Chapter VII: ; to Professor C. R. Bardeen for reading special parts; to

Doctor J. S. Evans for reading Chapter VI and part of V; to Doctor W. F. Lorenz, of the Mendota Hospital, for reading Chapter VIII; to Judge E. Ray Stevens for reading Chapter IX, and to Helen M. Guyer for several readings of the entire manuscript.

Grateful acknowledgment is made to all of these readers, to various publishers and periodicals for the use of certain of the illustrations, to the authors of the numerous books and papers from which much of the material in such a work as this must necessarily be selected, and to my artist, Miss H. J. Wakeman, for her painstaking endeavors to make her work conform to my ideas of what each diagram should show.

M. F. G.

CONTENTS

CHAPTER PAGE

I HEREDITY 1

Blood heritage--Kind determined by origin--Ancestry a network--
Ancestry in royalty--Offspring derived from one parent only--Dual
ancestry an aid in studying heredity--Reversion--Telegony--
Prenatal influences apart from heredity--Parent body and germ not
identical--A hereditary character defined--Hereditary mingling a
mosaic rather than a blend--Determiners of characters, not
characters themselves, transmitted--Our knowledge of heredity
derived along three lines--The method of experimental breeding--
The statistical method--Galton's law of regression--Correlations
between parents and offspring--The biometrical method,
statistical, not physiological--Mental as well as physical
qualities inheritable.

II THE BEARERS OF THE HERITAGE 20

The cell the unit of structure--Unicellular organisms--Importance
of cell-theory--Heredity in unicellular forms--Reproduction and
heredity in colonial protozoa--Conjugation--Specialization of
sex-cells--The fertilized ovum--Advancement seen in the Volvox
colony--Natural death--Specialization in higher organisms--Sexual
phenomena in higher forms--Cell-division--Chromosomes constant in
number and appearance--Significance of the chromosomes--Cleavage
of the egg--Chief processes operative in building the body--The
origin of the new germ-cells--Significance of the early setting
apart of the germ-cells--Individuality of chromosomes--Pairs of
chromosomes--Reduction of the number of chromosomes by one-half--
Maturation of the sperm-cell--Maturation of the egg-cell--Parallel
between the two processes--Fertilization--Significance of the
behavior of the chromosomes--A single set of chromosomes
sufficient for the production of an organism--The duality of the
body and the singleness of the germ--The cytoplasm in
inheritance--Chromosomes possibly responsible for the
distinctiveness of given characters--Sex and heredity--Many
theories of sex determination--The sex-chromosome--Sex-linked
characters in man--In lower forms.

III MENDELISM 67

New discoveries in the field of heredity--Mendel--Rediscovery of
Mendelian principles--Independence of inheritable characters--
Illustration in the Andalusian fowl--The cause of the ratio--
Verification of the hypothesis--Dominant and recessive--
Segregation in the next generation--Illustrated in guinea-pigs--
Terminology--The theory of presence and absence--Additional
terminology--Dominance not always complete--Modifications of
dominance--Mendel's own work--Dihybrids--Getting new combinations
of characters--Segregations of the determiners--Four kinds of
gametes in each sex--The 9:3:3:1 ratio--Phenotype and genotype--
The question of blended inheritance--Nilsson-Ehle's discoveries--
Such cases easily mistaken for true blends--Skin-color in man--
Questionable if real blends exist--The place of the Mendelian
factors in the germ-cell--Parallel between the behavior of
Mendelian factors and chromosomes--A single chromosome not
restricted to carrying a single determiner.

IV MENDELISM IN MAN 97

Probably applicable to many characters in man--Difficult to get
correct data--A generalized presence-absence formula--Indications
of incomplete dominance--Why after the first generation only half
the children may show the dominant character--Eye-color in man--
Hair-color--Hair-shape--Irregularities--Digital malformations--Eye
defects--Other defects inherited as dominants--Recessive
conditions more difficult to deal with--Albinism--Other recessive
conditions in man--Breeding out defects--Other inheritable
conditions in man.

V ARE MODIFICATIONS ACQUIRED DIRECTLY BY THE BODY INHERITED? 121

Which new characters are inherited?--Examples of somatic
modifications--Use and disuse--The problem stated--Special
conditions in mammals--Three fundamental questions--External
influences may directly affect the germ-cells--Such effects
improbable in warm-blooded animals--Poisons may affect the
germ-plasm--How can somatic modifications be registered in
germ-cells?--Persistence of Mendelian factors argues against such
a mode of inheritance--Experiments on insects--On plants--On
vertebrates--Epilepsy in guinea-pigs--Effects of mutilations not
inherited--Transplantation of gonads--Effects of body on germ,
general not specific--Certain characters inexplicable as inherited
somatic acquirements--Neuter insects--Origin of new characters in
germinal variation--Sexual reproduction in relation to new
characters--Many features of an organism characterized by
utility--Germinal variation a simpler and more inclusive
explanation--Analysis of cases--Effects of training--Instincts--
Disease--Reappearance not necessarily inheritance--Prenatal
infection not inheritance--Inheritance of a predisposition not
inheritance of a disease--Tuberculosis--Two individuals of
tubercular stock should not marry--Special susceptibility less of
a factor in many diseases--Deaf-mutism--Gout--Nervous and mental
diseases--Other disorders which have hereditary aspects--Induced
immunity not inherited--Social, ethical and educational
significance of non-inheritance of somatic modifications--No cause
for discouragement--Improved environment will help conserve
superior strains when they do appear.

VI PRENATAL INFLUENCES 151

All that a child possesses at birth not necessarily hereditary--
The myth of maternal impressions--Injurious prenatal influences--
Lead poisoning--The expectant mother should have rest--Too short
intervals between children--Expectant mothers neglected--
Alcoholism--Unreliability of most data--Alcohol a germinal and
fetal poison--Various views of specialists on the effects of
alcoholism on progeny--The affinity of alcohol for germinal
tissue--Innate degeneracy versus the effects of alcohol--
Experimental alcoholism in lower animals--Further remarks on the
situation in man--Much inebriety in man due to defective nervous
constitution--Factors to be reckoned with in the study of
alcoholism--Venereal diseases--The seriousness of the situation--
Infantile blindness--Syphilis--Some of the effects--A blood test--
Many syphilitics married--Why permit existing conditions to
continue?--Ante-nuptial medical inspection--The perils of venereal
disease must be prevented at any cost--Bad environment can wreck
good germ-plasm.

VII RESPONSIBILITY FOR CONDUCT 195

All mental process accompanied by neural process--Gradations in
nervous response from lower organisms to man--Behavior of many
animals often an automatic adjustment to simple external agents--
Tropisms--Certain apparently complex volitions probably only
tropisms--Complicating factors--Many tropic responses apparently
purposeful--Tropisms grade into reflex actions and instincts--
Adjustability of instincts opens the way for intelligent
behavior--Modification of habits possible in lower animals--Some
lower vertebrates profit by experience--Rational behavior--
Conceptual thought probably an outgrowth of simpler psychic
states--The capacity for alternative action in higher animals--The
elemental units of the nervous system are the same in lower and
higher animals--Neuron theory--Establishment of pathways through
the nervous system--Characteristic arrangements of nerve cells
subject to inheritance--Different parts of the cortex yield
different reactions--Skill acquired in one branch of learning
probably not transferred to another branch--Preponderance of
cortex in highest animals--Special fiber tracts in the spinal cord
of man and higher apes--Great complexity in associations and more
neurons in the brain of man--The nervous system in the main
already staged at the time of birth--Many pathways of conduction
not yet established--The extent of the modifiable zone unknown--
Various possibilities of reaction in the child--Probable origin of
altruistic human conduct--Training in motive necessary--Actual
practise in carrying out projects important--Interest and
difficulty both essential--The realization of certain
possibilities of the germ rather than others is subject to
control--We must afford the opportunity and provide the proper
stimuli for the development of good traits--Moral responsibility.

VIII MENTAL AND NERVOUS DEFECTS 228

Prevalence of insanity--Imperfect adjustments of the brain
mechanism inheritable--Many mental defectives married--
Disproportionate increase in number of mental defectives--Protests
voiced by alienists--Examples of hereditary feeble-mindedness--
Difficult to secure accurate data--Feeble-mindedness and insanity
not the same--Many types of insanity--Not all insanities of the
same eugenical significance--Difficulties of getting genealogies
of specific forms of insanity--Certain forms of insanity seem to
behave as Mendelian recessives--Grades of feeble-mindedness--About
two-thirds of feeble-mindedness inherited--Some results of
non-restraint of the feeble-minded--Not all cases of mental
deficiency inherited--Epileptics--Feeble-mindedness probably a
recessive--Many apparently normal people are carriers of
neuropathic defects--Tests for mental deficiency--The backward
child in school--The exceptionally able child--Cost of caring for
our mentally disordered--Importance of rigid segregation of the
feeble-minded--Importance of early diagnosis of insanity--Opinion
of competent psychiatrists essential--Some insanities not
hereditary--Importance of heredity in insanity not appreciated.

IX CRIME AND DELINQUENCY 263

Heredity and environment in this field--Feeble-mindedness often a
factor--Many delinquent girls mentally deficient--Institutional
figures misleading--Many prisoners mentally subnormal--Inhibitions
necessary to social welfare--The high-grade moron a difficult
problem--Degenerate strains--Intensification of defects by
inbreeding--Vicious surroundings not a sufficient explanation in
degenerate stocks--Not all delinquents defectives--No special
inheritable crime-factor--What is a born criminal?--Epileptic
criminal especially dangerous--The mental disorders most
frequently associated with crime--Bearing of immigration on crime
and delinquency--Sexual vice--School instruction in sex-hygiene--
Mere knowledge not the crux of the sex problem--Early training in
self-restraint an important preventive of crime and delinquency--
Multiplication of delinquent defectives must be prevented.

X RACE BETTERMENT THROUGH HEREDITY 289

Questionable charity--Past protests--An increasing flood of
defectives--Natural elimination of defectives done away with--Why
not prevent our social maladies?--Eugenics defined--Improved
environment alone will not cure racial degeneracy--Heredity and
environment--Inter-racial marriage--Human conservation--Kindness
in the long run--The problem has two phases--Constructive eugenics
must be based on education--Inferior increasing more rapidly than
superior stocks--An unselected population may contain much
valuable material--The lack of criteria for judging fitness--The
college graduate--Native ability, independence and energy
eugenically desirable--Four children to each marriage required to
maintain a stock--Factors contributing to low birth-rate in
desirable strains--The educated public must be made to realize the
situation--Utilization of family pride as a basis for constructive
eugenics--The tendency for like to marry like--Public opinion as
an incentive to action--Choosing a marriage mate means choosing a
parent--The best eugenic marriage also a love match--The
elimination of the grossly unfit urgent--Suggested remedies--
Inefficacy of laws which forbid marriage of mental defectives--
Systems of mating impracticable in the main--Corrective mating
presupposes knowledge of eugenics--Segregation has many
advocates--Sterilization as a eugenic measure--To what conditions
applicable--In insanity--In feeble-mindedness--In cases of
epilepsy--Sterilization laws--Social dangers in vasectomy--Our
present knowledge insufficient--Sterilization laws on trial--An
educated public sentiment the most valuable eugenic agent--The
question of personal liberty--Education of women in eugenics
needed--Much yet to be done--A working program--Which shall it be?

GLOSSARY 343

REFERENCES FOR FURTHER READING AND STUDY 355

INDEX 361

BEING WELL-BORN