent of Man; matters concerning which he was
little better informed than any other non-specialist. It was
still more the fault of Spencer, who became so enamored of
the analogy between organism and society that he came almost
to believe it an identity. Then the Germans got hold of it and
constructed huge volumes of uninspired muddlement about the
"structure and life of the social body."

The analogy between a society and an organism is a pretty
one, as developed by Spencer. Its development was not with-
out use. But of what use? It is of no use at all in proving
anything about society. An analogy is no proof of anything.
Consider the exhorter who described the life-cycle of the
butterfly and wound up triumphantly: "Now who shall say
that there is no proof of immortality!" Proof demands facts,
ever more facts, all sorts of facts bearing on the subject. Out
of them comes the theory, and from them the theory is cor-
rected and re-corrected. It is most essential that the facts
shall not be selected, either to be acclaimed or to be ignored.

An analogy, on the contrary, is a specially selected fact or
relation. It is picked out of many possibilities because it is
thought most vividly to set forth some idea already developed
and fixed in mind. It is not the search for truth that the
analogy-user is after; it is the exposition of a position already
taken. Analogy is perhaps the most effective device for exposi-
tion; but it is the tool of the preacher, not of the discoverer.
Its supreme effectiveness is found, probably, in the parables of
Christ,^ who, in trying to transmit spiritual truths to simple
minds, took recourse to homely analogies on all sides.

There can be no direct "reasoning from analogy," there-
fore. People who write on social evolution are regularly
charged with trying to do that, and generally justly; perhaps
if a writer starts out by saying that it cannot be done, it will

1 For example, Matt, xiii., 31, 33.

I30 THE EVOLUTION OF MAN

be believed by some of his readers that he Is not endeavoring

to do It.

But the analogy, correctly understood and not burdened
with a weight It cannot carry, can perform a service of great
value. If In one field of Investigation (say the organic) we
know that certain phenomena are produced In a certain way,
and if in an adjacent, less understood field (say the social) we
find analogous phenomena, we are justified by long experience
in the inference that the unknown producing factors in the new
field are probably similar to the known ones In the older range.
If, in particular, we find adjustments In the organic field pro-
duced by the so-called Darwinian factors, and If we discover
that the social range shows social forms representing adjust-
ments to the life-conditions of society. It Is reasonable to Infer
that the factors producing social adjustments may be similar
to those producing organic adjustments. This is the more
likely in view of the fact that all members of human society
are organisms, so that the two ranges — of organic and of
social life — are not merely contiguous, but Interpenetrative.
If organic forms are evolved by the action of the Darwinian
factors of variation, selection, and heredity, their joint action
resulting in adjustment to life-conditions, it is a hint to us that,
in default of any more promising lead, we had better look for
counterparts of the Darwinian factors In the social range.

This suggestion has been unreflectingly and unconsciously
adopted In popular usage. It is seen that habits and customs
are passed on from generation to generation somewhat as
bodily qualities are. It Is necessary to use some term to cover
the process. The biological term Is heredity. It Is easier to
catch up a term In use than to Invent a new one. Hence
writers speak of "social heredity." It Is like speaking of
"brass andirons." However, it is vaguely realized that habit
and custom are not transferred by actual heredity, through the
germ-plasm; and the perception of the unanalyzed difference

SOCIETAL EVOLUTION 131

involved is indicated by the adjective "social" — not plain
"heredity," but "social heredity." The upshot of the matter
is that even the casual observer has noted the likeness between
things social and things organic and biological.

It seems to me that we had better take this hint from
analogy and work on it. Evolution is proved and accredited
in the organic field; at Darwin's centenary scientists of all de-
scriptions united, in a volume called Darwin and Modern
Science, in bearing witness to the fruitful suggestion received
by them from the Darwinian theory. We had better see
whether that theory can not help us in discovering some order
and sense in social phenomena. I think it has helped some of
us in just that way. Our courses in the science of society,
representing the best we have to give to our students, have for
many years begun with the effort to make sure that they all
secure a layman's knowledge of organic evolution.

My predecessors in this course of lectures have shown that
the evolutionary process does not stop short of man as an
animal. Huxley,^ in comparing him with the anthropoids,
summarizes as follows: "Thus, identical in the physical pro-
cesses by which he originates — identical in the early stages of
his formation — identical in the mode of his nutrition before
and after birth, with the animals which lie immediately below
him in the scale, — man, if his adult and perfect structure be
compared with theirs, exhibits ... a marvelous likeness of
organization. He resembles them as they resemble one
another — he differs from them as they differ from one
another." But if man is thus similar to the animals, it would
appear that he must come under the same need of physical
adjustment to life-conditions. If so, he should show differ-
ences comparable to those exhibited by animals as the result
of adjustment to widely diverse life-conditions. Being the
most widely ranging of all animals, he might be expected to

2 Huxley, T. H., "Man's place in nature," 1901, p. 83.

132 THE EVOLUTION OF MAN

show the greatest physical diversities. He does not. Does
this mean that evolution stops short of man? Let us first get
some of the facts before us.

Human beings are much alike over both time and space.
For many thousands of years man has been substantially the
same kind of a physical being as he is to-day. Over all the
earth he is pretty much the same sort of animal. One who
has followed the efforts of scientists to distinguish the varieties,
or races, of mankind can realize how essentially alike they are.
Conviction of this essential similarity has led to the assertion
that "man is unchanged in a changing environment." But this
seems to mean, on the face of it, that somewhere during the
course of human development evolution is suspended; for evo-
lution Is adjustment to environment.

Certainly mankind has encountered widely diverse environ-
ments. Men live in countries where the temperature falls far
below zero ; also where it rises considerably over one hundred
degrees Fahrenheit. They Inhabit regions which are cold
and dry, cold and damp, hot and dry, and hot and damp.
They live at sea-level or thousands of feet above it. They
persist where there is much animal life of all kinds, or where
there Is little of any kind. Of all animals the most widely
distributed over space, men have encountered all varieties of
earthly environment. Yet they are essentially alike. The
most widely distributed; the least changed — "unchanged In a
changing environment."

Through time also, with Its secular and often radical
changes of life-conditions, alteration In man's physical make-up
has been relatively sHght. Animals adjust even to so regular
and recurrent a set of conditions as the succession of the sea-
sons, while man has remained practically the same through
the protracted ups and downs of centuries and millenia. Is
it possible that the evolutionary process is stayed and that man
is exempted from It? Of course it Is not halted; and he is

SOCIETAL EVOLUTION 133

not exempt. The process merely changes its mode. It is no
longer evolution of the organic type, resulting in structural
adjustment; it is evolution of another grade, resulting in
another sort of adjustment. There must be adjustment just
the same, as a condition of existence. Evolution goes on as
long as adjustment to immutable life-conditions goes on — that
is, as long as life lasts. It is this typically human phase of
evolution which we want to identify and examine.

When human beings get into a situation (a cold climate, for
instance) which, for animals, evokes physical adaptation (such
as a thicker coat), we find, perhaps, some small adjustment
by way of bodily change ; but typically and generally what we
see is the employment of materials external to the body — skins,
wood, metal — which are interposed to form the instruments
of adjustment. It takes a certain brain-action to arrive at
such utilization of the things available in nature. When bees
build combs, it is by an instinct that represents a single adjust-
ment, once and for all, whereas man has, in the brain, a sort
of specialized adjustor capable of being turned upon this and
then upon that situation. His brain is somewhat like one of
these tool-handles which include in one instrument the possi-
bility of a variety of operations, except that the brain is in-
finitely more protean in its transformations.

The brain clothes its adjustments in material form. They
are thus realized or made real — materialized, or rendered in
terms of matter — externalized, or worked out in things ex-
ternal to the body. Every such realized thought is a piece of
culture or of the apparatus of civilization. Such are the
climbing-irons of the linesman, which are the cultural counter-
part of the natural climbing-foot; such is the aeroplane, as
compared with the wings of the bird. Tools, weapons, houses,
parachutes — all these are objects of material culture which are
counterparts of what nature has developed over countless ages
of organic evolution — for the beaver, whose tools are teeth;

134 THE EVOLUTION OF MAN

for the stag, whose weapons are hoofs and horns; for the
nautilus, whose house is his shell; and for the dandelion seed,
which sails about on its supporting structure.

But not all these cultural products are made of substances.
They are often immaterial forms of organization and conduct.
Specialization of labor is a cultural adjustment for readier self-
maintenance, saving as it does time, effort, and material, and
yet winning to a better product. Marriage is a cultural ad-
justment by which two very differently endowed sexes get
along together and rear young. Government is a cultural
adjustment resulting in orderly and peaceful human relations.
All economic, political, and other social systems, economies,
and institutions are cultural adjustments to life-conditions of
maintenance and sex, and of others presented to men in their
earthly life. Good government is as much a favorable adjust-
ment as is the web foot of a duck, and polygamy is as obsolete
an adjustment for us as five toes came to be for the horse.

If this is so, the fact of adjustment, and the need of it, is
as patent in the case of mankind as it is in that of other
animals or of plants. Only it is attained, in the former case,
by factors not precisely the same as in the latter. We shall
come to these factors presently. The outstanding fact, thus
far, is that plant and animal adjustments are typically physical,
while human adjustment is typically not physical. It is mental.

It is also social. Civilization is the product of numbers and
the contact of numbers. The new invention, representing a
better adjustment to life-conditions, say the gas-engine, never
springs full-fledged out of the brain of any individual. The
one who gets the credit for it is at best but the last of a long
line of experimenters, who has added the finishing touch —
where, indeed, he is not the exploiter who merely appropriates
the results of a long series of labors in which he has borne no
part. Much less did any individual invent marriage or prop-
erty, though tradition sometimes accredits them to a mythical

SOCIETAL EVOLUTION 135

law-giver. To arrive at any of these cultural adjustments de-
mands the give and take, and the gradual accumulation, pos-
sible only where there are a number of human beings cooperat-
ing in the effort to maintain and perpetuate the race, that is,
in a society. Cultural adjustment is therefore social; or,
better, since the word ''social" is so vague, it is "societal."
It is a thing that occurs only in society. It is "of society," and
that is what "societal" means. The securing of such cultural
adjustment is, therefore, by "societal evolution."

This is the new mode or grade of evolution that replaces for
man the organic mode or grade. Organic evolution goes but
a short way in explaining human relations, even though, since
man remains always an animal, it is basic to the whole of
human existence. Natural selection continues to operate upon
men, for instance, through the ravages of some diseases;^ but
in general it is replaced by another kind of selection which may
be called societal. Natural selection could never result in a
religious adjustment, for example. Such an adjustment is not
of the organic grade. At best, natural selection cannot exceed
that grade ; in fact, it is a risky contention to assert that even
the fittest human animals are surviving and multiplying in com-
parison with the unfit. The alarmists about race-suicide,
counter-selection, racial degeneration, and the like, are com-
plaining that we are breeding all the time from the worse ele-
ments in the population. We may be, if animal-fitness is the
sole criterion; and we may be, even though we realize that
there are other criteria. But it is essential to note that societal
fitness — fitness to be a member of society — is not identical with
physical fitness. It is enlightening to run over a list of those
men who have served society best and see how many of them
were physically defective.

If natural selection is not effectively in operation in pre-
serving the fittest human animals, because societal criteria

8 Holmes, S. J., "The trend of the race," 1921, chs. VIII and IX.

136 THE EVOLUTION OF MAN

always cut across organic criteria, it is certainly out of its range
when it comes to institutional development. If we read that
cannibalism or feudalism has perished by "a sort of natural
selection," the very qualification in the phrase indicates that
the user of it is merely employing an analogy. We are, I
repeat, upon another plane of evolution where the processes
and survival-values are somewhat altered from those existing
in nature. The attempt to carry natural selection over to the
new plane is wholly unproductive.

It is understood, then, that evolution in the societal range
is of a different kind, quality, brand, or variety from that
operating in nature. Societal adjustments, we go on to infer,
are probably produced by the operation of factors present in
the organic field, though these factors must needs be somewhat
metamorphosed in their manifestations in the societal range.
To one who has in mind such considerations as the foregoing,
there is nothing to do but to try out the Darwinian factors
upon societal phenomena. But upon what shall he try them?
Of course, upon the aforesaid cultural adjustments: inven-
tions, systems, economies, organizations, and the rest. Are
these societal adjustments, like the structural ones of plants
and animals, the end-results of variation, selection, and hered-
ity, operating in their societal modes and manifestations?

A great many of the cultural adjustments are, as we see
them in institutional form, as in marriage or religion, im-
mensely complex. It is expedient to seek them in their simpler
phases, just as one would reduce a complex fraction in order to
be able to handle it. The simplest form of all societal institu-
tions is custom. They all come out of it. Custom is also a
conception difficult to handle because it is all-pervasive and
eludes the grasp. It required a sort of tour de force to seize,
define, and thus reduce to usable form this elusive and floating
conception. This was done by my predecessor. Professor,

SOCIETAL EVOLUTION 137

Sumner.* I am bound to say that he did not give much atten-
tion to the possibility of extending evolution into the societal
field ;** but he furnished, in any case, the necessary basis for
such an enterprise. We shall review his findings in their salient
aspects.®

When the first societies of which we know appear to view,
they are already provided with a set of ways, or a traditional
procedure, by which they carry on self-maintenance, and every
other of their activities as well. These ways represent a con-
currence of group-members in the practice of expedients, eco-
nomic, political, religious, or other, which have been proved
to them, in the event, to be successful ones. These expedient
ways have been called the folkways or mores. Language is
one of the most typical of the mores; division of labor is
another. No one planned them, but they grew up and are
practiced unquestioningly, unconsciously, and automatically.
They correspond to habits in the individual. Taken all to-
gether, they constitute the code of behavior in a society. They
represent the proper way to act, and, even though they are not
subjected to any rational or critical examination, there exists
the conviction that they are the only right ways, the only ones
fit to live by. The mores, says Sumner, are "the popular
usages and traditions, when they include a judgment that they
are conducive to societal welfare, and when they exert a coer-
cion on the individual to conform to them, although they are
not coordinated by any authority." It is just as well to have a
technical term for them, for they are not precisely customs, or
social habitudes, or ethics, or morals.

They become uniform and universal in a group, and also
imperative ; and, often over long periods, they are so resistive

* Sumner, W. G., "Folkways," etc., 1907.
6 Cf. Keller, A. G., "Societal evolution," 1915, pp. 328-330.
® Certain of the following paragraphs a;re a reproduction of Keller,
A. G., "Through war to peace," 1918, parts of chs. VI and XVIII.

138 THE EVOLUTION OF MAN

to change as to appear invariable. Many of them are strongly
sanctioned by religion; in fact, practically all of them that are
of long standing are supported by the readiness of the spirits,
ancestral or other, to punish infringement or alteration. They
thus come to form a prescribed body of rules of behavior for
life in society that well deserves the title of "the social code."

Within the range of societal self-maintenance, the mores
determine how the struggle for existence and the competition
of life shall go on, thus rising to meet and cope with certain
vital and perennial life-conditions. Another inescapable and
vital life-condition is laid down in the bisexuality of the human
race; there are the relations of the sexes to be ordered, in the
interest of the society's well-being. Innumerable mores attend
upon the association of man and woman, parents and children,
and they work out into various forms of marriage and the
family. A big group of mores always surrounds some vital
condition of society life, like that of sex, and forms the ap-
proved method of dealing with it. Another such condition, for
further example, was felt in the vividly conceived presence of
a world of ghosts and spirits, an imaginary environment to
which men adjusted themselves by the unplanned development
of a set of mores covering forms of avoidance, exorcism, con-
ciliation, and propitiation of spiritual beings.

But these several sets of mores, "mere custom" at first,
gradually attained a stage of organization where they became
institutions, as, for example, matrimony or religion. There
is no human institution that has not risen from the matrix of
custom; the rise of new institutions, now as always, is out
of the same prolific source. And, as they take more definite
form and somewhat disengage themselves from the mass of
custom, the institutions do not lose, but carry with them, that
approval and that conviction as to their indispensability for
welfare that were accorded to the mores. Anything that is in
our mores is right, and so our institutions are the best. "The

SOCIETAL EVOLUTION 139

mores," says Sumner, again, "can make anything right and
prevent condemnation of anything." They are the approved
ways of meeting the conditions of living, and are developed,
accepted, and practiced without much intervention of reasoned
purpose.

They are to a society what, for example, density and color
of fur are to arctic animals ; namely, automatic adaptations to
environment. Life-conditions are present and society has to
live under them. This is rendered possible, or easy, or easier,
by adjustments in the manner of life or ways of living. Thus
we have a societal code characteristic, for instance, of the
arctics or of the tropics, of isolation or accessibility, of over-
population or under-population, of the country or of the city,
of peace or of war.

With this understanding as to the nature of custom, the
lowest terms of all of society's institutions, and knowing that
customs and institutions are adaptive to life-conditions, we are
now to inquire whether there are, acting upon the mores,
forces which are the counterparts of those productive of adap-
tation in the organic range. Are variation, selection, and
heredity, or factors which are their counterparts in the form
of evolution typical of human society, present and active in
the field? If so, what is their mode of operation?

The factor that leads off in any evolutionary process is varia-
tion. Without it all would be uniformity, equality, and change-
lessness. The existence of variation in custom and in custom-
born institutions is evident to anyone; demonstration of its
presence would consist in an endless rehearsal of obvious
detail.

Variation in the mores represents a series of tentatives, de-
parting more or less from the accepted code, that are struck
out upon by individuals in the pursuit of their interests. The
individual's function is that of an agency for variation. These
slight departures from the code are in evidence all the time; in

I40 THE EVOLUTION OF MAN

fact, the society's code is a sort of average or mean or type,
about which cluster the codes of classes, sects, and other larger
and smaller sub-groups. The individual may adhere to a num-
ber of these sub-groups, as his interests dictate. He may
belong, for instance, to the miners' union, the Baptist church,
the Socialist party, the Masonic lodge, at one and the same
time. When interests change, other and new codes may
appear, some of them departing widely in character, perhaps,
from the general or typical code of the society at large. In
general, the rise of such variations is a consequence of dis-
comfort under the prevailing code; interests strain toward a
better realization by way of change, small or great.

It is to be noted that variations upon customs and institu-
tions may exhibit a high degree of rationality. They may
represent true experimentation, because they may be set forth
consciously and deliberately, after intensive study of situations
and of societal laws, with the intention of securing more ex-
pedient adjustment of society to its life-conditions. But they
come to nothing — they do not get into the mores — unless there
is general concurrence in them. They remain stillborn unless
verification is immediate, concrete, and positive. Rational
variations — new details in the program of adjustment — are
presented in every age. Whether they are adopted or not is
another matter, for, as we shall see, there is not much of the
rational in the selective process, except as the latter is seen,
in retrospect, to have worked out expedient adjustments
through the action of human agencies inspired by the most
diverse and often irrelevant motives. If deliberate and plan-
ful action enters anywhere into the process of societal evolu-
tion, it is in connection with variation; for variation is, as we
have seen, very much in the competence of individuals, and it
is the individual, not the crowd, that will occasionally be found
to think in terms of society.

Among these variations, whatever their provenance, selec-

SOCIETAL EVOLUTION 141

tion takes place. Such variations may be short-lived and ex-
hibited by only a few, or there may be a concurrence of many
which carries them forward until, perhaps, the code of the
society at large has been profoundly modified. Some of the
variations live and some die out. Here is the fact of selection.
All through history, codes and institutions have appeared,
have persisted for a time, and have been altered or have
passed completely away. But the process of societal selection
is somewhat involved. I should prefer, for the moment,
merely to record its presence.

The remaining factor is heredity. It Is clear enough to
anyone that the mores are not inherited but learned — acquired
anew by each generation. Language is the best example : men
have used it time out of mind, but no one is ever born with
a command of it. Mores are also passed over from one group
of adults to another. Hence heredity is not present in the
societal range. But there is something there which discharges
essentially the same function and is a genuine counterpart.
Without variation, we have seen, all would be monotony and
changelessness; but without heredity or some factor similarly
conservative, all would be chaos and discontinuity. Even
social life is not altogether that; and it is not that because in it
too there operates a conservative factor.

Transmission of the mores is by tradition. What matter
if its channels are through the eye and ear, and not by way
of the germ-plasm? Tradition, like heredity, tends to repeat
the type. It is brought about through imitation, either spon-
taneous or induced. Spontaneous imitation is a natural ac-
tivity, common to animals and man, and especially marked,
among human beings, in the young. The receiver of the mores,
thus transmitted, wants to receive, and takes the initiative in
the transfer, as when the small boy apes his father. But such
acquisition is also capable of being induced, where there is no
likelihood that it will be spontaneous, by precept and disci-

142 THE EVOLUTION OF MAN

pline. This is education, in its broadest sense. The receiver
may be indifferent or even unwilling to receive, and the giver
commonly takes the initiative, as, for example, in the "uplift-
ing" of a "lower" race. Also, while spontaneous imitation
carries all the mores indiscriminately, education carries a more
or less wisely selected body of mores. It is clear that the
former is the more natural, elemental, impersonal, spontaneous,
and automatic process; the latter is effective as it succeeds in
reproducing the essentials, at least in semblance, of the former,
but in comparison it appears artificial. It involves, it has been
noted, an antecedent choice or selection from the main body
of the mores: we will teach the young certain things, and
others we will try to keep from them as long as possible. This
choice is supposed to be a reasoned and purposeful one; but
such a selection has little of the sureness and severe correct-
ness of an automatic selection.

These evolutionary factors are operative in the life of every
society, from the family group to the nation. And they do not
stop there. They are effective, on the grand scale, in the life
of human society as a whole. There is a world-code that has
been in process of formation with the establishment of prox-
imity between the nations; for that proximity, brought about
by the annihilation of distance, has meant altered conditions
of life for many societies; and variations that have been dem-
onstrated, under selection, to be expedient, have been trans-
mitted until enough mores have come to be held in common
by all, or nearly all, to justify the term "international code"
or "world-code." Variations around this code, or in departure
from it, may now be originated by a whole nation, and sub-
mitted for world-wide acceptance or rejection. Slavery, for
example, has been rejected, while democracy has widened its
range. And of late has stood forth Germany, as champion of
a code that is still undergoing the ordeal of selection. These
national variations on the world-code cannot be tested up as

SOCIETAL EVOLUTION 143

soon as, or shortly after, they appear — as Mormonism was
tested up on the American national code — and the process of
selection is the more imposing when it comes. We turn now to
a survey of the essentials of the selective process.

It is about the factor of selection and its operation that the
students and experts, genuine or alleged, in the social sciences,
are at considerable variance. Few would dispute the opera-
tion of variation and transmission; hence I have reserved the
contentious topic of selection for special consideration. And
first let us be clear as to what "selection" means. The ordi-
nary use of the word conveys the idea of picking out some-
thing desirable or good from a collection of things not so good
or not so desirable. Such a conception of selection is a posi-
tive one. But that conception ought not to be carried over to
color either natural selection or societal selection. The truth
of it is that it is the unfit animals and plants which are selected
— for death — and it is incidental to that process that we have
a "survival of the fittest." It is the inexpedient custom that is
selected — for disappearance — and it is incidental to that even-
tuality that the more expedient custom or institution survives.
The useful conception of selection is therefore a negative one.
If one does not get this firmly into his head, he is likely to be
looking, in the primitive way, for some benign or malign
agency where only impersonal natural or societal law prevails.

To attain to selection there is need of struggle and competi-
tion. It is not by discussion nor by guesswork nor by soulful
yearning that the relative speed of several runners is settled;
it is by a race. In nature there is the struggle for existence,
and plant or animal forms succumb under it. Well, the life
of societies also has been characterized by perennial struggle.
It is sometimes to the death, and under such circumstances
the selection is sharp and decisive, as it is in nature. Again,
however, failure in the societal struggle is not visited by such
dire penalties. Competition between societies runs all the way

144 THE EVOLUTION OF MAN

from wars of annihilation to rivalries in things of the spirit.
The degrees of intensity of selection among the mores corre-
spond to the degrees of violence and decisiveness in this com-
petition.

The ultimate form of societal selection — one from which
there is no appeal — is the war of annihilation. It was the
tribunal before which all the earhest and most important
collisions in societal policy were settled. War is still the court
of last appeal when all milder forms of settlement have, as in
the year 19 14, failed. It is not supposed to involve annihila-
tion nowadays, though, as the popular fancy noted, the treat-
ment accorded Belgium and northern France savored of Attila
the Hun.

Of course the mores do not fight each other, though we say,
figuratively, that Protestantism fought Catholicism, or that
there is a warfare between religion and science. It is not the
codes of mores that fight; it is the men practicing the codes
who do that. But the codes rise and fall with the successes of
their sponsors in the competition. If a tribe that practices
cannibalism comes into collision with another which abhors
the custom, and is overcome, there is not likely to be much
anthropophagy in that region for some time. For even if
the conquered cannibals are not massacred, but enslaved, they
lose, along with their power, their self-determination in the
matter of their code. I think it will be clear, upon reflection,
that great wars generally issue in so-called "new eras," "new
worlds," or "new dispensations," which mean new codes of
adjustment.

In the course of time the minor collisions of codes have
come to be settled without much or any bloodshed. Enlight-
ened states refuse to concern themselves much about the reli-
gious beliefs of their constituent groups, where once execution
and persecution were rife. Revolutions have been tamed down
into elections. Commercial and industrial warfare is carried

SOCIETAL EVOLUTION 145

on at the polls. Ballots replace bullets. But selection goes on
just the same, so long as there is a competition, with winners
and losers. Bagehot^ has an important chapter on the "Age
of Discussion," from which it appears that the voice and the
pen have somewhat ousted the sword in the settlement of
codes and policies.

This is not the place to go fully into the various forms taken
by societal selection. It is plain enough, however, that there
are plenty of them. It is only because they are so much a
matter of course, being registered daily in the press for anyone
whose attention has been called to their bearing upon societal
evolution, that it sometimes comes as a shock, especially since
we are nourished so largely upon romance and phantasms, to
see that competition is always the indispensable precondition to
development. If we think we have got on since primitive
times, we may set it down to the diversities produced by varia-
tion and shown up in the incessant conflicts between men ad-
hering to their differing codes. There is no fault to be found
with the effort to minimize the tragedies of competition by
setting up rules of the game ; but those who dream of universal
equalization, communalization, and pacification are proposing
to abandon the agencies which have brought us from savagery
to the civilization which we now acclaim.

The recurrent dispute about societal selection is as to
whether or not men deliberately plan out and realize society's
destiny. The plants and animals are supposed by most people
to be under the sway of a vast force which they can in no way
control ; natural selection is thought to operate over them and
to determine their destiny, as it were, from without. So far as
they are concerned, they seem to be totally unconscious of
what is going on, and have no say about their own destiny.
But men do not like to believe that about themselves, nor about
the nation to which they belong, nor even about the human

7 Bagehot, W., "Physics and politics," 1902, ch. V.

146 THE EVOLUTION OF MAN

race. They like to think that a people chooses its paths and
policies, and consciously and purposefully advances toward
some selected end. They make much of what might be called
a rational selection by a people between codes and policies pre-
sented to them for adjudication. The country is figured as
thinking things out for the country's welfare, as sifting evi-
dence and being intellectually persuaded as to this and that.
It seems to be assumed that '^he people" can think in terms
of a nation and will form a public opinion that operates as
intelligent self-direction.

Most of this sort of contention is myth-making, like the
philosopher's picture of the ''noble savage" — he never having
seen one. Perhaps some rare statesman may rise to the power
of thinking in terms of high generality; but it is at his peril,
at least during his lifetime, that he tries to realize those
thoughts. Lofty talk is appreciated, but action on the basis
of wide generalization is repellent, as "unpractical" or "ideal-
istic." Long after his death, such a statesman may get a
statue ; but that will be in consequence of the verdict of history,
arrived at when the heat and passion have died down.

What moves men — the masses of men, whose numbers,
social bulk, and formidable inertia are commonly left out of
adequate account by theorists — is not thought, but emotion.
And what sets emotion going is interest. And the circle of
interest is, for most men, very narrow and very closely drawn
around one's self. What sets the revolutions in motion, with
the result of drastic selection in the codes, is not the cerebration
of anyone over great issues, but the unendurable discomfort
and awakened emotions of the masses. Their interests have
been so outraged that anything seems likely to be better than
the present. Hence a passion to overturn things and take a
new start. It is the opportunity of the agitator, for misery is
indefinitely credulous — hopelessly thoughtless — never intellec-
tual and analytical. The "quadrennial revolution" or "bi-

SOCIETAL EVOLUTION 147

ennlal revolution," as an American election has been called,
is a conflict of interests rather than one of state-craft: debtors
versus creditors, ins versus outs. How can the masses pass
intelligently on an issue like that of the tariff or the gold
standard, when it takes a super-expert to understand them?
Add to this the thick-and-thin adherence to party, the shufflings
and compromises of leaders, the personal animosities, the cam-
paign of emotional propaganda, and what becomes of the
election as an agency of rational selection between proposed
adjustments to the nation's life-conditions?

The fact is that there are a number of phases of any nation's
code which are beyond the pale even of criticism; reason is not
invited to scrutinize them, and if it attempts to do so, it is
roughly bidden to desist. There are plenty of details in any
code of mores which we cling to with as deep emotion as the
savage shows for his medicine-bag, and which it would be
sacrilege to submit to the searchlngs of reason. One cannot
expect rational selection in the field of religion, nor of marriage
and the family. The Mohammedan is not ready to analyze
the merits and demerits of Islam, and abide by the results; nor
the monogamist to make a cold-blooded study of the merits
and demerits of pair-marriage. The people love one public
figure, and overlook or smile at his defects ; they hate another,
and jeer at or misrepresent his virtues. Where feeling is
strong, reason counts for little. It is cynically said that the
chief function of the human mind is to think up reasons for
doing what one wants to do, or to find good reasons for having
done what one wanted to do.

These considerations may seem dismal to one who would
like to believe that men think out society's destiny; but they do
not seem discouraging to one who believes that the operation
of the big, impersonal, automatically working forces always
gets truer results than do the feeble powers of the human
mind; that natural law is far more reliable than men's enact-

148 THE EVOLUTION OF MAN

ments. Most men would make hopeless errors In the piloting
of society. But they are generally pretty clear as to their
immediate personal interests. If these interests are in the
hands of the interested — if people are minding their own
business — they are in the custody of precisely those who are
best capable of handling them. People with common interests
make common cause and form competing groups; and out of
the competition of such groups selection affecting the destiny
of the whole society is bound to come.

It is bound also, in the long run, to result in adjustment.
It is by such automatic, unplanned selection that all that we
call improvement in adjustment has come to pass. The big
man is the individual who correctly diagnoses the trend of
events and rides In upon a wave of public opinion formed
under a variety of motives which are often totally irrelevant to
the results attained. That a wave of public opinion shall be
raised, It is necessary that there shall exist a popular dis-
content, or irritability that can be excited to express Itself in
action, and, given this condition, it is necessary to fit the appeal
to the variety of interests involved — interests which will be
found to be for the most part personal, local, and but slightly
or not at all relevant to any central principles. Masses of
men do not look critically into the rational merits of a case.
In this country, for instance, it is generally assumed that dis-
comfort is due to governmental inefficiency or worse, and
therefore hard times are likely to result in the upset of an
administration. The process by ex parte conviction and snap-
judgment is natural enough, and is shocking to those only who
revolt at seeing things as they are.

It will be a long time before public opinion will form itself
deliberately upon thought In terms of society. Few can en-
visage so large and complex a thing. The eugenists seem to
hope that people will come to mate or refrain from mating
with the interests of future generations in mind; but only the

SOCIETAL EVOLUTION 149

very enlightened few can be imagined as so doing. Human
beings act upon interest as they see it; and interests are bound,
for the masses of mankind (who must do the selecting that is
done), to be narrowly circumscribed.

That this is a counsel of despair is nothing against it, if it
is true. But it is not such a counsel. Societal evolution is a
vast process, where the forces are massive and act with un-
hurried deliberation, endlessly interlocking, within a spacious
field. There are dim ages of the process behind us, and ages
untold yet to come. Selection occurs at every stage, and is
but an episode along the course.

How then can men do anything, if all Is determined by such
cosmic power? Why struggle? Well, man can do something
with gravitation, with the expansive power of steam, with the
germ-plasm stream, although he can control the processes
themselves in no degree. He can move things about, into the
path or out of the path of natural forces. He can fix the mill-
wheel beneath the falling water. He can place the cylinder in
the way of the steam. He can isolate or bring together the
sexes of animals. This has been done so successfully for
man's interests and welfare that man has conceived the idea
that he is master of nature. But what he has done is to learn
nature's ways and adapt his action to them. At a pinch he is
nature's plaything and victim: the earth shakes a little, and
his great works collapse; the volcano spills a little gas over
its crater-rim upon a town, and the lords of nature lay them
down and are still.

It is not otherwise with the elemental forces of the societal
realm. They cannot be mastered; they must be studied and
known and adjusted to, as a condition of societal well-being.
The efforts of many a would-be benefactor and upllfter of the
race are sterile or even harmful because he is trying to do
what he would realize, if he knew what a society is, and what
can and cannot be done with it, to be out of the question.

I50 THE EVOLUTION OF MAN

Every one knows that water will not run uphill; yet in the
societal realm there have been plenty of well-meaning people,
through the ages, who have worn out and wasted their lives
in unhappiness, trying ineffectually to overcome a societal
tendency and law which are equally inevitable. If an ignora-
mus plays about in a chemical laboratory, we keep our dis-
tance, for we expect trouble as a result of ignorance of chemical
substances and laws. Knowledge of the experimenter's good
intentions or orthodoxy does not reassure us at all. But we
easily permit the uninformed meddler to prowl about the
structure of society, poking and tinkering, apparently in the
belief that, provided his intentions are good, nothing but
human weal can result. We are bound to learn, sometime,
that powerful forces are at work within the societal range, and
that ignorant tampering is even more dangerous here than
elsewhere because so many more people have to endure the
consequences. Then we shall want more knowledge of these
forces, that we may adjust to them.

Intelligent adjustment to the known inevitable is as rare
on earth as automatic adjustment to the unknown inevitable
is common. But the former is an abridged and less painful
process. Adaptation is sure, because it is the condition of
comfort and of life itself. Adaptability is that which hurries
and eases the process. Of all earthly things that which pos-
sesses the supreme capacity for swift adaptation is the human
mind. But that capacity is undeveloped, fettered in its action
by pseudo-knowledge, bias, caprice, and sentimentality — except
where tests and verification are immediate and conclusive, and
where, therefore, knowledge is almost automatically acquired.
Nowhere is real knowledge and science so little in intelligent
demand as in the societal realm, for the latter is self-sown to
whims and dreams of all varieties. It is thought that man can
here have his own will; here, at last and at least, he is lord.
He senses no elemental powers in the field. Here, of all places,

SOCIETAL EVOLUTION 151

he needs but to plan and "create" ; pass resolutions and regula-
tions; think out Utopias in bed and then rise and gird himself
to their realization ; abolish property, or the family, or govern-
ment, or religion. Naturally he is taken by the theory that
societal evolution is by individual purposeful action. Naturally
he regards insistence upon the control exerted by spontaneous,
automatic, and impersonal forces as an assault upon his "free
will."

Sometimes, in a crisis, the verities stand forth and enforce
to themselves an attention which they do not get in ordinary
times. Many people have been for some time perplexed and
in weak despair because their comfortable little formulas have
cracked and broken under the weight of explanation laid upon
them. Perhaps it is a favorable occasion to offer the conten-
tion that "social theory" is not wholly academic after all.

I

CHAPTER VI
THE TREND OF EVOLUTION^

EDWIN GRANT CONKLIN

PROFESSOR OF BIOLOGY, PRINCETON UNIVERSITY

If In the manner of the Olympian gods we mortals could
have viewed from some exalted place the grandest drama
which has ever unfolded itself on this planet, namely, the
origin and evolution of life, and if In the manner of the modern
"movie" we could have seen this drama speeded up so as to
bring the whole of it within the sight and experience of any
one person, with what surprise should we have watched the
marvelous appearances and transformations which at almost
every step have marked Its progress, and how utterly impos-
sible it would have been to have predicted Its future course or
from Its small and weak beginnings to have foreseen its mag-
nificent developments, its tragic failures, its stupendous suc-
cesses ! What merely human intellect could have foreseen In
those earliest protoplasmic particles *'the promise and potency
of all life," the million species of animals and plants, the
monsters of the deep, the giant saurians, the mighty beasts,
and finally man? Who could have predicted the marvelous
adaptations for nutrition, locomotion, offense and defense
reproduction, sensation, and coordination? Who could have
foretold from the earliest reactions of this primeval proto-
plasm the complicated and subtle behavior of plants and ani-
mals and men? Who could have foreseen in these reactions

1 A portion of this chapter appeared in the Yale Reineiv for July, 1922.

THE TREND OF EVOLUTION 153

the development of an intellect capable of studying or appre-
ciating, even to the extent of wondering at, this marvelous
drama? Who could have foreseen in the earliest stages of
the association and dependence of individuals the future socie-
ties of ants or bees or men? Indeed, who at any stage in this
greatest drama of all time could have predicted the next scene,
much less the final ending?

If to human intellect every former stage in this process
would have been unpredictable, what likelihood is there that
future stages may be predicted? Surely these considerations
should weigh heavily with anyone who attempts to forecast
even the next step in evolution and they should make it plain
that the final outcome is almost as completely hidden from us
as it was from the original amoeba.

But in evolution, as in the succession of generations of indi-
viduals, there have been cycles which have repeated again and
again particular principles, problems, and solutions, just as
one theme may form the groundwork of a great symphony.
All that has been said of the impossibility of predicting the
course and outcome of evolution could have been said with
equal accuracy of the development of an individual. Who
that had not before witnessed the process of development
could possibly see in an egg the promise and potency of all
that will develop out of it, — the complicated body, the remark-
able instincts, the emotions, intelligence, and consciousness, — in
short, the personality of a human being? But, owing to the
fact that this process of development repeats itself again and
again with slight variations, it is possible to predict its general
course and outcome though not always its particular details.
And so in the case of evolution we find that certain principles
and cycles repeat themselves again and again and they make
it possible to foresee at least dimly and in ghostly outline the
mighty shadows and shapes of the future.

It is in this spirit only and not with the vain imagining that

154 THE EVOLUTION OF MAN

any human being can predict particular events that depend
upon so many factors as are involved in the development of
an individual or the evolution of a race, that I venture to
direct your attention to the trend of human evolution.

Causes and Directions of Past Evolution

And first it is necessary to consider the chief causes of evo-
lution in the past and the most important paths which it has
followed, for there is no way of looking into the future except
by the light of the past. Unfortunately our knowledge of
the causes of evolution is not very complete, but the majority
of biologists agree that inherited variations, or mutations,
constitute the building materials of evolution, while natural
selection, or the elimination of the unfit, is the workman or
architect that selects or rejects these materials.

Inheritance and Variation. In order to be of any evolution-
ary value a variation must be inherited. Thousands of varia-
tions occur in organisms which are not inherited; they come
with changes in food, climate, use or disuse or other conditions
of environment and when these conditions change they disap-
pear. These environmental variations are known as ^'fluctua-
tions"; they represent changes in development rather than in
heredity, modifications of the developed organism rather than
of the germ-plasm. On the other hand, inherited variations
are caused by changes in the germ-plasm itself. These changes
may be of two kinds, ( i ) those which are due to new com-
binations or recombinations of old inheritance factors, or what
is known as "Mendelism," and (2) those which are caused by
sudden alterations in the individual factors or genes, such
transformations being known as "mutations."

Formerly these three types of variation, namely, fluctuations,
Mendelian combinations, and mutations, were not clearly dis-
tinguished, and Darwin assumed that all kinds of variation

I

THE TREND OF EVOLUTION 155

might be of evolutionary value. We now know that fluctua-
tions have no evolutionary value; Mendelian combinations
probably play a secondary part in supplying the materials of
evolution, though this part is not negligible ; mutations, on the
other hand, are the fundamental and initial steps in evolution.
Fluctuations and new Mendelian combinations occur in count-
less numbers ; indeed, they may be said to be universally present
among organisms; mutations, on the contrary, are relatively
rare. Nevertheless, they are by no means uncommon; during
the past dozen years Professor T. H. Morgan and his asso-
ciates have found and studied about four hundred mutations
in the pomace fly, Drosophila; few of these were beneficial
changes and almost all of them would have disappeared in a
state of nature, but this probably indicates that natural species
and varieties are the products of very severe selection, that
thousands of mutations have been eliminated where one or a
few survive. Many of our numerous breeds of domestic ani-
mals and cultivated plants have appeared as mutations, and
while we cannot assume that all that have been preserved are
intrinsically useful nor that all useful mutations have been pre-
served, the great number of breeds that have arisen among
domestic animals and cultivated plants indicates that useful
mutations occur in suflicient numbers to furnish the materials
for evolution.

There can be no question that the same fundamental prin-
ciples are involved in the evolution of man as in the evolution
of any other organism. Inheritance and variation, fluctua-
tions, Mendelian combinations, and mutations occur in the
human race, just as in plants and animals. Furthermore, there
is good evidence that this is true not merely of the body but
also of the mind and society of man. The fundamental prin-
ciples in all kinds of evolution are similar and if mutations and
new Mendelian combinations, but not fluctuations, are the ma-
terials of physical evolution, and natural selection is the

156 THE EVOLUTION OF MAN

builder, it is altogether probable that the same is true of intel-
lectual and social evolution.

Mutations and Their Causes. Regarding the causes of mu-
tations we know very little, but it seems logically necessary to
assume that these causes are both intrinsic in the germ-plasm
and extrinsic in the environment; or, in the language of Dar-
win, "Although every variation is either directly or indirectly
caused by some change in the surrounding conditions, we must
never forget that the nature of the organization acted upon
essentially governs the results." The same outer conditions
acting upon different species or individuals produce different
results and the possibilities of evolution are always limited by
the organization of the germ-plasm. Some conceivable muta-
tions do not and cannot appear because of these limitations.
"Whales never produce feathers, nor birds whalebone," said
Huxley; and probably no one ever really saw a green horse or
a purple cow. But, although mutations cannot take place in
all conceivable directions, there is no justification, in recent
experimental work, for extreme views of orthogenesis which
regard mutations as taking place in only a single direction.
Furthermore, an extensive study of mutations shows that they
are as frequently injurious as beneficial; indeed they are rarely
as well fitted for existence as the stock from which they come.

It is highly probable that mutations take place in response
to changes in environment, but it is necessary to remember
that the environment of the germ-plasm is not merely the outer
world but also the inner environment of the body organs and
fluids and cells, and the innermost environment of the cyto-
plasmic and nuclear substances which surround the inheritance
factors or genes.

Inheritance of Acquired Characters. But in spite of the fact
that mutations probably occur in response to changes in the
inner or outer environment, it is practically certain that modi-
fications or fluctuations of developed organisms are not trans-

THE TREND OF EVOLUTION 157

mitted to the germ cells so as to reappear in the next genera-
tion. In short, there is no inheritance of specific characters
acquired by the soma. Evolutionary changes do not first
occur in developed organisms and then by some mysterious
process get into the germ-plasm, but evolution consists in an
evolution of germ-plasm which then manifests itself in the
developed organism.

It is known as a matter of fact that acquired somatic char-
acters are not usually, if ever, inherited. Environment, train-
ing, education, may greatly modify glands, muscles, nerves, and
brains, but they do not change the germ-plasm so as to produce
these identical modifications in the next generation. In a few
instances it seems probable that chemical substances in the
bodies of parents, such as hormones, or anti-bodies, may in-
fluence the germ cells or developing embryos so as to produce
bodily changes in offspring similar to those in the parents, but
in general it may be said that there is no satisfactory evidence
that the specific modifications of development, due to particular
conditions of life, enter into the germ-plasm and appear again
in the next generation, in the absence of the environment which
first called them forth. In short, the effects on development
of environment, training, and education are not inherited
through the germ cells and the hope of permanently improving
the human race, or any other species, in this manner can only
lead to disappointment and failure.

Social Inheritance. At the same time it must be remem-
bered that man transmits to his descendants not only a par-
ticular germ-plasm which determines bodily qualities and men-
tal capacities, but he also hands down through language, edu-
cation, and customs, his own acquirements, experiences, and
possessions as well as those of former generations. This has
been called "social inheritance" to distinguish it from "ger-
minal inheritance"; it is inheritance in the legal rather than in
the biological sense. In this sense we have inherited from our

158 THE EVOLUTION OF MAN

ancestors language, literature, science, property, customs, in-
stitutions. These are no part of our germ-plasm, nor even
of our blood and brain, but rather of our environment. Be-
cause of this social inheritance society may advance from age
to age, each generation starting where the preceding one
ended, as in a relay race, — whereas in our germinal inherit-
ance each generation begins where the previous one began,
namely from an egg cell, and the whole course of development
must be repeated in each generation. Civilization is the re-
sult of the accumulations of social inheritance, and the future
progress of society must depend largely upon this capacity of
profiting by the experiences of former generations.

Natural Selection. If mutations are the materials, natural
selection is the architect and director of evolution, for although
it does not originate fitness it continually eliminates the unfit
and in the long run preserves only the fit. In certain quarters
it has been fashionable of late to decry the importance of
natural selection, but more and more, biologists are coming
to recognize that it is the most important directing and per-
fecting factor in evolution.

Natural selection in its widest meaning involves not merely
the overproduction of individuals and the consequent struggle
for existence with elimination of the unfit, as Darwin formu-
lated it, but it also includes the overproduction of many vital
activities, such as motions and reactions, with the elimination
of the unfit, as in the process known as "trial and error."
Thus useful behavior is the residue left after useless responses
are eliminated, and it is not necessary to hold with Darwin
that fitness is always the result of the elimination of unfit
persons. It is often the result of the elimination of unfit re-
actions. In short, natural selection is not only personal but
also intra-personal.

Furthermore there are many kinds of fitness not only for
different environments but also for different organisms and

THE TREND OF EVOLUTION 159

lines of evolution. Physical, intellectual, and social fitness are
very different things, and it is possible to have any one of
these without the other two. The past evolution of the human
race has been guided by the elimination of the unfit, whether
physical, intellectual, or social, and the future progress of the
race must depend on this same process.

The Paths of Progress. Even a cursory study of the living
world would justify the opinion that evolution has proceeded
in all possible directions; crab-like it moves forward, back-
ward, and sidewise. This is especially true of the minor
stages of evolution represented by mutations, for these ap-
parently occur in all directions without reference to their utility
or inutility; however, in order to survive and become estab-
lished, a mutation must run the gauntlet of natural selection
and injurious mutations are eliminated. Much more is this
true of species and larger groups which have had a longer and
more severe trial than mutations and are consequently
peculiarly adapted to their environments. In particular in-
stances simplification and degeneration have occurred but in
the main evolution has been progressive, that is, it is marked
by increasing complexity of structures, functions, and adapta-
tions, just as development from the egg to the adult is gener-
ally progressive, though in some instances and stages it is
retrogressive. Particularly when one surveys the whole course
of phylogeny or ontogeny it is evident that there has been
progress from relative simplicity to complexity.

Definition of Progress. The very word "progress" calls
forth a reaction from some people not unlike their response
during the war to the word Kiiltur. A few persons seem
to deny the existence of any such thing as progress, while others
insist that it is too indefinite to admit of any formulation.
Undoubtedly progress may occur in many different directions
and toward different goals, but everywhere and always in the
living world, it has certain fundamental characteristics. As is

i6o THE EVOLUTION OF MAN

generally true in complex phenomena It is best defined in terms
of causes rather than of results.

Everywhere in the living world, progress is brought about
by increasing specialization and cooperation, or, in the lan-
guage of biology, by increasing differentiation and integration.
Whether it be the development of an egg into an adult, the
evolution of primitive animals and plants into their more com-
plex descendants, or the development and evolution of the
body, mind, and society of man, progress everywhere is caused
by increasing specialization and cooperation. In the develop-
ment of an egg, which is the symbol and epitome of all prog-
ress, there is segregation of different structures and functions
in different cells and parts of the body, that is, there is mor-
phological division of substance and physiological division of
labor, and at the same time there is increasing perfection of
functions and adaptations. In the evolution of limbs or eyes
or brains there is a similar increase in the complexity of differ-
entiation and integration. In both the ontogenetic and the
phylogenetic development of intellect and of society, there is
increasing complexity and perfection of function and adapta-
tion. All kinds of progress, whether of body, mind, society,
art, industry, or science, are marked by increasing specializa-
tion and cooperation. As thus defined, progress may lead in
different directions to very different ends, as is shown in the
various types of locomotion, offense and defense, sense organs,
nervous systems, etc., found in the animal kingdom. In man it
has led to increased cranial and intellectual capacity, increased
control over environment and greater freedom, increased size
and complexity of social units, etc. But progress in each of
these many paths is caused by increasing complexity and per-
fection of specialization and cooperation.

Limits of Progress. Biological progress, however, always
has its limits; sooner or later differentiation reaches a stage
beyond which it cannot go without destroying the internal

THE TREND OF EVOLUTION i6i

balance, or integration, and the adaptability to external condi-
tions. Furthermore, in the higher types of organization the
mutual dependence of parts becomes so great that when one
of these is injured or breaks down it carries with it to destruc-
tion the entire organism. As Professor Minot used to say,
''Death is the price we pay for our differentiation." Germ
cells and embryonic cells are potentially immortal, but tissue
cells are not self-sustaining and the more highly they are dif-
ferentiated the greater is their dependence and the more
certain is their ultimate death.

The record of the rocks is full of instances in which groups
of organisms have progressed to greater and greater com-
plexity and have then become extinct. The roads of progress
are strewn with the remains of creatures fearfully and won-
derfully specialized, but which were unable to preserve inter-
nal balance or to adapt themselves to new environments and
which therefore perished. Indeed, in practically every instance
the road of ever increasing progress ends in extinction. But
just as in the succession of generations highly differentiated
cells and individuals die and new generations arise from rela-
tively undifferentiated eggs, so when highly differentiated
species become extinct new lines of progress start from gen-
eralized rather than from highly specialized types.

It is of course conceivable that differentiation might go on
indefinitely in any line, the elephant might get a longer trunk,
the giraffe a longer neck, and man a larger and larger brain,
but while such things are conceivable they are not practicable
for the reasons named. In any line of evolution progress is
most rapid at first and then it gradually slows down until it
stops, and in every well-tried path of evolution, progress has
practically come to an end; further progress, if it occurs, must
be in new lines and from relatively undifferentiated stock.

Progressive Evolution of Man. There have been three
main lines of human evolution, — physical, intellectual, social, —

1 62 THE EVOLUTION OF MAN

and it is generally assumed that in each of these lines we may
look forward to endless progress. The infinite perfectability
of man is a fundamental article of faith with many people,
and yet all biological evidence indicates that it is not supported
by fact. Not only the history of other organisms but also that
of man himself indicates that progress in any particular line
is limited.

In bodily evolution man has made no very marked progress
during the last twenty thousand years at least. Undoubtedly
there have been minor changes in the human body, probably an
increasing resistance to certain diseases due to the elimination
of those persons who were more susceptible, as well as certain
degenerative changes in sense organs, hair, teeth, and toes;
but such changes are insignificant when compared with those
which marked the transition from pre-human ancestors to man,
or even those changes which brought about the differentiation
of the primary races of mankind. The physical evolution of
man has slowed down almost to a' standstill, and if it is to go
forward again it will probably be in new lines and in response
to new and very different environmental conditions.

The opinion is widely held that intellectual evolution is
advancing rapidly and in justification of this belief is instanced
our increasing knowledge of the world and of man. But it
is necessary to distinguish between intellect and knowledge,
between the capacity for knowing and things known. Un-
doubtedly we know many more things than the ancients or
even than our own parents, but has there been any increase in
intellect comparable with the increase in knowledge which has
marked the last few centuries? On the contrary, those who
have devoted much attention to this subject are of the opinion
that no modern race is intellectually equal to the ancient Greek
race. Not only did this race produce a larger number of illus-
trious men than has any other race during an equal period of

THE TREND OF EVOLUTION 163

time but the general intelligence of the citizens was probably
higher than in any modern nation.

Undoubtedly popular education brings to light many per-
sons of marked intellectual capacity who in former years might
have remained "mute, inglorious Miltons"; there are many
more opportunities to-day for discovering the inherited capaci-
ties of men than there were in ancient times, but anyone who
thinks that intellectual capacity is undergoing rapid evolution
needs to consider seriously the widespread emotionalism, irra-
tionalism, and superstition of this twentieth century of en-
lightenment as compared with the golden age of Greece in the
fourth or fifth century B. c. Indeed, since the times of the
Cro-Magnon race, probably twenty thousand years ago, there
has been no marked increase in man's cranial capacity, and
probably little or no increase in his inherent intellectual ability.
There are better opportunities to-day than ever before for the
development of the individual but the intellectual evolution
of the race, no less than the physical, has slowed down until it
has practically stopped.

In human society, however, tremendous changes are taking
place and many of these are in the direction of progress. The
great advances in our knowledge of and control over nature,
which are such a distinctive feature of our present civiUzation,
are the results of cooperative effort. The developments of
science, literature, and art, of agriculture, industry, and com-
merce, of education, government, and religion, are the products
of increased specialization and cooperation of society. The
fact that social change is going on so much more rapidly than
either physical or mental evolution is due to the fact that past
experiences and acquired characters are handed down through
"social inheritance," but not through the germ-plasm. If we
consider those social changes only which are due to modifica-
tions of the germ-plasm, such as inherited instincts and capaci-
ties, we find that evolution is probably no more rapid in

1 64 THE EVOLUTION OF MAN

society than in the case of the body or mind of man. Within

historic times the social instincts of men have not changed

more fundamentally than their intellectual capacities or their

germ-plasm.

Unlike any other form of evolution, the rapid changes which
are taking place in human society are not due to changes in
germ-plasm, nor even to changes in the developed individual,
but merely to changes in environment. They are not even
skin-deep, they are only clothes-deep. It may be questioned
whether these changes are really evolutionary at all since they
do not involve changes in germinal inheritance, intellectual
capacity, or social instincts, but are merely the accumulation of
experiences from generation to generation, as an individual
accumulates knowledge from year to year. Indeed, the prog-
ress of human society is much more like the development of
an individual than it is like the evolution of a species.

But whether we regard social development as a form of
phylogeny or of ontogeny, as a result of inheritance or of
environment, we cannot fail to see that it is going forward at
a rapid rate and that it is fraught with the most stupendous
possibilities for the future. The only great progress which
the human race has made during the past twenty thousand
years has been social, and so far as we can now see into the
future the progressive evolution of mankind must depend to
a great extent upon society. It is particularly in the field of
discovery and invention that progress has been most notable.
Nothing could more strikingly illustrate this than the compari-
son of the state of the world one hundred years ago with that
of to-day. Whole regions of the universe have been explored,
the very existence of which was not dreamed of a generation
ago. Inventions which would seem incredible or magical were
they not so common are everyday conveniences. Diseases and
epidemics which were once regarded as the direct acts of an
inscrutable Providence or of unscrupulous demons are now

THE TREND OF EVOLUTION 165

prevented or controlled. All this notable progress in the con-
quest of nature is the result of cooperative effort. No one
person, however great his contributions, could have made any
important advance alone and unaided. Every discovery is
based upon many others which have gone before, and all civi-
lized countries and ages have contributed to the advancement
of knowledge. In short, progress during historic times has
not been in the individual but in the association of individuals,
not in the inherited capacities of persons but in the organiza-
tion of society.

Not only the direction of social evolution, but also the future
evolution of the body and mind of man will be determined to
a great extent by society. Progress through natural selection
is exceedingly slow and wasteful, intelligence is a great time-
saver as contrasted with ''trial and error," and intelligent arti-
ficial selection affords the most rapid and satisfactory means
for the improvement of the human race. There is no doubt
that mankind could, if it would, breed a more healthy, more
intelligent, more moral type than the general average of the
existing race. By means of artificial selection, requiring no
more intelligence than that which is now used in the breeding
of domestic animals, weakness of body, of mind, and of social
instincts could be largely eliminated, and the average of the
race could be raised to a level more nearly that of the best
existing individuals. To a large extent mankind will deter-
mine its own destiny on this planet. Whether it has wit enough
to save itself from the dangers which now threaten is a serious
question.

Present Conditions and Tendencies

Our watchers on Olympus would see in present conditions
and tendencies of the human race some promising prospects
but much cause for grave concern. Perhaps the conditions
which would cause most anxiety are the nullification or com-

1 66 THE EVOLUTION OF MAN

plete reversal by man of some of the most important principles
which have guided evolution in the past. For the first time in
the history of life upon the earth, a single species now has the
power of controlling to a large extent its own evolution, and
it has begun by radically changing some of the conditions of
progress which have prevailed hitherto. A large part of the
human race is now engaged in the most stupendous and dan-
gerous experimentation upon itself; without any adequate
knowledge of the mechanism of evolution it has begun to tinker
with that mechanism, throwing certain parts out of gear, de-
stroying others, and in general paying little or no attention to
the results.

Decreasing Influence of Natural Selection. In spite of some
notable exceptions, the leading biologists of the world agree
that natural selection has been the most important guiding
and perfecting principle in past evolution, and on the whole
it has made for progress. At every step in the past course of
evolution it has sifted the unfit from the fit, and while it has
not originated fitness, It has preserved it, and in general it has
directed evolution Into paths of progress by closing up other
paths. Those whose only conception of natural selection is
that of a Hfe and death struggle between individuals of the
same species may well rejoice that mankind Is to a certain
extent freed from this struggle, and that In human society
cooperation Is becoming a more Important means of progress
than competition. But natural selection in its widest sense
means the elimination of the unfit, whether these are reactions,
Instincts, customs, persons, races, or species; and if In human
society cooperation Is more beneficial than competition, co-
operation rather than competition will be favored by natural
selection. And In similar manner if intelligence Is more bene-
ficial than brute strength or cunning or instinct. Intelligence
will be favored. In short, there are many kinds of fitness in
different lines, and In the case of man, if natural selection were

THE TREND OF EVOLUTION 167

not interfered with, it would lead to the partial or complete
elimination not only of the physically unfit but also of those
who are mentally and socially unfit.

Of course man cannot wholly eradicate natural selection
from human life ; the most monstrous forms cannot possibly be
saved and the more abnormal they are the earlier they die; the
seriously defective rarely come to maturity or are capable of
reproduction and even those that survive and reproduce are
usually handicapped at every stage. Natural selection remains
and will probably ever remain an important factor in human
evolution, but just as far as is possible it is being minimized
or set aside in civilized states. In the finest fervor of altruism
and with the most extraordinary expenditure of money and
effort civilized society manages to save many of those who
are feeble in mind and body as well as criminals and enemies
of society. And no doubt much of good is gained in this way,
for not only are great minds and souls sometimes lodged in
frail bodies but it is probably more valuable to the race to pre-
serve a spirit of altruism and social justice than it is to rid
society of its degenerates by ruthless methods. Nevertheless,
neither justice nor altruism requires that such persons be per-
mitted to propagate their kind; lasting progress cannot be
based upon a one-sided development of body or mind; ideally,
as well as biologically, life and progress are balanced as it
were between many different forces, principles, and ends, and
neither physical, intellectual, nor social developments should
go so far as to destroy either of the others.

Galton says, ''Our human stock is far more weakly through
congenital imperfection than that of any other species of
animals, whether wild or domestic." It cannot be doubted that
this greater weakness and imperfection is due to failure to
eliminate the unfit, but there is no clear evidence as to whether
congenital physical degeneracy is increasing or decreasing at
the present time. Athletics, physical education, medicine, and

1 68 THE EVOLUTION OF MAN

sanitation have made great advances in recent years and this
has had a beneficial influence on the health and vigor of this
generation, but there is no satisfactory evidence that these
effects are inherited. The average length of life has been
increased, chiefly by saving the babies, but the maximum length
of Hfe has not been raised; men live no longer now than in
the time of Methuselah, and since longevity is hereditary, it
may well be that the artificial prolongation of the lives of those
who are hereditarily weak and short-lived may actually reduce
the natural longevity of the race as a whole.

Mental and moral degeneracy runs in families, as is proved
by such cases as the "Jukes," "Kalikaks," "Zeros," "Nams,"
"Ishmaels," etc., but social selection against such groups is
pretty severe and it does not seem probable that extreme de-
fectives of this class are increasing very rapidly. Inmates of
custodial institutions are usually prevented from having off-
spring and they do not greatly threaten racial standards; the
greatest danger comes from somewhat less defective indi-
viduals who are at large and are free to have as many children
as they can.

Retrogressive Selection of Civilization. Much worse than
this partial failure of natural selection is the retrogressive
selection of civilization. If society had deliberately set about
the propagation of the unfit it could hardly have devised
more effective means than many of those which are now in
vogue. Frequent wars have taken the best blood of. the na-
tions, and while casualties In modern battle are more or less
indiscriminate, soldiers represent a selected group; those who
go to war are usually the young, the strong, the capable, while
the weak. Incompetent, and degenerate are left behind as unfit
for military service. Furthermore, these casualties must be
doubled when their Influence on the race Is considered, for In
general every man killed leaves one woman unmated for life.
As a result of the last war millions of women can never marry

THE TREND OF EVOLUTION 169

or have children. Among these are some of the best human
stock the world possesses, — and thus the race is made poorer
for many generations to come. Enforced celibacy in many
religious orders and societies of scholars has led to the ex-
tinction of some of the world's most gifted lines. The present
customs of mate selection condemn many of the finest women
in the world to spinsterhood, while the feather-brained and
sexually-daring "flappers" readily find mates. On the other
hand, personal ambition and selfishness, the prevalence of
prostitution and illicit sexual relations, the fear of misalliances,
divorce, and alimony are potent causes of bachelorhood. In
both cases the results are that many of the best human lines
are wiped out. Galton has shown that on the average people
who marry at twenty-two will leave twice as many descendants
at the end of a century as those who marry at thirty-three and
in a few generations they will actually possess the earth. And
yet the increasing time required for education, as well as more
luxurious standards of living, have made early marriages
almost impossible among professional and business classes,
with whom the most vigorous and fertile years of the repro-
ductive period are years of sterility. Finally, luxury, soft
living, and selfishness have made children unwelcome among
many married people who have shown qualities of success in
life and whose hereditary traits are above the average. Under
such conditions the general average of intelligence and social
fitness in the race as a whole must inevitably decline.

There is an evident tendency to assortative mating in
modern society due not merely to similarity of social status
and ideals but also to the more potent factor of propinquity.
Generally men and women representing the extremes of the
social or intellectual scale do not marry and it has been claimed
that owing to this fact there is a constant tendency for society
to be split up into hereditary classes. Some authors maintain
that the more intelligent and the less intelligent elements of

I70 THE EVOLUTION OF MAN

society are separating more and more widely, that the success-
ful are being split off from the unsuccessful, and that, in gen-
eral, human society Is differentiating Into hereditary classes
owing to the tendency of like to mate with like. However,
when one considers the world as a whole, rather than a few
small social groups. It Is plain that any such tendency to form
hereditary classes is more than overbalanced by other factors.
The permanent stratification of society is prevented by the
rising of genius from the lower levels and the sinking of medi-
ocrity from the higher, by the boiling of the social melting pot,
by new mutations and Mendelian combinations, all of which
contribute to cast down the mighty from their seats and to
exalt those of low degree. In the past history of mankind
there have been many attempts to establish hereditary classes;
where now are the castes of rulers and slaves, statesmen and
soldiers, scholars and priests, craftsmen and farmers, of an-
cient Egypt, Assyria, Greece, and Rome, or even of medieval
Europe ? The instincts of the race as a whole are against the
establishment of such hereditary classes and in favor of demo-
cratic equality of opportunity, with social position dependent
upon individual merit rather than upon family name or class
privilege, and these instincts are probably sound both socially
and biologically.

Some advocates of eugenics have dreamed of the establish-
ment of an Intellectual aristocracy by the segregation and
intermarriage of the most highly gifted members of society,
such as the prize scholars in colleges and universities. No
doubt this could be accomplished if some power could bring
about such segregation and propagation, but unless these prize
scholars combined many excellent physical and social qualities
as well as mental ones such segregation would probably lead
to very unsatisfactory results. It would seem to be better for
prize scholars to marry prize athletes and thus preserve the

I

THE TREND OF EVOLUTION 171

general all-round excellence of the race, rather than to attempt
to develop an intellectual or social aristocracy.

Decreasing Birth-rate of Intellectual Classes. There is no
doubt that intellectual ability is an inherited trait, in spite of
the fact that great men have sometimes come from unknown
ancestors and unknown men from great ancestors. Mental
capacity probably depends upon a number of inheritance
factors, and occasionally each of two mediocre parents may
supply factors which the other lacks, thus giving rise to an
excellent combination which is the initial step in the production
of a great man; on the other hand, even superior parents may
sometimes furnish a bad combination of inheritance factors,
and the resulting child may be mediocre or inferior. But
Galton has shown that in an equal number of distinguished
and undistinguished families there are about five hundred times
as many chances that a distinguished man will come from the
former as from the latter. No doubt environment is an im-
portant factor in the development of intellect but the possi-
bilities of such development are marked out in the germ-plasm.
Superior intellectual ability is inherited no less than inferior
ability, genius no less than feeble-mindedness.

It is therefore most important for the intellectual progress
of the race that the more intelligent classes should increase
and multiply and that the less intelligent should be relatively
less fertile, — and yet the reverse of this is true. In spite of
individual exceptions, the graduates of our colleges and uni-
versities probably represent on the whole the most intelligent
portion of our population ; they have been sifted out from their
less gifted fellows by the grammar schools, high schools, and
colleges, until, on the average, they are a very highly selected
group. But this group is not perpetuating itself. The aver-
age number of children per graduate of Harvard and Yale
for the years 1 881-1890 was about 1.5. Up to the year 1901
the average per graduate of Vassar and Bryn Mawr was about

172 THE EVOLUTION OF MAN

.8, of Mt. Holyoke about .7, and of Smith College a little
less than .6. In other words, as Cattell says, the average
graduate of Harvard or Yale is the father of threq-fourths
of a son and the average graduate of the women's colleges
named is the mother of rather less than one half of a daughter.
The birth-rate among the members of the honor society, Phi
Beta Kappa, is much lower than that of the average graduates,
and in general it may be said that the higher the intellectual
attainments, the lower is the average birth-rate. This is true
not only of college graduates but of the more intelligent people
generally. Among American men of science, Cattell finds that
the birth-rate has decreased in a single generation from 4.66
per family to 2.22. Since in the general population it takes
an average of three or more children per family to preserve
present numbers, it will be seen that these highly selected lines
are dying out. And as rapidly as others of superior intelli-
gence rise out of the general population they also become rela-
tively infertile. Thus the intellectual cream of the race is
continually skimmed off, and it is a question how long it will
continue to rise.

There is great enthusiasm to-day among certain people, who
are generally childless, for small families; the race is to be
regenerated by birth control. But this "reform" begins among
those who, because of good hereditary traits, should have large
families. If only those who should not have children were to
practice birth control, it would be a blessing to mankind, but
there can be no doubt that thus far it has greatly reduced the
number of children among the intelligent and prudent classes,
without influencing to any extent the birth-rate among the
unintelligent and imprudent. Whether this result will be re-
versed In the future no one can predict. Alexander Graham
Bell believes that It will, in time, benefit the race by eliminating
those among the intelligent classes who are lacking in parental
instincts. Irving Fisher says there are three possibilities in

THE TREND OF EVOLUTION 173

birth control : ( i ) it may cause depopulation and ultimately
extinction of the human race; (2) it may reduce the repro-
duction of the prudent, intelligent, and ambitious, leaving the
imprudent and unintelligent; (3) it may cut off the strain of
the silly and selfish, the weak and inefficient. There is little
if any likelihood that the first of these possibilities will ever
be realized; depopulation may result in certain countries but it
will never become universal through birth control. The second
possibility is already an actuality so far as the reduction of the
birth-rate among the most progressive people is concerned.
It does not seem probable that the third possibility can greatly
benefit the race before much damage has been done by the
second. Of course if those who preach and practice birth
control are, when measured by the highest standards, silly,
selfish, weak, or inefficient to a greater degree than others,
then, and then only, is it working for the betterment of the
race. It seems incredible that people of good hereditary traits
should think that they can improve the human breed by com-
mitting racial suicide. ^'There be those which have made
themselves eunuchs for the kingdom of heaven's sake," but
when before in the history of the world have sane men made
themselves eunuchs in order to win the kingdom of the earth?
Those feminists who declare that they would rather die than
have children have made their choice between the only alter-
natives possible, — death to their lines and to their participa-
tion in the future of the race, or children.

But while the more progressive lines are, as a whole, dying
out, the general population of this country and of the world
is more than maintaining itself, and the less intelligent, inde-
pendent, and aggressive portions of the population are prob-
ably increasing most rapidly of all. Thus the Scriptures are
being fulfilled that *'the meek shall inherit the earth." It is
often said that a high birth-rate among the lower classes Is

174 THE EVOLUTION OF MAN

always offset by a high death-rate, but in civilized society this

Is by no means the case.

In a recent paper of great interest and importance, Pearl
has shown that the 'Vital index," that is, th'e ratio of births to
deaths within a given time, differs greatly in different elements
of our population; it is lowest among the old American stock,
and highest among the foreign-born population. In New Eng-
land and in New York State, the native population of native-
born parents produces only about .8 or .9 of a birth for each
death, while in the country at large "the native population
produces only a fraction over one baby for each death. In
other words, the native population . . . is in about the same
state as France before the war, and not in as vigorous a state
as the French population is now." As contrasted with this, he
says, "Generally speaking, the foreign population produces in
this country approximately two babies for every death."

In so far as this foreign population is equal in quality to the
native stock which it is replacing there is no cause for alarm in
this, and except for sentimental regrets on the part of the old
American stock, it may be welcomed as a rejuvenating factor,
but if this foreign stock is in the main inferior in quality to
that which it is replacing, then indeed is there cause for con-
cern.

Race Differentiation vs. Race Amalgamation. Another
important principle in past evolution which is being reversed in
the case of man is that of racial isolation and differentiation.
Since all types of mankind interbreed freely, it is evident that
distinct races could not have been established and perpetuated
except by the aid of isolation, chiefly geographical. On the
whole, race differentiation has made for progress; it has led
to the establishment of races peculiarly fitted to the environ-
ments in which they are found and it has favored the estab-
lishment of types superior in certain directions though they
may be inferior in others.

THE TREND OF EVOLUTION 175

However, with increasing means of communication, and as
a result of migration and commercial relations, there is no
longer complete geographical isolation of any people and the
various races of mankind are being brought into closer and
ever closer contact. Man is now engaged in undoing the work
of hundreds of centuries; if in the beginning God *'made of
one blood all nations of men," it is evident that man is now
making of all nations one blood. In the United States prac-
tically all the races of mankind are represented and a study of
the census returns shows that all the European races in this
country are being rapidly fused together. Pearl has recently
shown that from "one fourth to one half as many children are
produced in a given year from mixed matings (in which one
partner is American) as from strictly American-born persons.
Amalgamation of the immigrant elements into the previously
existing complex is certainly going on apace."

The ^'typical American" is the product of the fusion of
various European races and we, at least, believe that the re-
sults of such race mixtures are good. Even European races
are rarely if ever pure, but represent mixtures of many dif-
ferent stocks. If "pure" English, Irish, Scotch, Dutch, Ger-
man, Russian, French, Spanish, or Italian lines are traced
back only a few generations they are found to include many
foreign strains. The author of Robinson Crusoe wrote two
centuries ago of the "True-born Englishman" :

These are the heroes that despise the Dutch,
And rail at new-come foreigners so much;
Forgetting that themselves are all derived
From the most scoundrel race that ever lived;
A horrid crowd of rambling thieves and drones
Who ransacked kingdoms, and dispeopled towns;
The Pict, and painted Briton, treach'rous Scot,
By hunger, theft, and rapine, hither brought;

176 THE EVOLUTION OF MAN

Norwegian pirates, buccaneering Danes,
Whose red-haired offspring everywhere remains;
Who, join'd with Norman French, compound the breed
From whence your "true-born Englishmen" proceed.

Even the primary races of mankind are rapidly fusing in
many parts of the world. In the United States from 15 to 20
per cent of the total negro population of about 10,500,000 are
mulattoes and these are increasing more rapidly than the pure
blacks. In South American countries it has been estimated
that there are about 26,000,000 whites, Indians, and negroes,
and about 20,000,000 of mixed blood. In Australia and New
Zealand, after only a little more than a century of contact
with the whites, there are about as many "half castes'* as full-
blooded aborigines. Similar tendencies to amalgamation of
the primary races are found in Mexico, the West Indies,
Africa, Indo-China, the islands of the Pacific, and in other
parts of the world. It is said that there are no cases in his-
tory where two races, however different, have for long occu-
pied the same territory and yet have preserved their racial
purity. Even the Jews, who are a peculiarly separate and
distinct race, have received large admixtures of Gentile blood
in every country in which they have lived. Fishberg says that
in western Europe, America, and Australia from 25 to 50 per
cent of all Jews who marry, marry non-Jews.

If this movement goes on, as we have every reason to expect
that it will, it can only end in the more or less complete fusion
of existing races, and it needs only the vision that can look
ahead a few thousand years at most to see all races blended
into a common stream. What the results of such fusion may
be we can only guess, though its effects in ancient Egypt,
Greece, Italy, and more recently in various countries of
eastern Europe, the West Indies, Mexico, and South America
are by no means reassuring. Hybrids are not necessarily in-

THE TREND OF EVOLUTION 177

ferior, and they are sometimes superior to either of the parent
races. MendeHan inheritance holds good in the crossing of
human races as well as everywhere else and It leads to all
kinds of combinations of the qualities of the parents. Accord-
ingly some hybrids may be expected to show the bad qualities
of both parent races while others show the good qualities of
both, but it is practically certain that the general or average
result of the crossing of a better and a poorer race is to strike
a balance somewhere between the two.

If only good ore goes into the "melting pot" there is no
cause to fear for the result; and if those hybrids which com-
bine the good qualities of the parent races could be segregated
and bred, a race superior to any existing human type could
probably be established. This is just the method followed by
breeders in the production of improved races of plants and
animals, many of which are the products of deliberate hybridi-
zation. But the breeder ruthlessly eliminates inferior stock
and breeds only from the best, and If by some similar process
it were possible to eliminate from reproduction the inferior
racial combinations and to perpetuate the best, we might expect
to get from this great experiment in human hybridization a
very superior breed of men combining the good qualities of all
the constituent races. It seems very doubtful whether any such
result as this will ever be attained, and in the absence of such
selection and segregation the general result of race amalgama-
tion must be an averaging of the qualities of the parent races.

The character of a composite race will depend not only upon
the qualities but also upon the relative numbers of the races
which enter into it, and the latter will depend upon the present
numbers of existing races, their rate of Increase, cultural de-
velopment, and the habitable portions of the globe which they
control. In all of these respects the white races hold the lead,
followed in turn by the yellow, the brown, the black, and the
red races, and It is evident that unless the white races destroy

178 THE EVOLUTION OF MAN

one another, commit race suicide, or die at the top, they are
destined to furnish the principal contribution to the future
population of the globe.

The Limits of Population. Finally, the human population
of the world is rapidly approaching Its maximum — for while
populations tend to Increase continually the limits of the habi-
table globe remain fixed and the means of subsistence are sub-
ject to the law of diminishing returns. Pearl estimates that
within 200 years the population of the United States will have
reached its maximum of about 200,000,000. Alfred Marshall
calculates that the population of the entire world will have
reached its maximum of about 6,000,000,000 in 200 years.
These estimates assume that increase of population and of
means of subsistence will In the future conform to the same
mathematical formulae as hitherto, — an assumption that is
probably justified. If these estimates are correct the grand-
children or great-grandchildren of persons now living may see
the maximum population of this country, and perhaps of the
world, attained. Even if by means of greatly improved agri-
culture or by revolutionary scientific discoveries this time
should be doubled it would still be a relatively short period
before the limits of the possible population of the globe would
be reached. Thereafter the population will remain stationary,
either through increase of the death-rate or decrease of the
birth-rate. Under these conditions it is probable that both
natural and artificial selection will be intensified. It Is reason-
able to expect that on the whole natural selection will make
for progress and it does not seem probable that artificial means
of limiting population will continue to cut off the better stocks
and to favor the worse.

There is ground to hope, therefore, that in a crowded globe
both natural and artificial selection will make for the improve-
ment of the race, but such Improvement is likely to be slow and
painful. Natural selection, under various aspects, is still the

THE TREND OF EVOLUTION 179

most potent factor in directing evolution though it is extremely
slow in its action and excessively wasteful. There is reason to
hope that in the near future intelligent human selection may
cooperate with natural selection, thus rendering progress more
rapid and more merciful. Certainly eugenical education should
begin to bear fruit, — that is, more children of the better sort
and fewer of the worse variety, — within the next generation.
Unless it does we may be sure that the time will come when in
a crowded globe natural selection will reassert itself and there
will be a return to "nature's simple plan" of promoting fitness
by the ruthless elimination of the unfit.

The Immediate and the Distant Future

The Immediate Future. In the midst of all these condi-
tions and tendencies of the human race, — the decreasing in-
fluence of natural selection, the retrogressive selection of
civilization, the decreasing birth-rate of the more intelligent
classes, the Increasing amalgamation of races, the rapid ap-
proach of the time when the earth will be fully populated and
its natural resources exhausted or greatly diminished, — In the
whirl of all these changes it does not seem probable that human
evolution will long remain stationary. On the whole, It must
be admitted that these tendencies do not point to racial prog-
ress, and some of them presage retrogression, degeneration,
and decay unless they can be overcome.

There is much In the modern world that reminds one of the
period of decline of former civilizations, and especially of
Greece and Rome, and many persons have wondered whether
our civilization is not traveling the downward road to a similar
end. In both Greece and Rome the decline was preceded by
a large amount of race mixture, and a decreasing birth-rate
among the higher classes, while It remained relatively un-
changed elsewhere. Momsen says that the decay of Rome
was due mainly to **the difference between the fertility of the

i8o THE EVOLUTION OF MAN

higher and the poorer classes." Tenny Frank^ concludes that

In Nero's day, about 90 per cent of the plebeians on the streets

of Rome had oriental blood, while the whole Empire was a

"melting pot" In which the oriental was a large part of the

ore:

Race suicide curtailed the stock of the more sophisticated,
the aristocracy, and the rich. Before our day, only at Greece
and Rome was reproduction under rational control and there
the race went under. Of forty-five patricians In Caesar's day
only one is represented by posterity when Hadrian came to
power. Of the families of nearly four hundred senators re-
corded In 65 A. D. under Nero, all trace of a half is lost by
Nerva's day, a generation later. The voluntary choice of
childlessness accounts largely for the unparalleled condition —
and is probably the most important phase of the whole question
of the change of race.

A striking parallel to what Is found In most of the civilized
world to-day! Whatever may have been the causes of the
decline of former civilizations. It is plain that there were left
In other parts of the world strong human reserves that could
carry forward the standard of civilization which was dropped
by a dying race. But in a world where practically all western
nations are suffering from this sickness of civilization, and In
which racial amalgamation Is fusing all into a common type,
where are the reserves that can be rallied to the standard, if
civilization should again decay? If history should repeat
Itself and the western nations should go down as did Greece
and Rome, possibly Russia, or China, or Japan might take up
the banner and civilization once more begin Its westward
march around the world.

But there Is this important difference between present con-
ditions and those of any former age, — our knowledge of and

control over nature are vastly greater than ever before and the

i

^American Historical Revieiv, 21, 1916.

THE TREND OF EVOLUTION i8i

means of increasing and diffusing knowledge were never so
good as at present. If knowledge and education can save
the race the prospect is promising, for they were never before
so widespread; the possibilities of continued progress rest on
education, eugenics, and enlightened effort.

Education is the first and most important step in combating
these tendencies to racial decline. Assuming that the social
instincts of the major portion of mankind are sound and that
there is sufficient intelligence in the race at large to recognize
the dangers that threaten, it ought to be possible by education
to meet these dangers and overcome them. A more thorough
and widespread knowledge of the nature of man and of the
principles of heredity and development would lead to the
elimination of many of these dangers, for in the main we have
sinned through ignorance. Such knowledge would prevent the
importation and propagation of physical, mental, and moral
degenerates; it could prevent the amalgamation of better
races and families with poorer ones; it should increase the
number of good matings and of superior children; and it
should make human life healthier, happier, more rational, and
more efficient. Whatever good may come to the race through
better legislation, sanitation, eugenics, or euthenics will be
made possible by better education.

What part eugenics may play in the betterment of the hu-
man race cannot now be foreseen. There is no doubt that, by
means of a thoroughgoing system of eugenics, feebleness of
• body and of mind could be largely reduced and the race as a
whole made more healthful and intelligent; in short, the gen-
eral average of the race could be raised more nearly to the
level of the most perfect men and women of the past or
present. It Is doubtful whether eugenics can go farther than
this and there is no probability that it can ever produce a race
of supermen. Important as eugenics Is in preventing racial
degeneration it does not hold forth the hope of endless human

1 82 THE EVOLUTION OF MAN

progress. For the present at least the most that it can do is
to take the place of natural selection in limiting the propaga-
tion of the feeble-bodied and the feeble-minded and in favoring
that of the strong and sane. This would at once preserve and
perpetuate the best human lines and would in time raise the
average of the race as a whole but probably it would not pro-
duce a new and better species of man. The eugenist can
neither produce new mutations nor does he know what muta-
tions or new combinations of characters will be most useful
and most viable in future ages. If the fads and fancies of
reformers could be established in the germ-plasm and all men
could be made eugenically equal the whole race might come to
a rapid end. It is probably fortunate that men are not charged
with the duty of directing future evolution, and we can only
hope that nature, which has directed progressive evolution
from amoeba to man, without human guidance, may work
still greater wonders in future ages.

Finally the lesson of past evolution teaches that there can
be no progress of any kind without struggle ; in physical evolu-
tion progress has come through the struggle for existence and
for more abundant life ; in intellectual evolution, through striv-
ings for freedom and enlightenment; in social evolution,
through the victory of social instincts and ideals over anti-
social ones. The improvement of the human race, if not the
further evolution of man will depend in part upon enlightened
human effort. To us it is given to cooperate in this greatest
work of all time and to have a part in the triumphs of future
ages, not merely by improving the conditions of individual life
and development and education, but much more by improving
the ideals of society and by breeding a better race of men who
will "mold things nearer to the heart's desire."

The Distant Future. What the distant future may hold in
store for the human race we can only guess. It may be that
the entire race will become extinct and leave the dominance of

THE TREND OF EVOLUTION 183

the earth to other living things. Although this has been the
history of many dominant species in the past it does not seem
probable that It will be the fate of man, for he is able to adapt
himself to changed conditions, to modify his environment, and
to control his destiny as no other creature that has ever lived
on the earth has been able to do. If conditions of life should
ever become so adverse that the entire human race should be-
come extinct we may probably assume that all other higher
animals would also perish.

It Is possible that the entire race may suffer retrogressive
evolution and return to a less highly organized condition.
Many other types of animals have passed the climax of their
evolution and have then declined and their degenerate repre-
sentatives still survive. But in these cases other forms better
fitted for survival have taken their places and progress has
continued in other lines. Intellectual and social evolution has
reached a climax in man and it has so greatly increased his
control over himself and his environment that it seems scarcely
possible that it will universally and permanently decline and be
replaced by less adaptable and less efficient characters.

Perhaps in future ages the progressive evolution of man will
continue, somewhere and somehow. If higher species of man
evolve in the future it is not unlikely that this will occur, as in
the past, in connection with great secular changes, over which
man has no control, such as the rising and sinking of conti-
nents, the formation of deserts or mountains or oceans, or
changes in climate comparable to the glacial and interglacial
epochs, during which human evolution made such wonderful
progress.

In the present conditions and tendencies of the human race,
in the contest between progressive and retrogressive forces,
we see much cause for anxious concern, but thinking on the
distant past and the boundless future creates a feeling of de-
tachment and of philosophic calm like that of the dwellers on

1 84 THE EVOLUTION OF MAN

Olympus. We cannot see clearly the next scene, we can scarcely
imagine the next act, and the end of the great Drama of Evo-
lution, if there is to be an end, is a matter of faith alone.

O, yet we trust that somehow good

Will be the final goal of ill.

To pangs of nature, sins of will,
Defects of doubt and taints of blood.

BIBLIOGRAPHY

CONTAINING A SELECTED LIST OF REFERENCES FOR EACH
CHAPTER OF THE BOOK

CHAPTER I

Churchward^ A. The origin and evolution of the human race.

New York and London, 1922.
Dubois^ Eugene. Pithecanthropus erectus, ein menschenaehnliche

Uebergangsform. Batavia, 1894.
Elliot, G. F. Scott. Prehistoric man and his story. London, 1915.
Gregory, W. K. The origin and evolution of the human dentition: a

palaeontological review. Journal of Dental Research, Vol. 2, Nos.

1-4, 1920; Vol. 3, No. 1, 1921.
Hrdlicka, Ales. Skeletal remains suggesting or attributed to early

man in North America. Bureau of American Ethnology, Bulletin 33,

1907.
The most ancient skeletal remains of man. Annual Report of the

Smithsonian Institution for 1913, pp. 491-552, 1914; 2d ed., 1916.
Keith, Sir Arthur. The antiquity of man. London, 1915.
On the Broken Hill skull. London Illustrated News, November

19, 1921, p. 686.
Lull, R. S. Organic evolution. New York, 1917.
(ed.). The evolution of the earth and its inhabitants. New

Haven, 1918.
MacCurdy, G. G. Eolithic and Paleolithic man. American Anthro-
pologist, new series, Vol. 11, pp. 92-100, 1909.
Recent discoveries bearing on the antiquity of man in Europe.

Annual Report of the Smithsonian Institution for 1909, pp. 531-583,

1910.
OsBORN, H. F. Men of the Old Stone Age. New York, 3d ed.,
1919.

1 86 THE EVOLUTION OF MAN

The Pliocene man of Foxhall in East Anglia. Natural History,

November-December, 1921, pp. 565-576.
The dawn man of Piltdown, Sussex. Ibid., pp. 577-590.

Reinach^ Salomon. Repertoire de Tart quaternaire. Paris, 1913.

RuTOT, A. La prehistoire. 1918.

ScHOETENSACK^ Otto. Der Unterkiefer des Homo heidelbergensis,

Leipzig, 1908.
SoLLAS^ W. J. Ancient hunters. London, 1915.
Woodward^ A. Smith. On the Broken Hill skull. London Illustrated

News, November 19, 1921, p. 682.
A new cave man from Rhodesia, South Africa. Nature, November

17, 1921, p. 371.

CHAPTER II

Bardeen^ C. R. Height and weight in relation to build during post-
natal development. Carnegie Contributions to Embryology, Vol. 9,
No. 46, 1920.

Daffner^ F. Das Wachstum des Menschen ; anthropologische Studien.
Leipzig, 1902.

Deniker^ J. The races of man, an outline of anthropology and ethnog-
raphy. London, 1900.

Donaldson^ H. H. The growth of the brain. London and New
York, 1903.

Duckworth^ W. L. H. Morphology and anthropology. Cambridge,
1915.

Ellis^ H. Man and woman, a study of human secondary sex characters.
5th ed., London, 1914.

Hall, G. Stanley. Senescence, the last half of life. New York, 1922.

Jackson, C. On the prenatal growth of the human body, etc. Amer.
Jour, of Anat., Vol. 9, 1909.

Keith, Sir Arthur. Human embryology and morphology. 3d ed.,
London, 1913.

MiNOT, C. S. The problem of age, growth and death; a study of
cytomorphosis. New York, 1908.

Prentiss and Arey. Text-book of embryology. 3d ed., Philadelphia,
1920.

I

BIBLIOGRAPHY 187

Ranke, J. Der Mensch. 2 vols. Leipzig, 1887.
Stratz^ C. H. Naturgeschichte des Menschen: Grundriss der Soma-

tischen Anthropologie. Stuttgart, 1904.
WiEDERSHEiM, R. The structure of man, an index to his past history.

London, 1895.

CHAPTER III

Berman^ L. Glands regulating personality. New York, 1922.
Cannon^ W. B. Bodily changes in pain, hunger, fear, and rage.

New York, 1915.
CoNKLiN^ E. G. Heredity and environment in the development of

man. Princeton, 1920.
Foster^ M. Lectures on the history of physiology. Cambridge, 1901.
Haldane^ J. S. Mechanism, life and personality. New York, 1914.
Organism and environment as illustrated by the physiology of

breathing. New Haven, 1917.
Myerson^ a. The foundations of personality. Boston, 1921.
Parker^ G. H. The reactions of sponges, with a consideration of the

origin of the nervous system. Jour. Exper. Zool., Vol. 8, 1910.
^The origin and significance of the primitive nervous system. Proc.

Amer. Philos. Soc, Vol. 50, 1911.

Biology and social problems. Boston, 1914.

-The elementary nervous system. Philadelphia, 1919.

Robinson, J. H. The mind in the making. New York, 1921.
Schafer, E. a. The endocrine organs. London, 1916.

CHAPTER IV

CoNKUN, E. G. The direction of human evolution. New York, 1921.
Heredity and environment in the development of man. Princeton,

1920.
OsBORN, H. F. Men of the Old Stone Age, their environment, life

and art. 3d ed., New York, 1919.
Boas, Franz. The mind of primitive man. New York, 1913.
Keller, A. G. Societal evolution. New York, 1915.

1 88 THE EVOLUTION OF MAN

Angell^ J. R. Chapters from modern psychology. New York, 1912.

Watson^ J. B. Behavior — Introduction to comparative psychology.
New York, 1914.

Thorndike, E. L. Animal intelligence. New York, 1911.

Washburn, M. F. The animal mind. 2d ed.. New York, 1917.

Jennings, H. S. Behavior of the lower organisms. New York, 1915.

LoEB, J. Comparative physiology of the brain and comparative psy-
chology. New York, 1900.

Forced movements, tropisms and animal conduct. Philadelphia,

1918.

CHAPTER V

Sumner, W. G. Folkways. Boston, 1907.

Collected Essays. 4 vols. New Haven, 1914-1918.

What social classes owe to each other. New York, 1911.

Keller, A. G. Societal evolution. New York, 1915.

Through war to peace. 2d ed.. New York, 1921.

Colonization. Boston, 1908.

Bagehot, W. Physics and politics. New York, 1902.
Darwin, C. R. Descent of man. New York, 1898.
Galton, Sir F. Hereditary genius. New York, 1870.

Essays in eugenics. London, 1909.

GuMPLOWicz, L. Der Rassenkampf. Innsbruck, 1883.

Haycraft, J. B. Darwinism and race progress. 2d ed.. New York,

1900.
Holmes, S. J. The trend of the race. New York, 1921.
Huxley, T. H. Man's place in nature. Collected Essays, New York,

1901.
LiPPERT, J. Kulturgeschichte der Menschheit. 2 vols. Stuttgart,

1886.
ScHALLMAYER, W. Vererbung und Auslese im Lebenslauf der Volker.

Jena, 1903.
Seward, A. C. (editor). Darwin and modern science. Cambridge,

1909.
Spencer, Herbert. Principles of sociology. 3 vols. New York, 1877-

1896.

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CHAPTER VI

Bell^ a. G. Is race suicide possible? Jour. Heredity, Vol. 11, 1920.
CoNKLiN^ E. G. The direction of human evolution. New York, 1921.
Darwin^ C. R. The origin of species by means of natural selection,

etc. New York, 1898.
The variation of animals and plants under domestication. 2 vols.

London, 1905.
The descent of man. 2d ed., New York, 1898.

Fisher^ I. Impending problems of eugenics. Sci. Monthly, Vol. 13,

1921.
FoREL^ A. Human perfectibility in the light of the facts of evolution.

International Monthly, Vol. 4, 1901.
Frank^ T. Race mixture in ancient Rome. Amer. Hist. Review, Vol.

21, 1916.
Galton^ Sir F. Hereditary genius. New York, 1870.

Natural inheritance. New York, 1889.

Holmes^ S. J. The trend of the race. New York, 1921.

Huxley^ T. H. On the natural Inequality of men. Collected Essays,

New York, 1901.
Kellicott^ W. E. The social direction of human evolution. New

York, 1911.
Metchnikoff^ E. The nature of man. Chicago, 1903.
Morgan, T. H. The physical basis of heredity. Philadelphia, 1919.
OsBORN, H. F. Men of the Old Stone Age, etc. 3d ed.. New York,

1919.
Pearl, R. Vitality of the peoples of America. American Journal of

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Yerkes, R. M., et al. Army mental tests. Memoirs Natl Acad.

Sciences, Vol. 15, 1920.

INDEX

Abbott, Lewis, 22

Ability, intellectual, inherited trait,

171
Acceleration, prepubertal, 69
Acquired characteristics, inheritance

of, 156-157
Acromegaly, 64
Actions, intelligent, 105, 119

mechanical, 105

reflex and instinctive, theory of the
origin of, 107

tropisms, 105

volitional, 100
Activities, control of bodily, 84
Adams, Henry, 126, 128
Adaptation, intelligent, 106
Adaptive reactions, 113
Adjustment, automatic, 150

cultural, 136

Darwinian theory of, 126

human, 134

intelligent, 119, 150

material, 133

societal, 136
Adjustors, 84, 86

Africa, racial amalgamation in, 176
Age, Chellean, 22

Mesozoic, 19

of Pithecanthropus, 16

Pliocene, 9

Upper Siwalik, 16
Alimentary canal, development, 49

organs developing from, 52
Alterations, chemical, in senescence, 71
Amalgamation of races, 175
Amalgamation, tendency to, 176

Ameghino, F., 10

American, typical, 175

Amnion, 57

Amniotic cavity, 43

Amoeba, 105, 112, 153

Analogy, 129

Anatomical variations, 75-78

Animal, consciousness, theory of, 112

fitness, 135

intelligence, 104-112

life, changes in, 104

reactions, 121

size, 63

behavior of, 108
Animals, invertebrates, 39

mammals, 39

metazoa, 39

protozoa, 39

vertebrate, 39
Ant, instincts of, 108
Anthropophagy, 144
Anthropoids and man, Huxley's com-
parison, 131

phylogeny, 36
Anti-bodies, see Hormones
Antiquity, means of determining, 8
Appendix, comparison of, in various
animals, 74

vermiform, 73, 74
Archipallium, 46, 93
Areas, association, of brain, 120

frontal, of brain, 120
Aristotle, 81
Art, Aurignacian, 34
Art, Cro-Magnon, 32

192 INDEX

Arteries, development, 52

hardening of, 70
Arteriosclerosis, 70
Asia, birthplace of mankind, 5
Association areas of brain, 120
Association, inheritance, 157, 163
Assortative mating, 169
Attica, New York, 11
Auricle, of heart, 51

Bacillus bulgaricus, 71
Bagehot, W., 145
Banderlog, the, 109
Banolas, Spain, 24
Bee, instincts of, 108
Behavior of animals, 108

of man, 120

instinctive, 105

intelligent, 110, 122
Bell, A. G., 172
Birds, nesting instincts of, 108
Birth, 60
Birth control, 172

eflfects of, 173
Birth-rate, 171-174

American scientists, 172

of college graduates, 171

of intellectual classes, 171-174

Phi Beta Kappa, 172
Birth, ratio to deaths, 174
Births, multiple, 62

proportion of male and female, 62
Blood cells, development, 52

natural history, 52
Blood vessels, development, 52
"Blue baby," 60
Blumenbach's classification, 40
Body cavity, see Ccelom
Body proportions, changes in during

growth, 65
Body wall, formation of, 45
Bone, growth of, 67

growth shown by madder, 67
Bones, cranial, ossification of, 55

Boule, Marcelin, 24

Boy, growth of, 67-69

Brain cells, number in cortex, 93

Brain, cortex, 93, 120

Breuil, I'Abbe, 34

Broken Hill mine, Rhodesia, 28

Bronze, age of, 2

Bushmen, Africa, 12

Caecum, 73, 74

comparison in various animals, 74
Cancer, 65

Cannibalism, 136, 144
Capacity, human, 122
Capacity, mental, dependent on inherit-
ance factors, 171
Capillaries, development, 52
Carbon, 99
Catholicism, 144
Cattell, 172

Cavern, Lost Hope Inlet, 11
Celibacy, 169
Cells, 39

interstitial, 97
Cerebral cortex, 93

atrophy, 71

center of sensation, 82
Cerebral sacs, 45
Changes, retrogressive in various

organs, 73-75
Characteristics, acquired, inheritance
of, 156-157

of soma, 157
Child, change in proportions, 65
Chimpanzee, fossil, 20
Chorion, 57
Chronological table, 4
Chronology, European, 3
Churchward, A., 12
Circulation, change at birth, 60
Civilization, 115, 134, 158

European, 115

evidence of, 118

pre-Columbian, 11

INDEX

selection

193

Civilization, retrogressive

of, 168-171
Clarke, Dr. J. M., 11
Classes, hereditary, 170

intellectual, birth rate of, 171-174
Classification, of human races, 40
Cleft palate, 57
Coccyx, 11
Cochlea, 48

Code, new, of adjustment, 144
Codes, collision of, 144

rational selection of, 146
Coelom, 44
Collyer, 36
Combinations, Mendelian, 154, 155,

170
Competition, between societies, 143

tragedies of, 145
Conduct, 134

rational, 105
Congenital imperfection, 167
Consciousness, and experience, 113

and intelligence, 112-114
Control, voluntary, lack of in certain

actions, 106
Conversion, sexual, 97
Conviction, ex parte; 148
Cortex, of brain, 120

cerebral, 93
Counter-selection, 135
Cranial sutures, disappearance of, 67
Creation, Mosaic account of, 1
Creeping, sea-anemone, 88
Cretinism, 64
Cro-Magnon man, 31

art, 32

decline, 35

implements, 32

size, 32

skull, 32

skull and face, 33

skull, compared with Neandertal
man, 25

Cromer flints, 4

Cultural adjustment, 135, 136

societal, 135
Custom, 136

Darling Downs, Australia, 12
Darivin and modern science, 131
Darwin, C. R., 128, 131

formulation of natural selection, 158

on variation, 156
Darwinian factors, 130, 136

theory, 131
Dawson, Charles, 20, 22
Deaths, ratio to births, 174
Degeneracy in certain families, 168
Degeneration, senile, see Senescence
Dentition, 75
Dermis, 56

Descent of man, Darwin's, 129
Destiny, mankind, 165
Development, social, form of, 164

early prenatal period, 42-45

later prenatal, 45-63

postnatal, 63-70
Differentiation, and extinction, 161

relation to regeneration, 65
Diprothomo, 10

Discussion, Age of, Bagehot, 145
Drosophila, 155
Dubois, Dr. E., 13, 15
Diissel, Germany, 23

Ear, development, 48

vestigial muscles of, 73
Earthworm, nervous system, 85
East Anglia, England, 36
Ectoderm, 43

derivatives from, 43
Education, eugenical, 179
Education, Henry Adams, 126
Education, importance of, 181

in relation to mores, 142
Effect, cooperative, 165

194

INDEX

EflFectors, 85

sea-anemone, 89
Egg cells, 96, 158

development, 42

fertilization, 41, 42

potency of, 153
Ehringsdorf, Germany, 24
Elements, chemical, freedom of action
in living matter, 100

chemical, organized in nervous pro-
toplasm, 100

of animal body, 99
Embryo, circulation, change at birth,
60

condition, at birth, 61

development in utero, 57

prenatal conditions, 60
Embryonic area, 43
Emotion, 146
Emotionalism, 163
Emotions, 118
Endocrine organs, 49, 95
Endoderm, 43

derivatives from, 43
Environment and mutations, 156
Environment, diverse of man, 132
Eoanthropus daiusoni, 19-23
Eolithic period, 3
Eoliths, 3
Epidermis, 56
Eugenics, 170

importance of, 181
Eugenists, 148, 182
Evolution, and natural selection, 158

and progress, 127

direction of, 165

causes of, 153, 154

cycles in, 153

directions of, 159

drama of, 152

germ-plasm, 157

human, tendencies of, 179

intellectual, 162

main lines of, 161

of man, 155, 161, 162

only an adjustment, 127

neuromuscular system, 92

past, causes and directions of, 154-

165
progress and retrogression, 127
progressive, 183
reversal of principle, 166
societal, different from that in na-
ture, 136
Expedition, American Museum, 7, 12,

37
Experimentalists, animal, 110
Experimentation, animal difficulties of,

108-110
Experimentation, in relation to varia-
tions, 140
Extremities, phantasmal, 82
Eye, development, 48
Eyelid, vestigial, 72

Face, development of, 56
Factors, Darwinian, 130

individual, 154
Female, characteristics of, 96
Femur, development, 55
Fertilization, 41, 42
Feudalism, 136
Fishberg, 176
Fisher, Irving, 172
Fishes, spawning instincts of, 108
Fitness, animal, 135

in natural selection, 158

societal, 135
Flints, Foxhall, 36

giant of Cromer, 36

rostro-carinate, 36
"Fluctuations," 154
Foramen, ovale, 60
Fore-brain, 45
Forest beds, pre-Glacial, 19
Fossil man, Africa, 11

Asia, 12

Broken Hill mine, 12

INDEX

195

conditions of preservation, 7

Cro-Magnon, 31-36

Dallas, Texas, 10

Dawn man, 19-23

Heidelberg, 16-19

Heidelberg, age, 19

intelligence of, 114

Lansing, 10

Mousterian, 23

Neandertal, 23-28

Nebraska loess, 10

Piltdown, 19

Piltdown, age of, 22

pre-Mousterian, 35

Rancho La Brea, 10

record of discovery, 9

South American, 10

Tertiary, 36

Upper Paleolithic, 31

Upper Pliocene, 36

Vero, Florida, 10
Frank, T., 180
Freedom of mind, 101
Frog, 112

intelligence of. 111
Frontal, areas of brain, 120

Galley Hill skull, 35

Galton, F., 167, 169, 171

Geikie, 19

Genes, 154

Genial pit, 22

Genital organs, external, development

of, 54
Germ cells, 157

Germany, champion of a code, 142
Germinal cells, union, 42
Germinal inheritance, 157
Germ-plasm, 154, 158, 163, 164, 171,
182

environment of, 156

evolution in, 157
Gill clefts, 49
Girl, growth of, 67-69

Gonads, development, 53

grafting, 71

migration, 54

producing sex cells and hormones,
97
Government, a cultural adjustment,

134
Gower, Wales, 31
Graduates, college, children of, 171
Gravel beds, Hastings, 19
Gravels, Piltdown, 19

Trenton, 10
Greece, decay of, 179
Gregory, W. K., 14, 16, 19, 22
Grimaldi, 34

features of, 34

relation to Bushmen, 34
Grotte des Enfants, France, 34
Ground sloth, 11
Growth, 63

bone, 67

curves for height and weight, dl

controlled by internal secretions, 64

decreasing rate of, 64

hereditary factor in, 64

period of, 64

relative rate of, in organs of body,

retarded by certain factors, 64
Grypotherium, 11

Guinea pigs, gonad transplantation
in, 96

Habits, fixed, 107

Haeckel, 100

Hair, development, 56

fetal, 56, 77

regulation of development by hor-
mones, 56

slopes, 56

tessellated junctions of, 56
Haldane, 102
Harelip, 57
Heart, auricles, 51

196 INDEX

development, 50

ventricles, 51
Height, average of, 69
Helix, of ear, 73
Hermaphroditism, spurious, 53
Hernia, formation of, 53
Hind-brain, 45
Homo neandertalensis, 23-28
Homo {Paleanthropus) heidelb erg en-
sis, 16-19
Homo primigenius, 23-28
Homo rhodesiensis, 28-31
Homo sapiens, 18, 31-36, 40

differentiation, 36

Grimaldi type, 34
Hormones, 50, 96, 157

eflFect upon personality, 95

of interstitial cells, 97

relation to nervous system, 95

see Internal secretion
Horse, evolution of, 9, 64
Hrdlicka, A., 10
Human intelligence, 114-122
Human race, present conditions and

tendencies, 165-179
Humerus, containing supracondylar
foramen, 77

development, 55
Humors, 95

and Hormones, 95
Hunter, J., experiment of, 67
Huxley, T. H., 131, 156
Hybrids, 176
Hydrogen, 99, 101
Hypophysis, see Pituitary body

Ideographs, 2

Implements, Eolithic, 19, 22
Indian, North American, 116
Indo-China, amalgamation in, 176
Industries, Magdalenian, 12

pre-Crag, 36

table of, 4
Inferences, human, 121

Inguinal canal, 53
Inheritance, and variation, 153-156
social, 142, 157

factors and mental capacity, 171

germinal, 157
Instinct and reason, 105
Instinctive, actions, theory of the
origin of, 107

manipulations, 119
Instincts, 106, 111

animal, 108

biological utility of, 106

hereditary, 106
Institutions, human, rise of, 138
Intellect, development of, 153
Intellectual power and cultural sur-
roundings, 116
Intelligence, 122, 166

and consciousness, 112-114

and relation to nervous system, 119

animal, 104-112

evolutionary processes of, 112

frog. 111

function of nervous system, 104

future development of, 122-125

guinea pig, 111

human, 114-122

individual, field of, 119

prehistoric man, 114

primates. 111

rudimentary power of, 112

variation in human races, 115
Interest and emotion, 146
Intermarriage, 170

Internal secretion, development of
organs, 49

influence of puberty, 69

see Hormones
Interstitial cells, 97
Intestine, appendix of, 73, 74

caecum of, 73, 74
Intussusception, 63
Invention, an adjustment, 134
Inventions, great progress in, 164

INDEX

197

Iron, age of, 2
Irrationalism, 163
"Ishmaels," 168

Isolation, geographical, lack of, 175
racial, 174

Jacob's cavern, 11

Jaw, Heidelberg man, 16

shrinkage of, 75
Jews, amalgamation of, 176
"Jukes," 168

Kaa, 109

"Kalikaks," 168

Keith, Sir A., 10, 11, 18, 20, 22, 26, 28,

30, 35, 36
Krapina, Austria, 24
Kultur, 159

Labor, division of, a mores, 137
La Chapelle-aux-Saints, France, 24
La Ferrassie, France, 24
La Naulette, Belgium, 24
La Quina, France, 24
Language, 118

a mores, 137

advantage of, to man, 118

as a mores, 141

man's control over, 120

responsible for man's superiority,
120
Lanugo, 77

League of Nations, 128
Le Moustier, France, 24
Life-conditions, 139
Life cycle, 70
Lightfoot, John, 1
Limbs, development, 55

pentadactyl, 55
Liver, development, 50
Lungs, development, 49

Magazine, Natural History, 11

Male, characteristics of, 96
Mammalia, Pleistocene, 12
Mammals, instincts of, 108
Mammary glands, supernumerary, 77
Man, ability to accustom to different
environments, 133

American, 40

and anthropoids, 131

behavior of, 120

bodily evolution of, 162

Caucasian, 40

controlling his evolution, 166

dispersal of, 6

Ethiopian, 40

evolution of, 155

fossil, see Fossil man

Java, see Pithecanthropus, 14

Malay, 40

Mongolian, 40

Mongoloid, 11

Neandertal, 14

nervous system of, 84

nervous system, summary of evolu-
tion in, 102

New World, 11

normal life cycle, 72

phylogeny, 36

Prehistoric, species, 13

Primitive, language of, 118

progressive, evolution of, 161-165

races of, 38, 40

similarity of, 132

structural relations, 39

structural unit of, 39
Manipulations, instinctive, 119
Mankind, birthplace of, 5
Mantle, 46
Marriage, 136, 147

a cultural adjustment, 134

hindered by modern conditions, 169

productivity of, 169
Marshall, Alfred, 178
Mastodon, engraving of, 11

remains of, 11

198 INDEX

Mate selection, 169
Mating, assortative, 169
Mauer, Germany, 16

sands, 16, 17
Maupas, theory of, 72
McGregor, J. H., 15, 18, 20
Mechanism, neuromuscular, 85
"Melting pot," 177

Roman Empire, 180
Mendelian combinations, 154, 155, 170

inheritance, 177
Mendelism, 154

Mental life, various factors which in-
fluence, 124
Metazoa, 39

MetchnikofI, theory of, 71
Mexico, racial amalgamation in, 176
Mesoderm, 43

derivatives from, 43
Mid-brain, 45
Miller, G. S., Jr., 20
Minot, on diflFerentiation, 161

theory of, 72
Moir, J. Reid, 22
Momsen, 179
Mores, 137, 138, 139

and education, 142

and imitation, 141

and life conditions, 138

and sex, 138

code of behavior, 147

learned not inherited, 141

transmitted by tradition, 141
Morgan, T. H., 155
Morula, 42

Mousterian industries, 3, 4
Mowgli, 109
Mulattoes, 176
Murals, cavern, 12
Muscle, rectus, 76

sternalis, 76

subtegumentary, 76
Muscles, development, 53

effectors, 85

shifting of position, 55

vestigial, 73
Mutations, 154, 155

and environment, 156

directions of, 159

their causes, 156
Myelin sheath, 47
Myotomes, 44

"Nams," 168

Nasal cavity, development of, 57

Natural law, 147

Natural sciences, future achievements

in, 123
Natural selection, 135, 158, 178

elimination of the unfit, 143, 166
Naturalists, observations of, 108-110
Neandertal man, anatomical features,
24

ideas concerning, 28

modern representatives of, 28

skeleton, 23, 24

skeleton compared with Cro-Magnon
man, 25
Neolithic period, 2
Neopallium, 46, 93
Nerve cells, 46

development, 49

evolution, 49

number in cortex, 93

see Neurones
Nerves, afferent, 48

motor, 46

myelin sheath, 47

sensory, 46
Nervous elements, lacking in sponges,

92
Nervous organization, sea-anemones,

86
Nervous system, adjustors, 84, 86

and organization, 99

and personality, 81-83

and sex, 94-99 '

INDEX

199

central, 84, 86

diffuse, 87

earthworm, 85

effect of interstitial secretions, 98

effectors, 85

in relation to intelligence, 104

influenced by environment, 95

intricate structure of, 84

man and higher animals, 84

organization, 84

receptors, 85

reflex mechanism, 47

rudiment, 44

summary of evolution in man, 102

sympathetic, 85

vertebrates, 93
Neural groove, 44

tube, 44
Neuromuscular mechanism, 85
Neuromuscular system, evolution of,

92
Neurones, 46

internuncial, 84

motor or efferent, 84, 85

see Nerve cells

sensory or aflPerent, 84, 85
New Zealand, mixed races, 176
Nitrogen, 99
Nose, development, 57
Notochord, 44
Nourishment of embryo, prenatal, 57

Obercassel, Germany, 32
Old age, see Senescence
Oldoway ravine, 11
Olfactory, archipallium, 93

cortex, 93

organ, development of, 57

organ, retrogression in, 73

pits, 57
Ontogeny, 52, 164

course of, 159
Organicism, 102
Organism, structural unit of, 39

Organization, 134

and a society, analogy between, 129
in relation to nervous system, 99-101
nervous, of sea-anemones, 86
sponges, 90-91

Organs of body, relative rate of
growth, 66

Orthogenesis, 156

Osborn, H. F., 4, 18, 34, 35, 36

Ouse, Sussex, 19

Ovum, fertilization, 41, 42
structure, 42

Pacific Islands, racial amalgamation

in, 176
Paleolithic period, 2
Pallium, 46
Pan vetus, 21
Pancreas, development, 51
Parables, 129

Parathyroid gland, development, 49
Parr, Thomas, 70
Particles, protoplasmic, 152
Pathways, hereditary, 106
Pearl, R., 174, 175, 178
Pech de I'Aze, France, 24
Perception, sense, 116
Personality, and nervous system, 81-83

influence of sex glands upon, 98
Phantasms, 145
Phylogeny, 52, 164

course of, 159

provisional, of man and anthropoids,
36
Pineville, Missouri, 11
Pithecanthropus erectus, 12-16
Pituitary body, development, 49
Placenta, development, 58

filter against bacteria, 59

intervillous spaces, 58

osmosis in, 58

passage of materials through, 58-60

separation of fetal and maternal
blood, 58

200

INDEX

villi, 58
Pleistocene, 8, 10, 17, 22, 36
Plica semilunaris, 73
Pliocene, 16
Polydactylism, 55
Pomace fly, 155
Population, and subsistence, 178

effect, of the world, 178

foreign-born birth-rate, 174

limits of, 178-179

maximum, 178

native birth-rate, 174

negro, of United States, 176

South American countries, 176

United States, 178
Postnatal retardation, 68
Prepubertal acceleration, 69
Primary germ layers, 43
Primates, intelligence of. 111
Primitive streak, 43
Processes, rational. 111

selective, 143
Products, cultural, 134
Progress and evolution, 127

due to specialization and coopera-
tion, 160

definition of, 159-160

limits of, 160-161
Propagation, by selection, 170
Proportions of body, changes in during

life, 65
Protestantism, 144
Protoplasm, primeval, 152
Protozoa, 39
Puberty, 69

influenced by internal secretion, 69
Pygmies, 5

Race, composite, characteristics of, 177
differentiation and amalgamation,

174-178
mixtures, 175

Race suicide, 135
Roman Empire, 180

Races, blending of, 176

difference in intelligence, 115

primary, of mankind, 176
Racial isolation, 174
Rational, conduct, 105

processes. 111
Reactions, adaptive, 113

animal, acquiring of, 121

reflex, 106

spontaneous, 107

summary of, in various animals. 111

tropistic, 113
Realm, societal, elemental forces in,

149
Reason and instinct, 105
Recapitulation, Law of, 52
Receptors, 85

sea-anemone, 89
Recombinations, 154
Reflex actions, 106

theory of the origin of, 107
Regeneration, in amphibia, 65

in man, 65

power of, 65
Rejuvenescence, 71
Religion, 136, 147

evolution of, 123
Reproductive system, development, 53
Retardation, postnatal, 68
Retrogression, 73-75
Rhodesia, Broken Hill mine, 12
Rhodesian man, 28-31

skull, 30
Ribs, variation in number, 75
Roman Empire, race suicide, 180
Rome, decay of, 179
Rubner, 72
Rutot, A., 4

Schoetensack, Dr. O., 16, 19
Science and religion, 144
Sea-anemone, creeping, 88

effect of stimulation, 86

effectors, 89

INDEX

201

feeding of, 87, 88

nervous organization, 86

receptors, 89

sense organs, 90

structure, 86

tentacle, effect of detaching, 87
Secretions, interstitial, effect on ner-
vous system, 98
Segments, 44
Segregation, 170
Selection, 130, 143

a negative process, 143

ordinary, improvement by, 148

essential processes of, 143
Selenka, Madame, 13
Self-direction, 146
Self-maintenance, 137
Senescence, 70-72

theories of, 71
Senile degeneration, see Senescence
Sensation, 82
Sensations, primitive, 101
Sense organs, retrogressive changes in,
73

sea-anemone, 90
Sense perception, 116
Sensorium commune, 81
Sex and nervous system, 94-99
Sex, cause of, 62

center of society, 98

conditions, indifferent, 53

definition of, 95

determination before birth, 62

glands, see Gonads

reversal of, by gonad transplanta-
tion, 96

transformation of, 96
Sextuplets, 62

Sexual characteristics, determined by
gonad, 97

primary, 96

secondary, 96, 97

secondary, controlled by gonad, 97

Shere Khan, 109
Skeleton, cartilage, 55

development, 55

membrane, 55
Skin, development, 56
Skull, Calaveras, 9

cap. Pithecanthropus, 13, 14

Gibraltar, 23

pre-Neandertal, 18
Slavery, an adjustment, 128
Smith, Elliot, 20
"Social theory," 151
Societal, adjustment, 136

code, 139

evolution, past processes, 149

fitness, 135

range, forces at work, 150

realm, 149

selection, in relation to war, 144

selection, various forms taken by,
145
Societies, struggle of, 143
Society, and organisms, analogy be-
tween, 129

human, changes in, 163

relation of to sex, 98

stratification of, 170

systems, cultural adjustments, 134
Sollas, W. J., 12, 34
Specialization, and progress, 160

relation to regeneration, 65
Spencer, H., 129
Sperm cells, 95

in fertilization, 42

structure, 42
Spider, instincts of, 108
Sponges, 90-92

lack of nervous tissue, 92
Spy, Belgium, 23
Steinach, 71, 97, 98

gonad transplantation, 96
Stimulation, effect of, in sea-anemones,
87

202 INDEX

Stone, age of, 2
Sumner, W. G., 137, 139
Superstition, 163
Supracondylar foramen, 77
Survival of the fittest, 143
Sympathetic system, 85

Tail, in man, 77
Tariff, protective, 128
Tasmanians, 3
Teeth, cynodont, 14

decay, 75

dentine, 57

development, 57

enamel, 57

first set, 67

fourth molar, 7S

Heidelberg man, 18

permanent, 67

pulp, 57

retrogressive changes, 74

taurodont, 14
Tendency, tropistic, 106
Tentacle, sea-anemone, 87
Tests, psychological, American Army,

117
Tetraprothomo, 10
Thames gravels, 35
Thymus glands, development, 49

fate of, 50

migration, 50
Thyroid glands, development, 49

migration, 50
Tools, not used by lower animals, 118
"Trial and error," 158
Transmission, of mores by tradition,

141
Transplantation, gonad, 96
Trinil, Java, 12, 13
Tropisms, 105, 106
Tubercle, Darwin's, of ear, 73

Urinary system, development in rela-
tion to genital system, 53

Uterus, contractions at birth, 60
digestion of wall by embryonic cells,
58

Variation, 130, 139

accidental, in relation to reflexes,
107

anatomical, 75-77

and experimentation, 140

and inheritance, 154-156

and the world-code, 142

depend upon verification, 140

environmental, 154

rational, 140
Vas deferens, 71

Vascular system, development, 51
Veins, development, 53
Ventricles, 51

Vermiform appendix, 73, 74
Vertebral column, 44
Vestigial structures, 72-75
Villi, of placenta, 58
"Vital index," 174
Volition, 107
Volitional actions, 100

War, and retrogressive selection, 168

form of societal selection, 144
V^ater, 101

currents, in sponges, 91

percentage, in body, 64
Weight, average, 69

increase in prenatal development, 63
Weismann, theory of, 71
West Indies, racial amalgamation in,

176
Woodward, Smith, 20, 30
World-code and variations, 142

Yale Babylonian Collection, 2
Yolk sac, 43, 44

"Zeros." 168

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3 ? 8 0 8 ^ M

3S1-G