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HUMAN GENETICS
AND ITS SOCIAL IMPORT

HUMAN GENETICS

AND ITS

SOCIAL IMPORT

S. J. HOLMES

Professor of Zoology in the
University of California

FIRST EDITION
THIRD IMPRESSION

McGRAW-HILL BOOK COMPANY, INC.

NEW YORK AND LONDON
1936

PRINTED IN THE UNITED STATES OF AMERICA

parts thereof, may not be reproduced

in any form without permission of

the publishers.

THE MAPLE PRESS COMPANY, YORK, PA.

'Preface

WHEN Herbert Spencer wrote his well-known book on
The Study of Sociology he devoted a chapter to
showing that sociology rests upon biological foundations and
that preparation in biology is therefore necessary for the
proper cultivation of the social sciences. The progress of
biology has yielded abundant support for this conclusion and
has shown that the connections between biology and sociol-
ogy are more numerous and intimate than was probably
appreciated even by Spencer. If one looks through a number
of recent general treatises on sociology, it will be found that
most of them devote considerable space to biological sub-
jects, amounting in some cases to a quarter or a third of the
contents of the book. In endeavoring to select those aspects
of biology that will prove to be of the greatest service to
students of social phenomena one is often perplexed by
doubts as to whether one has made the best choice of
material to present. Biology contributes to the social sciences
in many ways. In fact, anything that helps us to understand
man has its value for students of social relationships. Being
compelled, there ore, to limit his field the author has confined
himself mainly to the phenomena of human heredity and
natural increase, and to some of the social consequences that
are the products of these biological factors.

It is especially important that the student who attempts
to arrive at correct judgments on controversial topics in
eugenics and other fields of social biology should obtain some
acquaintance with the common statistical and other fallacies
that so often lead the unwary astray. Attention is called to
a number of these, and I hope that the perusal of the present
volume may do something toward developing a critical
attitude of mind and an ability to form reasonable con-

vi PREFACE

elusions, whether or not they finally prove to be right, on
matters upon which opinions are now divided. We face many
problems of social biology that urgently call for solution.
What shall be done with the hereditarily defective classes?
How shall we control immigration in the best interest of
future generations ? In what ways can we hope to overcome
the evils of the differential birth rate ? These and many other
questions bring us face to face with issues upon which we
find people stoutly maintaining opposed views. We cannot
answer any of these questions without some knowledge of
genetics. They are social problems, but they can be solved
only by a study of biological facts.

It is desirable that readers of the present volume should
have some acquaintance with the fundamentals of general
biology, although very little technical knowledge is presup-
posed. Students should have access to some of the general
treatises on genetics and they should be able to consult the
more recent standard works dealing with problems of popu-
lation. A few suggested readings in connection with the topics
of the several chapters have been indicated, and a series of
questions at the end of each chapter has been appended in
the hope that they may prove helpful in giving the student
who attempts to answer them a more adequate comprehen-
sion of the subjects treated.

The author is indebted to his colleague Dr. S. Light for
reading the first nine chapters, and to his wife for her
critical perusal of the entire manuscript. Dr. R. C. Cook has
kindly permitted the reproduction of several figures from the
Journal of Heredity ', of which he is the editor. Thanks are
due to Dr. C. B. Davenport for the privilege of reproducing
Figs. 38 and 39 from Eugenical News.

S. J. HOLMES.

.BERKELEY, CALIF.,
April, 1936.

(Contents

PAGE

PREFACE v

CHAPTER I
HEREDITY AND ITS CELLULAR BASIS i

CHAPTER II
ARE ACQUIRED CHARACTERS INHERITED ? 19

CHAPTER III
MENDEL'S LAW 29

CHAPTER IV
HEREDITY AND SEX 42

CHAPTER V
THE INTERACTION OF FACTORS 52

CHAPTER VI
THE LINKAGE OF HEREDITARY TRAITS 66

CHAPTER VII
VARIABILITY — ITS KINDS AND ITS CAUSES 76

CHAPTER VIII
THE MEASUREMENT OF VARIATION 87

CHAPTER IX
HEREDITY IN MAN 98

CHAPTER X
HEREDITY AND ENVIRONMENT 112

CHAPTER XI
HEREDITY IN MENTAL DEFECT AND DISEASE 126

CHAPTER XII
NATURE AND NURTURE IN MENTAL DEVELOPMENT 149

viii CONTENTS

PAGE

CHAPTER XIII
GENETIC FACTORS IN CRIME AND DELINQUENCY 171

CHAPTER XIV
THE SOCIAL-PROBLEM PEOPLE 183

CHAPTER XV
CHOICE IN MATING. ...... .188

CHAPTER XVI
THE BIRTH RATE AND THE CAUSES OF ITS DECLINE 196

CHAPTER XVII
THE DIFFERENTIAL BIRTH RATE 216

CHAPTER XVIII
DEATH RATES 238

CHAPTER XIX

THE SELECTIVE ACTION OF MORTALITY •. . 253

CHAPTER XX
THE BIOLOGICAL EFFECTS OF WAR 274

CHAPTER XXI

THE EFFECTS OF POPULATION GROWTH . . 290

CHAPTER XXII
THE GROWTH OF CITIES AND ITS DEMOGRAPHIC EFFECTS . . 319

CHAPTER XXIII

THE BIOLOGICAL EFFECTS OF MIGRATION 330

CHAPTER XXIV
INBREEDING AND CROSSBREEDING 349

CHAPTER XXV
PROPOSED MEASURES FOR RACE BETTERMENT 359

BIBLIOGRAPHY 387

INDEX 405

HUMAN GENETICS AND
ITS SOCIAL IMPORT

CHAPTER I
HEREDITY AND ITS CELLULAR BASIS

IF ALL human beings had precisely the same hereditary
qualities, many of the social problems that confront us
would wear a very different aspect. But the inherited traits
of people are far from being exactly alike. It is a cardinal
principle of human biology that, with the exception of
identical twins, all men are born unequal, whatever may be
said concerning their freedom or their inalienable rights.
No one can doubt that the anthropological characters
which distinguish Negroes, Nordics, Chinese, and Hindus
profoundly affect the social, political, and economic relations
of these peoples to other members of the human species.
And within each race there are hereditary differences in
physical form, facial contour, resistance to disease, intelli-
gence, temperament, and countless other characteristics
that influence the way in which individuals adjust them-
selves to their social environment. Hereditary differences,
whether racial or individual, are therefore of interest to
students of social problems as well as to the biologist. The
more scientific knowledge we have concerning them the better
able we shall be to deal with the problems they present.

The science of genetics, which is concerned with heredity
and variation, has made enormously rapid progress during
the past generation. Through its spectacular achievements
it has attained more nearly the status of an exact science

2 HUMAN GENETICS AND ITS SOCIAL IMPORT

than any other branch of biology. One reason for this is
that genetics, like physics and chemistry, has come to be
mainly an experimental science. Previously most of what
was known about heredity was gained by collecting instances
of the transmission of some unusual trait. Writers on
heredity accumulated many records of curious and interest-
ing cases such as the perpetuation of extra fingers and toes,
or the history of the family whose members could not endure
the smell of cheese. Much was learned about heredky by
simple observation, but, as in physics and chemistry,
little progress was made in discovering the laws to which
the phenomena conform until the subject was attacked by
the method of controlled experimentation.

In addition to the insight gained through experimental
breeding, our knowledge of genetics has been greatly en-
riched by the remarkable discoveries made by the cytologists
regarding the cellular basis of hereditary transmission.
Genetics and cytology have advanced hand in hand, inas-
much as the discoveries in the one field help us to interpret
the phenomena observed in the other. In fact, some knowl-
edge of cytology is now essential for a proper comprehension
of genetics. Our first chapter, therefore, is devoted to the
cell and some of the peculiar cellular processes associated
with sexual reproduction.

One of the most fruitful generalizations of biology is the
cell theory, according to which the bodies of higher plants
and animals are made up of more or less individualized
little units called cells. The first recorded observations on
cells are credited to Robert Hooke, who described the cells
of cork in his Micrographia published in 1665. In the eight-
eenth century cells of various kinds were observed by
Malpighi and by Grew in the tissues of plants and animals,
but it was not until 1838-1839 that the cell theory was
formulated by the botanist Schleiden and the zoologist

HEREDITY AND ITS CELLULAR BASIS 3

Schwann. This new doctrine of the make-up of organic
bodies had a profound influence upon the development of
morphology, physiology, and more recently genetics. Accord-
ing to this theory cells bear much the same relation to the
body as do bricks to a house. The body thus interpreted
is an aggregate of little units, each with a life and indi-
viduality of its own, but all cooperating in different ways
to maintain the life of the whole. Cells are especially adapted
to perform a variety of functions — muscle cells for con-
traction, nerve cells for conducting impulses, and gland
cells for specific kinds of secretion. Each kind of cell has its
particular part to play, just as individuals following different
occupations play their parts in human society. For this
reason, the expression "cell state" has often been applied
to the organic body, and many analogies have been drawn
between the social organism and the physiological organism.
Whether with Herbert Spencer we speak of "society as an
organism," or with Haeckel we designate the organism
as a society or cell state, we express a fundamental likeness
between a society and an individual organism in that each
consists of more or less autonomous units whose activities
are subordinated to a common end.

The original proponents of the cell theory held certain
erroneous views as to how cells originate, but it soon came
tq be established that new cells are produced only by the
division of other cells. The doctrine formulated by the
pathologist Rudolf Virchow, Omnis cellula e cellula^ soon
came to be an integral part of the cell theory and exemplifies
a further fundamental similarity between the social and the
biological organism. The continued life of a society is brought
about by the reproduction of its members, just as the
reproduction of an individual organism is due to the mul-
tiplication of its component cells. Indeed, reproduction in
both cases depends ultimately upon cell division. Embryonic

4 HUMAN GENETICS AND ITS SOCIAL IMPORT

development in the light of the cell theory is interpretable
as the result of the division of cells, the growth of cells,
the differentiation of cells, the arrangement of cells, and
their mutual interactions — enormously complex series of
processes, which, for reasons almost as mysterious as ever,
are guided and controlled in such a way as to produce and
maintain the beautifully coadapted aggregate of parts
constituting the adult organism. Biologists look upon the
cell as containing somehow the secrets of this almost miracu-
lous phenomenon of embryonic development. All multi-
cellular animals begin their embryonic development as a
single cell, the ovum. To outward appearances, the ovum
of a human being differs very little from an ovum that
will give rise to a sheep, a dog, or a rabbit. Nor does it
differ very conspicuously from an ovum that will develop
into a jellyfish or even a plant.

The enormous potential differences inherent in these
seemingly simple cells have led many biologists to postulate
that the egg must possess a highly complex organization.
There must be as many kinds of eggs as there are kinds of
organisms. The eggs need not be so complex as the organisms
to which they give rise, nevertheless there is no escape from
the conclusion that every hereditary trait by which one
species differs from another must have as its basis some
differential peculiarity of the ovum. The same statement
applies even to the individual hereditary differences within
the same species. The ova giving rise to persons who inherit
color blindness, six fingers, or the absence of incisor teeth
differ from the ova that produce normal individuals by at
least one factor corresponding to each of thbse peculiarities.

Since the secret of the mechanism of heredity is contained
somehow in the make-up of the cell, let us consider some
of the chief features of cell structure. A typical cell consists
of a small bit of living protoplasm, or cytoplasm, containing

HEREDITY AND ITS CELLULAR BASIS 5

a nucleus and surrounded by a cell wall. The latter structure,
which was the first part of the cell to attract the attention
of the older observers and which is responsible for the
application of the term cell to those units of organic struc-
ture, is occasionally absent, as, for instance, in the white
corpuscles of the blood. The cytoplasm, which usually
constitutes the greater part of the cell, consists typically
of a more or less jellylike protoplasm. This substance,
which was designated by Huxley as "the physical basis of
life," is a colloidal substance consisting of exceedingly

FIG. I. — Diagram of a typical cell, c, centrosome; ch, chondriosomes; ry/, cytoplasm; cw, cell
wall; n, nucleus; nl nucleolus; nm, nuclear membrane.

complex proteins and containing water, salts, carbohydrates,
fats, and various products of its own metabolic activity.
The nature of these contents and the peculiar structure of
protoplasm itself vary according to the type of cell. In a
cell of voluntary muscle, the cytoplasm has a highly differen-
tiated fibrillar structure specialized in relation to contraction.
The cytoplasm of a gland cell, or an epithelial cell of the
skin, presents a very different appearance. There are many
types of cells whose cytoplasmic structure varies in accord-
ance with their diverse functions. In the ovum the cyto-
plasm commonly contains spheres or granules of yolk
which serve as food material for the developing embryo.

6 HUMAN GENETICS AND ITS SOCIAL IMPORT

Some cells contain very large amounts of this substance;
in birds, for instance, the so called yolk of the egg consists of
one enormously enlarged cell.

The nucleus of a cell usually has much the same structure
however varied the character of the cytoplasm by which
it is surrounded. It is generally spherical in form, and its
contents, which are enclosed by a thin nuclear membrane,
present the appearance of a network in whose meshes lie
numerous granules of a material called chromatin. This
chromatin has a marked affinity for certain dyes, which
are used for staining nuclei, so that they may be sharply
distinguished from other parts of the cell. At times the

FIG. a. — Amitosis, or direct cell division in ovarian nurse cells of the potato beetle, Lepti-
notarsa. (From Wieman?)

chromatin of the nucleus is aggregated into definite bodies,
usually rod-like or thread-like in form, called chromosomes.
As a rule chromosomes appear only during cell division,
after which they again assume the appearance of a network.
The older students of the cell looked upon cell division
as a very simple process. Both the nucleus and the cell
body were supposed to become pinched in two forming two
daughter cells. In some cases, cells do divide in this way
(amitosis), but this is a very exceptional procedure and
usually occurs only in cells that are more or less pathological
and destined to undergo few subsequent divisions. The
regular and typical mode of cell division is accomplished by a
remarkable process, called mitosis, or karyokinesis. Com-
monly mitosis is inaugurated, by the division of a small

HEREDITY AND ITS CELLULAR BASIS 7

body, the centrosome, lying in the cytoplasm close to the
nucleus. The two daughter centrosomes gradually move
apart, and around each appear numerous rays, giving rise

FIG 3. — Karyokinesis, or mitotic cell division. A, resting stage showing two centrosomes
near the nucleus; B, beginning stage showing spindle and coiled thread of chromatin; C,
later stage with larger spindle and eight chromosomes; D, polar view of chromosomes at the
middle of the spindle; E, side view of spindle; F, a slightly later stage in which each chromo-
some is divided lengthwise; G, dividing chromosomes on spindle; H, the chromosomes pulled
apart; 7, end stage showing division of the cytoplasm; J, completed division into two
daughter cells. (From

to a stellate figure called the aster. Between the asters
there develops a spindle-shaped body that appears to be
traversed by a number of fibers. As the centrosomes move
farther apart, the astral rays extend farther into the cyto-
plasm and the spindle enlarges. The nuclear membrane

8 HUMAN GENETICS AND ITS SOCIAL IMPORT

disappears, and the chromosomes, which in the meantime
had been forming from the nuclear network, become drawn
upon the spindle, taking up a position around the central
part of it. Each chromosome as it lies on the equatorial
region of the spindle appears to be divided lengthwise, the
division being often manifest as a sort of double thread, long
before the chromosomes take up their position in the mitotic
figure. The chromosomes which seem to be attached to
fibers extending from the centrosomes are then drawn
apart. As the chromosomes approach the two poles of the
spindle, they lose their regularity of outline and, after
becoming surrounded by a new nuclear membrane, are
finally incorporated into the two daughter nuclei. In
the meantime the cytoplasm divides into two parts, thus
completing the division of the cell. The spindle fibers and
asters, which seem to have been called into existence to
afford a mechanism for this peculiar kind of division,
completely disappear after their work is done. Only the
centrosomes may remain (and not even these in all cases) to
form the starting point of the next ensuing division.

In this elaborate process each of the chromosomes is
divided longitudinally into two equal parts. As was pointed
out by Roux, the whole process of mitosis seems to be
especially evolved for the achievement of this end. We now
know that the precisely equal division of each and every
chromosome is a matter of great importance in relation to
heredity. There has accumulated a vast amount of critically
tested evidence to the effect that chromosomes contain the
factors which give rise to hereditary characters. Usually
the number of chromosomes is constant in a given species,
although it may vary between different species even of the
same genus. In man the chromosome number is forty-eight, in
the common fruit fly Drosophila melanogaster it is eight,
and in the round worm Ascaris megalocephala it is four,

HEREDITY AND ITS CELLULAR BASIS 9

and in one variety, univalens, only two. The chromosome
number stands in no definite relation to position in the
scale of life. In some of the one-celled Radiolaria the chromo-
some number is said to be over one thousand.

At one time there was a good deal of controversy over
the so-called individuality of the chromosomes. Although
the number of chromosomes is normally constant for a given
species, it might be, and in fact it was, maintained that this
constancy does not involve the persistence of each chromo-
some as an individual unit through the resting stages of
the nucleus. Many characters of organisms, it was urged,

O c* U r> o fi o> u ort «<»«»• n •»»»••• »••«•«*

)> « AJ »> filttci r> «M )| O It >< o »«»•«»» >»«i i»4-

FIG. 4. — Chromosomes of man showing pairs of chromosomes from four spermatogonia.
(After Evans and Swezy.)

are reproduced in numbers which are almost always the
same. In common with nearly all mammals we have seven
vertebrae in our necks, and a definite number of ribs, fingers,
toes, and teeth, but no one supposes that these structures are
represented by so many preformed parts in the germ plasm.
The constant number as well as the structure of all these
parts is the result of developmental processes. Organs are
reproduced, not simply handed on. Hence it was inferred
by some biologists that the constancy of chromosome
numbers could be interpreted in the same way.

Usually no traces of individual chromosomes can be
discerned in the resting nucleus of the cell. In this stage
the chromosomes appear to be merged into the general
nuclear network in which the visible chromatin is in the

io HUMAN GENETICS AND ITS SOCIAL IMPORT

form of threads, granules, or irregular masses of larger size.
When the chromosomes again take shape . in preparation
for the next cell division it may well be doubted if each
chromosome is composed of the same material as it was
before it entered the resting stage. But despite many
biological analogies that might be cited to the contrary,
there is now very convincing evidence that chromosomes
preserve their identity through successive cell divisions.
Not only are chromosomes constant in number, but in
many organisms individual chromosomes may be seen to
retain their peculiarities of size and shape. This fact affords
additional presumptive evidence for continuity, but it is
not necessarily conclusive since it might be explained as
due to the same sort of causes that lead to the repetition of
similar shapes and sizes in the bones of our fingers and toes.
If we could try the experiment of removing one or more
chromosomes or possibly adding one or more extra ones
and then see if the abnormal number was retained, we
might obtain a crucial answer to our problem. Cytologists
are able to perform marvelously delicate operations in
dissecting the living cell, but the particular operation I
have mentioned has not yet been accomplished. However,
it is not really necessary to perform this experiment because
Nature occasionally does it for us. Sometimes the chromo-
some number is doubled or even increased still more, or
again it may be halved, and the changed number of chromo-
somes is found to persist through the resting stages of
the nucleus. In other cases one or more chromosomes are
lost, or there may be one or more extra chromosomes, and
in these cases also the abnormal number is retained. Oc-
casionally only a part of a particular chromosome is lost
and this mutilated condition may be recognized through
successive cell divisions. There are also other mishaps
which befall the chromosomes at times, such as a piece of

HEREDITY AND ITS CELLULAR BASIS n

one chromosome being broken off and joined to another
one in various positions, sometimes at one end or sometimes
near the middle. Even these anomalies persist through many
cell divisions and from generation to generation, and
constitute permanent modifications of the hereditary pecu-
liarities of the group. From such facts as these it is now
practically certain that chromosomes retain their individual-
ity through the resting stages of the nucleus. Just as each
cell comes from a preexisting cell, so does each chromosome
come from a preexisting chromosome. But what happens
to the chromosomes when they can no longer be distinguished
in the resting nucleus ?

Apparently each chromosome must constitute a particular
region of the resting nucleus, a sort of compartment of its
own, so that when a chromosome emerges it is constituted of
the same material as before. In the fish Fundulus and in
some other forms the chromosomes as they separate in
mitosis swell up into separate vesicles which remain more or
less separate in the resting stages of the nucleus. In fact,
each chromosome may be said to form a little nucleus of
its own. Where the vesicles are closely packed together, the
outline of each may be so obscured that the individual
vesicles can no longer be distinguished. Probably something
like this occurs in the usual type of cell division.

The persistence of chromosomes as individual units has
a very important bearing on our interpretation of the
physical mechanism of hereditary transmission. The chromo-
somes behave like so many little organisms multiplying by
fission. In many species, as we shall see later, the chromo-
somes may be seen to be composed of still smaller units called
chromomeres arranged in a linear series. Sometimes the
chromosomes resemble strings of beads, as in those of the
onion shown in Fig. 5. Still more remarkable details of
chromosome structure have recently been discovered in the

12 HUMAN GENETICS AND ITS SOCIAL IMPORT

salivary glands of the larvae of the fruit fly, Drosophila.
For some peculiar reason the chromosomes in these gland
cells have assumed a perfectly enormous size, being about
150 times as large as they are in ordinary cells. In stained
preparations they show a very definite banded structure.
Some of the bands are fairly broad and clear, others are
faint, but hundreds of individual bands have been identified,
and their position is normally constant in all the chromo-

FIG. 5. — Chromosomes of the onion Allium triquetrum. The chromosomes appear to be made
of strings of chromomeres which show a paired arrangement. (After Belling.')

somes of a given pair. An illustration of the so-called Jf-chro-
mosome, or sex chromosome, is shown in Fig. 6. It is now
possible, as is explained in a later chapter, to associate
definite hereditary factors, or genes, with regions of indi-
vidual chromosomes marked by these bands. Thanks to the
occurrence of these giant chromosomes it is demonstrable
that the little rod-like bodies that appear during mitotic
cell division have a high degree of regional differentiation.
The chromosomes of the fruit fly have now been mapped out
in a degree of detail that may seem incredible to those who
have not been initiated into the mysteries of modern genetics.

HEREDITY AND ITS CELLULAR BASIS 13

One can, for instance, locate the position of the genetic
factor which causes the eye of the fruit fly to be white
instead of red in a particular region very close to a band
near the left end of the X-chromosome. Many other heredi-
tary factors have been located with an equal degree of

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FIG. 6. — Giant Jf-chromosome from the salivary gland of the fruit fly Drosophila. For
an explanation of the abbreviations see the map of the Jf-chromosome on p. 73. (After
Painter.)

precision in the same or some other chromosome, and we
may conclude, therefore, that each component part of a
chromosome reproduces itself with great fidelity, and that
the reproduction of chromosome parts is an essential element

FIG. 7. — Chromosome vesicles of the fish Fundulus. Each chromosome swells up to form
a separate vesicle which persists through the resting stages of the nucleus. Ordinarily the
outlines of individual chromosomes can not be discerned in the resting stages, possibly
because the vesicles are so closely pressed together. Compare the right-hand figure. (After
Richards.)

in the transmission of hereditary traits. Some idea of the
method by which these remarkable conclusions have been
established will be given in a later chapter.

Although the chromosome number of a given species is
maintained through countless series of cell divisions, there

i4 HUMAN GENETICS AND ITS SOCIAL IMPORT

is one point in the life cycle in which there is an exception
to this rule. In the animal kingdom this occurs during the
formation of the sex cells, or gametes. During sexual repro-
duction, the egg cell is fertilized by a sperm cell from the
sex gland of a male. In this process the nuclei of the
male and female gametes unite to form the nucleus of
the fertilized ovum. If the egg and sperm cells contain the
number of chromosomes characteristic of the species, the
number in the fertilized egg would be doubled in each

FIG. 8. — Diagram of the fertilization and first cleavage of the egg, showing the entrance
of the sperm, the transformation of its head into the male pronucleus, the enlargement of
the latter and its approach to the egg nucleus, the union of the egg and sperm nuclei and the
division of the maternal and paternal chromosomes in mitosis. (After Sharp.)

generation. This consideration led Professor Weismann to
postulate that prior to fertilization the germinal elements
responsible for heredity must be reduced to one-half their
previous number. This prophetic declaration received a
striking confirmation through the study of the behavior of
chromosomes during the final stages in the formation of the
germ cells. In both oogenesis and spermatogenesis, it was
found that, during the last two divisions, the chromosomes
were reduced to half their previous number. The act of
fertilization restores the number characteristic of the
species.

HEREDITY AND ITS CELLULAR BASIS

One may well ask why the sex cells should go through
these peculiar maturation divisions and reduce their chromo-
some number to one-half if the original number is to be
soon restored again in the act of fertilization ? The answer

Spermatogenesis GAMETO GENESIS Qogcnesis

Primordial Germ Cell
(Diploid chromosome number)

Division Period

Growth Period,
Synopsis

Ist.Mat.DiV.
Chromosomes re-
duced to haploid
number

2nd. Mat. Division,
(quantitative)

Fertilization

Cleavage

Spermatozoa

FIG. 9. — The formation of male and female sex cells (gametogenesis). Note the selective
pairing of chromosomes in synapsis in spermatocyte I and oocyte I and the subsequent
reduction from eight to four in the maturation divisions. (From JVieman.)

to this question will give the clue to the biological significance
of sex. It is evident that, although reduction and fertilization
do not change the chromosome number, they effect a new
combination of chromosomes, in that the chromosomes of
the resulting individual are one-half of maternal and one-half

16 HUMAN GENETICS AND ITS SOCIAL IMPORT

of paternal origin. In other words, these processes provide
the possibility of biparental inheritance.

Many years after the essential character of maturation
and fertilization was established, another important feature
of chromosome behavior was discovered, which proved to
be of the highest significance in relation to the mechanism
of heredity. This is the process of synapsis, or the pairing
of the chromosomes, which takes place previous to the
maturation divisions. When the chromosomes come together
in pairs they do not fuse completely, but are intimately

FIG. 10. — Pairs of chromosomes in the synapsis ofGasteria. Note the pairing of corresponding
chromomeres. (Ajter W. R. Taylor.}

associated for a time, after which they are separated in the
maturation divisions and go into different germ cells. There
is convincing evidence that this pairing does not take place
at random, but that each chromosome derived from the
female parent pairs with a corresponding, or homologous
chromosome derived from the male parent. Chromosomes
are thus very discriminating as to the other chromosomes
with which they pair. Each chromosome, drawn by what
subtle affinity we do not know, somehow finds its predestined
mate. This highly selective pairing insures that, after the
pairs separate, each germ cell gets a complete set of all the
different kinds of chromosomes in the body. We now know
that it is highly important that these sets be retained intact.

HEREDITY AND ITS CELLULAR BASIS 17

In any one germ cell, the proportions of chromosomes of
maternal or of paternal origin may vary — this is a matter
of chance — but each germ cell has one representative of
all the different kinds of chromosomes characteristic of
the species. After fertilization, each individual has two sets.
Hence, sexually reproduced individuals are duplex in their
inheritance.

It is natural to correlate the equality of chromosome
contributions from the two parents with the fact that both
parents contribute about equally to the hereditary qualities
of their offspring. Here is one of the many facts supporting
the so-called chromosome theory of heredity. But there
are many other facts which show that we must look to the
chromosomes and the way they get distributed and combined
in the processes of sexual reproduction for the reasons why
hereditary traits are handed on as they are. Let us now turn
to the consideration of the ways in which heredity works.

Suggested Readings

Numbers in parentheses refer to dates of references listed in the
Bibliography.

Shull ('31), chaps. 3, 4. Newman ('32), chap. 14. Further information in
Sharp ('34) and Wilson ('28).

Questions

1. Why is the experimental method superior to mere observation and
description in the attempt to discover the causes of phenomena ?

2. What method is most employed in the study of morphology, taxon-
omy, embryology, physiology, biochemistry, psychology, and the social
sciences ?

3. In what other respects besides those mentioned in the text does a
society resemble an individual organism ?

4. If amitotic cell division occurred during the development of the
germ cells, how would it probably affect the subsequent chromosome
mechanism ?

5. Do organisms differ hereditarily in more characters than they have
chromosomes ?

1 8 HUMAN GENETICS AND ITS SOCIAL IMPORT

6. How many chromosomes are there in the mature egg cells and
sperm cells of man, the common fruit fly, and Ascaris megalocephala,
variety univalens?

7. If one species of mammal had forty-eight chromosomes and another
forty-four chromosomes, how many chromosomes would you expect to
find in the hybrid resulting from crossing the two species ?

8. Suppose a species had a range of chromosomes from large to small.
Would it be possible through breeding for some forms to contain all the
large chromosomes and others to contain all the small ones ?

9. Why does synapsis result in maintaining intact the chromosome
sets of a species ?

10. What are the evidences for the individuality of the chromosomes ?

11. In what respects are oogenesis and spermatogenesis alike and in
what respects do they differ ?

12. Make a diagram of the chromosomes of the fruit fly, the chromo-
somes of the egg and the sperm cells, and those of the fertilized egg. How
are these chromosomes distributed to the cells that arise from the cleavage
of the egg ?

CHAPTER II

ARE ACQUIRED CHARACTERS INHERITED?

|.^ORMERLY heredity was looked upon as involving
i somehow a transfer of qualities from the various parts
of the parental body to corresponding parts of the bodies
of the offspring. The red hair or snub nose of a child was
thought to be derived in some way from the red hair or
snub nose of its father or mother. How such a transfer of
qualities could take place was not apparent, but there
were various theories about it. In accordance with this
concept it was natural to conclude that characters acquired
by the parents can be handed on, at least in some degree,
to subsequent generations. According to the great French
naturalist Lamarck, the evolution of organic life is largely
the result of the transmission of acquired characters. At
present most geneticists regard the Lamarckian theory with
much suspicion. Many people are strongly disposed to
believe in the transmission of acquired characters, however,
because it seems to offer greater possibilities for the progress
of the race. They do not like to think that the culture and
training which individuals acquire have no effect upon the
inborn qualities of their offspring. There are of course two
sides to this aspect of the question. If children do not
profit by the education and experience of their parents,
they escape being afflicted by the mutilations, deformities,
and general decrepitude that fall to the lot of so large a
proportion of humanity. Among human beings at least the
transmission of acquired characters might prove to be more
of a misfortune than a benefit.

20 HUMAN GENETICS AND ITS SOCIAL IMPORT

At one time biologists considered that acquired characters
are about as likely to be transmitted as any others. In
fact, no sharp distinction was made between characters
that are due to heredity and those which are acquired as a
result of experience with the environment. According to
some of the earlier theories of heredity, such as Spencer's
ingenious theory of physiological units and Darwin's theory

FIG. ii. — J. B.Lamarck. (After Locy.)

of pangenesis, both acquired characters and congenital
characters are supposed to be handed on by essentially
the same type of mechanism. In his great work on Variation
of Animals and Plants under Domestication , Darwin accumu-
lated an enormous fund of information concerning variation
and hereditary transmission, and in the last chapter he
set forth what he modestly called a provisional theory of
heredity. He supposed that all parts of the body give off
minute vital units called gemmules, which are capable of
growth and multiplication. These gemmules were supposed

ARE ACQUIRED CHARACTERS INHERITED? 21

to collect in the germ cells. During development, the gem-
mules derived from the various parts of the body were
supposed to impress their several characteristics upon the
corresponding parts of the offspring. If for any reason the
distribution of gemmules was disturbed, a variation would
result. If a part were increased through use, it would give off
more gemmules, and the germ cells having more gemmules
of this particular kind would produce offspring with the part
more fully developed. Darwin's theory thus lent itself very
readily to the explanation of the transmission of acquired

FIG. 12. — Diagram illustrating the course of the gemmules according to Darwin's theory
of pangenesis. The gemmules from the parts of the body, S, S, etc., are supposed to collect
in the germ cells, G, and to give rise to corresponding parts of the body in the offspring.

characters. Since Darwin believed in this doctrine, and
sometimes appealed to it in his evolutionary speculations,
he felt that an adequate theory of heredity must be able
to explain the possibility of such transmission. His' theory
of pangenesis gave a concrete expression of the common
conception of heredity to which we have alluded, as involving
transmission from parts of the body of parents to correspond-
ing parts of the body of their progeny. The process may be
represented by the foregoing diagram (Fig. 12). Gemmules
are of course purely hypothetical entities. Their postulated
behavior was soon recognized as improbable from the stand-
point of physiology. The theory of pangenesis, although
it was worked out in a very ingenious way and subsumed

22 HUMAN GENETICS AND ITS SOCIAL IMPORT

many facts of heredity and variation under a common
standpoint, never succeeded in securing much support and
was finally completed abandoned.

Among other theories to explain the transmission of
acquired characters are the various forms of the mnemic
theory, according to which heredity is somehow akin to
memory, and development is analogous to recollection.
This doctrine first set forth by Hering has made a strong
appeal to Semon, the late Samuel Butler, and also Mr.
Bernard Shaw. But the theory is too vague and nebulous
to appeal to most hard-headed geneticists. The Lamarckians
have always found difficulty in presenting a plausible theory
as to how acquired characters can be handed on. One is
not justified, however, in asserting that a process cannot
occur because there seems to be no reasonable explanation
of how it could happen. We have by no means unraveled
all the intricacies of life processes, and we cannot afford
to be dogmatic about Lamarckian inheritance because it
is not what we would expect in the light of our present
knowledge of the mechanism of heredity. But we should be
skeptical and not accept the theory unless adequate evidence
can be produced in its support.

A potent factor in causing biologists to become distrustful
of the Lamarckian theory was the attacks of Weismann
during "the eighties and nineties. Weismann had a theory
of heredity of his own, based upon the concept of the con-
tinuity of the germ plasm. The germ plasm was supposed
to be derived, not from the body or soma, but from the
antecedent germ plasm of the parents, which was supposed
to be passed on in an unbroken stream through countless
generations. A part of the germ plasm becomes differentiated
into the body cells, but a small portion of it persists un-
changed in the germ cells. In Weismann's view the germ
cells give rise to the body cells, but the germ cells are not

ARE ACQUIRED CHARACTERS INHERITED? 23

strictly speaking derived from the body but from antecedent
germ plasm. The reason why offspring resemble their parents
is because both arise from a common substance, of which
their bodies are the carriers. This is a very simple way of
looking upon heredity. Moreover, it harmonizes very nicely
with the cell theory. Weismann held that the part of the
cell responsible for hereditary transmission is the nucleus
and more particularly the chromosomes. And since chromo-
somes arise from the division of antecedent chromosomes,
these bodies would seem to be admirably adapted to serve as
carriers of hereditary factors.

Germ,
cells

FIG. 13. — Diagram illustrating Weismann's conception of the continuity of the germ
plasm. The germ cells produce other germ cells, and also the other cells that constitute the
body, or soma.

The one feature that distinguishes Weismann's theory
most sharply from the theory of Darwin is that hereditary
qualities are not derived from the bodies of parents. Like
plants arising from a common stolon or runner, successive
generations are similar because of their common origin.
If this theory is correct, it would seem to preclude the
transmission of acquired characters, because there seems to
be no way in which such characters can be passed into
the germ plasm. According to this theory, therefore, one
would not expect acquired characters to be inherited.

Having espoused his theory of the continuity of the
germ plasm, Professor Weismann was very naturally led to
examine the evidence for the transmission of acquired
characters and came to the conclusion that it was far from
conclusive. His criticisms convinced a large proportion of

24 HUMAN GENETICS AND ITS SOCIAL IMPORT

his biological colleagues that the Lamarckian theory had
been accepted upon insufficient grounds. Many biologists,
however, remained devoted Lamarckians, and while the
theory has steadily lost adherents, there are still able
biologists who stoutly defend it.

One of the first and most frequently mentioned tests of the
Lamarckian theory was the experiment of cutting off the
tails of mice to see if the progeny would have shorter tails.
Although twenty-two generations of mice were subjected
to this indignity their progeny continued to produce tails
of the usual length. There have been reports of isolated
cases where an accidental mutilation has been followed by a
similar defect in the offspring. But there is no assurance that
these cases may not be due merely to coincidence. Many
savage tribes have the custom of gashing their cheeks,
stretching their ears, filing their teeth, and flattening their
skulls, but their children are born sound and normal,
despite untold generations of such treatment. Biologists
should feel grateful to their less enlightened brethren for
these long-continued experiments on the hereditary effects
of mutilations. There is no good evidence that the rite of
circumcision has been productive of any inherited results.
Even the Lamarckians concede that the evidence for the
inherited affects of mutilations is mostly negative. They
usually contend, however, that mutilation affords no real
test of the Lamarckian theory, because if a part is removed,
it is thereby rendered incapable of affecting the germ cells.
But granting the relevancy of this contention, it may be
pointed out that many kinds of mutilations, such as those
shown in the figure, do not involve the loss of any part,
but are merely changes in configuration, which, according
to the theory, should produce some inherited effect.

The experiments on Lamarckian inheritance extending
through the largest number of generations have been carried

ARE ACQUIRED CHARACTERS INHERITED? 25

on with the common fruit fly, Drosophila. In order to test
whether disuse of the wings would lead to their gradual
reduction in a series of generations Lutz bred Drosophilas
in small vials in which they were unable to fly. After forty-
nine generations, the average wing length was found to be
fully as great as at the beginning of the experiment. A
common explanation of rudimentary organs is that they
result from the inherited effect of disuse. The theory seems

FIG. 14. — Mutilations practiced by different peoples. The two figures to the left represent
the distorted foot of a Chinese lady. The right figure, after Haardt and Audouin-Dubreuil,
shows an extreme distortion of the lips by means of flat disks. Generations of these and
other deformities have failed to cause any noticeable effect upon the progeny.

plausible, but it lacks experimental proof. Dr. Payne bred
fruit flies in the dark to see if their eyes would become
reduced in size. Many cave animals which live in almost
total darkness have either lost their eyes entirely or else
possess eyes in various stages of atrophy. But Dr. Payne's
fruit flies, even after sixty-nine generations in the dark,
showed no reduction in the size of their eyes or in their
ability to react to light. It is easy to say that some effect
might be produced if the flies were kept in darkness for
several thousand generations instead of sixty-nine. One

26 HUMAN GENETICS AND ITS SOCIAL IMPORT

must concede that this is possible, but possibilities of this
sort do not constitute a satisfactory basis for accepting a
theory.

While the results of these experiments are distinctly
negative, other experiments have yielded results which
have been claimed to support the Lamarckian doctrine. A
number of these have been reported by the enthusiastic
Lamarckian, Paul Kammerer, but the careless methods
employed, the lack of adequate controls, and the rather
sensational and declamatory manner in which the results
were described have caused most biologists to look upon
Kammerer's work with profound distrust. The veteran
Russian physiologist Pavlov, justly famous for his classical
investigations on the digestive glands and conditioned
reflexes^ described some experiments in which it was claimed
that the progeny of mice, trained to come at the sound of a
bell, learned to respond much more readily than the progeny
of mice which were untrained. This startling announcement
from so eminent a scientist was widely quoted. Similar
experiments were repeated by other scientists who failed
to confirm these results. And finally Pavlov, himself, stated
that, owing to sources of error involved in the experiments,
they could not be interpreted as yielding support to the
Lamarckian doctrine.

The most thoroughgoing and carefully controlled experi-
ments to test the inheritance of the effects of learning were
carried out by Dr. W. McDougall upon rats that were
trained to swim through the right passage of a maze. Several
generations of rats were put through the experiment, and
McDougall reported that the progeny of the trained rats
were able to learn the maze more readily than those of
rats which were untrained. The experiment was repeated
by Crew who failed to obtain the same results, and who is
disposed to explain the findings of McDougall on grounds

ARE ACQUIRED CHARACTERS INHERITED? 27

other than the transmission of acquired characters. Others
have criticised the experiments because the effects of
selection were not adequately guarded against. Even
McDougall did not claim that his results afforded a demon-
stration of Lamarckian inheritance, although they were
held to yield strong support to this doctrine.

One might be disposed to think that the problem of the
transmission of acquired character would be rather easy
to settle, but the investigation of the subject is beset with
many sources of error. Many experiments have been adduced
in support of the Lamarckian theory, but they have all
been criticised as inadequate. It would scarcely be profitable
to discuss these experiments in detail. We shall have to be
content with referring the student to the suggested readings
on this subject at the end of chapter and the further list
of references at the end of the volume.

Suggested Readings

Detlefson ('25), Guyer ('27), chaps. 15, 16. Newman ('32), chap. 31.
Thompson ('13), chap. 7. See also Kammerer ('24), McDougall ('27), ('30),
Weismann ('91), ('93).

Questions

1. Is germ plasm necessarily different from body plasm ? If not, is this
fact opposed to the doctrine of its continuity ?

2. What biological facts are plausibly explained by the Lamarckian
theory ?

3. The workers of the hive bee are normally sterile. What bearing does
this fact have on the theory that their instincts have been gradually
evolved through the transmission of acquired characters?

4. Discuss the Lamarckian theory in relation to protective coloration,
the devices of seeds to facilitate dissemination, and the structures of
flowers which favor cross-pollination through the visits of insects.

5. Is the transmission of immunity to disease from mother to offspring
through the placenta an evidence of Lamarckian heredity ?

6. What bearing does the doctrine Omnis chromosoma e chromosoma
have on the probability of the transmission of acquired characters ?

28 HUMAN GENETICS AND ITS SOCIAL IMPORT

7. What are the results of transplanting ovaries from one animal to
another, and how do they bear on the Lamarckian theory ?

8. If alcoholic habits run in families, is it an evidence of Lamarckian
heredity ?

9. According to Darwin's theory of pangenesis would you expect that
the removal of an organ would have a hereditary effect?

10. If a child's parents both became deaf from scarlet fever, would you
expect that the child's hearing would thereby become affected ?

11. Is there any other explanation of the origin of rudimentary organs
except that they result from the inherited effects of disuse ?

CHAPTER III

MENDEL'S LAW

THE discovery that has done more than anything else
to reduce the manifold phenomena of heredity to
law and order was made by an Austrian monk Gregor
Johann Mendel. By training Mendel was a physicist, but
from his boyhood he had a strong interest in studying plants
and animals. He had read Darwin's Origin of Species and
the works of some of the older breeders of plants. Perhaps,
he thought, some light on the species problem may be
gained through a careful study of plant hybrids. For various
reasons be chose for experimentation the common garden
pea, Pisum sativum. There were several varieties of this
plant available, differing in sharply defined characters,
and Mendel focussed his attention on these particular
features of the plant. In the garden of the monastery at
Briinn, Austria, Mendel carried on for several years his
experiments in crossing different varieties of garden peas.
His principal results were embodied in a paper published
in the Proceedings of the Natural History Society of Briinn
in 1866. This paper ranks as one of the finest achievements
of experimental research. Nevertheless, no one paid any
attention to it. There seems to be only one brief reference to
it in the scientific literature before 1900. Somewhat sadly
Mendel was wont to remark, "Meine Zeit wird schon
kommen" — My time will surely come. But it did not come
until after he was dead. In 1900 through a remarkable
coincidence Mendel's work was brought to light by three

men, DeVries, Correns, and Tschermak, each of whom

30 HUMAN GENETICS AND ITS SOCIAL IMPORT

confirmed Mendel's results by independent investigations
of his own. Then the science of genetics took on a new
lease of life. It grew mightily. As a consequence more has
been learned about heredity in the past thirty-five years
than had been learned in all preceding time. Let us look at
some of the results achieved by this patient and sagacious
monk.

FIG. 1 5.— Gregor Johann Mendel. (From A. F. Shull.)

When Mendel crossed a tall with a dwarf pea, he found
that the immediate progeny were all tall. Likewise when he
crossed a yellow with a green pea, the progeny were all
yellow. The characters tall and yellow were called dominant,
while dwarf and green were called recessive. The appro-
priateness of the latter term is shown by the fact that in
the second generation of hybrids, the recessive character
reappears. And what is more remarkable it reappears in a
definite numerical ratio, one-fourth of the progeny showing

MENDEL'S LAW 31

the recessive character, while three-fourths exhibit the
dominant character. By a painstaking analysis Mendel
demonstrated that the peas having the dominant trait
were not all alike; two- thirds of them when self fertilized
produced offspring which gave the same ratio of three domi-
nants to one recessive, while one-third of them produced
nothing but pure dominants. One may write a general
formula for the second generation of hybrids as

iDD + iDR + iRR

Both the pure or homozygous dominants, DD, and the
pure recessives, RR, breed true indefinitely, while the
mixed or heterozygous forms, DRy produce dominants and
recessives in the 3:1 ratio. This separation in the second
generation of the characters that entered the cross is called
the principle of segregation and represents the essence of
Mendel's brilliant discovery. He found that all the seven
pairs of characters with which he experimented in garden
peas segregated out according to the 1 :2:i ratio in the second
generation.

A mind having Mendel's bent for accurate analysis
was naturally led on to inquire what would happen if
peas were crossed differing in two pairs of characters. In
practice this proved a more difficult problem to solve, but
in principle the solution was simple enough. The members
of each pair were segregated out in the second generation
quite independently of the members of the other pair. Thus,
when a tall yellow pea was crossed with a dwarf green pea,
the first, or Fiy generation were all tall yellow peas, but the
second generation showed the following combinations:

9 tall yellow + 3 tall green + 3 dwarf yellow + i dwarf
green

This is the ratio which would be obtained if the members
of each pair were segregated independently of those of the

32 HUMAN GENETICS AND ITS SOCIAL IMPORT

other. It illustrates what is called the "law of independent
assortment/' Mendel demonstrated that this principle
applies to all the characters of peas with which he experi-
mented. He also showed that if three pairs of characters
are combined in a cross the same law obtains, but the ratios
of the various combinations of characters are more involved.

Sperms

SMOOTH

'YYSS

YELLOW
SMOOTH

YYSs

YELLOW
SMOOTH

YySS

YELLOW
SMOOTH

YYSs

YELLOW
WRINKLED

YYss

YELLOW
SMOOTH

YySs

YELLOW
WRINKLED

Yyss

YELLOW
SMOOTH

YySS

YELLOW
SMOOTH

' YySs

GREEN
SMOOTH

'yySS

GREEN
SMOOTH

yySs

YELLOW
SMOOTH

YySs

YELLOW
WRINKLED

Yyss

GREEN
SMOOTH

'yySs

GREEN

WRINKLED

FIG. 1 6. — Diagram illustrating the dihybrid ratio obtained from crossing peas differing
in two pairs of characters, a smooth yellow with a wrinkled green pea. Each of the four
kinds of gametes of one individual can unite with any of the four kinds of gametes of the
other individual and thus produce sixteen combinations shown in the squares. (From Haupt.)

If, for instance, we cross a tall, yellow, round seeded pea
with a dwarf, green, wrinkled seeded pea, the second genera-
tion of the hybrid would be:

27 tall round yellow + 9 tall round green -f 9 tall wrinkled
yellow -f 9 dwarf round yellow + 3 tall wrinkled green +
3 dwarf round green + 3 dwarf wrinkled yellow + i dwarf
wrinkled green

With four characters the ratios would be still more com-
plicated.

MENDEL'S LAW 33

The demonstration that particular characters could be
combined and segregated in perfectly definite mathematical
ratios was a surprising revelation. Mathematical exactness
is rarely encountered in the phenomena studied by biologists,
and had Mendel been trained in the biological sciences
instead of physics and chemistry, he might never have
made his great discovery. According to Mendel's law,
inheritance is essentially alternative so far as each unit
character is concerned. Botanists and zoologists were
familiar with inheritance of this type, but they regarded it as
exceptional. Different characters in the parents were sup-
posed to blend in the offspring and to produce a fairly
permanent intermediate condition. There was no perma-
nent blending in Mendel's peas. The progeny were
round or wrinkled, tall or dwarf, and not something halfway
between.

After Mendel's unnoticed papers were brought to light,
biologists were spurred on to ascertain to what extent the
principles that obtained in the crossing of garden peas
might apply to plants and animals in general. Experiments
on the breeding of all sorts of plants and animals were soon
undertaken, and Mendel's law was found to hold true for a
great variety of organisms in both the plant and animal
kingdoms.

Quite naturally the question as to why the characters of
plants and animals are inherited according to definite
mathematical laws came prominently before the minds of all
students of heredity. Mendel himself had speculated upon it,
although nothing was known in his day of the cytological
changes involved in the production of the germ cells. Never-
theless, he hit upon an interpretation which, so far as it
goes, was shown later to be fundamentally correct. It was
the doctrine of the purity of the gametes, or sex cells, for
the factors upon which alternative inheritance depends.

34 HUMAN GENETICS AND ITS SOCIAL IMPORT

Mendel supposed that in the formation of the germ cells
by the F\ hybrid the factors for the two contrasted characters
were separated so that each germ cell would contain one
or the other factor, but never both or neither. Half of the
germ cells would contain the dominant factor, and a half
the recessive factor in a given pair of characters. If these
germ cells meet at random in all possible combinations,
they will produce offspring according to the ratio

iDD + iDR + iRR.

Let us suppose that we have two bags containing equal
numbers of red and green beads in each and I take a bead
at random out of each bag. I might draw a green bead out
of both, a red bead out of both, or a red bead out of the
first and a green bead out of the second, or vice versa.
In the long run my pairs of beads would consist approxi-
mately of y± reds, J4 greens, and H red and green. One
may also obtain Mendelian ratios by tossing two pennies,
which — if we toss them often enough — will turn up heads in
y± the throws, tails in J4, and a head and a tail in % the
throws. These ratios follow the laws of chance. Given
enough cases, phenomena due to pure chance may conform
to very definite statistical laws. Mendel showed that the
segregation of hereditary characters obeys the laws of chance
frequency distribution, and he rightly conjectured that the
reason why they do this is because the contrasted unit
factors in hybrid organisms come to be separated in the
formation of the gametes, or sex cells. Since these cells
with their different factors occur in equal numbers and are
free to unite in all sorts of combinations, these combinations
will on the average be formed in accordance with Mendel's
law.

Apparently something must occur during the formation
of the germ cells which is analogous to tossing pennies,

MENDEL'S LAW

and .the study of chomosome behavior in gametogenesis
has now revealed what it is. We have seen that when the
germ cells are formed, corresponding chromosomes of male
and female origin meet during synapsis, and then become
separated to pass into different germ cells. If now we make

D D

Poire n+s

R R

DD DR DR RR

FIG. 17. — Gametes, or sex cells in Mendelian heredity. The parents DD and RR have each
two factors for the dominant or the recessive character. Their sex cells will have only one
such factor and the F\ will therefore contain a dominant and a recessive factor from each
parent. The progeny of the Fi will have various combinations of the dominant and recessive
factors in the ratio iDD + iDR + iRR.

a very simple assumption that the factors for Mendelizing
characters are borne by individual chromosomes, we have a
very natural and plausible explanation of Mendelian hered-
ity. According to this assumption, the germ cells would be
pure for the factors for contrasted characters, and hence
their random combinations would give rise to Mendelian
ratios. In fact, Mendelian heredity may be said to be the
inevitable outcome of the pairing of homologous chromo-

36 HUMAN GENETICS AND ITS SOCIAL IMPORT

somes during synapsis and their subsequent distribution to
different germ cells.

In order to explain the typical dihybrid (9:3:3:1) ratio,
it may be assumed that the factors for different pairs of
characters are borne by different pairs of chromosomes, each
of which is assorted independently of the other in gameto-
genesis. We may then represent what takes place in crossing
a round yellow with a wrinkled green pea somewhat as
follows: Each plant we may assume is pure breeding, or
homozygous and has two sets of chromosomes. Each charac-
ter such as round or green is represented by something
occurring in both members of one pair of chromosomes and
hence in all the germ cells produced by the plants. In the
round yellow peas, we may assume that the factors for
round are carried by one chromosome pair, and those for
yellow by another. We may suppose that wrinkled green
peas are like the round yellow ones except that the factors
for yellow and round are replaced by the factors for wrinkled
and green in the corresponding pairs of chromosomes.
Now when the two varieties are crossed, the FI hybrid has
in all its cells factors for round, wrinkled, yellow, and green,
and when the germ cells of the hybrid are being formed,
the chromosome with the factor for round, and the chromo-
some with the factor for wrinkled pair in synapsis. And
at the same time the chromosome with the factor for
yellow pairs with the chromosome containing the factor for
green. When these chromosomes separate and go into
different germ cells, the chromosome having the factor for
yellow and the chromosome having the factor for round
may happen to go into one germ cell, and the two chromo-
somes with the factors for green and wrinkled into the other,
or else, as is equally likely, the chromosome with the factor
for yellow and the chromosomes with the factor for wrinkled
may go into the one cell and the chromosomes with the

MENDEL'S LAW

factors for round and green into the other. As a result
the FI hybrid will produce four kinds of germ cells in equal
numbers as follows: Round yellow, round green, wrinkled
yellow, wrinkled green.

When two FI plants cross, or if an FI plant produces seed
by self-fertilization, each of the four kinds of female germ
cells may unite with any of the four kinds of male germ cells,
thus producing sixteen combinations. One common way of
determining what combinations are likely to be formed in
the second generation of a cross is to write the formulas
of the germ cells of one parent along the top of a square
and the germ cells of the other along the left side. Then
the square is divided into smaller squares according to the
number of different kinds of germ cells involved, and the
various combinations are written in each square. In repre-
senting genetic factors it is customary to designate the
dominant ones by large letters and the corresponding
recessives by small letters, thus R would stand for round,
r for wrinkled, Y for yellow, y for green. A pure, round
yellow pea would be RRYY, a wrinkled green pea rryjy, and
the FI hybrid RrYy. Using this nomenclature we may work
out the expected F2 generation by the checkerboard method
as is illustrated in Fig. 16. In working out the expected
results of any mating the procedure is: first to ascertain
the possible gametes produced by the parents, and then
to find the various combinations which these gametes
form. For instance, if we wished to know what would
probably result from crossing the FI in our example back
to the green wrinkled parent, we take the four types of
gametes produced by the FI and combine each with the one
type of gamete (ry) produced by the wrinkled green pea.
The result will be four kinds of progeny, round yellow,
round green, wrinkled yellow, and wrinkled green in equal
numbers.

38 HUMAN GENETICS AND ITS SOCIAL IMPORT

In order to get a real grasp of the principles of Mendelian
heredity, it is necessary to work out a number of problems.
One does not acquire proficiency in algebra or geometry
without solving problems, and it is much the same with
genetics. Accordingly several questions for solution are
given at the end of the chapter.

If we would form a picture of the hereditary mechanism,
say of a human being, we should represent first a double
set of chromosomes forty-eight in number, of which twenty-
four are derived from the father and twenty- four from the
mother. Carried somehow in these chromosomes are the
factors involved in the production of hereditary charac-
teristics. These are called genes. We look upon genes as
little self-perpetuating units. We may say that all genes
come from antecedent genes, just as all cells come from
other cells. Each cell of the body contains all the genes
that were originally present in the fertilized egg, from which
the body cells were derived. How genes act to produce
characters we do not know. A pea giving rise to wrinkled
seed may differ from a pea producing round seed only in a
single pair of genes out of possibly thousands. We may sup-
pose that the gene for wrinkled peas produces an enzyme or
ferment that transforms some of the starch of the seed
into sugar. In some way particular genes must affect the
surrounding cytoplasm, causing it to change in some specific
way, and hence to produce a visible change in the organism.
Different genes produce very different effects, probably in
most cases in a very indirect way. One gene may cause
a small pit in the human ear, which has been observed to be
transmitted through several generations, another may cause
an individual to have six fingers instead of five, and another
may cause its possessor to develop Huntington's chorea late
in life and die of convulsive seizures. Manifold are the effects
of genes. The cooperative action of a large number of genes

MENDEL'S LAW 39

is required to build up an organism, but it not infrequently
happens that genes cause deviations from the normal, as in
Huntington's chorea, which are anything but advantageous.

Where genes produce such marked departures as to cause
the death of the organism, they are called lethal factors.
Many kinds of lethal factors have been identified in different
organisms. In some varieties of Indian corn, one-fourth
of the seedlings developed no chlorophyll and formed weak
albino plants that soon died. The lack of chlorophyll depends
upon recessive genes that exercise a lethal effect by prevent-
ing the plant from building up its carbohydrates under
t'he influence of sunlight. In a strain of fruit flies, a part
of the larvae developed pigmented tumors that have a
fatal effect, and in horses a recessive factor has been described
that causes a closure of the intestine with fatal results to
the young colts soon after they are born. Lethal genes
produce their fatal effects in many ways 'just as other genes
produce many kinds of normal variations. Among the
children of the family all drawing their genes from the com-
mon lottery of the parental germ plasms, Mary may have
red hair, John hare lip, William may have epileptic fits,
Polly's second and third toes may be connected by a fleshy
web, and Algernon may be a musical prodigy. The shuffling
and sorting of the chromosomes produce almost no end of
diverse combinations of hereditary traits. If a man and
his wife were to have a thousand children instead of a
maximum of less than thirty probably no two of them,
unless they happened to be identical twins, would have
the same hereditary endowments.

Suggested Readings

Jennings ('30), chaps, i and 2. Shull ('31), chaps. 7-9. Sinnott and
Dunn ('32), chaps. 3, 4. Wells, Huxley, Wells ('29), book 4, chap. 4.
Further discussions in Babcock and Clausen ('27), Altenberg ('28),
Conklin ('30), Dunn ('32), Jennings ('35), Morgan ('19), ('28).

4o HUMAN GENETICS AND ITS SOCIAL IMPORT

Questions

1. In guinea pigs rough hair RR is dominant over smooth rr. What is
the genetic formula of the .Fi of a cross between a rough and a smooth
guinea pig? What germ cells does the .Pi produce? What will be the second,
or Fz generation ?

2. What will result from crossing the F\ back to the white parent ? to
the black parent?

3. A cross between a white and a black guinea pig gives seven black
and six white offspring. What is the genetic composition of the parents ?

4. Crossing two peas gives 298 round and 101 wrinkled seed. What was
the genetic make-up of the parents ? What character is dominant ?

5. What part does synapsis play in securing the purity of the gametes
for contrasted Mendelian factors ?

6. Would you expect Mendelian inheritance in forms reproducing
asexually ?

7. Would you expect Mendelian inheritance if chromosomes did not
preserve their individuality?

8. Why are apples, peaches, and many other fruits propagated by buds
or grafts ? What commonly happens when these fruits are raised from seed ?
Why?

9. In guinea pigs black is dominant over white. If a rough black is
crossed with a smooth white guinea pig what will be the FI, the germ cells
of the Fiy and the proportions of the different types in the Fz ?

10. Make a diagram of the chromosomes of the rough black and the
smooth white guinea pigs, putting the factors for rough, RR, or smooth,
rr, in one pair of chromosomes, and the factors for black, BBy or white, bb,
in another pair. Diagram the chromosome make-up of the F\ and the
four types of germ cells of the F\.

11. What will result from a cross between theFi and the smooth white
parent ? between the Fi and the rough black parent ?

What will be the immediate progeny of a cross between guinea pigs of
the following genetic formulas ?

RRBb X rrBb
rrBb X Rrbb
RRbb X RrBB
RRBB X rrBb

12. In man brown eyes are dominant over blue. A brown-eyed man
with a blue-eyed mother marries a woman both of whose parents were
blue-eyed. What would be the expected eye colors of the children ?

MENDEL'S LAW 41

13. If these parents had four children what is the chance that they
would all be blue-eyed ?

14. Does the fact that three children in such a family are blue-eyed
affect the probability that the fourth child will be blue-eyed ?

15. Stubby fingers (brachydactylism) is a dominant character. What
is the chance that the child of a normal woman and a stubby fingered
father will inherit the trait if the father is heterozygous ?

CHAPTER IV
HEREDITY AND SEX

ONE very important outcome of the study of gameto-
genesis is the solution of the age-long riddle of the deter-
mination of sex. A very large number of organisms resemble
the human species in producing males and females in
approximately equal numbers. One might be prone to
regard this as a providential arrangement in the interest
of monogamous unions but we find it among animals who
are quite promiscuous in the matter of mating, as well as in
polygamous species in which an old and powerful male
monopolizes most of the females and drives away all rivals.

This approximate numerical equality of the sexes long
remained an unexplainable fact. The first real light began
to dawn when it was discovered that in the spermatogenesis
of certain species of insects there is an odd, or unpaired
chromosome which fails to divide, and is passed bodily
into one or the other of the two spermatocytes. In 1902
McClung advanced the theory that this odd chromosome is
a determiner of sex, since half of the sperm cells contain this
chromosome and half do not. There are many species in
which the odd, or X-chromosome instead of having no
mate has a mate of smaller size called the Y-chromosome.
Apparently it matters little whether a y-chromosome is
present or not. The important point is, in any case, that
sperm cells fall into two classes, half of them containing
the Jf-chromosome and the other half containing the
Y-chromosome or no ^-chromosome.

A startling theory, such as McClung's, did not have to
wait long before being tested. Not only were sex chromo-

HEREDITY AND SEX 43

somes studied in a large number of species both plant and
animal, but attention was turned to the study of the chromo-
somes in the body cells of both sexes. It was found that
in the formation of the mature egg cells, all the eggs receive
the same number of chromosomes, and that an ^f-chromo-
isome was present in every mature egg. It is only the sperm
cells that fall into two classes. This being so, it was natural
-t6 suppose that if an egg was fertilized by a sperm containing
an Jf-chromosome, it would produce a female, and if fertilized

»,

FIG. 1 8. — Sex chromosomes of the male bug Anasa. a, polar view of the division of the
first spermatocyte; b, side view of the second division showing the large sex chromosome
passing undivided into the lower cell; c and d polar views of the last division showing ten
chromosomes in one group and eleven including the undivided sex chromosome in the other.
(After Wilson.}

by sperm without an Jf-chromosome, but only a Yy it
would produce a male. Here was a very neat and simple
theory, almost too simple to be true. And cytologists
began to turn their microscopes on the cells of the male
and the female of the species in order to count their chromo-
somes. It turned out that in most species studied, the females
have an even number of chromosomes, including two
Jf-chromosomes, whereas the males have only one J^-chro-
mosome, in some species with, and in others without, a
y-chromosome. These facts lent strong support to the view

44 HUMAN GENETICS AND ITS SOCIAL IMPORT

that the chromosome differences of the sexes are really
responsible for the determination of sex.

A large amount of research on the chromosomes of sex
cells and body cells has yielded abundant confirmation of
this hypothesis. Sex determination would then appear to
be settled at the time of fertilization, when the individual
receives his or her allotment of chromosomes. All the
theories as to how the sex of unborn offspring could be
changed at will seemed to be swept away at once.

In most animals, man among the rest, and in some plants
it has been found that it is the male which produces two
kinds of gametes, or is the heterozygous sex. The birds
and the Lepidoptera (butterflies and moths) among insects
are exceptions to this rule in that the male is homozygous
and the female heterozygous for sex determining factors.
These facts have thrown much light upon the interpretation
of what is called sex-linked heredity. Certain hereditary
characteristics such as the horns in male deer, and the
mammary glands of the female are regularly associated with
sex and are known as secondary sexual characters, but sex-
linked characters are transmitted in a somewhat different
way. Let us take an illustration from human heredity. If a
normal woman marries a color-blind man, all her children,
male and female, will be normal, but her daughters may
transmit color blindness to their sons. The gene for this
trait is recessive and does not appear in the presence of its
corresponding normal factor. The peculiar inheritance of
color blindness is readily explained simply by assuming
that its gene is carried by the Jf-chromosome. The daughters
of a color-blind man and a normal woman have the defective
gene in the Jf-chromosome derived from the father, and a
normal gene in the ^-chromosome derived from the mother.
Although not showing the trait themselves, the daughters
would bequeath the gene to half their sons who, having but

HEREDITY AND SEX 45

one Jf-chromosome and no normal gene to counteract its
influence, develop color blindness. Sex-linked characters
thus present an exception to the rule that recessive traits
can manifest themselves only in a homozygous individual.
The fruit fly, Drosophila melanogaster, has over two hundred
sex-linked characters. In man there are much fewer sex-
linked characters known. Among these is hemophilia, a
condition in which the affected person bleeds very readily
owing to the imperfect clotting of the blood.

According to the usually accepted opinion, each sex may
carry factors for the opposite sex as well as its own. Like
other characters sex is a matter of genie balance. Males
derive their Jf-chromosome from their mother, and females
derive one of their Jf-chromosomes from their mother and
the other from their father. It is a curious fact that in the
honeybee, the eggs which are unfertilized and which derive
their chromosomes exclusively from the female develop
into drones, or males, while the addition of the chromosomes
of the male in the eggs which are fertilized results in the
production of females. Two doses of the ^-chromosome
produce a female, and only one produces a male. Appar-
ently sex is determined ordinarily by the quantitative relation
between the amount of Jf-chromosome material to the
rest of the germ plasm. This conclusion is strikingly borne
out by the fact that in Drosophila it has been found that
occasionally there are two ^-chromosomes and three sets
of the other chromosomes, in which case the individual is
more or less intermediate between a male and a female,
and is called an intersex. It has been supposed that the
^-chromosome contains factors that tend to make an indi-
vidual a female and that the male-producing factors are
in the other chromosomes. Where one Jf-chromosome is
present there are two male-producing sets of factors (iM)
present and the result is a male. Where there are iF and

46 HUMAN GENETICS AND ITS SOCIAL IMPORT

FIG. 19. — Sex-linked heredity in Drosophila. A yellow white-eyed female is crossed with
a gray, red-eyed male. The immediate (Fi) progeny consist of gray, red-eyed females and
yellow, white-eyed males. In the Fi female crossing over occurs in some of the gametes so
that the yellow and white factors previously linked become separated and lie in different
gametes. The result of crossing the F\ female back to the original male parent is to produce
the eight types indicated below. (After Morgan.}

HEREDITY AND SEX

producing factors, the balance is turned toward the
female sex. Where the ratio is iF . to yM, a more nearly
intermediate condition is presented and results in an inter-
sex. According to this interpretation sex determination is
really a matter of dominance. In most animals we may say
that iF is more potent than 2M, and that iM is more
potent than iF. In the birds and the Lepidoptera, iM is
more potent than iF, but iF is more potent than

X-

Y-

Femotle Mojle

FIG. 20. — Diagram illustrating the distribution of sex determining factors in the chromo-
somes. The factors for femaleness are assumed to lie in the AVchromosome, those for maleness
in the other chromosomes, or autosomes. Two F factors in the Jf-chromosomes outweigh
the two sets of m factors in the autosomes and produce a female. Where there is only one
^-chromosome the two sets of m factors outweigh the one F and produce a male.

The fact that each sex contains both sex factors not only
helps us to explain the phenomena of sex inheritance and
the exceptional occurrence of intersexuality, but it enables
us to understand why the sex of an organism can sometimes
be changed. In some hermaphrodite animals (i.e., those
having both male and female sex organs in one individual)
the sex may be at first male and later female. The common
eastern oyster regularly changes its sex with the seasons.
Gould has shown that the free-swimming larvae of the
slipper shell Crepidula which settle down near an adult
female become males. Otherwise, after passing through a

48 HUMAN GENETICS AND ITS SOCIAL IMPORT

more or less hermaphroditic period, they develop into
females. Probably some substance given off by the female
affects the sex differentiation of the young Crepidulas.
In this way the mollusks which are situated near together
are caused to be of opposite sex, and hence the eggs which
are discharged from the female are more apt to be fertilized.
A similar case is afforded by the marine worm Bonellia.
In these forms environment determines whether an indi-
vidual develops into a male or a female. Each embryo
contains the genetic factors for both sexes, and external
conditions decide which kind of sex factors assume the
predominant role in development.

In organisms having sex chromosomes the determination
of sex is largely independent of the environment and is
definitely established at the time of fertilization. There are
some forms, however, in which the potencies of the opposite
sex determining factors appear to be more nearly balanced,
so that under exceptional circumstances the influence of the
chromosome complex may be overcome. A few years ago
Dr. F. A. E. Crew described a hen which, after having laid
eggs, developed the plumage and peculiar behavior of a
rooster. Later she (or he) became the father of several
chicks. A post mortem examination showed that the ovary
had been nearly destroyed by tuberculosis and that testicular
tissue had developed in its stead and produced spermatozoa.
A little later Riddle described a case of transformation of
sex in pigeons due also to ovarian infection with tuberculosis.
Then followed experiments by Domm and others to ascertain
if the sex of fowl could be changed by the castration of
young females. In birds there is only one functional ovary,
the left, the right sex gland being represented by a small
rudiment. It was shown that early removal of the functional
ovary caused this rudiment to increase in size and, in many
cases, to develop into a testis, although varying amounts

HEREDITY AND SEX 49

of ovarian tissue may regenerate at the same time. Where
the newly formed tissue is mostly testicular there is a fairly
complete transformation of sex. Within certain limits,
therefore, early castration may cause females to change
into males. A somewhat analogous case is found in toads.
If a male toad is castrated a rudimentary structure called
Bidder's organ (really an abortive ovary) enlarges and
becomes transformed into a true ovary, which may produce
eggs capable of fertilization and development.

It is now definitely established that the sex of frogs can
be determined by temperature. Under ordinary circum-
stances frogs' eggs produce males and females in about equal
numbers. In many cases young frogs pass through a her-
maphrodite period in which rudiments of both male and
female sex organs occur in the same individual. Later either
testicular or ovarian tissue predominates and the individual
becomes exclusively male or female. Sometimes the her-
maphrodite condition persists until adult life, and there
are several instances of such individuals which have produced
functional eggs and sperm. Witschi has shown that when the
eggs of the wood frog are subjected to a high temperature
the sex organs of those which are genetically females develop
into testes and all the frogs become males.

In most animals a change in the sex glands causes a
change also in the secondary sexual characters. Among
many species, including the higher vertebrates, changes in
secondary sexual characters are largely effected through
the influence of the sex hormones, or internal secretions
of the sex glands. A striking illustration of this fact is
afforded by the experiments of Steinach in transplanting the
sex glands of young rats. Male rats are distinguished from
females by their larger size, coarser hair, and greater pug-
nacity. Steinach found that if the testes of young male rats
are removed and ovaries grafted in their stead, the rats

50 HUMAN GENETICS AND ITS SOCIAL IMPORT

attain about the size of females and do not develop the
coarse hair and pugnacious disposition characteristic of the
male sex. Their mammary glands became functional also
and in some instances they gave suckle to young. Females
in which the ovaries had been replaced by testes developed
the size, coarse hair, and sex instincts of males.

These changes in structural characters and in instinctive
behavior demonstrably result from the bodily influence of
hormones secreted by the sex glands. When these glands
are incompletely or abnormally developed the condition is
often manifested by changes of external appearance and
activities. It is a curious fact that crosses between different
varieties or species sometimes result in various degrees of
intersexuality. Within each group male-producing and
female-producing factors have developed degrees of potency
which ordinarily insure approximately equal numbers of
the two sexes. When varieties are crossed the normal balance
of sex determining factors may be disturbed thus causing the
appearance of an intersexual condition. How far varied
combinations of genetic factors may influence the degree
of sexual differentiation in human beings is uncertain.
There are masculine types of women and feminine types of
men. Neither class is particularly attractive to most normally
constituted persons. It seems likely, therefore, that the
choice of mates in the human species has a tendency to
maintain, if not to increase, the distinctive peculiarities
of the two sexes.

Suggested Readings

Lindsey ('32), chap. 9. Shull ('31) chaps. 14, 15. Sinnott and Dunn ('32),
chap. 9. Wells, Huxley, Wells ('29), book 4, chap. 6.

Questions

I. In what way does the inheritance of sex resemble that of a cross
between heterozygote, DR, and a double recessive, RR ?

HEREDITY AND SEX 51

2. What would happen to a female if one of her J^-chromosomes dis-
appeared before the first division of the egg ?

3. In plants which produce both ovules and pollen is sex determined
by differences in chromosomes?

4. If a character depends upon a gene in the Y-chromosome how would
it be inherited ?

5. A color-blind man marries a normal woman and one of her daughters
marries a normal man and the other daughter marries a color-blind man.
Give the expected distribution of color-blindness in the children of each
mating.

6. In what way does the inheritance of such a character as the beard
differ from that of a sex-linked character ?

7. Suppose that a sex-linked character is dominant, as in some forms
of night blindness in man. What will be the progeny, male and female,
of a normal male and an affected (heterozygous) female? of a normal
female and an affected male ? of one of the daughters of the latter union
and a normal male ?

8. Without sexual reproduction would there be any Mendelian
segregation ?

9. Why does a recessive sex-linked character appear in the male and
only rarely in the female ?

10. What reasons can you give as to why in some species one sex is
more numerous than the other?

11. What forms would be more variable, those produced sexually or
those produced asexually ? Why ?

12. What is Darwin's theory of sexual selection ?

13. Both hemophilia (bleeding) and atrophy of the optic nerve are
recessive sex-linked characters in man. What would be the result of mating
a man having optic atrophy and a woman having hemophilia? Of one of
the daughters of this union with a normal man ?

CHAPTER V
THE INTERACTION OF FACTORS

WE COME now to a topic of the greatest importance
for the proper comprehension of the workings of
heredity. First of all it is essential to bear in mind that
characters are never transmitted per se, but they are always
a product of a large number of genes. When we speak of
characters that behave like units in inheritance, one may
easily gain the impression that each character is caused by
a particular gene, much as each kind of plant is produced
by a certain kind of seed. The analogy, however, is apt to
be misleading. Geneticists have pretty much given up
talking about unit characters. They speak instead of unit
factors. A single factor may cause the difference between
brown and blue eyes, but this is very different from saying
that blue eyes are caused by a single gene. There are demon-
strably many genes which, in one way or another, affect
the development of the eyes. When some of these are
modified they may cause cataract, color blindness, misplaced
lens, atrophy of the optic nerve, or a multitude of other
hereditary or partly hereditary defects of the eyes, whether
they are blue or brown. Genes are differential factors. Alter
a single gene and the blue eyes which might thus arise would
still be the result of the coordinated workings of perhaps
hundreds of genes.

There are several classes of genetic factors, distinguished
according to how they act in the development of a given
feature of the organism. Sometimes there are two or more
factors in different pairs of chromosomes which produce

THE INTERACTION OF FACTORS

much the same kind of effect. These are commonly called
multiple factors. When, for instance, a certain brown-
seeded variety of oats was crossed with a white-seeded
variety, the second generation of hybrids was found to
consist of about fifteen browns to one white. This result

B,B2

b, B2

b, b;

B,BZ

b,Bz

B,B2
B, B2

B, b2

b, B2
B,B2

bj b2
B| B2

B,B2

B,b2

b,B2

bj b2

Btb2

B.| b2

Bib2

Blbi

!;=;

B, b2

bj B2

b, b2
b, B2

B,B2

B,b2

b,B2

b, b2

b,b2

b, b2

Brown

B I B |

White

| |

FIG. 21. — Diagram illustrating the inheritance of brown color when it is due to two pair
of factors which segregate independently. Where there is one or more factors for brown
Bi or Bz, the progeny are brown. Only one of the 16 combinations, b\bib\bi, is white.

was shown to be due to two independent pairs of factors for
brown. The 15:1 ratio is a modification of the typical 9:3:3:1
ratio in that the first three groups all look alike because
they all have at least one of the dominant factors for brown
color. In a cross between a red and a white variety of
wheat, the second generation was found to yield sixty- three

54 HUMAN GENETICS AND ITS SOCIAL IMPORT

reds to one white. Here the result was shown to be due
to three independent factor pairs for color. Among the
sixty-three colored class some have more factors for dark
color than others, but where dominance is nearly complete
these cannot be distinguished by inspection. In some cases
of multiple-factor inheritance the results are cumulative,
the indvidual having the largest number of factors showing
the character developed to the highest degree. Apparently
something like this occurs in the skin color of crosses between
Negroes and whites. The genes for black pigment are not
completely dominant over those for lighter color, and the
first generation of mulattoes is intermediate in shade.
The children of the mulattoes, however, are apt to have
varied combinations of black and white genes and hence
they exhibit a considerable range of skin color from nearly
black to nearly white.

The discovery of multiple-factor heredity has afforded
a very plausible solution to one difficulty which sorely
puzzled the early Mendelians. In some cases the -Fi genera-
tion is intermediate between the two parental types and
gives rise to progeny which are also more or less intermediate.
Crosses between large and small varieties of rabbits result
in the formation of an intermediate and fairly stable type.
Some geneticists were disposed to distinguish between two
radically different kinds of heredity, the one following
Mendel's law, the other resulting in so-called blending
inheritance. The analysis of several cases of multiple-factor
heredity gave rise to the hypothesis that what appear to be
permanent blends are really the result of many factors
having somewhat similar bodily effects. The multiple-factor
hypothesis is supported by the general fact that the second
generation of hybrids, as in the offspring of mulattoes, is
more variable than the first, thus revealing a tendency to
the segregation of factors which, on account of their large

THE INTERACTION OF FACTORS

numbers, rarely produce again quite the same combination
found in the original ancestors. As thus interpreted blending
inheritance is essentially Mendelian. This opinion which is
supported by many experimental tests is held by most
geneticists at the present time. Altogether, it seems to be the
most reasonable hypothesis in the light of the genetic evidence
and what is known of the cytological basis of heredity.

FIG. 22. — Variability of skin color in the offspring of mulattoes. (.After Davenport. Copyright
by 'Journal of Heredity?)

There is a class of genes called modifying factors, because
they affect more or less the expression of certain characters.
Thus in fruit flies having eosin-colored eyes there are several
factors whose position has been located in diverse parts
of the chromosome system which modify eosin color, making
it a little darker or a little lighter. Each of these modifiers
behaves like an independent Mendelian unit and has little
effect, so far as can be determined, upon other kinds of
eye color.

Then there are factors that are called complementary
inasmuch as each alone produces no visible effect, but when

56 HUMAN GENETICS AND ITS SOCIAL IMPORT

combined may cause a certain character to appear. A well-
known example of such factors is furnished by two pure-
breeding varieties of sweet peas which when crossed give
rise to a purple and red flower similar to that of the ancestral
Sicilian species from which our numerous cultivated varieties
have descended. The Mendelian explanation of this curious

OWhite G
OVery pale purple

HO Pale purple

ORed

fm Purple

• Blue

HH Deep purple

FIG. 23. — Results of crossing two races of white sweet peas, A and B. The F\ is purple
like the ancestral Sicilian species. The Fz presents a striking degree of variability as a
result of the segregation of several factors for color. (From Conk/in, after Punnett.)

phenomenon is that both white varieties lack something
necessary for the production of color, but that they do not
both lack the same thing. We may say that color requires
the presence of two factors C and P. If either is absent the
flowers are white. The one pea we may represent as CCpp,
and the other as ccPP. When their gametes Cp and cP
unite they bring together the complementary factors
C and P required to produce color. There is thus a restoration

THE INTERACTION OF FACTORS 57

of the complement of factors present in the wild ancestral
species.

The phenomenon of reversion has long been familiar to
breeders of plants and animals. Darwin noted that crosses
between different color varieties of pigeons sometimes pro-
duced birds of a bluish color with dark bars across the wings
like the ancestral blue rock pigeon from which most of our
domestic varieties have been derived. Again, the crossing of
rabbits of different color, say an albino and a yellow, for
example, might give rise to a rabbit of grayish color like that
of the wild species. These mysterious reappearances of old
ancestral characters were interpreted as due to something
carried in the germ plasm in a latent or inactive state until
as a result of some peculiar circumstance they were awakened
to full epiphany. An understanding of Mendel's law now
enables us to supply an explanation of this puzzling phe-
nomenon. The hypothesis that reversion is caused by bring-
ing together complementary factors is one that can be put
to experimental tests, and it has been able to meet the
theoretical requirements. Some cases of reversion are brought
about by the outcropping of recessive traits that may have
been obscured by more recently appearing dominant factors.

What may be called reversion by restoration is a not
uncommon effect of the crossing of domestic varieties derived
from a common source. In some varieties one genetic factor
necessary to produce a character may become recessive or
possibly lost; in another variety a different factor may
become recessive or lost. The cross between the two may
restore the ancestral combination. It may happen that the
varieties come to differ in several factors. In such a case the
FI produced by the cross may be heterozygous for several
pairs of genes, and consequently the second, or F2 generation
may present a great diversity of characteristics. The purple
sweet pea arising from the cross between two whites may

58 HUMAN GENETICS AND ITS SOCIAL IMPORT

produce a varied combination of colors among which are
purples, reds, pinks, and the two ancestral white varieties.
In the second generation colored and whites are in the ratio
of 9 colored to 7 white. This is a modification of the 9:3:3: i
ratio in which the three latter classes have the same appear-
ance, although they are genetically different.

There are several modifications of the typical Mendelian
ratios. We may have, as you have seen, a 15:1 ratio, and
there may be also 9:7, 9:3:4, 12:3:1, 13:3, and 10:6 ratios.
At first the occurrence of these unusual ratios proved dis-
concerting to the experimental breeder. When he finds them
he has to invent a hypothesis by which they can be explained.
But if he is a really good geneticist, he will not be content
with a mere plausible theory. He will test his supposition
as he can often do by appropriate crosses and see if his
findings tally with theoretical expectations. In order to
explain the varied results of breeding experiments, geneticists
have been led to hypothecate several kinds of factors, i.e.,
multiple, modifying, cumulative, lethal, complementary, etc.
By this means many apparently nonconforming cases have
been explained in accordance with the fundamental principles
of Mendelian heredity.

It is important to bear in mind that the various modifica-
tions of typical Mendelian ratios that have been observed
are brought about by the ways in which genetic factors
interact in the production of visible characters. The pairing
and segregation of genes go on in precisely the same way
whether the characters appear in one ratio or in another.
One common source of difference in Mendelian ratios is
variations in dominance. In some forms one member of a
Mendelian pair does not completely dominate over the other,
but produces a more or less intermediate condition in the
heterozygous offspring. When a red and a white four-o-clock
are crossed the F\ is pink, inasmuch as the gene for red color

THE INTERACTION OF FACTORS

does not completely suppress the influence of its white mate.
The pink F\ generation gives rise to progeny consisting of
one red, two pink, and one white, the reds and the whites
being both homozygous, and the pinks revealing their mixed
composition by their intermediate color.

Sometimes the characters interact in such a way as to
produce something different from either. An illustration of

FIG. 24. — Incomplete dominance in the cross between a red and a white variety of four
o'clock, Mirabilis jalapa. The Fi of this cross is pink, but this heterozygous type forms in
the Fz generation reds, pinks, and whites in a i : 2 : i ratio. (After Correns.)

this fact is produced by the blue Andalusian fowl which were
long known never to breed true but to produce some black
and white fowl in addition to blue. It was shown by Bateson
and Punnett that the blue Andalusians were heterozygous,
and that the only way in which to obtain nothing but blue
birds was to cross blacks with whites. In some way the
factors for white and black conspire to produce blue instead
of either color alone or an intermediate shade. Fowls with pea

60 HUMAN GENETICS AND ITS SOCIAL IMPORT

comb and rose comb are pure-breeding varieties, but when
crossed neither character is dominant over the other, both
combining to produce the so-called walnut comb, which is
quite different from either. Thus the interaction of comple-
mentary factors may give rise to quite unexpected novelties.
How different gene combinations may conspire to produce

P Gen.

F2 Gen.

FIG. 25. — Andalusian fowl. (From Wolcott.}

visible characters in the developing organism no one can
predict in advance. We are almost completely ignorant of the
ways in which genes work to achieve their effects. We see
only the end result of what may be a very long and complex
chain of interactions.

The influence of a gene may depend not only upon other
genes with which it is associated, but also upon environment.
In some cases external factors may determine whether a

THE INTERACTION OF FACTORS

character is dominant or recessive. In the fruit fly, Droso-
phila, a strain was obtained having an abnormal distribution
of the color bands of the abdomen. Crosses with normal fruit
flies produced offspring with abnormal abdomens, thus show-
ing that the character behaves as a dominant. The degree of
dominance was found to be subject to much variation, and
if the flies were reared in a dry environment, the anomaly
commonly failed to appear at all. In the proper environment

FIG. 26. — Inheritance of comb form in poultry. A, pea comb; 5, rose comb, C, walnut comb,
resulting from crossing A and B. (After Shull.)

flies with the gene for abnormal abdomen are indistinguish-
able from ordinary flies. If these normal appearing flies are
bred under usual conditions, however, their progeny will all
reveal the presence of the defective gene. They differ from
normal fruit flies in having a gene which gives them the
capacity to respond to certain environmental stimuli by
developing an abnormal abdomen.

There are many hereditary characteristics whose degree of
expression is dependent upon surrounding conditions. A
variety of Primula, P. sinensis rubra^ produces red flowers

62 HUMAN GENETICS AND ITS SOCIAL IMPORT

at ordinary temperatures. When raised at a high temperature,
its flowers are white, resembling those of a white-flowered
variety, P. sinensis alba. Whether the plant inherits redness
or whiteness, therefore, depends upon its environment. What
it really inherits, of course, is the capacity to respond to a
certain temperature by becoming red and to a higher tem-
perature by becoming white. In this it is hereditarily different
from P. sinensis alba^ which is white at all temperatures.

Not infrequently a hereditary character may be developed
to varying degrees even under what seem to be the same
external conditions. Here dominance may be influenced by

FIG. 27. — Normal and abnormal abdomen in Drosophila melanogaster. The normal con-
dition in the male is shown in a and in the female in c. The abnormal abdomens of the two
sexes are shown in b and d. (After Morgan by permission of the J. B. Lippincott Company.)

the presence or absence of other genetic factors, or by slight
environmental differences which commonly escape notice.
Polydactylism (supernumerary ringers or toes) ordinarily
behaves as a dominant character both in human beings and in
lower animals. The gene responsible for this anomaly is
present in all cells of the body, but it often happens that only
the hands or only the feet are affected, and frequently only
one hand or one foot. The character is expressed in all
degrees from six or more well formed digits to a mere super-
numerary stub or protuberance. There are several cases in
which normal individuals of polydactylous ancestry have
produced polydactylous children. The fact that in pedigrees

THE INTERACTION OF FACTORS 63

polydactylism sometimes skips a generation is doubtless to be
attributed to the occasional failure of dominance. That the
gene often fails to manifest itself in one hand or one foot
makes it seem not unlikely that it would sometimes fail of
expression altogether. In other words, some individuals may
be genetically polydactylous and somatically normal.

Imperfect dominance is by no means a rare phenomenon.
Numerous illustrations of it may be found in the inheritance
of human traits. Families often manifest diatheses or proclivi-
ties to certain disorders without necessarily becoming
affected. One may be prone to have diabetes or bronchial
asthma, but in the absence of the proper exciting cause he

•• •

A 6

FIG. 28. — Two pedigrees of polydactylism. In pedigree A the trait is clearly dominant.
In pedigree B since it skips a generation it is probably incompletely dominant. (Ay after
Lukas; B, after Koehler.}

may remain entirely normal. Some strains of mice are
much more apt to contract pneumonia than others, and
probably the same remark applies to human beings, but
in the absence of the proper germs these can be no pneu-
monia. Sometimes hereditary immunities can be broken
down by sufficient doses of virulent disease germs, or by
weakening the resistance of the body through lack of food
or exposure to cold.

Heredity is often looked upon as peculiarly fatalistic.
It is true our allotment of genes is fixed at the time of
fertilization. But if we inherit the gene for a certain trait
it does not necessarily follow that we will have that trait.
Within certain limits we may escape our heredity. One
may be prone to develop insanity, but under proper condi-

64 HUMAN GENETICS AND ITS SOCIAL IMPORT

tions the dread malady may never appear. There are, of
course, many traits which we are powerless to evade. We
cannot change the color of our eyes, or our membership in a
given blood group. If a child were feeble-minded owing to
an inherited deficiency of the thyroid gland, it might be
converted into a person of normal intelligence by the
administration of thyroid extract. That the defect can be
overcome is no proof that it is not primarily due to heredity.
Possibly future discoveries will place in our hands the means
of counteracting many of our hereditary ills, but it would be
hazardous to predict how much progress in this direction
may eventually be made.

Suggested Readings

Shull ('31), chap. 1 6. Sinnott and Dunn ('32), chap. 5. See also references
for chap. 3.

Questions

1. What will be the result of crossing a blue Andalusian fowl with (a) a
white fowl, (b] a black fowl ?

2. If an entirely white child were born to two mulattoes, would it be a
pure Caucasian ?

3. If all members of the Jones family developed bronchial asthma
whenever they ate rye bread, what would you say of the probable role of
heredity in causing the attacks ?

4. Give three reasons why a character may skip one or more
generations.

5. If when a defect occurs in a family it is found also in one-fourth of
the brothers and sisters, what would you infer as to its mode of inheritance ?

6. Yellow in mice is a dominant character and lethal when homozygous.
Hence all yellow mice are heterozygous. What would be the expected
progeny of a cross between a yellow mouse and a gray mouse ?

7. If a sex-linked factor has a lethal effect, what would be the sex ratio
in a cross between a heterozygous female and a normal male ?

8. If a walnut comb fowl, RRPP, is crossed with a pea comb, rrPP,
what will be the expected progeny ? What will result from crossing a walnut
comb with a rose comb, RRpp ?

THE INTERACTION OF FACTORS 65

9. If the ovary is removed from a mallard duck, she develops the
brilliant plumage of the male. Is this coloration an inherited character ?
If so, in what sense ?

10. Tortoise-shell cats are almost always females and may be produced
by crossing yellow and black. What would result from crossing a tortoise-
shell female with a black male? with a yellow male?

11. Two shepherd's-purse plants with triangular pods give when crossed
fifteen plants with triangular pods to one with oblong pods. What is the
genetic constitution of the parents ? Some of the progeny with triangular
pods, when crossed, give three triangular to one oblong. How do you
explain this result?

CHAPTER VI

THE LINKAGE OF HEREDITARY TRAITS

WHILE most inherited characters are segregated out
independently of others there are many exceptions
to this rule. The first exception to the law of independent
assortment was discovered by Bateson and Punnett, who
found in crossing sweet peas that certain characters showed
a marked tendency to be inherited together. This phe-
nomenon, which is known as linkage, was later observed
in the fruit fly by Morgan, who advanced the ingenious
theory that linked characters depend upon factors borne
in the same chromosome. The common fruit fly is admirably
adapted for breeding experiments and the science of genetics
owes a great debt to these small insects. They are easily
raised by the thousands in small bottles. They breed rapidly,
generations succeeding one another about every three weeks.
They have few chromosomes, only four pairs, a very for-
tunate circumstance as it proved in studying linkage.
There is a large pair of sex chromosomes, XX in the female
and XY in the male. There are two pairs of rod-shaped
chromosomes of nearly equal size and a pair of small rounded
fourth chromosomes. The work of Morgan and his able
associates showed that the numerous heritable characters
of Drosophila are inherited in groups, and that the number
of linkage groups, i.e., four, exactly corresponds to the
number of pairs of chromosomes. One large group is sex
linked and hence probably associated with the X-chromo-
some. Two other large groups occur that are associated with

the large second and third chromosomes, and one very small

THE LINKAGE OF HEREDITARY TRAITS 67

linkage group which, it was tempting to conclude, is carried
by the small fourth chromosome. This supposition has
been repeatedly verified by observing the genetic behavior
of flies in which one of the fourth chromosomes had been
lost or which possessed three of these chromosomes, or in

FIG. 29. — T. H. Morgan. (Copyright by the Journal of Heredity.}

which a part or the whole of the fourth chromosome had
become attached to one member of another pair.

One of the peculiar features occurring in most cases of
linkage is that the association of the characters is not
complete. For instance, when a fruit fly having long wings
and gray body color was crossed with a fly having vestigial
wings and black body color, the F\ generation were all gray,
long-winged flies (vestigial and black being recessive).

68 HUMAN GENETICS AND ITS SOCIAL IMPORT

The FI females crossed back to the black, vestigial-winged
male parent gave the four expected types, but they did not
appear in equal numbers as they do in typical dihybrid
crosses. Instead there were 41.5 per cent gray long, 41.5 per
cent black vestigial, and 8.5 per cent gray vestigial, and 8.5
per cent black long flies. The characters entering the cross
together were found to come out together to a greater extent
than they would according to the principle of independent
assortment. When the linked characters enter the cross in a

FIG. 30. — The fruit fly Drosophila melanogaster. Left figure male; right female.

Morgan?)

different combination, as in crossing a gray, vestigial- winged
with a black, long-winged fly, the F\ female crossed with
a black, vestigial-winged male produces 41.5 per cent gray
vestigial, 41.5 per cent black long, 8.5 per cent gray long, and
8.5 per cent black vestigial progeny. Linked characters, as
these results show, are occasionally separated. But why ? The
associations are found to be exchanged in fairly definite ratios
as in the experiments cited. Apparently, if linked genes are
associated in the same chromosome they must somehow get
exchanged occasionally, and it is natural to infer that the
exchange occurs during the period of synapsis, when, as

THE LINKAGE OF HEREDITARY TRAITS 69

we have seen, there is a pairing of chromosomes of male
origin with corresponding chromosomes of female origin.

The French cytologist Janssens in studying the sperma-
togenesis of the newt Batrachoseps had observed that during
synapsis the paired chromosomes twist about each other.
This observation suggested to Dr. T. H. Morgan that the
exchange of linkage relations might be due to the fact that
when the paired chromosomes separate they break apart
at the points where they cross, and the broken ends of
different chromosomes then unite and thus effect an exchange
of segments. Hence the phenomena of crossing over observed

XX X Y

FIG. 31. — The chromosomes of Drosophila melanogaster. XX and XY represent the sex
chromosomes. (After Bridges.}

in studying linked characters might be explained as due to
an actual crossing over of segments of chromosomes. Both
linkage and crossing over, therefore, are plausibly interpreted
from a common standpoint.

It has been found that characters are linked in various
degrees. In some instances crossing over is observed in only a
fraction of i per cent of cases; in others, it occurs in almost
50 per cent, and hence approaches free assortment. These
different degrees of linkage are explained by supposing that
closely linked genes are situated close together in the chromo-
somes, so that it is unlikely that a break will occur between
them. The farther apart the genes lie the more likely they
will become separated. Upon this hypothesis it is possible

70 HUMAN GENETICS AND ITS SOCIAL IMPORT

to construct a chromosome map by arranging the genes in a
linear series according to their relative cross-over frequencies.
In Drosophila the relative positions of several hundred
genes have been mapped out in this way.

When a new character appears in Drosophila it can be
quickly determined by breeding experiments to which

o
o
o

cx-

B b-

V v

o
o
o

o
o
-o
o
o
o
o
o

FIG. 32. — Diagram illustrating the mechanism of crossing over. In the fruit fly the
characters of gray color and long wings are linked and presumably are carried by genes in
the same chromosome. If gray (5) and long (V) enter the cross together from one parent
and the corresponding recessive genes for black (b} and vestigial wings (v) enter from the
other, and the chromosomes cross and break between the loci of these genes and then
exchange segments, the one chromosome would contain the genes for black (b} and long (f^)
and the corresponding chromosome would contain the genes for gray (B) and vestigial
wings (v). Usually cross-overs occur between these loci in about 17 per cent of cases.

linkage group it belongs. Then its frequency of crossing
over with other characters of the group is worked out,
and its relative position is assigned in the chromosome map.
This daring attempt to explore the chromosome has had to
justify its acceptance by meeting all possible objections.
Geneticists are a very skeptical and critical lot, but none
of them has succeeded in devising a rival theory of linkage

THE LINKAGE OF HEREDITARY TRAITS 71

and crossing over which has gained a considerable following.
Not only do the numerous facts of normal heredity fit
in with the requirements of the theory, but now and then
the chromosomes behave in anomalous ways, and in many
cases it has been possible to correlate these anomalies with
equally irregular behavior in the transmission of visible
characters. To illustrate, the geneticist finds that a group of
characters normally belonging in the second linkage group
suddenly becomes sex linked. He supposes that a part of the
second chromosome has become broken off and attached to

0th*

FIG. 33. — Paired chromosomes of Callisia showing chiasmas, or crosses between the threads.

(After Sax.}

the Jf-chromosome, and he can tell about how big the piece
is likely to be. Then he makes a preparation of the sex cells
and finds upon microscopic examination that the X-chromo-
some has an extra piece attached to it, and that one of the
second chromosomes is shorter than its mate. Predictions like
this have been made and verified many times over in recent
studies on the fruit fly. The so-called chromosome theory
of heredity has come to be supported by so overwhelming a
mass of evidence, and has been verified so many times by
crucial test experiments, that practically all the hard-headed
and skeptical geneticists the world over have no hesitation
in accepting it.

Some day we might imagine the geneticist showing Mr.
Smith a map of his heredity and saying: "Here in the four-

72 HUMAN GENETICS AND ITS SOCIAL IMPORT

teenth chromosome six units to the left of the attachment of
the spindle fiber is the gene for that crooked little finger
which you have probably derived from your paternal great-
grandfather. At this point in the twenty-first chromosome
between your gene for red hair and the gene that predisposes
you to bronchial asthma is the factor which causes you so
much trouble from indigestion. In your fourth chromosome
eight units from the left end (geneticists speak familiarly of
the right and left ends of chromosomes) is a gene that would
probably cause you to inherit your father's shortsightedness
were it not prevented by its corresponding gene derived from
your mother." Whether or not we shall ever be able to present
such definite information for the edification of Mr. Smith,
our illustration in no wise exaggerates the precision of the
statements that can be made concerning the germ plasm of
the fruit fly. While physicists have been exploring the atom,
geneticists have been mapping out the chromosomes and
completing a picture of a region that was an entire terra
incognita to Darwin and Mendel.

Chromosomes have been mapped out in great detail in the
common Drosophila melanogaster and less completely in other
species of the genus. Less detailed maps have also been
made of the chromosomes of Indian corn, the Jimson weed
(Datura), the sweet and garden peas, and a few other plants
and animals. In man little progress in studying linkage has
been made because we cannot breed people at will and it
takes many years to secure results. A serious drawback is
encountered in the circumstance that each married couple
does not produce several hundred children. Our knowledge
of human heredity has to be picked up when and where
opportunity offers. Everything that we know about it,
however, fits into the general Mendelian scheme, and there is
no ground for concluding that it differs in any essential
respect from heredity in other organisms.

THE LINKAGE OF HEREDITARY TRAITS

100

yellowCB)
RairywinaCW
Scute CHf
.1 \ uo lethal -7
• \0.6broc<dCW)
• -\ I. prune CE)
1.5 white CE)
. facet CE)
.1 Notch CE)
> AbrwrmalCB)
i echinusCE)
I bif idCW)
i < ;.J rubyCE)
\l3.7crossveinlessCW)
\l6.±clubCW)
17.± deltexCW)

20. cutCW)

21. singed CH)
27.5tanCB)
27.7 lozenge CE)

0. telegraph CW)

2. Star CE)

3.± oiristoiless(B)

6.± expanded CW)

12.+ GullCW)
13. Truncate CW)
14.± dachsousCB)
16. Streak (B)

ffl

0. roughoid CE)

31.
•35.

dachs (B)
Ski-H CW)

33. vermill ion CE)

36.1 miniature (W)

36.2 duskyCW)
38.tfurrowedCE)

43. sable (B)
44.4 garnet CE)

54.2 small wing
54.5 rudimentarytW)-
56.5 forked 00
•31. BarCE)

•41. Jammed CW)

-46.* Minute-e(H)

-48.5 black CB)

48.7 jaunty (W)

•54.5 purple CE)

57.5 cinnabarCE)"*

60.± safraninCE)

58.5 small eye i~64.± pink-wing(EW)

67. vestigia I CW)
68.± telescope CW)

59. fused CM
59.6 BeadexCW)
62. Minute-nCH)
65. cleftCW)

70. bobbed CH)

72. Lobe CE)

• 74.± .gapCW)
•75.5 curved CW)

83.5 fnngedCW)

ben+CW)
shavenCB)
eyeless CE)
rotated (B)
Minute-IYCH)

20. divergent CW)

26. sepia CE]
26.5 hairy (B]

35. rose CE)
36.2 cream-m CE)

40.1 Minute-hCH)

40.2 tiltCW)

40.4 Dichaete CH)
42.2 threadCB)
44. scarletCE)

48. pink CE)
49.7 maroon CE)
\[50.± dwarf (B)
lla. curled.CW)
Hairy wing
Stubble (I

58.5 spineless C
L7 bithorax(B)

N39.5 bithorax-b
\62. stripe CB)
. glass CE)
66.2 Delta CW)
69.5 hairless CH)
70.7 ebony CB)
72. bandCB)

75.7 card ina ICE)
76.2 white ocelliCE)

male fertility

Long bristled

XUY

•90. humpy (B)

99.5 arcCW)
100.5 plexus (W)
10?.± lethal -Ha
(105. brown CE) x
U05.± blistered CW)
106. purpleoidCE)
|107.± morulaCE)
1107. speck CB)
107.5 balloon (W)

91.1 rough CE)

tsSa^d'cwr^016^1^
94.1 Painted CW)

100.7 claretCE)
101. Minute (H)

106.2 Minute-gCH)

FIG. 34. — Chromosome map of Drosophila melanogaster indicating the positions of some
but not nearly all the genes which have been located. The arrows designate the points
where the spindle fibers are attached. The letters in parentheses indicate the part of the
body in which the characters appear: 5, body; £, eye; //, hairs; W> wings. The genes for
fertility in the y-chromosome have not been definitely located. (From Sharp adapted from
Morgan, Sturtevant, Bridges and Stern.}

74 HUMAN GENETICS AND ITS SOCIAL IMPORT

The recent studies of the structure of the giant chromo-
somes of the larvae of Drosophila, which we have alluded
to in Chap. I, have enabled geneticists to associate many
genetic factors with particular bands in the chromosomes.
By studying many cases of breaks and reattachments of
chromosomes, together with their correlated genetic phe-
nomena, it is found possible to locate quite accurately the
actual position that particular genes occupy in the chromo-
somes. One cannot identify the genes with any visible features
of chromosome structure. We do not know whether the genes
are in the stained bands or in the unstained material. But
it can be stated that a given gene is very close to a particular
band. This is as far as the genes have been hunted down at
the present time. Certain genes have been shown to be a
little closer together here or a little farther apart there than
was formerly supposed, but the conclusions as to the linear
order of the genes have only been more fully confirmed by
this recent work.

Suggested Readings

Lindsey ('32.), chap. 9. Morgan ('28), chaps, i, 2. Newman ('32), chap.
23. See also references for chap. 3.

Questions

1. The characters of an animal fall into eight linkage groups. What
would you infer as to its number of chromosomes ?

2. In Drosophila black color and vestigial wings when they enter a
cross together come out together in 81.5 per cent of cases; similarly
vestigial wings and cinnabar tend to be associated in 90.5 per cent of cases.
What may be inferred as to the distances separating the genes for these
characters in the chromosome ?

3. A is linked with B in 90 per cent of cases and with C in 85 per cent of
cases. B is associated with C in 95 per cent of cases. What are the relative
positions of the genes for A^ B and C in the chromosome ?

4. If A was associated with B in 90 per cent and with C in 85 per cent
of cases as before and if B was associated with C in 80 per cent of cases,
what conclusion would you draw as to the relative positions of their genes ?

THE LINKAGE OF HEREDITARY TRAITS 75

5. Suppose A, 5, and C occur as in question 4 and a new character D
was found to cross over with B in 5 per cent and with C in 10 per cent of
cases, how frequently might it be expected to cross over with At What
would be its position in the chromosome with respect to A^ B and C?

6. If half of the characters normally associated with the fourth chromo-
some in Drosophila should suddenly become associated with characters
whose genes are carried in the second chromosome, what happening might
cause the change?

7. If a character were closely linked to a lethal gene, how would its
prevalence be affected?

8. Why is it more difficult to study linkage in mammals than in the
fruit fly ?

9. To how great an extent is the doctrine of the individuality of the
chromosomes modified in the theory of crossing over?

10. If a Drosophila with linked characters ABCDE in the order men-
tioned were crossed with abcde and the F\ crossed back to the recessive
type abcde^ producing some flies with the combination ABcdE and others
with the combination abCDe, how would you explain the result?

CHAPTER VII

VARIABILITY— ITS KINDS AND ITS CAUSES

VARIATION and heredity are commonly used as
antithetic terms. The study of each of these phenomena
has thrown much light upon the other. What we are chiefly
interested in concerning heredity is how the characters that
distinguish one individual or variety from another are
transmitted. If all members of a species had exactly the
same hereditary traits the problem of why offspring are such
faithful copies of their parents would present a fascinating
topic for speculation, but we would probably be able to
contribute little toward its solution. It is because organisms
vary and we are able to study the way in which their varia-
tions can be combined and separated that we have been
able to discover laws of heredity, and to interpret these laws
in terms of chromosome behavior. It is owing to the fact
that garden peas present well-defined hereditary variations
that Mendel discovered his fundamental laws of heredity.
And it is only through the study of linkage and crossing over
that it is possible to determine the location of particular
hereditary factors in individual chromosomes. In short, most
of our understanding of heredity is rendered possible only
through the study of variations.

Variations fall into a number of classes. The most funda-
mental distinction is that between (i) somatic variations, or
those arising in the body as a result of its own activities or
the influence of the environment, and (2) germinal variations,
which depend upon changes in the germ plasm. If one

develops his muscles through exercise, or acquires a coat of

VARIABILITY— ITS KINDS AND ITS CAUSES 77

tan through exposure to the sun, such variations are purely
somatic, and in the opinion of most geneticists they have no
influence upon the germ cells and hence no effect upon sub-
sequent generations. Whether or not somatic variations, or
acquired characters, play any part in evolution depends upon
whether or not they can affect the germ cells in such a way
as to cause similar variations to appear in the offspring.
This, as we have seen, is at least a questionable possibility.

There is no doubt whatsoever that variations which
originate in the germ plasm are capable of hereditary
transmission. To a considerable extent the new variations
which arise are the result of varied combinations of genes
and represent simply the expression of Mendelian segrega-
tion. When a black sheep turns up in a flock that has pro-
duced nothing but white sheep for several generations, the
new type is probably the product of the meeting of two
recessive genes for which both parents were heterozygous.
Blackness in sheep is known to be a recessive character and
hence when black sheep are bred together nothing but black
progeny is produced. When a purple pea is formed by crossing
two whites and when the purple hybrid produces a variety of
other colors, whites among the rest, the striking display of
variability is really nothing but the result of different com-
binations of old factors. What superficially appear as excep-
tions to the laws of heredity are really manifestations of the
way in which heredity works. Such variations are analogous
to the different kinds of hands one may obtain by shuffling
and dealing a deck of cards. They represent only new com-
binations of old things.

From time to time germinal variations of another kind
make their appearance. There are many cases in which the
normal number of chromosomes is doubled, giving rise to
four sets of chromosomes instead of two. Occasionally there
are three sets of chromosomes, or rarely only one. Sometimes

78 HUMAN GENETICS AND ITS SOCIAL IMPORT

the abnormal duplication of chromosomes affects only one
or two pairs; or, again, a single chromosome or rarely more
may be lost. All such changes in chromosome number affect
the visible characters of the organism to a greater or less
extent. Sometimes parts of a chromosome are lost or dupli-
cated, or a part may be broken off from one chromosome and
stuck onto another. Such translocations are common in the
progeny of plants and animals treated by radium or X-rays.
Numerous chromosome anomalies have been described,
especially in Drosophila, and the peculiar genetic phenomena
that followed have been explained as a result of the excep-
tional chromosome behavior.

The germinal variations of most fundamental significance
are those occurring in the constitution of the genes them-
selves. These are called gene mutations. Through the study
of linkage, it is now possible to locate quite precisely the
region of a chromosome in which a new gene mutation
occurs. In a given locus in the sex chromosome of Drosophila
there have been twelve different mutations described,
each causing a characteristic change in the color of the
eyes.

The term mutation as commonly used in the literature on
genetics connotes a sudden discrete mutation which breeds
true. Formerly more than now, the term was applied mainly
to extensive departures from the normal type, such as gave
rise to hornless breeds of cattle, the navel orange, or strains of
albino mice. Such stable and discrete germinal variations
were found to range in magnitude from monstrosities to very
small changes which are barely detectable. There may be no
essential difference between a germinal variation, which can
be observed in only one spot on a butterfly's wing, and one
that causes a widely divergent variety. Even a single gene
mutation may produce so profound a disturbance of normal
development as to cause the death of the organism.

VARIABILITY— ITS KINDS AND ITS CAUSES 79

Both gene mutations and those due to chromosome
anomalies may play an important part in the origination of
new varieties and in the general course of organic evolution.
The first process is doubtless the more important and funda-
mental. For the most part both kinds of variations appear to
arise spontaneously without apparent cause. They just
happen. But why ? The problem of the causes of variations
has long been of interest to the evolutionist. The Lamarckian
had at least a partial answer to the problem in that he could
account for variations as due to the transmission of acquired
characters. Many variations as we have seen are due to
Mendelian segregation. The other types of germinal varia-
tions we have discussed are due to whatever causes the
anomalous behavior of chromosomes and the alteration of
individual genes. But however variations may be caused, a
good deal of insight has been gained into the real nature of
variability, because we can now distinguish the different
classes of variations in a way that was impossible a generation
ago.

This insight does not in itself give us a plausible explana-
tion of variability, but it is helpful in giving a clear under-
standing of just what is to be explained. Gene mutations are
frequently considered as due to some alteration in the chemi-
cal constitution of the gene. A gene is a very small body not
very many times larger than some of the larger molecules of
protein. Some geneticists have held that a gene consists of a
single organic molecule. One might interpret gene mutation
as caused by the addition or loss of an atom or radical, or
possibly as due to some internal rearrangement of atomic
groupings. From this viewpoint it might be thought possible
to induce gene mutations by agencies which might exercise
some chemical effect upon the germ plasm. Accordingly
experiments have been tried by introducing substances into
the body and testing their possible effect upon the offspring.

80 HUMAN GENETICS AND ITS SOCIAL IMPORT

Fruit flies have been exposed to alcohol, ether, methylene
blue, and other chemicals, but out of many thousand progeny
of the treated individuals, no more mutants appeared than
among the progeny of untreated flies bred as controls.
Several other efforts to induce mutation by means of chemi-
cals have yielded negative results. Apparently, the germ
plasm possesses a high degree of stability. It is doubtless for
this reason that organisms have been able to perpetuate
their kind over long periods of time with very little change.

There have been some experiments reported in which it
has been claimed that heritable modifications have been
induced by chemical means. One of the most noteworthy of
these was performed by Dr. C. R. Stockard upon guinea pigs
exposed to the influence of alcohol. With commendable
caution the animals employed were first bred and found to
produce normal offspring. They were then exposed to the
fumes of alcohol about five or six times a week for a period of
several months. In each trial they were made to inhale the
fumes of alcohol until they manifested signs of incipient
intoxication. After this preparation for parenthood they were
bred. Among the descendants of the first three generations
there were several weak and defective offspring. There were
smaller litters than in the animals bred as controls and more
of the young died soon after birth. In a later communication
Stockard reports that the fourth generation of the alcoholized
guinea pigs were almost free from defects and apparently
rather more vigorous than the controls. This result he at-
tributed to the elimination of the defective germ plasm which
may have been caused by the poisonous influence of alcohol.

If alcohol was really the cause of the inherited defects
observed, these experiments may have an important bearing
on the origin of hereditary defects in man. Human beings
have long indulged in alcoholic beverages to a degree that has
been productive of many physical and mental disabilities. It

VARIABILITY— ITS KINDS AND ITS CAUSES 81

has been conjectured that alcohol may injure the germ plasm
and thus be a cause of mental defect and physical disorders of
all sorts. For some reason new strains of hereditary defectives
arise from time to time, and it is perhaps natural that their
origin should be attributed to alcohol or other "racial
poisons." But it should also be borne in mind that defective
mutations arise from time to time in almost all kinds of
organisms. For this reason one should subject the evidence
that alcohol is the cause of hereditary defects to a very care-
ful scrutiny. The influence of alcohol on the birth weight of
white rats has been studied by MacDowell and by Hanson
and Heys, but they arrived at different results. MacDowell
has found that the descendants of alcoholized rats learn a
maze rather more slowly than the descendants of their litter
mates which were not given alcohol. The possibility is not
entirely excluded that the parents of the treated and the
control strains may have been genetically different from the
start, a possibility by no means excluded by the fact that they
belonged to the same litter. Dr. Agnes Bluhm has made
extensive investigations on the effect of alcohol upon fertility,
weight at birth and longevity of the descendants of white
mice, and has concluded that alcohol has an unfavorable
effect upon the progeny which in some respects continued as
far as the seventh generation.

Pearl, on the other hand, reports that the descendants of
alcoholized fowl were on the whole superior to those of
untreated individuals. The number of fertile eggs produced
by the alcoholized strain was less than in the controls, and
the conclusion was drawn that alcohol causes the weaker
germ cells to be eliminated. It has been suggested that
Stockard's and Pearl's results are not necessarily opposed,
since alcohol might cause germ cells to become injured as well
as effecting the elimination of cells less able to withstand its
influence.

82 HUMAN GENETICS AND ITS SOCIAL IMPORT

F. M. Durham has repeated Stockard's experiments on
guinea pigs, but she exposed the animals to a longer period of
alcoholization. No defects were observed in the offspring of
the treated animals, although a larger number were studied
than in the experiments of Stockard. Durham is inclined to
believe that the defects observed in Stockard's guinea pigs,
in so far as they were hereditary, were due to the accidental
outcropping of recessive genes.

Dr. M. F. Guyer has attempted to induce germinal varia-
tions by a different method. Making a preparation of the
ground-up lenses of the eyes of rabbits, he injected this
material into the blood of a fowl. After a number of treat-
ments the blood of the fowl, which had presumably developed
an antibody to lens substance, was injected into pregnant
rabbits. Of the sixty-one rabbits which were born to the
treated mothers in one set of experiments, four had well-
marked defects in one or both eyes, and the eyes of five others
were more or less abnormal. One of the most common defects
observed was opaque lenses. Defects of the eye were obtained
in four separate and presumably unrelated strains of treated
animals. The defect once started was found to be hereditary.
Apparently it behaves as a partially recessive trait. Defec-
tive-eyed rabbits mated with normal ones usually have
normal progeny, but the mating of two defective-eyed rabbits
produced mostly defective-eyed progeny, although occasion-
ally a normal individual would arise.

The objection that, possibly, eye defects may have hap-
pened to turn up in the progeny of the treated female, Dr.
Guyer has endeavored to meet by repeating the experiment
with different lines and by breeding a considerable number
of control animals. Only one case of defective eyes was
observed in more than 2,000 controls and Dr. Guyer remarks
that "Whatever the final explanation of just what has taken
place in the germ plasm may be, it seems reasonably sure

VARIABILITY— ITS KINDS AND ITS CAUSES 83

that the results are in some way the outcome of the experi-
mental treatment."

These experiments have been interpreted by some La-
marckians as supporting the theory of the transmission of
acquired characters. Dr. Guyer himself does not put this
interpretation on his results. He suggests as an alternative
possibility that "the eye and the germ of the fetus are influ-
enced separately by the antibodies which have entered from
the mother's blood by way of the placenta."

Guyer's experiments aroused widespread interest and led
others to attempt to duplicate their results. J. S. Huxley
and A. M. Carr-Saunders have repeated Guyer's experiments
without obtaining any defective-eyed progeny from the
treated animals. The spontaneous appearance of defective
eyes in normal rabbits has been recorded in several instances
and seems not to be so rare an event as Guyer supposed. The
experiments of Ibsen and Bushnell and later Ibsen, who
endeavored to duplicate Guyer's results, failed to yield
confirmatory evidence. Out of fifty-nine offspring of treated
female rabbits only one showed a slight defect, but a slight
eye defect was noticed also in the offspring of rabbits that
had not been treated. Of 170 offspring of rabbits whose lenses
had been destroyed by a needle (a procedure which according
to Guyer results occasionally in defective-eyed progeny) all
were normal eyed as were all the grandchildren. On the other
hand, "six markedly defective-eyed animals have been found
among the 920 having an untreated ancestry." Three of these
occurred in one family. In a later communication reporting
the results of further experiments there were no eye defects
in 177 rabbits of the first generation produced from treated
parents, nor in 148 of the second generation. The only defec-
tive-eyed animals occurred in a family of three produced by
an F2 female and an FI male, but there was evidence that the
defects in these individuals were caused by an infection.

84 HUMAN GENETICS AND ITS SOCIAL IMPORT

There are several sources of error in experiments designed
to induce variations. One of the chief of these is the uncer-
tainty as to whether the animals chosen for experimental
treatment are genetically different from those used for con-
trols. If one essayed to test the efficacy of an experimental
treatment which was alleged to cause the production of black
sheep, it might well happen that some of the treated animals
were heterozygous for blackness, while all the control animals
were free from this defect. This might happen of course
several times over. It seems not unlikely that a good deal of
the discrepant results of experiments designed to test the
hereditary influence of alcohol and other substances may be
due to differences in the genetic make-up of the animals
chosen for the experiment. From the a priori standpoint the
production of variations by the administration of chemical
substances seems probable enough, but on the whole the
evidence for the efficacy of most so-called "racial poisons"
leaves much to be desired.

In the effort to produce variations by artificial means a
number of investigators have turned to the employment of
X-rays and radium. Both these agencies are able to produce
chemical effects within the body. Severe dosage of X-rays
or radium has been shown to injure or even to kill the chro-
matin of irradiated germ cells, and it seems a probable
inference that changes induced in the chromatin might prove
to be a source of hereditary variability. Bagg and Little
subjected an inbred strain of mice to X-rays and found that
in the second and subsequent generations the progeny
exhibited a number of variations such as club feet, defective
eyes, absence of one or both kidneys and other anomalies.
Similar results were later reported by Bagg in the progeny
of an unrelated strain of mice subjected to X-rays.

The most extensive and indubitable results of treatment
with X-rays were reported by H. J. Muller, who found

VARIABILITY— ITS KINDS AND ITS CAUSES 85

that the percentage of mutations appearing in the progeny
of irradiated fruit flies was increased to a startling degree.
Many of the gene changes so produced proved to be lethal,
but in addition to these, mutations of all sorts appeared in
great profusion. The mutation rate was speeded up about
150 times as compared with that of the controls. This work
was soon confirmed by many other workers and is now a
common method of inducing mutations on a large scale.

Radium also has been shown to be a fertile source of
mutations in both animals and plants, and some rather
striking results have been reported in causing mutation in
Drosophila by exposure to a nearly fatal degree of heat.
Unquestionably environmental factors are able to modify
the germ plasm so as to cause stable hereditary variations.
From the standpoint of adaptation most of these variations
are either unimportant or positively injurious. We are still
ignorant as to what causes the new strains of hereditary
defectives that are continually arising in our human stock.
The lame, the halt, and the blind keep turning up, and while
many of these defects tend to be weeded out and disappear,
there is something which continues to keep up the supply.
Is it alcohol, disease, bad environment, or as has been
suggested, the radiations which emanate from the earth ?
It is not unreasonable to suppose that untoward agencies
may result in hereditary defects, but it should be remembered
that defective mutations arise in all sorts of organisms
quite irrespective apparently of the conditions under which
they live.

Suggested Readings

Guyer ('27), chap. 17. Jennings ('30), chaps. 14, 15. Wells, Huxley,
Wells, book 4, chap. 7.

Questions

i. If a recessive gene should arise, when and under what conditions
would it become manifest ?

86 HUMAN GENETICS AND ITS SOCIAL IMPORT

2. Which are the more common, dominant or recessive mutations ?

3. Is the dark color of tropical races due to the effect of sunlight in
successive generations ? Does environment tend to produce a similar color
in Swedes and Lapps living for generations in a similar climate ?

4. If size is determined by the influence of endocrine glands, can it be
due to genetic factors ?

5. What is the essential difference between the production of a herit-
able germinal variation by environmental means and the transmission of
an acquired character in the Lamarckian sense ?

6. What device was employed by the thrifty Jacob to produce the
desired variations in cattle? See Genesis, Chap. 30, 32—43.

7. Which would you expect to be the more variable, self-fertilized or
cross-fertilized plants ?

8. Do you think Darwin was right in attributing the variations of
cultivated plants and domestic animals largely to the influence of changed
conditions of life? What alternative explanation might be offered?

9. Compare the influence of alcohol on the race due to (a} its possible
effect in causing hereditary defects, and (£) its effect as a selective agent
in eliminating unfavorable variations that might arise.

10. Why did Burbank make numerous crosses in his efforts to produce
valuable varieties of plants?

11. A breeder crosses a black female and an albino male rabbit and
obtains some black and some albino offspring. He subsequently breeds
the black rabbit to another black and obtains a few albinos along with
blacks. He attributes the albinos in the second mating to the influence
of the previous albino male parent. What other explanation for the albino
offspring can you offer? Do you think that the influence of a previous
male parent (telegony) is probable in the light of present knowledge of the
physical basis of heredity ?

CHAPTER VIII
THE MEASUREMENT OF VARIATION

MANY variations such as the heights of human beings
form a regularly graded series between the two
extremes. Such variations are called fluctuations or some-
times modifications, and for the most part they represent
merely somatic changes and are not hereditary, at least
to any recognizable extent. Germinal variations may occur
among them, but they are not easily distinguished from
those which are environmentally caused. When enough
cases are collected the phenomena of variability often
exhibit statistical uniformities which it is desirable to
measure. The Belgian astronomer, meteorologist, and
anthropologist, Quetelet, was greatly impressed by the
fact that when human beings are studied in the gross their
peculiarities exhibit a uniform character in striking contrast
to the capriciousness of individual behavior. By tabulating
the results of numerous measurements of the heights of
soldiers he found that these distributed themselves about
the mean, or average, in fairly close agreement with the
mathematical laws of probability.

The statistical study of variation initiated by Quetelet
was carried further by Francis Galton who employed it
extensively in his valuable pioneer investigations in genetics.
The mathematical treatment of biometric problems has been
ably developed by Karl Pearson, the director of the Labora-
tory for National Eugenics founded by Galton in University
College, London. A large part of the formulas employed
by workers in biometry are the products of Pearson's
investigations.

88 HUMAN GENETICS AND ITS SOCIAL IMPORT

Variations which fluctuate about the mean value are
often represented graphically in the form of a so-called
frequency curve, or frequency polygon. Suppose that we
wish to make a curve of the variability in the heights of a
thousand men. We first lay off on a base line a number of
points corresponding to the various classes of height into
which we divide our group, beginning at the left with the
class including the shortest individuals. If our group is
divided into classes differing by one inch in height, we
should erect over the point in our base line corresponding

-2(T HT Q, M Qa(T 19

FIG. 35. — The normal frequency curve. M, mean. The lines over j^,i and ^3 divide the
areas of the curve on either side of the mean into two equal parts. The dotted perpendiculars
over <r and — <r are separated from the mean by a distance equal to the standard deviation.
The distance between <7 and — <r includes 68.3 per cent of the area of the curve. 95.5 per
cent of the area lies between iff and — 2<r and 99.7 per cent lies between yj and —30". (After
Babcock and Clausen.)

to the shortest individuals a perpendicular whose length
is in proportion to the number in that class. Then we do
the same with each class successively and finally draw a
line over the tops of the several perpendiculars. The per-
pendicular corresponding to the most numerous class,
which in this case would be near the center of our figure,
would represent the mode. The perpendicular representing
the mean, or average height, would divide the frequency
polygon into equal areas and would lie quite close to the
mode. The formula for computing the mean is M = S/77 '/ny
S meaning sum, and//7 the frequency of the variants, and

THE MEASUREMENT OF VARIATION 89

n the number. This means simply that to get the mean
height of a number of human beings we multiply the various
heights by the number of individuals of the height in ques-
tion, add them all together, and divide by the total number
in the group. In most frequency curves the mean is not
far from the mode, or, in other words, average individuals
usually constitute the most numerous class as is notoriously

A 5 6 7 8 9 10

0 133 55 23 7 2 2 0

FIG. 36. — Curve of variability of the buttercup. The mode is at one extreme, there being no
flowers with less than five petals.

the case with the height of human beings. Commonly also
the curve is approximately symmetrical on either side of the
mode. Sometimes the curves are asymmetrical, or skew,
and the mode may be even at one extreme. DeVries found,
in counting the petals of buttercups, that there were 133 with
five petals, none with a less number, 55 with six, and 23, 7, 2,
and 2 with seven, eight, nine and ten petals respectively.
The variability of this form would be represented graphically
by a one-sided curve with its mode at one extreme.

9o HUMAN GENETICS AND ITS SOCIAL IMPORT

Occasionally frequency curves have two or more modes.
Should we tabulate the sizes of individuals in which the
two sexes differ markedly we should obtain a double humped
curve with one mode for females and another for males.
An interesting illustration of the probable significance
of a bimodal curve is furnished by plotting the variability
of the head lengths of the spermatozoa of certain insects.
It was found by Zeleny and Senay that when the lengths
of the sperm heads were measured and plotted they gave a
frequency polygon such as is shown in Fig. 37. The probable
explanation is that the spermatozoa fall into two classes,
the one containing the ^f-chromosome having larger heads

FIG. 37. — Bimodal curve based on measurements of the lengths of 500 sperm heads from a
single male of Corizus lateralus. (.After Zeleny and Senay.)

than the other in which this chromosome is absent. The
bimodality is indicative of the dimorphism of the population
of spermatozoa.

The shape of frequency curves tells a number of things
about the range, average amount, and distribution of
variability within a given species or group. If the curve
has a wide spread, it indicates that the group is highly
variable. If it is very narrow, the individuals clustering
closely about the mean, the variation within the group is
manifestly very slight. It is often desirable to obtain a
definite measure of the amount of variability in a group in
order to compare it with the variability of some other group.
The eminent zoologist, W. K. Brooks once maintained that
males are more variable than females, and that one of the
important functions of the male sex is to furnish the vari-

THE MEASUREMENT OF VARIATION 91

ability which is an essential prerequisite for evolution.
If we wish to ascertain whether men are more variable
than women, we would not be able to do so by simply
watching the crowds which pass along the street. Evidently
we should have some fairly precise method of measuring the
degree of variability in order to solve such a problem. With
the biometric methods devised by Pearson a number of
workers began to measure the relative variability of the
two sexes in several species of animals. If the males are
really deserving of the proud position which Brooks has
accorded them, the facts should be readily demonstrable
by the use of a little biometry. When the relative variability
of the sexes was subjected to accurate measurement, it
turned out as a rule that they were about equally variable,
although in some species the greater variability was exhibited
by the females.

The first step in obtaining a measure of variability is to
ascertain the extent to which each individual deviates from
the mean of the group. We can find the average deviation
from the mean by multiplying the figure expressing the
extent of deviation of each class by the number of individuals
in each class, adding all the products together and then
dividing by the total number. The formula for the average
deviation is A.D. = S/D/». The measure of variability
most commonly employed, however, is the standard devia-
tion. In deriving this each deviation is squared, the squared
deviations are then added and divided by the total number,
and the square root of the quotient represents the number

sought. S.D. = I— — •• Frequently the standard deviation

is represented by the Greek letter <r.

It is evident that the standard deviation is expressed
in terms of the units of measurement employed. The standard
deviation for the height of men is a certain number of inches

92 HUMAN GENETICS AND ITS SOCIAL IMPORT

or fractions thereof, and the standard deviation for weight is
stated in terms of pounds or other units of weight. If we
are dealing with variations in different kinds of organisms
it is necessary to reduce them to a common standard. The
standard deviation of the weight of a lot of elephants would
doubtless be many pounds, but a group of mice could not
possibly include variations of that magnitude. If we wish
to compare the variability of elephants and mice as to weight,
we would have to consider the variability of each in relation
to the mean of its own group. For this purpose use is made
of the coefficient of variability, which is obtained by multi-
plying the standard deviation by 100 and dividing it by the
mean. This gives the relative variability in terms of the per
cent of the mean, the formula being C.V. = (100 X <r)/M.
Expressions for means, standard deviations, and other
measures may have very different degrees of reliability
owing to the different numbers of cases upon which they
are based. If I should make assertions as to the relative
stature of Norwegians and Italians based on averages of
four individuals of one group and five of the other, I might
be led into serious error, because I might happen to get
hold of unusually tall Italians and very short Norwegians.
Evidently the larger the number of individuals measured,
the more reliable the averages are likely to be. What is
called a probable error is, as its name implies, a measure
of the extent to which a figure is likely to be wrong. All the
expressions we have discussed are apt to be a little wrong
on account of the fact that they are based on a limited
number of cases. The probable error is taken to be a value
such that a given instance is as apt to fall within as without
that value. If a thousand people should all endeavor to
get a very exact measure of the height of a given individual,
most of their measurements would doubtless differ by a
slight amount. The differences would probably fall into a

THE MEASUREMENT OF VARIATION 93

fairly regular curve, symmetrically distributed about the
true value. In what statisticians call the normal curve the
lines dividing each half into equal areas are called quartiles
and the distances of these quartiles from the means would
represent the probable error of a given measurement. This is
a definite fraction, 0.6745 °f tne standard deviation, provided
our curve is what is called the normal curve of error. The
formulas for the probable errors of the mean, standard
deviation, and coefficient of variation are as follows:

P.E.M = 0.6745 °

RE.,

C V

0.6745-^

The probable error of the difference of two quantities is
0.6745 times the square root of the sum. of the squares of
the sigmas of these quantities.

P.E.^, = 0.6745 V<rx2 + ay2

If a difference is more than three times its probable error,
it is probable significant, i.e., not due to chance.

Besides studying the variations of individual traits, it is
often desirable to investigate the extent to which one kind
of variation is tied up with another. We might be curious
to know the extent to which the weight of human beings is
related to their height. It is a matter of common knowledge
that short people are generally lighter in weight than tall
people, although there are occasional exceptions. We
might also like to know how breadth between the shoulders
is related to height or to weight. Or again we might desire
to find out how infant mortality varies in relation to the
wages of the father, or the amount of schooling of the

94 HUMAN GENETICS AND ITS SOCIAL IMPORT

mother. Where things tend to vary together, we suspect
that there, is some causal connection between them, or that
both may be influenced by a common cause. The mathe-
matical expression which indicates the extent to which two
things vary together is called a coefficient of correlation.
It is always expressed as some fraction of i and it may range
from o to +i or —i. If, for instance, people tend to have
large families in proportion as they are lacking in money,
we would say that there is a negative correlation between
wealth and family size, as in fact there seems to be.

Coefficients of correlation are extensively employed not
only in genetics and in other departments of biology, but
in psychology, education, economics, and the social sciences
in general. The first to make use of coefficients of correlation
in the study of heredity was Francis Galton, who was the
first also to work out a mathematical formula for their
computation. The method was perfected by Karl Pearson
to whom we owe the formulas now most frequently employed.
The so-called biometric school of Galton, Pearson, and their
coworkers has made extensive studies on the correlation
between parents and offspring and between siblings for a
number of hereditary traits. Many of the correlations were
found to center around 0.5. In longevity, which shows a
tendency to run in families, the correlation is much weaker
owing to the occurrence of many deaths in infancy and
childhood, and the influence of mortality arising from purely
fortuitous causes. It is often assumed that a parent-offspring
correlation affords a measure of what is called the "strength
of heredity." What it really measures, as commonly em-
ployed, is the degree to which the offspring and one of its
parents tend to vary together in relation to the mean of their
groups. It is inferred that this correlation is due to their
common inheritance. When we are dealing with such char-
acters as eye color, which is not sensibly affected by environ-

THE MEASUREMENT OF VARIATION 95

mental factors, this inference is justified. If, however, we
were studying the possible heredity for stoop shoulders and
dealt with a population in which it was customary for fathers
and sons to follow the trade of shoemaking, we might be in
doubt as to whether the correlation between fathers and
sons for this character was due to heredity or their traditional
occupation. The fact that fathers and sons are both long-
lived may be due in part to the fact that both live in a
measure under conditions which in some families tend to
prolong life and in others tend to shorten it. A parent-
offspring or a fraternal correlation, therefore, may at times
be due to causes other than heredity, and we have to inter-
pret the correlation in the light of the possible factors
which may bear upon the problem.

Another circumstance which should be considered in
interpreting the significance of correlation is that degrees of
correlation are determined not only by similarities, but also
by dissimilarities. A correlation is a measure of covariance,
and where there is no variation there is no correlation.
This fact has been brought out by the studies of heredity
in pure lines of beans carried on by the Danish geneticist
Prof. Johannsen. The beans with which Johannsen worked
are normally self-fertilizing and were found to present no
hereditary variability. A pure line consists exclusively of
homozygous individuals, and hence all the variability it
contains is of a somatic noninherited kind. The variations
of one individual are no more apt to be like those of its
parent than those of any other member of the group.
Hence there being no tendency for parent and offspring to
vary together there is no correlation.

I might study parent-offspring correlations in a dozen
different pure lines and obtain a negative result in all of
them, although each line might be genetically different
from all of the others. If now I mix them all up so that within

96 HUMAN GENETICS AND ITS SOCIAL IMPORT

my group I get a considerable amount of genetic variability,
I would get a certain degree of correlation because parents
and offspring would tend to depart from the general mean
in the same way. As a matter of fact, parents and offspring
tend to resemble each other more closely in a pure line than
in a heterozygous and diversified population. Nevertheless,
the parent-offspring correlation would be o in the pure line
and anywhere from o to i in the mixed group.

From the nature of the case, correlations are based upon
somatic resemblances. There is no resemblance in color
between a purple sweet pea and the two white parents from
which it might arise, nor is there much resemblance between
the purple FI and its variously colored progeny. But all
these striking differences in color are quite as much the
result of heredity as the close similarities within a strain of
white peas. In such a case, the study of heredity by working
out correlations for color would be of little value. In general,
the methods of analysis followed by the Mendelians have
proved much more fruitful than the statistical studies on
heredity made by the biometricians. This is no reflection
upon the value of biometric methods. They have their
legitimate and very useful place in numerous problems
of genetics and even in Mendelian analysis, but we should
recognize their limitations and know when and where to
apply them.

Suggested Readings

Lindsey ('32), chap. n. Walter ('30), chaps. 2, 3. Babcock and Clausen
('27), chap. 17.

Questions

i. A plant produces 2 flowers with 8 petals, 6 with 9, 17 with 10, 30 with
n, 50 with 12, 32 with 13, 19 with 14, 7 with 15, 3 with 16 and i with 17
petals. Construct a frequency curve from these data, and calculate the
mean, standard deviation, and coefficient of variability.

THE MEASUREMENT OF VARIATION 97

2. How much does the mode in this curve differ from the mean ? How
much does it differ from the mean in Fig. 36?

3. What is the probable error of the mean in question I ?

4. Why is the standard deviation of the F2 of a cross usually greater
than that of the Fi ?

5. Why is the variability of the F\ usually no greater than that of the
parental types?

6. Among the progeny of the Fz would you expect to find some lines
presenting much more variability than others? Illustrate and explain.

7. What would be stated by saying that there is a negative correlation
of —i between fertility and years of schooling?

8. Why is a coefficient of correlation between parents and offspring
not an adequate measure of the " strength of heredity " ?

9. Suppose that a character is not influenced by the environment.
Why would the correlation between parents and offspring for this character
probably be considerably less than i ?

10. What is the effect of a high degree of somatic variability upon
parent-offspring coefficients of correlation ?

11. How might a parent-offspring correlation be brought about in a
pure line ?

12. How does the employment of measures of variability afford support
for the multiple factor theory of so-called blending inheritance ?

CHAPTER IX

HEREDITY IN MAN

THE immense amount of research in genetics that
followed and was stimulated by the rediscovery of
Mendel's law of heredity in 1900 has abundantly demon-
strated the wide applicability of the principles that Mendel
so thoroughly established for his garden peas. That all
sorts of animals and all sorts of plants from the highest
down to and probably including many one-celled organisms
should transmit their hereditary qualities in precisely the
same manner is a very remarkable fact. The investigations
of the cytologists have shown the reason for this in the
striking similarities of chromosome behavior in the reproduc-
tive processes of plants and animals. In the light of such
facts, it is scarcely credible that man, whose differences from
the anthropoid apes entitle him at most to membership in a
distinct family, should differ from other organisms in the
way in which his hereditary traits are transmitted.

Inevitably the rediscovery of Mendel's law led to a
reawakening of interest in human heredity. One of the first
traits studied from the Mendelian standpoint was eye
color. It had been known especially through the studies of
Galton that the inheritance of eye color is often alternative,
and that matings of two brown-eyed individuals or a brown-
eyed and a blue-eyed individual may produce children
whose eyes are brown, blue, gray, or even the pink color
characteristic of albinos. As a rule blue-eyed parents produce
nothing but blue-eyed children, a fact which indicates that
blue is recessive to darker colors. The results of most matings

HEREDITY IN MAN

are consistent with this interpretation. Eye color, however,
is a highly variable character and is apparently influenced
by modifying factors and variations in dominance. Occa-
sionally a brown-eyed child is born to parents whose eyes
would ordinarily be classed as blue, although it may be
that one or both parents were heterozygous with very
imperfect dominance of the gene for dark pigment. It
would hardly be safe to decide a case of disputed parentage
on the theory that two blue-eyed parents cannot have a
dark-eyed child.

In the transmission of hair color, the darker shades tend
to dominate over the lighter ones. One would not expect a
dark-haired child from two flaxen-haired parents, but
light-haired children are often born to dark-haired (pre-
sumably heterozygous) parents. Red color in hair seems
to be transmitted independently of the dark melanin pig-
ments, and it may be totally obscured if much melanin is
present, or it may produce a chestnut hue if the dark
pigment is less plentiful. Where there is little melanin, the
redness may be very conspicuous. The factors causing the
various shades of human hair are probably numerous, as is
demonstrably the case with the inheritance of coat color
in mammals. There are many instances in which the hair
color in children is somewhat darker than that of either
parent. Similar phenomena are commonly observed also
in rabbits and other rodents.

Kinky or woolly hair which is a normal racial character
in many tribes of Negroes is a partially dominant (or
partially recessive) feature. Baldness is transmitted as a
sex-limited trait, being dominant in man and fortunately
recessive in women. In skin color, the darker shades are
partially dominant over the lighter ones. All shades are
dominant over albinism, which is commonly due to the
complete absence of pigment. Albinos, whether they occur

ioo HUMAN GENETICS AND ITS SOCIAL IMPORT

among human beings or the lower animals, have pink eyes,
imperfect vision, and are relatively deficient in vitality.
Although albino mutants have arisen thousands of times,
and although albino races of rats, mice, and rabbits have
been reared for many generations, no albino variety has
ever succeeded in establishing itself in a state of nature.
The curious condition known as partial albinism charac-
terized by spots devoid of pigment in an otherwise dark
skin behaves as a dominant character. The white forelock
or flare, which often runs through several generations, is a
variety of this trait.

The ordinary shades of skin color probably depend upon
many factors. The mulattoes arising through crosses between
Negroes and whites have an intermediate skin color, and
their children show considerable variation indicative of the
Mendelian segregation of color factors, but the number
of such factors involved is uncertain. Stature, like skin
color and size inheritance generally, is a multiple factor
character. Children may be either taller or shorter than their
parents, owing to the peculiar combinations of factors
influencing growth. The number of such factors is very
difficult to ascertain. In the exceptional case of achondro-
plastic dwarfs a single gene may be responsible for lack of
growth, possibly as a result of some glandular disturbance
which causes the bones to cease growing in length. These
dwarfs usually have large heads and deformed bodies.
The women are often incapable of giving rise to a normal
birth, and recourse must be had to a Caesarean operation.
In some cases the trait appears to be dominant and in
others recessive, and sometimes it seems to occur inde-
pendently of genetic factors. Dwarfs in whom the parts of
the body occur in normal proportions are commonly not
traceable to hereditary influences. Among the hereditary
anomalies of growth, the condition known as split hand or

HEREDITY IN MAN

101

lobster claw is one of the most unfortunate. The digits are
fused together and disproportionately developed. The
trait commonly behaves as a dominant. The afflicted

FIG. 38. — Family showing the inheritance of syndactylism, or lobster claw. The trait
is shown in the father and in both children. A brother of the father was syndactylous and
another brother had one supernumerary toe. The three sisters of the father were normal.
(From Eugenic al News.)

individuals are incapacitated for most employments. Never-
theless, there are several records of their marrying and
transmitting their defect through several generations.
Pearson has reported the case of a woman who bequeathed

102 HUMAN GENETICS AND ITS SOCIAL IMPORT

this undesirable defect through four generations to thirty-
two descendants, a considerable proportion of whom have
spent a large share of their lives in workhouses. An even more
severe deformity, in this case consisting of the complete
amputation of hands and feet, has been described in a
family from Brazil. The mother was normal, but in the

FIG. 39. — Family from Brazil showing hereditary absence of hands and feet. The man
in the picture is the uncle of the children shown, but the father, who is no longer living, also
had the same deformity. Of the twelve children in this family six were normal and six were
deformed. (From Eugenic al News.)

father and all three of the children there were neither hands
nor feet. Other pedigrees have been described in which a
hand or a foot was lacking through three generations.

An extraordinary number of hereditary defects have
been observed in the eyes. Among these are atrophy of the
optic nerve, misplaced lens, glaucoma, absence of the
iris, cleft iris, nearsightedness, cataract, pigmentary retinitis,
color blindness, night blindness, paralysis of the eye muscles,

HEREDITY IN MAN 103

drooping eyelids, and various types of blindness. Some of
these such as color blindness, night blindness, and atrophy
of the optic nerve are usually transmitted as recessive sex-

- Many normal descendants

• • •

o-rO m +-rn • 6

Died at 15 \

1 6^0

... .

FIG. 40. — Dominant inheritance of glaucoma. The mother in the first generation developed
glaucoma and became blind after some of her children were born. Her husband's descendants
by a later marriage were all normal. All of the six children of the first generation suffered
from glaucoma, but only one produced children, two of whom developed glaucoma. The
trait was passed on through two of these children who were apparently normal and also
through one who was glaucomatous. The trait commonly develops fairly late in life and
some who did not develop it may have done so had they lived longer. In this pedigree
glaucoma behaves like an imperfect dominant. (Data from Courtney and Hill.}

linked traits, but some pedigrees have been described in
which color blindness and night blindness are sex-linked
dominants.

Q-r-Q

FIG. 41. — The inheritance of cataract. The condition of the two original parents is
unknown. The character here behaves as a dominant. Note that an affected male in the
second generation has transmitted the defect to children by both wives. Where an individual
is free from cataract the children are also free. In some pedigrees children inherit cataract
from parents who do not manifest it in some cases because they died before the defect had
developed. {After Nettleship.}

Deafness, although not infrequently caused by infections,
such as scarlet fever, meningitis, measles, and syphilis,
is in other cases transmitted as a recessive trait. Dr. Alex-

io4 HUMAN GENETICS AND ITS SOCIAL IMPORT

ander Graham Bell in his memoir on The Formation of a
Deaf Variety of the Human Race calls attention to the
tendency of the deaf to marry the deaf, and the danger that
deaf children may result from such unions. Even when both
parents are deaf, all the children may be normal, but in
other cases they are all deaf. In the former case, the deafness
of one or both parents may have been secondarily acquired,
and in the latter both parents may owe their defect to the
same recessive gene. Where recessive deafness is present
in a stock it is apt to be brought out by consanguineous
marriages. In a number of inbred communities deafness is

ch-o

D (>yHH Q-p-D

FIG. 42. — Inheritance of red-green color blindness. Only the males are affected but the
trait is passed through females. {After Groenouw.)

common. According to Bell one out of twenty-five of the
population of the western part of Martha's Vineyard in
1 8 80 was a deaf mute.

There are several forms of hereditary deafness. In most
of these the individual is born deaf, but congenital deafness
is not always due to heredity. In many families deafness
comes on slowly, leading to almost complete lack of hearing
late in life. Where this is due to otosclerosis the condition
often appears to behave like a dominant trait. There are
different hereditary types of deafness which may be inherited
in different ways.

As is abundantly illustrated in Cockayne's recent volume
on Inherited Abnormalities of the Skin our integument
manifests a considerable variety of hereditary disorders,

HEREDITY IN MAN

105

quite aside from the anomalies of hair and pigmentation.
The curious condition called ichthyosis (fish skin) in which
the skin develops hard scales or bony plates is often trans-
mitted as a somewhat variable dominant. In some pedigrees
it seems to show sex linkage, appearing in males and not in
females. Keratosis, a thickening of the palms and soles, is
transmitted as a sex-linked recessive. The "porcupine man"
whose horny skin was shed every year is said to have had
six children who shared his peculiarity. The trait was con-
tinued for two additional generations.

Diabetes is commonly transmitted as a recessive trait.
Since diabetes is more apt to occur in people who consume
a large amount of carbohydrates the problem of its hereditary
transmission is more or less complicated by the influence
of the environment. Many hereditary traits manifest
themselves as proclivities, or diatheses to disease without
necessarily producing that disease except under certain
conditions. In both plants and animals disease-resistant
and disease-susceptible strains are well known. Susceptibility
exists in all degrees and whether a disease is contracted may
depend upon the dosage of the germs or the vitality of
the individual exposed to infection. Frequently the im-
munity of a strain may be broken down by repeated or
very heavy inoculations of pathogenic bacteria. Wright
and Lewis have demonstrated by controlled breeding
experiments that some strains of guinea pigs are much more
susceptible to tuberculosis than others, and this has been
found true for different breeds of cattle. A breed of sheep
in Algeria is resistant to anthrax, which is highly fatal to
ordinary varieties. Domestic fowl are ordinarily immune
to anthrax, probably because their bodily temperature,
which is higher than that of mammals, is too high to permit
the propagation of the anthrax bacilli. In a famous and
spectacular experiment Louis Pasteur demonstrated that

io6 HUMAN GENETICS AND ITS SOCIAL IMPORT

chilling fowl by immersing them in cold water caused them
to contract anthrax when they were inoculated with this
disease. The germs multiplied abundantly in the blood
of the infected birds and caused the death of those left
exposed to cold. The birds put in warm surroundings, which
quickly raised their temperature, recovered from the disease.

Hereditary diatheses are shown not only in relation to
diseases caused by germs, but to disease provoked by other
exciting causes. It has been shown that heredity plays
an important role in asthma and hay fever, which may be
occasioned by pollen, food, and a great variety of other
substances to which the individual may have become
sensitized. The studies of Adkinson on a large number of
pedigrees point to the conclusion that the diathesis to
asthma is a recessive trait.

The role of heredity in causing cancer has long been a
matter of speculation. Statistical investigations carried
on under the Imperial Cancer Research Fund showed that
there are apparently no more cancers in the parentage of
persons dying of this disease than in the rank and file
of humanity. Accurate pedigrees showing the incidence of
cancer in successive generations are difficult to obtain
because a generation or two ago diagnosis was so imperfect
that probably most deaths due to cancer were not so re-
corded. If a trait is caused by recessive genes that are
sparsely scattered through the population, most individuals
showing the trait will come from parents who do not show
it, just as most black sheep in a flock come from white sheep.
A parent-offspring correlation in such a case would be
exceedingly weak. Since cancer is a disease of old age many
individuals who might be due to die of cancer because of
their heredity are carried off in the meantime by some
other malady. The investigation of the hereditary factor
in cancer by the collection of mass statistics is therefore

HEREDITY IN MAN

107

very unsatisfactory. Many pedigrees have been collected
showing that cancer appears with unusual frequency in
certain families, but with all humanity to draw from one
might collect many such cases purely as a result of chance
association. There are some cases, however, for which this
explanation seems improbable. Dr. Warthin has described
one family in which twenty-seven cases of cancer, mostly
of the stomach and intestines, appeared in three generations.
Purtscher has described the case of a family in which several

6 rj • • 6 4 • 6 6

FIG. 43. — Two pedigrees of cancer. ?, persons too young to manifest cancer. (After Rice.)

members died of a rare cancer-like growth known as retinal
glioma. The father who died of sarcoma had eleven children,
three of whom died of retinal glioma. One of these, a daugh-
ter, married and had a boy who died of the same malady,
and there were two other cases among the children of
members of the family who remained free of the tumor, but
who were apparently carriers of the disease. The one thing
that is clearly established about the causation of cancer is
that cancers are apt to be produced by chronic irritations.
A suggestive case is afforded by three brothers, all smokers,
who developed cancer of the lip in middle life. A fourth

108 HUMAN GENETICS AND ITS SOCIAL IMPORT

brother did not smoke, but he nevertheless developed
cancer of the lip in his sixty-fifth year.

In animals diatheses to cancer are clearly demonstrable.
Miss Maude Slye, who has spent many years in studying
cancer in mice, has developed strains of mice showing
various degrees of cancer mortality from o to 100 per cent.
According to Miss Slye cancer in mice is a recessive Men-
delian trait, but whether one or more genes are involved is a
matter of dispute. In different strains cancer shows a marked
proclivity to attack particular organs such as the lungs,

FIG. 44. — Family with blue sclerotics. Individuals marked / also with fragile bones
For some peculiar reason these unlike characters are closely associated in heredity. (After
Burrows.}

liver, skin, and mammary glands, and the same tendency
is indicated by many pedigrees of human beings.

It would require a large book to give an adequate account
of hereditary human ills. Defective genes produce the great-
est imaginable variety of effects. They may manifest their
influence in a misplaced lens, a dislocated hip, atrophy of the
optic nerve, short stubby fingers, a proclivity to bronchial
asthma, deafness, blindness, muscular atrophy, fragility of
bones, hemophilia, harelip, baldness, excessive hair, super-
numerary teeth, or lack of teeth, dark-colored urine, or a
small harmless pit in the lobe of the ear. These and numerous
other departures from normality are all the products of a
long chain of effects and a complex series of interactions of
parts. Truly, we are fearfully and wonderfully made.

HEREDITY IN MAN 109

One of the noteworthy peculiarities of human heredity is
the variability with which a given trait is manifested in
different pedigrees. Now a trait is clearly dominant. In other
cases it appears to be recessive, or again it may be partially
dominant, occasionally skipping a generation. Hereditary
characters may vary greatly in their degree of development,
as we have seen in the case of polydactylism. They also
vary in their qualitative expression. In seeking an explana-
tion for this feature of human heredity we should bear in
mind two facts: (i) Characters which are much alike may be
due to different genetic factors and hence may show different
modes of inheritance. In the fruit fly Drosophila genes affect-
ing eye color are scattered about in different loci of the
chromosomes. So also are factors affecting wing venation,
body color, bristle development, and size of body. Hereditary
blindness in human beings is brought about by several kinds
of defects. It is not improbable that different cases of heredi-
tary deafness, color blindness, and various other hereditary
defects in man are due to quite different genes.

(2) Even where defects are known to be due to the same
gene, there may be several mutant changes in one gene as in
the locus for white eye in Drosophila, which produce more
or less similar manifestations; but the greatest cause of
hereditary diversity is due to the varied company of other
genes. Every character is the product of many factors. Let us
suppose that a given gene is responsible for the development
of insanity sometime after middle age. If the gene in ques-
tion has to work out its effect in company with other genes
causing migraine, spastic paralysis, or mental deficiency, the
manifestations of insanity would doubtless vary to a con-
siderable degree. One might compare the effects of a gene in
different constitutions with the growth of a plant in different
kinds of soil and in company with different kinds of plants.
We cannot expect all so-called unit characters to be invari-

i io HUMAN GENETICS AND ITS SOCIAL IMPORT

able any more than we can expect all plants of a given variety
to be the same in all kinds of environments and associations.
A plant grown amid others may not only fail to attain its
normal size, but it may undergo changes of form and habit of
growth. Gene effects are never produced singly. The action
of every gene is conditioned by the actions of multitudinous
other genes. And since the genes of the human species con-
stitute an exceedingly varied company, it is inevitable that
each gene should express itself in many different ways. This
is especially true of those genes which affect complex traits
such as the peculiarities of human behavior. It is scarcely
conceivable that insanity or epilepsy should present the same
degree of uniformity as might be found in eye color or in the
tints of the skin, and if these complex traits are highly vari-
able as a result of diversities of genie composition, they may
be expected to manifest a great deal of variation also as a
result of environmental influences.

The relation of environment and heredity will be treated
in the following chapter.

Suggested Readings

Lindsey ('32), chap. 17. Pearson ('27). Shull, ('31), chaps. 21, 22. For
further information on special topics see Baur, Fischer, Lenz ('31), Blacker
('31), Crew ('27), Davenport ('11), Gates ('29).

Questions

1. In studying human pedigrees, how can you tell whether a given
character is dominant or recessive ?

2. If a congenital deaf mute marries a person who became deaf through
inherited otosclerosis, what would probably be the condition of the
children ?

3. Make a list of twenty human traits indicating the mode of inherit-
ance in each case.

4. Do you think it likely that a trait may be inherited in a mono-
hybrid ratio in one strain and in a dihybrid ratio in another ?

5. Why do you think that a trait due to a single pair of genes should
present many variations in its manifestation in different lines ?

HEREDITY IN MAN in

6. Would a dominant sex-linked character appear more frequently in
males or in females?

7. How do Negroes and whites differ in their resistance to tuberculosis,
pneumonia, scarlet fever, erysipelas, and most diseases of the skin ?

8. What can you say as to the probable number of genes in which
whites, Negroes, and Mongolians differ?

9. In what respects do you think that you differ hereditarily from
other members of your family ?

10. A student registering for a course in genetics was asked, "How
many times have your bones been broken?" The reply was, "Three."
What led the instructor to suspect that the student had fragile bones ?

n. If a normal-haired woman with a bald father marries a normal-
haired man, what may be expected of the children ?

12. If a very rare trait appears in three generations of a family, what
would you conclude as to its probable mode of inheritance ?

13. If a trait is dominant, sex-linked, and lethal when homozygous or
when not'counteracted by a corresponding normal factor, what would be
the sex ratio of the offspring of mothers showing this trait?

CHAPTER X
HEREDITY AND ENVIRONMENT

WHETHER heredity or environment is chiefly re-
sponsible for the development of this or that trait
has been the subject of no end of controversy. We have the
hereditarians who are accused of attaching altogether too
much importance to the germ plasm, and the environmental-
ists who like to think that heredity counts for little especially
in the affairs of men. On this question there are all grades of
opinion between the extremes of both camps.

It is quite natural that the doctrine that all men are
created free and equal should make a strong appeal to the
champions of equal rights. The teachings of Rousseau, the
founders of our own government, and other leaders who
strove valiantly in the cause of human freedom during the
latter part of the eighteenth century, emphasize the influence
of environment and opportunity in bringing about the ob-
served inequalities among human beings. Mr. John Stuart
Mill, whose humanitarian spirit pervades all his writings,
remarked that "of all vulgar modes of escaping from the
consideration of the effects of social and moral influences on
the human mind, the most vulgar is that of attributing the
diversities of conduct and character to inherent natural
differences" — a statement which is supported with cordial
approval by Mr. T. H. Buckle in his History of Civilization.
In a similar vein Henry George declared that "the influence
of heredity, which it is now the fashion to rate so highly, is
as nothing compared with the influences which mold the
man after he comes into the world." As representing the
opposed standpoint of the hereditarians we may quote

112

HEREDITY AND ENVIRONMENT 113

the matured opinion of Francis Galton that "nature prevails
enormously over nurture when the differences in nurture do
not exceed what is commonly found among persons of the
same rank of society and in the same country."

Heredity and environment represent two large groups of
factors, which are concerned in the production of all char-
acters. In one^sense neither is more important than the other
because both are all-important. We can only compare the
effects of differences in heredity with the effects of differences
in environment. When we properly limit our inquiry it is
often possible to arrive at a definite solution of our problem.
In many cases the preponderating influence of hereditary or
environmental differences is clear. Whether a man has a
black or a white skin, blue eyes or brown, straight or kinky
hair, depends mainly upon his allotment of genes. Whether he
speaks English, Russian, or Chinese depends mainly upon his
social environment. But even the color of a man's skin or
eyes, and the degree of kinkiness or straightness of his hair
may be affected to a slight extent by environmental forces,
and whether he speaks a given language well or poorly, or is
even able to learn a language at all, may depend upon his
peculiar heredity.

It is evident that each character presents its own peculiar
problems with reference to the relative influence of nature
and nurture. Many problems of this kind are difficult to
solve, because of the imperfection of our measures of the
hereditary or environmental influences involved. We know
in a general way that both hereditary and environmental
differences affect stature, weight, general health, longevity,
intellectual aptitudes, and traits of character, but in a mixed
population of human beings whom it is not feasible to subject
to experimental tests, it is difficult to arrive at an accurate
measure of the extent to which the variability of these traits
is to be attributed to genetic or environmental factors.

ii4 HUMAN GENETICS AND ITS SOCIAL IMPORT

As we learn more of the mechanism of development, we
find that the environment influences organisms in unex-
pected ways. Without a sufficient supply of iodine an other-
wise comely and intelligent child might be transformed into
a coarse, stunted, and repulsive-looking imbecile. Not im-
probably a similar result might be produced by a change in a
gene which would check the development of the thyroid
gland. As a matter of fact thyroid deficiency is to a certain
extent a hereditary character. One of the most striking

FIG. 45. — Three photographs of the same child suffering from thyroid deficiency. Before
treatment with thyroid extract growth was stunted and abnormal. After three weeks of
treatment the child made remarkable improvement as is indicated by the middle figure.
The parents then had the thyroid treatment discontinued and before long the symptoms
of cretinism began to reappear. In six months the child presented the appearance shown in
the right hand figure. (Copyright by Journal of Heredity.)

achievements in the study of the glands of internal secretion
is the discovery that children suffering from thyroid de-
ficiency may be converted into normal, intelligent human
beings by the administration of thyroid extract. Both
heredity and environment are capable of producing much
the same kind of developmental defects. For this reason, the
shortcomings of heredity may in some cases be compensated
for by supplying the proper environmental influence.

If we knew just how genes exert their influence upon the
developing organism, we might be able to overcome many
hereditary defects. Some kinds of dwarfism are probably

HEREDITY AND ENVIRONMENT 115

due to a defective development of the anterior lobe of the
pituitary gland. In fact, some cases of dwarfism have made
a satisfactory growth under gland treatment, but whether
the dwarfism was an inherited defect is not known. Even
sex, which is commonly determined by the sex chromosomes,
may sometimes be changed by environmental factors. What
under ordinary circumstances is determined by heredity,
under extraordinary circumstances may be determined
by the environment. Both heredity and environment are of
course essential for the production of either a male or a
female. In this case environment determines whether the
male-producing or the female-producing genes, which are
present in every individual, assume the predominant role.
The so-called environmental determination of sex is quite
analogous to the environmental determination of dominance
in a heterozygous individual.

Possibly the future may give us the means of controlling
the activities of genes to a much greater extent than seems
likely today. We may find substitutes for gene deficiencies,
so that people can get along without several kinds of genes
which are now essential. But the more we are able to com-
pensate for gene deficiency, the more we become dependent
upon the environment for the maintenance of life and health.
The cretin must continue to take his thyroid tablets or
lapse back into imbecility. We might imagine a remote
future in which people would have to be continually dosing
themselves with gene substitutes in order to keep alive —
which on occasion might prove to be a very precarious
situation, to say nothing of its other drawbacks.

What we are interested in knowing are the kinds and
degrees of effects which may be produced by a given environ-
mental change, or a given change in hereditary constitution.
Under certain conditions, such effects may be measured
with a fair degree of accuracy. If I have a uniform lot of

ii6 HUMAN GENETICS AND ITS SOCIAL IMPORT

beans derived from a pure line, I can measure the effect
of applying a certain kind of fertilizer, provided I keep all
other conditions the same which might influence the growth
of the plants. I might also measure quite accurately the
effect of genetic differences between two varieties by raising
all the plants under identical conditions of nurture. Then
I could compare the genetically caused differences with
those due to environment and determine which were the
greater. But whether the one or the other produced the
greater effect would depend upon the particular genetic
and environmental influences I chose to compare. I might
sow some seed in very rich soil, and some on stony ground
and obtain enormous differences in yield due to environment.
Or again, I might choose strains genetically much alike,
or again very different, and thus obtain a wide range of
results due to hereditary diversity.

The question of the relative influence of hereditary and
environmental differences has been investigated for a
number of human traits by Pearson, Elderton, and other
biometricians, and they have come to the conclusion that
for the traits studied heredity is much more potent than
environment in causing the observed differences. The
method employed is to work out correlations between
related individuals for the various traits. These are assumed
to give a measure of the potency of heredity. Correlations
are also worked out between these traits and various environ-
mental factors. If it is found that a parent-offspring correla-
tion is of the order of 0.5, as it is for many characteristics,
and the environmental correlations are much weaker, such
as o.i or 0.2, the conclusion is drawn that heredity is much
more potent than environment in causing the observed
differences.

As we have already seen, a parent-offspring correlation
is not necessarily, or even usually, an adequate measure

HEREDITY AND ENVIRONMENT 117

of the strength of heredity. Were we to study the relative
effects of hereditary diatheses and environmental exposure
upon the occurrence of tuberculosis, we could not assume
that a parent-offspring correlation of 0.5 which was found
by Pearson and Goring is necessarily due to heredity.
It might, as has been claimed, be due to the transfer of
infection or exposure to a common environment.

It should also be pointed out that not only may parent-
offspring correlations be due to environment instead of
heredity, but correlations with environmental differences
may be due to heredity instead of environment. If I were
to study the effect of an urban environment upon stature
and measured a considerable number of Italians (who are a
relatively short people) in New York City and an equivalent
number of the old American stock (who are fairly tall) in
the rural areas of New York State, I might be betrayed into
concluding that a difference due mainly to racial heredity
was caused by conditions of life in a large city. Theoretically,
coefficients of correlation may throw much light on the
nature-nurture problem, but they have to be employed with
caution, and with an ever-watchful eye to alternative
possibilities of interpretation.

A valuable side light upon our problem is furnished by
the study of twins. Francis Galton was the first to recognize
that twins fall into two classes: (i) ordinary, or fraternal
twins, who may or may not be of the same sex, and are not
much more alike than other brothers and sisters; and (2)
identical twins, who are usually very much alike and are
always of the same sex. It is now fairly well established that
identical twins come from the same fertilized egg. They
are analogous to the quadruplets that arise from a single
egg in the armadillo after it has undergone a certain degree
of development as a single individual. Unless some unusual
departure from ordinary chromosome behavior occurs

ii8 HUMAN GENETICS AND ITS SOCIAL IMPORT

during early development, identical twins would have
precisely the same heredity. Often their similarity is so
close, that their friends and sometimes even their parents
have difficulty in telling them apart. They are living testi-
monials as to the potency of heredity as a cause of likeness.

FIG. 46. — Six pairs of identical twins. In all these pairs both members belonged to the
same blood group and had almost exactly the same shade of eye color and hair color. Both
of the girls of the lower left pair had only two upper incisor teeth. In both boys in the lower
right figure the second and third toes of both feet are joined by a fleshy web. (From photo-
graphs by Dr. R. Stohler.}

It is commonly assumed that environmental factors are
on the average the same for identical and fraternal twins,
and hence we have the opportunity of comparing like and
unlike heredity under the same environmental conditions.
On the other hand, it may be claimed that identical twins
are, ipso facto > more apt to be exposed to similar influences,

HEREDITY AND ENVIRONMENT 119

and hence tend to become more nearly alike than fraternal
twins. The only actual investigation of this question has
been carried on by Dr. Paul Wilson in a fairly large number
of twin pairs, and he finds that identical twins as compared
with fraternal twins of the same sex, more often dress alike,
are more frequently in the same grade and room in school,
have more friends in common, are less frequently separated,
and have more similar tastes in food and more similar records
for diseases and for general health. Differences in environ-
mental exposure are greater between twins of unlike sex
than between identical and fraternal twins of the same sex.
This is a very important fact since differences between
identicals and fraternals of the same sex are commonly
much greater than differences between fraternals of the
same sex and fraternals of different sex.

If we could experiment freely with human beings it would
be very interesting to compare the results of the following
combinations:

Like heredity under the same environment;
Like heredity under different environments;
Unlike heredity under the same environment;
Unlike heredity under different environments.

Since we cannot deal with human beings as we do with
guinea pigs, we have to select those cases which approximate
most closely to the conditions specified. There are many
instances of identical twins exposed to environments which
are very similar. Of course, the environment is never quite
the same for two human beings even when they are reared
in the same home and attend the same classes at school.
One twin might contract a disease, experience a nervous
shock, or receive an inspiration through personal influence
which might have a marked effect upon the development of
physique or character. These inevitable environmental

120 HUMAN GENETICS AND ITS SOCIAL IMPORT

differences affect some characteristics much more than
others. In eye color, hair color, configuration of the external
ear, head index, general body build, texture of skin, dentition,
vision, hearing, and blood grouping, the similarities of
identical twins are as a rule very striking and very much
closer than those of fraternal twins. Characters which are
much affected by environmental factors show a greater
degree of variation. There are several diseases which when
they occur in one member of a pair of identical twins usually
occur in both, whereas in fraternal twins they are commonly
manifested in only one member of a pair. With other diseases,
such as whooping cough and mumps, the distribution
between identicals and fraternals is not greatly different.

The study of twins has proved very valuable in throwing
light on the role of hereditary diatheses in various maladies.
The influence of heredity in tuberculosis has long proved
to be a peculiarly knotty problem, since the well known
tendency of tuberculosis to run in families might be explained
as a result of either heredity or environment. Diehl and
Verschuer have recently compiled data on the incidence
of tuberculosis in fraternal and identical twins and their
results may be summarized in the following table:

Group A

Group B

Group C

Identical twins

Fraternal twins of like sex

14.

Fraternal twins of unlike sex

In group A are included cases in which both twins are
tuberculous and in which the time of onset and course of
the disease are similar. In group B both twins are tuberculous,
but the disease differs in severity, time of onset, or organs
affected. In group C, one twin was tuberculous and the
other not. Although the number of cases is not large the

HEREDITY AND ENVIRONMENT 121

striking differences in the incidence of tuberculosis in identi-
cal and fraternal twins furnish strong evidence for a hered-
itary diathesis to this disease. One particularly impressive
instance is furnished by a pair of identical twins in which
tuberculosis developed in the bone of the heel of both
members.

Notwithstanding many remarkable similarities, identical
twins may present rather marked differences. Dahlberg
has found that identical twins differ more in weight at
birth than ordinary twins of the same sex, but in a short
time the identicals show the greater similarity. This as
well as other differences may be due to the fact that identical
twins are more closely associated in utero than ordinary twins
and tend to interfere more with each other's development.
Accidental variations of position might result in unequal
rates of growth, or in handicapping one member in some
other way. If one twin is stillborn, the liability of the other
member to be stillborn is about three times as great in
identical twins as in fraternal twins. This may be due in
part to their closer association and to the fact that there is a
more intimate connection between the blood systems of
identicals than between those of fraternals.

Another factor making for inequality is "mirror imaging"
—the right side of one twin sometimes shows a tendency to
resemble the left side of its cotwin. The degree to which
identical twins tend to develop complementary asymmetries,
may depend upon the stage at which they come to be
separated. For a time both develop as one individual,
and it seems not unreasonable to suppose, as suggested by
Newman, that when separation is delayed mirror imaging
becomes more pronounced. It is possible that this tendency
might have far-reaching effects, not only upon physical
traits but also upon personality. If, for instance, it caused
one twin to be left-handed this circumstance might have a

122 HUMAN GENETICS AND ITS SOCIAL IMPORT

considerable influence on the development of the individual
in several ways.

It is a curious fact that identical heredity should be
associated with conditions which are provocative of differ-

FIG. 47. — Japanese twins probably identical but showing unequal development. At birth
they were attached to one placenta and had almost exactly the same weight and head
circumference. Their finger prints and palm patterns are remarkably similar. Up to school
age they could scarcely be distinguished. In their second school year they began to exhibit
differences in growth. One twin M developed diabetes insipidus and grew less rapidly than
the other who was free from this malady. .Arrays showed that the pituitary fossa was
larger in the larger twin. The cause of the unequal development of the twins is unknown.
(Copyright by Journal of Heredity.)

ences. How far identical heredity is directly responsible
for the development of unlikeness in identical twins is
uncertain. Mirror imaging is apparently more frequent in
conjoined twins than in ordinary identical twins. Keeler
found that among laterally joined double monsters, "ten
out of thirteen asymmetrical pairs of characters, or 77 per

HEREDITY AND ENVIRONMENT

123

cent are mirrored," while in fourteen pairs of identical
twins only 22 per cent of such characters are mirrored.
In conjoined twins complementary asymmetries are rela-
tively frequent in internal organs, a condition which may

FIG. 48. — Identical twins reared apart. (From Popenoe in the Journal of Heredity.)

well be the occasion of physical maladjustments in one
or the other individual.

Although so-called Siamese twins are often remarkably
alike, there are some cases in which one twin is better
developed than the other. Two Siamese twins, D and V>
studied by Koch differed in height by 4 cm. "Consistent
superiority is exhibited by D [the taller one] in all the intelli-

124 HUMAN GENETICS AND ITS SOCIAL IMPORT

gence tests as well as those of scholastic abilities, such as
arithmetic, vocabulary, composition and reading com-
prehension," but the differences in the Army Alpha Tests
were less than those of three-fourths of the average twin
population and were about a third as great as the average
variability of a fourteen-year-old population. In general,
conjoined twins are less similar than identical twins who
are separate. This may be due to a certain amount of
interference during development together with a greater
degree of mirror imaging.

Suggested Readings

Jennings ('30), chaps. 5, 6. Newman ('32), chaps. 37, 38. Further refer-
ences on twins, Dahlberg ('26), Hirsch ('30), Holzinger ('35), Lauterbach
('25), Muller ('25), Wingfield ('28).

Questions

1. Mention several characteristics of plants or animals which are
greatly influenced by genetic factors and also by environmental conditions.

2. .What can vou say of the role of genetic and environmental factors
in diabetes, astnina, and hay fever ?(,- vrUvta

3. In what diseases of man do genetic differences play little part ?

4. In what diseases of man do environmental differences play little
part?

5. Do environmental factors ordinarily cause differences in height as
great as those between Norwegians and African pygmies ?

6. Which do you think is more affected by the environment, height or
-Height?

7. Would you class differences in hair color due to age as hereditarily
or environmentally caused ?

8. Is there any limit to the differences which environment might make
between individuals of like heredity? > ••

9. Is environment more effective in making like individuals unlike or
in making unlike individuals alike?

10. Is it possible for two fraternal twins to have the same heredity? /*

11. In studying the relative roles of heredity and environment is it
important to ascertain the differences environment can make or to con-

HEREDITY AND ENVIRONMENT 125

sider the extent of the differences which arise under environmental condi-
tions that are commonly met with?

12. What other reasons beside those mentioned might cause both
members of a pair to die in utero more frequently in identical twins than in
fraternal twins?

13. In what respect may freckles or sunburn be both a hereditary and an
acquired character ? ' ^'>\juj('*' W^-**-*'

CHAPTER XI
HEREDITY IN MENTAL DEFECT AND DISEASE

A^IONG the hereditary ills with which human beings
are afflicted those affecting the development of the
mind are probably first in order of importance. These mental
ills are of many varieties, but they may be grouped into two
fundamental classes: (i) the lack of normal mental growth,
or mental deficiency; and (2) abnormal mental development,
or mental disorder.

Mental deficiency (amentia) may be due either to heredi-
tary causes (primary amentia), or to environmental factors
(secondary amentia). Occasionally a disease of childhood
such as meningitis or encephalitis leaves a previously normal
child with deficient intelligence. Congenital syphilis is
sometimes responsible for mental defects as well as for many
nervous disorders of children. Wassermann tests to ascertain
the presence of syphilitic infection have been administered
to the mentally defective inmates of several institutions,
but the percentages of positive reactions reported were
very unequal. If a mental defective gives a positive reaction
for syphilis, it is no proof that the disease is the cause of
the defect. Tredgold (Mental Deficiency) remarks that
"on the whole, I doubt, whether syphilitic aments con-
stitute more than 2 to 3 per cent-ofjniental defectives."
The percentage of syphilis seems to be greater in low types
of mental defectives than in those of higher grade. In
general, it is unlikely that syphilis is responsible for more
than a small percentage of mental deficiency.

A small amount of mental defect is due to thyroid defi-

ciency, inherited or acquired. Head injuries at birth and

126

HEREDITY IN MENTAL DEFECT AND DISEASE 127

accidents during development are probably responsible for
a larger number, although many cases of head injury and
internal hemorrhage do not result in noticeable mental
impairment. In a study of 20,473^01868 of difficult labor
Dayton found no relation between degree of difficulty and
the degree of mental deficiency.

FIG. 49. — A microcephalic idiot. Although over thirty years old the mental age of this
individual is about one and one half years. He can neither dress himself nor talk. (Courtesy
Leon F. Whitney.)

Feeble-mindedness occurs in all degrees. Idiots, the
lowest class, have an intelligence quotient from o to 25,
and their mental capacity does not develop beyond that of
children of two to four years of age. The imbeciles have an
intelligence ranging from 25 to 50, and their intelligence
corresponds approximately to that of children from three to
seven years old. The morons who constitute the next higher
grade have an intelligence quotient from 50 to 70, or, as
defined by the American Association for the Study of the
Feeble-minded, from 50 to 74. The morons grade into the

128 HUMAN GENETICS AND ITS SOCIAL IMPORT

borderline and dull-normal people, and the latter are con-
nected by insensible gradations with individuals of normal
and superior intelligence. Pearson and Jaederholm have
contended that mental defect varies in a continuous manner.
Both the idiots and the geniuses are represented by relatively
few numbers. According to the findings of the Mental
Deficiency Committee who made an extensive survey of
certain regions of Great Britain, the idiots constituted only
3.6 per cent of the mentally deficient population; the
imbeciles constituted 16.6 per cent, and the feeble-minded
80.3 per cent. There are more borderline cases and dull

FIG. 50. — Pedigree of the V family showing mental defect and microcephaly. All indi-
viduals in black mentally defective; those marked M are known to be microcephalic. The
mental condition of those marked ? unknown. (After E. A, Whitney.}

normals than morons, while people of average ability
constitute the most numerous class. The further they pass
beyond mediocrity toward the highest types of intelligence
the smaller the number of individuals. The distribution of
intelligence resembles that of height or weight and approxi-
mates very closely a typical symmetrical frequency curve
of variability (see Fig. 59). Only arbitrary distinctions can
be made, therefore, between the various classes, whether of
mental defectives or of geniuses.

The variability expressed in the typical bell-shaped curve
is a product of many influences both genetic and environ-
mental. The manifestations of mind are so varied in char-
acter and degree that it is evident that many genetic factors
must be involved in their production. Feeble-mindedness

HEREDITY IN MENTAL DEFECT AND DISEASE 129

has sometimes been considered as a simple recessive Men-
delian trait, but there is much evidence that it is usually
the product of a variety of genetic factors. There are prob-
ably some types of feeble-mindedness which depend primarily
upon a single recessive gene. Among these is the peculiar
condition known as amaurotic family idiocy. This defect
is almost entirely confined to people of Jewish extraction.
There is a degeneration of the retina leading to blindness.

_6 4
4666

(b)

FIG. 51. — Pedigrees of amaurotic idiocy. In (b) all the affected individuals are descended
from two brothers and both pedigrees show more than one affected person in a family.
[(a) after V. Starck; (b) after Hermann.]

The condition involves grave nervous disorders and leads
to death usually in the first year of life. Since the trait is
lethal amaurotic children are always born to normal parents,
but sometimes more than one case appears in a family.
The defect is especially apt to be brought out in consanguin-
eous marriages. For this reason, it is probable that it depends
upon a recessive gene. There is a similar malady called
juvenile amaurotic idiocy which appears in older children
and also leads to imbecility and blindness. Although the

130 HUMAN GENETICS AND ITS SOCIAL IMPORT

defect is rare, it not infrequently affects more than one
child in a family.

Another clearly recessive type of mental defect has been
studied by Sjogren in an inbred community in Sweden.
All the affected children belong to a clearly defined type of
low-grade imbeciles. Most of them could not be taught to
read or write; others learned very imperfectly, and they
usually spoke indistinctly and only in monosyllables.
One large group of interrelated families produced forty-
eight of these imbeciles. Sometimes two or more appeared
in the same family along with normal siblings. As a rule
they were of good physical development, and the thirty-nine
who were given Wassermann tests showed a negative
reaction. On account of their low mentality these imbeciles
were kept in homes or in institutions and did not propagate
their kind. In every case the mental defectives were born
to parents who were normal.

Writers on mental defects and diseases often make the
assumption that if a trait is not found in the ancestors of
an affected individual it is probably not due to heredity.
There have been many estimates as to the percentage of cases
of feeble-mindedness, epilepsy, and insanity which are due
to heredity, the inference being that if the trait appeared
in the ancestry in a certain percentage of cases, in that
percentage, heredity could be assigned as its cause. Knowl-
edge of the principles of Mendelian heredity shows the
untenability of this view. Where a relatively rare recessive
trait is involved, it may appear only very rarely in both
parents and offspring. If the trait interfered with reproduc-
tion it might never appear in both parents and offspring.
When we limit our standard of feeble-mindedness to cases
of low grade we find that in most cases the feeble-minded
come from ancestors classed as normal. Nevertheless, as
in the group studied by Sjogren, the defects might be due

HEREDITY IN MENTAL DEFECT AND DISEASE 131

132 HUMAN GENETICS AND ITS SOCIAL IMPORT

to genetic causes. The frequency with which a trait runs in
families is not necessarily an index of the extent to which it is
due to heredity.

It has been shown by the studies of the Mental Deficiency
Committee and other investigations that there are fewer
mental defectives among the parents of idiots and imbeciles
than among the parents of the higher grades of the feeble-
minded. This is probably because there are a number of
recessive genes each of which may give rise to mental
deficiency of a low type. Such cases represent more or less
pathological types of defect due to a pair of genes which
profoundly disturb the course of normal development.
The mental deficiencies of this type seem to stand apart
from the normal gradations of mental ability much as a
case of achondroplastic dwarfism stands apart from the
normal fluctuations of human stature.

It is not the more or less clearly defined pathological
cases of mental deficiency that constitute the greatest
eugenic problem,, because they are not a self-perpetuating
class. The most serious problem is presented by the morons
and the borderline cases who may be considered as repre-
senting the lower levels of the normal range of mental
ability. Many individuals of this group pass as normal
although rather stupid people. To a considerable degree
they come from poor stock, although occasionally they may
be born to very intelligent parents. According to several
writers the feeble-mindedness of this class is inherited as a
recessive Mendelian trait, but this conclusion has been
criticized by a number of geneticists. In support of this
theory is the fact that feeble-minded children are often
born to normal parents, whereas if both parents are feeble-
minded practically all their children are feeble-minded also.
According to Goddard, of the 220 children born of forty
marriages in the Kallikak family in which both parents

HEREDITY IN MENTAL DEFECT AND DISEASE 133

were feeble-minded all but two were feeble-minded also.
In a larger series of 482 children of feeble-minded parents,
all but six were said to be feeble-minded. Feeble-mindedness
of the type usually found in degenerate human strains
is no unitary characteristic. It is a highly variable character
which can only be discriminated from normal intelligence
by a purely arbitrary criterion. Most critical students
of the genetics of mental deficiency are inclined to adopt
the multiple-factor hypothesis, and it is not improbable
that several of the factors involved may be dominant or
partly dominant in their effects.

FIG. 53. — Inheritance of feeble-mindedness. A, alcoholic; /', died in infancy. Note that
in the two cases in which both parents are feeble-minded all the children surviving infancy
are feeble-minded also. (Data from Goddard.)

If intelligence is a multiple-factor character, we can
understand why the matings of two people of low mentality
usually produce only feeble-minded progeny, just as the
mating of two small rabbits produces only rabbits of small
size. Unquestionably children are frequently more intelligent
than either of their parents. They may derive from each
of their parents the genes most conducive to mental develop-
ment, and hence rise higher than their source. But if children
have a rather poor lot of parental genes to draw from, it is
not likely that they will obtain a chance combination which
will enable them to achieve a very high degree of intellectual
distinction. The usual charts illustrating pedigrees of mental
defectives give a rather misleading picture of the real
situation. In the charts people are either normal or feeble-
minded, whereas they present a series of intergrading

i34 HUMAN GENETICS AND ITS SOCIAL IMPORT

conditions which might be classed differently by another
observer. Crosses between rabbits of different sizes give
rise to a varied progeny according to the different combina-
tions of genes influencing growth. Large rabbits usually
have large offspring and small rabbits have small offspring.
Matings of intermediate sizes give rise to rabbits of different
size. If we had to designate every rabbit as either large or
small as we designate people as normal or feeble-minded,
we would get pedigree charts much like those illustrating
the inheritance of mental defects.

The multiple-factor hypothesis enables one to account
for the frequency with which feeble-minded children result
from matings in which one parent is feeble-minded and the
other normal. Not improbably many of these so-called
normals who marry into feeble-minded stock are not very
much superior to their mates. It is natural that their children
with their varied allotments of genes should in some cases
be above the standard for normality and in other cases
below. If we adopt the hypothesis that feeble-mindedness is
a recessive character, we should have to assume that a
large proportion of the general population is heterozygous
for mental defect.

A very instructive investigation of the origin of mental
defectives has been made by Dr. Penrose on one hundred
mental defectives not of the pathological type. The mental
capacities of the parents, so far as they could be ascertained
by careful study, were graded into the classes of superior
(including persons of normal intelligence), dull, and defec-
tive. A similar rating was made of the capacities of the
brothers and sisters of the offspring studied. The results
are expressed in Table I.

As is shown by the table the proportion of defectives
increases as the intelligence of the parents decreases. The
lowest ratio of mentally deficient children is found where

HEREDITY IN MENTAL DEFECT AND DISEASE 135

both parents are of superior or normal intelligence. Where
both parents are defective most of the children are defective
or dull, only one being considered of normal mentality.
While children may rise higher than their source they are
much less apt to rise very high if their source is low. The
familial distribution of intelligence shown in the table is
about what might be expected if differences in mental
development are largely determined by the varied assort-
ment of genes. Some of these cases may, of course, be due
to environmental causes, although environment does not
readily account for the fact that defective parents are
particularly prone to produce defective children.

TABLE i. — THE PARENTAGE OF MENTAL DEFECTIVES

Matings of parents

Character of offspring

Normal

Dull

Mentally
deficient

Superior X superior (45)

126

36
ii
8
o
i

12
I

Superior X dull (i 8)

Superior X defective (12)
Dull X dull (9)

Dull X defective (9)

Defective X defective (7)

Some very pertinent data on the role of heredity in
causing mental defects are furnished by recent studies on
twins. Luxenburger has summarized the data on mental
deficiency in identical twins up to 1930, and he finds that
out of eleven cases in which mental defect occurs both
twins were defective in ten cases and showed a similar type
of defect. In four cases in which feeble-mindedness occurred
in indubitably fraternal twins, in all cases it affected only
one member of the pair. In six instances in which the
identity of the twins was doubtful both twins were affected
in four cases. Dr. J. C. Smith found sixty-six pairs of twins

136 HUMAN GENETICS AND ITS SOCIAL IMPORT

among the 6,700 registered mental defectives in Denmark.
In fourteen out of the sixteen cases of identical twins both
members were feeble-minded, and there were two in which
the mental defect was limited to one member. In the fraternal
twins of the same sex the mental deficiency was clearly similar
in kind in only one of the fifteen pairs. The proportions were
much the same, three similar and thirty-two dissimilar,
in the fraternal twins of opposite sex.

Results equally striking have been reported by Humm
who found that in thirty-two pairs of identical twins in
which mental defect occurred it was present in thirty-one
cases in both members, and in thirty cases was of a similar
kind. In thirty-two pairs of like-sexed fraternal twins,
both were feeble-minded in fourteen cases; five were mentally
defective in different ways, and one member was normal
and the other feeble-minded in thirteen cases. Among the
twins of unlike sex, seven had similar mental defects, four
had dissimilar mental defects, and in fourteen pairs one
was defective and the other normal. If further investigations
confirm these extraordinary findings it will appear very
probable that most mental deficiency is genetic in origin.

Insanity, like feeble-mindedness, is due to both hereditary
and environmental causes. Like feeble-mindedness also it
occurs in many varieties and degrees of manifestation.
For these reasons and others besides, the genetics of insanity
presents many baffling problems. But despite such difficul-
ties, a good deal of light has recently been thrown on the
role of heredity in several types of mental disorders.
The environmental causes to which insanity has been
attributed are many. Besides worry, depression, severe
mental shock and physical injuries, insanity may result
from several kinds of diseases. Chief among these is syphilis,
which is now recognized as responsible for the disorder
known as general paresis, or general paralysis of the insane.

HEREDITY IN MENTAL DEFECT AND DISEASE 137

The disorder commonly terminates fatally and, according to
Dr. Mott, 20 per cent of the deaths in the London County
Asylum are due to this cause, besides "another 5 to 10 per
cent of cases of brain disease dying in asylums with softening
of the brain."

It was formerly the fashion more than now to attribute
a great deal of insanity to alcohol. Unquestionably excessive
alcoholism sometimes leads to insanity, but its influence
in this respect has often been exaggerated by zealous re-
formers. According to some alienists a role of great impor-
tance is played by focal infections. In a book on The Defective,
the Delinquent, and the Insane, Dr. H. H. Cotton has reported
a high percentage of cures following the removal of infected
teeth, tonsils, or parts of the intestine of insane patients.
These findings have not generally been confirmed by the
experience of other alienists. The recovery of an insane
patient after an operation is adduced as a proof that the
insanity was not hereditary. But this conclusion is based
upon a prevalent misconception of how heredity works.
Many people have severe and long-standing focal infections
without showing a trace of mental unsoundness. If infected
teeth or tonsils occasion an attack of insanity, it is not
unreasonable to suppose that an individual is already
predisposed by virtue of his hereditary diathesis. The fact
that a patient recovers after an aggravating condition is
removed is no proof that a diathesis to mental disorders
was not present. On the other hand, the presence of such a
diathesis is not proved. Why focal infection should be the
occasion of insanity in some people and not in others we do
not know. All that can be said is that many analogies
suggest the cooperation of the "insane diathesis."

The study of the genetic factors in insanity is made difficult
by a number of circumstances. The classification of the
various types of insanity is admittedly in a very unsatis-

138 HUMAN GENETICS AND ITS SOCIAL IMPORT

factory state. Several typical forms are distinguished,
such as manic-depressive insanity, dementia praecox or
schizophrenia, and others, but there are many intermediate
and overlapping forms. It is inevitable that the particular
symptoms of a mentally diseased individual should be greatly
influenced not only by his physical condition, but by educa-
tion, habits of life, emotional experiences, and the in-
numerable circumstances that have molded his personality.
And to the many environmental influences must be added
the varied effects of different combinations of genes, which

cT T 4 — , — i~ T ~i

FIG. 54. — Pedigree of manic-depressive insanity. Milder cycloid cases indicated by half
darkened circles or squares. (After Hoffmann.}

conspire to modify the operation of any gene defect that
may be primarily responsible for the insane diathesis.

It is a well-established fact that the insanities which run
in families usually conform to a particular type. Most
kinds of hereditary insanity depend on recessive or partly
recessive factors, and hence the majority of individuals
who owe their insanity to heredity come from parents who
are not insane. Out of 651 cases of manic-depressive insanity
studied by Riidin, about three-fourths came from parents
both of whom were normal. In the siblings of these three-
fourths, only about 7 per cent had manic-depressive insanity.
If, however, an individual with manic-depressive insanity
had one parent with manic-depressive insanity, the same
type of insanity was found in 24 per cent of his siblings. In

HEREDITY IN MENTAL DEFECT AND DISEASE 139

similar studies of 721 patients with dementia praecox
whose parents were free from this disorder, it was found
that 4.5 per cent of the siblings were afflicted with dementia
praecox; but if one parent and one child had it, 6 per cent
of dementia praecox was found among the siblings. Hoffmann
found among 154 children of dementia praecox parents
thirteen to fifteen, or 8.6 to 10 per cent were cases of the
disorder. Both Riidin and Hoffmann conclude that dementia
praecox depends upon two pairs of genetic factors.

These authors found that among the brothers and sisters
of individuals with dementia praecox a large percentage
were mentally peculiar (schizoid) to a greater or less degree.
It has been suggested that these schizoid individuals are
heterozygous for the incompletely recessive factors upon
which dementia praecox depends. Under favorable circum-
stances, some of these might topple over into the limbo of
insanity. Not improbably if such individuals become insane
they would be more amenable to cure.

There are other varieties of insanity in which the role of
heredity is more obscure. In the type known as Huntington's
chorea, however, heredity is apparently the all-important
factor. This malady is inherited as a typical Mendelian
dominant. Davenport and Muncey have worked out the
family history of 962 cases who derived from six or seven
ancestors including three brothers who came to the United
States in the seventeenth century. The disease usually
begins relatively late in life after the individual has married
and had children. It starts as irregular muscular movements
or tremors. Later the gait becomes unsteady, speech is
impaired, the mental faculties deteriorate, and the symptoms
finally lead to a fatal termination. It might be thought that
the hereditary character of this fatal malady would be so
generally recognized that it would lead to its disappearance,
but considerations of heredity usually have little effect

1 40 HUMAN GENETICS AND ITS SOCIAL IMPORT

upon the matings of human beings. When the parents of
Emma T. warned her that Jesse H., whom she wished to

FIG. 55. — Pedigree of Ludwig II, (L) and Otto I, (0) of Bavaria who were descended from
William of Braunschweig-Luneburg, W. All three were affected with dementia praecox. The
half black squares or circles represent psychopathic individuals, mostly schizoid. Note that
the two lines from the same ancestor come together in the parents of the two affected
brothers. (Data from Strohmayer.)

marry, would probably become choreic because his mother
suffered from this disorder, she replied that she would

HEREDITY IN MENTAL DEFECT AND DISEASE 141

i4a HUMAN GENETICS AND ITS SOCIAL IMPORT

marry him anyway, so that she could take care of him.
As events turned out, "She had to care not only for him,
but also for four affected children."

The role of heredity in causing insanity is strikingly
exemplified in the study of the mental disorders of identical
and fraternal twins. Luxenburger has reported on the
occurrence of dementia praecox in seventeen pairs of twins
adjudged to be identical. In ten of these both members were
clear cases of dementia praecox. There were three pairs in
which one member had dementia praecox and the other twin
probably had this same disorder. Only in two instances
was one twin considered to be normal. With a larger series
of fifty-six dementia praecox cases in twins, Lange finds
that both twins had the disorder in fifty-two pairs. In four
others one member was designated as schizoid. There was a
pair in which one member was "abnormal," and one case
in which the afflicted individual met with an injury to the
skull.

Recently Rosanoff, Handy, and Plesset have reported
on a study of ninety pairs of twins in which one or both
members were affected with manic-depressive insanity.
Of the twenty-three pairs of identical twins, both members
were manic-depressives in sixteen cases and only one member
of a pair was affected in seven cases. Of the sixty-seven
pairs of non-identical twins, both members were affected
in eleven cases and only one in fifty-six cases. It is apparent
from such data that both heredity and environment play a
part in causing manic-depressive insanity. It is very signifi-
cant that in all the cases in which insanity occurs in both
identical twins the disorder was of the manic-depressive
type and never of different types, although in some cases the
symptoms were rather different.

In a similar study of dementia praecox in twins the same
authors found twenty-eight cases of probably identical

HEREDITY IN MENTAL DEFECT AND DISEASE 143

twins in which both members were affected and thirteen in
which the insanity was confined to one member of the pair.
In nonidentical twins both were affected in fifteen cases
and only one member in eighty-six cases. If we take the
percentage of cases in which both twins are affected, we
find that it is 68.3 per cent in the identicals and 14.9 per cent
in the fraternals. The fact that in several cases of identical
twins only one individual develops insanity indicates that
heredity may not be the sole cause of the affliction. What is
inherited is apparently a proclivity or diathesis to insanity
which under certain conditions may fail to produce its dire
effects.

Epilepsy, like insanity and feeble-mindedness, has long
been observed to run in families to a certain extent, although
it often appears quite sporadically for reasons that cannot
be explained. There are many kinds of epilepsy, and un-
questionably the disorder is sometimes caused by injury or
disease. Some cases are attributed to head injuries at the
time of birth. The prevalence of syphilis among epileptics is
apparently considerably higher than in normal individuals,
but the reported percentages of epileptics giving a positive
Wassermann reaction are so exceedingly varied as to make
the role of syphilis in the causation of epilepsy very uncer-
tain. One relatively rare variety known as myoclonus
epilepsy is the subject of a well-known memoir by Lundborg,
who has traced all the seventeen known cases in Sweden
to a single ancestor. The malady was transmitted like a
single-factor recessive character. Owing to its recessive
nature, the trait frequently appeared among the offspring
of consanguineous marriages.

Inherited epilepsy usually behaves as a recessive or partly
recessive trait, although Gordon has described a few families
in which it seems to be an irregular dominant. In one family
in which both parents were epileptic, one daughter was

i44 HUMAN GENETICS AND ITS SOCIAL IMPORT

epileptic while the other was not. The epileptic daughter
had four children of whom two had the malady. One of
these produced two sons, both epileptics, while the other
epileptic individual had a daughter so afflicted. One normal
daughter married and produced three epileptic children.
The daughter of the original pair that did not develop
epilepsy married and had two children, one normal and one
epileptic. The epileptic offspring married and produced four
children, three of whom became afflicted with the same
disorder.

Such a clustering of cases within a family can hardly be
due to chance. It is likely that the different kinds of epilepsy

FIG. 57. — The inheritance of epilepsy through four generations, (dfter Gordon.)

are inherited in different ways. Owing to the fact that
epilepsy is usually a recessive or partially recessive character
of relatively rare occurrence, many cases of inherited
epilepsy doubtless arise in families in which no other in-
stances of its appearance have been observed. This circum-
stance has led many writers to minimize the role of heredity
in the production of this disorder. As in other similar cases
the study of twins has revealed the probable working of
genetic factors that would not otherwise be evident. In
four pairs of presumably monozygotic twins reported by
Humm, epilepsy appeared in both members in three cases
and in only one member in one case. In all the six pairs of
dizygotic twins with epilepsy the malady was confined

HEREDITY IN MENTAL DEFECT AND DISEASE 145

to one member of each pair. Olkon has described a pair of
identical twin boys in which both were affected with a
peculiar type of epilepsy beginning at an early age. Luxen-
burger has compiled records of epilepsy in seven pairs of
probably identical twins and finds that in five pairs both
members were similarly affected. Four additional pairs
of twins with epilepsy have been reported from Holland
by Dr. J. Sanders. In one pair, Mien and Nel, who were said
to be monozygotic by the physician who attended their
birth, both girls had their first attack of epilepsy in their
fourth year within a few days of each other, and the later
course of the seizures was much the same in both. In a
pair of identical twin boys, Jan and Cor, epileptic attacks
occurred in both boys before the end of their second year.
The general character of the attacks, their premonitory
symptoms, and after-effects were similar in both boys. The
father also was subject to epileptic fits from his twelfth to
his thirtieth year. In a third pair of twins both members
had their first epileptic seizure on the same day, but one
girl commonly had more severe symptoms than the other;
and while both appeared at first to be about equally bright,
the twin who was afflicted to the greater degree suffered
more mental deterioration than her sister, so that there
came to be a considerable disparity in their general intel-
ligence. A fourth pair of twins described by Sanders con-
sisted of a boy and a girl, both epileptic. Both had several
convulsions early in life, and they continued to have similar
epileptiform symptoms up to the time at which their case
was described.

Recently Dr. K. Conrad has published a study of epilepsy
(Rev. Neurologique, 64, p. 485, 1935) in 258 twins. In the
thirty pairs adjudged to be identical there were twenty-one
concordant and nine discordant cases. It is an interesting
fact that Conrad's study was presented before the Interna-

146 HUMAN GENETICS AND ITS SOCIAL IMPORT

tional Neurological Congress following a paper in which
Prof. Abadie contended that epilepsy is a constitutional
disorder in which heredity plays a very minor part. Instances
of epilepsy in twins are as yet not very numerous, but the
evidence thus far accumulated points strongly to the im-
portance of genetic factors in causing this disorder, although
they may often require the cooperation of some unfavorable
environmental influence to enable them to become manifest.
The nervous system of man seems to be especially prone
to hereditary ills, and we can mention only a few of the many
types which have been described. One very unfortunate
malady, Leber's atrophy of the optic nerves, which leads
to more or less complete blindness, is commonly inherited
as a recessive sex-linked character, appearing therefore,
except rarely, only in males. In some cases, however, the
defect is transmitted as a simple dominant. A relatively
rare nervous disease, multiple neurofibromatosis, involving
the formation of tumors on the nerve trunks, is usually
transmitted as a dominant character, although it occa-
sionally skips a generation. Another dominant defect
frequently considered to be nervous in origin is progressive
muscular atrophy. Macklin and Bowman described a family
in which there were twenty-one affected individuals in three
generations with atrophied peroneal and calf muscles of
the lower part of the leg. In other families with inherited
muscular atrophy, different sets of muscles, such as those
of the arms, trunk, or face are apt to atrophied. Other
defects produce hereditary tremors, and a peculiar rare
disorder which causes individuals to move both their hands
in the same manner (bimanual synergia) is characteristic
of certain families. Some of the numerous hereditary dis-
orders of the nervous system are manifested by very varied
symptoms, while others are remarkably specific. Little is
known of the developmental physiology of these defects.

HEREDITY IN MENTAL DEFECT AND DISEASE 147

Why some gene changes cause the optic nerve to atrophy,
while others lead to the development of tumors on the
sheaths of nerves or give rise to dementia praecox or the
atrophy of certain motor ganglion cells of the spinal cord,
we can only vaguely conjecture. Human heredity involves
the cooperative activities of hundreds and probably thou-
sands of genes each of which plays its part in the develop-
ment of the body. There are hundreds if not thousands of
ways in which development may go wrong as a consequence
of the modification of particular genes. And doubtless many
new gene mutations will arise which will result in hereditary
defects never heard of before.

Suggested Readings

Gates ('29), chap. 15. Holmes ('21) chap. 3, ('33), chap. 2. For further
information see Barr ('29), Baur, Fischer, Lenz ('31), Doll et al. ('32),
Goddard ('14), Myreson ('25), Rosanoffet al. ('34), ('35), Tredgold ('30).

Questions

1. It was formerly claimed that insanity tends in the course of genera-
tions to become transformed into imbecility and finally to extinguish
itself. Is this probable from the standpoint of genetics?

2. What are some of the chief difficulties in determining Mendelian
ratios in hereditary forms of insanity ?

3. If you wished to ascertain whether insanity tends to be associated
with genius, how would you investigate the problem and what sources of
error should be guarded against ?

4. Can most light be thrown on the inheritance of insanity through
working out coefficients of correlation between relatives or by the intensive
study of pedigrees ?

5. What are some of the chief varieties of amentia ?

6. What can you find out concerning the condition of the brain in
amentia ? in insanity ?

7. Is the circumstance that Mongolian idiocy is especially prone to
occur in the last member of a series of children a conclusive proof that
particular genetic factors are not required for its production ?

8. If a pair of identical twins were heterozygous for a factor tending to
cause insanity, would one member be more apt to be sane and the other

148 HUMAN GENETICS AND ITS SOCIAL IMPORT

insane than if both twins were homozygous? What analogy might there
be between this case and the appearance of abnormal abdomen in
Drosophila ?

9. Suppose it were possible through the proper nurture to prevent the
development of all cases of dementia praecox. What bearing would this
fact have on the genetics of this malady? Consider again the analogy with
abnormal abdomen in Drosophila.

10. What facts indicate that some forms of mental defect and insanity
are caused by partially dominant factors ?

11. Why are some forms of mental deficiency and epilepsy unusually
common in inbred communities ?

CHAPTER XII

NATURE AND NURTURE IN MENTAL
DEVELOPMENT

THAT some people are naturally bright and others
naturally stupid is a matter of common observation.
Are the mental differences between individuals determined
mainly by their peculiar hereditary endowments or by their
environments and educational opportunities? All except a
few extremists concede that these differences may be due to
both hereditary and environmental influences, but opinions
diverge greatly as to which of these factors plays the pre-
dominant role. The question is of crucial importance for
both theoretical and practical eugenics. We find learned
and able representatives on both sides of this question,
and it will continue to be a fruitful subject of controversy
until the results of investigation furnish conclusive proofs in
support of the one or the other position.

In considering this problem one should endeavor to main-
tain a judicial instead of a partisan attitude, weighing the
arguments pro and con in the endeavor to form the best
judgment as to which position is favored by the preponder-
ance of the evidence. In a large proportion of the questions
which one encounters in the social sciences, a conclusive
answer one way or the other cannot be given. One has,
therefore, to make the best judgment possible. One may be
persuaded as to the correctness of a certain standpoint and
cling to his convictions until absolutely compelled to abandon
them, but this is the attitude of a pleader rather than an
impartial judge calmly endeavoring to discover which view

is most probably right.

149

150 HUMAN GENETICS AND ITS SOCIAL IMPORT

Attitudes on the nature-nurture problem are very apt to
be determined by the way in which the answer might
affect other beliefs to which a person is committed. There
is a strong bias in favor of the natural equality of man and
consequently a reluctance to admit that inequalities of
mental ability are determined by heredity. Social reformers
are often loath to admit that inferior mental development
may be due to the germ plasm, because they prefer to
regard it as resulting from remediable causes that can be
largely overcome through their beneficent ministrations.
Religion, economic theories, race prejudice, and other
factors are potent influences in determining attitudes on
our problem, as a perusal of the controversial literature
on the subject will make apparent.

In endeavoring to arrive at the most probable conclusion
on this controverted topic, one should consider it broadly
from the standpoint of the antecedent probabilities of the
case. At the same time, one should keep clearly in mind that
it is unsafe to attempt to settle the question from this stand-
point alone. Whatever may be the precise way in which mind
and body are related, there can be no question as to their very
intimate association. As the body develops from an embryo
through the stages of infancy and childhood to maturity the
mind undergoes parallel changes. During the long course of
evolution body and mind have evolved together. The mental
qualities of different species of animals vary enormously, and
unless variations in mental endowments were inherited it is
difficult to see how the minds of animals should differ so
greatly, or how the mental powers of man could have come
to be so superior to those of other animals. In the individual
person, influences affecting the brain have an effect also upon
the mind. Brain injury through accident or disease leads to
mental impairment, and the recovery of mental health often
follows upon the restoration of the normal physical condition.

NATURE AND NURTURE IN DEVELOPMENT 151

All this shows that mind and body manifest a strong ten-
dency to vary together. If bodily variations are due to genes,
as they manifestly are, one would expect, therefore, that
mental changes would be effected through the same cause.
The recessive gene productive of amaurotic idiocy not only
causes severe physical disabilities, which result in early death,
but it produces an impairment of mental development, re-
sulting in a low order of imbecility. The dominant gene that
is responsible for Huntington's chorea exercises its baneful
influence at a much later period of life, but its physical symp-
toms are accompanied by a grave impairment of mentality.
One can draw no hard and fast distinction between physical
and mental characters. So many physical disorders, both
hereditary and acquired, have their mental symptoms that
any discussion of the inheritance of mental as distinct from
physical traits is futile. Emotional peculiarities are demon-
strably dependent upon the development of the endocrine
glands, and the latter vary, like other organ systems of the
body, as a result of differences in hereditary factors. If one
were to maintain that mental qualities are unaffected by the
inherited constitution of the body, it could be only on the
basis of some peculiar theory of the relation of mind and
body for which it might be difficult to find adequate support.

In a previous chapter, evidence has been adduced in sup-
port of the view that mental defects and diseases are, at least
to a certain degree, the product of defective genes. If the
lower grades of mental development may result from poor
germ plasm, it would seem not unlikely that differences in
genetic constitution might occasion varied intellectual en-
dowments among normal and superior individuals. Consider
the structural and physiological peculiarities among your
normal friends and acquaintances, with their differences in
stature, weight, bodily form, shape of head, facial expression,
and numerous other characteristics resulting from their

152 HUMAN GENETICS AND ITS SOCIAL IMPORT

varied combinations of genes, and in the light of what we
know of the relation between physical and mental traits, it
will hardly seem probable that the latter are not affected by
these variations of hereditary composition.

Few, however, would deny that hereditary influences
exert some effect on the development of the mind. Most en-
vironmentalists maintain that such influences are less potent
in determining mental development than the influence of
varied environments and cultural advantages. We have here
a problem of the relative influence of two factors, the potency
of each of which is conceded by all but extremists of both
camps. It is, of course, possible that the answer to the ques-
tion may differ according to whether we are dealing with
mentally defective and diseased individuals or with people
in the higher intellectual levels. In such types of mental
defect as that followed by Sjogren in an inbred community
in Sweden the case for the hereditarian is quite clear. That the
superiority of Shakespeare or Newton is due more to a fortu-
nate allotment of genes than the influence of favorable nur-
ture is a very different problem.

Genius is often regarded as a mysterious and unaccount-
able phenomenon appearing somehow quite regardless of
parentage. The first effectually to controvert this notion was
Francis Galton, whose work on Hereditary Genius published
in 1869 showed that superior mental ability has a marked
tendency to run in families. This conclusion was supported,
not by amassing cases that happened to bear out the thesis,
but by compiling lists of the most eminent persons and mak-
ing a study of their near relatives. It was found that eminent
people have eminent near relatives many times as frequently
as do ordinary, undistinguished individuals. Moreover, the
chance that the relative of a great man will also become great
was found to decrease with the remoteness of the relationship.
Additional support for Gal ton's conclusion was furnished by

NATURE AND NURTURE IN DEVELOPMENT 153

a later work on English Men of Science and in a volume
written in collaboration with Dr. E. Schuster on Noteworthy
Families.

In the earlier studies on the inheritance of mental abilities,
reputation for distinguished achievement was used as a
measure of intelligence. Later, use was made of the scholastic
records of related individuals in schools and colleges. Pearson
and his coworkers have shown that siblings resemble one an-
other in scholastic tests to about the same degree that they

A d> 66 i-i-o 6 i-r-o

R7 I Re I

Sb fT> 6

FIG. 58. — Pedigree of the Darwin family. Black squares represent men distinguished for
intellectual achievements. R, members of the Royal Society; Ri, Josiah Wedgwood, F.R.S.,
founder of the Wedgwood pottery works; R%, Erasmus Darwin, celebrated physician,
scientist, and proponent of evolution in the eighteenth century; Rt, Charles Darwin; Rs,
Francis Gal ton; Ri, George Darwin, astronomer and mathematician; Rsy Francis Darwin,
Professor of Botany in the University of Cambridge. The fourth son of Charles Darwin,
Leonard Darwin, was president of the first two international congresses of eugenics, author of
works on eugenics, and president of the Geographical Society. The son of George Darwin,
C. G. Darwin, is a prominent physicist.

do in various physical traits. Correlations between parents
and offspring for scholarship based on records of fathers and
sons attending Oxford University showed a fairly high posi-
tive correlation (about 0.3), although less than that between
brothers (0.5). This, it was inferred, was because methods of
instruction and standards of grading, etc., were more similar
for brothers than for fathers and sons.

When mental tests came into vogue, numerous studies were
made on the scores of children of the same family. The
studies of Pintner on 180 pairs of siblings gave a correlation
of 0.39, those of Rensch on 365 pairs, a correlation of 0.45,

154 HUMAN GENETICS AND ITS SOCIAL IMPORT

and those of Willcocks on 365 pairs in different environments
a correlation of 0.5. These results are typical of many others,
so one may infer that insofar as intelligence is measured by
these tests it runs in families to a very considerable extent.

Such findings, however, do not convince the environ-
mentalist that the familial distribution of intelligence is
due to heredity. He would explain it as due to the unequal
distribution of educational opportunity and incentive in
different families. Demonstrably the ability to pass an
intelligence test is in part due to previous training. Given
two persons of the same hereditary endowment one of
whom has had no educational advantages, while the other
has been engaged in intellectual pursuits that have exercised
his mind upon a number of different problems, it is evident
that in almost any kind of test devised the two individuals
would make quite different scores. Even when efforts are
made to eliminate the influence of mere information in
passing intelligence tests it is not possible to get rid of the
influence of scholastic experience. No test measures innate
ability. What is measured in every case is a product of both
heredity and experience with the environment. One may
explain the fact that Mary is more intelligent than Lucy
in either one of two ways. If it is said that Mary's parents
were more intelligent than Lucy's, one might reply that
Mary's parents had the better educational opportunities,
and that therefore heredity has had nothing to do in making
the one girl more intelligent than the other. Two people
might argue the question indefinitely without convincing
either party. According to some writers the question of the
relative influence of nature and nurture on mental develop-
ment has come to a practical impasse. The problem is a
general one which, as we have seen, is encountered in many
relations. Where it is presented in lower organisms, which
can be subjected to controlled experiments, it is possible to

NATURE AND NURTURE IN DEVELOPMENT 155

arrive at a decisive answer. Could we expose people with
the same heredity to different conditions of the environ-
ment, we might obtain an accurate measure of the various
kinds of environmental influence. If, on the other hand,
we could keep the environment just the same for persons
of different heredity, we might obtain a fair measure of the
extent to which heredity is responsible for their differences.
Unfortunately for the solution of our problem, we cannot
subject human beings to the kind of experimentation that
would be ideally most desirable. Moreover, in most cases
it is impossible absolutely to rule out the influence of either
hereditary or environmental differences. Nevertheless, there
are ways of studying these effects and of gaining some
measure of their extent.

In considering the influence of environment upon intel-
ligence, we should distinguish between two classes of effects:
(i), the stimulation of development beyond the normal
standard, and (2), the thwarting or retardation of normal
development. There seems to be no limit to the latter kind
of influence short of causing the death of the individual.
It has been shown that, in general, children with many
physical defects have also a low mentality. Ayres found
that out of 3,304 children in New York those rated as dull
had a higher percentage of physical defects than those rated
as bright. This may be due not to the fact that physical
defects cause mental retardation, but because both kinds of
defects result from a common cause either in bad heredity
or in an unfavorable environment. There has been some
concern over the possible influence of malnutrition on
mental development because during the great war many
children suffered much from lack of adequate food. Accord-
ing to the investigations of Blanton, the permanent effects
of malnutrition were relatively slight. Several experimental
studies have shown that when undernourished children

156 HUMAN GENETICS AND ITS SOCIAL IMPORT

are given proper food their physical condition improves, but
there is no significant change in their I.Q's. There is also
little relationship between diseased tonsils or adenoids and
mental development, nor is removal of the offending organs
followed in general with an increase of intelligence. Mental
retardation in schools has been found by Smillie and Spencer
to increase with severity of infection with hookworm, but this
may be due to the fact that the more heavily infected chil-
dren come from poorer types of homes which are associated
with the low mental status of the parents.

As we have already pointed out, there are several diseases
which sometimes lead to an impairment of mental develop-
ment. Pintner found that children who are congenitally
deaf are mentally retarded by two or three years. Among
the children whose deafness was acquired, the later the
onset of deafness, the higher the average LQ. of the children.
The lowering of the LQ. in deaf children is probably to be
ascribed not only to the effect of the deafness per se, but
to the influence of the cause of deafness (meningitis, syphilis,
and other diseases) which have a certain tendency to
produce mental retardation.

Aside from the effects of disease, inequalities of mental
development may be produced by intrauterine causes,
birth injuries, alcoholism, drug addiction, and the various
agencies adversely affecting the health of the individual.
In exceptional cases injury or disease may make all the
difference between an intelligent person and a low grade
imbecile, but the extent to which repressive factors are
responsible for the mental differences commonly observed
among human beings cannot be precisely ascertained. More
commonly differences in intelligence are attributed to
training, but in order to ascertain whether or not this view
is correct we need to know something of the possibilities
and the limitations of training in promoting intellectual

NATURE AND NURTURE IN DEVELOPMENT 157

development. By feeding his animals in different ways, a
farmer may cause some of them to become mere runts and
others to grow beyond the average size, but no amount or
kind of food will cause his sheep to become as large as
cattle or even make his Bantam chickens attain the size
of Plymouth Rocks. So far as physical growth is concerned,
environment has its very distinct limitations. Is this true
also for the development of the mind ? Most of us can recall
many individuals, some of whom we have known from
our early school days, who, we are quite sure, would never
blossom out into great intellectual leaders in any imaginable
environment. Even in the absence of any scientific tests of
intelligence it is apparent that in most individuals the
capacity for very distinguished intellectual achievement is
not there. Education may do much for people. For some
people it can do much more than for others. For idiots
and imbeciles it can do relatively little. For borderline or
dull-normal people, it can do more, but can it cause them
to get over their dullness? A Pascal or a Macaulay may
astonish the world with the extent of his early acquisition
of knowledge. Apparently the more one is favored by heredi-
tary gifts the more he will profit from his favorable oppor-
tunities. If Macaulay had been brought up in ignorance on a
desert island doubtless he would never have become famous.
If, unknown to the parents, another boy had been sub-
stituted and reared in the same environment, would he have
exhibited Macaulay's phenomenal memory and powers of
understanding? As a matter of fact, people show varying
degrees of capacity for intellectual development. Even
the best of all pedagogical procedures cannot make a
genius out of a dull boy. As a rule intellectual capacity is
exhibited early and is commonly retained throughout life,
although not infrequently there are individuals who do not
justify their early promise. The studies of Cox on the boy-

158 HUMAN GENETICS AND ITS SOCIAL IMPORT

hood of great men have brought out the fact that, contrary
to a rather prevalent opinion, great men exhibit as children
an unusual degree of precocity.

In an investigation more or less complementary to that
carried on by Cox, Dr. Terman has studied the home life,
preschool training, physical development, temperament,
and other peculiarities of a thousand children in California
schools who made a grade of 140 or more in an intelligence
test at the beginning of the study. The grade 140 is an
exceptionally high one, since it is reached by less than
one-half of I per cent of school children. These gifted
children were not abnormal or freakish, as prodigies are
commonly considered to be, but on the whole they proved
to be a normal, healthy, socially adaptable group of young-
sters, keenly interested in sports and other nonscholastic
activities. In school they received no more attention (in
fact rather less) than the rank and file of pupils. Their pre-
school advantages were probably somewhat better than those
of the average student, and many of them gave evidence
of unusual intellectual interest before they entered school.

Several years later these same students were studied
again. In the more advanced grades of school and in college,
their records were high. Phi Beta Kappa and the other
honors at graduation were obtained three times as often
as by college students in general. "Nearly three-fourths
of the total marks earned in High School by gifted girls
and nearly one-half of those earned by gifted boys are of
the A grade." There were a few irregularities of behavior
of course; one boy from a broken home committed suicide,
but as a rule the infractions of the moral code were not
serious. Judged by their development thus far these children
have abundantly justified their early promise.

Since these children constitute an unusually intelligent
group, it is of interest to learn something of their ancestry.

NATURE AND NURTURE IN DEVELOPMENT 159

To a large extent the fathers of these children came from
the professional classes or were engaged in pursuits requiring
an unusual degree of knowledge or skill. It is a striking fact
that nearly one-fourth of the names in the Hall of Fame
were found in the ancestry of this group.

A strict environmentalist would attribute the persistent
superiority of these gifted children to the advantages of
their home life, or possibly more subtle influences, but
before one is justified in adopting this position, it should be
shown that a favorable environment is at least capable of
producing the effects ascribed to it. If it were possible to
rear a large random sample of children from infancy amid
surroundings which are highly favorable for their intellectual
development would these children show an average I.Q.
of 140 ? It may be said that we cannot tell because the experi-
ment has not been tried, but many other experiments have
been tried whose results have an important bearing on the
question. If we could make exceptionally intelligent people
out of children of ordinary heredity by exposing them to the
proper kind of nurture the possibilities in the way of educa-
tion would exceed the most sanguine dreams of the most
optimistic educator. But what are the facts ? If we select a
fair sample of children whose I.Q.'s have been fairly tested,
how much is the best type of training that has been devised
capable of raising their level of intelligence ? Is it 5, 10, 20,
50, or 100 or more points ? Were the average improvability
shown to be very great, say 100 or more points, the environ-
mentalists might well argue that training can account for
all the intellectual differences among human beings, barring
the effect of a certain amount of environmentally caused
retardation. This would not prove that these differences
actually were the result of environment and training, but
only that they might be. On the other hand, if in no case
training was proved capable of raising the I.Q. of children

160 HUMAN GENETICS AND ITS SOCIAL IMPORT

as much as 10 points, the hereditarian might well argue that
most of the differences in I.Q. were probably due to genetic
factors, especially in view of the fact that both high and
low I.Q.'s tend to run in families. Whatever may be said of
possibilities, the results of retests on children exposed to
different environments and methods of instruction, while
they have indicated a certain amount of improvement in
I.Q. under more favorable conditions of nurture, have not
demonstrated any very striking increase in intellectual
power.

There have been several studies on the results of trans-
ferring children from bad home environments to better
homes or institutions, but for the most part this has not
resulted in any marked improvement of the I.Q. Freeman
finds that children adopted into better homes have a higher
I.Q. than those adopted into poorer homes. The correlation
between grade of home and I.Q. of adopted children was
0.52 + 0.06. There was a certain amount of selective place-
ment calculated as 0.34 + 0.07 at the time of adoption,
so that a part of the relationship between the intelligence
of the foster children and the character of the home was
due to the original selection of more intelligent children
for the better homes. The higher I.Q.'s of the children in
these homes is, according to Freeman, due in a considerable
measure to their environment.

In a study of adopted children in California made by
Miss Burks the observations were made on children adopted
soon after birth, so that opportunities for selective place-
ment on the basis of intelligence were practically eliminated.
The families of the foster parents were a little superior to
the average. The average I.Q.'s of their own children was
115.4; those of the foster children, 107.4. The correlation
between the I.Q. of adopted children and the quality of the
home was 0.35 ± 0.05. It is of interest that in the superior

NATURE AND NURTURE IN DEVELOPMENT 161

home, the range of variability as well as the average LQ.
was increased, being from 40 to 160. In the fairly similar
environments of superior homes some influences, which the
hereditarian would say were the genes, evidently were
responsible for enormous differences of measured intelli-
gence. Miss Burks' conclusion was that "home environment
contributes about 17 per cent variance in I.Q.'s; . . . the
total contribution of heredity (i.e., of innate and heritable
factors) is probably not far from 75 to 80 per cent."

If environment affords the chief factor in determining the
differences between human beings, we should expect that
children reared from an early age under very similar condi-
tions would show a much greater similarity in intelligence
than children in general. Miss Lawrence finds that children
reared in an institution since infancy are about as variable
in intelligence as are children of corresponding ages in the
public schools. Davis found that the degree of mental
similarity between children in an orphanage where conditions
of nurture are relatively uniform showed no relationship
to length of sojourn in the institution. Uniformity of nurture,
in so far as this can be secured, does not result in any marked
similarity in intellectual development.

In recent years a great deal of material of much interest
to eugenists has been accumulated on the relation between
occupation and intelligence. When the army mental tests
were made data were collected on the I.Q.'s of different
occupational as well as national groups. As might be inferred,
members of the professions — doctors, lawyers, accountants,
and especially engineers — tested high. Those in clerical
work occupied a somewhat lower rank. Then came various
classes of skilled workers. Those who made the lowest
scores were miners, teamsters, and unskilled laborers.
Since the degree of education varied in much the same order
as the intelligence quotients, the question arose as to how

1 62 HUMAN GENETICS AND ITS SOCIAL IMPORT

far these results are indicative of differences in native
intelligence.

It is not often that opportunities for testing the intelli-
gence of a large general sample of the adult population
are presented. There are in fact, relatively few studies on
adult intelligence available, but children in schools afford
much more readily measurable material for the mental
testers, and millions of school children have been subjected

33.9%

20.1%

8.6%

23.1%

ao%

2.3 # | 2.3%

0.33% [ j 0.55%

56-65 66-75 76-85 86^5 96-105 106-115 IIH25 126-135 136-140
FIG. 59. — Distribution of the intelligence quotients of 905 pupils according to Terman.

to intelligence tests of all sorts. Several studies have been
made on the I.Q.'s, as well as the scholastic grades of students
in relation to the occupations of their parents. Quite uni-
formly the children of parents in the professional groups
make the highest average scores. The children of unskilled
laborers show the lowest I.Q.'s, and those of the inter-
mediate occupational groups make intermediate records.
The I-Q.'s of children show much the same gradation in
relation to occupation as those of the fathers. Why? The
position of the hereditarian is that only individuals of
superior intelligence get into the professions, whereas,

NATURE AND NURTURE IN DEVELOPMENT 163

barring exceptional cases, the lower occupational classes
on the whole include relatively more individuals in the
lower intellectual levels. The environmentalists would
explain the lower I.Q.'s of the unskilled laborers' children
as the result of the poorer advantages afforded by the homes
from which they came. Sometimes a very bright child comes
from a home of lowly status, a fact which the hereditarian
would attribute to good hereditary material in a low social
and economical level. Who is right? Or are both right to a
certain extent?

Some interesting data on this question have been supplied
by Miss E. M. Lawrence from her studies of the I.Q.'s of
over 380 illegitimate children who had been reared in an
institution. The children had practically no contact with
their fathers, and they were all less than one year old when
they were given up by their mothers. The environmental
conditions of the children were favorable and uniform.
Information was collected on the occupation of the parents,
and the I.Q.'s of the children were found to have much the
same relation to the father's occupation as was shown by
children in the public schools of London, although the
differences between the classes were not quite so marked.
Miss Lawrence concludes that the correlation between
intelligence of children and social status of the parents
"is not mainly due to the direct social influence of the home,
but is a genuinely biological fact."

In another group of orphan children Jones and Carr-
Saunders have studied the relation between the I.Q.'s
of the children and the occupations of their fathers. Here
much the same gradation was found as in children in the
public schools. Children from the lower occupational classes
showed a slight average gain (about two points in I.Q.'s)
after a few years of residence, while those of the higher
groups showed a drop of nearly one point. There was thus a

164 HUMAN GENETICS AND ITS SOCIAL IMPORT

slight tendency for differences in LQ.'s to decrease with
longer residence in the institution, but the decrease was so
small as to be within the probable error of measurement.
The authors conclude: "There is no reason to suppose, so
far as this evidence is concerned, that environmental
influences are the whole or even the major part of the differ-
ences in intelligence between children of different social
origin/' At least if environment caused these differences it
must have done so before the children were placed in the
institution.

Miss Alice M. Leahy recently made a study of the I.Q.'s
of foster children in Minnesota who were placed in homes
before they were six months of age. Mental tests taken
later showed that the intelligence of the children correlated
closely with the occupational grouping of the par-
ents and but slightly with the intelligence of the foster
parents. The influence of the parents who supplied the
heredity was apparently more potent than the influence
of the parents who constituted an important factor of the
environment.

As in other aspects of the nature-nurture problem, many
significant bits of evidence on our problem are furnished
by the study of twins. Since identical twins have the same
heredity, whatever differences they may exhibit in mental
traits must be attributed to environmental causes. Differ-
ences between fraternal twins are due to the combined
influence of heredity and environment, and the hereditary
differences may vary all the way from complete identity
to those which cause one individual to become a genius
and the other an idiot. Several studies have been made
of the relative degrees of resemblance in the mental traits
of identical and fraternal twins, and while the different
investigations are not in entire agreement, they show that
in general the I.Q.'s of identical twins differ much less than

NATURE AND NURTURE IN DEVELOPMENT 165

those of fraternal twins whether of the same or of opposite
sex. According to Holzinger's studies on fifty pairs of
identical twins and fifty-two pairs of like-sexed fraternal
twins, the average intrapair difference in mental age was
8.4 for the identicals and 15.9 for the fraternals.

Wingfield in studying the correlations between twins
from the public schools of Canada found a correlation
(corrected for age) of 0.91 for identical pairs; 0.83 for
like-sexed pairs; 0.72 for fraternal pairs; and 0.62 for unlike-
sexed pairs. Hirsch found the correlation between the I.Q.'s
of thirty-eight pairs of similar twins to be 0.97 ± 0.012, a
surprisingly high correlation, while between dissimilar twins
it was 0.53 + 0.071.

It is sometimes assumed that if, on the average, the
I.Q.'s of identical twins differ by 5 points, while those of a
comparable group of fraternal twins differ by 10 points,
the influence of nurture (assumed to be 5 points) and that
of nature (10 — 5) would be practically the same. But would
this conclusion follow? In all measurements there is a
certain amount of variation to be attributed to errors of
measurement. What is measured in all of these studies is
ability to pass a certain type of intelligence test, whatever
this may imply as to general intelligence. Two persons may
have exactly the same heredity and exactly the same
acquired ability to pass a given test, but their scores would
doubtless not be identical. A certain amount of variability
might be due to the person who scored the test. Another
element is luck in answering questions. If two persons knew
how to spell 950 out of a lot of 1,000 words and each was
asked to spell 100 words chosen at random from the list,
one person might be fortunate enough to make a perfect
score, and the other might be unlucky enough to make
50 per cent of errors. To the extent that an element of sheer
luck is involved in a test, to that extent variations in scores

1 66 HUMAN GENETICS AND ITS SOCIAL IMPORT

are not indicative of any variations in real ability either
inherited or acquired.

Other disturbing factors are contributed by purely
accidental happenings that may influence the performance
of one or the other individual. Something eaten for breakfast
that did not agree with one twin might cause him to fall
short of giving an adequate account of his real ability.
The results of every kind of test are due to causes of variance
that to a certain extent have no relation to the real capacity
or acquirements of the individual tested. How much of the
difference in scores between identical twins should be
attributed to this nonsignificant kind of variability, and
how much is due to differences in knowledge or capacity we
do not know. Most experienced mental examiners would
concede that tests fall short of ideal accuracy by a few points
at least. If such variance as we have discussed is as much
as 5 points (which is a very conservative estimate) the
average difference of 8.4 reported by Holzinger for identical
twins would be mostly nonsignificant. The true difference
might be only about 3 or 4 instead of 8.4 between identicals
and somewhat less than 15,9 between fraternals, and thus
the differences attributed to nature would be greater than is
indicated by the uncorrected figures.

These considerations should be kept in mind in evaluating
the results of measurements of the intelligence of identical
twins reared apart as compared with the intelligence of
identical twins reared together. Studies on identical twins
reared apart should afford valuable information on the
role of different environments in causing differences in
intelligence. In some cases very remarkable similarities
in mental score are reported in spite of differences in environ-
ment and educational advantages. In some other cases
consistent differences in I.Q. are shown which exceed the
average differences between fraternal twins. The average

NATURE AND NURTURE IN DEVELOPMENT 167

difference of ten sets of identical twins reared apart, who
were studied by Newman, was 7.7 points; this is less than
the average difference of fraternals reared together, which
was 9.9. The average differences in scores of fifty pairs of
identical twins reared together was 5.3 (Stanford-Binet test).
The greatest difference in the I.Q.'s of identical twins
reared apart was 17.7 points on the Stanford-Binet scale in
favor of the city bred and better educated girl. This dif-
ference, which was paralleled by other mental tests, doubt-
less represents a real difference in intelligence, but whether
it is due mainly to education or to factors in the nature of
handicaps to development we do not know. Physically one
twin, Mary, was about an inch shorter and was about a
size smaller in most physical measurements.

Unfortunately, cases of identical twins reared apart who
have been subject to mental measurement are as yet few
in number, so that we know little of their normal range of
mental differences. In general, such twins are much more
nearly alike than ordinary individuals of the same age, sex,
and socioeconomic status and are even more similar than
fraternal twins reared together, a part of whose similarity
is due to their common parentage. It should be borne in
mind, however, that separation does not necessarily involve
marked differences in environmental influence, nor does
living in the same household necessarily mean exposure to
similar influences on mental development.

One case of identical twins described by Gesell is especially
noteworthy on account of the very superior intelligence
shown by both members. Both girls began to talk and to
walk when eleven months old. Before they were four years
old they were able to read in English, French, and Esperanto.
"Formal arithmetic was begun at six and in less than a
year they were solving mentally problems in fractions and
percentage. At the age of nine both were doing Junior

168 HUMAN GENETICS AND ITS SOCIAL IMPORT

High School work. They speak French fluently, and have
made progress in Italian and have embarked upon Russian.
They are much alike in tastes and dispositions. Their
mental tests and their vocabulary tests give almost the
same score." Physically they are very similar in many ways,
including the presence in both of a small pigmented mole a
little above the outer corner of the mouth. That the pro-
nounced mental superiority oi these twins is due to heredity
is indicated not only by their close similarity, but by their
ancestry in that "scientific and linguistic ability of a high
order and physical energy are some of the traits which are
found in the two immediate generations/' Doubtless these
twins enjoyed unusual educational opportunities, but it is
evident that ordinary children would not have profited
by these opportunities to nearly so great an extent.

As to the precise way in which heredity functions in the
transmission of intelligence, we have little knowledge. The
doctrine that superior ability is a recessive unit character is
probably no longer taken seriously. That intellectual devel-
opment is dependent upon many genetic factors is indicated
by the fact that it appears to vary quite continuously from
the lowest to the highest level. If people were graded accord-
ing to their levels of intelligence their variability could be
expressed in a fairly normal frequency curve, similar in
shape to the curves obtained by measuring their heights or
weights. The great majority, as common observation
discloses, cluster around mediocrity as might be expected
according to the multiple-factor hypothesis.

But there are not only different degrees of intelligence,
there are also different kinds. As a rule, when people are
unusually proficient in one subject they excel also in others.
Nevertheless, there are special aptitudes of many kinds and
occasionally there are highly intelligent people who are
unable to make normal progress in mathematics or languages.

NATURE AND NURTURE IN DEVELOPMENT 169

There is evidence that special abilities as well as general
intelligence runs in families, but the proper evaluation
of the hereditary factors involved is complicated by the
coincident influence of environment and family tradition.

If we would sum up what appear to be reasonable con-
clusions in regard to the role of nature and nurture in mental
development, the following would seem to be justifiable
statements:

Both heredity and environment may cause very great
differences in the mental development of human beings.

Hereditary factors can make the difference between a
low grade idiot or imbecile and the native endowments of
the highest type of genius.

Environment can depress or inhibit the development of
the mind to any degree consistent with the maintenance of
life.

To a certain extent nurture can increase intelligence
as this trait is measured by any kind of test yet devised.
Its power of doing so varies in different individuals, being
very slight in idiots and imbeciles and becoming greater
as hereditary capacity is increased.

The power" of nurture to increase intelligence is limited.
There is no known method of making superior intelligence
out of poor hereditary material. What is known of the
effects of training makes it improbable that nurture is
capable of producing the very high quality of intelligence
found in certain family strains. At the same time, without
favorable nurture, the members of such families would
probably not have become noteworthy for their achieve-
ments. The fact that both high and low ability runs in
families is due to both hereditary and environmental
factors.

Different occupational groups are characterized by differ-
ent average levels of intelligence, although the extent to

170 HUMAN GENETICS AND ITS SOCIAL IMPORT

which the differences are due to genetic instead of environ-
mental factors cannot at present be estimated with precision.
There is still room for reasonable differences of opinion
as to the role of nature and nurture in causing unequal
degrees of intellectual development.

Suggested Readings

Holmes ('21), chap. 5, ('23), chap. 6 ('30), ('33) chap. 3. Jennings ('30),
chap. 7. Lorimer and Osborn ('34), chaps. 8-10. For further discussions see
Burks ('28), Ellis ('26), Freeman ('28), Galton ('69), ('74), ('06), Lawrence
('31), Leahy ('35), Newman ('29-^2), Schwesinger ('33), Spearman ('27),
Terman ('25), Freeman ('34).

Questions

1. If you were perfectly free to experiment with human beings in any
way that was desired, what experiments would you devise to test the
relative influence of nature and nurture in mental development ?

2. If children are well fed and cared for and have normal playmates,
would children under five years of age develop intellectually much more
in the home of a great man than in the home of a day laborer ? If so, what
would be the chief influences involved ?

3. What can you say of the influence of nature and nurture on the
intellectual development of Abraham Lincoln ?

4. What influences in addition to those mentioned are apt to affect
the attitudes of people on the nature-nurture problem ?

5. Are there noticeable differences in intelligence between the members
of your family ? If so can you account for these as a result of experience ?

6. Does environment commonly have more influence on the develop-
ment of character and temperament than upon the development of
intelligence ?

7. What are some families noted for outstanding ability in music, in
mathematics, in science?

8. What is the most plausible explanation of the mental differences
between the members of a pair of Siamese twins ?

9. What reasons can you assign for the conclusion that superior
intelligence is not determined by a single genetic factor ?

10. What is meant by the "constancy of the I.Q."?

11. If the differences between the I.Q's. of identical twins were no
greater than the probable errors of measurement, what conclusion would
you draw ?

CHAPTER XIII

GENETIC FACTORS IN CRIME AND DELINQUENCY

THE role of genetic factors in the causation of crime is
difficult to appraise. The kinds of acts which are
branded as crimes vary from age to age and from country to
country. Probably some kinds of heredity more than others
predispose people to commit antisocial acts, but whether
an individual actually becomes a criminal depends largely
upon the accidents of his environment. Even the most
exemplary person might have become a criminal under
just the right combination of circumstances.

The problem of controlling crime has proved to be one
of the most baffling with which civilized peoples and espe-
cially Americans have to deal. Society rids itself of some of
its criminal members by putting them into prison or through
the cheaper and more certain expedient of capital punish-
ment. Prisons and reformatories, so called, may keep
criminals out of the way for a time, but as agents of reforma-
tion they are usually worse than failures. Speaking of the
influence of penitentiaries H. E. Barnes has remarked in a
recent work, The Repression of Crime , "instead of reforming
the criminal they are in reality institutions for the training
of more efficient and determined criminals."

Since the volume of crime is enormously greater in some
countries than in others, it is reasonable to seek for the
explanation of this fact in the influence of the social environ-
ment instead of heredity. The theory that most criminals
are born and not made is not generally regarded as tenable

by modern students of criminology. Lombroso held that

171

172 HUMAN GENETICS AND ITS SOCIAL IMPORT

there are certain individuals whose inherited constitution
has destined them for a life of crime. As a result of measure-
ments made upon numerous criminals Lombroso concluded
that the born criminal is characterized by certain anthropo-
logical marks among which are prominent cheekbones,
asymmetry of face, scanty beard, and various other anatomi-
cal peculiarities, both external and internal. According to
Lombroso these peculiar features are due largely to atavism,
or reversion to a primitive, brutish type of humanity.

The theories of Lombroso were put to a statistical test
by Goring, who made careful anthropometric measurements
of about three thousand inmates of English prisons. Most
of the characters which Lombroso regarded as indicative of
criminal propensities were found to be no more prevalent
among English convicts than in the general population.
Goring, therefore, came to the conclusion that "there is no
such thing as an anthropological criminal type." Never-
theless, he held that criminals commonly have a bad heredity
that is manifested more in intellectual deficiency and emo-
tional abnormality than in measurable anatomical char-
acters. In some respects, however, physical differences
were found to occur between different classes of criminals.
Murderers were larger and stronger than individuals con-
victed of burglary or petty thieving, who were as a rule
physically rather undeveloped. On the whole, the work of
Goring has been regarded as having given the coup de grace
to the claims of the anthropological school.

Recently Dr. Hooton has again attacked the subject of
criminal anthropology and has reported upon the results
of an extensive series of measurements on different classes of
criminals. He finds that in the native-born American popu-
lation, murderers are heavier, taller, larger chested, more
hairy, and have greater head circumference than individuals
in the general population. Other types of criminals he

FACTORS IN CRIME AND DELINQUENCY 173

states have their typical anthropological characteristics
also. "In the sum total of their metrical and proportional
features," says Dr. Hooton, "the criminals are also distinct
from the civilians. The differences consist principally of a
marked inferiority of bodily dimensions on the part of
criminals, but also include some striking deviations in
proportion."

Only a preliminary announcement of Dr. Hooton's
results has as yet been published. After explaining that he
holds no brief for Lombroso, whose methods he concedes
are open to severe criticism, Hooton remarks that "I am
beginning to suspect that Lombroso, like Darwin, was
right." Apparently, the last word on the significance of
criminal anthropology has not yet been said.

After the conclusions of Lombroso on criminal anthro-
pology had come to be more or less discredited, the dis-
tinguishing feature of criminals was sought rather in their
low intelligence than their physical peculiarities. This was
largely due to the techniques for mental testing which had
been developed by the French psychologist Binet. Mental
tests were given to large numbers of prisoners and juvenile
delinquents, and the general verdict was that these offenders
are characterized by a relatively high degree of mental
deficiency. The statement of Dr. Fernald that "at least
25 per cent of the inmates of our penal institutions are
feeble-minded" is typical of the results of many studies.
The percentage of prisoners in England who are feeble-
minded was estimated by H. B. Donkin as 20 per cent.

One of the most extensive studies on the intelligence of
criminals has been carried out by Dr. W. P. Root, who
has given intelligence tests to 1,916 prisoners confined in
the Western Penitentiary of Pennsylvania. The average
I.Q. of all prisoners tested was 76.2, a grade only a little
above the level indicative of feeble-mindedness. The per-

174 HUMAN GENETICS AND ITS SOCIAL IMPORT

centages of prisoners in the several grades of intelligence
were as follows:

TABLE 2. — INTELLIGENCE QUOTIENTS OF THE INMATES OF WESTERN PENITENTIARY,

PENNSYLVANIA

Per Cent

Imbecile 3.6

Moron 34-6

Borderline 19.2

Dull normal 23 .7

Normal J 5 • 4

Superior 2.8

Very superior 0.7

The LQ. was found to vary considerably with the different
types of crime. For embezzlers, it was high, 103.75; for
homicides it was low, 70.9; and for burglars and robbers,
it was 81.75 and 84.3 respectively.

It has been pointed out that in many studies of the
intelligence of prisoners the criteria of feeble-mindedness
used have been very unequal and are sometimes not stated
at all. It has also been urged that most studies do not com-
pare the intelligence of prisoners with that of the general
population. Dr. Hermann Adler finds that the intelligence
of criminals in several of the prisons in Illinois is about the
same as that shown in the extensive mental measurements
which were made in the United States army at the time of the
World War. As a result of studies on the inmates of several
prisons Dr. C. Murchison has come to the conclusion that
the intelligence of criminals as a class compares favorably
with that of the general population as revealed by the army
mental tests. Unquestionably many of the studies on the
intelligence of criminals are open to the criticisms which
Murchison has directed against them. L. D. Zeleny has
made an attempt to evaluate the diverse findings on the
intelligence of prisoners by reducing the results of different
studies to a common basis for comparison. It was found

FACTORS IN CRIME AND DELINQUENCY 175

that the percentages rated as feeble-minded varied with the
test used from 24.1 to 36.7. Where mental age was used as a
criterion,, the ages selected varied from eight to thirteen years
and the percentage of feeble-mindedness varied from 2.1 to
47.3 ! Moreover, where comparisons with the general popula-
tion have been made, the criteria of feeble-mindedness
among the noncriminals have not been the same. Combining
the statistical results of 163 studies in which Binet tests
were made on white prisoners, Zeleny finds that out of
61,999 persons tested, 18,613, or 30.0 per cent, were adjudged
mentally defective. By adopting as a criterion of feeble-
mindedness the mental age of eleven and reducing the
results of all studies to the same standard, Zeleny finds
that the percentage of mental defectives in the prison
population as compared with that in the army draft is
as 1.8 to i.

Zeleny points out that in Murchison's studies the intelli-
gence of native white prisoners was compared with that
of the entire white draft, which included both native and
foreign-born whites. Since the I.Q. of the latter was con-
siderably lower than that of the former, the average does
not give a fair basis of comparison. If the intelligence of the
native born in prisons is compared with that of the native
born in the draft, the percentage of mental defectives
becomes changed from 14.4 per cent in prisoners and 14.3 per
cent in the draft to 17.8 per cent in prisoners and 14.3 per
cent in the draft. By applying the same standard to Adler's
data, the proportion of defectives in the prisons of Illinois
in relation to that in the draft is changed from approximate
equality to 1.22 to i.

It is generally conceded that prisoners may be somewhat
less intelligent than criminals in general. The number of
individuals convicted of almost inconceivably stupid crimes
makes it likely that it is the less intelligent criminal who is

ij6 HUMAN GENETICS AND ITS SOCIAL IMPORT

most apt to be caught, whereas the embezzlers, swindlers,
fraudulent promoters, and other high-class scoundrels
usually succeed in evading the law. Persons of subnormal
mentality are apt to be found in the lower economic levels
and are hence more frequently tempted to commit crime
under the pressure of want. Being less able to foresee the
consequences of their conduct, they are more prone to act
on the impulse of the moment, regardless of the result.
Whatever relations may exist between mental defect and
crime is probably indirect. The prison population is largely
recruited from persons whose education is below the average
as is clearly illustrated by the extensive statistical studies of
Murchison and Root. For this reason, they tend to make a
poorer showing in mental tests than their native ability
would entitle them to.

How far the army draft ratings may be considered as
representing the distribution of intelligence in the general
population is open to question. Murchison admits that
"it would seem reasonable to presume that the army norms
are too low to be representative of the adult civil popula-
tion of the country," but he contends that "the criminal
norms are even more unrepresentative for the same reason!"
The army tests served a useful purpose at the time by
affording a rough classification of individuals according to
their aptitudes, but there is strong evidence that education
had a marked effect upon the scores that were made, since
it is hardly credible that the native ability of the recruits
from different states should differ as greatly as the records
indicate. Hence these tests as a measure of native intelli-
gence leave much to be desired. They afford about the only
large sample of the adult population that has been subject
to mental measurements. But they do not give us a very
satisfactory basis for judging how the intelligence of prisoners
compares with that of civilians.

FACTORS IN CRIME AND DELINQUENCY 177

The intelligence of juvenile delinquents has been tested
in a large number of groups. The general verdict of the
testers is that subnormal intelligence is much more fre-
quently found in delinquent boys and girls than in those
who have kept out of trouble. Comparisons with normal
individuals are more satisfactory than in the case of adult
prisoners, because more adequate standards are furnished
by the same type of mental tests applied to school children
of corresponding ages. The percentages of delinquents
classed as feeble-minded vary considerably in the different
groups studied. This may be due to the kind of individuals
designated as delinquents, and also to the standards em-
ployed in adjudging children to be feeble-minded.

One of the most extensive studies of juvenile delinquents
has been carried out by Healy on four thousand repeated
offenders in Chicago and Boston. Of these, 13.5 per cent
were classed as "clearly feeble-minded." The standard of
classification used is indicated by the remark concerning
this group — "Practically all have an intelligence quotient
of less than 75, and most of them of 70 or less." Of the
offenders 72.5 per cent were rated as "definitely mentally
normal."

Of 1 60 white boys admitted to the Lee School for delin-
quents in Philadelphia, A. A. Owens reports fifty-three,
or 33.2 per cent, were ranked as morons having an I.Q.
between 50 and 70; 35 per cent were borderline cases,
19.4 per cent dull normals, 11.2 per cent normal, and only
1.2 per cent with superior intelligence (I.Q. over no).
According to the study of Mr. Cyril Burt on delinquent
boys in England only 8 per cent were classed as feeble-
minded. Most of the studies on the intelligence of delinquent
boys and girls indicate that the proportion of individuals
of more than average intelligence is much smaller than in the
general school population.

178. HUMAN GENETICS AND ITS SOCIAL IMPORT

It is scarcely needful to point out that many persons of
defective intelligence are perfectly harmless and tractable
creatures. Weak-minded girls, however, are notoriously
prone to be led into sexual irregularities, because they are
easily seduced by designing males. In our industrial society,
prostitution is the natural fate of the unprotected feeble-
minded girl. It is not surprising that studies of the men-
tality of prostitutes should reveal a high percentage of
subnormal intelligence.

Several writers have emphasized the importance of mental
abnormality, rather than mental deficiency as a cause of
crime. According to Lombroso and other criminologists,
epilepsy is a factor of importance, especially in crimes of
violence. Some of the most gruesome crimes have been
committed under the influence of epileptiform seizures.
Healy and Bronner find 5.5 per cent of epileptics among
delinquents from Chicago, and 1.6 per cent in those from
Boston, the low percentage from the latter city being
attributed to the fact that in Massachusetts there are
special state institutions which care for a large part of the
epileptic children. Inasmuch as epilepsy occurs in less than .3
per cent of the population, these percentages are significant.

A number of studies of prisoners have found over 50 per
cent of the prison population to be in some respects mentally
abnormal. The National Committee for Mental Hygiene
has reported abnormal mental conditions found in jails
and penitentiaries as shown in Table 3.

Undoubtedly mental abnormality is responsible for many
crimes. Persons who are unbalanced, like those with defective
intelligence, find unusual difficulties in adjusting themselves
to their social environment. Bad heredity is primarily
responsible for many of these difficulties. The high per-
centage of delinquents coming from broken homes is to
some extent indicative of temperamental peculiarities on

FACTORS IN CRIME AND DELINQUENCY 179

the part of the parents. The bad environment which is so
potent a factor in juvenile delinquency is often a product
of bad heredity. But even if all bad heredity could be
eliminated the problem of crime would still be with us.

TABLE 3. — MENTAL ABNORMALITIES IN PRISONERS

Penitentiaries

County jails

Number of prisoners

8 <8i

3206

Mentally diseased or deteriorated, per cent

4..Q

Epileptic, per cent

O 1

i T

Psychoneurotic, per cent

v" 1

I 2

1 • 6

I 2

Psychopathic, per cent

18 6

27 A

Mentally defective, per cent

12 C

•*/ '4

11 Q

Borderline, defective or subnormal, per cent

14. 4.

117

A • /

Some rather striking evidence of the importance of
genetic factors in the causation of crime has recently been
brought to light through the study of the criminal careers
of identical and fraternal twins. A few years ago Dr. J.
Lange investigated all the twins in the prisons of Bavaria,
together with a number of other pairs, and has embodied
his findings in a small volume which has been translated into
English under the title Crime as Destiny. By means of inter-
views, court and police records, conversations with relatives,
and other methods of securing information, Lange succeeded
in obtaining quite full histories of most of the individuals
included in the investigation. Thirty pairs of twins were
found one or both of whom had a prison record. Of these,
thirteen pairs were identical and seventeen pairs fraternal.
Lange states, "Among the thirteen monozygotic pairs the
second twin was imprisoned in ten cases. Among the seven-
teen dizygotic pairs the second twin had been imprisoned
in only two cases. This leads us to the following conclusion:
as far as crime is concerned monozygotic twins on the whole
react in a definitely similar manner, dizygotic twins behave
quite differently. If, therefore, we attach importance to the

i8o HUMAN GENETICS AND ITS SOCIAL IMPORT

twin method of investigation we must admit that so far
as the causes of crime are concerned inherited tendencies
play a preponderant part."

In commenting on these figures. Dr. J. B. S. Haldane,
who has written a preface to the English translation of
Lange's volume, remarks that "the odds that they are
significant of a real difference are about seven thousand to
one." Mere statistics, however, fail to give an adequate
idea of the remarkable similarities in the careers of many
of these identical twins; one needs to read the detailed
histories as set down in Lange's book. In the identical twins
studied there is a curious likeness in the types of crimes
committed by the two members of a pair, and there were
also striking resemblances in temperament, intelligence,
and general behavior. In reading Lange's book one can
hardly resist the impression that these twins are under the
spell of a fatalistic urge to similar kinds of misconduct.
That identical twins commit the same types of crimes may
be attributed in part to their close association, but close
association without identical heredity fails to produce the
same results.

The studies of Legras on several twin pairs in Holland
are confirmatory of the findings described in that in all the
four pairs of monozygotic twins observed both members
were criminal, whereas in each of the five pairs of dizygotic
twins criminality was confined to one member of a pair.
More recently Rosanoff, Handy, and Rosanoff have investi-
gated a fairly large series of twins among adult prisoners,
juvenile delinquents, and children presenting problems of
behavior. The results are summarized in Table 4.

It appears that when one member of a pair of monozygotic
male twins has a prison record the other member was a
convicted criminal also in twenty-two of the pairs, whereas
only one member was convicted in eleven cases. Among the

FACTORS IN CRIME AND DELINQUENCY 181

TABLE 4. — CRIMINALITY, JUVENILE DELINQUENCY, AND BEHAVIOR PROBLEMS IN

TWINS1

Type of twins

Adult
criminals

Juvenile
delinquents

Behavior
problems

Like sex, probably monozygotic:
Males, both affected

Males, one affected. .

Females both affected

14.

Females, one affected

Like sex, probably dizygotic:
Males, both affected

1 1

Males one affected

Females, both affected

1-7

Females, one affected
Opposite sex, dizygotic:
Both affected

3
i

o
8

Only male affected

Only female affected

IO '

Totals ....

1 07

176

1 After Rosanoff, Handy, and Rosanoff.

dizygotic twins there were only three concordant cases
as compared with twenty which were discordant. In the
juvenile delinquents both members of a twin pair were
apt to have a bad record whether they were monozygotic
or dizygotic. There was a much higher percentage of delin-
quencies among the females in this group, but most of these
were due to sexual irregularities, which are apparently a
very contagious type of delinquency in both types of twins.
In general, the findings of Rosanoff, Handy, and Rosanoff
are similar to those of Lange and Legras. The evidence
which has now accumulated shows quite clearly that like
heredity in environments which are as a rule of much the
same kind is associated to a rather surprising degree with
similarities in criminal careers.

Suggested Readings

Guyer ('27), Haynes ('30), chaps. 2, 4. Huntington and Whitney ('27),
chap. 8. Lange ('30).

182 HUMAN GENETICS AND ITS SOCIAL IMPORT

Questions

1. What hereditary traits might dispose people to commit crimes?

2. Do you know any families in which bad temper or disagreeable
dispositions seem to be inherited?

3. How do you account for the fact that in some primitive peoples
stealing and lying are very rare, whereas other peoples are notorious for
their dishonesty ?

4. Are different peoples characterized by different degrees of excita-
bility, impulsiveness, and revengefulness, and have these traits any con-
nection with proneness to commit crime ?

5. Does crime tend to be associated with insanity ?

6. What do you think that, on the average, broken homes may imply
as to the quality of the parents?

7. What reasons can you assign for the high percentage of crime in the
United States ?

8. How has crime in the United States been affected by immigration ?

9. What can you find out about so-called crime areas in cities ?

10. Does the similarity of criminal records in identical twins prove that
propensities for particular types of crime are inherited, or does it simply
indicate that similar environments may produce much the same kind of
effects on persons of the same heredity ?

11. Is the sterilization of criminals a justifiable procedure on biological
grounds ? on the ground that it would promote social welfare ?

CHAPTER XIV
THE SOCIAL-PROBLEM PEOPLE

THE social damage wrought by defective and disordered
mentality has been brought out very clearly by
several studies of families showing a high percentage of
feeble-mindedness and mental abnormality. One of the
first of these studies was carried out by Mr. Dugdale, who
in the course of an investigation of the prisons of New York
found in one locality that a considerable number of the
inmates were related by blood. This circumstance led
Mr. Dugdale to ferret out the genealogical history of these
prisoners, and he traced the stock back to a Dutch settler,
Max Juke, who was born in the early part of the eighteenth
century. The two sons of Max married into a family con-
taining six sisters, five of whom were disreputable characters.
Dugdale followed their descendants through five generations
and unearthed a most unsavory record of pauperism,
prostitution, illegitimacy, and crime. Among these descend-
ants there were 50 prostitutes, 60 thieves, 160 paupers or
recipients of poor relief, and 7 murderers. About one-fourth
of the children were illegitimate. The cost to the state
occasioned by the shortcomings of this group was estimated
as $1,308,000, but the indirect damage, moral and other,
cannot be adequately measured. The descendants of some
of the sisters were noted for pauperism; those of Ada Juke,
known as Margaret, the mother of criminals, were especially
notorious for crime.

Such was the melancholy record of this family at the time
Dugdale wrote its history in 1875. About forty years later,

Dr. A. H. Estabrook investigated the further history of the

183

184 HUMAN GENETICS AND ITS SOCIAL IMPORT

family, and found that by 1915 it had increased to 1,258
living members, but that there was little improvement in
the character of the later generations. Taking the whole
family up to 1915, 378 were prostitutes, 86 keepers of
brothels, and 118 were criminals. Of the 698 children who
had attended school, 394 were retarded three or more years,
and 107 were mentally deficient to such a degree that they
needed institutional care. According to Estabrook probably
40 per cent of the Jukes were mental defectives.

The history of the Kallikak family, which is the subject
of a fascinating chronicle by H. H. Goddard, is in many
respects parallel to that of the Jukes. One branch of this
family took its origin in an affair between a revolutionary
soldier, Martin Kallikak, and a feeble-minded girl whom he
met in a tavern. As a result this girl had an illegitimate son
whom she named Martin Kallikak, Jr. Young Martin
married and raised a family of ten children. These proved
to be idle and shiftless individuals given to vice and petty
crime. Of the 480 descendants of this branch of the family,
the investigators were able to secure records of the mentality
of only 189 persons, but of these 143 were adjudged to be
mentally deficient and 43 were considered normal. In
this group, according to Goddard, "There have been 36 ille-
gitimate children, 33 who were sexually immoral, mostly
prostitutes, 24 confirmed alcoholics, 3 epileptics, 82 died
in infancy, 3 criminals, 8 kept houses of ill fame." There
were 1,146 individuals resulting from marriages of the
Kallikaks with other families, usually of a low grade of
mentality. Of these 262 were rated as feeble-minded, 197
were considered normal, while the mental status of 581 was
undetermined.

Besides the strain of degenerate progeny, there are other
descendants of Martin Kallikak, who make quite a different
showing. After the episode with the feeble-minded girl,

THE SOCIAL-PROBLEM PEOPLE 185

Martin married a Quaker woman of good ancestry. Seven
children resulted from this union. All of these children
married into good families and their descendants included
lawyers, doctors, judges, educators, and prominent citizens
of many kinds. There were no feeble-minded, or illegitimate
children, and little alcoholism or immorality.

These two sharply contrasted strains doubtless owe their
characteristics to a combination of hereditary and environ-
mental causes. Even though it may not have been possible
to make very accurate estimates of the mentality of many
individuals in such stocks, there is little doubt that both the
Jukes and the Kallikaks were characterized by a high
percentage of mental deficiency. Some individuals have been
rated by trained observers; others were classified on the
basis of less trustworthy evidence. In most cases one would
not go far wrong in assuming that the village idiot was
mentally deficient even in the absence of any scientific
tests. With borderline individuals and persons who have
had poor educational advantages rating ' on the basis of
hearsay evidence may be an unsafe procedure. Granting
that an injustice may have been done to some worthy
individuals of the Juke and Kallikak families, enough is
known about many of them to indicate quite clearly their
mental inferiority. Some individuals have become respectable
and fairly intelligent members of society, especially those
who migrated away from the rest of the group. Both stocks
represent a great variety of different heritages and great
inequalities of mental endowment are to be expected. Were
it not for their bad environment, both groups would probably
have been less objectionable.

In considering the roles of environment and heredity in
such stocks as the Jukes and Kallikaks, we should bear in
mind that bad heredity has a strong tendency to create
bad environment. Low mentality tends to go along with

1 86 HUMAN GENETICS AND ITS SOCIAL IMPORT

poor education and an inferior economic and social status.
Pauperism, vagabondage, illegitimacy, and intemperance
tend sooner or later to become a part of the traditional mores
of the group. People of this class are prone to mate with
their own kind, and as a result whole communities grow
up characterized by a large amount of consanguinity which
brings out undesirable recessive traits. This fact is illus-
trated in the history of several notorious stocks such as the
Tribe of Ishmael, the Zero family, the Nams, the Hill Folk,
the Pineys and other human derelicts. Some strains, due
probably to tradition, are characterized by criminality,
others by pauperism or vagabondage, and others again by
prostitution or intemperance, but most of these stocks
have more than their quota of all these undesirable char-
acteristics. Recently Lidbetter has published a detailed
study of the paupers of East London, in which he shows
that there are pauper stocks whose members subsist mainly
upon charity, generation after, generation. A number of
these lines have a high percentage of insanity, epilepsy,
and mental and physical defectiveness.

Stocks of the kind described do not include very many
defectives of the lowest grade. They consist of persons
who are naturally dull or stupid together with a number
with normal intelligence. Many of them can be improved
greatly by training and good surroundings, although there
are others who are hopeless under any circumstances. Such
stocks are sometimes referred to as constituting the "social-
problem group." Social problems are not confined to any
single stratum, but the stratum lying above the level of
imbecility and below the average level of intelligence,
furnishes much more than its quota of problems of many
sorts. Where there is mental abnormality as well as defective
intelligence, which is not infrequent, the social damage is
considerably greater.

THE SOCIAL-PROBLEM PEOPLE 187

Suggested Readings

Dugdale ('02), Goddard ('12), Lidbetter ('34). See also Estabrook ('16)
and ('23), and Estabrook and Davenport ('12), Winship (1900).

Questions

1. What are the reasons for the high birth rate in such stocks as the
Jukes and Kallikaks ?

2. What influences tend to offset the high birth rates of these stocks ?

3. Is it better for such stocks to marry their own kind or to marry into
the normal population?

4. Do you think that better environment and educational opportunities
would lead to an increase or to a decrease of the social-problem group ?

5. What influences tend to bring people of the social-problem group into
the same localities ?

CHAPTER XV

CHOICE IN MATING

IN SEXUALLY reproduced organisms the kinds of
individuals that are produced depend upon the kind of
matings which take place among the progenitors. Among
the higher animals reproduction is not entirely determined
by chance associations, but each sex may exercise a certain
amount of choice in the selection of mates. If the animals
which are chosen as mates differ on the average from those
which are rejected, selective mating cannot fail to have at
least some influence upon the course of biological evolution.
Choice in mating affords an opportunity for psychological
factors to modify the hereditary qualities of a species.
According to Darwin, choice in mating, or sexual selection,
is an important subsidiary factor in the evolution of the
higher animals. A large part of Darwin's Descent of Man
is devoted to presenting evidence for the operation of sexual
selection in causing the evolution of so-called secondary
sexual characters. Darwin attempted to explain the more
striking coloration of male birds, their powers of song, and
their instinct to display their attractions during courtship,
as due to a continued selection by the females of the more
aesthetically pleasing males. Not only in birds, but to a
certain extent in mammals, reptiles, and even amphibians,
fishes, insects, and spiders, the males are distinguished by
characters which would appear to be more ornamental than
useful. Since these features could hardly have been evolved
by natural selection, Darwin conjectured that they owe
their existence to sexual selection. They were deemed useful

188

CHOICE IN MATING 189

at least in the sense of enabling their possessors to succeed
in mating and perpetuating their kind.

This ingenuous and plausible theory aroused much adverse
criticism into the merits or demerits of which we shall not
enter. Whether or not the beard, deeper voice, and other
secondary sexual characters of the human male owe their
origin to sexual selection, as Darwin maintained, there is
no doubt that this factor has played a not unimportant
part in human evolution and that it is operative in full
vigor at the present time. People obviously do exercise
choice in mating, at least in modern civilized society, and
the way in which this choice is exercised has an important
influence in determining the quality of the children who are
born. The deformed, the sickly, the repulsively ugly, and
those with mean and surly dispositions are fortunately
less successful in the choice of mates than the healthy,
comely, physically vigorous, and kindly disposed. From the
racial standpoint this is all to the good. Dr. Knight Dunlap
in his little volume on Personal Beauty and Race Betterment
contends that beauty of face and figure are the outward
and visible signs of racially valuable qualities of mind and
body. We are pleased with characteristics indicative of
vitality, intelligence, quick sympathy, and geniality. The
secondary sexual characters suggestive of reproductive
capacity have an appeal to the mating instinct as has been
stressed by Mr. Havelock Ellis. In so far as sexual selection
is determined by the native impulses of human beings, it is
doubtless eugenic in its effects. The attraction of women for
strong, manly, and intelligent men, and the tendency of men
to choose beautiful, vivacious, and kindly women, are
forces ever working to produce a superior race of human
beings. Although in primitive society the free exercise of
choice in mating was much restricted by rigid tribal customs,
taboos, and the exercise of parental authority, women,

1 9o HUMAN GENETICS AND ITS SOCIAL IMPORT

as Howard, Westermarck, and others have shown, never-
theless enjoyed a certain amount of freedom of choice in
marriage. Greater liberty of choice was exercised by the
men; and the custom in many tribes of not allowing a man
to marry until he had demonstrated his power and courage
by some sort of feat at least kept the weaklings from prop-
agating their defects. On the whole, sexual selection in
primitive society was probably a force working for race
betterment.

The development of modern civilization, and especially
the great changes that have occurred in industry, have had
their effects upon sexual selection as they have upon other
factors of biological evolution in the human species. The
natural predilections of men and women for superior indi-
viduals of the opposite sex undoubtedly continue to influence
marriage selection, and will always do so as long as human
nature remains the same. But other forces have entered
upon the scene which tend to put sexual selection on a very
different basis.

Properly to evaluate the workings of selective mating
we should have some means of comparing those who are
mated with those who are not. A study of this kind has
never been undertaken for any community of human
beings. We cannot assert positively whether in any city or
country those who are married are either superior or inferior
to those who are not. Certainly common observation dis-
closes many excellent and attractive people who are un-
married, and also many married people whose repulsive
qualities make one wonder how they succeeded in attaching
themselves to their unfortunate mates. In endeavoring to
ascertain how sexual selection works out we have to base
our conclusions on the marriage rates and ages at marriage
of different classes of the community. Concerning the
proportion of men in different occupational classes who are

CHOICE IN MATING

191

married in the United States the following data have been
compiled by the Census of 1900.

TABLE 5. — PERCENTAGE OF MEN MARRIED IN DIFFERENT OCCUPATIONAL GROUPS
IN THE UNITED STATES

Groups

Percentage married
over 1 5 years of age

Percentage married
over 25 years of age

All occupations

71 .4

<rq. c

Clergymen

06 8

7Q. ^

Physicians and surgeons

or o

77 7

Lawyers

ql.l

72.O

Farmers except laborers

ql .6

87.3

Merchants

QO q

7q.T

Carpenters

89.8

77-^

Teachers

69.4

47.2

Salesmen . . •

fq .4

41.2

Farm laborers

•to.l

19.2

The percentage married in these occupational groups
depends to a considerable degree upon age as is indicated
by the percentages aged twenty-five or over. The low
percentage married among farm laborers in 1900 is largely
due to the fact that as a group they are young, only 30.3 per
cent being twenty-five or more years of age. The percentage
of men in the professional groups who marry is fairly high.
Cattell has found that the percentage of American men of
science who were married was 89.5, and Huntington and
Whitney found that the per cent of men who have married
in Who's Who in America (1926-1927), was 87.3, or probably
somewhat higher if reasonable allowance is made for those
who failed to state whether they were married or not.

The percentage of male college graduates who marry
is about the same as in the general population, although the
age at marriage is considerably higher. We have already
pointed out that the percentage of women graduates who
marry is low, being on the average between 50 and 70 per
cent. In many occupations especially of a higher grade the

192 HUMAN GENETICS AND ITS SOCIAL IMPORT

percentage of women who remain unmarried is high. It is
especially high among teachers. The proportions of women
who are gainfully employed have been increasing for several
decades. As a result, a large proportion of the more capable
women remain single to the detriment of our racial heredity.
The age at marriage in both men and women is higher
among the educated than in the uneducated classes. Among
graduates of both sexes and still more among the members
of the learned professions, it is considerably higher than
in the general population. Skilled laborers marry later
than the unskilled. Those engaged in agricultural pursuits
marry earlier than city dwellers. Notestein has compiled
data on the ages of wives at their first marriage in the
United States from 1900-1905, and the percentages married
are given in the following table:

TABLE 6. — PERCENTAGES OF WOMEN AT TIME OF FIRST MARRIAGE IN DIFFERENT
AGE GROUPS IN SAMPLE AREA OF THE UNITED STATES, 1900-1905. l

Age at first
marriage

Occupational group

Professional

Skilled

Unskilled

Farm owner

Farm laborer

15-19
20-24
25-29
30-34

8.2

42.5
36.2

9-5

31-5

46.2

'5-7

4.8

39-9
37-8
14.4

4-5

28.7

44-5
17.7
6.0

51-3
36-3
9-5

2.2

35-44

3-5

1.8

3-4

3-i

0.7

1 Data from Notestein.

The age at marriage for wives has a greater effect upon
fertility than that of the husband, although the age of the
latter has also a considerable influence. Ages of husband and
wife at the time of marriage show a certain degree of correla-
tion in that both tend to be high in the higher occupational
groups. It may be noted that the relation of age at marriage
to occupational status is much the same as the relation of
fertility to occupational status, and doubtless the latter

CHOICE IN MATING 193

relation is in part determined by the former. Contrary to a
common opinion there is a strong tendency for like to mate
with like. Data collected by Galton showed that people of
similar eye color tend to mate more frequently than people
of dissimilar eye color. This conclusion was confirmed by
the more extensive studies of Pearson who showed also
that there is a tendency to assortative mating on the basis
of stature. The tendency of the tuberculous to marry the
tuberculous, and the deaf to marry the deaf, may be due
to the segregation of such people in a common environment,
and perhaps in part to a mutual sympathy arising out of
their common affliction. There is a considerable degree of
assortative mating on the basis of education and social
status. As a rule educated men marry educated women and
ignorant men marry ignorant women. Mental defectives
tend to mate with mental defectives as is abundantly illus-
trated in the chronicles of the Jukes, Kallikaks, Tribe of
Ishmael, and other notorious degenerates.

Propinquity is a potent influence in determining the
choice of a life partner and accounts for many alliances
otherwise inexplicable. D. M. Marvin found that in 49,000
marriages in Philadelphia people married others of the same
occupation twice to three times as frequently as they would
if matings were due to chance. People of similar kind are
often thrown together as a result of their occupations or
their social positions. In inbred communities persons of
common descent are brought into association thus causing a
certain amount of assortative mating. The same tendency is
often fostered by religion. There is more or less social pressure
leading people to marry others of the same religious belief.
This acts quite strongly in preventing marriages between
Protestants and Catholics and between Christians and
Jews. Within the various Protestant sects the tendency to
marry within the fold is due much more to association than

i94 HUMAN GENETICS AND ITS SOCIAL IMPORT

to differences over doctrine. Formerly the Quakers and other
sects expelled members who married outside the group,
but such regulations are now largely abandoned, and the
whole influence of religion in breaking up a population into
isolated groups is much relaxed.

In general, people prefer to mate with others of the same
race or natural group. This is partly a result of the natural
clannishness of the human species and partly due to other
factors, regional and social. Most of the marriages between
immigrants in the United States occur among people who
come from the same country. In the second and subsequent
generations of our own immigrant population there are
more marriages between members of different national
groups. Our census data on the proportions of our population
of mixed parentage are apt to give a misleading impression
of the extent of intermarriage between persons of different
racial or national origin. An Italian who marries a native-
born American is apt to choose one of Italian parentage.
In a study of marriages between native born and foreign
born parents of students in the University of California
I have found that such marriages are largely confined to
persons of the same general stock. Thus in marriages between
an Englishman and a native-born woman, the wife was of
English parentage in 42 cases, American in 19, Scotch in n,
German in u, Irish in 10, French in 8, Scotch-Irish in 4,
with a smaller number of cases of other European nationali-
ties. German men married native-born women of German
parentage in 58 cases, American in 18, French in 4, and in
no more than two instances did they marry members of
any other one national group. And it is likely that a fair
proportion of the wives classed as native American were
of the same derivation as their husbands.

The so-called "melting pot" is not blending our immigrant
stocks as rapidly as is often supposed. These stocks fre-

CHOICE IN MATING 195

quently persist as inbreeding groups for many generations.
The out-marriages which occur are most apt to be between
related peoples such as the English, Scotch, and Germans,
rather than between these groups and the Italians, Greeks,
or Armenians. Nevertheless, the process of racial assimilation
is slowly going on and is contributing to enhance the hetero-
zygosity of the native Americans.

Suggested Readings

Darwin, C. ('71), part III. Darwin, L. ('26), Dunlap, ('20). Holmes ('21 ),
chap. 10 ('23), chaps. 9, 10. Popenoe and Johnson ('33), chaps, n and 14.

Questions

1. Look up Darwin's treatment of sexual selection in the human species
in The Descent of Man. What characteristics of the male sex are supposed
to owe their origin to sexual selection ?

2. Contrast the working of the "law of battle" with the effects of
female choice.

3. In what respects is sexual selection working eugenically and in what
respects is it working dysgenically under present conditions ?

4. If you wished to ascertain the general effects of sexual selection in
man, what kinds of facts would you like to have collected ?

5. What can you say of frequency of marriage among celebrated women
as compared with celebrated men ?

6. In what respect would you think that late marriages would have a
eugenic effect ?

7. What laws in your state affect choice in marriage ? Which of them are
desirable and which are the reverse ?

8. In what ways might sexual selection be made a potent factor in
racial improvement?

CHAPTER XVI

THE BIRTH RATE AND THE CAUSES OF ITS
DECLINE

UP TO this point our discussion has been devoted to
the principles of heredity and the varied types of
human heredity, both physical and mental. Hereditary
variability forms the basis of all biological evolution. And
since the human species is characterized by a very unusual
amount of genetic diversity, it is capable of relatively rapid
evolutionary changes.

The direction which evolution takes depends upon (i)
what kinds of variations appear, and (2) what variations
are able to increase most rapidly in numbers. That human
evolution may take many directions is shown not only
by our great intraspecific variability, but by the fact that
mankind has become diversified in so many ways in different
parts of the globe. Consider the varied physical character-
istics of Hottentots, hairy Ainus, Indians, Nordics, Poly-
nesians, Mongolians, and African pigmies, and it will be
apparent that as the human species has spread over the
surface of the globe it has diverged along numerous branching
and rebranching lines. The kinds of variations which come
to prevail at any time or place depend upon their relative
rates of natural increase, and this depends upon relative
fertility and relative mortality. If two stocks have the same
degree of fertility, the one having the lower death rate will
eventually prevail. If both have the same mortality, the
one with the higher fertility will prevail. What counts in

the process of evolution is, of course, the balance of

196

BIRTH RATE AND CAUSES OF ITS DECLINE 197

births and deaths. Both factors are always acting in the
drama of life, but it will be convenient to treat of them
separately.

In studying birth rates, it is desirable to have some
numerical measure of their magnitude. The measure most
commonly employed is the so-called crude birth rate, or the
number of births a year per thousand population in that
year. It does not give a very accurate measure of the actual
fertility of a people because it is affected by the proportions
of the sexes and the age composition of the population.
The more people in a country who are either too old or too
young to have children, the lower the birth rate. Since the
age composition of the population varies greatly in different
countries, birth rates are sometimes expressed by the
number of births per thousand women in the child-bearing
period, which is commonly taken to be from fifteen to
forty-five years of age. This rate is affected by the proportion
of women who are married, and hence birth rates are some-
times estimated in terms of the number of births per thou-
sand married women in the child-bearing period. For
countries in which the percentage of illegitimate births is
low, this measure of the birth rate affords a fairly satisfactory
index of the relative fertility of the female population.

It is often desirable to distinguish between reproductive
capacity and actual reproductive performance. The Popula-
tion Association of America has recommended that the
term fecundity be applied to the former, and fertility to the
latter. We shall conform to this usage, although some writers
employ these terms in the reverse sense. The fecundity
(i.e., reproductive capacity) of the normal human female
is quite high. Records of over twenty births are not uncom-
mon among the women of certain peoples, although even
in primitive society the physical limit of fecundity is seldom
reached. The liability of a woman to conceive falls off rather

198 HUMAN GENETICS AND ITS SOCIAL IMPORT

rapidly with increase of age at marriage. Galton has esti-
mated the fertility of women marrying at ages seventeen,
twenty-two, twenty-seven, and thirty-two as roughly in
the ratio of six, five, four, and three respectively. An increase
of the average age at marriage, therefore, would have a
potent effect in lowering the birth rate.

The birth rates of the races and peoples of the globe show
very great inequalities. During the past century the birth

40
35
30
25

France-

1871-75 81-85 91-95 1905 1915 19Z5 1930

FIG. 60. — The decline of the birth rate in England and Wales, France, Germany, and Italy,

1871 to 1930.

rate among nations of advanced culture has undergone a
marked decline. There is more or less uncertainty as to
its trend in most countries before 1850. In the Scandinavian
countries and in France the birth rate seems to have slowly
declined from near the beginning of the nineteenth century,
with more or less irregular fluctuations due to wars and
conditions of trade. Until recently the birth statistics of the
United States have been very inadequate, but to judge from
the decreasing proportion of children under five years of

BIRTH RATE AND CAUSES OF ITS DECLINE 199

age given by the reports of the Census, the birth rate has
been declining since about 1810. In England, Germany,
and some other European countries the decline of the birth
rate set in during the seventies, while in southern and eastern
Europe it did not begin to decline until later and still con-
tinues to be fairly high. In Australia and New Zealand
the birth rate, which was quite high in the seventies and
eighties, has rapidly fallen until it is now little more than

Year Number PerCent /•
1 1 Change C
1800 976
1810 976 0.0
1A90 09A -A.Q

Children per 1,000 Women
100 200 300 400 500 600 700 800 900 I.OC

1830 8T7 -5.5
1840 835 -4.8

IflRfl fiQQ -Ifi^

I860 714 + 2.3
1870 649 -91
1880 635 - 1.8
1890 554 -12.8
1900 541 -2.4
1910 508 -6.1

1930 407 -16.3 •••^••l^MMMB
1934 350 -14.0 ^••••••••M

FIG. 61. — Number of children under five years of age per 1,000 women sixteen to forty-four
years of age inclusive in the United States from 1800 to 1934.

half as high as it was fifty years ago. Among the Asiatic
peoples the birth rate is high, although in most countries
accurate birth statistics are not available. In Japan the
birth rate has been over 30 per thousand (32.4 in 1930)
ever since reliable birth records have been kept.

Where birth rates are high, death rates are usually high
also, although these rates vary independently to a con-
siderable degree. As the birth rate has fallen, the death rate
has fallen, and at times the more rapidly, so that the rate of
natural increase has become greater. This was a not uncom-
mon condition in European countries during the latter half
of the nineteenth century. But for several years past, the

200 HUMAN GENETICS AND ITS SOCIAL IMPORT

excess of births over deaths has in general been growing
less. There are two reasons for this. First, there is a natural
limit to the reduction of the death rate, and, as this limit
is approached, further reductions are made more slowly.
Second, in the period following the World War the birth
rate in Europe and in the United States has fallen to un-
precedented levels. Every year sees the populations of the
more advanced countries drawing more closely toward a
stationary condition. And the present financial depression
has apparently accelerated the decline.

In seeking for the causes of the decline of the birth rate,
we should distinguish between a purely statistical decline,
and one which is caused by a reduction in the average
number of children to which each woman gives birth. When
we measure birth rates by the number of births per thousand
inhabitants it is evident that if the mortality of nonreproduc-
ing individuals is decreased while the number of births
remains the same, the birth rate will go down. A reduction
of infant mortality produces a population with relatively
more children, and hence depresses the birth rate. A good
illustration of a largely spurious decline of the birth rate
is afforded by the Japanese in California. Soon after the
so-called picture brides entered the state, the Japanese
population consisted largely of recently married adults with
few children. The number of children born per thousand
Japanese in the state soon came to be very high. As more
children were born the Japanese population consisted of
relatively fewer reproducing individuals and hence the
birth rate went down. It would be bound to fall, even though
each Japanese woman continued to bear children at the
same rate. If we wished to compare the fertility of Japanese
women with that of other women in the population it would
be better to consider the number of births per thousand
married women of child-bearing age.

BIRTH RATE AND CAUSES OF ITS DECLINE 201

It is evident that one factor in the decline of the birth
rate as commonly expressed is the reduction of the death
rate, and especially infant mortality, which has occurred
during recent decades. Rates are affected by causes which
influence the denominator as well as the numerator of the
fractions by which they are expressed. The immigration
of persons in the child-bearing period of life would tend to
increase the birth rate and decrease the death rate. Birth
and death rates of individual towns and cities, for instance,
are influenced considerably at times by the presence of
colleges, hospitals, prisons, and other institutions which
bring in people whose fertility or mortality rates differ from
those of the general population.

The causes which affect real fertility are many. Among
these are the factors which determine the frequency of
marriage and age at marriage. Both age and rate of marriage
vary considerably from country to country, and they have
their evident effects upon fertility. As may be seen in the
table, the proportion of women who are married in the
younger age groups varies greatly in different countries.
In Sweden, Germany, and England and Wales less than
2 per cent of the women between ages fifteen and nineteen
are married, while in Bulgaria over 10 per cent are married.
In Bulgaria 63.3 per cent in ages twenty to twenty-four
are married, while in England, Germany, and Sweden less
than 30 per cent are married. As is shown by the data on
the fertility of married women at different ages the birth
rate of women rapidly declines as they grow older. Hence
where a large proportion of the younger women are married
the birth rate tends to be high.

While age and frequency of marriage may be important
factors in causing the differences between the birth rates of
different countries, they have been rather minor factors in
causing the decline of the birth rate within each country.

202 HUMAN GENETICS AND ITS SOCIAL IMPORT

The reason for this is that these factors have either changed
but slightly, or else such changes as have occurred would
tend to increase the birth rate instead of causing it to decline.
During several decades the proportion of women who are
married in the United States has been increasing. This is
especially noticeable in the younger age groups. In 1890
the percentage of men between twenty and twenty-four

1890 1900 1910 1920 1930

FIG. 62. — Percentages of the population of the United States who were married, 1890 to

1930.

who were married was 22.2; in 1930 it was 30.9. In 1890
the percentage of women between twenty and twenty-four
who were married was 50.3; in 1930 it was 54.4. In most
countries of Europe the average age of both men and women
at marriage has been declining slowly for several decades.
The percentage of women in Europe who are married has
fallen in some countries and risen in others, but, on the
whole, changes in marriage rates have had no marked
influence on the fall of the birth rate.

Some writers have ascribed the decline of the birth rate
largely to hereditary changes in fertility. Herbert Spencer
sees in the decline of the birth rate an illustration of a general

BIRTH RATE AND CAUSES OF ITS DECLINE 203

biological law based on "the inverse variation between
individuation and genesis." As more energy is expended in
intellectual tasks, less is available for the perpetuation of the
species. Education, he points out, leads to sterility, which is
most pronounced in women, but is manifested to a less
extent in men. Consequently with advancing civilization
the birth rate tends to decline.

Professor Gini thinks that human races pass through
cycles of fertility. Primitive races are fertile, but as civiliza-
tion advances they undergo degenerative changes which
involve diminished fertility and finally extinction. As
stocks rise and go to seed they are replaced by more primitive
peoples who have retained their pristine vigor and fertility.
Here an appeal is made to hypothetical biological forces,
which for some reason cause cyclical changes in fecundity.
Whether such an appeal is necessary depends largely on
whether or not other factors exist which might account for
the phenomenon.

Dr. G. R. Wagner-Manslau thinks that the "declining
birth rate is a huge selection of modern civilized peoples
toward weak desire for the child brought about by marriage
for money." Its basis is conceived to be genetic. Since
people with few children are more apt to rise in the social
scale, and since there is a tendency to marry the more
successful types, there is thus brought about a general
decline of the birth rate. But even if a social selection may
have led to a decline in the fecundity of the upper social
strata, it can hardly have led to a decline in the proletariat
or in the general population.

Naturally, the birth rate is influenced by factors affecting
the general health and vigor of a people. Women living in a
rural environment where they engage in manifold labors
are affected by natural sterility much less than their urban
sisters, who live under conditions much more unfavorable

204 HUMAN GENETICS AND ITS SOCIAL IMPORT

for the development of physical vigor. Many women who
want children are unable to have them owing to physiological
causes that are often obscure, but which operate with greater
force in women living in an urban environment. This may
be partly due to the nervous tension under which so many
women live. More of it probably results from the lack of
wholesome physical exercise in the open air, or from irregular
unhygienic modes of living.

Among the causes which affect fertility, venereal diseases
unquestionably occupy an important place. Gonococcus
infection is a not uncommon (perhaps the most common)
cause of sterility in the male sex because of the blocking
of the vasadeferentia which prevents the exit of spermatozoa.
Sterile marriages are frequently due to the absence of
spermatozoa in the seminal fluid. According to Meaker the
male is responsible for about a third of the cases of sterility
in marriage.

In women gonorrhea often causes severe havoc. In many
cases a woman contracts the disease from her husband after
he thinks he is cured. The infection may extend to the
uterus and Fallopian tubes, and even the peritoneum. If
a pregnant woman is infected, the baby may contract the
disease during delivery and become blind. After delivery
the infection may spread rapidly and lead to inflammatory
conditions which later result in sterility. Many one-child
marriages result from the devastations of this disease. The
percentage of cases of sterility due to gonorrhea have been
variously estimated as from 13 to 50 per cent. Often the
disease lingers on in a latent form in which it may escape
notice. According to Alexander four-fifths of all women who
are infected are unaware that they have this disease.

Syphilis causes sterility less frequently than gonorrhea,
but since it is a prevalent cause of stillbirths and affects
the birth rate indirectly by undermining vitality it is an

BIRTH RATE AND CAUSES OF ITS DECLINE 205

important factor in reducing fertility. The proportion of
stillbirths due to syphilis has been estimated by Dr. Willey
as 32.8 per cent. The damage done to health by the two chief
venereal diseases is incalculable. How widespread these
diseases are is difficult to ascertain. Their prevalence varies
greatly in different countries and cities. According to reports
from eight hundred physicians of Hamburg, Germany,
1.3 per cent of the men between fifteen and fifty contract
syphilis each year, and Lenz estimates that 45.5 per cent
of infection is a minimal percentage, while Weinberg esti-
mates the percentage of syphilitic males as 50. These esti-
mates based on urban populations have been considered
by some physicians as much too high. The examination of
the recruits for the U. S. Army revealed about 5 per cent
of syphilitic infection, but only the more obvious cases were
detected. Gonococcus infection is more common. According
to Lenz, from 40 to 50 per cent of all men and from 20 to
25 per cent of all women in Germany have contracted the
disease at least once. Knowledge of prophylactic measures
whose partial efficacy has been demonstrated in the U. S.
Army and Navy has doubtless become much more wide-
spread than formerly. Partly for this reason, syphilis has
decreased, but this is due also to improved methods of
treatment which shorten the infective stages of this malady.
While venereal diseases decrease the birth rate they are
probably not responsible for its downward course because
they were widely prevalent long before the birth rate started
to decline.

In the opinion of most students of the subject the greatest
factor in the decline of the birth rate is the voluntary restric-
tion of the birth supply. As Levasseur has stated in dis-
cussing the declining birth rate of France, "It is superfluous
to look for subtle causes. The decisive fact is simple: the
families in France have not many children because they

206 HUMAN GENETICS AND ITS SOCIAL IMPORT

do not want to have many children." If the decreasing birth
rate has been largely brought about voluntarily, there are
two aspects of the subject to be considered: (i) the reasons
why people desire fewer children, and (2) the means by
which the desired end is achieved. Our ancestors took
childbearing as a matter of course. People obeyed their
reproductive impulses, and if God decreed that they have
children they accepted the situation and got along to the
best of their ability. For the Rev. T. R. Malthus the only
feasible way of avoiding the burdens of large families is
"prudential restraint." This involved the postponement of
marriage until the reduction of fertility would decrease the
population to a point at which all could enjoy a fair measure
of prosperity. The idea that there was any way of checking
the birth supply without having recourse to means that
were positively criminal never entered the heads of most
of the great grandmothers of the present generation. Aside
from delayed marriages and prudential restraint within
marriage the only methods of preventing large families known
to most people were infanticide and abortion, and these were
not resorted to except under very unusual conditions.

A change of attitude began to appear after the origin of
the birth control movement. Contraception had been
practiced to a certain extent from early times, but it was
not employed extensively by modern civilized peoples
before the nineteenth century. Especial importance has
been attributed to the Bradlaugh-Besant trial in 1877.
This arose over the publication of a book by Dr. Knowlton
on The Fruits of Philosophy in which contraceptive methods
are described and advocated as a means of relieving mothers
from the burdens of a large family. The issue of this work in
England by Charles Bradlaugh and Mrs. Anne Besant led
to the prosecution of the publishers, who received a heavy
sentence, which was revoked by a higher court. Contracep-

BIRTH RATE AND CAUSES OF ITS DECLINE 207

tion had been advocated previously by Francis Place,
Richard Carlile, Robert Dale Owen, and others, but the
rank and file of the population were little affected by their
propaganda. The excitement created by the Bradlaugh-
Besant trial brought the subject prominently before the
public mind and affords an excellent illustration of how
movements are sometimes powerfully advanced by a little
persecution. The immediate result was to increase enor-
mously the circulation of Knowlton's book and subsequent
pamphlets on the same subject, among which was Mrs. A.
Besant's Law of Population, which ran through several
editions and sold several hundred thousand copies. According
to N. Himes, "No less than a million tracts furnishing contra-
ceptive information were sold between 1876 and 1891."

About the time of this trial the birth rates in England
began to decline. To how great an extent the trial was
responsible for this is uncertain. Pearson is inclined to
emphasize the influence of the passage of the Factory
Acts, which limited the employment of children in industry.
Child labor had come to constitute an important factor in
the textile and other industries of England. Children were
kept at work for long hours amid the most unhygienic
conditions, sometimes chained to their tasks, "fed upon the
cheapest and coarsest food; and slept by turns and in relays
in filthy beds which were never cool." Mortality was appall-
ingly high, but the supply was plentiful and cheap. The
outcry against these barbarities led to the passage of a
series of acts to regulate the ages and hours at which children
could be employed. The Education Act of 1876 making
school attendance compulsory also contributed to mitigate
the evil. The employment of children in the textile industries
was curtailed in England in 1878, and it is noteworthy,
as Pearson has pointed out, that in manufacturing cities,
such as Bradford and Leeds, there was a marked fall in the

208 HUMAN GENETICS AND ITS SOCIAL IMPORT

birth rate at about this time. The child was no longer a
financial asset and became a liability instead; so children
like other commodities proved to be responsive to the law of
supply and demand.

In the agricultural counties the birth rate did not begin
to decline until several years later. Doubtless birth-control
propaganda was not so widespread in the rural as in the
industrial regions, but there was less temptation to limit
the family. In the voluntary restriction of births there
have to be both the will and the way. With the increase of
population, the growth of cities, the wider dissemination of
education, and a greater desire for higher standards of living,
the custom of family limitation gradually became more
prevalent.

It is customary to attribute the voluntary reduction of
births largely to economic causes. James Bertillon brought
together the statistics of several large cities including Paris,
Vienna, and Berlin, showing that the poorer the district the
larger the average size of the family. He concluded that
"L'aisance entraine la sterilite." In support of this conclusion
there is cited the fact that as prosperity has increased the
birth rate has fallen. On the other hand, lack of adequate
income is often assigned as the reason for family limitation.
In cities where it is more inconvenient to have a large
number of children, and where each additional mouth to
feed imposes an added burden upon an already inadequate
income, the economic incentives to keep the family small
are very strong. Among the land owners in France it has
become a settled custom to have only a few children in
order not to subdivide the patrimony among too many
descendants. It would seem, therefore, that we are justified
in making two statements concerning the relation of eco-
nomic factors to the birth rate; (i) as people become wealthy
they tend to limit their families; and (2) people commonly

BIRTH RATE AND CAUSES OF ITS DECLINE 209

limit their families for economic reasons. The existence of
these apparently opposed tendencies has given rise to a
great deal of confusion in discussions of the subject. The
reconciliation of the apparent contradiction involved in
these statements lies in the fact that wealthy people do not
limit their families because they are wealthy, but because
wealth brings other interests and is usually associated with a
higher level of culture. There are social duties and dis-
tractions which make a large number of children an unde-
sirable encumbrance. Besides, large families in the upper
strata are unfashionable, and the influence of class sentiment
keeps the children few in number.

It should be borne in mind also that the correlation
between low fertility and wealth is partly due to the fact
that it is easier for a family to rise in the economic scale if
there are few children to support. On the whole, however,
it is not wealth, but the things that go along with wealth
that lead to small families among the well-to-do. Among
these factors a prominent place must be given to education.
In a study of the sizes of families sending students to the
University of California I find that as the education of
parents increases, the size of the family goes down. The
results are shown in the following table:

TABLE 7. — RELATIVE SIZES OF FAMILIES ACCORDING TO THE EDUCATION OF PARENTS

Education of father

Education of mother

Grammar school

High school

College

Grammar school

4-17
3-89
3-44

3-55
3-38
3-24

3-35
3-H
3.10

High school .

College

The average number of children is highest where both
parents have no more than a common school education,
and lowest when both parents have attended college.

210 HUMAN GENETICS AND ITS SOCIAL IMPORT

In a more homogeneous population consisting of rural
families of Connecticut, Whetten found that the average
number of children decreased as the education of the parents
increased, but that if only the native-born Protestant fami-
lies are considered, the differences in family size almost
entirely disappeared. Within this group, formal schooling
apparently affected the birth rate very little.

As a rule, educated people are not content with a low
standard of living, and they are quick to perceive that
large families lower these standards. Naturally, knowledge
of contraception would be more rapidly spread among them.
To a certain extent a negative correlation between education
and fertility is due to relatively late marriages, but it is
demonstrable that this is a subordinate factor. A desire to
succeed in life and to attain a higher social and economic
status is more apt to be found among people of education.
The object of their striving is not so easily attained if
children are begotten early in life. Arsene Dumont has
called attention to a process in human society which he
calls "social capillarity." Individuals, as they rise from a
lower to a higher class, like oil in a lamp wick, tend to limit
the number of their offspring. Ambition thus leads to
sterility. In a democratic society where a rigid caste system
does not occur, this movement may go on freely. We have
been doing much to give everyone the advantages of educa-
tion in order that those with the capacity to profit by it
most will be able to attain positions to which their natural
ability entitles them. With education available for all,
so that children of unusual merit from the poorest families
will be enabled to forge ahead and qualify for success and
sterility, the rapidity with which the differential birth rate
operates will be greatly increased.

Another factor in the declining birth rate is the emancipa-
tion of women and their increasing employment in industry.

BIRTH RATE AND CAUSES OF ITS DECLINE 211

Formerly the duties of the home required most of a woman's
time. With numerous labor-saving devices and the fact
that so many articles are made in factories that were formerly
made in the home, the work of the housewife has been
greatly reduced. Besides, many more occupations are made
available for women. It is now no longer necessary to marry
for support, and it is no longer a disgrace to be an old maid.
A much larger proportion of the female sex is self-supporting,
and many married women add to the family income by
pursuing employments outside the home. Children inevitably
constitute an obstacle to all these activities. Women have
become more self-reliant and independent. In many countries
they have acquired political rights equal to those of men,
and equal property rights have gradually been accorded
them. The life of continued childbearing and household
drudgery that formerly fell to the lot of so many mothers
of preceding generations has little appeal to the modern
emancipated woman. More and more women are taking the
regulation of the birth supply into their own hands.

How far religion influences the birth rate is difficult to
estimate because its effects are so closely associated with
those of other factors. Birth rates vary considerably with
members of different denominations. The peoples of Catholic
countries, Hungary, Spain, Portugal, and Italy, are as a
rule more fertile than those of Protestant countries, such
as England, Norway, Sweden, and Australia. In the United
States families of Catholics are larger than those of Protes-
tants. This is not due merely to the fact that Catholics are
relatively more common among the families of recent
immigrants from Southern Europe, but the same statement
applies to older residents of the country. According to
Huntington and Whitney the average size of the family
among the parents of people in Who's Who was 5.3 for
Mormons, 3.3 for Roman Catholics, 3.1 for Baptists,

212 HUMAN GENETICS AND ITS SOCIAL IMPORT

2.7 for Congregationalists, and 2.6 for Jews. In studying the
size of the families from which students of the University
of California come, I find that it is 4.44 for Catholics, 3.48
for Protestants, and 3.73 for Jews. On the other hand, in
Vienna, the population of which is mainly Catholic, the birth
rate has fallen since the war to 10.0 per thousand. In the
parts of Germany which are predominantly Catholic the
birth rate is higher than in those parts which are pre-
dominantly Protestant. The same statement is applicable
to the cantons of Switzerland. The number of children per
family in Prussia among Catholic, Protestant, and Jewish
families in which the husband and wife were of the same
religion were as follows:

TABLE 8. — CHILDREN PER FAMILY IN DIFFERENT RELIGIOUS DENOMINATIONS IN

PRUSSIA

Religion

1880-1884

1890-1894

1900-1904

i9J3

1922-1924

1926

Catholics

f .2

{•2

5.3

4.7

3-0

3-3

Protestants

4-5

4.2

3-8

2.9

2.0

2.2

Jews

4-3

3-3

2.8

2.2

1.8

The Catholic Church has emphasized the obligation to
obey the command "Be fruitful and multiply and replenish
the earth." It has taken a decided stand against the employ-
ment of artificial methods of preventing conception. The
Pope's encyclical letter states the position of the Church
by saying. "Since the conjugal act is meant to create new
life, those who willfully deprive it of its power, act contrary
to nature and do something disgraceful and immoral."
But notwithstanding the official pronouncements of the
Church, the voluntary limitation of births is practiced
extensively in Catholic countries. It was in France, whose
population is mainly Catholic, that the decline of the birth
rate first started and reached (until very recently) its lowest
level. In most countries the average size of the family has

BIRTH RATE AND CAUSES OF ITS DECLINE 213

been reduced among both Catholics and Protestants. When
conditions render such limitation desirable, the Catholic
Church does not object to family limitation on principle,
although it has always emphasized the duty of procreating
new life. It objects to accomplishing this end by unnatural
means. In fact the Pope has explicitly stated that "social
and eugenical indications should be considered if legal and
moral means and certain limits are taken into account.''

Probably the attitude of the Church has some effect in
checking the limitation of the birth supply, but it is insuffi-
cient to counteract the social, educational, economic, and
other incentives which lead people to limit their families.
Some students of the subject consider that religion per se
has very little effect upon the birth rate. In several Catholic
countries cultural standards are relatively low, and this is
often true of the Catholic population of certain areas as,
for instance, in the United States. Associated with this is
the lower economic status of the Catholic elements of the
population. In the Catholic parts of Germany where the
birth rate is high, the population is mainly rural as in
Bavaria and East Prussia, or largely Polish. In the urbanized
Protestant population of Saxony the birth rate is very
low, while the Protestant city of Berlin is almost in the
van of the low birth rate cities of the world (9.9 per thousand
in 1930). Even Paris has a considerably higher birth rate
(14.7 in 1930). It seems evident that where the educational,
social, and economic status of a population favor a low
birth rate, fertility is low regardless of the religion of the
population.

In considering the causes of the declining birth rate one
must not neglect the influence of fashion. The effect of
fashion in this regard is not due to mere imitation. There
come to be more or less settled customs in respect to repro-
duction due to various reasons. Family limitation is prac-

2i4 HUMAN GENETICS AND ITS SOCIAL IMPORT

ticed, not only from selfish motives, but because parents
wish to give their children educational and other advantages
which are only possible when the family is kept small in
size. In countries with an abundant population parents
are not apt to feel under a strong obligation to swell the
numbers of the inhabitants. Why then should they continue
to have children beyond the small number they can com-
fortably support? In France it has long been -customary to
standardize the family size, and to a less extent the custom
is coming to be followed in other countries. Large families
are often looked down upon as an indication of parental
folly. And most women do not care to incur the unfavorable
comments of their neighbors for breeding like rabbits.
The small family system is encouraged not only from motives
of prudence, but because it is a part of good social form.

Suggested Readings

East ('23), chaps. 8-1 1 . Fisher ('32), Holmes ('32), ('33), chap. 4. Lorimer
and Osborn ('34), chaps. 2-4. Pearson ('n). Thompson ('35), chaps. 9-11.

Questions

1. What advantages and what disadvantages are there in the use of
crude birth rates?

2. How is the birth rate affected statistically by an increase in infant
mortality ? Explain. How do you think that the actual number of births
would be affected by this cause?

3. How would a decline of the birth rate affect our statistics on the
prevalence of insanity, the mortality from cancer and from cholera infan-
tum ? Explain.

4. How and why would a decline of the birth rate affect the marriage
rate?

5. How is the birth rate affected by a decline of the birth rate ?

6. How would a reduction of mortality after age sixty affect the birth
rate ?

7. Why is the age composition of Germany more favorable for a high
birth rate than that of France ?

8. How is the crude birth rate of a city affected by the presence of a
college, an old people's home, a maternity hospital ?

BIRTH RATE AND CAUSES OF ITS DECLINE 215

9. What do you think of the relative importance of the following
influences on the birth rate: religion, income, education, social position?

10. Have the efforts of rulers to check the decline of the birth rate met
with conspicuous success ? What have been the chief reasons for endeavor-
ing to increase the birth rate ?

11. Suppose that the production of children were brought completely
under voluntary control in all classes; do you think that the race would
continue to reproduce itself without loss?

12. How did the low birth rate of France help her to pay her indemnity
after the Franco-Prussian war?

13. What relations tend to prevail in different countries between birth
rates, immigration and emigration ?

CHAPTER XVII
THE DIFFERENTIAL BIRTH RATE

THE fact that the decline of the birth rate is to a large
extent the result of volition helps to explain the ways
in which it has worked out in different classes of the popula-
tion. Formerly large families were found in all social classes.
In a well-known study of the decline of the birth rate in
London, David Heron found that there was a positive
correlation between fertility and various undesirable social
characteristics, such as mortality from tuberculosis, high
infant mortality, insanity, and bad living conditions, but
that this situation had developed during the preceding
fifty years. In 1851 the net fertility was in favor of the
classes of the higher social status. In Germany, until within
the nineteenth century, the well-to-do peasant married
before the worker without property. Apprentices in trades
seldom married, and persons belonging to guilds commonly
deferred marriage until they attained a more or less assured
position. Among the successful types there was little family
limitation, and, according to Lenz, the effect of differential
fertility was, on the whole, eugenic. According to Whetham,
the average number of children to fertile marriages of the
British landed gentry contracted between 1830 and 1840
was 7.1; but it fell to 3.13 from 1881-1890, a drop of over
50 per cent. Among the people whose names occur in Who's
Who Whetham found that, excluding clerical and military
families, there was an average of 5.2 children per marriage
contracted before 1870, while for marriages contracted

after 1870, the average was 3.08.

216

THE DIFFERENTIAL BIRTH RATE 217

In considering the effect of differential birth rates it is
desirable to know how many children per family are required
to maintain a stock without loss. It is obvious that more
than two are required because, in addition to the two
children who will replace their parents, others are needed
to supply the places of those who die before reaching ma-
turity and those who fail to marry. Evidently the number of
children needed depends upon the death rate and the
marriage rate. In his celebrated pronouncement on race
suicide Theodore Roosevelt estimated that, on the average,
four children per marriage are needed to keep a stock from
decreasing in numbers. With the reduction of infant and
child mortality which has occurred since this statement was
made, the required number of children is now somewhat
less. According to the calculations of Dublin it is about 3.1.
Estimates made in Germany have given 3.3 (Grassl 1914);
3.2 (Burgdorfer, 1924-1926), and 3.4 (Lenz 1924-1926) as
the required numbers under prevailing rates of marriage
and mortality. In general it may be said that stocks produc-
ing less than 3 children per family will decrease in numbers in
successive generations.

With this fact in mind it is instructive to compare the
birth rates of different social and occupational groups.
There have been several studies of the families of the
graduates of colleges and universities, and they agree in
showing that the birth rate in this class has declined to a
very low point. Records for Harvard give an average of
1.9 children per marriage of graduates, or, allowing for the
18.9 per cent who are not married, 1.6. For Yale graduates
the corresponding figures (1893, 1896, 1897) are 1.9 and
1.5; and for the graduates of Swarthmore College (1896-
1912) they were 2.15 and 1.9. The records for graduates of
women's colleges are considerably lower than those from
men's colleges because of the smaller percentage who marry.

2i 8 HUMAN GENETICS AND ITS SOCIAL IMPORT

The percentages of married graduates of Vassar have varied
from 53 to slightly over 70, and the number of children per
marriage from 2.4 to 1.9, and the number per graduate
from 1.5 to I. The percentage of women graduates of the
University of California who married between 1872 and 1910
inclusive is 55. For most women's colleges the percentage of
graduates who marry is probably between 50 and 60.
The low birth rate of the graduates of women's colleges is
probably due not so much to the influence of college educa-
tion as to the mores of the group to which the college girls
belong. Mary Roberts Smith found that 343 married college
women had 566 living children, or 1.65 per marriage, while
313 noncollege women of the same social class — sisters,
cousins, or friends — had 582 living children, or 1.87 per
marriage. The small difference is probably due to the fact
that the college women married about two years later
than the group which did not attend college. Similar findings
have been reported by Goodsell.

The studies made on the number of children born to
college graduates make it evident that, on the whole, the
fertility of this group falls distinctly below the maintenance
level for men, and very far below for women. A similar
situation is afforded by other classes distinguished for their
intellectual achievements. Cattell finds that the average
number of children in the families of American men of
science is 1.88. The people whose names get into Who's
Who in America have families averaging little over two
children. Huntington finds that 384 faculty members of
Yale University who were born before 1890 have on the
average 1.65 children. Although some of the younger mem-
bers may have more children, they will be few in number
and probably would not bring the average up to 1.8. Other
studies indicate that much the same situation prevails
in other institutions. The families of professional people in

THE DIFFERENTIAL BIRTH RATE 219

general — lawyers, doctors, engineers, teachers, and investi-
gators— the people who are especially distinguished on the
basis of intellectual training, are now reduced below the
level necessary for continuous propagation. The kind of
heredity which these stocks represent is, therefore, being
lost to the race.

To a great extent the members of these classes come from
the larger class of college graduates. The latter come mainly
from a fairly intelligent, more or less prosperous stratum of
society who are appreciative of the value of education at
least to the extent of sending their children to college. Such
people would be a serious loss to the community. Do they
constitute a self-perpetuating group?

I have endeavored to answer this question, so far as the
parents of the students in the University of California
are concerned, by ascertaining the number of children
in the families from which these students came. The average
number based on the parents of over 16,000 students was
3.66 per family. One might consider that this number is
sufficient for maintenance, and so it is for these particular
families. But before concluding that the general stratum of
which these parents are a fair sample is sufficiently fertile
to perpetuate itself, we must take into consideration a
source of error which has often led to false conclusions in the
field of eugenics. It arises from the fact that if we start with
any group chosen at random from the general population,
whether school children, inmates of sanatoria or asylums,
and then ascertain the size of the families from which these
individuals came, the families will be larger than the general
average of their kind. Families having no children would
obviously not be represented at all. Families with ten
children would be represented ten times as frequently as
families with one child. Consequently our group would be
especially selected for large family size.

220 HUMAN GENETICS AND ITS SOCIAL IMPORT

If we find that insane, feeble-minded or tuberculous
children in an institution come from families that are
larger than the average, it does not necessarily follow that
the stocks which furnish them are unusually prolific. They
may or they may not be, but in order to ascertain whether
they are or not, we must compare averages obtained in the
same way. By knowing the numbers of children in the several
families constituting a given group, we can calculate the
extent of the bias in favor of large families and estimate the
true average of the group from which it was chosen, provided
the choice represents a true random sample. By making
such an estimate, and considering only fertile marriages,
the average size of the families represented in our University
of California group would be reduced from 3.66 to less than 3.
If we make further allowance for childless marriages, which
in such a group probably average about 15 per cent, the
number would be reduced still more.

In a similar study made by Baber and Ross on families
sending students to the University of Wisconsin, it is found
that the average size of the family was 3.76, and that the
families of the uncles and aunts of the students average
3.24. The families of the latter group were not weighted
for large size, but they included no sterile marriages. The
fact that parents of college students have larger families
than their brothers and sisters is probably due mainly
to the fact that the families were selected for large size.
This tendency would be partly counteracted by the cir-
cumstance that the parents of a small family might better
afford to send a child to college than parents of a large family.
On the whole, it seems probable that the stratum of people
who send students to college fall somewhat short of being a
self-perpetuating group.

This conclusion is in harmony with the data on the rela-
tive birth rates among members of different occupations.

THE DIFFERENTIAL BIRTH RATE

221

Occupational fertility has been studied in Great Britain,
Germany, and some other European countries and more
recently in the United States. The findings tell much the
same story. One of the best investigations has been carried
on in England by Dr. T. H. C. Stevenson based on the
census of 1911. Occupations were classed in eight groups.
The first five includes workers arranged according to status
from the professional and upper classes (group I), to unskilled
workers (group V). The sixth, seventh and eighth groups
comprise textile workers, miners, and agricultural laborers
respectively. The relative standardized fertility rates per
hundred families of these groups are shown in the table, as
well as their trend since about the middle of the century.

TABLE 9. — CHILDREN BORN PER 100 FAMILIES IN ENGLAND AND WALES ACCORDING

TO OCCUPATIONAL GROUPS AND DATE AND DURATION OF MARRIAGE.

STANDARDIZED RATES

Date of

Duration of

Occupational class

marriage

III

VII

VIII

1906-1911

o-5

7°

100

105

101

1901-1906

5-10

171

197

211

219

242

185

263

246

1896-1901

10-15

242

284

323

362

275

399

363

1891-1896

15-20

303

359

405

412

463

359

5'7

470

1886-1891

20-25

357

422

482

491

54i

435

610

552

1881-1886

25-30

413

481

544

55°

596

501

671

618

1871-1881

30-40

497

567

615

616

652

567

717

667

1861-1871

40-50

607

665

696

690

7*5

648

777

719

1851-1861

50-60

662

733

746

735

763

696

797

779

Over 60

682

777

729

792

781

732

870

820

Total

277

321

353

359

392

3i9

433

399

It may be noted that the fertility in the professional
group is very low and that there is an increase as we pass
to the lower occupational groups. Moreover, if we compare
the differences in fertility between the lower and the higher
groups, we find that they are much less pronounced in

222 HUMAN GENETICS AND ITS SOCIAL IMPORT

marriages occurring between 1851 and 1861 than in those
taking place at a later date.

In Prussia in 1912, according to Lenz, there were the
following numbers of children per marriage in the classes
listed:

TABLE 10. — CHILDREN PER MARRIAGE IN DIFFERENT CLASSES IN PRUSSIA IN 1912

Number
Occupation of Children

Officers and professional classes 2.0

Technical workers 2.5

Skilled workers 2.9

Factory workers without technical training 4.1

Agricultural and day laborers 5.2

Statistics on the size of the families among followers of
various occupations in the United States have been tabulated

5.5 -j

5.2

4.5-

3.5-

L
<D

2.9

2.5-
2-
1,5-
1-

.£>
_C

e
£

Unskilled worke

lied cxrtizotns

2.o

2.0

ried workers
•"ddesmen

.- ^!1

0.5-

jic
tn

_04-

V1^

C/)

FIG. 63. — Children per marriage in Prussia in 1912 according to occupation.

in our volumes on birth statistics for a few years since 1924,
and data on the subject were collected, but not published,
for the Census of 1910. According to Sydenstricker and
Notestein the number of children per 100 wives in a large
sample of a population in 1910 were as follows:

THE DIFFERENTIAL BIRTH RATE

223

TABLE n. — NUMBER OF CHILDREN PER 100 WIVES IN SELECTED AREAS OF THE

UNITED STATES

Area and class

Number of children

Mothers of all ages
at marriage

Mothers aged 20-24
at marriage

Urban sample:
Professional

'5>

152

178
213

233

258

277

148
146
170
206

221
248

*53

Business

Skilled workmen

Unskilled workmen

Rural sample:
Farm owners »

Farm renters

Farm laborers

The age of wives at marriage varied in these groups,
being about five years later in the professions than among the

Urban sample
Rural sample-

Professional

Business

Skilled workers

Unskilled laborers— -

Farm owners

Farm renters

Farm laborers

300

100 150 200 250

Children Per 100 Wives

FIG. 64. — Children born to 100 wives according to occupation of husband in selected areas
of the United States in 1910. (Data from Notes tein.)

farm laborers and over four years later than in the unskilled
workers. However, for wives marrying at any particular
age, such as twenty to twenty-four for instance, the same
occupational trend is shown as in the whole group. It is
significant that the percentage of wives forty to forty-nine

224 HUMAN GENETICS AND ITS SOCIAL IMPORT

years of age who remained childless increases as the birth
rate declines, while the percentage who have had five
children or more is fairly parallel with the occupational
trend of the birth rate.

TABLE 12. — PERCENTAGE OF CHILDLESS WIVES AND THE PERCENTAGE OF WIVES

BEARING FIVE OR MORE CHILDREN ACCORDING TO AREA AND SOCIAL CLASS

(Ages of wives forty to forty-nine)

Area and class

Percentage
childless

Percentage with
five or more children

Urban

ir. 7

i6.q

Professional
Business

17.7

16 o

10.9

12 A.

Skilled workers

I C I

21 C

Unskilled workers

14.0

** • J

33.6

Rural

Q 2

^Q O

Farm owners

IO I

or 2

Farm renters

6.8

4Q.2

Farm laborers

7.0

CO 2

The inverse relation between fertility and occupational
status, according to Kiser, has increased between 1900
and 1910, at least in the East North Central states. Ogburn,
who has compared the sizes of families in relation to occupa-
tion between 1900-1930, states, "The greatest decline was
among the families of the professional group where it was
10 per cent." The data from the United States agree with
those from England and Wales in showing that differences
in the fertility rates of occupational classes have been in-
creasing. These differences are now very marked, and they
show that in general the birth rates increase in proportion
as the occupations require little intelligence or skill.

F. Lenz, T. Lenz, and K. Barnes in studying over 3,000
children in the schools of Kronach find that the average
number of children per family varies inversely with scholastic
grades and levels of intelligence. The scholastic records
and number of children per family were as follows:

THE DIFFERENTIAL BIRTH RATE 225

TABLE 13. — THE RELATION OF SCHOLASTIC RECORD AND ABILITY TO FAMILY SIZE

IN KRONACH

Number of children

Scholastic record

per family

3-30

3-47

3.81

4.24

4.11

Rating for ability

3.28

4-03

4-43

5-05

5-15

S. Dawson's studies of the relation between intelligence
quotients and family size in a group of 1,239 children of
workmen and tradesmen in England showed that in the
highest group with an I.Q. of 114 and over the average was
3.41; for the medium students (I.Q.'s 85-114) it was 4.43,
and for the dull (I.Q. less than 85) it was 4.73. The correla-
tion between intelligence and family size was —0.30. Studies
by Bradford on 450 city children gave a correlation of
— 0.35, and those of Chapman and Wiggins on 670 children
a correlation of —0.33.

From the biological point of view these facts would have
little significance if the differences between the groups
represented have no relation to heredity. If the distribution
of intelligence is essentially the same in all social and occupa-
cional groups, it matters little, so far as the inherited qualities
of the race are concerned, which groups produce the greatest
number of children. Socially and in other ways it might
make a good deal of difference of course, but whether the
differential birth rate works dysgenically or not depends
upon whether the classes characterized by different degrees
of fertility differ also to some extent in their genetic endow-
ments. This question, which we have discussed in a previous
chapter, is one of crucial importance, and, in considering it,

226 HUMAN GENETICS AND ITS SOCIAL IMPORT

we should free ourselves from all forms of class bias which
have a strong influence in determining the attitudes of people
on this subject. Perusal of the controversial literature on
eugenics will reveal the existence of two kinds of class
prejudice which may be described as the aristocratic and
the proletarian. According to the first, occupancy of a
lowly station in life is ipso facto an evidence of innate
inferiority. According to the proletarian bias, the marks of
inferiority which may be associated with a lowly station
in life are due to the unjust distribution of wealth and
opportunity in our present social order. Those who are
actuated by the latter bias are prone to resent the conclusion
that the differential birth rate in relation to social and
occupational class is in any way dysgenic. To assert that
ordinary unskilled laborers have an I.Q. lower than skilled
artisans or successful business men is regarded as adding
insult to injury. Superior occupational status and especially
financial success is attributed not so much to superior
intelligence as to the accidents of fortune or to a selfish
acquisitiveness which facilitates the attainment of success
in the scramble for wealth and position. Hence the con-
clusion that the present differential birth rate is dysgenic
is by no means lacking in vigorous opponents. Com-
monly the opposition is based on some of the following
assumptions:

1. That intelligence tests and even scholastic records
are no measure of native ability. This position, although
seldom adopted in the bald form stated, we have discussed
in a previous chapter.

2. That superior intelligence, even though inherited,
is so dependent upon the fortunate concourse of genes
in the Mendelian shuffle that it is about as apt to arise
from stupid parents as from intelligent ones. Hence the
differential birth rate does little harm. At least an approach

THE DIFFERENTIAL BIRTH RATE 227

to such a position has been made by Dr. H. S. Jennings,
who, while admitting the great importance of heredity,
has stated that "superior parents often produce mediocre
or inferior offspring; inferior parents at times produce
mediocre or superior offspring. In consequence of this
situation, decrease or even stoppage of the superior indi-
viduals or of the inferior individuals has very little effect on
the average grade of the next generation."

3. That inherited levels of intelligence make no difference
in occupational status. If a rigid caste system prevails in
which sons follow the footsteps of their fathers, this might
possibly be true. But in most countries at present, and in our
own in particular, there is a great deal of change from one
occupational level to another, both upward and downward.
Does native ability count for nothing in determining these
changes ? Common observation, to say nothing of other
evidence, indicates that it is an important factor in what is
commonly called success. It is not the dull people in the
lower levels who rise to superior status. The moron, border-
line, and dull-normal groups naturally gravitate into the
ranks of unskilled and relatively poorly paid labor. That
on the whole the intellectual levels below mediocrity com-
monly get into pursuits which require an unusual mental
equipment is hardly a reasonable conclusion.

4. That the average differences between occupational
groups are not great enough to indicate that they cannot
be entirely accounted for as a result of educational advan-
tages and opportunity. It must be admitted that a part
of the differences can be so explained, but that the explana-
tion is entirely adequate is open to the objections stated
in the previous paragraph.

5. That the sterility of the upper classes can be continually
supplied from below while the lower strata continue to
reproduce their own kind.

228 HUMAN GENETICS AND ITS SOCIAL IMPORT

Opposed to these interpretations most eugenists would
contend:

1. That human beings manifest different degrees of
intelligence which to a considerable extent are dependent
upon differences in genetic constitution.

2. That the higher occupations more than the lower ones
are followed by individuals who have the good luck to have
drawn a favorable combination of genes.

3. That the children of parents in these higher groups
owe at least a part of their superiority in intelligence quo-
tients and scholastic records to their somewhat superior
heredity.

4. That the sterility of the higher groups represents a loss
to the race of the more highly endowed hereditary types.

5. That the rise of people from the lower occupational
groups into the higher ones where they become relatively
sterile tends to rob the lower groups of the good hereditary
material they contain, leaving them to be recruited more
and more from the less well endowed members who fail to
rise. Thus the tendency of society to "die off at the top"
results in the impoverishment of our racial heredity as a
whole.

6. The differential birth rate under present conditions
is on the whole dysgenic in its effects.

There are, of course, all sorts of intermediate positions
between the opposed standpoints we have mentioned. The
student will have to draw his own conclusions as to what
position is the most reasonable in the light of the available
evidence.

The negative correlation between fertility and intelligence
as it is measured by different kinds of tests is what one
might naturally anticipate, because people with little
intelligence would not be likely to exercise prudence and
foresight in regard to reproduction any more than they do

THE DIFFERENTIAL BIRTH RATE 229

in other affairs of life, if as much. Birth control involves a
measure of sophistication and at present it is employed
relatively little by unsophisticated people. Although the
practice at first prevailed in the higher social strata, it
has gradually filtered down through the ranks of society
until, in several regions, it has caused a marked decline
of the birth rate in the proletariat. In fact, were it not for
the participation of this numerous class, the general birth
rate could not have fallen as much as it has in several
countries. Birth restriction has been much more extensively
employed by the proletariat since the World War, especially
in Germany where the notion of a birth strike (Geburtstreik)
has become widespread among the industrial workers.
Some students of vital statistics are convinced that the
differential character of the birth rate is decreasing because
contraceptive practices have invaded the lower social and
economic levels. In Berlin there is little difference between
the birth rates of the proletarian and the well-to-do dis-
tricts. In Hamburg in 1910 the birth rate was about twice
as high in the proletarian sections as in those with a prosper-
ous population, but from 1926 to 1930 the differences were
very much reduced. Similar trends have been recorded
for Dresden and Konigsberg. Both Stockholm and Oslo
showed high birth rates in the poorer districts before the
war (1911-1914), but the decline has been so rapid in the
poorer districts that in 1927-1928 it was very little higher
than in the rich districts. In London and Edinburgh the
same tendency is manifest, but it has not proceeded so far.
In Paris the poor districts were much more fertile than the
rich ones from 1906 to 1910 (in some cases nearly twice as fer-
tile), but since 1925 the differences have been very much less.
We have few data on how the differential birth rates
have been changing in cities of the United States and in
most other countries. It is safe to say that in most places

230 HUMAN GENETICS AND ITS SOCIAL IMPORT

they have not as yet gone very far toward equalizing the
birth rates of different social classes. What has happened
in the places where the inequalities of the birth rate have
been largely effaced is not that the fertility of the higher
social classes has increased (generally it has slowly de-
creased), but that it has decreased so much in the lower social
classes that the total birth rate has come to be below the
level required for maintenance. Were the present rates to
continue all classes would become extinct together.

Probably the general trend now is toward the equalization
of birth rates at a lower level. As this movement progresses
the dysgenic working of differential fertility will be reduced
and may eventually be followed by a greater fertility of the
successful types. It has been suggested that the present
dysgenic period of our biological history is only a temporary
stage which will be passed through as the practice of birth
control has completed its downward course throughout the
masses. We may at least cherish this possibility as a pious
hope. But with this must be joined another pious hope that,
before this happy consummation is reached, the population
will not have begun to decrease in numbers.

While there is a pronounced tendency for birth rates to
rise as our measures of intelligence indicate that intelligence
quotients are low, there are some exceptions to this rule.
Butt and Nelson have found that in two counties in Utah
parents with more than the average schooling have slightly
larger families than those with less schooling. The parents
were mostly farmers, largely of the Mormon faith, and
constituted a fairly homogeneous group. In a rural section of
Vermont, Conrad and Jones have found that there is
practically no relation between intelligence of parents and
family size. Here again there was a fairly homogeneous
rural population like the Utah farmers which still retained
the older traditions of high fertility.

THE DIFFERENTIAL BIRTH RATE 231

Exceptions of a somewhat different kind have been
reported by Huntington and Whitney, who found that
among the 800 Yale graduates of the classes of 1893, 1896,
and 1898 the men who were graded high by their colleagues
on the basis of their general value to society had, as a rule,
larger families than the graduates who were graded low.
The men were classed in ten groups according to the degree
of success they had attained. The percentage who were
married increased with the degree of success and the number
of children per father increased from 2.2 at one extreme to
3.1 at the other. Similar relationships were found by J. D.
Phillips for graduates of Harvard, and by F. A. Woods for
individuals in Whos Who in America. Huntington remarks,
"No matter whether we take lawyers, ministers, engineers,
bankers, artists, military men, writers, business men, or
professors, the successful men on the average have decidedly
more children than the less successful."

All these groups, however, are characterized by a reproduc-
tive rate that falls below the maintenance level, so the
tendency noted represents a sort of back eddy in the general
stream. Dr. Huntington suggests that "the distribution in
families arising from birth control has run its course among
the distinguished men and that they are returning to a
normal situation wherein they will have enough children
to replace themselves and to provide for a small increase
from generation to generation/' — a sentiment to which the
eugenist would say Amen.

In considering the fertility of the people of low intelligence
we may dismiss the very lowest types, the idiots and im-
beciles, as practically negligible from the standpoint of
eugenics. They are relatively few in number, and, as they
are usually kept under surveillance in their homes or in
institutions, they rarely produce offspring. With the morons
it is a different matter. Stocks like the Jukes, Kallikaks,

232 HUMAN GENETICS AND ITS SOCIAL IMPORT

and Tribe of Ishmael flourish like the green bay tree, and
there are many records of the unrestrained prolificacy of
feeble-minded women, as is illustrated by the reproductive
performances of Polly and her eleven illegitimate children
who were responsible for 31 feeble-minded progeny among
their 56 descendants. However, one should not base con-
clusions on selected cases. What we are interested in knowing
is whether the moron group as a class is more prolific than
persons of normal intelligence.

Unfortunately, there are only a few scientific studies on
the birth rates of the feeble-minded. Most mental measure-
ments are made upon children instead of parents. In one
investigation made by Green on family size in 211 feeble-
minded parents, it was found that the average number of
children was 6.43 + 0.17. These results were obtained
from records of family histories in the Eugenics Record
Office at Cold Spring Harbor, N. Y. The families may have
been somewhat larger than normal on account of the method
of selection, but only a small proportion of the women
studied were mothers of the individuals on the record
charts. It is significant that there was almost no decrease
in family size since 1840. In the Eugenics Survey of Vermont,
it was found that where one or both parents were feeble-
minded or insane the average size of the family was 3.5,
or including still births and children dying in infancy,
4.3 — figures somewhat larger than those of normal families
(3.04 and 3.34).

Popenoe reports that 112 feeble-minded mothers of
inmates of the Sonoma State Hospital in California had an
average of 4.09 children (4.95 pregnancies), which when
corrected for selection was reduced to 2.84 (3.17 pregnancies) ;
but, on account of the age of the mother, these families were
not quite complete. This fertility is certainly not excessive
even for a state with a low birth rate such as California.

THE DIFFERENTIAL BIRTH RATE 233

More is known about the fertility of parents of mental
defectives than about the fertility of defectives themselves.
According to the report of the Mental Deficiency Committee
of Great Britain, parents of very low grade mental defectives
have families of about the average size. Since, as we have
seen in a previous chapter, such children are nearly as apt
to come from people in one intelligence level as in another,
this is perhaps to be expected. The same investigators have
found, however, that the parents of mental defectives of a
higher grade are characterized by an unusually high birth
rate. This also might be expected if there is a negative
correlation between intelligence and fertility, since defec-
tives of this class are, as we have seen, more commonly
derived from parents of a relatively low mental level.
Similar results are reported by Thurstone and Jenkins
who find that in Chicago, idiots and imbeciles with an
I.Q. of less than 40 come from families of about the average
size, while defectives with LQ.'s from 50 to 80 come from
families about one-third larger than those with children of
normal or superior intelligence.

In his investigation of the families of 1,111 mentally
defective children in Liverpool Dr. Caradog Jones found
that the average size of families containing one or more
defective children (age five to twenty-two) was 7. 2, of whom
2.5 had died, leaving 4.7 living children per family. The
average size of a random sample of 4,379 working-class
families in Liverpool was 3.92 children born, and 2.97 living
children. Even allowing for the different basis of selection
in the two cases the facts support Dr. Jones' conclusion
that, in Liverpool at least, " the subnormal group generally
is contributing considerably more than its fair share to the
future population." To a very considerable extent mentally
defective children in Liverpool come from the lower occu-
pational groups. In a sample of families found to contain

234 HUMAN GENETICS AND ITS SOCIAL IMPORT

at least one mentally defective person in a household census
of the general working-class population, the head of the
family was unskilled in 63 per cent of the cases as compared
with 39 per cent of unskilled laborers in the general survey.
In one-fourth of the cases the head was unemployed as
compared with one-tenth in the general sample; and over
40 per cent were below a defined poverty line as compared
with 1 6 per cent of all the families sampled in the same
area.

Most of our data on the fertility of families producing
mental defectives come from studies based on children in
special schools or classes. Dr. L. J. Whitney reports that the
average size of the family of 1,631 children in schools for
subnormals in an eastern city was 7.09. To a large extent the
children came from recent immigrant stocks, and the families
were probably larger than the average for this reason.
Keller, in studying the relations between family size and
defective intelligence in Gross-Winter, Germany, finds
that children in special classes for defectives came from
families averaging 4.47, while the number of children per
family in the primary schools was 4.15, and in secondary
schools 3.31. If these figures are corrected for the effects
of selection they would be 3.25, 2.98 and 2.46 respectively.
The figure for the special class children is too low because
their ages were from 6 to 14, and hence more children will
probably be born in these families. In the other cases the
families were more nearly completed, since the children were
older, being from 12 to 15 years of age. In a similar investiga-
tion in Mecklenburg, Winkler finds that the fertility of
families in special schools for defectives is "about one-fourth
higher than in those of more than average mentality."
In Bremen Kurz finds that children in special schools came
from families averaging 4.3 children while the average for
high schools was 2.10.

THE DIFFERENTIAL BIRTH RATE 235

One of the most extensive studies on the parentage of
defective and retarded children has been carried on by
Dr. Neil A. Dayton who made a survey of 20,473 such chil-
dren in the public schools of Massachusetts. These children
were found to come from families averaging 5.6. This number
reduced for selection of families of large size becomes 3.9,
which is somewhat larger than the estimated size of a
completed family in the United States in 1920, namely 3.6.
The larger size of the Massachusetts families is attributed
by Dayton to the high percentage of foreign-born parents
in the group examined. Making allowance for this factor
brings the average down to 3.5 which is not far from the
average family size in the entire country. Children with an
I.Q. less than 70 were classed as defective; those with I.Q.'s
from 70 to 89 were called retarded. Unfortunately the
family size of the normal children in the same schools was
not determined, since this would have furnished valu-
able data for comparison drawn from families in the same
communities. How far the sample studied is representative of
the general population as to urban and rural distribution is
uncertain. The average age of the mothers was about
forty-one, and hence Dr. Dayton concludes that the families
were practically completed. However, the percentage of
children born to mothers over forty in Massachusetts has
commonly been about five per cent, but if the average age
of the mothers was forty-one there must have been many
mothers younger than this to counterbalance those of older
ages, so it is not quite safe to assume that the families
were practically complete. At any rate, even if Dr. Day-
ton's estimates of family size are somewhat too low, the
fertility of most of the parents sending defective and re-
tarded children to the public schools of Massachusetts does
not greatly exceed that of the general average of the Amer-
ican people. Certainly it is more than sufficient for the main-

236 HUMAN GENETICS AND ITS SOCIAL IMPORT

tenance of this group, and doubtless considerably exceeds
the fertility of the families in that state which send their
children to college.

On the whole the evidence points to the existence of a
negative correlation between intelligence and fertility for
all grades of intelligence from the highest down to but not
necessarily including the lowest type of mental defectives.
There can be no doubt that in most countries of advanced
culture, the higher occupational groups are not perpetuating
themselves. With the general decline of the birth rate
inadequate reproduction has gradually proceeded downward
until, in several regions, the only groups which are maintain-
ing themselves are those in the lower levels. Conditions vary
considerably in different countries and in different areas
especially urban and rural in the same country, but the
tendency for high intelligence to be associated with low
fertility is very widespread in Europe and America.

Suggested Readings

Charles ('34). Holmes, ('21), chaps. 6 and 7. Huntington and Whitney
('27), chaps. 4-6, 15-20. Jones, D. C. ('32). Ogburn and Tibbitts ('32).
Wiggam ('24), chaps. 18, 19.

Questions

1. How is the quality of the birth rate affected by the feminist move-
ment, the celibacy of the priesthood, the decrease of illegitimacy ?

2. Why does the average person come from a family of more than the
average size?

3. Why do great men come from predominantly boy-producing
families, and great women from predominantly girl-producing families?

4. Eminent persons are more apt to occur among the first-born children
of a family. Are the reasons for this genetic or cultural ?

5. Why does Utah have a high birth rate ?

6. Do you think that in the future birth control will be eugenic or
dysgenic ?

7. What are some of the involuntary and some of the voluntary causes
of the decline of the urban birth rate ?

THE DIFFERENTIAL BIRTH RATE 237

8. Why has the rural birth rate declined with especial rapidity in the
last few years?

9. Look up in the United States birth statistics the family size of the
different national groups. What relation has fertility to the cultural and
economic status of these groups ?

10. Look up the family size of various occupational groups in the United
States birth statistics. What groups are above and what groups are below
the maintenance level ?

11. What are some of the purely statistical reasons for a decline in the
birth rate, and what are the more important real reasons for the decline ?

12. If people reduce their birth rate for economic reasons, why is the
birth rate lower in well-to-do areas than it is in poorer ones ?

13. In studying the influence of religion on the birth rate, what sources
of erroneous inference should be considered ?

14. What is the average size of the family in the class to which you
belong ? Does this indicate a birth rate sufficient for maintaining the stock
under existing rates of death and marriage ?

CHAPTER XVIII

DEATH RATES

IN ORDER to ascertain how rapidly a population increases
in numbers it is necessary to have records of the rate
at which people die as well as the rate at which they are
born. The measure of mortality most commonly employed
is the number of individuals dying during the year per
thousand population of that year. This is called the
crude death rate. And its interpretation is beset with all
the sources of error to which attention has been called in
discussing the crude birth rate. Since people are more apt to
die at some ages than at others the general death rate of a
country is influenced, like the birth rate, by the age com-
position of the inhabitants. A community composed of very
young or very old people, for instance, would have a high
mortality since the death rate in both these age groups is
higher than in the middle period of life. If the local newspaper
or Chamber of Commerce boasts of the low death rate of
one's town it does not necessarily indicate that the locality
is a particularly healthful one in which to live, because the
town may contain a large number of young workers or
college students whose low death rate reduces the general
average.

In order to make proper allowance for differences in age
composition it is customary to employ standardized death
rates obtained by reducing all death rates to a common
basis. This is done by finding what the rates of different
regions would be if their populations had the same age
composition as a given population taken as the standard of

238

DEATH RATES 239

comparison. One standard commonly employed is the popu-
lation of England and Wales in 1901. To calculate the
standardized death rate of a region one needs to know the
death rate for each age period. Then one can estimate
how many deaths would have occurred in each period had the
age composition of the inhabitants been the same as that
of the standard population. When this is determined one
may calculate how many deaths per thousand would have
occurred in the total population of the region.

The choice of a population as a standard is a purely
arbitrary proceeding, and the populations of different
countries and at different times have been used for this
purpose. Sometimes mortality rates are further adjusted for
non-residents, inmates of hospitals, or other persons not
typical members of the community.

Mortality records have not been systematically kept
over a long period of time. What is known about the mor-
tality of people in past centuries has to be gathered from
the records of ages at death that happen to have been
preserved, and these are very incomplete. Records of
baptisms, marriages, and deaths were first kept in England
and France in the sixteenth century. In 1662 John Graunt
of London published the first treatise on vital statistics
entitled Natural and Political Observations Mentioned in
the Following Index ^ and Made upon the Bills of Mortality.
Graunt brought out several significant facts concerning
mortality, such as the relatively high death rate of males,
the high death rate in infancy, and the greater mortality of
urban than of rural inhabitants. His work afforded a stimulus
to later studies in the same field, but for a long time progress
in recording vital statistics was slow. Only a few countries
published adequate mortality statistics before the nine-
teenth century, and there are still many parts of the earth
in which no records of deaths are kept.

24o HUMAN GENETICS AND ITS SOCIAL IMPORT

For a long time information on the mortality of the people
of the United States was very incomplete. A few states and
cities have published fairly satisfactory reports on deaths
for many decades, and data on mortality for the entire
country have been compiled at ten year intervals in the
reports of the Census, but they are confessedly very in-
accurate. Since 1900 the Census has issued annual volumes
on mortality statistics for the Registration Area for Deaths.
This area, in which the registration of deaths is fairly com-
plete, has gradually increased from a few states until it
now includes all the states of the Union. Similarly the
Registration Area for Births has also increased until it
comprises the entire country. As a result of these improved
facilities for biological bookkeeping, changes in population
can be followed much more accurately than was possible a
few years ago.

Reliable mortality statistics are quite evidently necessary
for the construction of that very useful compendium of
information about life and death known as a life table.
Sometimes the same thing is called a mortality table, but
either name is appropriate, since the table gives us informa-
tion concerning both probable further duration of life
and chance of dying within the year at any given age. Life
insurance rates are based on life tables, and since one's
expectation of life decreases as one gets older, a policy
taken out after age forty costs more than one begun earlier
in life. If a man is over age sixty-five most companies will
not insure him at all.

If taking the data supplied by a life table, we construct a
curve representing the mortality of human beings at different
ages, we find that it takes a peculiar course. Erecting
perpendiculars at each age along a base line at heights which
are proportional to the death rates at these ages, we see
that our curve starts at a high point because the first year

DEATH RATES

241

TABLE 14. — LIFE TABLE FOR MALES AND FEMALES IN ILLINOIS, 1929-1931,

ACCORDING TO COMPUTATIONS OF THE METROPOLITAN LIFE INSURANCE Co.
(The probable expectation of life and death rates are given for the several ages.)

Age

Males

Females

Exp. of
life

Death
rate

Exp. of
life

Death
rate

59.02

60.30

62.82

46.28

61.78

9-l3

64.84

8.01

6i.34

5-23

64-36

4.71

60.66

4.22

63.66

3.46

59-91

3-35

62.88

2.95

59.11

2.84

62.06

2.52

54.78

1.72

57-63

i-3i

50.24

2.09

53.00

1.70

45.82

2.95

48.52

2-55

41.51

3-37

44.16

3.08

37.21

3-92

39-85

3-52

32.97

5.21

35-55

4-13

28.89

7.17

31-32

5-34

24.98

9.78

27.21

7.20

21 .26

I3-40

23.24

IO.OO

17.77

19.23

19.49

14.60

14.58

27.48

16.01

21.39

II .70

40.01

12.83

32.00

9-l8

58.25

10.02

48.31

7.02

86.55

7.60

74.17

5.29

128.55

5.66

116.67

3-98

183-43

4-23

167.61

3.02

249.88

3.06

234-74

of life is a very hazardous period. Then the curve slopes
downward quite rapidly, and afterward more slowly through
the years of childhood and reaches its lowest point about
age eleven. After this people begin to experience the effects
of really growing old. The death rate rises slowly through
the teens, more rapidly in middle life, and still more rapidly
in old age, until in the nineties it shoots upward with a
steep ascent. Curves of mortality vary with time and place,
but however high or low the general death rate may be,
they always preserve the same general form.

242 HUMAN GENETICS AND ITS SOCIAL IMPORT

Deaths are due to both hereditary and environmental
factors, but the main features of the mortality curve are
the product of internal causes. We are like clocks con-
structed to keep going for a certain length of time. Accident
or disease may bring us to an untimely end, but no amount
of care or coddling will enable us to live much beyond the
span which Nature has allotted us. Progress in medical
science has increased the average longevity of human
beings by several years, but this has been accomplished
largely through reducing mortality in infancy and childhood,
and to a less extent in adult and middle age. The expectation
of life in ages over eighty has changed very little. Even
in the most healthful of all possible worlds there would
probably be few centenarians. As Young has shown in his
volume On Centenarians most of the reported cases of
people, such as Thomas Parr, who are alleged to have lived
much over a hundred years are of very dubious validity.

The general death rate in Europe and America has been
declining for the past few hundred years, but the most rapid
decline has occurred during the nineteenth and twentieth
centuries. This is due to the more widespread diffusion of
education, and the progress made in curing diseases and
preventing their spread. The course of the decline for several
countries is shown in the following table:

TABLE 15. — DEATH RATES OF SELECTED COUNTRIES, 1841-1932

1841-
1850

1851-
1860

1861-

1870

1871-
1880

1881-
1890

1891-
1900

1901-
1910

1911-
1913

1921-
1925

1926-
1928

I932

England
France ....

22.4

2T Q

22.2
2-7 Q

22.5

2-? 6

21.4
2? 7

19.1

22 I

18.2

21 C

J5-3

IQ A.

13-8
18 i

12.2
17 2

II.9

1 6 Q

12. 0

ic 8

Germany
Sweden

26.8

20. 6

26.4
21 .7

26.9

2O 2

27.2

18 i

25.1

16 Q

•** • J
22.2

16 4

ly .4

I8.7
1.4. Q

10 . J

16.0

I "? Q

1 / • •*•
13-3
12 I

ii. 8

122

15'0

10.8

IT 6

Massachusetts

18.2

I9.4

19.8

19.6

18.9

±^.y

16.6

1 J -y
15.2

12.5

12. 0

II.5

A part of this decline is spurious since it results to some
extent from the changing age composition of the population

DEATH RATES

243

240
220
200
180

160

140

120

100

Underll-4 5^ 1014 15-19 20-24 25-2930-34 35-394044 45^9 5054 55-59 60-64 $tt 70-74 75-79 80 and

Years of Age over

FIG. 65. — Curve illustrating death rates at different ages in the United States in 1930.

(After Willcox)

100,000

90,000

20 30

40 50

Acie

FIG. 66. — Number of survivors of each age and sex out of every 100,000 born in the original
death registration states in 1901 and 1929. (.After WiehL}

244 HUMAN GENETICS AND ITS SOCIAL IMPORT

arising from the decline of the birth rate. As the proportion
of infants and young children becomes reduced, the death
rate in a population will also be reduced. Thus for several
years past, the age composition of the population of Europe
and the United States has been relatively favorable for a
low death rate. The populations of most countries are
growing older, i.e., the average age of people is increasing.
In the course of time this will cause the death rate to become
higher again when it leads to a relatively large proportion

81808-12

1828-32 1848-52

1888-92

1908-12 1927-28

1868-72
Years
FIG. 67. — Death rates of European countries, 1808 to 1928. (From Thompson.)

of people in the older age groups; but so long as the pro-
portion of people in the relatively healthy periods of life is
increasing, the death rate will fall.

One large factor in the real decline of the death rate is the
reduction of infant mortality. For several reasons it is
desirable to have a special index of the infant death rate.
Instead of being expressed in terms of thousands of the
population under one year of age, a matter which is difficult
to determine with much accuracy, it is customary to express
it as the number of infants dying in a year out of every
1,000 infants born during that year. Formerly infant mor-

DEATH RATES

245

tality was high everywhere, and in many regions it still
continues to be high. During the past few years it has
fallen rapidly in several countries. There has thus been
a partial compensation for the fall of the birth rate, although
the number of children kept from dying is far less than the
number who have been kept from being born.

TABLE 16. — INFANT MORTALITY RATES PER HUNDRED BIRTHS, 1871-1930

1871-
1880

1881-
1890

1891-
1900

1901-
1905

1906-
1910

1911-

J9'5

1916-
1920

1921-

1925

1926-
1928

1930

England and Wales.
Germany

14.9

27 4

14.2

22 C

!5-3

21 7

i3-8

IQ q

11.7

17 A.

II. 0

16 o

9.0

14. C

7-6

12 2

6.8

q 6

6.0

8 ±

France

17 2

16 7

16 A

11 Q

12 6

12 A

**• ->

12 I

y -v

7 8

Norway

IO. C

9.8

q .7

M-y

8.1

7 o

6 6

6 2

•4

r 2

•w

r o

/ • °
1 6

Italy

2O Q

iq r

17 6

16 7

I C 2

IA o

ICO

J • *
12 C

j iW
12 2

IO C

AJ -w

•*•• J

w< J

The reduction of infant mortality has often been assigned
as one of the causes of the declining birth rate. Where family

New Zealand

Sweden

United States

England and Wales

Trance

Germany

Italy

Japan

Roumania

Chile

0 20 40 60 80 100 120 140 160 180 200 220 240
FIG. 68.— Infant mortality rates (per 1,000 births) in different countries. (From Thompson.}

size is standardized, the death of a child often causes the
parents to desire another child in its stead. Hence the more
frequently children die the more frequently they will tend
to be born. On the other hand, it is often urged, especially
by the Neo-Malthusians, that a high birth rate tends to
cause a high infant mortality. Where there are many children
who have to be supported on limited resources, conditions

246 HUMAN GENETICS AND ITS SOCIAL IMPORT

in the home are apt to be less favorable for the health of
the children. With fewer children and a better standard of
living infant mortality is naturally reduced.

There is a general tendency for high birth rates and high
infant mortality rates to go together, although there are
occasional exceptions to this rule. This fact does not prove
that the high birth rate is the cause of the high infant mor-
tality or vice versa. Both may derive from a common cause
in the ignorance or improvidence of the parents. Under
primitive conditions of life many children are born and many
die. When people become more enlightened they regulate
the birth supply, and at the same time they prevent the
early death of more of their offspring. As in so many other
situations in human biology, the causal relations involved
do not all appear on the surface. A low infant mortality
may be partly caused by a low birth rate. Also a low birth
rate may be partly caused by a low infant mortality. But,
perhaps to a greater extent, both are caused by other factors.

Obviously death rates in infants and adults alike are
greatly affected by the surroundings in which people live.
Climate, food, diseases, parasites, and other hazards to
health, produce striking differences in the mortality rates
of different regions of the earth. The first attempt to con-
struct a canal across the Isthmus of Panama occasioned
such an appalling mortality among the workers that it
had to be abandoned. Through overcoming many environ-
mental causes of death, biological discoveries have now
made it safe to live in many regions formerly almost un-
inhabitable. Further discoveries will doubtless add to the
average duration of human life, but how much longer can
human beings hope to live ?

In 1930 the average expectation of life of white males
in the United States was 59.0 years and that of white females,
62.62 years. In 1901 it was 48.23 for white males, and

DEATH RATES

247

51.08 for white females. Over ten years had been added to
the average duration of life in three decades. In 1789 the
average expectation of life was estimated roughly to be
about thirty-five years. There have been some attempts to
project estimates of longevity into the future. According

190

1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932
Colored 185 151 161 131 132 108 110 117 113 111 112 100 106 102 102 96 86
White 99 91 97 83 62 72 73 73 67 68 70 61 64 63 60 57 53
FIG. 69. — The decline of the infant mortality rate (per 1,000 children born) in the white
and colored population of the birth registration area of the United States, 1916 to 1932.
The curves for the whites and the colored have similar ups and downs. The rise in 1918 was
due to the epidemic of influenza.

to the estimates of Whelpton, American whites of the year
1980 may expect to have an average longevity of seventy-
three years — which is a little better than the Scriptural
allotment of three score years and ten — but they cannot
look forward to much increase after that. When this happy
time arrives people in their eighties will be standing on every
street corner, and it might be found that there were too
many of them for the good of the country.

248 HUMAN GENETICS AND ITS SOCIAL IMPORT

One factor which affects mortality, as was pointed out
by the able vital statistician Dr. William Farr, is density
of population. The more thickly people are massed together
the higher will be their death rate. According to Dr. Farr,
the mortality of a population increases as the sixth root of
its density, but this rather venturesome attempt at mathe-
matical precision known as Farr's law has not been found
to be of general validity, especially under modern con-
ditions of life. Doubtless density of population is one con-

woo 1905 1910 1915 1920 1925 1930

FIG. 70. — Death rates in urban and rural areas in the Registration States of 1900, 1900 to

1930. (After Willcox.}

tributing cause of the relatively high mortality of people
living in cities. Where people are crowded together in the
slums, poverty, disease, and unfavorable surroundings
conspire to take a heavy toll of life, but in some cities many
people may live in limited areas in which conditions are
relatively wholesome. It is not surprising, therefore, that the
relation between density of population and the death rate
should be found to be of the most general character and
subject to many exceptions.

For a long period the death rates of urban dwellers have
been higher than those of their rural compatriots, so much
so that the populations of most cities, and especially large

DEATH RATES

249

cities, have been incapable of maintaining themselves
without being replenished from the surrounding country.
In general it is the rural areas which supply the material
for population growth, and since larger and larger propor-
tions of the population of most civilized countries are coming
to live in cities, the demographical effects of urbanization
constitute a factor of increasing importance in the biological
changes occurring in the human species.

For several decades over one-half of the population of
several European countries (England, Holland, Belgium,
Germany) have lived in cities. The population of the United
States has long been mainly rural (it was over 95 per cent
rural in 1800), but the census of 1920 showed that the
population was over 51.4 per cent urban and 48.6 per cent
rural. In 1930 it was 56.2 per cent urban and 43.8 per cent
rural. This enormous growth of cities, involving as it does a
decrease in the birth rate and an increase in the death rate
of ever larger proportions of the population, has acted as a
check upon the more highly civilized peoples of the earth.

The trend of urban mortality like that of mortality in
general has been downward, especially in recent years as is
shown in the following table.

TABLE 17. — DEATH RATES IN LARGE CITIES, 1866-1930

Date

Berlin

Paris

London

Vienna

1866-1870

31-9

26.8

24.4

34-2

1871-1875
1876-1880

3^-7
29-3

i „;,

22.5

32.9

1881-1885

26.5

24.4

21 .O

28.5

1886-1890

22.5

23.0

2O. O

25-5

1891-1895

20.5

21 .2

19.8

24.1

1896-1900

18.1

I9.I

I8.5

21. 1

1901-1905

17.0

17.9

16.1

I9.I

1906-1910

15.2

I7.8

H-7

I7.I

1921-1926

12. I

l6.4

12.2

I5.I

1930

II .2

13-3

II.9

13-4

250 HUMAN GENETICS AND ITS SOCIAL IMPORT

In some regions the urban death rate is lower than in the
surrounding rural area. This is frequently due to the favor-
able age composition of the city population. Dorn has shown
that in Ohio, for instance, the crude death rates of the
native whites were higher for both sexes in the rural than
in the urban population, but that if the rates are adjusted
for age composition the urban rates are higher than the rural.

TABLE 18. — DEATH RATES PER THOUSAND NATIVE POPULATION OF OHIO, URBAN

AND RURAL

Rate

Male

Female

Rural

Urban

Rural

Urban

Crude

II. 0

8-7

9-9

IO.O

10.5
8-3

8.8
8.6

Adjusted

In some respects city life frequently offers conditions more
favorable for low mortality than those of the country.
Nowadays, the water supply of most large cities is free
from the contaminations that were formerly responsible
for the spread of cholera, typhoid fever, and other diseases.
Inspection of the milk supply has aided in reducing mortality
in infancy and childhood, and the efficient health administra-
tion and superior medical services of many cities have gone
far toward overcoming the natural handicaps of urban life.
Also, in several regions the education and standard of living
are higher in cities than in the surrounding country. For
these and other reasons the relation between the mortality
of city and country is subject to much variation. In general,
death rates have fallen more rapidly in urban than in rural
areas. This is in part due to the simple fact that there
was more room for improvement. Even infant mortality
rates, which have usually been much higher in urban areas,
have now fallen so much the more rapidly in cities that they
are sometimes lower than in the surrounding country.

DEATH RATES

251

In the United States Registration Area for Births the urban
and rural rates of infant mortality as shown in the following
table have declined at unequal rates. Up to 1928 the urban
rates have been the higher. For the last few years, however,
the urban rates have been lower than the rural.

TABLE 19. — MORTALITY RATES OF WHITE INFANTS IN THE BIRTH REGISTRATION
AREA OF THE UNITED STATES, 1919-1932

1919

1920

1921

1922

1923

1924

1925

1926

1927

1928

1929

1930

i93i

1932

Urban

whites. .

Rural

whites..

So far as their death rates are concerned, there seems to
be no reason why cities should continue to be the centers of
extinction that they have been in the past. It is chiefly
their very low birth rate that makes cities such potent
destroyers of humanity. And there is little reason to con-
clude that urban birth rates will increase.

Suggested Readings

Newsholme ('23), chaps. 17, 19-21. Thompson ('35), chap. 12. Thomp-
son and Whelpton ('33), chap. 7. Willcox, ('33).

Questions

1. What information concerning longevity is furnished by a life table?
Look up your own expectation of life and your chance of dying within a
year. Compare these findings with your vital prospects when you reach age
sixty.

2. Look up the death rate and infant mortality rate of your own city
or town. How do births compare with deaths?

3. How would an increase of the birth rate affect the general death
rate? Explain. Would it necessarily involve an increase in the infant
mortality rate as the latter is commonly measured?

4. How would an increase of mortality after age forty-five affect the
marriage rate? the birth rate? the insanity rate?

252 HUMAN GENETICS AND ITS SOCIAL IMPORT

5. How would the death rate of a city be affected by the presence of an
insane asylum, a college, army barracks, a large cannery?

6. Why do you think that mortality is higher in unmarried men than
in the married ? Does this fact prove that marriage increases longevity ?

7. City A has a death rate of eleven per thousand and city B has a
death rate of fourteen per thousand. Is city A necessarily the more whole-
some place in which to live ? Explain.

8. If a city has a death rate of nine per thousand what inference would
you draw as to its age composition ? If there were no migrants into or out
of the city how would the death rate be likely to change in subsequent
years? Explain.

9. Compare for both sexes in the United States life tables for 1910,
1919-1920, and 1930 the expectation of life at ages ten, fifty, and eighty-
five. What do the results indicate as to the increase in the span of life as
compared with the increase in the average duration of life?

10. Is it likely that a community can maintain indefinitely a death rate
of ten per thousand inhabitants ? If so, what would be the average duration
of life?

11. Look up in any United States life table the death rates of the two
sexes, whites and Negroes, native-born and foreign-born inhabitants at
ages one, five, ten, thirty, fifty, seventy, eighty-five, and over. How would
you interpret these findings?

CHAPTER XIX
THE SELECTIVE ACTION OF MORTALITY

ACCORDING to the theory of natural selection pro-
<L\. pounded by Mr. Darwin, the differential death rate
plays a role of major importance in the evolution of life.
Darwin conceived of all organisms as engaged in a struggle
for existence, not merely against the forces of their environ-
ment, but with competitors of their own and other species.
"Owing to this struggle for life," he says, "any variation,
however slight, and from whatever cause proceeding, if
it be in any degree profitable to an individual of any species,
in its infinitely complex relations to other organic beings
and to external nature, will tend to the preservation of that
individual, and will generally be inherited by its offspring.
The offspring, also, will thus have a better chance of sur-
viving, for, of the many individuals of any species which
are periodically born, but a small number can survive. I
have called this principle, by which each slight variation,
if useful, is preserved, by the term of Natural Selection,
in order to mark its relation to man's power of selection.
We have seen that man by selection can certainly produce
great results and can adapt organic beings to his own
uses, through the accumulation of slight but useful variations,
given to him by the hand of Nature. But Natural Selection,
as we shall hereafter see, is a power incessantly ready for
action, and is as immeasurably superior to man's feeble
efforts, as the works of Nature are to those of Art."

Natural selection is regarded as an agency always acting
upon organisms, continually preserving adaptive variations

253

254 HUMAN GENETICS AND ITS SOCIAL IMPORT

that may arise and thus ever tending to bring about a
more adequate adjustment of the organism to its environ-
ment. Darwin believed also in the Lamarckian theory of the
transmission of acquired characters, but he thought that
this factor played a distinctly subordinate role in the
process of organic evolution.

FIG. 71. — Charles Darwin. (From photograph by Major Leonard Darwin.)

Whether Darwin's theory of natural selection affords a
satisfactory explanation of evolution is a much argued
question which we shall not attempt to discuss. That
organisms are preserved or eliminated as a result of differ-
ences in hereditary constitution has been abundantly
demonstrated by observation and experiment. There can
be no doubt, therefore, that natural selection is a force
which is in active operation in the organic world whether
we consider that it gives a sufficient explanation of evolution
or not.

THE SELECTIVE ACTION OF MORTALITY 255

Before discussing the operation of natural selection in
the human species it should be pointed out that in a broad
and general sense natural selection embraces both the
differential death rate and the differential birth rate. The
former aspect of the selective process was emphasized most
by Mr. Darwin, although it is clear that he conceived of
natural selection as including the latter as well. Since we
have considered the differential birth rate we shall confine
our attention to the selective action of mortality or, as it is
sometimes called, lethal selection, as contrasted with repro-
ductive selection, which is based on differences in reproduc-
tive rates.

One way in which the action of natural selection is shown
in man is through the inheritance of longevity. It is a well-
known fact that there are long-lived as well as short-lived
families. The matter has been subjected to a mathematical
investigation by Professor Karl Pearson who studied the
longevity of families listed in Foster's Peerage, Burke's
Landed Gentry, and, in connection with Miss Beeton,
in the Society of Friends. Correlation coefficients for length
of life were worked out for fathers and sons, fathers and daugh-
ters, mothers and sons, mothers and daughters, and for sib-
lings. The correlations found are given in the following table:

TABLE 20. — CORRELATIONS FOR LENGTH OF LIFE

Correlation

Father and son over 24, peerage 0.115 + °-°21

Father and son over 19, landed gentry o. 142 + 0.021

Brothers, peerage o . 260 + o . 020

Brother and adult son, friends o. 135 + 0.021

Brother and minor son, friends 0.087 i 0.022

Mother and adult daughter o. 149 + 0.020

Mother and minor daughter o. 138 + 0.024

Adult brothers 0.285 ± 0.020

Older and younger brothers 0.229 + 0.019

Adult sisters 0.332 + 0.019

Most of these correlations, as well as those found by Pearl
and others, are relatively low as compared with correlations

256 HUMAN GENETICS AND ITS SOCIAL IMPORT

for most physical and mental characteristics. This is due
in part to the large element of fortuitous mortality involved.
It is of interest that the correlations between siblings are
higher than those between parents and offspring, whereas
if the resemblances were due merely to heredity we should
expect about the same degree of correlation. One is hardly
justified in considering all of the correlations between
parents and offspring for length of life as due to heredity,
since a part of it may result from similarities of environ-
ment to which both parents and offspring are exposed.
There is also a danger of obtaining a spurious correlation
for longevity if we base our conclusions on data extending
over a period of time in which the average duration of life
has changed. In studying correlations for length of life in
royal families I have found that if we take only those individ-
uals living in a given half century, the correlations for
length of life are considerably less than those obtained by
including records covering two or more centuries. Doubtless
both heredity and environment conspire to cause longevity
to run in families, but it is difficult to obtain separate
measures of the extent of their influence.

According to Pearson, not only length of life, but general
health is inherited. There is also, as the studies of Pearson,
A. G. Bell, and others have shown, a tendency for longevity
to be correlated with fertility. Long-lived, healthy, and
fertile stocks, therefore, tend, other things equal, to prevail
over and supplant short-lived, unhealthy, and infertile
stocks. Of course, accidents, maleficent microbes, and other
causes of untimely death interfere with the truly selective
action of mortality. But, on the whole, natural selection is
ever acting to weed out the maladapted and to cause the
better endowed types to replenish the earth.

The operation of natural selection in man is also shown
by the fact that there are many kinds of hereditary defects

THE SELECTIVE ACTION OF MORTALITY 257

and disorders which lead to the elimination of their posses-
sors. Hemophilia, which is inherited as a recessive, sex-
linked character often results in death through bleeding
caused by a failure of the blood to clot. Natural selection,
therefore, tends to eliminate strains that inherit this defect.
Similarly, Huntington's chorea tends to be eliminated
although many individuals marry and transmit the defect
before their fatal malady overtakes them. Amaurotic family
idiocy probably depends upon a recessive gene and since the
trait is uniformly fatal very early in life, the strains which
carry it will tend, although very slowly, to die out. Several
other hereditary maladies are known which result in
death at various periods of life. However, there are
others that are responsible for deaths in early stages
of embryonic development as there are in several species of
animals.

A great deal of selective elimination results from hereditary
diatheses to germ diseases and other types of disorder. In
so far as tuberculosis depends upon a hereditary proclivity
to that extent natural selection tends to eliminate the more
susceptible elements of the race. How far the increasing
immunity of peoples long exposed to tuberculosis is due to
this cause is, however, difficult to ascertain. There are
hereditary diatheses to diabetes, heart disease, several types
of malignant growths, many nervous disorders, and other
defects and diseases, all of which reduce the chances of
survival. It may be said that natural selection is always
busy at the task of eliminating from the human race its
many kinds of hereditary defects and diseases. One might
suppose that since natural selection has been engaged in
this enterprise for many hundreds of thousands of years,
to say nothing of the millions of years before man became
man, the human race, by this time, would be freed of its
burdens of hereditary deficiency. Doubtless it would have

258 HUMAN GENETICS AND ITS SOCIAL IMPORT

been were it not for the appearance of new mutations,
most of which from the standpoint of survival, are either
indifferent or disadvantageous. In this respect man is in the
same situation as other organisms in which genetical study
has shown that new mutations, mostly unfavorable, are
being continually produced. Most of these new experiments
are speedily eliminated by natural selection. Only occa-
sionally does a mutation arise which better fits the organism
to survive in the struggle for existence. Hence, if all kinds
of variations were to survive and propagate, the disadvan-
tageous ones would gradually accumulate, and the species
would slump backward to a lower level of efficiency. This
tendency to slump which results from the cessation of natural
selection was called by Weismann panmixia. It represents
a factor which is always working in the interests of degenera-
tion, and to which the occurrence of rudimentary organs and
degenerate types of organisms was in part attributed.

It is commonly held that natural selection in man has
largely been set aside through our arts of saving lives. In
primitive men, whose survival often depends upon strength,
acuity of sense and mental alertness, such variations as
split hands, club feet, hereditary deafness and blindness,
or other disabling infirmities that are now perpetuated
through several generations, would be quickly eliminated.
Perhaps one reason why we are so heavily burdened by
defective heredity is because unfavorable variations have
been allowed to accumulate, which normally would have led
to extinction. Some writers are seriously concerned over the
prospect that our fostering the weak will cause the race to
become more and more decrepit as time goes on. There is no
danger, however, that we shall ever be able to eliminate en-
tirely the operation of natural selection, and the extent to
which we have been able to reduce its action has commonly
been exaggerated. To a large extent mortality has been re-

THE SELECTIVE ACTION OF MORTALITY 259

duced through the removal of causes of death whose action
is mainly fortuitous. Some causes of death like hemophilia
are highly selective; some, such as lightning are mainly
nonselective; and others are selective in various degrees.
The elimination of causes of death which are about as apt to
kill one person as another can do no racial damage, but if the
advances of medical science result in the increase of consti-
tutionally inferior people, there is no escape from the con-
clusion that they are responsible for a real danger to the race.
Probably this danger can be obviated by the proper eugenic
measures — but this matter belongs to a later stage of our
discussion.

In endeavoring to ascertain how civilization has influenced
the action of natural selection it is important to consider the
relation of mortality to levels of intelligence. The rate death
of low-grade imbeciles and idiots is relatively high. Of the
625 idiots and imbeciles concerning whom he had mortality
records Dr. Barr found that " the largest number of deaths
occurred between ten and twenty years; but comparatively
few passed the twenty-fifth year and exceptional cases
occurred from thirty to forty years." According to Clark
and Stowell the lowest grades of mental defectives in the
hospitals and schools of New York City have a death rate
four times as high as the feeble-minded in general, and
among the latter the death rate is about twice as high as
among normal children. Since the lowest types of mental
defectives are more or less pathological products, their
high death rate is to be expected. Dayton finds that in
Massachusetts the expectation of life of mental defectives
at two years of age increases as the degree of defect decreases.
For idiots it is twenty-one years for females and twenty
years for males. For imbeciles it is thirty-eight for females
and twenty-nine for males and for morons it is forty-six
for females and fifty-two for males, whereas in the general

26o HUMAN GENETICS AND ITS SOCIAL IMPORT

population of the state it is fifty-nine for females and fifty-six
for males.

Evidently natural selection is tending to get rid of mental
defectives. To a certain extent it is doing the same with the
insane. The death rate of inmates of asylums for the insane
is much higher than that of the general population of
corresponding ages. Epilepsy is not infrequently associated
with early death. And there are other nervous disorders
in which heredity plays a large part which either shorten
life or prevent marriage and the procreation of children.

Passing to the normal ranges of intelligence levels, we
find that in general there is an inverse relation between
intelligence and mortality. In the professional classes and
in such groups as English men of science studied by Galton,
American men of science studied by Cattell, and the people
whose names get into Who's Who> the death rate is low.
This is due not merely to the fact that as a rule a person
has to be twenty-five years old or more to be included in
these groups, but it is due to the greater life expectancy, age
for age, as compared with that of the general population.
It is safe to assume that these classes, with occasional
exceptions of course, are characterized by a degree of
intelligence somewhat above that of the rank and file of
human beings. So far as death is a respecter of persons,
we may conclude that in the highest and in the lowest mental
levels it is working in the way that the eugenist might
desire. How deaths are distributed in relation to levels of
intelligence within the broad belt of humanity lying between
these extremes, we have to judge mainly on the basis of
data on the mortality of the several occupational groups.
There are certain sources of error involved in the inter-
pretation of such data. Some dangerous trades take a heavy
toll of their workers quite irrespective of the intelligence
required in these pursuits. Agricultural laborers do not

THE SELECTIVE ACTION OF MORTALITY 261

rate very brilliantly on the basis of intelligence tests applied
to their offspring, but their death rate is low owing to the
wholesome nature of their work in a rural environment.
Besides, people often change their occupations. Early in
life they may be casual laborers, and especially in the
%United States they may rise from humble tasks such as
splitting rails to much higher employments. A comparison
of the crude death rates of different occupational groups is
especially apt to be misleading, because the age composition
of the groups is subject to great variation. There may be
many persons below twenty among unskilled laborers, but
practically none among doctors or lawyers.

We may take as typical of the general character of occu-
pational mortality the results of a study made by Dr.
T. H. C. Stevenson on the data supplied by the Census
of England and Wales in 1921-1923. A general sample of
the findings is shown in the accompanying table:

TABLE 21. — MORTALITY PER 100,000 OCCUPIED AND RETIRED MALES 15-65 IN
ENGLAND AND WALES, 1921-1923

Class

15-19

20-24

25-34

35-44

45-54

55-64

Infant mortality

142

*37

261

484

985

2,247

205

307

376

589

1,090

2,469

III

243

347

380

59°

1,070

2,508

248

367

420

669

1,173

2,482

299

408

498

880

M°7

3,061

It may be explained that Class I in the table includes the
upper and professional classes; Class III consists of skilled
artisans; Class V is composed of unskilled and casual
laborers; and the Classes II and IV include workers of a
status intermediate between those of Classes I and III,
and III and V respectively. The table shows that in each
group the mortality rises as we pass from the upper to the
lower occupational classes. The same general tendency is

262 HUMAN GENETICS AND ITS SOCIAL IMPORT

shown by the occupational mortality of other countries.
In so far, therefore, as these occupational groups are char-
acterized by different average levels of intelligence, we may
say that natural selection is operating on the basis of mental
endowments. It is a matter of interest and perhaps much
biological significance that the infant mortality in these groups
follows the same course as the mortality of the parents.

In our modern industrial world the morons and dull
normals are relatively poor actuarial risks. They gravitate

(0
L

i.
0

•15

C (/) (0

O QJ L

'S m cu
to in o

o o o

Commercioll
oi-Boiches

Merchants

Middle class
officials

Lower official

Unskilled

•10
-5

43 11.3 13.0 13.5 14.Z 18.9 Z4.\

FIG. 72. — Infant mortality rates per 100 births according to occupation in Prussia, 1912-
1914. (Data from Rot/.)

into the lower occupational groups in which the pay is
poor and in which living conditions are not the best. Besides,
their progeny suffer from a high infant and child mortality.
So far as its lethal aspects are concerned natural selection
tends to eliminate dull minds as it eliminates weak bodies.
It is not unreasonable to suppose that the effect of our
modern industrial development through creating a great
diversity of employments and subjecting human beings to
very unequal environmental influences has been to cause
natural selection to act with a greater degree of discrimina-
tion on the basis of variations in intelligence. When occupa-
tions were little diversified and most people followed similar

THE SELECTIVE ACTION OF MORTALITY 263

pursuits and lived in much the same way, the average lot
of the dull-normal individual was not greatly different
from that of the exceptionally intelligent. In our industrial
world inequalities of station are associated with differences
in mortality to a greater extent than is found in a less
highly differentiated economic order. We may have partly
overcome the action of natural selection in eliminating the
physically weak and abnormal, but at the same time we
may have made it more highly selective as regards levels of
intelligence.

Natural selection is not only hard on the moron, but also
on those whose peculiar emotional and temperamental
traits make them social misfits. In so far as criminals,
vagabonds, paupers, chronic alcoholics, and other types of
human wreckage are the victims of their unfortunate
heredity, it may be said that lethal selection is working to
rid society of these undesirables. Their mortality is relatively
high, and their children, when they have any, suffer from a
high death rate. Among women prostitution tends to
eliminate a class whose heredity on the average is probably
of a rather inferior sort. According to a number of studies
the intelligence level of prostitutes is low (most of them
come from the lower occupational groups), and there is a
considerable amount of mental abnormality, although how
far the latter is the cause instead of the effect of their calling
is uncertain. They are often sterilized by venereal diseases, or
their children suffer from a high mortality from inherited
syphilis and unfavorable surroundings. Although prostitutes
come from relatively prolific stocks, it is probable that as a
class they are not a self-perpetuating group — which is
doubtless a fortunate circumstance from both the racial
and the social point of view.

Many of the discussions on the role of natural selection
in man have been concerned with the selective operations

264 HUMAN GENETICS AND ITS SOCIAL IMPORT

of infant mortality. From the evolutionary standpoint,
it matters relatively little what happens to people after
they have ceased to reproduce their kind. The fact that
in the United States mortality after age forty-five has
been actually increasing, may be unfortunate for the welfare
of society and especially for the life insurance companies,
but it has little significance for biological evolution. Since
the large part of human mortality before the end of the
reproductive period occurs in infancy and early childhood,
the extent to which the death rate is selective during this
period is of especial biological importance. When we consider
the appalling death rate of infants in many regions and the
fact that all infants require much care and protection for
their successful upbringing, it is evident that many well-
endowed infants must perish along with the weaklings.
Moreover, many infants are exceptionally weak and puny
as a result of environmental causes such as premature birth
or temporary ill health of the mother. Once the perils of
early life are past these infants may develop into excep-
tionally strong and healthy individuals. As man gradually
evolved from lower forms, infants became progressively
weaker and in need of more and more care. Similar develop-
ments have occurred in many kinds of birds in which the
young are the most helpless and dependent of creatures
kept alive only by the active ministrations of their parents.
Infantile weakness of this sort is not related to any con-
stitutional inferiority of later life and evolution in the
direction of greater weakness in early life is entirely com-
patible with the biological advancement of the species.
It would be a mistake, however, to conclude that all infantile
inferiority has no evolutionary significance.

The problem of how far infant mortality is selective on the
basis of genetic differences has been the subject of much
controversy. The idea that any biological advantage might

THE SELECTIVE ACTION OF MORTALITY 265

result from the selective elimination of young infants is
viewed with evident alarm by many humanely disposed
people. They like to feel that progress in saving the lives of
helpless infants has not resulted in the accumulation of
inherent weaknesses or defects, and they are led to empha-
size, perhaps unduly, the nonselective character of infant
mortality. Those who contend that natural selection operates
in the first year of life have often been accused of advocating
the abolition of the hygienic procedures which have led to
the salvage of so many infant lives. It is one thing to point
out that the reduction of infant mortality has its racial
dangers and another thing to defend the barbarity of an
infant death rate that sweeps away every third or fourth
child. The question at issue can be settled by an appeal not
to sentiment but to facts. If the death rate in infancy is not
affected by genetic differences this period is unlike every
other stage of life. Deaths in infancy may be due to fortuitous
and nonselective causes to a greater extent than in subse-
quent years — this seems likely — but it is hardly reasonable
to suppose that hereditary factors are not responsible for a
part of the mortality occurring at this time. Amaurotic
family idiocy, which is commonly fatal in the first year of
life, is probably dependent upon recessive genes, and there
are other maladies that work in a similar way.

It has been shown in a number of studies that infant
mortality is relatively low in long-lived stocks. Data col-
lected by Ploetz from royal and princely families in Germany
indicate that where children were raised under as favorable
conditions as the times afforded, the mortality under five
years of age decreased as the age at death of either the
father or the mother increased. The relations are shown in
the subjoined table. Much the same relations were disclosed
in families of the middle class. In studying the inheritance
of longevity in New England genealogies I find that as a

266 HUMAN GENETICS AND ITS SOCIAL IMPORT

TABLE 22. — CHILD MORTALITY AS RELATED TO THE MORTALITY OF CHILDREN IN
ROYAL AND PRINCELY FAMILIES

Longevity of parents

16-25

26-35

36-45

46-55

56-65

66-75

76-85

and

Totals

over

Children of mother:

Number of children. . .
Died before six years . .
Per cent dying

20
29.9

396
133
33-6

403
116
28.8

5*7
163
3i-5

712
194

27.2

601

1 60
26.6

387
87
25-5

67
4
6.0

3,15°

877
27.8

Children of father:

Number of children. . .
Died before 6 years . . .
Per cent dying

23
12

52.2

90
29

32.2

367
"5

3i-3

545
171

3i-4

725

200
27.6

983
254
25.8

444
105
23-6

33
i

3-o

3,210

887

27.6

rule the infant death rate is low as the age at death of the
parents increases. The relations were as follows:

TABLE 23. — PARENTAL LONGEVITY AND INFANT MORTALITY ACCORDING TO NEW
ENGLAND GENEALOGIES

Longevity of parents

10-25

25~35

35-45

45-55

55-65

65-75

75-85

85-

Fathers:
No. of children

2
5O.O
13

5
38.46

i7
24.29

93
32
34-40

168

38
23.17

J45

31-03

268

66
24.63

185

36
19.46

388

77
19.84

290
46
14.86

547
96

J7-55

408
70
17.16

560
no

19.64

501

19.16

253

35
13-83

337
53
15.72

Number dying under 5 years. .
Per cent dying under 5 years. .
Mothers:
No. of children

Number dying under 5 years. .
Per cent dying under 5 years. .

From the preceding data it seems likely that the genetic
constitution which enables people to attain long life also
helps their infants to escape the perils of the hazardous
first year.

In some studies made by Pearson, Snow, and Crum
an attempt has been made to demonstrate the action of
natural selection in early life by showing that there is a

THE SELECTIVE ACTION OF MORTALITY 267

negative correlation between the infant death rate and the
later mortality of childhood, the inference being that when
more children die in infancy the survivors are less apt to
die later on. This conclusion has been attacked by a number
of critics who for the most part have advanced irrelevant
arguments against it and have failed to call attention to its
most vulnerable point of attack, namely, the fact that
several causes of infant deaths, such as the infectious
diseases of children, confer an immunity upon the survivors.
If, for instance, children are exposed to measles at age one
and again at age five, fewer will die from measles at the
latter age, not necessarily because measles removed the
weaklings at age one, but because the group has been
immunized and hence protected against a later attack.
On account of the influence of immunity we may conclude
therefore that the existence of a selective death rate is not
proved by the negative correlation referred to; neither is it
disproved. There is a certain presumptive evidence of a
differential death rate based on variations in vitality afforded
by the ratio of male to female deaths in early, life. At this
time boys are more prone to die than girls — a fact for which
Nature seems to have made provision in that more boys
than girls are born. The sex ratio at birth is about 105 to
106 boys to 100 girls. In deaths during the first year the
ratio of boys to girls varies from nearly 140 to about no.
The lower the mortality rate the higher is the ratio of boy
deaths to girl deaths. It is a striking fact that the sex ratio
at death is highest soon after birth and falls rather rapidly
after the second or third month to the twelfth, and after
that more slowly through the years of childhood. The sex
ratio at death in the United States (1916-1923) was as
follows for the several subdivisions of the first year:

Month o-i 1-2 2-3 3-5 6-8 9-12
137.2 138.4 134.1 130.6 123.4 116.6

268 HUMAN GENETICS AND ITS SOCIAL IMPORT

In stillbirths the sex ratio (boys to 100 girls) is high.
If we follow the course of sex mortality back into uterine
life, we find that it is high in early abortions (of about the
fourth month or pregnancy), and decreases until about the
seventh month, after which it rises until the critical period
of birth. In the U. S. Registration Area for Births the sex
ratio of abortions over a period of several years were 375
for the third month, 210.6 for the fourth, 145 for the fifth,
a lower ratio for the sixth, and the lowest of all for the
seventh, 118.4. After this it rises, being 121 in the eighth
month and 137.9 in the ninth.

The high death rate of boy babies has been attributed
to the fact that they are a little larger than girl babies and
have somewhat larger heads. Hence they are more apt to
suffer from the ordeal of birth, which is often a severe one
for the child as well as the mother. The sex ratio of children
dying from injuries at birth in the Birth Registration Area
of the United States from 1914 to 1923 was 161.6 in whites
and 155.9 m Negroes. Evidently, therefore, birth injury
is one source of high male mortality in infancy, but this fact
cannot explain the very high sex ratio of early abortions.

Why, therefore, do boys die so much more frequently than
girls both in utero and in infancy and childhood? It has
been suggested that this may be due to recessive sex-linked
factors. It has also been suggested that boys are inherently
weaker than girls as a result of the peculiar chromosome
complex which causes them to be boys. From all causes of
death (with the exception of whooping cough and, for ana-
tomical reasons, gonococcus infection) boys die more readily
than girls — a circumstance which is indicative of a greater
constitutional weakness. This greater physical toughness
of the female is characteristic of the human species through-
out life, as may be seen by consulting any life table. There
are more women than men in the older age groups, and

THE SELECTIVE ACTION OF MORTALITY 269

their expectation of life in the eighties is higher than that
of men.

During infancy there is much variation in sex mortality
from different causes of death. The sex ratio is high for
malformations of the heart 143.8, intestinal obstructions
162.8, hernia 371.2, nervous diseases 134.6, nephritis 147.3,
and relatively low from external causes 113, and some
epidemic diseases. That the sex ratio is high in proportion
as the general infant mortality rate is low may be explained
on the ground that as nonselective or partly selective causes
of death are removed, the death rate which remains in
spite of all efforts to reduce it is based to a relatively
greater extent upon genetic differences associated with
sex. It would seem probable that causes of death which
are responsible for a high lethal sex ratio are also selec-
tive within each sex on the basis of inherent differences in
vitality.

There is a kind of selective elimination in infancy not
directly connected with toughness of constitution on the
part of infants themselves, but which may be of great
importance from the racial standpoint, namely, selection
on the basis of parental intelligence. A young moron may
be a tough and husky physical specimen, but if he is born
to parents who are also morons, his chances of surviving
infancy are thereby considerably reduced. Poor food,
inadequate care, the wrong kind of treatment during illness,
and other disadvantages resulting from the ignorance and
stupidity of parents, are responsible for the deaths of many
physically normal infants. Natural selection, therefore,
bears heavily upon the progeny of the dull and stupid.
As we pass up the scale of the various occupational groups
we find a steady decrease in infant mortality as in the
mortality of adult life. In a broad and general way infant
mortality is correlated with parental intelligence although

270 HUMAN GENETICS AND ITS SOCIAL IMPORT

this relationship is obscured by the effect of poverty and
its attendant drawbacks. It has been shown in several
investigations that infant mortality is strongly associated
with low wages of the father. In a study of infant mortality
in seven large cities of the United States the relation of the
infant death rate to the earnings of the father as well as the
race and nationality of the mother were found to be as
indicated in the following table:

TABLE 24. — INFANT MORTALITY RATES IN SEVEN CITIES ACCORDING TO THE COLOR
AND NATIVITY OF THE MOTHER AND THE EARNINGS OF THE FATHER1

Mortality rates

Earnings

Total

Native white

Foreign-born white

Colored

Average . . .

I IO.O

q-} q

121.7

IC2. 1

Under $450

166.9

170.0

167. 1

162.7

$4CO-$C4Q. . .

I2C.6

121 .O

118.4

l63.7

$CCO-$64Q. .

116.6

no.8

121 .8

122.8

$650-1849

107.5

99-5

119.6

102.7

$8CO-$I,O4q. . .

82.8

76.4

Q4-Q

$I,050-$I,249

64.0

62.6

68.4

$1,250 and over. . . .

59-1

57-6

6o.O

No earnings

210.9

187.5

234.2

i After Woodbury.

It is unquestionable that the striking differences in infant
mortality rates here indicated are to a large extent the
result of the social, economic, and educational status of the
family. How far differences in intelligence levels may be
responsible for differences in infant mortality within each
group we do not know. Infant mortality has been found to
be correlated with many things, i.e.y poverty, educational
status, age of parents, high birth rate, interval between
births, order of birth, employment of mothers, overcrowding,
and breast feeding. The problem of disentangling all the
causes involved is beset with formidable difficulties. Pearson
has found that there is a correlation of 0.21 between infant

THE SELECTIVE ACTION OF MORTALITY 271

mortality and the use of a "baby pacifier, an India rubber
tantalizer, and a bacilli collector pushed between the baby's
lips, at which it sucks ineffectively and indefinitely." Do
the baby pacifiers kill the babies, or are both high mortality
and the use of these devices associated with the ignorance
and carelessness of the mothers ? The latter seems to be the
more probable conclusion. To how great an extent poverty,
ignorance, and various other factors involved have a real
causal connection with infant mortality is capable of only
a partial solution. Ashby in his volume on Infant Mortality
has remarked that "The unanimous verdict of the doctors
who made the observations are that neither the surroundings
of the infant nor the exact character of the milk obtained
were as important factors in the health of the infant as the
intelligent character of the mother." Even amid squalid
surroundings — perhaps even more there than elsewhere — the
intelligence of parents has much to do with the survival of
their offspring.

In the light of the facts set forth in the present chapter
we may conclude that on the whole the action of the differen-
tial death rate is eugenic in that it eliminates both the
physically weak and the mentally dull. But lethal selection
alone does not determine the direction of biological evolu-
tion. This is due to the combined action of lethal selection
and reproductive selection, or natural selection in the broader
inclusive sense of this term. In our modern life these two
factors frequently work at cross purposes. From the evidence
available reproductive selection is as a rule the more effective
influence. When we consider the proportions of surviving
children we find that the high birth rate classes usually
have the greater net fertility despite their higher mortality.
The net reproductive rates for six large occupational classes
in the United States for 1928 have been calculated by
Lorimer and Osborn as follows:

272 HUMAN GENETICS AND ITS SOCIAL IMPORT

TABLE 25. — NET REPRODUCTIVE RATES IN DIFFERENT OCCUPATIONAL CLASSES

Net

Reproductive
Class Rate

Professional o . 76

Business and clerical 0.85

Skilled labor 1 .06

Semiskilled labor 1 .03

Agriculture 1 . 32,

Unskilled labor 1.17

The two first groups are not reproducing themselves and
will have to be recruited from the lower groups, thus draining
them of the more intelligent hereditary strains that they still
possess. This situation which is characteristic of our present
industrial age, whatever it may have been in past times,
may possibly be a temporary phase. In some countries,
as we have seen, the recent decline of the birth rate has been
more rapid in the lower social classes. A similar trend is
observed in infant and child mortality. When infant mor-
tality is as low as 40 per thousand it is difficult even were it
racially desirable to reduce it much further, but where it is
150 to 200 it readily yields to improved conditions of nurture.
Not improbably the death rate as well as the birth rate
may come to be more nearly on the same level in the pro-
letariat and in the upper and professional classes. We may
hope that the net results of the selective processes will be on a
more eugenic basis than they seem to be at the present
time.

Suggested Readings

Darwin ('96), chap. 4. Dublin ('17). Holmes ('30), ('31), ('33), chap. 5.
Pearson, ('12).

Questions

1. Why, according to Darwin, does natural selection cause varieties to
diverge until they become distinct species?

2. In what way does the theory of natural selection explain the evolu-
tion of adaptive structures ?

THE SELECTIVE ACTION OF MORTALITY 273

3. Why did Darwin concede that natural selection cannot account for
a character in a species primarily of value only to some other species ?

4. Does a high death rate necessarily imply that natural selection is
in active operation ? Explain.

5. Mention six selective and six mainly nonselective causes of death
in man in addition to those referred to in the text.

6. In what ways does natural selection act differently from the way it
acted in former times ?

7. Can voluntary selection ever compensate entirely for the action of
natural selection ?

8. What characteristics have been explained on the theory that natural
selection acts upon groups instead of upon individuals per se?

9. How do you think the race would be affected by a reduction of
infant mortality to twenty per thousand births ?

10. What reasons are there for thinking that natural selection is active
during embryonic development?

11. Mention ten hereditary defects of the eyes. Do you think that such
defects are liable to accumulate in the future?

12. What ground do you think there is for concluding that man faces
"a bald and toothless future"?

13. What do you think will be the racial effect of obstetrical procedures
to facilitate childbirth?

14. Discuss the possible atrophy of the mammary glands in the future
of the human species.

15. From the standpoint of biological fitness is it better for the human
species to live under conditions which entail a high death rate ?

CHAPTER XX

THE BIOLOGICAL EFFECTS OF WAR

IN CONSIDERING the influence of war on the biological
evolution of the human species it is important to remem-
ber that by nature man is a fighting animal. Nature has
equipped many kinds of animals with fighting instincts and
special weapons for offense and defense which are convincing
testimonies as to the importance of conflict in the struggle
for life. The horns of deer, sheep, and cattle, the protective
mane of the male lion, and the powerful tusks of the wild
boar are all structures whose development has doubtless
been determined by their service in encounters the issue of
which is often a matter of life or death. Anger with its
concomitant the fighting instinct is a common attribute of
higher types of animal life. Typically anger is aroused by
some sort of interference. The dog resents the removal of
his bone, and the large male sea lion drives away all rivals
for any of the females that he has managed to appropriate.
Children usually get on well together until one child takes a
plaything belonging to another or otherwise interferes
with some privilege or the free exercise of some activity,
and then there is trouble. We may consider the fighting
instinct as one expression of the will to live. Its biological
usefulness is obvious, especially in a world in which no rights
are respected that cannot be defended.

One of the most conspicuous features of the fighting
instinct in animals is that it frequently takes the form of
group pugnacity. This is especially true with animals that
live in social groups. Most insects are quite devoid of com-
bative propensities. The struggles of the predatory forms

274

THE BIOLOGICAL EFFECTS OF WAR 275

to overcome their prey cannot properly be described as
fighting; they are merely incidental to the regular business
of procuring food. Most insects cannot be provoked to
resist any kind of interference, but among the social insects
it is a different matter. Highly social groups have been
independently evolved in the insects among the ants, the
bees, and the wasps, and also among the remotely related
termites. And all these insects exhibit a high degree of
pugnacity. Nevertheless, an ant, bee, wasp, or termite
rarely resents an interference with its activities as an individ-
ual, but its ire is at once aroused by any danger threatening
the habitation of its group. Stir up a hornet's nest, an
anthill, a bumblebee's nest, or a group of termites, and the
hostile reaction will be prompt and decided. These insects
are ready to fight to the death in the defense of their group;
and in many species of both ants and termites a special
caste of warriors with large heads and strong jaws has been
evolved in the service of defense. The pugnacity of these
creatures has nothing of self seeking; it is almost entirely
altruistic. Nature has endowed them with instincts which
lead them to risk their lives that their fellows may be
protected. Individuals are pawns in the game and are
sacrificed with little hesitation in order that the game may
be won.

In the insects, group pugnacity has been evolved pari
passu with the development of social life. It goes along with
instincts for mutual aid upon which all highly developed
social life depends. The same principle is also manifested
among the less highly socialized birds and mammals. A
timid bird may fly in the face of an enemy which threatens
her young.

For the poor wren,

The most diminutive of birds, will fight,

Her young ones in the nest, against the owl.

276 HUMAN GENETICS AND ITS SOCIAL IMPORT

Among chimpanzees which commonly run in troops there
is a strong tendency for individuals to keep closely asso-
ciated, and an attack made upon any member brings the
whole crowd upon the offender. Among chimpanzees kept
in captivity a newcomer is regarded with suspicion if not
positively attacked, but after a time the stranger becomes
adopted as one of the group. The rule with these social
animals is helpfulness toward members within the group and
hostility to outsiders. To a certain extent this is the rule
also among tribes of primitive men. In fact, a certain degree
of clannishness is characteristic of all human beings, however
cultivated.

According to the Darwinian theory the social sympathy
and instincts for mutual aid in social animals have developed
because of their utility in promoting social solidarity and
effective cooperation. In the struggle for existence group
is pitted against group, and those having the instincts
leading to mutual support tend to supplant other groups
with less cooperation. A society in which each member
promotes the welfare of his fellows is more apt to survive
than one in which each individual is concerned exclusively
with his own welfare. As Karl Pearson has remarked in his
excellent lecture on National Life from the Standpoint of
Science, "The safety of a gregarious animal — and man is
essentially such — depends upon the intensity with which the
social instinct has been developed. The stability of a race
depends entirely on the extent to which the social feelings
have got a real hold on it. ... No tribe of men will work
together unless the tribal interest dominates the personal
and individual at all points where they come into conflict.
The struggle among primitive men of tribe against tribe
evolved the social instinct. The tribe with the greater social
feeling survived; we have to thank the struggle for existence
for first making man gregarious, and then intensifying,

THE BIOLOGICAL EFFECTS OF WAR 277

stage by stage, the social feeling. Such is the scientific
account of the origin of our social instincts; and if you come
to analyze it, such is the origin of what we term morality;
morality is only the developed form of tribal habit, the
custom of acting in a certain way toward our fellows, upon
which the very safety of the tribe originally depended."

From the Darwinian standpoint, which is so clearly
expressed in the passage quoted, both man's fighting instinct
and the higher qualities which lead him to give unselfish
service to his fellows are alike produced by natural selection
for the sake of their survival value in the struggle for exist-
ence. If this be the true interpretation of why we are both
kindly and pugnacious, conflict must have played an impor-
tant part in making man a social animal. Even the gentlest
and most unselfish of the original impulses of human nature
may be viewed as products of the intergroup struggle for
survival. To express the matter in somewhat cynical terms
we may say that it pays to be kindly to one's fellows in order
to be more effective against one's enemies.

During the long period of human evolution before the
beginnings of recorded history, conflicts must have occurred
between relatively small groups. This is true of primitive
peoples today. Only in advanced stages of civilization is it
possible for peoples to become welded together into large
organized societies. When this is done the working of group
selection suffers marked changes. And with the progress of
invention there came to be great changes also in the methods
of waging war. In the hand to hand encounters of primitive
men the strongest and most resourceful contestant was the
most apt to survive and hand on his traits. Victory often
meant the extermination or enslavement of at least the men
of the conquered group, although the Children of Israel
were rather more thorough in killing the men, women, and
children of their unfortunate enemies. Wars of extermination

278 HUMAN GENETICS AND ITS SOCIAL IMPORT

have been carried on by some tribes of North American
Indians, the Dyaks, and other primitive peoples, but even
among most savages the victors usually spare the women and
children and often many of the men of the conquered tribe.
Not infrequently there is a mingling of the blood of the
victors and the vanquished, but notwithstanding this fact
primitive warfare is, on the whole, probably eugenic in its
effects. With the advance of civilization the biological
effects of war become subject to many changes. As was
pointed out by Herbert Spencer "Though, during bar-
barism and the earlier stages of civilization, war has the
effect of exterminating the weaker societies, and of weeding
out the weaker members of the stronger societies, and thus
in both ways furthering the development of those valuable
powers, bodily and mental, which war brings into play, yet
during the later stages of civilization, the second of these
actions is reversed. . . . But when the industrial develop-
ment has become such that only some of the adult males
are drafted into the army, the tendency is to pick out and
expose to slaughter the best-grown and healthiest; leaving
behind the physically-inferior to propagate the race."

The dysgenic effects of modern warfare to which Spencer
calls attention have been strongly emphasized by many
recent writers. Dr. D. S. Jordan devoted much of the energy
of his later years to setting forth the destructive biological
influence of war. In collaboration with H. E. Jordan he
made an inductive investigation of the actual effects of the
Civil War on the population of a selected area of Virginia.
It was shown that the leading men of the community were
the first to enlist, and that a large percentage of them
(20 to 40 per cent) died before the close of the war; that
war took the physically fit, the unfit remaining behind;
that the volunteers, who were on the whole superior as
soldiers to the conscripts, suffered more severely, and that,

THE BIOLOGICAL EFFECTS OF WAR 279

on the whole, "the men of highest character and quality
bore largely the brunt of the war and lost more heavily
than their inferiors." University men both north and south
volunteered in large numbers early in the war, and their
death rate in battle was higher than that of the rank and
file of the soldiers. During this war the South especially

FIG. 73. — David Starr Jordan. (From Eugenics.)

suffered grievously from the loss of its best man power, a loss
which will continue to be felt for many years.

The removal of those fit for military service tends to give
the unfit, the deserters — there are many of these in all wars —
and those who contrive through lack of courage or patriotism
to avoid participation in the struggle, a greater opportunity
to marry and beget offspring. According to Lenz, modern
warfare, instead of causing men to be more courageous and
patriotic has the reverse effect, since those possessing these

280 HUMAN GENETICS AND ITS SOCIAL IMPORT

socially desirable qualities are eliminated, while those
lacking them tend to be spared to hand on their qualities
to their descendants. Hence war would make a people less
warlike. This might not be a matter of regret if it did not
involve the sacrifice of other qualities, which the race can ill
afford to lose.

As to the effect of selective elimination on those taking
part in battle the data for different wars are not in entire
agreement. The losses among officers are commonly greater
than among the common soldiers, except in the case of
generals and other superior officers who are usually at a
safe distance behind the firing line. The German storm
troops, who were an exceptionally efficient group, sustained
much higher losses than the average soldiers during the
World War. The losses in the flying corps were terrific,
and also among the picked men who manned the submarines.
Of those who entered service from the universities and
gymnasia of Germany, it is estimated that not more than
half were living at the close of the war. The flower of the
youth from the universities of France, England, Belgium,
and Austria suffered an exceptionally high death rate; and
in the United States, which suffered relatively little, the
losses among the college youth, to judge from the studies of
Hunt in the case of Harvard University, were higher than in
the rank and file of the soldiers.

The losses sustained by armies are by -no means restricted
to the battle field. Most wars have been accompanied by
epidemics of various kinds which have often proved to be
more fatal than the attacks of the enemy. In the Spanish-
American War several times as many soldiers died of diseases
as were killed by the Spaniards. During the Crimean War
four times as many soldiers died of diseases as were killed
at the front. With the advance of medical science the
proportions dying of disease in recent years have been

THE BIOLOGICAL EFFECTS OF WAR 281

greatly reduced. Despite the length of the World War
only about a tenth of the losses of the Germans were due to
disease, although the armies of some of the other nations
suffered more severely.

In considering the selective effects of mortality due to
war one must reckon with the deaths occasioned in the
civil population. During war there is commonly an increased
death rate and especially an increase of infant mortality
among the noncombatants. As a result of the Thirty Years'
War the population of Germany was reduced to one-half
or one-third of its former numbers. Owing to circumstances
growing out of the World War the civil population of Russia
lost many millions. Usually it is the civil population of the
defeated countries which suffers most severely. Doubtless
the greatest handicaps are in all cases borne by the eco-
nomically poorer classes, but beyond this fact there is little
to indicate how the selective action of mortality works
out in the general population. If a severe ordeal leaves a
stronger race of survivors, war may have a eugenic influence
on the civilians which may counteract, to a certain extent,
its dysgenic effects upon the combatants. We know little
concerning the way in which selection works in the nation
at large, and it may work very differently in different cases.

This is probably true also of the mortality on the firing
line. Losses occurring in armies composed of more patriotic
volunteers may be highly dysgenic, whereas those sustained
by an army raised by a draft which spares the more intelli-
gent and competent persons engaged in industry may
not be more dysgenic than the death rate in normal times.
Whether our army in the World War had as high an average
intelligence as the male population in general is very doubt-
ful. The extent to which military selection is dysgenic, and
even whether it is dysgenic at all, depends on circumstances
which vary from war to war. The dysgenic effects of war

282 HUMAN GENETICS AND ITS SOCIAL IMPORT

have often been greatly exaggerated. That, as has been
contended, Greece, Rome, and other ancient countries fell
as a result of degeneration caused by the loss of their best
men who were killed in battle is a very questionable generali-
zation. Whatever decadence these people suffered was
probably due much more to a differential birth rate than
to a differential death rate. Probably war often works
dysgenically, but it is by no means the greatest of dysgenic
ills.

Thus far we have considered only the effect of war on the
genetic constitution of the individuals composing the group.
But war is not merely a struggle between individuals, for
tribe contends against tribe and nation against nation.
Organized groups function as units in the struggle for
existence, and, granting that war takes the best within each
group, if it leads to the replacement of an inferior by a
superior people, it may result in biological advancement.
During the course of history there has been a successive
replacement of one kind of people by another. In so far
as war leads to the survival of better endowed stocks it
may be said to be an important factor in the biological
evolution of the human species.

That war constitutes ari indispensable agent of progressive
evolution is the favorite thesis of those who defend it upon
biological grounds. Conspicuous among these is General
Bernhardi whose book Germany and the Next War attracted
widespread attention just before the conflict of 1914. "In
the extrasocial stuggle, in war," says General Bernhardi,
"that nation will conquer which can throw into the scale
the greatest physical, mental, moral, material, and political
power, and is therefore the best able to defend itself. War
will furnish such a nation with favorable vital conditions,
enlarged possibilities of expansion and widened influence,
and thus promote the progress of mankind; for it is clear

THE BIOLOGICAL EFFECTS OF WAR 283

that those intellectual and moral factors which insure
superiority in war are also those which render possible a
general progressive development. . . . Without war inferior
or decaying races would easily choke the growth of healthy
budding elements, and a universal decadence would follow.
. . . Might is at once the supreme right, and the dispute
as to what is right is decided by the arbitrament of war.
War gives a biologically just decision, since its decisions
rest on the very nature of things."

However the process of group selection may have operated
in past times, modern warfare rarely leads to the replace-
ment of one people by another. A defeated nation may
suffer loss of territory and have to pay indemnities, but its
population may go on increasing and may grow more
rapidly than that of its victorious rival. Consider the wars
that have occurred in the modern history of Europe. The
inhabitants of no country have been exterminated as a
result of defeat. From the biological standpoint a country
may be said to be victorious whose population is caused to
multiply the more rapidly as the result of a war. It frequently
happens that the military victory is won by one country
and the biological victory by another. Moreover, most
European nations are composed of a variety of ethnic
elements so that only to a minor degree do conflicts occur
between natural groups. A conflict along lines of real bi-
ological cleavage would throw each country in Europe into
a many-sided civil war. From the biological standpoint all
the bloody wars by which Europe has been devastated
have resulted only in a futile waste of life. Certain countries
may gain power, wealth, and prestige as a result of a suc-
cessful war, and these are the chief things for which they
fight; but when these ends have been attained terms of
peace are agreed upon which usually have no relation to
or concern with the biological stuggle for existence. As a

284 HUMAN GENETICS AND ITS SOCIAL IMPORT

matter of fact victory or defeat has usually had little
relation to population growth.

Where humanitarian considerations have prevented the
extermination of the vanquished or their forcible expulsion
from the conquered territory, group selection of the kind
postulated by the proponents of the biological value of
war simply does not work out. An exceptional case is pre-
sented when primitive people of a sparsely settled country
are conquered by a more highly civilized nation. It cannot be
doubted that the Anglo-Saxons were enabled to increase
greatly in numbers owing to a series of successful conflicts
with the aboriginal inhabitants of North America, Australia,
and New Zealand who resisted their advance. The result
was that a primitive people was largely supplanted by those
of a higher culture. To a less extent wars of this type have
led to the increase of the Spanish, Portuguese, and French
in the foreign lands which they acquired through conquest.
But conditions favorable for this sort of racial replacement
are growing distinctly less as civilization advances. During
the past four centuries primitive peoples in many regions
have given way before the advance of the whites. Most
parts of the tropics are unsuitable for permanent colonization
by members of the white race. The policy of the whites
has been to control and exploit these regions, and so long
as such efforts are successful the tropics may contribute
to the support of an increased white population. In almost
all parts of the world in which whites control dependencies
having a large number of colored inhabitants, the originally
hostile relations have been succeeded by a reign of peace.
In the exploring and settling period the relations of whites
and aborigines were mainly antagonistic. As a result, native
peoples in many parts decreased in numbers. Many tribes of
American Indians have become greatly reduced in numbers
or completely eliminated. The Australian aborigines have

THE BIOLOGICAL EFFECTS OF WAR 285

been decreasing in numbers as the white population has
grown and extended its domain. The Tasmanians are
completely gone. Throughout Polynesia and Melanesia
an extensive depopulation has been going on which has
threatened with extinction the inhabitants of many islands.
In large parts of Africa that have been raided to supply the
slave trade there has been a marked decrease of the native
population. The whites have proved to be a deadly scourge
to many of their less enlightened competitors. As a result
of the advent of the whites, native peoples have suffered
not only from war but from the forcible recruiting of labor,
alcoholism, the demoralization of established customs,
and from many diseases which at times have decimated their
ranks. During its expansion the white race has wrought
fearful havoc upon many primitive peoples. In this period
natural selection in the form of racial replacement was in
very active operation and resulted in rapid and extensive
changes in the population of the globe.

But the succeeding period of peaceful relations presents
us with a very different spectacle. Under the settled con-
ditions of white control the natives, instead of being driven
to the wall, have come to receive many advantages through
their association with a more highly developed race. Medical
science and sanitation have contributed greatly to reduce
the death rate. Internecine wars have been largely abolished.
Humane and considerate treatment has replaced the original
relations of hostility; but more important than all these
is the fact that through the development of natural resources
the whites have made it possible to support a much larger
indigenous population than was formerly able to subsist.
Native peoples are coming to work into advantageous
industrial relations with their white employers, and the
whites have come to recognize in native labor a valuable
financial asset which it is profitable to conserve and increase.

286 HUMAN GENETICS AND ITS SOCIAL IMPORT

Natives have gained much from the economic opportunities,
medical services, educational advantages, and stable ad-
ministration afforded by the more enlightened peoples in
control. The status of primitive peoples has gradually
changed from that of enemies that must be overcome to
members of an industrial society enjoying in common with
the whites the benefits of peaceful cooperation.

It is doubtless owing in large part to this change of status
that the primitive peoples of various parts of the world
have come to show a positive increase after a period of
declining numbers. The widespread depopulation going
on in the islands of the Pacific inhabited by Polynesians
and Melanesians has given place in most islands to a surplus
of births over deaths. The Maoris of New Zealand, who have
frequently been referred to as a disappearing race, have
been increasing for several years, and the 1931 Yearbook
of New Zealand states that they have been increasing more
rapidly than the Europeans. The native inhabitants of
Java have increased over tenfold under the administration
of the Dutch, and as a result of British rule the population of
thickly inhabited India has increased over 50 per cent.
There has been a marked increase of the Negro inhabitants
of the parts of South Africa under British control, and it is
not unlikely that the recent increase in the rate of growth of
the Negro population of the United States is the result of
more advantageous relations with the dominant whites.

In recent years the effects of white control in various
parts of the globe have been to increase the growth rate of
native peoples. This affords a larger supply of cheap labor
which the employing classes have found it financially
profitable to conserve. Purely humanitarian motives have,
of course, played a part in leading the whites to promote the
welfare of their more primitive neighbors, but the motive of
economic interest has probably played the more effective role.

THE BIOLOGICAL EFFECTS OF WAR 287

It is important to bear in mind that whatever may be the
immediate economic advantages resulting from the associa-
tion of whites and more primitive peoples, the different
races are none the less biological rivals. The whites have
promoted the increase of their colored brethren in many
parts of the world. And throughout the world there has
been a growing spirit of resistance to white domination.
Have the whites been raising up potential enemies that some
day they will no longer be able to control ? The interracial
struggle for existence has entered upon a new phase which
differs sharply from the previous period of active strife,
in that conditions favor the more rapid increase of the
subject peoples. This increase will involve a greater con-
sumption of food, leaving less available for export. As the
world fills up with people, those countries that depend on
other regions for their food supply and for materials for
their manufacturing industries may find their position
growing increasingly difficult. Several of these countries
now have a birth rate that is considerably below what is
necessary for maintaining a stationary population, and
are faced with the possibility of an actual decrease in
numbers in the not distant future. And there is still room
in the world and means of support for many additional
millions, and according to some estimates several addi-
tional billions of people. From what quarters will the addi-
tional population come ? The days when the white race sent
forth its millions of colonists have passed. Some of the chief
sources of emigrants of the last century have dried up,
and others are approaching the same condition. The future
growth of world population seems destined to come largely
from the prolific colored races that are yet little influenced
by birth control and whose people are habituated to a low
standard of living. Looming up ominously in the future
is the prospect of industrial competition by the colored

288 HUMAN GENETICS AND ITS SOCIAL IMPORT

races, which may deprive the whites of many advantages
that they owe to their superior technical skill and equip-
ment. As the colored inhabitants of white dependencies
increase in numbers, education, and economic efficiency,
the hold of the whites upon their dominions will become more
feeble, and the whites may eventually be forced to relinquish
their control over many territories that are now important
sources of revenue. Some of the nations of southern and
eastern Europe may be able to send forth colonists for
several years, but the prospect of much further expansion
of the white race in foreign territories does not appear to be
bright.

In the meantime the nations of Europe are torn by
rivalries that lead them to impose heavy taxes on their
peoples to support preparations for impending wars and to
adopt economic policies in relation to neighboring countries
to the disadvantage of all parties concerned. The whites
are their own worst enemies. There can be no question that
the devastating effects of the World War and the discords
which followed it have proved to be a severe handicap to
the whites in the interracial struggle for power and dominion.
Grievously as some of the European nations have suffered
from this conflict, they are making vigorous efforts to prepare
for another one, which can result only in untold injury to
all participants.

From the biological viewpoint at least all this is worse
than folly. Group loyalty is a valuable asset in the struggle
for existence. But there is a danger that minor group loyalties
may obscure the larger loyalty to race, just as excessive
and antisocial individualism may tend to destroy the minor
group.

Suggested Readings

Bernhardi ('14). Holmes ('21), chap. 9, ('32 b). Jordan ('07), ('15),
Jordan and Jordan ('14). Nieolai ('18). Pearson ('05). Cox ('22), chap. 3.

THE BIOLOGICAL EFFECTS OF WAR 289

Questions

1. Compare the effects of primitive warfare with those of modern
warfare from the standpoint of biological evolution.

2. Among modern European nations is rapidity of population growth
associated with frequency of victory in war ?

3. In modern times, do the people of smaller nations commonly suffer
much disadvantage as a result of their weakness ?

4. How do you think that war affects the choice of mates on the part
of women ?

5. What is the trend of the birth rate during and after wars ?

6. What is a common effect of endemic diseases upon the successful
invaders of a country?

7. Does the fact that war involves a great sacrifice of life indicate
that it has a dysgenic influence?

8. Does acceptance of the Darwinian theory of natural selection
logically involve the justification of war on biological grounds?

9. Are wars justifiable on biological grounds which lead to the expan-
sion of such peoples as the Anglo-Saxons ?

10. What practices of victorious peoples tend to nullify the presumed
biological advantages of a successful war ?

11. Did any European country gain any biological advantage as a
result of the great war?

12. In the interest of evolutionary advancement should more highly
developed peoples endeavor, peaceably or otherwise, to supplant their
less favored rivals ?

13. If you wished to evaluate the net biological results of a war, what
statistical data would you find advantageous to possess ?

14. How does war affect the mixture of different racial stocks ? Con-
sider in this respect the history of England and of Rome.

CHAPTER XXI
THE EFFECTS OF POPULATION GROWTH

THE growth of populations creates many problems,
biological, political, economic, and social, of which
only a few of the more pressing can be considered here.
Widespread interest in and appreciation of population
problems was greatly stimulated by the celebrated Essay
on Population by the Reverend T. R. Malthus, the first
edition of which was published in 1798. There had been
discussions on population before this time by Raleigh,
Bacon, Franklin, Hume, Condorcet, Wallace, Townsend,
and others, to say nothing of the writers of antiquity, but
it was Malthus's Essay which first brought the subject
prominently into the limelight. The Essay owed its origin
to a series of arguments between young Malthus and his
father, who was much impressed with the views of Condorcet
and Godwin on the perfectability of mankind. Godwin,
like Rousseau and other doctrinaire theorizers of the eight-
eenth century, held that most of the evils from which man-
kind suffers arise from the unequal distribution of power and
wealth. In his Political Justice he contended that "if human
beings would do away with force and laws and live according
to reason there would be no crimes, no administration of
justice, and no government. Besides this, there will be
neither disease, anguish, melancholy, nor resentment.
Every man will seek with ineffable ardor the good of all."

This sublime confidence that the millennium could be
ushered in, almost at once, young Malthus was unable to
share, and it was largely in order to show the futility of

Godwin's grandiose scheme and others of similar ilk that

290

THE EFFECTS OF POPULATION GROWTH 291

he was led to develop the objection that, even granting
an era of peace, plenty, and happiness would follow from
the proposed reforms, people would soon increase rapidly
in numbers until the old scourges of poverty, disease, and
hardship would be upon them again. Population, as Malthus
pointed out, tends to increase at a geometrical rate. Since
the number who can live at any given time or place is
necessarily limited by the materials required to sustain
life, a population comes to increase more rapidly than its
means of support. When numbers become too great they
are kept down by various checks, chief among which are
war, pestilence, and famine. According to Malthus, the
poverty and misery of great masses of mankind are not
solely the results of the iniquitous institutions imposed
upon them by unscrupulous rulers, as Godwin maintained,
but they result largely from the natural impulses of human
beings to procreate their kind. In a word, populations have a
natural tendency to grow until conditions become so bad
that further increase is automatically checked. This, as
Malthus admits, "tends to subject the lower classes of
society to distress and to prevent any great permanent
amelioration of their condition/'

It cannot be said that any of the fundamental tenets of
Malthus's Essay was original. Similar ideas had been clearly
though rather briefly expressed by previous writers. Mal-
thus's achievement lay in supporting his theses by a
thorough inductive investigation of conditions prevailing
in different parts of the earth both past and present, as it
was Darwin's great achievement to furnish a strong inductive
argument for evolution and the operation of natural selec-
tion. The Essay attracted widespread attention and elicited
many replies. Like Darwin, Malthus soon became "the
best abused man of the age." The fact that his doctrine
seemed to hold out nothing but a gloomy prospect of con-

292 HUMAN GENETICS AND ITS SOCIAL IMPORT

tinued misery for the majority of mankind naturally con-
tributed to its unpopularity. Radical reformers attacked
it because it spoiled their pretty Utopian schemes for re-
modeling society. Theologians fulminated against it because,
in attributing human misery to causes intrinsic in the
nature of things, it seemed like an indictment of the ways
of Providence. Southey sneered at it as implying that "God
makes men and women faster than He can feed them."
A nice sort of a world this which Malthus accused the
Creator of making! For a reverend gentleman such impiety
was inexcusable, and especially for one who, after preaching
the evils of overpopulation, should have the effrontery to
marry and beget children.

Amid this chorus of vituperation there were several
judicious criticisms which caused Malthus to modify certain
features of his views. The Essay passed through six editions
in the lifetime of its author, growing in the meantime
from a modest pamphlet to a book, which led eventually
to its issue in two or three volumes. Despite its unwelcome
conclusions Malthus's Essay was prompted by a humani-
tarian spirit. It advocated what seemed to the author the
one way out of the miseries which human beings bring upon
themselves by following their urge to reproduce their kind.
This was "moral restraint," leading to the postponement
of marriage or the abstention from begetting children in
marriage until adequate means were assured for raising a
family. If people have the foresight and self-control required
for the proper regulation of numbers in relation to means of
subsistence there would be plenty for all. Labor, like other
commodities, would command a price commensurate with
the demands for it. Human beings, unlike the lower animals,
have it in their power to keep down their members to the
point at which they will not press unduly upon the means of
subsistence. Population with its inherent tendency to

THE EFFECTS OF POPULATION GROWTH 293

increase at a geometrical rate must be checked somehow.
If mankind does not employ the preventive checks, Nature
will take the matter in hand and keep down the surplus
by her* none too gentle methods. Obviously the former
method is much to be preferred.

The doctrines of Malthus have played an important
part in the subsequent development of political and economic
theories, and they have continued to be a fruitful subject
of controversy down to the present time. One of their most
important influences was in suggesting to both A. R. Wallace
and Charles Darwin the idea of natural selection, and this
fact has greatly enhanced their indirect influence in the
social sciences. Much criticism has been wasted in wrangling
over matters which are not essential to the fundamental
thesis that population tends to outrun its means of support
and hence brings about its own checks. A good deal of the
opposition to Malthus arose from the circumstance that
soon after the publication of the Essay there was a period of
unparalleled production of wealth which arose from the
application of science to industry. Inventions of labor-
saving machinery, the employment of steam power and
later electricity, the improvements of production in agricul-
ture, the immense growth of trade, and the rapid utilization
of the natural resources of many lands led to an enormous
increase in the means of subsistence for the nations under
Western civilization. The natural consequence of this was
an extraordinarily rapid increase in numbers. During the
nineteenth century the population of Europe, according to
the estimates of Willcox, increased from 187,693,00x5 to
406,577,000, and that of England and Wales from 10,600,000
to 32,435,000 and that of the United States from 6,000,000
to 76,938,000. Similar increases occurred in other parts
of the world settled by the white race and also to a less
extent among several of the colored races.

294 HUMAN GENETICS AND ITS SOCIAL IMPORT

One contributory cause of this rapid increase was the
reduction of the death rate owing to the advances of medical
science and the general spread of enlightenment during
this period, but unquestionably the more fundamental
cause was the great increase of the means of subsistence
which resulted from industrial development. In no era of
recorded history has there been so extensive an increase in
population, and probably there will never be again. The
nineteenth century stands out as the one period in the
development of mankind which has seen the most rapid
increase in numbers.

The great increase in the means of subsistence which led
to this unprecedented population growth caused many to
conclude that the doctrines of Malthus had been refuted
by the course of events. But Malthusianism continued to
be attacked on several other grounds. Militarists who wanted
more soldiers, capitalists who wanted more cheap labor,
and ecclesiastics who wanted more souls to add to the
adherents of their faith, united in their denunciations.
Even the socialists, who one would think would be favorably
disposed toward Malthus's teachings, were largely either
offish or hostile. Karl Marx referred to Malthus only in
terms of contempt as an apologist for the iniquities of the
employing classes, but he appears not to have thought
out any consistent population theory of his own.

Malthus's teachings have, as a rule, met with a more
favorable reception from the orthodox economists, most of
whom adopt his views with more or less modification.
Recently there has been a tendency toward a "return to
Malthus." It is becoming apparent that the increase of the
means for supporting population growth cannot continue
to go on at the pace characteristic of the last century.
The basic limiting factor in population growth is food, and
the possibilities of food production on this planet are strictly

THE EFFECTS OF POPULATION GROWTH 295

limited. Several countries in Europe do not, and some of
them probably cannot, produce enough food for their own
support. A good deal of Asia outside of Siberia is not very
far from the same situation. As to the United States, East
has estimated that "with our present standards of farming,
the country will support only 166,000,000,' and we have
about 130,000,000 now. Of course, with intensive cultivation
production may be increased, but if our numbers continue
to increase as in the past it will not be long before no amount
of cultivation would yield enough to insure us against the
possibility of going hungry during the lean years. Food-
exporting countries, as our own has been, will soon require
all their food for their own people. The world is rapidly
filling up. It would be unprofitable to discuss just how many
people it is capable of supporting, but whether the saturation
point will be reached in fifty or one hundred, or even two
hundred years does not invalidate the conclusion that we
are drawing distinctly nearer the time when the food re-
sources of the earth will no longer suffice for further increase
in numbers. Civilization also requires many other things
besides food. It is hazardous to set limits to the achievements
of invention in providing materials and sources of energy
for the needs of industrial life, but in the matter of food
man is limited to the productive power of the land with
such minor supplements as can be fished out of the sea;
and these resources are by no means so bountiful as is often
imagined. There is a possibility that the chemists may
fabricate synthetic foods, but the probability that they will
ever discover a means of production that will be more
effective and economical than the green plant is very
remote.

There have been many speculations as to the future
growth of population. Some of the forecasts are wild and
fantastic, but those which are based upon a careful study

296 HUMAN GENETICS AND ITS SOCIAL IMPORT

of the facts are much less widely divergent. Besides the
forecasts of future growth based on the possibilities of food
supply there are those which depend upon a study of the
course of population increase in the past. These rest upon the
supposition that the growth of populations follows a fairly
definite law which can be expressed in a mathematical
formula. According to Pearl and Reed the typical course
of population growth, like the growth of an individual
organism, may be represented graphically by an S-shaped
logistic curve. This means that populations at first grow

FIG. 74. — S-shaped logistic curve illustrating population growth according to the conception

of Pearl and Reed.

slowly, then increase at an accelerated rate, and finally
slow down as they approach their maximum size. Pearl
has endeavored to show that the actual course of population
growth in several countries fits such a curve with a fair
degree of accuracy.

These curves approach an upper limit represented by a
horizontal line that typifies the maximum population
obtainable. From the equation of the curve one can cal-
culate by extrapolation what the maximum population of a
country will be, provided of course, that the growth continues
to follow the same formula as in the past. Pearl concedes
that changed conditions may and actually do change the
course of population growth as predicted by the formula.

THE EFFECTS OF POPULATION GROWTH 297

Such a change as the transition from a pastoral to an agricul-
tural life or a marked change in industrial development,
may alter very materially the course of population increase.
As the eminent statistician. Sir G. H. Knibbs, remarks,
"any attempt to prognosticate the future numbers of Man,
by extrapolating the curve of his growth in the past must
fail, not merely because we have no exact numerical record
of his past, but also because the factors which determine his
numbers are numerous, and are liable to momentous
changes." Knibbs contends that "human populations
certainly do not conform to the law of growth which the
logistic curve expresses, excepting accidentally and for a
limited period."

Whatever may be the precise curve or curves which most
closely describe the course of human increase, it is evident
that they must be of a form which indicates an approach
with increasing slowness to an upper limit. The period of
increasing returns, so far as means for supporting population
are concerned, which appeared in several countries of
northern and western Europe and the United States during
the nineteenth century, has now been succeeded by a period
of decreasing returns. Rates of population growth in these
countries, as measured by the excess of births over deaths,
are diminishing. For several countries the net rates of
increase in the present century, omitting the upset period
of the war, are indicated in Table 26.

The net increase in the United States before 1860 was over
30 per thousand, and over 25 for the rest of the century.
Since 1910, when it was estimated by Thompson and
Whelpton to be 18.3 per thousand, it has fallen to 9.8 in
1930; 7.1 in 1931, and 6.4 in 1932. In the countries of
southern and eastern Europe and in Japan net rates of
increase continue high, although in several of them the
birth rate has fallen. They are now in much the same

298 HUMAN GENETICS AND ITS SOCIAL IMPORT

situation as the nations of northern and western Europe
were fifty years ago, and they may have a similar history.

TABLE 26. — NET RATES OF POPULATION INCREASE IN SEVERAL COUNTRIES DURING
THE TWENTIETH CENTURY

1898-1902

1908-1912

1918-1922

1927-1928

1930

1933

Austria

12 O

10.7

•3. I

^ .0

-I. T

I . I

Denmark

IT 7

II "?

8 T

7 q

6 7

England, Wales
France
Germany

11.4
1.6
14 q

II. 0

0.9

IT I

7.2
2.8
f o

4-7
1.6

6 7

4-9

2-4
6 r

2. I

o-5
-j r

Italy

10 7

II q

r •?

IO q

12 4.

IO O

Russia

17 O

16 7

iq 2

21 1

Spain
Australia

6.4
16.4

9.6

16 c

5-3

14. 2

10.5
121

II-7
II 1

ii. 4

8 2

New Zealand

16 o

17 1

121

IO 2

8 6

Japan. .

II . C

ii. o

Q.q

iq q ('28)

14.2

n fl

In some respects the comparison of crude birth rates and
death rates gives a misleading picture of what is happening

53 7.2 9.6 12.8 III 23.2 31.4 39.8 SO;! 62.9 76.0 92.0 105.7 122.8

1800 1810 1820 1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930
FIG. 75. — Growth of the population of the United States from 1800 to 1930.

to a people. Barring the effects of migration the surplus of
births over deaths gives a reliable index of the rate of growth

THE EFFECTS OF POPULATION GROWTH 299

at any given time, but it is important to consider that this
surplus depends, not merely upon the actual fecundity and
health of a people, but also upon its age composition. A
country may have more births than deaths and yet not be
reproducing with sufficient rapidity to insure the continued
maintenance of its stock, even if women should continue
to produce as many children and the death rate in each
age were to remain unchanged. Let us imagine a population
between ages twenty and forty-five in which births were
only a little more numerous than deaths. Fifteen years later
most of the women would be too old to have many children,
and their offspring who had been born in the meantime
would not have reached the reproductive age. With the
change of age composition there would soon be more deaths
than births. Since the actual growth of a population depends
so largely on its age grouping it would be of interest to
know how rapid its increase would be if the age-specific
birth rates and death rates were to remain the same. If
the age-specific rates were constant the population would
in time outgrow the effect of its changing age distribution
and would settle down to a uniform rate of increase which
would remain unchanged thereafter. We may therefore
speak of the stabilized rate of increase of a people, meaning
thereby the rate which would obtain when the influence
of its anomalous age composition had been outgrown.
The first step in the calculation of such a rate is to ascertain
how many daughters would be born to one thousand females.
For this we must know how many births occur among
mothers in the several age groups. If one thousand mothers
produce thirteen hundred daughters, it is not certain that
the race will be self-perpetuating, because some of these
daughters would die before reaching maturity. If every
woman produces a daughter who lives just as long as her
mother, the population would neither increase nor decrease

300 HUMAN GENETICS AND ITS SOCIAL IMPORT

in numbers. How many daughters would live long enough to
replace their mothers can be ascertained by means of a
life table for females. If we know the number of females
born to one thousand mothers, we can easily calculate the
number of boy babies from the sex ratio at birth (106:100).

The calculation of stabilized rates of increase is of impor-
tance because if such a rate is a negative quantity it means
that there is inadequate reproduction, even though there
may be a considerable surplus of births over deaths. In his
volume, The Balance of Births and Deaths, Kuczynski has
shown that most of the nations of northern and western
Europe are in this situation. While they still have a surplus
of births over deaths, were it not for their favorable age
composition, they would be actually decreasing in numbers.
Even with no further fall in age-specific birth rates or death
rates their rates of growth will inevitably diminish. Sta-
bilized rates of increase for several countries are shown in
Fig. 76. It is of interest to note that, although in 1930
Germany had a greater rate of net increase than France,
her stabilized rate was below that of France on account of
her peculiar age composition.

While the decline of the birth rate is going on and for
some time afterward the population tends to pile up in the
adolescent and middle age groups, and hence it becomes
favorable for a high net rate of increase. In France the birth
rate has been declining for a much longer period than in
Germany and her population has more nearly reached a
stabilized condition. As may be seen in Table 26 the net
increase of France has varied relatively little for several
decades. Northern European countries in which the decline
of the birth rate set in during the latter part of the nine-
teenth century show a much greater decline in their rates of
population growth. The inhabitants of these countries
increased at a phenomenal rate during the nineteenth

THE EFFECTS OF POPULATION GROWTH 301

-S

FIG. 76. — Stabilized rates of natural increase (in black) as compared with the excess of
births over deaths in several countries of Europe, 1929-1930. (Data from Burgdorfer.}

302 HUMAN GENETICS AND ITS SOCIAL IMPORT

century, but they have had their heyday. Only recently
have vital statisticians awakened to this fact. They were
concerned more over the possibilities of impending over-
population. It is only since the World War that the stabilized
growth of northern and western Europe has passed from a

193.0 I960

FIG. 77. — Relative increase of Germanic, Latin, and Slavic peoples of Europe, 1910 to 1930,
with the proportions in 1960 if the same relative rates are continued. (Data from Burgdorfer.)

positive to a negative quantity. In part this is due to the
loss of men in the war and the disturbances of the sex ratio,
but there were other causes of decrease which affected
countries not involved in the conflict. One can only speculate
as to the trend in the future. Perhaps the birth rate will
cease to decline when it has reached a certain stage. One
might cite France as a country that has reached a level of

THE EFFECTS OF POPULATION GROWTH 303

reproductivity to which other nations are approaching.
Population, as Malthus has shown, has a natural tendency
to recoup its losses, and, when a decline sets in, the popula-
tion may automatically respond by a more rapid growth.
Many students of population hold that several countries
of Europe are overpopulated already and that a little
reduction in numbers should be welcomed rather than
deplored.

In the United States we have been accustomed to think of
ourselves as a young and rapidly growing nation with plenty
of room in which to expand and an almost unlimited capacity

C
«0

|20

I—

»15
a.

1 n

**•

***,

, Bir

thra

•«•«»,,

»•»

<-s-

V^-s.

***+<

••••

-c

Deart

7 ra+

• •••

1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970
FIG. 78. — Birth rates and death rates in the United States and their probable future trend

according to Dublin.

for the production of food. But our country has been rapidly
filling up. We are long past the period when free land is to
be had for the asking. Most of our tillable land is under
cultivation and we are approaching the conditions found in
the old world. We have a fairly large but steadily diminishing
surplus of births over deaths, but Dublin and Lotka have
shown that even in 1920 this was largely due to our favorable
age composition. What these authors called the true rate
of increase, instead of being n per thousand as measured
by the excess of births over deaths, would be only 5.5 per
thousand if we make the proper corrections for age dis-
tribution. In 1928 they estimated that the true rate of
increase was onlv 1.8. I have endeavored to calculate the

304 HUMAN GENETICS AND ITS SOCIAL IMPORT

stabilized rate of increase of the white population of the
Birth Registration Area in 1930 and find that it is a little
less than o, or possibly slightly above if we allow for incom-
plete registration of births. With the further decline of the
birth rate since 1930 our stabilized increase has probably
become a minus quantity. In other words, were it not for the

1850

1870

1890

1910

1930 Final stabilized

FIG. 79. — The changing age composition of the population of the United States, 1850 to
1930, and the age composition when the population is finally stabilized. The graphs indicate
the percentages of the population in the several age groups.

favorable age distribution of our population we would not
be increasing in numbers at the present time.

This inadequate reproduction, which has now come to
characterize a considerable proportion of the white race,
is not so much the product of the unfavorable conditions
resulting from overpopulation as it is a consequence of
sophistication and the desire not to be encumbered by a
numerous progeny. Countries with an inadequate stabilized

THE EFFECTS OF POPULATION GROWTH 305

rate of increase are those in which birth control has been
extensively practiced for several decades. Some countries
which are notorious examples of overpopulation still continue
to aggravate the situation by a high net rate of increase.
They are under strong pressure to send emigrants to other
lands or to acquire territory for their surplus humanity
at the expense of their neighbors. Population pressure has
long been a strong incentive to migration and to conflict.
The white race, before its period of rapid expansion, acquired
a large part of this world's territory, a fact which con-
tributed to further .its growth. Out of Europe have come
millions who have settled most of North America, Australia,
and New Zealand, large parts of South America, parts of
Africa and Asia, and numerous islands in various parts of
the world. The so-called yellow peril has proved to be much
less menacing than the white peril has been to the colored
denizens of many lands. The enormous expansion of white
humanity is one of the great basic events in the recent
history of mankind. Not only did the whites desire more
land for settlement, but they wanted to control and exploit
the wealth of other regions. Highly industrialized countries
can support a large population only when they can secure
an abundance of raw materials and find markets for their
manufactured goods. They naturally desire to obtain the
food, coal, iron, oil and other products of foreign lands.
They become dependent upon trade for their support,
and they naturally endeavor to protect this trade. Where
they have the power they are tempted to adopt an imperi-
alistic policy. Nations desire to be strong that they may
enjoy a sense of security and not be helpless when their
interests are threatened. A nation which is able to grab
and exploit new territory may increase its wealth and raise
the standard of welfare of its people. It can therefore support
a larger population and hence increase its military strength.

306 HUMAN GENETICS AND ITS SOCIAL IMPORT

If its population grows unduly the average standard of
living goes down, people are tempted to seek their fortunes
elsewhere, and the statesmen who control the political
destinies of the country look about to secure a larger place
in the sun.

Sometimes people suffer grievously from overpopulation
without realizing what is the matter with them. The majority
of their inhabitants can secure none of the luxuries and few
of the necessities of life. They have to work long and hard
for a living at the bare subsistence level. They accept their
lives of hopeless toil as decreed by fate and go on marrying
and begetting children who suffer an appalling mortality
in infancy and childhood. Many millions of the inhabitants
of this world of ours live under conditions of overcrowding
which make life little else than a long struggle against want.
If conditions can be remedied by appropriating the lands
of their neighbors, the people might easily be persuaded
that it would be better for some of them to die gloriously
upon the field of battle than to starve in obscurity.

Different rates of population growth have played an
important part in shaping the course of human history.
They are a chronic source of instability and trouble. The
international complications which they occasion have led
to numerous wars in the past, and, even with the best
intentions on the part of nations to preserve peace, they
will continue to present the statesmen of the future with
many embarrassing situations. Back of the alleged causes
and immediate occasion of the World War were the rivalries
for the means of supporting the increasing numbers of the
chief participants in the conflict. Unfortunately the same
rivalries still persist and are made even worse after the
imposition of the terms of peace.

It has become a part of the settled policy of a number of
European countries to increase their numbers as a means to

THE EFFECTS OF POPULATION GROWTH 307

power. Recent German literature dealing with population
problems is filled with lamentations over the low rate of
population growth in Germany occasioned by the rapid
fall of the birth rate among the masses, and voices eloquent
pleas for increasing the population by all possible means.
The French, always fearful on account of the dangers arising
from their slow rate of natural increase, have vainly at-
tempted to suppress the Neo-Malthusian movement, and to
encourage larger families as a means of self-protection.
Italy, although poor in natural resources, and having a
population that has to be supported on a relatively low
standard of living, is endeavoring to increase her population
by checking emigration, encouraging births, and securing
dominion for expansion in Africa. Militarists the world
over are advocates of a high birth rate. When Napoleon
was asked, "What woman is worthy of the greatest glory?"
he is said to have replied, "She who has produced the largest
number of sons for the defense of her country."

The study of population growth not only reveals the real
source of many conflicts, but from the humanitarian stand-
point it is a subject of the greatest import. The welfare of
human beings is closely dependent upon how many of them
inhabit a given area. Where people are closely massed
together they fall far short of realizing their best capacities
for development. Hard toil, ignorance, squalor, vice, and
disease are the inevitable consequences of too many people
in relation to the means for their support. The life of the
masses in such overpopulated countries as China, India,
and Japan does not present a pleasing picture. Through
industrial development or improved agriculture a country
may raise its general standard of living, but if the people
should then proceed to breed up to the saturation point,
no permanent advantage would result. Should a successful
war lead to expansion the benefit might prove to be only

308 HUMAN GENETICS AND ITS SOCIAL IMPORT

temporary if it led to no change in the net reproductive
rate. There can be no permanent relief to the evils of
overpopulation except through the control of population
growth.

But countries may suffer from having too few people
as well as from having too many. In a sparsely settled
region people are advantaged by an increase in numbers.
Without a considerable population a society cannot secure
the benefits of the division of labor and the exchange of
services which afford some of the chief advantages of social
life. Up to a certain point labor brings increasing returns
as a population grows. The conscious or unconscious recogni-
tion of this fact leads countries such as our own was a
century ago to make efforts to increase in numbers by
inviting immigration. But at some stage the period of increas-
ing returns is followed by a period of diminishing returns
in which people have to work longer and harder for what
they get. Evidently the sensible thing to do would be to
reach a happy medium, or what is called the optimum
population. The concept of an optimum population for a
given area is somewhat indefinite. Some countries are
obviously underpopulated, and others, according to any
reasonable standard, grossly overpopulated, but opinions
differ as to how the optimum should be defined. A militarist
would probably desire a dense population even if it involved
a considerable sacrifice of individual welfare. So might an
ecclesiastic who considers that the chief function of this
world is to supply souls to inhabit the next. Commonly the
optimum population is regarded as that which is most
conducive to the welfare of the greatest number of persons.
Professor Wolfe has defined the optimum as that which
gives the greatest per capita income. Professor Fairchild
defines the optimum in terms of the standards of living.
It has been pointed out that the optimum from an economic

THE EFFECTS OF POPULATION GROWTH 309

standpoint, may not necessarily be the same as the optimum
from a social or cultural standpoint. It is much more difficult
to measure social and cultural values than those dealt with
by the economist, but even according to a purely economic
criterion it is not a simple matter to ascertain just when the
optimum has been reached. Has the economic optimum
been passed in the United States? Apparently we are not
suffering greatly from overpopulation, and the country
could comfortably support many more people with its
present resources. W. S. Thompson has shown that in
agricultural production we have passed into a period of
diminishing returns when farm labor is less rewarding than
in former years. Whether the same statement applies to
most other branches of industry we do not know, so that
our question is one to which economists have not as yet given
us a definite answer.

An optimum population varies from time to time with
progress in methods of creating and distributing wealth.
For an industrial people it is greater than for one engaged
in hunting and fishing like the North American Indians.
It will also vary according to age distribution and the
quality of the individuals. Hence it is difficult to determine
very precisely what is the most desirable number of people
for a country at any given time. Nevertheless, an approxi-
mate solution of the problem is highly important because
human welfare is so profoundly influenced by the relation
between numbers and means of support.

Populations, as Malthus showed, have an unfortunate
tendency to reach their maximum numbers, but human
beings have contrived to avoid the drastic checks of Nature
to a greater extent than Malthus suspected. The labors of
anthropologists and other students of primitive culture
have added enormously to the knowledge of the customs
of aboriginal peoples that was available in Malthus's day.

310 HUMAN GENETICS AND ITS SOCIAL IMPORT

As is shown very convincingly by Carr-Saunders in his
excellent volume on The Population Problem the regulation of
numbers is widely practiced by the different tribes and
peoples of mankind. Infanticide is a common custom among
primitive men. It was practiced in ancient Greece and Rome,
but it later disappeared almost entirely under the influence
of Christianity. Among primitive peoples there is also an
extensive practice of abortion. Prevention of conception
is less common, but various methods of attaining this end
are employed by many tribes. The habit of prolonged
lactation in the endeavor to prevent conception during this
period is a common custom in primitive society. Besides,
many tribes have sexual taboos which prevent the husband
from living with his wife for a period following the birth
of a child. The number of children a woman may bear is
often regulated by tribal custom. If the number is exceeded,
the infant must be put to death. Many of the primitive
methods of checking natural increase may be crude and
brutal, but they are less cruel than those imposed by Nature
as a penalty for overmultiplication.

We cannot describe the many ways by which numbers
have been regulated by different peoples of the world, and
we shall refer to the volume of Carr-Saunders for further
details on this subject. The chief point is that mankind
quite generally has succeeded in avoiding, in a measure,
the more drastic checks to overpopulation. Peoples have
by no means always been successful in checking an undue
increase in numbers. They have gone at the business in a
crude, half-conscious and bungling manner, and have
commonly stopped far short of limiting population at the
optimum level. But at least they have realized that too
many people are undesirable and have acted accordingly.

The modern birth control movement is part and parcel
of the effort to prevent the undue increase of numbers

THE EFFECTS OF POPULATION GROWTH 311

which has been widely prevalent throughout the races of
mankind. It aims to achieve the same end without recourse
to infanticide, abortion, restriction of marriage, or sexual
taboos. Undoubtedly this movement is chiefly responsible
for the reduced rates of population growth in a large part
of the white race and to a less extent in some colored peoples.
Had it not been for this fact the population of Europe
would have been much greater than it is. According to the
Neo-Malthusians this would have led to an intolerable
degree of overcrowding, reduced the standard of living,
and caused a higher death rate and a greater number of
wars. The opponents of the Neo-Malthusians might urge
that many more people would have enjoyed life, more
geniuses would have been born, and the white race would
have spread more rapidly and enlarged its domain to the
ultimate advantage of humanity in general.

Among the population problems which give the greatest
concern to many countries is the ethnic composition of
their inhabitants. Most countries have peoples of different
stocks in their midst, and the relations of these diverse
elements vary all the way from good-natured tolerance to
open hostility. The origin of these associations is varied.
In many cases it is a result of slavery. The Greeks, Romans,
Egyptians, and other peoples of antiquity brought in
numerous captives to do the hard work. Later the slaves
were liberated and intermarried with and to a large extent
outbred their captors, and thus caused marked changes
in the ethnic composition of the inhabitants. Slavery is
responsible for the presence of Negroes in the United States,
South America, the West Indies, and to a -less extent in
other parts of the globe.

Frequently ethnic diversity is the result of conquest.
Few countries have been spared from successive inroads of
hostile invaders who have overrun the land and mingled

312 HUMAN GENETICS AND ITS SOCIAL IMPORT

with the indigenous population. Witness the population
of England with its Britons, Danes, Angles, Saxons,
and Normans, or in fact the population of most of the
countries of central and southern Europe or of Egypt,
Persia, and Mesopotamia, all of which from time to
time have been under the yoke of different conquering
peoples.

A third factor contributing to the diversified character
of populations is immigration. In modern times peaceful
penetration has acted more powerfully in this respect than
conquest. We owe to it most of the conglomerate nature of
our own population which led Theodore Roosevelt to speak
of the United States as a polyglot boardinghouse. An extreme
illustration of the mixture of diverse racial elements is
afforded by Hawaii. The development of the rich resources
of Hawaii has led to the influx of Chinese, Japanese, Koreans,
Hindus, Negroes, Filipinos, Porto Ricans, Portuguese,
and Americans, who together with the native Hawaiians
constitute a more diversified and polychrome mass of
humanity than is found in any other area of equal size on
the earth's surface. The development of cheap and rapid
means of transportation has contributed much toward
bringing different racial stocks together in the same territory.
This cannot fail to have important consequences both
biological and social.

The origin of racial diversities within a country often
has a great deal to do with the way in which the different
elements get along together. Where these elements preserve
a strong consciousness of kind and work together in the
pursuit of their own interests they are apt to meet with a
more or less antagonistic attitude. The Germans are greatly
exercised over the presence of the Jews as were the Russians
under the Czarist regime. They are also concerned over the
presence of the Poles and other Slavic peoples because of

THE EFFECTS OF POPULATION GROWTH 313

their portentous fertility. Since the World War and the
intensification of the spirit of nationalism which followed
it, we have had the spectacle of the Greeks being driven
en masse out of Turkey, and of Turks being forcibly expelled
from Greece, and more recently of Hungarians being hustled
out of Jugoslavia. Even more drastic measures of dealing
with unwelcome inhabitants have been practiced by the
Turks in Armenia. Nations desire a certain amount of
like-mindedness among their inhabitants. Where stocks
differ in language, physical appearance, religion, dress, and
social customs, antagonisms are apt to be more intense and
persistent. Internal discord is a menace to national security
in times of conflict and a source of many evils in times of
peace. Questions of relative superiority and inferiority of
the people living in a common country are apt to be fertile
sources of unfriendly relations. In some parts of Europe
the Nordics look down upon the Slavs, and in the United
States it is common for people of old American lineage to
regard themselves as a bit superior to other peoples of the
white race and especially to the blacks.

If a nation is composed of very different ethnic elements
their relative rates of natural increase become a matter of
much concern. This is true whether these elements differ
biologically in any significant respect or not. The mode of
government, the prevalent religion, and the social tradi-
tions— in fact, the whole spirit of a people — may be changed
by a process of racial replacement even though the genetic
endowments of the stock were practically the same. Good
old Puritan Massachusetts is now mainly Roman Catholic
in religion as a result of the immigration of people from
southern Europe and the emigration of her native American
inhabitants to other states. Parallel changes of many other
kinds result from the same causes. Hence not only the
biological character, but the civilization of a people may be

HUMAN GENETICS AND ITS SOCIAL IMPORT

changed through the differential fertility of its component
stocks.

The most conspicuous population problem facing the
people of the United States is occasioned by the presence
of some twelve million Negroes. Beginning with a cargo of
slaves imported by a Dutch trader in 1619 our Negro
population rapidly increased, partly through the importation
of more slaves and partly through its own birth rate. Owing
primarily to economic reasons the Negroes became confined
mainly to the Southern states, but since their emancipation
in 1863, they have been migrating in ever-increasing numbers
into the North and West. During the World War the north-
ward migration became very much greater in volume, and
it continued on a large scale during the decade between
1920 and 1930. As a result the "Negro problem" is fast
becoming nation wide. The rapid industrial development
of the Northern states and the curtailment of the extensive
inpouring of cheap labor from Europe conspired to create
opportunities for Negro workers who were anxious to
improve their economic status. Other influences such as
better educational advantages for their children and freedom
from certain social restrictions contributed though less
strongly to the same end.

Northern Negroes go mainly into the cities where they
suffer from a death rate nearly twice as high as that of the
native white population. Although there are now more
births than deaths among the Negroes of many Northern
cities this is demonstrably a consequence of favorable age
composition. The stabilized rate of increase is a minus
quantity in urban Negroes as it is among urban populations
generally. The great breeding ground of our Negro popula-
tion is the rural south. Relatively few foreign immigrants
have gone into the South, especially the rural areas. Had
they done so and compelled the migration of Negroes into

THE EFFECTS OF POPULATION GROWTH 315

the cities, one of our greatest population problems would
be on the way toward solving itself with a considerable
degree of rapidity.

The Negro birth rate has always been higher than that
of the whites, but it has declined as in the rest of the popula-
tion and for essentially the same reason. The Negro death
rate, however, has been so much higher than that of the
whites, that it has more than compensated for the advantage
of their higher birth rate. The whites in the United States
have increased much more rapidly than the Negroes, but
this has been due largely to an extensive influx of fertile
immigrants from Europe which for the years immediately
preceding the World War often amounted to over a million
per annum. With the restriction of European immigration
and the fall of the birth rate among the whites the net
increase of the two races has come to be more nearly the
same.

We cannot calculate the stabilized increase of the Negroes
with a high degree of accuracy, but from the available data
on births, deaths, and age distribution it is evident that the
stabilized rates of the two races are not far apart. A promi-
nent German writer on population problems, Dr. F. Burg-
dorfer, contends that unless the white population of the
United States continues to be recruited by immigrants
from abroad, it will gradually be outbred by the Negroes.
Prophecies as to population growth, however, are notoriously
unsafe, but whatever may be the trend in the future in their
struggle for numerical supremacy Negroes and whites in
the United States are running nearly a neck and neck
race at the present time.

A minor population problem, but one which a few years
ago was increasing to an extent that caused a good deal of
uneasiness in the Southwestern states, and in California,
has been created by immigration from Mexico, as will be

316 HUMAN GENETICS AND ITS SOCIAL IMPORT

further discussed in the chapter on migration. Our foreign-
born population of Caucasian extraction forms a considerable
proportion of our total inhabitants. Another large proportion
consists of the immediate progeny of foreign-born parents.
No attempt is made to enumerate those persons whose
grandparents or more remote ancestors were born abroad;
they are all counted as native-born Americans of native
parentage. All European countries have contributed to the
making of the American people. The earliest settlers came
mainly from northern and western Europe. Later the
stream was shifted to southern and eastern Europe, bringing
in peoples of different racial extraction, languages, and
traditions. A large proportion of our more recent foreign-
born population consists of people of relatively low economic
and cultural status whatever this may imply, if it implies
anything, as to eugenic worth. Obviously, it implies much
from the standpoint of the political, economic, and cultural
life of the American people. In the course of a few generations
immigrant stocks become pretty well Americanized, al-
though the process is delayed by the tendency of alien peoples
to segregate in groups where they marry among their own
kind and maintain their old traditions, sometimes for
generations.

As a rule, the foreign born have a birth rate which exceeds
that of the native-born Americans. According to the investi-
gations of the Immigration Commission on the birth rates
of native-born and foreign-born inhabitants in sample
urban and rural areas, the average number of children per
family in 1900 was 4.7 among the foreign born, 2.7 among
the native born, and 3.9 in native whites of foreign parentage.
In a study of family size among parents sending sons to the
University of California I have found that the average
number of children was 3.14 in the foreign born, and 2.89 in
the native born. Our birth statistics on the average number

THE EFFECTS OF POPULATION GROWTH 317

of children ever born to mothers who had given birth to a
child during the year uniformly show a higher number for
foreign-born mothers. Recently the birth rates of foreign
born mothers have fallen off quite rapidly. This is to a large
extend due to the fact that, since most foreign-born mothers
came here before the restriction of immigration, their
fertility is now showing the effects of more advanced age.
According to Thompson and Whelpton, the birth rate per
thousand women aged fifteen to forty-four in the Birth
Registration Area in 1920 was 90 for native-born white
women, 136 for foreign-born women, and 100 for Negro
women. In the Birth Registration Area for 1929 the rates
for these classes were estimated as 76, 92 and 85 respectively.
The decline was greatest in the foreign-born women and
least in Negro women.

Among the foreign born there are great differences in
fertility according to national origin. The Immigration
Commission found that the largest number of children per
family, namely 4.9, occurred among the French Canadians.
Large families are common among the Poles, Southern
Europeans, and especially Mexicans, Chinese and Japanese.
Among the English, Scotch, Irish, Germans and Swedes
births are not so numerous. The birth rates of the native
American population of native parentage are especially low
in the Northern and Eastern states where they are inade-
quate for maintenance. In the South and several states of
the West, the old American stock is more than perpetuating
itself. This stock is largely British and north European in
origin, but it seems incapable of maintaining itself when
subjected to strong pressure from a foreign immigrant popula-
tion. What the biological effects of this process of replace-
ment will be depends upon the inherent qualities of the
surviving types — a topic which will be touched upon briefly
in a later chapter.

3i 8 HUMAN GENETICS AND ITS SOCIAL IMPORT

Suggested Readings

Duncan ('29), chaps. 11-17. Dublin ('26), chaps. 5-7. East ('23), chaps.
3-6. Knibbs ('28). Kuczynski ('28). Lorimer and Osborn ('34), chap. i.
Reuter, ('23), chaps. 1-8. Thompson, ('35), chaps. 1-8, 24, 25. Thompson
and Whelpton ('33), chaps, i, 2, 4, 10, n. Wright ('23).

Questions

1. What do you consider the most significant principle brought out in
Malthus's Essay on Population?

2. Does the means of supporting life increase in an arithmetical ratio
as Malthus once stated ? If it does not, will it seriously affect the most
important features of Malthus's doctrine ?

3. If the net rates of increase of two elements of a population originally
present in equal numbers were as five to four what would be the numerical
proportions of these elements after five generations ?

4. What effects did the potato and its diseases have upon the popula-
tion of Ireland ?

5. How did the famine in Ireland affect the population of that country
and of the United States ?

6. What features of Malthus's doctrine were employed by Darwin in
formulating his theory of natural selection ?

7. What are the checks to increase among species of animals ?

8. In what ways do checks to increase in man resemble those in
animals and in what ways do they differ ?

9. What nations of the earth are now increasing most rapidly in
numbers ?

10. What can you say of the relation between the population of a
country and its military strength ?

11. What countries do you think are better off because they have a
relatively homogeneous population, and what countries suffer from having
too great a diversity of ethnic stocks ?

12. How will the increasing age of the American people affect school
attendance, birth rates, death rates, and general prosperity?

13. If there were fewer people in a country, would there be less
unemployment ?

14. How does Neo-Malthusianism agree with and how does it differ
from the teachings of Malthus ?

CHAPTER XXII

THE GROWTH OF CITIES AND ITS DEMOGRAPHIC

EFFECTS

THE growth of cities in the nations under Western
civilization has involved many changes in the sur-
roundings and customary pursuits of ever-increasing pro-
portions of the population. We live in a machine age which
has brought us railroads, steamships, automobiles, telegraphs
and telephones, the radio, and countless inventions and
conveniences which make life very different from what it
was a century ago. The changes that our industrial and
technical developments have wrought in everyday life have
naturally been greatest in cities, but they have influenced
even the remotest and most isolated regions. In recent times
the growth of cities has been enormous. A glance at the
following table giving the growth of a few of the larger cities
of the world shows that the population of most of these
cities has more than doubled, and that of others has increased
many times over since the middle of the last century.

TABLE 27. — POPULATION OF SELECTED LARGE CITIES SINCE 1800

1800

1850

1900

1920

1930

New York

7Q 2l6

606 IIC

1 417 2O2

c 620 048

6 010,446

London
Paris
Berlin

959,3 10

547,756
172,846

2,363,341
1,053,262

420,217

4,536,267
2,660,559

2,7I2,IQO

4,484,523
2,906,472
1,804,048

4,397,°°3 (I931)"
2,891,020

4,242, COI (iQll)

Chicago

2q q6l

I 6q8 C7C

2,701, 70 c

1,176,418

Vienna

211,040

446,4! C

1,727,071

1,865,780

1,868,328 (1925)

Philadelphia
Glasgow

41,220

77 l8<

121,376

^293,697
761 7OQ

1,823,779

1,034,174

1,950,961

1,088,417 (1931)

Moscow

188,654

112,878

1,174,671

1,027,336

2,781,300 (1931)

Leningrad

22O,2OO

487,300

763,875

2,228,300 (1931)

*The population of "Greater London" in 1931 was 8,203,942. This includes the so-called "outer ring.*

319

320 HUMAN GENETICS AND ITS SOCIAL IMPORT

At the beginning of the nineteenth century probably no
city contained as many as a million people and probably
not more than two, London and Paris, did so in 1850. This
enormous growth of urban populations during the last
century is obviously a reflection of our rapid industrial
development. Formerly agriculture was the principal occupa-
tion of the great majority of civilized mankind. Agriculture
still leads in Russia, Bulgaria, India, China, and several
countries of South America. In 1921 the percentage of
persons so engaged was 41.5 in France, 30.5 in Germany,
26.3 in United States, 22.7 in Australia and only 7.5 in
England and Wales. The United States has long been a
predominantly agricultural country. In 1820 about 72 per
cent of occupied persons over ten years of age were engaged
in agricultural pursuits, but the percentage has gradually
decreased until in 1930 it was only 21.4 per cent.

Until the eighteenth century agriculture had made little
improvement since ancient times. Methods of farming were
inefficient and wasteful, and little attention was paid to
securing profitable varieties of crop plants and farm animals.
Many improvements were made in scientific agriculture
in the eighteenth century, but they were relatively small
as compared with those effected in the century just past.
Improved methods of tillage and the development of
valuable varieties of grains, vegetables, fruits, and farm
animals through selective breeding greatly increased the
value of the farm products that could be raised from a
given area of land. The invention of agricultural machinery
made farm labor much more productive, so that it became
possible for a comparatively small number of workers to
raise more food than was produced by a much larger number
of workers employing the older methods of farming. The
result was that relatively fewer people were needed to work
on the farms, and hence the surplus rural population migrated

GROWTH OF CITIES AND ITS EFFECTS

321

into the cities to supply the labor required by the rapid
growth of industry. Urban migration is a perfectly natural
and in fact inevitable consequence of our economic develop-
ment. City growth and especially the growth of very large
cities has been facilitated by the development of rapid
transportation made possible through the application of
steam and electricity. Steam power has contributed greatly
to the development of factories, which for several reasons
tend to congregate in the larger centers of population.
And in addition to the powerful economic forces leading to

"•Public service*
DomesTic and
personal
Clerical

Trade cxnol
transportation

Manufacturing cxncl
mechanical incfusiries

-Minmqj
^•Agriculture

F870 1880 1890 1900 191.0 1920 1950

*No+ elsewhere classified

FIG. 80. — The changing proportions of persons over 16 years of age in different occupations
in the United States, 1870 to 1930.

urban growth there are other factors such as superior
educational advantages, amusements, and the natural
gregariousness of the human animal which have conspired
to further the same trend.

This unprecedented massing together of human beings
in cities cannot fail to have its biological effects. Some of
these are fairly easy to ascertain. Others, and among these
the more important ones, involve us in the same kind of
difficulties that so frequently perplex the student of the
social bearings of biology. The more obvious biological
influences relate to the age grouping, birth rates, death rates,
and ethnic composition of urban inhabitants. We may
consider first the matter of age grouping since it is necessary

Jransportcx+ion
MomufcHc-rurincj oinol

Mechanical

Indus+ries

322 HUMAN GENETICS AND ITS SOCIAL IMPORT

to keep this subject in mind when interpreting the signifi-
cance of the vital statistics of urban areas. Most cities have
relatively smaller proportions of children and old people
than are found in the country. The people who migrate to
cities are for the most part young adults or persons of middle
age who are drawn thither by the prospects of employment.
On the other hand, there is a tendency for old people to
migrate from the city to the country. As may be seen by
the table giving the percentages of the female population
of the United States in rural and urban communities, the
age distribution of urban females is especially favorable
for a high birth rate and a low death rate inasmuch as cities
contain relatively more persons in the middle periods of life.

TABLE 28. — PERCENTAGE OF THE FEMALE POPULATION OF THE UNITED STATES,
AGED 0-4 AND 20-44, 1910-1930

Ages

Rural

Cities

2,500-25,000

25,000-100,000

1 00,000-500,000

Over 500,000

0-4

20-44

0-4

20-44

0-4

20-44

0-4

20-44

0—4

20—44

1910

13.0

34-7

10.2

41.6

9-7

44.6

9-1

46.1

10.3

45.0

1920
1930

12.2

10.7

33-8
33-3

IO. I

8-7

39-5
38-9

9-7

8.2

42.9
41.6

9.1

8.8

44-7
43- *

9.8

7-7

44-7
45.0

Because of the peculiar composition of their inhabitants
cities often show a higher crude birth rate than that of the
surrounding country. If, however, the birth rate is measured
in terms of women of childbearing age (fifteen to forty-five)
instead of per thousand inhabitants, the relation is often
reversed. In many cases the birth rates of cities are increased
by the growing custom of rural women to come to a city
hospital to give birth to their children. Where the birth is
credited to the city instead of to the residence of the mother,
the urban birth rate is raised at the expense of the rural.

GROWTH OF CITIES AND ITS EFFECTS

In many cities of the United States, especially in the North
and East, the real birth rate tends to be high on account
of the large percentage of prolific foreign immigrants. Urban
birth rates of foreign-born women have commonly been
higher than the rural birth rates of native-born women,
and where the population of cities is largely composed of the
foreign born the urban birth rate may be higher than the
rural. If, however, we compare the birth rates of native-born

Class of

Population

Urban
7 Cities largely
American stock*

All cities over
100,000 population

All cities 2,500 to__7/H
100,000 population °^

Rural

Rural non-foirm
(mostly village) — 471
population

,--^93

Rural -farm

545

population
Leslie county
Eastern Kentucky-9 1 5
(9 5% on farms)

Abou
1,000
moii
Sta-

f 360
wome
ntonn
•ionar

chile
noire
popu
Y

\ren
neoe
lex -Ho

per
sscxr^
n

'to

200 400 600 800

Number of Children per 1,000 Women

• Par-Hand (Oregon), San Francisco, Los knoteles, Kansas Cif v,
Si Louis, NoishVTIle/oind Aitonta

FIG. 81. — Number of children under five years of age per 1,000 women, fifteen to forty-four
years of age, in the urban and rural areas of the United States in 1930.

and foreign-born women in the same kind of an environment,
we find that in both rural and urban areas the foreign-born
mothers have a higher fertility.

There can be no question that urban life decreases the
fertility of all classes subjected to its influence. Recently
the birth rate of foreign-born mothers has rapidly fallen
owing to the increasing age of the large numbers who came
here before the restriction of immigration.

As is stated in the chapter on the death rate, the mortality
of cities is as a rule higher than that of the surrounding

1,000

324 HUMAN GENETICS AND ITS SOCIAL IMPORT

country. In many cities there are more deaths than births,
and where there are not, the growth of the cities through
natural increase is usually due to the favorable age com-
position of their inhabitants. By and large, cities have been
centers of extinction. It is a well-recognized fact that the
rural districts supply the real material for population
growth. People are produced in the country to be destroyed
in the city. Hence were it not for the continual migration
from the country to the city many urban populations would
soon decrease in numbers. According to Whelpton, the
"true," or stabilized rate of natural increase in nine of the

TABLE 29. — CHILDREN 0-4 PER THOUSAND WHITE WOMEN, 20-44, IN THE UNITED

STATES IN 1920

Cities

Rnril

2,500-10,000

10,000-25,000

25,000-100,000

Over 100,000

Native born . .

720

477

434

390

34i

Foreign born.

998

873

861

766

679

largest cities of the United States in 1928 was a negative
quantity ( — 5.1 per thousand), and, according to Lorimer
and Osborn, "Effective fertility in 1925-29 in the urban
areas appears as only 5 per cent below replacement quotas
in Maine; in other states it runs: Vermont, 1 1 per cent below;
Massachusetts, 18 per cent below; New York, 27 per cent
below; Indiana, 7 per cent below and Illinois 23 per cent
below."

The stabilized rate of natural increase is likewise inade-
quate in the larger cities of Europe. This is especially true
of Paris, London, Vienna, and Berlin. According to Burg-
dorfer, Berlin would require a birth rate of 17.4 for mainte-
nance, but in 1927 the birth rate had fallen to the remarkably
low level of 9.9, a rate which would be still further reduced
to 7.6 in a stationary population. In the same year the birth

GROWTH OF CITIES AND ITS EFFECTS 325

rates were 1 1 . i in Dresden, 1 1 .6 in Frankfurt, 1 2.0 in Munich,
12.0 in Stuttgart, 12.2 in Hamburg — all far below the main-
tenance level. Hansen has remarked that if the rural popula-
tion of Germany consisted of Negroes, while the cities
were inhabited by the whites, it would not be long before
the entire population would be black. In the long run the
character of the population of a country is determined by
the kind of people who inhabit the land.

We may regard cities, then, as constituting a continual
drain upon the population of a country. As they increase
in size the drain becomes ever greater in magnitude. The
growth of cities has become an important factor in the
decreasing rate of population growth in the more highly
civilized peoples of the earth. It would be very desirable,
therefore, to know how the genetic qualities of migrants to
the cities compare with those of the people who remain
in the country. Galton has expressed the view that the more
intelligent and enterprising individuals of the rural areas
tend to seek their fortunes in the cities and thus lead to the
genetic impoverishment of the rural population. For several
reasons this seems to be a fair conclusion, but it is difficult
to secure the data required to subject it to a critical test.
In some regions at least, the cities may attract the vagabonds
and ne'er-do-wells to whom work on the farm makes little
appeal. In the United States and most other countries no
official records are kept of the comings and goings of people;
hence we must rely upon special studies of individual areas
for whatever evidence may be obtained upon this problem.
Unfortunately the evidence is not so plentiful or so con-
vincing as could be desired. We can mention only a
few of the studies which have been made. There is little
doubt that in isolated regions in New England and the
Middle Atlantic States which have become reduced in
population on account of poor soil, communities have

326 HUMAN GENETICS AND ITS SOCIAL IMPORT

suffered from the loss of their more intelligent members.
In some of these the percentage of mental deficiency is
high. The Hill Folk studied by Danielson and Davenport,
and later by Miller, affords an illustration of a community
characterized by poverty, mental deficiency, physical
defect, and unfortunately also by high fertility for several
generations. There are isolated communities of "poor
whites" in relatively barren regions of the South where
they have lived and inbred for many years. In Colvin
Hollow, Virginia, studied by Sherman and Henry, we have
an area of declining economic productiveness associated
with low mental status among the inhabitants. When the
region commenced to deteriorate "the more energetic
began to desert the log huts and migrate to other parts
of the state. A few were able to establish themselves and
quickly forgot their mountain associations. Many failed
and returned."

The studies of Gee and Corson on Rural Depopulation in
Certain Tidewater and Piedmont Areas of Virginia showed
that there was a distinct tendency for the more educated
persons to migrate away from the region. Of the 1,636 whites
studied, 40 per cent of those who had attended high school,
46 per cent of those reaching the seventh grade, and 55 per
cent of those who had gone to college or special training
schools had migrated, as compared with 35 per cent who
had reached the fourth grade or less, and 34 per cent of
those who got no further than the fifth or sixth grade. The
same relation between education and migration is shown
also by the 1,253 Negroes included in the investigation.
Of course, failure to obtain a certain grade in school may
be due entirely to circumstances having no relation to
innate ability, but several studies have shown that those
who drop out of school in the lower grades are frequently
characterized by a low average I.Q., and it is reasonable to

GROWTH OF CITIES AND ITS EFFECTS 327

infer that a part of this failure is the result of a real inherent
deficiency in intelligence.

Several studies on the relative I.Q.'s of urban and rural
children show that the latter as a rule make the lower
scores. Jones, Conrad, and Blanchard in a study of rural
and urban children in northern New England conclude that
while "a rural child moving to the city would increase his
intelligence-test scores merely as a result of changed environ-
ment ... it is unsafe, however, to infer that the average
retardation of rural children is chiefly due to environmental
factors." The authors conclude that "the most likely esti-
mate" is that about half the average difference between the
scores of urban and rural children "is attributable to factors
other than those derived from the social and educational
environment."

How far the average differences in the I.Q.'s of city and
country children are due to the superior educational advan-
tages of city schools is not easy to determine. In attempting
to estimate the character of urban migration, I am inclined
to place more emphasis upon the fact that individuals
graduating from high schools and colleges have a marked
tendency to migrate from the country into cities where
they find careers open to their talents. The schools are
selective agents in which persons with low native ability
are weeded out at various stages of their progress, and those
who survive to pass through the upper grades doubtless
have a somewhat higher measure of native ability than the
general school population. Sorokin and Zimmerman have
concluded that there is a "net law of rural-urban social
selection" according to which "the cities attract the extreme
while the farms attract and hold the mean strata in society."
There is evidence, however, that the nature of selective rural-
urban migration is subject to much variation in different
regions, and at present we do not have a sufficient number

328 HUMAN GENETICS AND ITS SOCIAL IMPORT

of critical studies to enable us to tell what the general
influence of urban selection is upon the population of any
country. If, on the whole, it exercises a dysgenic effect,
as seems not unlikely, it is highly important that we obtain
more detailed knowledge of its workings. Should the dis-
couragements which those engaged in agricultural pursuits
have had to face in recent years lead the more intelligent
to abandon farm life to be replaced by people of lower
standards of living and a lower grade of intelligence, the
native quality of the population will surely decline. Since
those who till the soil are the chief source of population
growth, it should be the policy of every nation to see that
its rural inhabitants consist of physically and mentally
sound and healthy stock.

Suggested Readings

Lorimer and Osborn ('34), chaps. 2, 4, pp. 59-66, 84-96. Thompson
('35), chaps. 17-20. Sorokin and Zimmerman ('29). Gee ('31 and '33).

Questions

1. What proportion of the population is foreign born and what propor-
tion consists of native Americans of native parentage in the following
cities: New York, Boston, Chicago, Philadelphia, Atlanta, New Orleans?

2. Are the populations of cities more or less homogeneous than those
of the surrounding rural areas ?

3. Compare the age composition of the following cities with that of
the states in which each is situated: New York, Chicago, Detroit,
Pittsburgh.

4. Look up the sex composition of a half dozen large cities. What do
you infer as to the cityward migration of the two sexes ?

5. How is urban selection likely to affect the future of the Jewish
people ?

6. Why are people in cities less susceptible to certain contagious
diseases than the inhabitants of the country ?

7. How do city and country compare as to the physical development
of their children ?

8. From the standpoint of maintaining health what are the advantages
and the disadvantages of large cities as compared with rural areas?

GROWTH OF CITIES AND ITS EFFECTS 329

9. In what ways do the industries of a city determine the selective
character of urban migration ?

10. How is urban life in the United States tending to influence the
relative rates of increase of native-born and foreign-born stocks ?

11. Why do chambers of commerce in cities endeavor to promote
increase in numbers? Is such increase a benefit to all classes of city
dwellers ? Are there any classes who are disadvantaged as a result of city
growth ?

12. On the whole, do you think that cities attract the most intelligent
or the least* intelligent of the rural population ?

13. What do you think will be the eugenic effect of the present depres-
sion in agricultural industry ?

14. Can you think of any feasible methods by which the state could
encourage people of superior natural endowments to live in the country?

CHAPTER XXIII

THE BIOLOGICAL EFFECTS OF MIGRATION

IN THE continuous replacement of one stock by another
which has gone on during the evolution of the human
species, the migration of peoples has played a very important
role. The invasion of other territories may or may not
involve war, but it is always productive of a certain amount
of racial change. Formerly peoples often migrated en masse.
In the raids of the Huns, Tartars, Goths and Vandals, and
the exodus of the Children of Israel from Egypt, the men,
women, and children with whatever chattels they possessed
sallied forth to seek their fortunes in new territories. The
causes of these migratory movements are varied. Over-
population, the pressure of hostile invaders, the failure of
the food supply as a result of drought or other causes, and
the allurements of the wealth and fertile soil enjoyed by
other peoples, are among the more common incentives
which have led people to try to possess themselves of other
lands. As civilization has advanced, these mass movements
of whole peoples have given way to the migrations of
individuals or small groups which for the most part involve
no breach of peaceful relations.

Peoples sometimes leave their home land on account of
political oppression or the desire to secure freedom of
religious worship, but the numbers influenced by such
considerations are relatively small; the prevailing motives
are and have always been economic. Countries which are
overpopulated often send forth many emigrants, and
sparsely settled countries which offer attractive economic

330

THE BIOLOGICAL EFFECTS OF MIGRATION 331

opportunities tend to receive many immigrants. The move-
ments of peoples, like the movements of currents of air,
are from areas of high pressure to areas of low pressure.

Migrations have been greatly facilitated by the develop-
ment of cheap and rapid means of transportation, as is
well illustrated by immigration into the United States.
Agents of steamship companies have permeated Europe
to secure possible passengers, and have set forth the great
advantages awaiting the worker in this land of plenty.
Crossing the ocean is a very different matter now from what
it was two centuries ago. Passage by steerage is cheap and
lasts but a few days. Many thousands come to the United
States when work is plentiful and return to their native
country when it is scarce. This is especially true of the
immigrants from southern Europe, and to a certain extent
of immigrants from Mexico.

Of all countries of the world the United States has received
the largest number of immigrants from other continents.
Between 1820 when the number of incoming aliens was
first recorded and 1929, it is estimated that about 38,000,000
entered the United States, the majority of whom, about
30,000,000, have remained permanently. In addition to the
immigrants entering the United States others have gone
into Canada, Mexico, Central and South America, so that
the total migrating to countries of the Western Hemisphere
since 1800 is considered to be about 57,000,000, most of
whom came from Europe. Besides, Europe has sent numerous
migrants to Australia, New Zealand, Africa, and many
other parts of the world. The total exodus from Europe
during the nineteenth century has been estimated at approxi-
mately 60,000,000. And this during a period when the
population of Europe was undergoing an unprecedentedly
rapid growth. The greater part of this vast movement of
peoples was an orderly and peaceful migration into countries

332 HUMAN GENETICS AND ITS SOCIAL IMPORT

in which the newcomers were welcomed or at least not
actively opposed. For the most part also it sprang from the
desire of workers to better their living conditions by settling
in comparatively new countries with many undeveloped
natural resources.

During the nineteenth century countries of other con-
tinents have sent forth emigrants, but the numbers do not
compare with those coming from Europe. One of the coun-
tries most prolific in emigrants is China. Frequently one to
two million Chinese have migrated into Manchuria in a
single year, although to a certain extent this may be regarded
as an internal migration. But Chinese are found quite
plentifully in the Philippines, East Indies, Formosa, Siam,
Hawaii, parts of South America, and the United States.
Japan which, like China, is greatly overpopulated has sent
forth emigrants into Korea, Manchuria, the Philippines,
Hawaii, and also into the United States until the number
was gradually reduced following the so-called gentlemen's
agreement. From India have come immigrants who have
gone to South Africa, Malaya, and many islands of the
Pacific, but the number, two to three millions, is insignificant
as compared with the millions living in the home country.

Although Asia has several times the population of Europe
and a vast proportion living under conditions of over-
crowding which create a powerful incentive to send her
people into other lands, relatively few Asiatics have migrated
beyond her borders. Europe has been in a very different
situation. Owing to her highly developed civilization, the
better organization and equipment of her fighting forces,
and especially her naval power, which gave her undisputed
control of the sea, Europe was able to seize upon large areas
of the earth to colonize and exploit. The most successful
nation in the acquisition and peopling of new territories
was Great Britain, whose dominions almost encircle the

THE BIOLOGICAL EFFECTS OF MIGRATION 333

globe. A leading role was once played by Spain, but she
has now lost most of her foreign possessions. To a somewhat
less degree extra territories have been acquired by the
French, Portuguese, Dutch, Germans, Danes, and Belgians.
The Europeans have grabbed while the grabbing was good.
The result has been that Asiatics are kept out of extensive
regions which they might have occupied. They look with
envious eyes upon thinly populated Australia and New
Zealand whose inhabitants view with apprehension the
increase of the teeming millions of their Asiatic neighbors,
and take all possible precautions to keep their population
white. Asiatics are accordingly excluded from Australia
and New Zealand in the fear that, once the gates are opened,
the population would eventually be overrun by incomers
with low standards of living who would gradually supplant
the whites in the struggle for existence. Asiatics likewise
find themselves debarred from the United States and
Canada, the two outlets most favorable for their expansion.
South America as yet offers few attractions, and her coun-
tries would probably restrict Asiatic immigration if it
threatened to increase unduly in volume. Africa, which is
almost completely under European control, offers limited
opportunities for immigration from Asia. Many Hindus
have migrated into the parts of Africa controlled by the
British, but they are now excluded from South Africa,
and their entrance into Kenya is discouraged; thus the
volume of immigration from India has become reduced.
Hindus are not particularly desired in most other British
possessions; hence they find relatively few places open to
them.

As countries increase in population they show a tendency
to restrict immigration. When the United States was a
young and sparsely settled country it welcomed the foreigner
with open arms. There were vast stretches of fertile land

334 HUMAN GENETICS AND ITS SOCIAL IMPORT

to be tilled, forests to be cut, and mineral wealth to be dug
out of the ground. We needed people to develop the sources
of wealth which abounded on every hand. We aspired to
become a populous, rich, and powerful nation. We were
persuaded, rightly or wrongly, that we enjoyed a greater
degree of political and religious liberty than the people
living in the monarchies of the old world, and we were glad
to offer them a haven of refuge from their oppressors. So
long as we were convinced that the immigrant was a valuable
economic asset we easily persuaded ourselves that it was a
very noble and gracious act to encourage his coming. Hence
we opened our doors freely to all comers. The famine in
Ireland during the forties sent great numbers of Irish to
this country, and there was soon a considerable immigration
from Germany, the Scandinavian countries, as well as Great
Britain. The great mass of European immigration in the
first three-fourths of the nineteenth century as well as
in the preceding century was of northern European origin
and therefore made no marked change in the ethnic com-
position of the American people. There was much inter-
marriage between the incomers of different nationalities
and between these and the native-born Americans. The
immigrant stocks proved to be thoroughly assimilable in
every way.

In the latter part of the nineteenth century and during
the earlier years of the twentieth the shift of the tide of
immigration from northern to southern and eastern Europe
brought in numerous Italians, Poles, Austrians, Greeks,
Hungarians, Russians, and Bulgarians together with a very
much reduced influx of the older immigrant stocks. Unlike
the peoples from northern and western Europe the majority
of the newer immigrants lodged in cities, many of them
never budging after their arrival at New York, Philadelphia,
or other ports of entry. The more recent immigrants were

THE BIOLOGICAL EFFECTS OF MIGRATION

335

mostly unskilled laborers who went into the mines and
factories or engaged in menial employments in the cities.
They afforded a plentiful supply of cheap labor, and their
coming was encouraged by employers, who wanted workmen
of low standards of living, the kind that would be satisfied
with very moderate wages. As compared with the older
immigration the southern European stocks were char-
acterized by a high degree of illiteracy. From 1899 to 1909,

I t

Sources of Immioiroints
into the United States

1840 IffbO I860 1900 1920

FIG. 82. — Proportions of immigrants entering the- United States from 1820 to 1920. The
vertical scale indicates the per cent that each nationality constitutes of the total immigrants.
(After Harper. Courtesy of Eugenics.)

54.2 per cent of the immigrants from southern Italy were
unable to read or write. The percentage of illiteracy in the
newer immigration during this decade was 35.8 as compared
with 2.7 in the older immigrant stocks. On the whole, the
newer immigrants, although they included many people
who formed valuable additions to our population, proved
to be rather more difficult to assimilate than the old. During
and after the World War many efforts were devoted to the
Americanization of these foreign elements in the hope of
converting them more rapidly into cooperative American
citizens. The tremendous volume of immigration imme-

336 HUMAN GENETICS AND ITS SOCIAL IMPORT

diately preceding the war rendered these efforts difficult
of accomplishment, and it came to be perceived that the
presence of so many illiterate aliens, whatever may have
been their native qualities, created many social, educational,
and other problems. The result was that many were con-
vinced that a very large number of such aliens was not an
unmixed blessing. American laborers felt the competition
of the cheap labor from southern Europe, and they exerted
their influence in favor of the restriction of immigration,
but their political efforts were opposed by organized groups
of employers in the coal and iron industries, meat packing
plants, railroads and steamship companies, and other
powerful organizations which spent millions in the endeavor
to sway public opinion in favor of the unrestricted immigra-
tion of aliens.

The volume of immigration was much reduced during the
World War, but for a few years after the Armistice was
signed it increased rapidly, reaching 802,000 in 1921, and
threatening to assume embarrassing proportions if suffered
to continue without restriction. Accordingly, Congress
was led to pass a law in 1921 limiting the number of aliens
admitted to 3 per cent of the number in the several nationali-
ties in the United States in 1910. In 1924 the number was
reduced to 164,667 and in 1929 it was further reduced to
I53?7I4- During the financial depression there has been an
unusual return movement, so that the departures have
exceeded the number entering the country.

The reduction of immigration from northern and western
Europe was doubtless due in part to the decline of the birth
rate in these regions. Another factor was the industrial
development of these countries, which created more favor-
able conditions of life, so that workers would not greatly
improve their lot by coming to the United States. Also the
supply of free land that formerly attracted so many northern

THE BIOLOGICAL EFFECTS OF MIGRATION 337

Europeans was exhausted and the immigrants would have
to become laborers on farms or in mines or compete with
southern Europeans in the cities. Among the southern and
eastern Europeans there were fewer employments to absorb
the growing population. The birth rate continued to be
high and there were greater temptations to seek better
opportunities in other parts of the world.

The establishment of the quota system limiting the
proportion of immigrants who could enter from any one
country led to a great reduction of immigration from
southern Europe. The aim of the assignment of quotas was
to preserve approximately the existing ethnic composition
of the American people. This was accomplished in accordance
with a general rule without making invidious discriminations
against any European nation. The quota system was not
applied to nations in the Western Hemisphere, and immi-
grants from Canada, Mexico, the West Indies,, and Central
and South America could enter in any desired numbers,
subject only to the literacy test and a small fee required of
all incoming aliens. The reduced numbers of laborers coming
from southern Europe had the effect of stimulating immigra-
tion from the countries of the Western Hemisphere, and
especially from Mexico. The Mexican invasion threatened
to give rise to race problems second only to those created
by the presence of the Negro. The great majority of Mexican
immigrants consisted of peon laborers mostly of Indian
blood. Owing to the demand for cheap labor in the large
farms, mines, and various industries in the Southwest,
Mexicans poured over the border in ever-increasing numbers.
Up to 1900 Mexican immigration had been almost negligible
in volume, seldom exceeding five hundred per annum. In
1908 the number rather suddenly increased from 915 to
5,682. By 1924 the number reached its maximum, namely
87,648, and in 1925, 1926, and 1927 the numbers were

338 HUMAN GENETICS AND ITS SOCIAL IMPORT

32,3783 42,638, and 66,766 respectively. In large areas of the
Southwest Mexicans performed most of the unskilled labor.
The pick and shovel men on the Southern Pacific and Santa
Fe Railroads were said to consist exclusively of Mexicans.
Being used to low standards of living the Mexican laborers
were content with low wages and poor living quarters, which
white laborers would not accept. They proved to be tractable
and fairly industrious, and on the whole more profitable to
employ than the casual white workers who could be obtained
for the wages offered. The result was that they drove white
labor out of one industry after another in the Southwest.
As their numbers increased, Mexican laborers pushed farther
to the North and East, and Mexican quarters grew up in
Omaha, St. Louis, Chicago, Pittsburgh, and other large
cities. In parts of the South, Mexicans replaced the Negroes
in several employments and proved to be one of the causes
of their migration into the Northern states.

Many of the employments of Mexicans are seasonal,
and they trek with their families from one place to another
as opportunities for employment determine. Frequently
they are unemployed and become a burden upon charity.
Although they possess many attractive qualities, it cannot
be said that they contribute much to the cultural life of the
communities they enter. Politically they are largely under
the sway of bosses who determine how they shall vote. Their
record for crime is distinctly bad, and in many communities
they create embarrassing social and educational problems.
Their birth rate is very high and in many localities the
majority of the children in the schools are Mexicans. The
studies which have been made on the intelligence of Mexican
children indicate that their average I.Q. is low, but to what
extent this is due to the disadvantages of their upbringing
instead of their heredity is not determined. At least the
Mexican peon has shown little evidence of intellectual

THE BIOLOGICAL EFFECTS OF MIGRATION 339

superiority. But granting that his defects are cultural and
not genetic it remains true that the average Mexican is
singularly slow of assimilation. Even today there are numer-
ous Mexicans in New Mexico, descended from the population
of the territory when it was taken over by the United States,
who are unable to speak the English language; and even
in the state legislature the proceedings have to be published
in both English and Spanish for the benefit of constituents
who are unable to read the English language.

The race mixture which occurs between Mexican peons
and whites is largely on the basis of illegitimate unions
between white males and Mexican females. There is a good
deal of miscegenation between Mexicans and Negroes and
between Mexicans and American Indians. Some Mexicans
are of pure Spanish extraction, but these constitute a small
minority. More have some admixture of Spanish or other
white blood, but the rank and file of Mexican laborers are
almost pure Indians.

Many people in the regions in which Mexicans have come
to be numerous made efforts to secure the curtailment of
Mexican immigration. A bill, the Box Bill, was introduced
into Congress with the aim of putting Mexico on the same
quota that applies to the nations of Europe. In the discus-
sions of this bill before both the Senate and the House
Committees on Immigration the large financial interests
who profited by cheap Mexican labor were represented by
numerous and able lobbyists who contended that many
industries were dependent upon the Mexicans, that white
labor could not be secured for the work that had to be done,
that the Americans who were forced out of their jobs went
into better paid positions, that most Mexicans were only
temporarily employed and subsequently returned to their
native country, and that the Mexican immigrants were on
the whole peaceable citizens and good neighbors who would

340 HUMAN GENETICS AND ITS SOCIAL IMPORT

be a valuable acquisition to the country. The chief argu-
ment was that the Mexicans were a valuable economic asset
and that their exclusion would have a disastrous effect
upon many industries.

On the other hand, those opposed to Mexican immigration
contended that the Mexicans were the reverse of a financial
asset to the working classes and the renters of land inasmuch
as they were driven out by Mexican competitors. Mr. Mc-
Kemy, Commissioner of Labor in Texas, stated that "Mexi-
can labor has supplanted native American labor to such an
extent that today fully 75 per cent of the common or un-
skilled labor in my State is performed by Mexicans. This
deplorable situation can be traceable to only one cause and
that is the inability of the American to compete with the
Mexican in living standards." American renters and small
farmers were almost completely eliminated from certain
sections of the Southwest by Mexican competition, and the
schools were largely filled by Mexican children.

The contention that Mexicans return to their native
country proved to be a specious argument. It is true that
there is much migration back and forth across the border.
But the very rapid increase of the Mexican population in
the Southwest, the large numbers of Mexican children in
the public schools, and the portentously high birth rate of
Mexican families showed only too clearly that we were
acquiring a new race problem of no small proportions. Owing
to the difficulty of adequately guarding the long border
between the two countries, numerous Mexicans have entered
illegally. Those who were unable to pass the simple literacy
test imposed or those who wished to avoid the payment of
the visa fee and head tax ($24) were often led to adopt the
simple expedient of paddling across the Rio Grande or cross-
ing through the brush into New Mexico, Arizona, or Cali-
fornia. The Commissioner of Immigration estimated that

THE BIOLOGICAL EFFECTS OF MIGRATION 341

those entering illegally were as many as those coming through
the regular channels. The census estimate of the number of
Mexicans who were born in Mexico and were living in the
United States in 1910 was 221,915; in 1920 it was 486,418;
thus showing a gain of 264,503. The excess of admissions
over departures of Mexicans between 1910 and 1920, accord-
ing to the reports of the Commissioner General of Immigra-
tion, was 163,105. Evidently more than 100,000 must have
entered without giving an account of themselves. By 1930
the foreign-born Mexicans amounted to 616,988 and the
total Mexican population was 1,422,533. Since the depression
large numbers of Mexicans finding no employment have
returned to their native country. In fact, since 1930 more
have departed than have come in. But whenever a demand
for labor arrives Mexican immigration will again assume large
proportions unless steps are taken to keep it within bounds.
I have dwelt upon Mexican immigration because it
presents' a typical illustration of the working of a process
that has repeated itself many times in the course of history.
People of inferior culture and low standards of living are
induced to enter a country because their labor is cheap
and they contribute to the prosperity of the employing
classes. The wealth of a country is increased by their coming.
The classes who are interested in cheap labor are politically
powerful, and governments, which are usually concerned
only with the more obvious economic bearings of the ques-
tions with which they deal, commonly disregard everything
else. The effect of such immigration upon the welfare
of the laboring classes of a country is as a rule given scant
consideration unless these classes have sufficient political
power to make their influence felt. Even the Immigration
Commission, which was appointed to make a study of all
aspects of immigration into the United States and which
reported its findings in twenty-eight substantial volumes,

342 HUMAN GENETICS AND ITS SOCIAL IMPORT

expressed the view that immigration is a purely economic
problem. Until recently it has been treated as such in
practically all the legislation which has been enacted on
the subject. The only discriminations made on the basis
of quality were to forbid the entrance of the insane, epilep-
tics, imbeciles, criminals, prostitutes, anarchists, or people
liable to become a public charge. But up to a few years ago
our administration of these regulations was almost un-
believably lax. These measures, so far as they went, doubtless
had a eugenic effect. They have gradually become wider in
scope and more effectively enforced. Aside from the exclusion
of Asiatics the quota regulations represent the first thorough-
going effort to regulate immigration on the basis of national
origin. Incidentally this meant to a certain degree the
control of immigration on the basis of racial stock, and
whether or not it is eugenic or dysgenic in its influence
depends upon the innate characteristics of the various
peoples who enter the country.

Properly to evaluate the genetic characteristics of our
incoming aliens amid their differences in language, traditions,
degrees of education, and the effects of varied environmental
influences is no easy task. The first extensive collection of
data bearing on this problem was supplied by the Army
Mental Tests during the World War. Mental tests were
administered to over a million men of all nationalities and
the average scores were calculated for each national group.
For those little familiar with the English language, a separate
test, the Beta test, was designed to obviate linguistic handi-
caps, the English-speaking recruits being given the so-called
Army Alpha Test. The average scores of recruits from
different countries were found to present rather wide varia-
tions. The records of a number of the leading national
groups are given in the table (Table 30). Recruits from the
nations of northern and western Europe (English, Scotch,

THE BIOLOGICAL EFFECTS OF MIGRATION 343

Scandinavians, and Germans) tested relatively high. Those
from southern Europe tested relatively low. Do these
different scores indicate differences in native intelligence?
Even those who had most to do in devising the tests and in
compiling the results have conceded that the scores are
influenced to a considerable extent by environment and
training. Most psychologists nowadays do not consider

TABLE 30. — PERCENTAGES OF GRADES A AND B AND D, D — , AND E IN THE ARMY
MENTAL TESTS ACCORDING TO NATIONAL ORIGIN

Country

Grades A and B Grades D, D — , and E

England 19.7

Scotland 13.0

White draft 12.1

Holland 10.7

Canada 10.5

Germany 8.3

Denmark 5.4

Sweden 4.3

Norway 4.1

Ireland 4.1

All foreign countries 4.0

Turkey 3.4

Austria 3.4

Russia 2.7

Greece 2.1

Italy 0.8

Belgium 0.8

Poland 0.5

8-7
i3.6

24.1

9.2

i5-o
13-4
19-4

25.6
39-4
45-6
42.0

37-5
60.4

43-6
63-4
24.0
69.9

such results as giving an adequate measure of differences
in genetic factors affecting mental development. Demon-
strably, as we have before remarked, training influences in no
small degree the ability to make a good score on any mental
test yet devised. This is shown by the fact that the scores
on the Beta test were found to improve with longer residence
in this country. It is indicated also by the wide range of
scores on Alpha tests in the native-born recruits from states
that differ from each other in the degrees of average educa-

344 HUMAN GENETICS AND ITS SOCIAL IMPORT

tion. Whether or not extrinsic factors account entirely for
the differences in scores is not definitely established.

And even if genetic differences occur as are indicated by
the test scores, it would not follow that the tests afford an
adequate gauge of the average intelligence of the populations
in the countries from which the representatives in the
army were derived. As we have seen, our recent immigrants
from the south of Europe include a large proportion of
unskilled and illiterate laborers whose average I.Q. is
probably below that of the general population of the country
from which they came. The same is shown by the studies of
Gamio to be true of Mexico. It is reasonable to conclude that
the under man is represented among recent immigrants to a
greater extent than among the literate and skilled incomers
from northern Europe, and the differences shown in the
table, therefore, may result in part from the kind of selection
occurring in the various national groups.

However we may interpret the findings of the army
mental tests, several investigations have shown that the
average scores of children of different national groups in
the schools give results which are roughly parallel to those
derived from adults in the army. In a study by Hirsch on the
intelligence of school children in four small mill towns of
Massachusetts the average test scores of different types of
tests showed the following gradations: Polish Jews, Swedes,
English, Russian Jews, Germans, Americans, Lithuanians,
Irish, British Canadians, Russians, Poles, Greeks, Italians,
French Canadians, and Portuguese. Over a third of the
Portuguese and French Canadians, and almost a third of the
Italians and Greeks had an I.Q. of less than 80. Whatever
handicaps were caused by foreign languages they did not
prevent high scores being made by the Polish Jews, Swedes,
Russian Jews, and Germans. Kirkpatrick's studies on the
I.Q.'s of children in Massachusetts gave averages on the

THE BIOLOGICAL EFFECTS OF MIGRATION 345

Beta test of 104 for Americans, 100 for Finnish, 83 for
Italians, and 100 for one French Canadian school and 74
for another. Bere found in comparing the Stanford Binet
Test scores of Italians, Bohemians, and Hebrew children in
New York City that the averages were 85, 93, and 98
respectively. On the Pintner-Paterson Performance Test,
however, the highest grades were made by the Italians and the
Bohemians, the Hebrews falling considerably behind, whereas
they were conspicuously in advance on the verbal tests.

Without going into details concerning the several studies
on the relation of intelligence and nationality in schools,
we may say that in general higher scores are made by
native American children and children of northern European
and Jewish ancestry, than are made by children of southern
European, Mexican, Indian, and Negro ancestry. To how
great an extent these differences are genetic and how far
they are environmental in origin we have no clean cut and
decisive evidence. Certainly environmental factors play a
part. Probably occupational selection also plays a part.
That genetic differences are also involved is a probability
whose degree will be estimated differently according to
one's familiarity with genetic principles, personal experience
with the ethnic groups, and various other factors by which
judgments in such matters are commonly influenced.

As might be anticipated the percentage of both mental
defectives and of intellectually superior individuals varies
with the average I-Q-'s as indicated by mental tests. The
mental deficiency rates in the army were found to be high
for Poles (5.8), Italians (5.5), Russians (7.4), Austro-
Hungarians (6), and less for Canadians (2.4), Scandinavians
(1.3), British (0.9), and Swiss (0.9). Even if the mental
differences revealed by intelligence tests are not genetic
they persist for at least two generations and probably more.
They are in any case, therefore, of very great importance in

346 HUMAN GENETICS AND ITS SOCIAL IMPORT

relation to the practical problem of regulating immigration.
Granting that a stock with inferior intelligence will ulti-
mately recover greatly from its handicaps, its presence in
large numbers may seriously affect the welfare of a nation
for a great many years. In crime certain foreign stocks
contribute much more than their quota, or proportion to the
general population. The quota for the Balkans, according
to the studies of Laughlin, was 278; for Italy 218, and for
Russia 126, as compared with 82 for native Americans.
According to the same investigator the foreign born con-
tribute more than their quotas of insanity, epilepsy, and
pauperism. That the native born contribute more than
their quota of feeble-mindedness may be due to the fact
that more cases of feeble-mindedness than of insanity and
epilepsy are detected and not allowed to enter the country.
The high ratio of the foreign born among the insane, etc.,
is probably due largely to their higher age composition,
although their relatively low educational and cultural
status is probably a contributory factor.

As a rule the crime records of southern Europeans have
been high, while those of the foreign born from northern
Europe have been below the average of the native-born
white Americans. Records for homicide have been especially
high for southern Italians, Mexicans, and Negroes. There
can be no question that whatever advantages have been
derived from the enormous immigration of the pre-war
period it has directly or indirectly been productive of a
number of drawbacks. How many generations will be
required to overcome the disadvantages resulting from the
presence of some of our immigrant stocks no one can tell.
To the extent that these disadvantages result from hereditary
deficiency they will remain indefinitely. There is much fine
hereditary material in practically all the immigrant stocks
we receive. The question of paramount importance from the

THE BIOLOGICAL EFFECTS OF MIGRATION 347

biological standpoint is how the average hereditary qualities
of our immigrants compare with those of our native popula-
tion. Immigration may prove to be an important factor in
determining the genetic quality of a people. Hitherto it
has been treated as a purely economic matter, as if material
wealth were more important than human beings. But, as
was well stated by Dr. Laughlin, "immigration is a long-time
investment in family stocks rather than a short-time invest-
ment in productive labor."

It has been urged that we are not justified in excluding
any people on eugenic grounds unless it is definitely proved
that they are of inferior hereditary quality. Granting that
the low mental ratings of certain peoples are not definitely
proved to rest upon a genetic basis, so long as the question
is an open one why should an immigrant-receiving country
assume the burden of proof? It might well be contended
that the wiser course would be to shift the burden of proof
to the other side and refuse to admit all aliens until it was
established that their genetic endowments are not inferior
to those of our own population. So long as action is called
for, it is best to be on the safe side. Whatever its racial
effects may have been in the past immigration can be so
regulated as to be made an important factor in race improve-
ment. By requiring high standards of admission from every
country so that only those of sound physique and demon-
strably good mentality and character are allowed to enter,
the American people would not only be improved as to
their hereditary qualities, but they would gain a population
which would soon prove to be a valuable asset in many
ways. At least until we begin to suffer from the ills of over-
population we should adopt an immigration policy which
would bring us only those who would raise the general
level of our own inhabitants. There is no reason why this
cannot be done. It would be simply political stupidity not

348 HUMAN GENETICS AND ITS SOCIAL IMPORT

to avail ourselves of the opportunity. But there is always
danger that, instead, the control of immigration will be
exercised by interests caring nothing about the quality of
the future population and bent only on securing the profits
to be derived from cheap labor. Eternal vigilance may be
required not only to preserve liberty but to prevent the
best interests of future generations from being sacrificed
on the altar of Mammon.

Suggested Readings

East ('27), chap. 14. Brigham ('23), ('30). Fairchild ('26). Grant ('34).
Lorimer and Osborn ('34), chaps. 6 and 7. Kirkpatrick ('26). Thompson
('35), chap. 24. Taylor ('28-'3o).

Questions

1. What relation is there between the birth rate and emigration in
England, Norway, Hungary, Italy, and France?

2. Why does Italy now discourage emigration and why does Canada
encourage it?

3. How does Australia control immigration ? In what respects has her
immigration policy been superior to that of the United States ?

4. Compare the immigrants into the United States in 1913 with those
in 1880 as to numbers, national origin, percentage of illiteracy, relative
numbers of skilled and unskilled workers.

5. Does the literacy test make for the improvement of the eugenic
quality of our immigrants ? Give reasons.

6. In your private opinion are there any stocks in the United States,
and if so which ones, that are undesirable additions to our population ?

7 Why did Malthus think that emigration affords no permanent
relief from overpopulation ?

8. What diverse interests have figured in the regulation of immigration
into the United States ?

9. What influence has Mexican immigration exerted on the migration
of southern Negroes into the Northern States ?

10. How has migration been provocative of race friction ? Give illustra-
tions from different parts of the globe.

11. Why has the rate of increase of the population of the United States
been greater during the first decades of the nineteenth century than it was
during the later decades ?

CHAPTER XXIV
INBREEDING AND CROSSBREEDING

HUMAN beings have followed many customs in regulat-
ing matings on the basis of blood relationship.
Frequently marriages are prohibited between near relatives
and sometimes between those distantly related. On the
other hand, the closest kind of inbreeding, — that is, the
marriage of brother and sister — has sometimes been prac-
ticed, as among the rulers of ancient Egypt and the Incas
of Peru. The reasons which have led to the diverse and often
fantastic marriage customs among the races of mankind
concern the student of cultural anthropology rather than
the biologist. We may safely conclude that marriages of
near kin were not prohibited because of observations on
their bad biological effects. Sometimes, to be sure, their
biological effects are bad; but it is not likely that uncultured
peoples with no knowledge of heredity would have found it
out.

The real influence of consanguinity in marriage has been
a matter upon which different views have been held even by
special students of heredity. But since the wide applicability
of Mendel's law has been established, geneticists are now
practically agreed as to the interpretation of the results.
The effects of inbreeding and crossbreeding in plants and
animals are varied. Sometimes close inbreeding leads to a
deterioration of the stock and sometimes it does not. Where
deterioration occurs it commonly reaches a limit in a few
generations after which it may be continued for a long period
without further change. Inbreeding has the effect of bringing

349

350 HUMAN GENETICS AND ITS SOCIAL IMPORT

out recessive defects which may be present in a stock and
thus producing offspring inferior to the parents. If the
parents are free from recessive defects, inbreeding produces
no bad results.

Among human beings also close inbreeding is sometimes
unfortunate and sometimes not, depending upon whether
the parties are free from the same types of recessive defects.
The marriage of Charles Darwin and his first cousin pro-
duced four distinguished sons; and many other cousin
marriages have likewise proved to be very fortunate in their
results. Many of our states prohibit cousin marriages and
Oklahoma even prohibits the marriage of second cousins;
but it is doubtful if such laws are biologically defensible.
Some cousin marriages should be encouraged and others
should be discouraged on biological grounds. Whether or
not such marriages should be contracted depends upon the
heredity of the parties concerned.

The biological effects of crossing the different races of
man is a subject upon which opposed views still prevail.
With groups which differ so little as the racial stocks of
Europeans, there is no convincing evidence of any bad
effects resulting from intermarriage. The people of most
European nations are notoriously of mixed racial origin.
Despite the many advocates on both sides of this question
there seems to be no clear indication that people who are
relatively pure racially are either superior or inferior to
others of highly mixed composition. Much information has
been collected concerning the way in which certain anthro-
pological features characteristic of races are inherited in the
hybrids. Some characters such as eye color behave as simple
Mendelian units, while others such as stature, size, and skin
color are dependent upon multiple factors and appear to be
blended in the progeny. But color of eyes and hair, head
form, thickness of lips, high cheek bones, shape and size of

INBREEDING AND CROSSBREEDING 351

the nose, and many other characteristics employed to dis-
tinguish races have, so far as is known, very little significance
from the standpoint of biological fitness. They may be
significant aesthetically, depending upon the particular
taste of the individuals interested, and hence may be
affected by sexual selection, but it is difficult to see how,
•per sey they could have much relation to survival.

The question of chief interest in relation to race crossing
is whether, as has often been alleged, the mingling of very
different races is productive of inferior progeny. Such
crosses should be judged in the light of both their biological
and their social effects. From the purely social point of view
interracial marriages are apt to be unfortunate because of
the very different traditions, customs, and mental attitudes
of the two races. It frequently happens that the half-breed
is a person of uncertain social status, and he may suffer
some degree of demoralization on this account. The status
of racial hybrids varies greatly in different regions. In
most parts of South America it is no drawback to be a
mongrel. In other parts of the world the psychological
attitudes of the people make the position of the cross-breed
very undesirable and cause much unhappiness in those who
venture to marry outside of their race.

In dealing with the purely biological aspects of race cross-
ing we should consider two problems: (i) the possible dis-
harmonies of constitution that might result, and (2) the
effects of crossing superior and inferior races, provided, of
course, any one race is superior or inferior to any other. In
regard to the first of these problems it seems probable, a
priori, that, on account of Mendelian segregation in the
second and subsequent generations, the mingling of very
distinct races would result in many inharmonious combina-
tions. Each race may be assumed to have evolved in the
course of time a fairly well adjusted combination of organs.

352 HUMAN GENETICS AND ITS SOCIAL IMPORT

If the members are tall or short, the proportions between the
lengths of legs, arms, breadths of shoulders, and sizes of
other parts would be much the same in each race. In so far
as these traits are inherited as Mendelian units, one might
find in the second generation combinations of long legs and
short arms, or various other associations of parts which
would detract from the general effectiveness of the whole.
As Davenport has pointed out, such combinations as large
teeth in small jaws are not uncommon, as well as the reverse
combination of large jaws and small separated teeth. "Noth-
ing is more striking," says Davenport, "than the regular
dental arcades commonly seen in the skulls of inbred native
races and the irregular dentitions of many children of
the tremendously hybridized Americans." In Davenport's
opinion, "A hybrid people are a badly put together people."
Perhaps they are apt to be a homely people, for beauty
implies a certain proportionate development of parts, and
such combinations as large heads and small jaws or the
reverse, or a disproportion between the size of the nose and
the rest of the countenance are not conducive to facial
beauty. According to Dr. Mjoen the crosses between very
different racial stocks, such as the Swedes and the Lapps,
are characterized by an unusual number of anatomical dis-
harmonies. On the other hand, the distinguished geneticist,
Dr. W. E. Castle, believes that there is little evidence of
disharmonies resulting from race crossing, at least where
the races are not widely dissimilar. In his experiments on
crossing large with small breeds of rabbits, Castle finds that
the progeny are intermediate in size and retain their inter-
mediate size in subsequent generations. Moreover, they are
vigorous, prolific, and show no indications of having in-
congruous jumbles of parts. One reason for this is probably the
fact that size depends upon many Mendelian factors. Also
the size of a particular organ is to a large extent determined

INBREEDING AND CROSSBREEDING 353

during development by its physiological relationships to the
whole organism. The influence of functional balancing and
adjustment would doubtless tend, in a measure at least, to
overcome any disharmonies resulting from Mendelian segre-
gation. Nevertheless, the fact that Mendelian segregation is
expressed somatically at all would seem to make it very
probable that it would sometimes lead to unfavorable
combinations -of characteristics. This is indicated by the
results of some wide crosses between plants in which the
second generation of hybrids consists practically of only two
types closely resembling the original forms that were crossed.
Out of the many combinations produced, apparently only
those closely resembling the two grandparents are able to
survive. In such crosses intermediate types do not persist,
and there is a reversion to the parental species. While there
seem to be cases of rather incongrous aggregates of parts in
many crosses between distinct races of men, we have as yet
little definite information concerning the extent to which
such crosses are productive of deterioration either physical
or mental. One can only say that there is a distinct danger
that undesirable effects may follow from the crossing of
remote races.

If one race is superior physically or mentally to another,
it would doubtless be better for the more highly endowed
race to preserve its own inheritance rather than to dilute it
by miscegenation. There are many who contend that, barring
possible minor differences of temperament or special apti-
tudes, all races are about on the same level of mental develop-
ment. Formerly backwardness in cultural achievements was
frequently regarded as indicative of deficient mental ability,
and, as a result of this conclusion, the native intelligence of
primitive peoples was greatly underrated. This fact is
brought out clearly in the well-known book of Dr. Boas on
The Mind of Primitive Man. Later studies on the intelligence

354 HUMAN GENETICS AND ITS SOCIAL IMPORT

of primitive peoples have been more critical than the rather
loose observations and deductions of the older anthropolo-
gists. When mental tests came to be applied, it was found
that different races made different average scores. Chinese
and Japanese children in the United States and Hawaii, when
given tests in which language handicaps are minimized, have
usually made very good records. The studies of Garth on
1,050 full-blooded American Indians gave an average I.Q.
of only 68.6. Also, 1,004 Mexicans and 1,272 Texas Negroes
tested by the same investigator made average scores of
78 and 75 respectively. Jamieson and Sandiford found that
Canadian Indians gave a score of 97 on the Pintner Non-
Language Test, 92 on the Pintner-Paterson Performance
Test and 80 on the National Intelligence Test. According to
Garth, the test scores of mixed bloods are higher than those
of pure-blood Indians, and several investigators have
reported that Negroes make higher scores in proportion as
they are light in color. The results of mental tests in Negroes
vary widely according to geographical area and the associated
differences in educational opportunities. The same is true,
as we have pointed out, for the whites. Unquestionably,
the low scores of races with inferior cultural status are at
least in part due to educational handicaps. Whether, as is
maintained by a number of anthropologists and psycholo-
gists, all mental differences can be thus accounted for is a
question which the mental tests alone do not enable us to
solve.

It is a fact of much interest in relation to this problem that,
if one may gauge intelligence on the basis of achievement, the
mental development of mulattoes is superior to that of the
pure blacks. As Reuter has shown, the intellectual leaders
among the Negroes show a very decided preponderance of
individuals with white blood. College graduates, doctors,
lawyers and writers of Negro extraction are mostly mulattoes.

INBREEDING AND CROSSBREEDING 355

Of 143 life members of the National Business League 14 were
black, 60 were dark or medium colored mulattoes, while
71 were light mulattoes or near-whites. Reuter has attempted
to explain the striking superiority of the mulattoes in all
intellectual achievements partly on the grounds that the
mulattoes enjoy a superior culture to the blacks, and partly
because in the period of slavery "the choicest females of the
black group became the mothers of a race of half-breeds."
How far the intellectual superiority of female slaves increased
their chances of bearing children to white fathers is quite
uncertain. After emancipation race mixture probably
occurred most frequently between the inferior members of
both races. The process of social selection may have favored
the mulattoes more than the pure blacks, but the extent of
this influence is a matter of conjecture. According to many
other students of the problem the most natural and reason-
able explanation of the superior achievements of the mulatto
is that they are due to the infusion of white blood.

In general we may say that the proper evaluation of the
native abilities of the different races of man presents formid-
able difficulties, and that our knowledge concerning it is in
a most unsatisfactory state. This is especially unfortunate
because the subject is an important one. For the proper
regulation of immigration and the determination of policies
of population control, to say nothing of legislation on inter-
racial marriage, such knowledge would be of much value.
But in view of the uncertainties of our knowledge it may be
urged that for a race which has demonstrated its capacity
for superior intellectual achievements it would be the part
of prudence to avoid amalgamation with other races concern-
ing whose genetic worth we do not have adequate informa-
tion. Ignorance is never a sufficient justification for taking a
leap in the dark. And until more scientific knowledge is
obtained on this highly controversial subject, for racial

356 HUMAN GENETICS AND ITS SOCIAL IMPORT

stocks which are now in the van, race mixture may be
regarded as a dangerous experiment.

The mingling of races goes on speedily enough in any case.
Owing to increased facilities for travel, peoples are coming
to be mingled together over extensive regions of the earth.
In its early stages the human race as it spread over the
surface of the globe became differentiated along many differ-
ent lines. Isolation favored divergence. But now barriers are
being broken down. The development of industry has greatly
fostered migration, and the amalgamation of races is proceed-
ing at an unprecedented pace. The period of increasing
differentiation is being followed by a period in which differ-
ences are becoming merged in a common heterogeneous
aggregate. Will the process of fusion ultimately make all
races one ? There are those who welcome such a consumma-
tion as affording a final solution to all embarrassing race
problems and helping to usher in a reign of peace and
universal good will. But how would it affect progress, bio-
logical and social ?

It should be pointed out that the biological effects of race
mixture depend to a large extent upon how the process goes
on. Where it results in the free intermarriage of the two races
it tends to produce an intermediate though highly hetero-
zygous stock. If, on the other hand, it results from the illegiti-
mate unions of the males of one race and the females of the
other, it is mainly at the expense of the race that furnishes
the females. In illegitimate unions between white men and
Negro women the women are prevented for some time from
bearing children to black fathers, while the white men are
not prevented from producing children by white mothers.
Inasmuch as in the United States most children resulting
from crosses between the two races come from the mating
of black women and white men, and only very rarely the
reverse, race assimilation becomes largely a one-sided process

INBREEDING AND CROSSBREEDING 357

in which white germ plasm is substituted for black in the
offspring. One may say that white genes are infused into the
Negro race, but that fewer black genes enter the white race.
The Negroes, therefore, are becoming bleached, whereas
the whites are not correspondingly blackened. When the
Negroes have a sufficient ingredient of white blood and for
this reason are no longer prevented from marrying whites,
the black genes may then become slowly disseminated in the
white race. But until this occurs race assimilation will be
largely at the expense of the Negro. Many light-colored
mulattoes "pass" as whites. The extent to which persons
with some Negro blood succeed in marrying whites is open
to much doubt. Even laws as drastic as that passed in Virginia
which forbids marriages between whites and persons having
the least trace of Negro blood cannot prevent the slow
infiltration of Negro genes into the white race. This process
may continue until it leads to complete amalgamation, but
if the Negroes are destined eventually to be absorbed by the
whites they will be considerably bleached before they are
assimilated.

Suggested Readings

Castle ('26 and '30). Davenport fn), chap. 5. ('13 a and b}. East and
Jones ('18). Holmes ('21), chap. n. Ludovoci ('33). Mjoen ('26). Reuter
('18, '31).

Questions

1. Why is deterioration through inbreeding very marked in some
lines and slight or nil in others?

2. Why does deterioration through inbreeding proceed with relative
rapidity in the first few generations and then more slowly until it prac-
tically ceases to occur?

3. If the marriage of first cousins produced an albino child, what would
be the chance that the next child would be an albino?

4. Since inbreeding brings out recessive defects would it be desirable to
encourage it in order that the genes for such traits be made manifest and
caused to disappear?

358 HUMAN GENETICS AND ITS SOCIAL IMPORT

5. In the pedigree of Otto and Ludwig of Bavaria (Fig. 55) what
individuals are probably heterozygous for dementia praecox ?

6. How do laws regulating racial intermarriage vary in different states ?

7. What efforts are being made in Germany to regulate intermarriage
between different racial stocks ?

8. What do you consider the more important, the social or the biologi-
cal consequences of racial intermarriage ?

9. Why do you think that the proportion of mulattoes to blacks in the
United States increased after emancipation and then decreased ?

10. Since miscegenation still continues, even if on a reduced scale, will
it eventually lead to the complete fusion of whites and Negroes ?

11. What legal restrictions, if any, should be imposed on consanguineous
marriages ? What laws on the subject are there in your own state ?

12. What is the prevailing attitude on race mixture in South America,
in most English-speaking countries, in most Mohammedan countries ?

13. Do you think race mixture will proceed more rapidly as time goes
on?

CHAPTER XXV
PROPOSED MEASURES FOR RACE BETTERMENT

WE ARE naturally prone to look upon evolution as
having reached, at least approximately, its final stage
in our present human species. But if we view the matter from
the vast perspective of geological time, it will seem highly
improbable that man will remain indefinitely in the position
he has now attained. If we could look upon our descendants
fifty or one hundred million years hence, provided that any
of them will be left, we might not recognize them as even
remotely our own kin. We may amuse ourselves by speculat-
ing as to what sort of creatures they might be, but our vision
into the near future is obscure enough; the remote future is
enshrouded in complete darkness.

Man's evolution is to a certain extent under his own
control. As horses can be bred for the racecourse or for
heavy draft animals, so human beings can be caused to
develop in this way or that according to the kind of selection
exercised in perpetuating the race. The control of human
biological evolution is the concern of practical eugenics, as
distinguished from theoretical eugenics, which deals with
human heredity and the causes by which it is changed. The
notion that human beings, like domestic animals, may be
improved by selective breeding never attained wide currency
until recent years, if indeed it can be said to have done so
now. One of the earliest advocates of practical eugenics was
the Greek poet, Theognis, who lived in the sixth century B.C.
In one of his poems he says:

With kine and horses, Kurnus, we proceed
By reasonable rules, and choose a breed
359

360 HUMAN GENETICS AND ITS SOCIAL IMPORT

For profit and increase, at any price,
Of a sound stock without defect or vice.
But in the daily matches that we make
The price is everything; for money's sake,
Men marry; women are in marriage given.
The churl or ruffian, that in wealth has thriven,
May match his offspring with the proudest race.
Thus everything is mixed, noble and base.
If, then, in outward manner, form and mind,
You find us a degraded, motley kind,
Wonder no more, my friend; the cause is plain,
And to lament the consequence is vain.

Among the Spartans there were several practices aimed at
creating a strong, brave, and healthy race. According to
Lycurgus only the best men should be permitted to beget
children. Ages at marriage were regulated by the theory
that children procreated when the parents were in their
period of greatest vigor would be exceptionally strong and
healthy. Newborn children were submitted to an inspector
who, if they were sound and healthy, decreed that they be
brought up. If they were weak or puny, they were not allowed
to live. Lycurgus taught that children belonged to the state
and not to the individual. And parental affection was not
suffered to foster children who would probably develop into
weak or unhealthy persons.

The Greeks in general recognized the value of good
heredity. "The fairest gift that one can give children," says
Heraclitus, "is to be born of noble sires." The practice of
"exposing" weak and deformed infants was common among
the Greeks and also the Romans and was advocated by both
Plato and Aristotle. Plato, who elaborated the most thorough-
going scheme of eugenics ever devised, would place the deter-
mination as to who should produce offspring and the number
of individuals composing the city state in the hands of the
rulers. In the ideal republic ample liberty of begetting off-

PROPOSED MEASURES FOR RACE BETTERMENT 361

spring was to be granted to the youth who distinguished
themselves in war or otherwise, and the custodians to whom
the children were committed should see that they received
the best nurture, "but the children of the more depraved
and such others as are in any way imperfect they will hide
in some secret and obscure place." The governors were to
determine the number of marriages contracted, and it was
recommended that "an ingenious system of lots should be
made, that the inferior man may accuse his fortune and
not the governors of the manner in which the couples are
joined." In short, the whole matter of perpetuating the
race, both as to numbers and quality, was to be managed
by the governors, even though they found it necessary
to resort to a little chicanery to accomplish their worthy
ends.

If romantic love and parental affection were given no
weight, and human beings were bred like so many cattle,
the race could doubtless be greatly improved in quality in a
few generations. Plato's scheme of eugenics, like so many
other measures advocated in the Republic, was never
regarded as feasible of adoption, and it has remained as a
philosopher's ideal, commendable in theory, but unsuitable
for practical application.

The eugenic proposals of Aristotle were much more modest.
He recommended that the husband should be twenty years
older than his wife, and that offspring should not be begotten
by men in their old age. He also held that the population
should be limited by restricting the period of propagation,
or, if this 'failed, through the employment of abortion. He
recognized the importance of superior parentage, and
counseled that "nothing imperfect or maimed be allowed to
grow up." Aristotle had no systematic plan for racial
improvement. His measures were negative and restrictive
rather than aimed at continuous race betterment.

362 HUMAN GENETICS AND ITS SOCIAL IMPORT

Beyond being exercised over the fall of the birth rate, the
Romans had little notion of eugenics. Neither did this
subject receive consideration during many centuries of the
Christian era. In 1683 Campanella in his City of the Sun
pictured an ideal society in which reproduction is not left
to the inclinations of the individual, but is regulated by the
state in the interests of posterity, more or less after the
fashion of Plato's Republic. After this scarcely any thoughts
on eugenics came to expression until well along in the
nineteenth century.

The influence primarily responsible for the modern
eugenics movement was the establishment of the doctrine of
organic evolution following the publication of Darwin's
Origin of Species in 1859. The great intellectual revolution
which resulted has profoundly affected all the sciences deal-
ing with man. Naturally, if man was evolved from some lower
form of animal life and is subject to the same biological laws
as the rest of the organic world, he must be capable of further
evolutionary changes. Darwin's cousin, Francis Galton, who
is universally recognized as the founder of modern eugenics
and to whom the name eugenics owes its origin, was greatly
stimulated by the ideas set forth in the Origin of Species.
His early work on Hereditary Genius, in which he brought
together many evidences that human beings differ greatly
in their inherited endowments of brains, inevitably implied
the possibility of raising the mental level of the race by
selective breeding. The idea of race betterment formed the
mainspring of much of Gal ton's work in heredity, biometry,
psychology, and anthropology. His books on Natural Inherit-
ance^ Inquiries into Human Faculty , Noteworthy Families,
English Men of 'Science ', Essays on Eugenics, and many articles
and addresses show that his life work was mainly devoted to
supplying a scientific basis for race improvement. In 1904 he
founded a research fellowship, and in 1905 a scholarship in

PROPOSED MEASURES FOR RACE BETTERMENT 363

eugenics in the University of London, and at his death his
fortune was bequeathed for the establishment of a professor-
ship of eugenics in the same institution. Largely as a result
of his influence, the Eugenics Education Society was founded
in 1908. This society has been active in stimulating eugenic
research and in spreading the knowledge of eugenics through

FIG. 83. — Sir Francis Gal ton. (From Gallon, Memoirs of My Life, Methuen and Company.")

its official organ, The Eugenics Review. The Gal ton Labora-
tory has been very productive in researches in human
heredity and eugenics. The first to occupy the professorship
founded by Galton was the noted mathematician, Professor
Karl Pearson who has developed many of the mathematical
methods and formulas used by workers in biometry. The
Galton Laboratory issues several publications, the Memoirs,
the Lecture Series, and more recently the Annals of Eugenics,
which contains more extended and technical contributions

364 HUMAN GENETICS AND ITS SOCIAL IMPORT

than those appearing in The Eugenics Review. The publica-
tions of the Galton Laboratory have attracted widespread
attention and have materially advanced the eugenics
movement.

In the United States the Eugenics Record Office, located at
Cold Spring Harbor, Long Island, N. Y., is more or less
, comparable to the Galton Labora-
^^ *%^ tory. It issues a series of Memoirs

il ^k and Bulletins on human heredity and

eugenics, and its Director, Dr. C. B.
Davenport, has been a very active
and productive worker in this field.
The Eugenics Record Office employs
a number of field workers who have
made many investigations of family
pedigrees especially in New England
and adjacent states. Eugenics soci-
eties have been formed in many
countries, Norway, Sweden, France,
Holland, Austria, Japan, Italy,
(From a photograph loaned by Mr. Russia, and especially Germany

Trevor Teele.) 11- ,

where there is now an active and
widespread interest in eugenic reform.

The number of periodicals devoted wholly or in part to
this subject has greatly increased, and discussions of eugenic
problems now find their way much more frequently into
many other journals both scientific and popular. Courses on
eugenics are given in many colleges, and the subject receives
attention in many courses on biology, psychology, and the
social sciences. Most of the societies concerned with eugenics
perform a twofold function of promoting research and dis-
seminating knowledge of the principles of the subject. There
is a growing appreciation of the role of heredity in several
fields in which this factor was formerly almost completely

FIG. 84. — C. B. Davenport.

PROPOSED MEASURES FOR RACE BETTERMENT 365

ignored. Students of population problems are now concerned
not only with the quantitative aspects of the subject, but
with the question of quality as well. This is shown in the
various conferences on population held in recent years, and
also by the contents of the journals dealing with population
problems.

One of the most important population problems is pre-
sented by the birth control movement, since this affects not
only the. quantity but also the quality of the population. At
its inception this movement was motivated largely by the
humanitarian desire to relieve parents among the wage
earners from the burden of large families. It was only too
apparent that the large families in the lower economic
classes entailed much hardship on parents and offspring alike.
The earlier proponents of birth control, R. D. Owen, Francis
Place, Richard Carlile, Charles Bradlaugh, Mrs. Anne
Besant, and J. S. Mill, were persuaded that the voluntary
limitation of offspring affords the only feasible means by
which the wage earners can secure a fair standard of living
and give their children the advantages needed for their
proper development. Birth control, however, made its
most rapid progress in the wealthier and more cultured
members of society. It is therefore responsible for a large
part of the differential birth rate about which the eugenists
complain.

On the other hand, the advocates of birth control contend
that it is their aim to spread the knowledge of contraception
through the lower strata and thus bring about an equaliza-
tion of the birth rates, as has, in fact, been done to a large
extent in a number of localities. It is useless to try to induce
the upper strata to outdo the proletariat in rapidity of child-
bearing. The only remedy for the dysgenic effects of birth
control, it is claimed, is more birth control. Besides affording
a protection against the evils of overpopulation and doing

366 HUMAN GENETICS AND ITS SOCIAL. IMPORT

away with much misery and hardship resulting from large
families supported on small incomes, birth control, it is
contended, really affords the most feasible method of eugenic
reform. Among eugenists in general there has been a gradual
change of attitude toward the subject from one of open
hostility, or at least suspicion, to one of qualified approval
or even ardent advocacy. Most eugenists realize that, as
Mr. Wiggam remarks, " birth control is a two-edged sword."
Whether its effects are eugenic or dysgenic depends upon
how it is employed.

Eugenic procedures may be grouped into two classes:
Those whose aim is to reduce bad heredity come under the
head of negative eugenics; those intended to increase good
heredity are classed under positive eugenics. This division is
based upon judgments of value, and hence it is possible that
there might be differences of opinion over what kinds of
heredity are good or bad. Similar differences sometimes arise
as to the evaluation of conduct as good or bad, but there is
in both cases a sufficiently broad basis of agreement for
many, if not most, practical purposes. Nearly all sensible
people would consider it very desirable for the race to get
rid of the genes responsible for hereditary insanity, epilepsy,
feeble-mindedness, blindness, deafness, split hands, and
other gross or incapacitating defects. Most people would
agree also as to the desirability of having more of the kinds
of heredity which make for sound physical development and
superior intelligence. There is no need to arrive at a general
consensus of opinion as to just what traits individuals should
or should not possess. In fact, it is highly desirable that a
people should contain a high degree of genetic diversity. A
good deal of criticism has been directed against eugenists
on the assumption that they propose to inaugurate a detailed
scheme of arbitrarily regulated matings in order to produce
their own favorite brand of human beings. But this kind of

PROPOSED MEASURES FOR RACE BETTERMENT 367

eugenist exists mainly in the imagination of the critics.
Beyond curtailing the procreation of persons with obviously
undesirable defects no one, except a few negligible extremists,
advocates any arbitrary interference with the propagation
of any kinds of hereditary traits.

Misconceptions of eugenics readily become very prevalent
because most people who are otherwise well educated are
woefully ignorant of the rudiments of biological knowledge,
and especially knowledge of genetics. Even cultivated people
sometimes ask in all seriousness: "Do you really believe in
heredity?" That the important function of perpetuating life
should be carried on in almost complete disregard of whether
the kind of life that is perpetuated will improve or deteriorate
the race is especially unfortunate when people are taking the
regulation of the birth supply more and more into their
own hands. Among our remote ancestors life was transmitted
solely in obedience to an instinctive urge, and natural selec-
tion took care of the failures. Now that procreation has come
to be largely a matter of voluntary choice and since so much
is done to preserve the unfit, it becomes increasingly impor-
tant that the perpetuation of life should be carried on
intelligently and with due regard to the welfare of future
generations.

In considering proposals for eugenic reform in the fields
of both positive and negative eugenics we must assign a
position of prime importance to eugenic education. If any
eugenic reform is ever to be achieved in a democratically
governed country, eugenic education is an indispensable
prerequisite. Measures for eliminating bad germ plasm and
schemes for increasing the birth rate among those with
superior heredity must at least meet with popular approval
before they can become effective, and popular approval will
not be forthcoming for any really adequate eugenic system
in the present condition of unenlightenment.

368 HUMAN GENETICS AND ITS SOCIAL IMPORT

Many of the methods coming under the head of negative
eugenics have to do with the regulation of marriage. From the
biological standpoint a large part of our legislation on
marriage in the United States is peculiarly unintelligent.
Laws regulating consanguineous unions are mostly useless.
Many states still permit the marriage of boys of fourteen
and girls of twelve years of age. The stocks in which mere
children marry are generally of inferior status and are likely
to be of poor quality. When the reproductive career is begun
at an early age two or three children are apt to be born
before most families get started. Both eugenically and
socially, child marriages are very undesirable and should be
prohibited. Regulations designed to restrict rash and ill-
advised marriages would probably have a eugenic effect in
addition to being desirable on other grounds. Marriages
contracted after a few hours' acquaintance are apt to prove
disillusioning to the impetuous contracting parties. Accord-
ing to Popenoe and Johnson, "In Los Angeles County alone
. . . more than a thousand couples each year go to the
courthouse and apply for a license to wed, and then do not
come back three days later to get it. What happens to these
abandoned romances would make an interesting investiga-
tion. While the facts often cannot be obtained, indications
suggest that a large proportion of them represent freak
marriages, fraudulent marriages, drunken marriages, run-
away marriages, and others whose consummation could have
been of no value to society."

Laws requiring a medical examination before marriage are
sometimes described as eugenic, but they are more properly
hygienic as their main intent is to check the dissemination
of venereal disease. Most states in which such laws have been
passed require a medical examination only of the males.
These laws may have a considerable value, although they
do not always work out in the way that was intended. There

PROPOSED MEASURES FOR RACE BETTERMENT 369

are a few clergymen who refuse to perform a marriage
ceremony unless the applicants can present a certificate of
health. Where blindness, obvious mental deficiency, and
many gross deformities or defects are transmitted by mar-
riage, generation after generation, to the affliction of numer-
ous descendants, one wonders with what conscience the
clergymen, priests, or others empowered to unite individuals
in the bonds of wedlock were able to perform the ceremony.
A person who solemnizes the marriage of hereditary defectives
is really a party to a criminal act, a crime against posterity
that may result in untold evils for a long time to come. And
yet such procedures go on apparently without eliciting many
qualms of conscience on the part of the officiating individuals.
Every day marriages take place which would not be tolerated
in most tribes of savages.

All of our states have laws forbidding the marriage of
idiots, imbeciles, and the insane, but these were passed not
so much for eugenic reasons as because the individuals con-
cerned were deemed incapable of making a legal contract.
Very little care is exercised in issuing marriage licenses, and
if an individual is refused a license in one county he can
generally get it in another. As a matter of fact, these laws
have little effect in preventing marriages that should not
occur. With the feeble-minded the prohibition of marriage is
apt to be inadequate as a means of preventing reproduction,
as is indicated by the very high proportion of illegitimate
children in mentally defective stocks.

It is generally recognized that there are many defective
individuals who in the interests of posterity should not be
permitted to reproduce their kind. The two methods most
commonly employed to prevent the multiplication of such
persons are segregation and sterilization. Segregation is
usually employed for other than eugenic reasons; the preven-
tion of reproduction during the periods of isolation is only

370 HUMAN GENETICS AND ITS SOCIAL IMPORT

an incidental result. Of the eugenic effects of the segregation
of criminals we know little; but for social reasons, if for no
others, it is doubtless desirable that criminals produce few
children. Most of the insane are confined either because they
are dangerous when at large or because they can be cared
for much better in special institutions for the purpose than
in private homes. In the United States there are roughly
about 300,000 insane in hospitals, and there is probably an
equal or greater number outside of hospitals. Discharges are
frequent, and it is estimated that about three out of every
four persons discharged as cured are apt to be committed
again at some future date. Many of the insane have had
children before their commitment, and children are begotten
by others after their discharge or during periods of parole.
Institutional segregation doubtless interferes with the repro-
duction of those suffering from mental disease, although it is
far from an adequate preventive under present conditions of
parole and limited periods of detention.

There are fewer feeble-minded than mentally diseased
persons in institutions, but a larger proportion of them are
unconfined. On the average the number segregated in the
United States is about 60,000. The White House Conference
of 1930 estimated that approximately 2 per cent of the
population is definitely feeble-minded — which means that
in the United States about two and one-half millions would
fall in this category. If this be true, the statement of E. R.
Johnson, the Superintendent of a large institution in New
Jersey, that no state provides facilities for the care of more
than 10 per cent of its mental defectives is well within the
facts. Many of the higher grades of mental defectives can
be made self-supporting, but the lower levels are entirely a
burden. The total cost, direct and indirect, of mental
deficiency is enormous. The segregation of all of the feeble-
minded would entail an expense that most communities

PROPOSED MEASURES FOR RACE BETTERMENT 371

could not be induced to defray. Yet the cost of their upkeep
has somehow to be met. Evidently, so long as the great
majority of the feeble-minded remain at large, the problem
of preventing their reproduction is not solved. From the
very magnitude of the undertaking segregation is failing to
supply an adequate remedy.

The alternative proposal that is widely advocated is
sterilization. In the male this is a slight operation consisting
in severing the vas deferens of each testis and thus preventing
the escape of spermatozoa. The operation commonly adopted
for sterilizing females involves cutting the oviducts, or
Fallopian tubes, thereby preventing the ova from gaining
access to the uterus. Neither operation interferes with the
sex functions and there are apparently no definite after-
effects upon general health or vigor. The chief and almost the
only effect of the operation in both sexes is to render the
individual sterile.

Laws authorizing the sterilization of defectives have
been passed in twenty-eight states of the Union, and up to
January i, 1935, 20,063 legal sterilizations have been
performed, 8,644 on males and 11,419 on females. California
has the distinction of having performed nearly as many
operations (9,931) as all the other states combined. In many
states the passage of sterilization laws has been followed by
practically no operations. Several of the sterilization laws
have been declared unconstitutional or otherwise set aside
by higher courts. The case of Buck vs. Bell, originally tried
in Virginia, was finally carried to the U. S. Supreme Court
which upheld the Virginia statute. In presenting the grounds
for the decision, Justice O. W. Holmes made the remark
that "three generations of imbeciles are enough."

There has been a good deal of opposition to sterilization on
several grounds. Some have regarded it as an unwarranted
infringement of personal liberty, and one which creates a

372 HUMAN GENETICS AND ITS SOCIAL IMPORT

dangerous precedent. It has been criticized as inflicting
"cruel and unusual punishment," and hence contrary to the
Constitution. It has been opposed on the ground that we do
not know that mental defects and diseases are transmitted
by heredity, and hence we should not deprive anyone of the
power of reproduction. There has been opposition on religious
grounds, especially by adherents of the Roman Catholic
Church, and it has been urged that by removing all danger
of producing offspring sterilization would lead to an increase
of sexual immorality and a greater dissemination of venereal
disease. A priori this seems to be a probable conclusion; but
like so many plausible deductions it is not borne out when
subjected to the test of inductive investigation. The sub-
sequent careers of many sterilized individuals in California
have been followed by Dr. Paul Popenoe in the endeavor to
ascertain to how great an extent sterilization may have acted
as an incentive to irregular sex behavior. Of the sterilized
feeble-minded males, "not a single case of the sort has
arisen/' This may be attributed to the fact that as a rule
feeble-minded males are not given to sex offenses. Then
among the sterilized insane "only one case was found where a
patient tried to use the fact of his sterilization as an argument
for promiscuity." On the other hand, the feeble-minded girl
is characteristically prone to loose sexual relationships.
About three-fourths of the girls in the Sonoma State Home
in California were sexually delinquent before they were
committed. After they had been sterilized and released
on parole, "only one out of every twelve has been a sex
offender." The follow-up study which included a canvass of
probation and parole officers and social workers familiar
with the history of the girls liberated on parole furnished
only about a half-dozen cases in which it was alleged that
sterilization may have afforded an inducement to sexual
irregularity. In two of these instances it seemed clear that

PROPOSED MEASURES FOR RACE BETTERMENT 373

the offenses would .have occurred anyway, but in any case
the percentage of sexual delinquency attributable to steriliza-
tion is relatively very small, about one in a thousand.

It cannot be asserted that sterilization is of itself an agent
of moral reformation. The reason why sterilization has been
working so successfully in California is because it is combined
with a policy of supervision after release. The sterilized girls
are placed so far as possible in responsible families, and if
their behavior is not satisfactory they may be sent back to
the institution. One cannot, of course, expect ideal behavior
in these girls, especially in the light of their previous history.
Many of them marry, and a study of 125 such marriages
showed that, on the whole, they have turned out as success-
fully as could reasonably be expected. Marriage acts as a
stabilizing influence, and apparently contributes to the
welfare of both parties. The fact that it results in no children
lightens the economic burdens of the married couple and
reduces somewhat the number of defective offspring. When
we consider the strong tendency to assortative mating on the
basis of levels of intelligence, it will not seem likely that the
men who marry these girls would have contributed much to
the improvement of our racial heredity. Hence the loss
of their genes is not to be deplored.

In California most of the feeble-minded and a considerable
proportion of the insane who have been committed to
institutions are sterilized before they are released. The great
majority of the persons sterilized either welcome the opera-
tion or make no objection to having it performed. Social
workers, parole officers and others in close touch with the
effects of the operation are, in general, strongly in favor of
it. Sterilization is coming to be practiced in several foreign
countries. The largest number of operations have been
carried out in Germany under the recent sterilization law.
During the first year of its operation sterilizations were

374 HUMAN GENETICS AND ITS SOCIAL IMPORT

performed upon 56,244 persons adjudged to be hereditarily
defective by the High Courts of Eugenics — over twice as
many sterilizations in one year as the total number performed
in the United States.

In no country do the number of individuals sterilized
constitute more than a small fraction of the hereditary defec-
tives who in the interests of the race should not procreate
their kind. Even if all defectives were sterilized there would
be a continuous supply from the reservoir of carriers.
Opponents of sterilization have urged that if all of the feeble-
minded and insane were prevented from reproduction, it
would make little difference with the number that would be
produced in any one generation. This statement is commonly
based on the assumptions that (i) mental defect is due to a
single recessive gene, and (2) that the defect is recessive to
the extent that heterozygous individuals appear normal.
Both of these assumptions, as we have seen, are open to
serious question. But, granting that they are both correct,
it is evident that sterilization would cut off at least a certain
proportion of our hereditary defectives. If a recessive trait
is rare, the sterilization of those possessing it will effect its
reduction with extreme slowness. If, however, the trait
should occur in only i per cent of the population, the steril-
ization of all affected individuals would reduce it by 17.4 per
cent in the next generation, and this reduction would be
permanent. With further reduction the rate of elimination
would be slower. The usual calculations of the rate at which
recessive traits can be eliminated are based upon the further
assumption that matings occur at random, and this assump-
tion is never realized. There is, especially in mental defect,
a strong tendency to assortative mating. Besides, for social
and economic reasons, people of limited mentality often tend
to segregate in certain areas. There, through a series of more
or less closely inbred generations, recessive genes may

PROPOSED MEASURES FOR RACE BETTERMENT 375

accumulate and give rise to a plentiful crop of subnormal
individuals, as is illustrated by the Jukes, Hill Folk, and other
defective stocks. If all feeble-minded individuals of these
stocks could have been sterilized, it would have made a
very great difference in the number of such individuals
born.

If one could eliminate all bad heredity from the human
race, mankind would either become extinct or greatly
improved in quality. According to Malthusian principles, if
fewer people with bad heredity were born, people with good
heredity would automatically respond by an increased birth
rate. It is open to serious question, however, whether
measures coming under the head of negative eugenics will
be sufficient to prevent the race from being perpetuated
mainly by people of subnormal quality. Certainly the
segregation or sterilization of the small percentage of persons
who are defective enough to warrant official commitment
cannot be expected to contribute much toward this end.
Negative eugenics based upon compulsory restrictions
probably cannot be carried out on a very extensive scale.
It has been contended that birth control in the borderline
and dull-normal groups, who are usually on an economic
status that would make small families desirable, would do
much more. How much the extension of contraceptive
information in these groups is likely to accomplish — and it
has possibilities of doing a great deal — is a question involving
all the uncertainties of predicting human behavior. But can
any or all negative eugenic procedures result in rescuing from
extinction the stocks that are now failing to perpetuate their
kind? In the opinion of many eugenists the present tendency
for success to be correlated with sterility can only be effec-
tively counteracted by providing incentives that will lead to
an increased birth rate of the better endowed elements of the
population. Whether anything can be done in this direction

376 HUMAN GENETICS AND ITS SOCIAL IMPORT

that is likely to be fraught with any considerable measure
of success is a problem of the greatest importance, but it is
one to which the general public shows little disposition to
give serious consideration.

In an address on The Possible Improvement of the Human
Breed under Existing Conditions of Law and Sentiment,
Francis Galton grappled with this problem, but the proposals
he put forward appear to be quite inadequate to meet the
situation, and serve chiefly to emphasize the fact that before
much can be accomplished "existing conditions of law and
sentiment" will have to be changed. Galton's proposal of
"granting diplomas to a select class of young men and
women" on the basis of eugenic worth, and his advocacy of
"the provision to exceptionally promising young couples of
healthy and convenient houses at low rentals" would at best
be likely to have only a slight effect upon the birth rate of
the more promising members of the community. An experi-
ment in accordance with the latter suggestion has been
carried out by Mr. Alfred Dachert in the Jardins-Ungemach,
near Strasbourg. Furnished houses at low rental are provided
for properly qualified young couples with the aim of increas-
ing their birth rate, and if after a reasonable interval the
experiment proves unsuccessful, the sterile couples are
required to give place to others. The most recent report on
the working of the enterprise (Eugenics Review, October,
1935) indicates that it is having the desired results. The birth
rate in the Jardins-Ungemach is 128 per one thousand
married women, as compared with a corresponding rate of
90 for the general population. To judge from their general
health and physical development the children are distinctly
above the average standard.

Philanthropists of the type of Mr. Dachert are rare. It
cannot be expected that his example will be followed by
many business executives unless conditions of sentiment

PROPOSED MEASURES FOR RACE BETTERMENT 377

among them on matters eugenic should undergo a very sur-
prising change. As a rule, employers do not care a fig about >
the fertility of their employees. Certainly, an individual
employer cannot be expected to hand out an additional
stipend every time Mrs. Moriarty has another baby. The
fact that the additional baby makes its appearance in a
family already too large to be comfortably supported on the
wages of the father concerns only this particular family, or
possibly also the public charities. The Moriartys may be
most excellent people whose increase in number would
constitute a highly desirable contribution to the race.
Assuming this to be true it would be to the advantage of the
state that their numbers are not unduly curtailed, and that
they enjoy a decent standard of living and receive a kind
of education which helps them to become valuable members
of the community. Granting that as a matter of social justice
this family should secure really adequate support, the
question arises as to who should pay for it. The individual
employer cannot afford to pay the father more than his
labor is worth. Since the state is benefited by the increase
of this family, it has been proposed that the state or the
community should defray at least a part of the cost of its
support, instead of compelling poor Mr. Moriarty to bear the
entire burden to the detriment of all of his offspring.

The family allowance system has been advocated as a
means of removing in a measure the penalties of parenthood,
and of securing a more just distribution of wages. To a
certain extent it has been put into operation in several
countries of Europe largely as a measure of relief to large
families, and as a means of encouraging the increase of
population in countries which sustained extensive losses
during the World War. In France, where the system has been
most fully carried out, family allowances are paid to wage
earners in proportion to the number of children in a family,

378 HUMAN GENETICS AND ITS SOCIAL IMPORT

both legitimate and illegitimate. The cost of the allowances
is defrayed, not by the individual employer, but by a group
of employers in the same industry or in the same region, so
that the burden is widely distributed and does not tempt
employers to discriminate against hiring men with large
families. In 1932 a law was passed making it obligatory for
all employers to contribute to some compensation fund. The
number of such funds increased from o in 1920 to 230 in 1930,
when about 350,000,000 francs were distributed to the
families of wage earners. The stipends have scarcely been
large enough to make any demonstrable increase in the birth
rate, although they have often been a distinct relief to many
struggling families. At first the labor unions looked upon the
system with hostility or suspicion, but in general, they have
now come to regard it with favor. The tendency of family
allowances would be to reduce the basic wage for the single
worker and to raise the income of workers with families.
The total cost of labor need be no greater than under the
usual system. Its chief effect is to secure a better distribution
of income in relation to needs.

There would seem to be no inherent difficulty in extending
the family allowance system until it came near meeting the
additional cost incurred by the increased number of children
in the family. If this is done it would doubtless have a
considerable effect in increasing the birth rate. Baptist and
Congregationalist missionaries are given a sufficient allow-
ance for each child, so that a large family costs little more
than a small one, a fact which may account for the consider-
ably larger size of such families as compared with those of the
regular ministers in these denominations. A few colleges,
Roberts College in Istamboul, the American University at
Beirut, and the London School of Economics afford family
allowances for their faculty members. In the last institution
they amount to thirty pounds annually from the sixth to the

PROPOSED MEASURES FOR RACE BETTERMENT 379

thirteenth year, and sixty pounds during the later period of
schooling.

That it is possible to increase the birth supply by affording
parents some relief from the financial difficulties incurred
by having children is indicated by the success achieved
through the legislation recently enacted in Germany. The
new regime has made strenuous efforts to counteract the
portentous decline of the birth rate in that country, not only
through patriotic propaganda, but by a number of regulations
for granting financial aid to parents. In 1933 the German
birth rate reached its lowest point of 14.7 per thousand
inhabitants. The encouragements afforded to young couples
by a system of loans to certain classes of workers, together
with other measures, has apparently increased not only the
number of marriages, but also the number of births. Eligible
couples may receive a loan up to a thousand marks, to be
repaid at the rate of i per cent a month. The loans are made
only when the wife has been employed at least nine months
during the two preceding years, one object of the loan being
the replacement of women workers by men. In 1933 there
were 631,152 marriages in Germany, or 9.7 per thousand
inhabitants, whereas in 1932 there were only 509,595
marriages, or 7.9 per thousand inhabitants. In 1934 the
marriages increased to 731,431, or 11.2 per thousand, and
37.4 per cent of the married couples received loans. The
birth rate in 1934 rose suddenly from 14.7 to 18.0 per thou-
sand, resulting in 47,825 more births than occurred in the
first quarter of the previous year.

Burgdorfer states that "sixty per cent of the increase in
births comes from marriages which were concluded with the
help of loans. But these external measures are not the sole
reason for the change." The decrease of unemployment and
the changing attitude of the people are considered to be
supplementary causes. A large part of the increase of births

380 HUMAN GENETICS AND ITS SOCIAL IMPORT

occurred in urban families. There has been a marked decrease
of abortions and illegitimate children. One reason for this is
that the parents of an illegitimate child find in the loan
system a means of taking care of the situation, and the
temptation to resort to abortion is reduced. According to
Mr. D. V. Glass (Eugenics Review, October, 1935), there were
between August, 1933, and March, 1934, "part cancellations
of loans in respect to the birth of 43,101 children who must
have been conceived before marriage." A considerable
proportion of these children, to judge from previous happen-
ings, would have been prevented by abortion were the parents
not able to receive a loan by marrying and to have a part of
it remitted by having a child.

Whether the increased number of births resulting from the
system of loans will improve the native qualities of the
German people may well be doubted. The motive back of
the enterprise is to secure greater military power through
increase in numbers. In this Germany has succeeded, at
least for the time being, in that her birth rate has shown a
conspicuous rise, while that of most other European countries
has continued to fall. From the eugenic standpoint the
German experiment is of interest in showing that it is possible
to raise the birth rate by relieving parents of a part of the
financial burdens of childbearing. If the system promotes the
fertility of certain classes of the working population, it should
be possible to increase any desired class in much the same
way.

It has been maintained that a family allowance system
based merely upon the number of children without regard to
the quality of their parentage would have a dysgenic influ-
ence, since the more undesirable elements of the community
would be the most apt to respond to the financial induce-
ments to fertility. On the other hand, it has been claimed
that raising the standard of living among the poorer people

PROPOSED MEASURES FOR RACE BETTERMENT 381

of the community would result in lowering their birth rate.
The lowest strata it is assumed do not artificially reduce their
birth rate, and hence their fertility would not be increased
by adding to their income. That indiscriminate family
allowances would have a eugenic influence seems very
doubtful. In order to insure the eugenic effect of such a
system there would have to be some means by which family
allowances were graduated according to the quality of the
recipients. Several such schemes have been proposed. In his
book Is America Safe for Democracy? Dr. William McDougall
has recommended that members of certain "selected classes"
be given 10 per cent of their income for every child under
twenty years of age. "If such increase of income/' says
Dr. McDougall, "proportional to the earnings and to the
number of children could be secured to each family of the
selected classes, the eugenic effect would, I submit, be very
great, far surpassing in this direction the effects of any other
eugenic measure that has been proposed."

The system, according to Dr. McDougall, could readily be
inaugurated with classes of state and municipal employees
and then extended to schools and colleges and to such other
occupational groups, membership in which is, on the whole,
an indication of eugenic worth. The Eugenics Society of
London has sponsored the family allowance system and has
issued through its Council a statement in which it is declared
that for both eugenic and social reasons "the economic
motive for childlessness should by all possible means be
diminished in all classes doing skilled work. The most potent
means of effecting this end is a scientifically designed system
of family allowances. The aim of such a system should be to
equalize the standard of living between parents and non-
parents doing equivalent work, within all grades affected,
in such a way that the amounts recovered per child by each
class of earner shall be proportional to the earnings."

382 HUMAN GENETICS AND ITS SOCIAL IMPORT

Although the family allowance system is coming to be
approved by an increasing number of publicists and econ-
omists, it is still very much of a controverted topic. It is
opposed to the spirit of individualism, which is a very
prevalent sentiment especially in the United States. The
consideration given to certain favored classes would not be
likely to meet the approval of the persons who were not
benefited and who might be compelled indirectly to con-
tribute to the support of those who were. The invidious
distinctions involved in the system would, therefore, tend
to make it unpopular in any democratically governed
country, and would give a fine opportunity for demagogues
to make an effective appeal to the interests of the less
favored classes. A people with sufficient biological enlighten-
ment might be willing to adopt a family allowance system
that would have a real eugenic effect, but at present such a
proposal would have a small chance of success. There would
probably be less opposition to discriminating allowances
paid by groups of employers than to a system managed by
the government. If there is no social injustice in workers
being paid more in some industries than in others, there
should be none in the payment of unequal allowances for
children. It is commonly assumed that the basic wage in any
employment should be sufficient to support a man, his wife,
and three children on a fair standard of comfort. If one
recognizes the principle that wages should be determined,
at least in part, by the needs of the worker's family, it would
seem reasonable from the point of view of the worker and
the state that wages should be adjusted to the size of the
family, provided of course that the family is really a valuable
one and not a social nuisance. The proponents of family
allowances point out that, according to the theory of the
basic wage mentioned above, many employees are being paid
for families which they do not have. As a matter of fact, it is

PROPOSED MEASURES FOR RACE BETTERMENT 383

not feasible to pay all workers a wage sufficient to support a
family of five on a fair subsistence level. Professor Paul
Douglas estimates that if this were done in the United
States, it would require 82 per cent of the total income of the
country and thus leave an insufficient amount to cover other
necessary expenditures. Other countries are in a similar
economic condition, and the general result is that the
children of a large proportion of wage earners' families suffer
from inadequate support.

If incomes were so distributed that families with children
received more than single workers, the general welfare of the
population would doubtless be enhanced. One of the most
important problems is the determination of the eugenic
worth of those who receive the allowances. The attempt to
gauge the genetic qualities of people, even provided that it
could be done with the required degree of accuracy, would be
difficult, not to say unpopular, in practice. If allowances were
made on the basis of a certain percentage of the earned
income, the general effect, it is alleged, would be to increase
the birth rate of the persons who have achieved success and
thus to rescue from extinction the abler classes of the popula-
tion. In such a method there would be many cases in which
eugenic breeding would not be promoted and in which
encouragement would be given to undesirable stocks and
withheld from many very desirable ones. But the general
effect would probably be a considerable improvement over
the present working of the differential birth rate. Several
systems of family allowances have been devised some of
which are eugenic in aim while others are planned solely
to alleviate the financial burdens of large families regardless
of quality. A family allowance scheme could readily be
worked out that would have a strong influence for race
betterment. The chief difficulty would be in persuading
people to adopt it.

384 HUMAN GENETICS AND ITS SOCIAL IMPORT

Just now people are not particularly interested in improv-
ing the hereditary qualities of the human breed. For the
most part they know little about heredity, nor do they have
much appreciation of the importance of hereditary differences
among men. Until a few years ago the idea that the race
might be improved by selective breeding scarcely entered
the head of one person out of a million. To the great majority
the idea is still foreign. And among the relatively few who
have some notion of eugenics there prevails an extraordinary
amount of misinformation and misunderstanding. The first
step toward an effective eugenic reform is therefore education.
And there is also need of further research devoted especially
to settling questions of crucial importance in order that there
may no longer be differences of opinion among qualified
students of the subject. When knowledge of the fundamentals
of eugenics is widely diffused, it may be expected to bear
fruit in many ways. Negative eugenic measures, which are
now usually carried out in an ineffectual and half-hearted
manner, will be much more thoroughly applied. People with
hereditary defects will be more careful about passing their
infirmities on to their descendants. Immigration will be
more effectively regulated according to the eugenic worth
of the entering aliens. There will be more discriminating
choice in marriage and hence fewer persons with inferior
endowments will be able to find mates. The influence that
doctors, clergymen, and teachers exert in the interests of
race betterment, which is now lamentably small as compared
with what it might become, will be much more effective.
There will be a greater sense of obligation on the part of
those possessing superior hereditary qualities to see that
their family strains are not suffered to die out. And people
will be more favorably disposed toward measures that will
encourage the increase of superior stocks. All these and other
desirable changes might conceivably follow from the spread

PROPOSED MEASURES FOR RACE BETTERMENT 385

of eugenic education. But, of course, these changes may not
occur. Instead, the trend of events may justify Bertrand
Russell's prediction that for the next few hundred years
"each generation will become stupider than its predecessors."
Then, as we become more stupid we shall be less and less
likely to remedy our racial ills. The situation offers a distinct
challenge to our capacity for properly guiding the course of
our biological development. We may fail in the task. But it is
only through eugenic education that we can hope to succeed.

Suggested Readings

Darwin, L. ('25, '26). Douglas ('26). Fisher ('32). Galton ('09). Hodson
('34). Holmes ('33), chaps. 6, 7 and Appendix F. Gosney and Popenoe ('29).
McDougall ('21), Appendix III, ('33). Popenoe and Johnson ('33), chaps.
7-9, 16-20. Wiggam ('24), chaps. 18, 19, 21, ('27), chap. 7.

Questions

1. List the hereditary defects which in your opinion should constitute
a legal bar to marriage.

2. Do you think that any kinds of criminals (and if so what kinds)
should be sterilized on either eugenic or other grounds?

3. In general what kinds of persons, if any, should be sterilized ?

4. Is it justifiable to sterilize any classes of people on other than
biological grounds?

5. If individuals outside of institutions should be sterilized how would
you determine who should undergo the operation ?

6. If a recessive trait is present in one-sixteenth of the population,
what proportion of the population would be heterozygous for this trait?
If all persons having the trait were prevented from reproduction, to what
extent would it be reduced in the two following generations?

7. On the whole do you think that venereal diseases have a eugenic or
a dysgenic effect ? Give reasons.

8. List in one column the forces which are acting eugenically and in
another those which are acting dysgenically.

9. Compare this list with a similar one made for primitive society.
10. Should voluntary sterilization be regulated by law, or left to the

individual and the medical profession ?

386 HUMAN GENETICS AND ITS SOCIAL IMPORT

11. What legal objections have been urged against sterilization?

12. Make a list of feasible measures for promoting race betterment.

13. Discuss the probable eugenic effects of indiscriminate family
endowment.

14. List the arguments pro and con in regard to the eugenic influence
of birth control.

^Bibliography

Obviously only a small part of the literature on the sub-
jects treated in this volume can be included in a brief
bibliography. A much more extensive collection consisting
of over 10,000 titles may be found in A Bibliography of
Eugenics by S. J. Holmes published by the University of
California Press in 1924. After this date the literature on
eugenics and related subjects has been published at intervals
in the Bibliographia Eugenica appearing in Eugenical News.
Many references on population problems are given in the
works of Thompson ('35) and Lorimer and Osborn ('34),
and also in the issues of Population Literature compiled by
the Population Association of America. Literature lists on
genetics are published in several recent books on the subject
included in the following list, /.*., Babcock and Clausen,
('27), Castle ('30), Fasten ('35), Morgan ('19; '28), and
Sinnott and Dunn ('32). Current literature on genetics is
listed in Biological Abstracts.

AGAR, W. E. 1931. ALamarckian experiment involving a hundred genera-
tions with negative results, Jour. Exp. Bio!., 8: 95—108.

ALTENBERG, E. 1928. How we inherit. Holt, N.Y.

ARMSTRONG, C. W. 1932. Practical family endowment, Eugenics Rev.,
24: 107-114.

BABCOCK, E. B., and CLAUSEN, R. E. 1927. Genetics in relation to agricul-
ture, McGraw-Hill, New York, 675 pp.

BABER, R. A., and Ross, E. A. 1924. Changes in the size of the American
family in one generation, Univ. Wis. Studies, 99 pp.

BAKER, C. E. 1933. Rural-urban migration and the national welfare,
Am. Assn. Geog., 23: 59-126.

BAKER, J. R. 1926. Sex in man and animals, Routledge, London, 171 pp.

BARNES, H. E. 1926. The repression of crime, Doran, N.Y. 382 pp.

387

388 HUMAN GENETICS AND ITS SOCIAL IMPORT

BARNES, I. 1929. The inheritance of pigmentation in the American Negro,

Human Bio/., i: 321-381.

BARR, M. W. 1904. Mental defectives, Blakiston, Philadelphia, 368 pp.
BAUR, E., FISCHER, E., and LENZ, F. 1931. Human heredity, Macmillan

New York.
BECK, P. G. 1934. Recent trends in the rural population of Ohio, Wooster

Ohio, 41 pp.
BEETON, M., and PEARSON, K. 1900. Data for the problem of evolution

in man. II. A first study of the inheritance of longevity and the

selective death rate in man, Proc. Roy. Soc., 65: 290-305, 1900. Also

Jour. Inst. Actuaries, London, 35: 112-129, 1899-1901.
1901. On the inheritance of the duration of life, and on the intensity

of natural selection in man, Biometrika, 1 : 50-89.
BELL, A. G. 1918. The duration of life and the conditions associated with

longevity, Washington, D.C., 59 pp.
BERNHARDI, F. VON. 1914. Germany and the next war, Longmans, Green,

New York, 288 pp.
BLACKER, C. P. 1934. The chances of morbid inheritance, Lewis, London,

449 PP-

. 1934. Voluntary sterilization. Oxford Univ. Press, London, 145 pp.

BOLIN, J. S., and HOLMES, S. J. 1927. Marriage selection and scholarship,

Jour. Hered., 18: 253-255.

BONAR, J. 1924. Malthus and his work, Macmillan, New York, 438 pp.
. 1931. Theories of population from Raleigh to Arthur Young, Green-
burg, New York, 253 pp.
BOSSARD, J. H. S. 1932. Residential propinquity in marriage selection,

Am. Jour. Soc., 38: 219-224.
BOWEN, E. 1931. An hypothesis of population growth, Columbia Univ.

Press, New York, 238 pp.
BRIGHAM, C. C. 1923. A study of American intelligence, Princeton Univ.

Press, 210 pp.

— . 1930. Intelligence tests of immigrant groups, Psychol. Rev., 37:

156-165.
BRITTEN R. H. 1934. Mortality rates by occupational classes in the United

States, Publ. Health Reps., 49 (38), 1 101-1 1 1 1 .

BURGDORFER, F. 1934. Sterben die weissen Vdlker? Callwey, Berlin, 90 pp.
BURKS, B. S. 19280. The relative influence of nature and nurture upon

mental development, 27^ Yearbook Nat. Soc. Study of Education,

Part I, 219-316.

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. 1928^. A summary of the literature on the determiners of the

intelligent quotient and the educational quotient, op. cit., Part II,

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Index

Abadie, J., Inheritance of epilepsy, 146
Abnormal abdomen in Drosophila, 62
Abortion, 268, 361
Acquired characters, inheritance of,

Achondroplastic dwarfs, 100

Adkinson, J., 106

Adler,H. M., 174,175

Agar, W. E, 387

Agriculture, 320, 321

Albinism, inheritance of, 98-100

Alcohol, inherited effects of, 80-82, 85

Alcoholism, 137, 156, 184-186, 263

Alexander, 204

Altenberg, E., 39, 387

Amaurotic idiocy, 129, 151, 257, 265

Amentia, 127

Amitosis, 6, 17

Andalusian fowl, 59, 60, 64

Anthrax, immunity to, 105, 106

Aristotle, views on eugenics, 360, 361

Armstrong, C. W., 387

Army mental tests, 124, 161, 342, 343

Ascaris, 8, 9

Ashby, H. T., on infant mortality, 271

Asia, emigration from, 332, 333

Assortative mating, 193-195, 373, 374

Asthma, inherited diathesis to, 63, 64,

166, 108
Atavism, 172
Australia, birth rate, 199
Average deviation, 91
Ayres, 155

Babcock, E. B., 39, 88, 96, 387
Babcock, M. E., 400

Baber, R. A., 220, 387

Bacon, F., 290

Bagg, H., 84

Baker, C. E., 387

Baker, J. R., 387

Baldness, heredity, 99

Barnes, H. E., on prison system, 171,

387

Barnes, I., 388
Barr, M. W., 259, 382
Barries, K., 224
Bateson, W., 59, 66
Batrachoseps, synapsis, 69
Baur, E., no, 147, 388
Beck, P. G., 388
Beeton, M., 255, 388
Bell, A. G., inherited deafness, 104,

256, 388
Belling, J., 12
Bere, M., 345

Berlin, birth rate, 208, 213, 229, 324
Bernhardi, F. von, 282, 283, 288, 388
Bertillon, J., 208
Besant, A., 206, 207, 365
Beta test, 342, 343
Bidder's organ, 49
Binet, A., 173

mental tests, 167, 175, 345
Biometry, 87^".
Birth control, 206, 365, 366
Birth injuries, 126, 127, 143, 156, 268
Birth rate, I96/, 246, 249, 287, 297-

300, 3i4~3I7> 32I~325> 337-340,

365, 366, 375>378-38i
Blacker, C. P., 110,388
Blanchard, M. B., 327, 396
Blanton, S., 155
Blending inheritance, 54, 55
Blindness, inheritance, 109^ 146, 204

405

406 HUMAN GENETICS AND ITS SOCIAL IMPORT

Bluhm, A., hereditary effect of alcohol,

Boas, F., 353
Bolin, J. S., 388
Bonar, J., 388
Bossard, J. H. S., 388
Bo wen, £.,388
Bowman, J. T., 146
Box bill, 339
Bradford, intelligence and family size,

225

Bradlaugh, C, 206, 207, 365
Bridges, C. B., 69, 73
Brigham, C. C., 348, 388
Britten, R. H., 388
Bronner, A. F., 178
Brooks, W. K., 90, 91
Buck vs. Bell, test of sterilization

statute, 371
Buckle, T. H., 112
Bulgaria, age for marriage in, 201
Burbank, L., 86
Burgdorfer, F., 217, 301, 302, 315, 324,

379, 388

Burks, B. S., 160, 161, 169, 388
Burt, C., 177, 389
Bushee, F. A., 389
Bushnell, L. D., 83, 395
Butt, N. L, 230
Buttercup, variability, 89

California, sterilization in, 372, 373
California, University of, family size

of students, 209, 219
marriage of graduates, 218
Campanella, T., 362
Cancer, inheritance, 106-108
Carlile, R., 207, 365
Carpenter, N., 389
Carr-Saunders, A. M., 83, 163, 164, 310,

389, 395> 396

Castle, W. E., 352, 357, 387, 389
Cataract, inheritance, 102, 103
Catholics, birth rate, 211-213
Cattell, J. McK., 191, 260, 389

Cell theory, 2-4

Cells, 3-8, 11, 14, 15

Centenarians, 242

Centrosome, 5-7

Chapman, J. C., 225, 389

Charles, E., 236, 389

Chiasmas, 71

China, 332

Chromatin, 6, 9

Chromomeres, n, 12, 16

Chromosomes, 6-18, 35-40, 42-47,
_ 66-75,77,78,90, 115

Cities, growth of, 3i9jf.
mortality in, 248-251

Clark, L P., 259, 389

Clarke, C. K., and Me Arthur, J. W.,
Huntington's chorea, 141

Clarkson, R. D., 389

Clausen, R. E., 39, 88, 96, 387

Cockayne, E. A., 104

Coefficient of variability, 92, 93

Coefficients of correlation (see Correla-
tion)

College graduates, birth rates, 217-220,

231
marriage rates, 191, 217, 218, 231

Color blindness, 102-104, IQ8

Colvin Hollow, 326

Complementary factors, 55-58

Condorcet, A. N., 290

Conklin, E. G., 39, 56, 389

Conrad, H. S., 230, 327, 389, 396

Conrad, K., 145

Consanguinity, 349 jf.

Constable, F. C., 390

Cook, O. F., 390

Cooper, J. M., 390

Correlation, 94-97, 106, 116, 117, 153,
J54, 256

Correns, C., 29, 59

Corson, J. J., 393

Cotton, H. H., 137, 390

Cousins, marriage of, 350

Cowdry, E. V., 389

Cox, C. M., 157, 158,389

Cox, H., 288, 389

Crepidula, sex determination, 47, 48

INDEX

407

Cretins, 114, 115
Crew, F. A. E., 26, 48, 1 10, 390
Crime, 171 jf., 183-186
Cross breeding, 349^.
Crossing over, 68-71
Crum, F. S., 266
Cumulative factors, 58
Cytology, iff.
Cytoplasm, 4-8

Dachert, A., 376, 390

Dahlberg, G., 121, 124,390

Danielson, F. H., 326

Darwin, C. R., 20, 21, 23, 28, 57, 72,

153, 188, 189, 195, 253, 255, 272,

291, 293, 350, 362, 390
Darwin, L., 153, 195, 385, 390
Darwinism, 276, 277
Datura, 72
Davenport, C. B., 55, no, 139, 187,

326, 352, 357, 364, 390, 391
Davis, J. J., 391
Davis, R. A., 161
Dawson, S., 225

Dayton, N. A., 127, 235, 259, 391
Deafness, 103, 104, 108, 156
Death rates, 199-201, 238 /., 298-300,

3H> 3I5>32I-324
Delinquency, 177-179
Dementia praecox, 138-140, 142, 143
Detlefson, J. A., 27, 391
De Vries, H., 27, 89
Diabetes, inheritance of, 63, 105, 257
Diehl, K., 124
Doll, E. A., 147, 391
Dominance, 30, 31, 58, 59, 61-64, 99~

101

Domm, L. V., 48
Donkin, H. B., 173
Dorn, H. F., 250
Douglas P., 383, 385, 391
Drosophila, 8, 12, 13, 25, 45, 46, 61,

62, 66-75, 78> 85> I09
Dublin, L. I., 217, 272, 303, 318, 391
Dumont, A., 210

Duncan, H. G., 318, 391

Dunlap, K., 189, 195, 391

Dunn, L. C., 39, 49, 64, 387, 391, 401

Durham, F. W., 82, 391

Dwarfs, 100, 115

East, E. M., 214, 295, 318, 348, 357, 391

Edin, K., 391

Elderton, E. M., 116, 392

Ellis, H., 170, 189,392

Ellis, R. S., 392

Embree, E. R., 389

Emigration, 305, 330-332

England and Wales, age at marriage, 201

birth rate in, 199, 207, 208

occupational mortality in, 261
Epilepsy, in criminals, 178

inheritance, 110, 130, 143-146
Estabrook, A. H., 183, 187, 392
Eugenics, 149, 359/.
Eugenics Record Office, 364
Eugenics Society, 363, 381
Europe, birth rate, 200

emigration from, 305, 331-337

marriages in, 202

population growth in, 297, 298, 300-

303

Evans, H. M., 9, 392
Eye color, 52, 98, 99, 113, 120
Eye defects, 52, 82, 83, 102, 103

Fairchild, H. P., 308, 348, 392
Family allowances, 377 ff.
Farr, Wm., 248
Farr's law, 248
Fasten, N., 387, 392
Fecundity, definition, 197
Feeble-minded, birth rate, 231-236

death rate, 259, 260, 269
Feeble-mindedness, 64, 126 J/"., 346,

37<>-373

Fernald, W. S., 173
Fertility, 196 /., 323, 324, 326, 381, 388

4o8 HUMAN GENETICS AND ITS SOCIAL IMPORT

Fertilization, 14, 15, 17
Fischer, E., no, 147, 388
Fisher, R. A., 214, 385, 392
Focal infections, role in insanity, 137
Foster children, 160, 161, 163, 164
Four o'clocks, inheritance of color, 59
Fragility of bone, inheritance, 108
France, birth rate, 198, 205, 212-214

population growth, 300-302
Franklin, B., 290
Fraser, L. M., 392
Freeman, F. N., 160, 170, 392
Freeman, F. S., 170, 392
Frequency curves, 88-90
Fruit fly, 12, 13, 39, 66-75, 8o> 85

(See also Drosophila)
Fundulus, n, 13, 1 8

Galton, F., 87, 94, 98, 113, 117, 152,
jyo, X93> I98> 26o> 325> 362~364>
376, 385, 392> 393

Galton Laboratory, 87, 363, 364

Gametogenesis, 15

Gamio, M., 344, 393

Garth, T. R., 354, 393

Gates, R. R., no, 147, 393

Gee, W., 326, 328, 393

Genes, 38, 39, 52, 54, 55, 57, 58, 60-63,
79, loo, 108-110, 113-115, 133, 134,

357

Gene mutations, 78, 79
Genetics, i, 2
Genius, inheritance, 152^".
Germ plasm, continuity, 22, 23
Germany, age at marriage in, 201

birth rate for, 199, 213, 216, 379

sterilization in, 373
Gesell, A., 167, 168
Gini, C, 203, 393
Glass, D. V., 380
Glaucoma, heredity, 102, 103
Glioma of retina, 107
Goddard, H. H., 132, 133, 147, 184, 187,

393
Godwin, W., 290, 291, 393

Gonorrhea, 204, 205, 268

Gordon, A., 143, 144, 393

Goring, C, 117, 172

Gosney, E. S., 385, 393

Gould, H. N., 47

Cover, M., 393

Grant, M., 348, 393

Grassl, J., 217

Graunt, J., 239

Greeks, ideas on eugenics, 359-361

Green, C. V., 232, 393

Grew, N., 2

Gun, W. T. J, 393

Guyer, M. F., 27, 82, 83, 85, 181, 393

Hacker, E., 394
Haeckel, E., 3
Haemophilia, 51, 257
Haggerty, M. E., 394
Hair color, 99, 120
Haldane, J. B. S., 180, 394
Hall of Fame, 1 59
Hamburg, birth rate, 229, 325

venereal diseases in, 205
Handy, L. M., 142, 180, 400
Hankins, F. H., 394
Hansen, G., 325
Hanson, F. B., 81
Hare lip, 108
Harper, R. M., 335, 394
Hart, H., 394

Harvard, birth rate of graduates, 217,
231

losses in war, 280
Haupt, A. W., 32
Hawaii, population of, 312
Haynes, F. E., 181, 394
Healy, W., 177, 178, 394
Henry, T. R., 326
Heraclitus, 360

Heredity, i, 2, 4, 19, 63, ii2/.
Hering, E., 22
Hermaphroditism, 47-49
Heron, D., 216, 394
Herrman, C., 394

INDEX

409

Herskovits, M. J., 394
Heys, F., 81
Hill Folk, 186,326,375
Himes, N., 207, 394
Hindus, emigration, 333
Hodson, C. B. S., 385
Hoffmann, H., 138, 139
Hogben, L., 394
Hollingworth, L. S., 394

Infant mortality, 244-246, 250, 251,

261-272

Infanticide, 310, 360, 361
Insane, 369, 370
Insanity, inheritance, 63, 109, no, 131,

i36-H3> 250, 25J
Intelligence, 114, 123, 124, H9/-
Intelligence quotients, 156, 158-167,

225, 233> 235, 326-328, 338
Isolation, 356
Italy, birth rate, 211

Holmes, O. W., 371

Holmes, S. J., 147, 170, 195, 214, 236,
272, 288, 357, 385, 387, 388,

394, 395 J

Hooke, R., 2
Hookworms, relation to intelligence, Jacob, breeding of cattle, 86

156

Hooton, E. A., 172, 173, 395
Hoover, G., 395
Hormones, 49, 50
Howard, G. E., 190
Hume, D., 290
Humm, D. G., 136, 144, 395
Hunt, H. R., 280, 395
Huntington, E., 181, 191, 211, 218, 231,

236, 395

Jaederholm, G. A., 128

Jamieson, E., 354

Janssens, F. A., 69

Japan, population growth, 297, 307

Japanese, birth rate for, 199, 200

emigration of, 332
Jenkins, R. L., 233
Jennings, H. S., 39, 85, 124, 169, 227,

396
Jews, birth rate, 212

Huntington's chorea, 38, 139-142, 151, Johannsen, W., 95

257

Hurst, C. C., 395
Huxley, J. S., 39, 50, 83, 85, 395
Huxley, T. H., 5

Ibsen, H. L., 83, 395

Ichthyosis, 105

Idiots, 127, 128, 132, 169, 259, 369
Illegitimacy, 183-186, 356, 369
Imbeciles, 127, 128, 130-132, 169,

259, 369
Immigrants, marriages of, 194

Johnson, E. R., 370

Johnson, R. H., 195, 368, 385, 396, 400

Jones, D. Caradog, 163, 164, 233, 236,

396

Jones, D. F., 357, 391
Jones, H. E., 230, 327, 389, 396
Jordan, D. S., 278, 279, 288, 396
Jordan, H. E., 278, 288, 396
Juke family, 183-185, 187, 193, 231,

375

Kallikak family, 132, 184-187, 193, 231
Kammerer, P., 26, 27, 396

Immigration, 312-317, 323, 331-337, Karyokinesis, 6-8

339-348, 355, 384
Immigration Commission, 316, 341
Inbreeding, 349 /.
Incas, 349
India, emigration from, 332, 333

Keeler, C. E., 122
Keller, X., 234
Keratosis, 105
Key, W. E., 396
Kirkpatrick, C., 344, 348

4io HUMAN GENETICS AND ITS SOCIAL IMPORT

Kiser, C. V., 224, 396
Knibbs, G., 297, 318, 396
Knowlton, C., 206, 207
Koch, H.L., 123
Kuczynski, R. R., 300, 318, 396
Kurz, K., 234

Lamarck, J. B., 19, 20

Lamarckism, 19-28, 79, 254

Landman, J. H., 396

Lange, J., 142, 179, 181,396

Lauterbach, C. E., 124, 396

Lawrence, E. M., 161, 163, 170, 397

Leahy, A. M., 164, 170, 397

Leber's atrophy, 146

Legras, A. M., 180, 181,397

Lennes, N. J., 397

Lentz, T., 397

Lenz, F., no, 147, 205, 216, 217, 222,

224, 279, 388, 397
Lenz, T., 224
Lepidoptera, 44, 47
Lethal factors, 39, 58
Levasseur, E., 205
Lewis, P. A., 105
Lidbetter, E. J., 187,397
Life tables, 240, 241
Lincoln, A., 170

Lindsey, A. W., 49, 74, 96, no, 397
Linkage, 66 f.
Little, C. C., 84

Lobster claw, inheritance, 101, 102
Lombroso, C., 172-174, 178, 397
London, birth rate for, 216, 229
London School of Economics, family

allowances, 378
Longevity, 94, 113, 242, 247, 256, 265,

266
Lorimer, F., 170, 214, 271, 318, 324,

328, 348, 387, 397
Lotka, A. J., 303, 391, 397
Ludovici, A. M., 357, 397
Ludwig of Bavaria, 140
Lutz, F. E., 25
Luxenberger, H., 135, 142
Lycurgus, 360

Macaulay, T. B., 157

McClung, C. E., 42

McDougall, W., 26, 27, 381, 397

McDowell, E. C., 81

McKemy, Mexican immigration, 340

Macklin, M., 146

MacPherson, J., 397

Mallet, B., 397

Malpighi, M., 2

Malthus, T. R., 206, 290-294, 318, 398

Malthusianism, 375

Malzberg, B., 397

Manic-depressive insanity, 138, 142

Maoris, 286

Marriage, age for, 191^"., 198, 201

rate of, 191^"., 198-203
Marvin, D. M., 193
Marx, C., 294

Maturation of sex cells, 14-16
Mean, 88-91, 93
Melanesians, 285, 286
Melcher, R. T., 391
Mendel, G. J., 29, 30, 72, 76
Mendel's law, 29 /., 52 /., 76, 77, 79,

96,98,100, 129, 130,349-353
Mental deficiency, 109, 114, 126 /.,

I51, !93> 259
Mental Deficiency Committee, 128, 132,

233

Merriman, W. E., 398
Metropolitan Life Insurance Company,

241

Mexicans, 317

Mexico, immigration, 315, 337-341
Microcephaly, 127, 128
Migraine, 109
Migration, 330 /., 356
Mill, J. 8,112,365
Miller, H. C, 398
Mirabilis, color inheritance, 59
Mirror imaging, 121-123
Miscegenation, 339, 351-357
Mitosis, 6-8, u, 14
Mjoen, J. A, 352, 357, 398
Mode, 88-90

INDEX

411

Mongolian idiocy, 147

Moore, E., 398

Morgan, T. H., 39, 46, 62, 66-69, 73,

74, 387, 398

Mormons, birth rate, 211, 230

Morons, 127, 128, 132, 259, 269

Mortality, 238^.

selective action of, 253^.

Mortality tables, 240, 241

Mott, F. W., 137

Mulattoes, 54, 55, 64, 100, 354, 355, 357

Muller, H. J., 84, 124,398

Multiple factors, 54, 55, 58, 100, 133-
135, 168,350

Muncey, E. B., 139, 390

Murchison, C., 174-176, 398

Muscular atrophy, inheritance, 146

Mutations, 78-81

Mutilations, alleged inherited effects,
24-26

Myoclonus epilepsy, recessive inherit-
ance, 143

Myreson, A., 147, 398

Nam family, 186
Napoleon, 306
Nash, H. B., 394
Natural selection, 253^.
Negative eugenics, 366 f.y 384
Negroes, i, 54, 55, 99, 100, 268, 286,
311, 312, 314, 315, 325, 326, 345,

346, 354, 356, 357
Nelson, L., 230

Neo-Malthusianism, 245, 307, 311
Nervous diseases, 146, 147
Nettleship, E., 103
Newman, H. H., 17, 27, 74, 121, 124,

167, 398

Newsholme, A., 251, 398
New Zealand, birth rate, 199
Nicolai, G. F., 288, 398
Nordics, i, 196, 313
Norway, birth rate, 211
Notestein, F. W., 192, 222, 223, 398,

401

Nucleus, 5-14
Nurture, ii3/., 149!-

Occupation and fertility, 221-224, 227
and intelligence, 161-165, T^9
and mortality, 260-263, 272

Ogburn, W. F., 224, 236, 399

Olkon, D. M., epilepsy in twins, 145

Oogenesis, 14, 15

Optimum of population, 308-310

Orphans, intelligence of, 163, 164

Osborn, D., 399

Osborn, F., 170, 214, 271, 318, 324,
328, 348, 387, 397, 399

Otosclerosis, 104

Otto of Bavaria, inherited insanity,
140

Owen, R. D., 207, 365

Owens, A. A., 177

Painter, T. S., 13

Pangenesis, 21, 28

Panmixia, 258

Paris, birth rate, 208, 213, 229, 324
growth of, 319, 320

Parker, S. L., 324, 395

Parr, Th., alleged longevity, 242

Pascal, B., 157

Pasteur, L., 105

Pauperism, 183, 186

Pavlov, I. P., 26

Payne, F., 25

Pea comb in poultry, 59-61, 64

Pearl, R., 81, 296, 399

Pearl, R. De W., 399

Pearson, K., 87, 91, 94, 116, 117, 128,
153, 193, 207, 214, 254, 255, 266,
270-272, 276, 277, 278, 363, 399

Peas, heredity of, 29-33, 36-38, 40, 56,

57, 72, 77, 95
Pease, M. S., 399
Penrose, E. F., 399
Penrose, L. S., 134, 135, 399

4i2 HUMAN GENETICS AND ITS SOCIAL IMPORT

Perkins, H. F., 399

Phelps, W. M., 391

Phillips,J. D., 231

Pineys, 186

Pintner, R., 153, 156,354

Pitt-Rivers, G. M., 399

Pituitary gland, 115

Place, F., 207, 365

Plato, eugenic proposals, 360-362

Plessett, I. R., 400

Ploetz, A., 265, 400

Polydactylism, inheritance, 62, 63, 109

Polynesians, 285, 286

Pope, pronouncement on birth control,

212, 213
Popenoe, P., 123, 195, 232, 368, 372,

385, 393, 400
Population, 290^".
Porteus, S. D., 400
Positive eugenics, 366, 367
Primula, 61, 62
Probable error, 92, 93
Prostitution, 178, 183, 184, 186, 263
Protestants, birth rate, 211-213
Protoplasm, 5
Prussia, children per marriage in, 222

occupational mortality in, 262
Pugnacity in social animals, 274-277
Punnett, R. C., 56, 59, 66
Pure lines, 95

Purtscher, inheritance of retinal glioma,
107

Quetelet, J., 87

Rabbits, inheritance, 57, 82, 83, 134, 352

Race mixture, 339, 351 /.

Radium as a cause of mutations, 84, 85

Raleigh, W., 290

Rathbone, E., 400

Recessive characters, 31, 32, 57

Reed,L.J.,96

Registration Area for Births, 240,

Registration Area for Deaths, 240

Religion and the birth rate, 211-213

Rensch, 153

Reuter, E. B., 318, 354, 355, 357, 400

Reversion, 56, 57

Rice, T. B., 107, 400

Richards, A., 13

Riddle, O., 48

Robbins, L,., 400

Roberts, E. H., 400

Rollins, W. A., 400

Roosevelt, T., 217

Root, W. T., 173, 176, 400

Rosanoff, A. J., 142, 147, 180, 400

Rosanoff, I. A., 180, 400

Rose comb, inheritance of, 60, 61, 64

Ross, E. A., 220, 387, 401

Rousseau, J. J., 112

Roux, W., 8

Riidin, E., 138, 139

Russell, B., 385

Ryan, J. A., 401

Sailer, K., 401

Sallume, X., 398, 401

Sanders, J., 145

Sandiford, C., 354

Sanger, M., 401

Sax, K., 71

Schiller, B., 401

Schiller, F. C. S., 401

Schizophrenia, 138-140, 142

Schleiden, M. J., 2

Schwann, T., 3

Schwesinger, G. C., 170, 400

Segregation, 369-371

Semon, R., 22

Senay, C. T., 90

Sex, 42

Sex determination, 42 jf., 115

Sex-linked heredity, 44-46, 66, 105, 146

Sex mortality, 267-269

Sex ratio, 267

Sexual selection, 51, 188^"., 384

Sharp, L., 14, 17, 401

INDEX

Shaw, G. B., 22

Sherman, M., 326

Shull, A. F., 17, 30, 49, 61, 64, 4oi

Siamese twins, 122-124, 170

Sinnott, E. W., 39, 49, 64, 401

Sjogren, T., 130, 131, 152

Skew curves, 89

Skin color, 54, 55, 100

Skin diseases, inheritance, 104, 105

Slavs, 302, 313

Slye, M., 1 08

Smillie, W. G., 156

Smith, E. A., 393

Smith, J. C., 135

Smith, M. R., 218, 401

Snow, E. C., 266, 401

Snyder, L. W., 401

Social problem group, 186

Sorokin, P., 327, 328, 401

Southey, R., 292

Spartan eugenics, 360

Spearman, C. E., 170, 401

Spencer, H., 3, 202, 278

Spermatogenesis, 14, 15

Spermatozoa, 90

Split hands, 100-102

Stabilized rates of increase, 299—304,

314,315

Standard deviation, 91-93
Standardized rates, 238, 239
Stature, 92, 100, 117
Steggerda, M., 391
Steinach, E., 49
Sterility, 204

Sterilization, 369, 371-375
Stevenson, T. H. C., 221, 261
Still births, 204, 268
Stockard, C. R., 80-82, 401
Stoddard, L., 401
Stohler, R., 118
Stowell, W. L., 259, 389
Strohmayer, W., 140
Swarthmore college, birth rate of

graduates, 217
Sweden, age at marriage, 201

birth rate, 211
Swezy, O., 9, 392

Sydenstricker, E., 222, 401
Synapsis, 16, 18,35,36, 68
Syndactylism, inheritance, 101-103
Syphilis, 103, 126, 136, 137, 143, 204,
205, 263

Tasmanians, 285

Taylor, P., 348, 401

Taylor, W. R., 16

Telegony, 86

Terman, L. M., 158, 162, 170, 401

Theognis, 359

Thompson, J. A., 27

Thompson, W. S., 214, 244, 245, 251,

297> 3J7> 3l8> 328> 348, 387> 402
Thurstone, L. L., 233
Thyroid gland and mental deficiency,

64, 114, 115, 126
Tibbitts, C., 236

Tortoise shell cats, inheritance, 65
Townsend, on population, 290
Translocations, 10, 67, 71
Tredgold, F. A., 126, 402
Tribe of Ishmael, 186, 232
Tschermak, E. von, 29
Tuberculosis, 48, 105, 120, 121, 257
Twins, 117-124, 135, 136, 142, 143,

164-168, 179-181

Ungern-Sternberg, R. von, 203, 402

Unit characters, 52

United States, birth rate, 198-200,

230

marriages in, 202

mortality, 240, 241, 243, 244 /., 264
population growth, 297, 298, 303,

304

Urban areas (see Cities)
Urban migration, 321 ff.

Variation, measurement of, 87 jf.
Variations, classes of, 76 Jf.
production of, 79 ff.

4i4 HUMAN GENETICS AND ITS SOCIAL IMPORT

Vassar College, marriage rate of

graduates, 218
Venereal diseases, 263

(See also Gonorrhea; Syphilis)
Vermont, eugenics survey, 232
Verschuer, O. von, 120, 402
Vibart, H. H. R., 402
Vienna, birth rate, 208; population, 319
Virchow, R., 3
Virginia statute on sterilization, 371

Wagner-Manslau, W., 203, 402

Wallace, A. R., 293

Walnut comb, inheritance, 60, 61, 64

Walter, H. E., 96, 402

War, biological effects, 274^.

Warthin, A. S., inheritance of cancer,

107

Wassermann tests, 126, 130, 143
Wedgwood, J., 153
Weismann, A., 14, 22, 23, 27, 258,

402

Wells, G. P., 39, 49, 85
Wells, H. G., 39, 49, 85
Westermarck, H., 190
Whelpton, P. K., 247, 251, 297, 317,

318,324,402
Whetham, W. C. D., 216
Whetten, N. L., 210, 402
Whipple, G. C., 402
White, F. W., 402
Whitney, E. A., 128, 181
Whitney, L. F., 127, 191, 211, 231, 234,

236> 395> 402
Wiehl, 243
Wieman, H. L., 6, 7, 15

Wiggam, A. E., 366, 385, 402, 403

Wiggins, D. M., 225, 389

Willcocks, R. W., 154

Willcox, W. F., 243, 248, 293, 403

Willoughby, R. R., 403

Wilson, E. B., 17, 43, 403

Wilson, P., 119

Wingfield, A. H., 124, 165, 403

Winkler, W. F., 234

Winship, A. E., 187, 403

Witschi, E., 49

Wolcott, R., 60

Wolfe, A. B., 308, 403

Woodbury, R. M., 270

Woods, F. A., 231, 403

Woods, H. M., 391

Wright, H., 3 1 8, 403

Wright, S., 105

Jf-chromosomes, 13, 42^"., 66, 69, 73
J!f-rays as a cause of mutations, 78, 79,
84,85

Y-chromosomes, 42, 43, 47, 51, 69, 73
Yale graduates, birth rate, 217, 231
Yerkes, R. M., 403
Young, T. E., 262, 403

Zeleny, C., 90

Zeleny, L. D., 174, 175

Zero family, 186

Zimmerman, C. C., 327, 328, 401

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