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Transcriber's note:
Text enclosed by underscores is in italics (_italics_).
Text enclosed by equal signs is in bold face (=bold=).
Text enclosed by plus signs is underscored (+underscored+).
Male and Female symbols are shown as [M] and [F]
respectively and denoting physical defects as [M-] and
[F-] respectively.
Subscripted numbers are enclosed by curly brackets
following a single underscore (example: F_{2}).
ABSTRACTS OF PAPERS READ AT THE FIRST INTERNATIONAL EUGENICS CONGRESS,
[Illustration]
University of London.
July, 1912.
English.
Charles Knight & Co., Ltd., 227-239, Tooley Street, London, S.E.
CONTENTS.
Section I.
Biology and Eugenics.
PAGE
I. Variation and Heredity in Man 5
G. SERGI.
II. On the Increase of Stature in Certain European Populations 6
SOREN HANSEN.
III. The So-called Laws of Inheritance in Man 7
V. GUIFFRIDA-RUGGERI.
IV. The Inheritance of Fecundity 8
RAYMOND PEARL.
V. Ethnic Psychology and the Science of Eugenics 9
ENRICO MORSELLI.
VI. The Inheritance of Epilepsy 10
DAVID F. WEEKS.
VII. The Influence of the Age of Parents on the Psycho-Physical
Characters of the Offspring 12
ANTONIO MARRO.
VIII. Genetics and Eugenics 15
R. C. PUNNETT.
Section II.
Practical Eugenics.
I. General Considerations upon "Education before Procreation" 17
A. PINARD.
II. Practical Organization of Eugenic Action 18
LOUIS QUERTON.
III. Marriage Laws and Customs 19
C. B. DAVENPORT.
IV. Eugenic Selection and the Origin of Defects 20
FRÉDÉRIC HOUSSAY.
V. Preliminary Report of the Committee of Eugenics Section of
the American Breeders' Association upon the Best Practical
Means for Cutting off the Defective Germ Plasm 21
B. VAN WAGENEN.
Section IIa.
Education and Eugenics.
VI. Eugenics and the New Social Consciousness 22
S. G. SMITH.
VII. Practical Eugenics in Education 23
F. C. S. SCHILLER.
Section III.
Sociology and Eugenics.
I. The Psycho-Physical Elite and the Economic Elite 24
ACHILLE LORIA.
II. The Cause of the Inferiority of Physical and Mental
Characters in the Lower Social Classes 26
ALFREDO NICEFORO.
III. The Fertility of Marriages according to Profession and
Social Position 27
LUCIEN MARCH.
IV. Eugenics and Militarism 28
VERNON L. KELLOGG.
V. Eugenics in Party Organization 29
R. MICHELS.
VI. The Influence of Race on History 30
W. C. D. and C. D. WHETHAM.
VII. Some Inter-Relations between Eugenics and Historical Research 31
F. A. WOODS.
VIII. Demographical Contributions to the Problems of Eugenics 32
C. GINI.
IX. Maternity Statistics of the State of Rhode Island, State
Census of 1905 34
F. L. HOFFMANN.
Section IV.
Medicine and Eugenics.
I. The Prophylaxis of Hereditary Syphilis and its Eugenic Effect 36
H. HALLOPEAU.
II. Alcohol and Eugenics 37
A. MJOËN.
III. Alcoholism and Degeneracy 38
M. MAGNAN AND M. FILLASSIER.
IV. Eugenics and Obstetrics 39
AGNES BLUHM.
V. Heredity and Eugenics in Relation to Insanity 40
F. W. MOTT.
VI. The Place of Eugenics in the Medical Curriculum 42
H. E. JORDAN.
VII. A Healthy Sane Family showing Longevity in Catalonia 43
I. VALENTI VIVO.
VIII. Some Remarks on Backward Children 43
RAOUL DUPUY.
Section I.
Biology and Eugenics.
VARIATION AND HEREDITY IN MAN. (Abstract.)
By Professor G. Sergi, _Professor of Anthropology, Rome_.
In his paper Professor G. Sergi wishes to show that in man after his
morphological characteristics are established there occur no profound
variations to change the typical forms which are naturally persistent.
The principal discussion concerns the different forms of the skull
which are important as characteristics of race. Professor Sergi
distinguishes in the human skull two principal and primordial forms:
the dolichomorphic and the brachymorphic are both very ancient, as they
are found contemporaneously in European human fossils. Consequently
he attacks the idea of the transformation of one form into another.
He does not find it demonstrated that the dolichomorphic type is
transformed into the brachymorphic, and considers the causes adduced
for this supposed transformation insufficient. It is neither the
effect of environment of the plains or of the mountains, or the
climatic influence of extreme cold, or the increase of volume of the
brain supposed to be due to greater cerebral activity owing to a more
developed culture, that the form of the skull is transformed into
another type. All these suppositions are contrary to facts, because
dolichomorphic and brachymorphic skulls are found alike in mountain and
plain, in northern and southern regions, among primitive and civilized
populations, in fact without any distinction.
The mutations that are believed to be found in the different
populations are due to the effect of intermixture and penetration of
new demographical elements, and not to the transformation of forms.
That is also proved by the crossing of the two different human types
from which no intermediary forms are derived: but instead there occurs
in the heredity a segregation analagous to that under the Mendelian
theory. If this were not so, to-day after many thousands of years of
intermixture of the most diverse races, there would be but a single
form derived from transformation; the demonstration of the facts proves
that this has not occurred.
There is a great persistence in human physical forms, the variability
is minimum after the formation of the races, and does not effect the
changes of type.
The same fact can be noticed for the external characteristics of man,
such as the colour of the skin, the colour and form of the hair, and
the colour of the iris. It is solely in the crossings that there can be
intermediary formations which have not indefinite heredity, because the
segregation of characteristics takes place also in this case.
But the studies and observations on this matter are still incomplete,
especially according to the Mendelian theory, and there is need of new
and careful observation.
As to the pathological inheritance, there exist facts that confirm it
in a general way, but the laws under which this heredity occurs have
not been fully verified.
ON THE INCREASE OF STATURE IN CERTAIN EUROPEAN POPULATIONS.
(Abstract.)
By Soren Hansen, M.D.,
_Director of the Danish Anthropological Survey, Copenhagen._
The improvement in stature in many European countries during the past
50 years is generally ascribed simply to improved hygienic and economic
conditions, but the question is really very intricate. The presence of
different racial elements, social selection with its tendency to draw
the well-made into towns, and the falling death-rate, etc., complicate
the investigations. In all countries there is a great lack of truly
comparable data from earlier years. The British Inter-Departmental
Committee on Physical Deterioration, for example, though it collected
an enormous amount of material, was unsuccessful in its endeavours to
solve the main question. Single cases, e.g., the comparison of factory
children with the boys of the York Quaker school (Anthropometric
Committee, Brit. Ass. 1883), are certainly of great interest, but how
can such cases be taken to represent the average?
Other countries possess a rich source of information in their
conscription lists. Thus, in Denmark these lists show an unmistakable
increase of 3.7 cm. (1-1/2 inch) in the average height of the adult
Dane during the past 50-60 years. Similar increases are noted from
Norway, Sweden and Holland. This increase suggests that there may have
been more or less periodic waves of increase and decrease in height,
since, on the one hand, we cannot imagine such an increase continuing
indefinitely, and on the other, we know that the men of, say, 1000
years ago were quite as tall as they are at present. What are the
agencies alternately improving or impairing the racial qualities? First
of all, have we sufficiently exact, numerical information regarding the
racial qualities?
A critical examination of all available data is very necessary. For
example, the weight of new-born children is stated to have increased
in England by 59 and 82 grams during the past 20 years, and in Denmark
we can point to an increase of 40 grams in 35 years. But when we
consider all the possible sources of error, it must be admitted that
these statements, and especially the former, require confirmation.
The material is not homogenous. Again, it is stated, that the average
height of adult women in France has increased by 3 cm. in the last 80
years--but when we read that the total number of measurements in the
last period was only 255, we cannot rely very much upon this statement.
On the whole, it may be said, that we have a few cases of definite
increase and a goodly number very doubtful. We really need to have
the first of the principal recommendations of the Inter-Departmental
Committee on Physical Deterioration carried out in all countries,
for, the more we subject the available data to critical scrutiny, the
more we see the hopelessness of attaining to any real and fruitful
conclusions, unless we have an efficient organisation of capable
workers, backed by governmental as well as private support.
THE SO-CALLED LAWS OF INHERITANCE IN MAN.
(Abstract.)
By Professor V. Guiffrida-Ruggeri,
_Professor of Anthropology, Naples._
The Mendelian laws find verification in man. Every race, whether a
sub-species or a variety, has an hereditary possession of certain
characters; a possession which is completely transmitted to the
descendants, in whom is preserved the same germ plasm as in the
progenitors.
The researches of C. B. and G. Davenport seem to have proved the
recessive character of albinism and its obedience to the Mendelian
law. Hurst has presented figures which show that the inheritance of
colour in the iris of the human eye obeys Mendelian laws. Davenport
has established the order of dominance by the form of hair, which also
obeys the Mendelian law.
De Quatrefages, many years before the re-affirmation of Mendel's
discoveries, wrote:--
"The union of individuals of different races involves a contest
between their two natures--a contest of which the theatre is the
field where the new being is organised. Now, this contest does not
take place _en bloc_, so to speak, as has been generally admitted.
Each of the characters of the two parents struggles on its own account
against the corresponding character (its antagonist, as has just
been said). When the hereditary energy is equal on both sides there
necessarily ensues a kind of process of which the consequence is the
fusion of the maternal and paternal characters in an intermediate
character. If the energies are very unequal the hybrid inherits a
character borrowed entirely from one of his parents; but this parent,
conqueror on one point, may be conquered upon another. Hence, there
results with the hybrid a _juxtaposition_ of characters derived from
each of the types of which he is the child."
Above all, I have wished to call attention to the so-called laws of
dominance, because of their great importance. We may conclude that in
the case of man the dominant characters are also the original ones.
THE INHERITANCE OF FECUNDITY.
(Abstract.)
By Raymond Pearl,
_Biologist, Maine Agricultural Experiment Station._
The purpose of this paper is to give an account (necessarily
abbreviated, and without presentation of complete evidence) of the
results of an investigation into the mode of inheritance of fecundity
in the domestic fowl, and to point out some of the possible eugenic
bearings of these results.
It is shown that while the continued selection, over a period of years,
of highly fecund females failed to bring about any change in average
fecundity of the strain used, this character must nevertheless be
inherited since pedigree lines have been isolated which uniformly breed
true to definite degrees of fecundity.
It is further shown that observed variations in actually realized
fecundity (number of eggs laid) do not depend upon anatomical
differences in respect to the number of visible oöcytes in the ovary.
The differential factor on which the variations in fecundity depend
must be primarily physiological.
Fecundity in the fowl is shown to be inherited in strict accord with
the following Mendelian plan:--
1. Observed individual variations in fecundity depend essentially upon
two separately inherited physiological factors (designated L_{1}, and
L_{2}).
2. _High_ fecundity is manifested only when both of these factors are
present together in the same individual.
3. Either of these factors when present alone, whether in homozygous or
heterozygous form, causes about the same degree of _low_ fecundity to
be manifested.
4. One of these factors, namely L_{2}, is sex-limited or sex-correlated
in its inheritance, in such way that in gametogenesis any gamete which
bears the female sex-determinant F does not bear L_{2}.
5. There is a definite and clear-cut segregation of high fecundity from
low fecundity, in the manner set forth above.
From the standpoint of eugenics it is pointed out that these results
furnish a new conception of the mode of inheritance of fecundity, and
may be helpful in suggesting a method of attacking the same problem for
man.
ETHNIC PSYCHOLOGY AND THE SCIENCE OF EUGENICS.
(Abstract.)
By Prof. Enrico Morselli,
_Director of the Clinic for Mental and Nervous Diseases, Genoa
University_.
All natural varieties or races of mankind differ, not only by their
physical, but also by their mental, characters. There exists,
therefore, an "Ethnic Psychology" which, along with "Ethnic
Somatology," constitutes the complete Science of Anthropology or the
Natural History of Man. This must describe and classify races and
populations under a double aspect--physical and psychical.
The psychical characters of races are in part _original_, and in part
acquired through _adaptation_. These persist in a race as long as
such mesological adaptation lasts; they vary with modifications of
the conditions of life, including social activities and inter-racial
relations.
In mixed unions, amongst different races, there are always some which
are more vigorous, biologically and mentally, more fully developed,
which impress their characters upon their descendants. For the vitality
and well-being of mixed or metamorphic populations a certain amount
of difference amongst the parent races is necessary, but too great a
difference is injurious to the offspring.
The offspring of mixed unions present in their psychology a _mixture_,
again a _combination_ or fusion of the mental characters of the parent
races: sometimes certain psychical characters of a race become the
_dominant_ characters.
All ethnic groupings have their destiny marked out by the grade
attained in _the human psycho-physical hierarchy_. Nevertheless, it
is necessary that each race or nation, when it knows its contribution
to the development of universal civilisation, should contemplate the
preservation of its own ethnic type. Differentiation amongst peoples is
an indispensable factor in human progress.
The science of eugenics should not look for the realisation of a
uniform type of man, but vary its aims and methods according to the
natural differentiation of races and nations, taking account of ethnic
psychology equally with ethnic somatology.
The humanity of the future will be physically and mentally superior
to the existing humanity, but the _amelioration of the species_ ought
not to aim at the equality of races and populations. These races
and populations ought not to lose their acquisition of particular
adaptations to different conditions of existence.
A science of universal or common eugenics should allow a eugenic
ethnology to exist, which should indicate and facilitate for each race
or nation the defence and propagation of its own _physical type_ and
its own _mentality_. The most vigorous and dominant races will always
be those which know how to create and preserve in sexual unions their
characteristics of structure and culture.
THE INHERITANCE OF EPILEPSY.
(Abstract.)
By David Fairchild Weeks, M.D.,
_Medical Superintendent and Executive Officer, the New Jersey State
Village for Epileptics at Skillman, U.S.A._
In this paper the writer has endeavoured to learn what laws, if
any, epilepsy follows in its return to successive generations, and
the relation it bears to alcoholism, migraine, paralysis, and other
symptoms of lack of neural strength.
The data used in the study was analysed according to the Mendelian
method which assumes that the inheritance of any character is not
from the parents, grandparents, etc., but from the germ plasm out
of which every fraternity and its parents and other relatives have
arisen. If the soma possesses the trait of the recessive to normality
sort, it lacks in its germ plasm the determiner upon which the normal
development depends, and this condition is called nulliplex. If the
soma possesses the trait of the dominant to normality sort, the
determiner was derived from both parents and is double in the germ
plasm, or normal, all of the germ cells have the determiner; or else it
came from one parent only, is single in the germ plasm, or simplex,
and half of the germ cells have and half lack the determiner.
The method of obtaining the data was by means of field workers, who
interviewed in their homes the parents, relatives and all others
interested in the epileptic patient. These visits have established
a friendly feeling toward and an intelligent understanding of the
Institution and its work.
The study is based on the data derived from 397 histories, covering 440
matings.
The matings are classified under the six possible types, of nulliplex ×
nulliplex, nulliplex × simplex, nulliplex × normal, simplex × simplex,
simplex × normal, and normal × normal.
Under the first type all those matings where both parents were
epileptic, one was epileptic and the other feeble-minded, or both
were feeble-minded, are classified. According to Mendel's Law, all of
the children should be nulliplex. The data showed all of the children
defective.
Under the type nulliplex × simplex, all matings where one parent was
epileptic or feeble-minded and the other "tainted," that is, alcoholic,
neurotic, migrainous, or showed some mental weakness, are classified.
From this type of mating, 50% of the offspring are expected to be
nulliplex and 50% simplex. From the matings where one parent was
epileptic or feeble-minded and the other alcoholic, there were 61%
mentally deficient or nulliplex, the remainder simplex. The figures
for the offspring from the other matings showed 47% nulliplex, and 53%
simplex.
For the third type, nulliplex by normal, all those matings where
one parent was epileptic or feeble-minded and the other reported
as mentally normal are classified. From this type of mating, the
expectations are that all of the children would be simplex. A study
of the ancestors of the normal parents showed these parents simplex
rather than normal. The analysis of the offspring showed at least 43%
nulliplex, which is a close fitting to the type of mating nulliplex ×
simplex.
The fourth type of mating is simplex × simplex. Here, all matings where
both of the parents were "tainted" are classified. The expectation is
that 25% of the offspring would be nulliplex, in reality 35% were found
to be mentally deficient.
Simplex × normal is the fifth type of mating considered. The matings
where one parent was tainted and the other supposedly normal, are
classified here. From a study of their ancestors these normal parents
appeared to be simplex, and the classification of the offspring showed
more than 25% nulliplex, which is the expectation from simplex ×
simplex mating.
The sixth type is normal × normal, and the matings where both parents
were reported normal is studied under this heading. Here, as before, a
study of the ancestors of these normal parents indicates that they are
simplex, and not normal. The classification of the children showed a
close fitting to the expectation from a simplex × simplex mating.
A special study of the matings where one or both of the parents was
migrainous or alcoholic, shows a close relationship between these
conditions and epilepsy.
The following conclusions are drawn from the study.
The common types of epileptics lack some element necessary for complete
mental development. This is also true of the feeble-minded.
Two epileptic parents produce only defectives. When both parents are
either epileptic or feeble-minded their offspring are also mentally
defective.
Epilepsy tends in successive generations to form a larger part of the
population.
The normal parents of epileptics are not normal but simplex, and have
descended from tainted ancestors.
Alcohol may be a cause of defect in that more children of alcoholic
parents are defective than where alcoholism is not a factor.
Neurotic and other tainted conditions are closely allied with epilepsy.
In the light of present knowledge, epilepsy, considered by itself,
is not a Mendelian factor, but epilepsy and feeble-mindedness are
Mendelian factors of the recessive type.
Tainted individuals, as neurotics, alcoholics, criminals, sex
offenders, etc., are simplex and normals or simplex and normal in
character.
THE INFLUENCE OF THE AGE OF PARENTS ON THE PSYCHO-PHYSICAL CHARACTERS
OF THE OFFSPRING.
(Abstract.)
By Antonio Marro,
_Director of the Lunatic Asylum, Turin._
The natural law of heredity holds good whether for the physical
characteristics or for those which are biological and moral.
The apparent anomalies which children present in not reproducing the
qualities of the parents, and the unlikeness frequently noted among the
children of the same family, only serve to reveal the presence of the
particular conditions of the parents at the time of begetting which has
influenced the offspring.
We have a proof of this law in the anomalies presented by the children
of parents who, at the time of begetting, were themselves in anomalous
conditions by reason of intoxication or disease.
Among the conditions of parents which are capable of influencing the
characteristics of children must be included the changes which their
organism undergoes by reason of advancing age.
I propose to study the effects of age on the physical and moral
characters of the children. My researches have extended to numerous
criminals and insane persons, as well as to scholars of the public
schools and other normal persons affected or not with special diseases.
Of my studies on criminals, the result is: that the children of
young parents are found in large numbers guilty of offences against
property; and this is natural. The first impulse to that is not due to
wickedness, which impels them to inflict harm on others, but to love of
pleasure, of revel, of idleness--all features of youth, during which
period the passions are very active, and no restraint present with
which to repress and subjugate them.
Swindlers alone are exceptions to this rule, but swindling is a crime
of riper years, according to the dictum of Quetelet.
Among crimes of personal violence, I have found a numerical superiority
in the children of aged parents. Assassins, homicides, those who show
the completest absence of sentiments of affection and often delusions
of persecution more or less pronounced, gave a proportion of children
of aged parents far greater than that furnished by all the other
categories of delinquents; the proportion is as high for fathers as for
mothers of advanced age.
Here, too, we note a certain correlation between the state of
discontent, of suspicion, of frigid egoism, which the decline of
physical energy tends to arouse in the old, and the absence of
affectionate sentiment and a tendency to delusions of persecution which
are usual in murderers. Among the insane, moral idiocy in particular,
and the degenerative forms in general, appeared more frequently in
children of aged parents.
As to schoolboys, I have noticed that the minimum of good conduct
and the maximum of better developed intelligence coincides with the
possession of youth by both parents.
The age of complete development corresponds to a maximum of good
conduct and a minimum of bad conduct, and retains a large proportion of
intelligent children.
In the period of decline of both parents, good conduct of children is
observed in a smaller proportion than in the preceding period, and high
intelligence in a very small proportion.
Among biological qualities I have made observations on longevity; among
persons of 70 and 80 whom I have examined there is a large proportion
of parents who themselves enjoyed remarkably long lives, which proves
the transmissibility from father to son of powers of resistance against
the stresses of life.
Among physical qualities I have made note of the fact that from
alcoholic or aged parents were descended children in whom degenerative
physical characteristics were most frequently apparent, recalling some
features of an inferior human type, such as exaggeration of the frontal
sinuses, the torus occipitalis, ears with the Darwinian tubercles
prominent, the forehead receding, etc. At the same time the ascendants
of those who presented typical and anomalous characters, due to morbid
influences of various kinds and following on faulty development of
the foetus, such as cretinism, congenital goître, nasal deflections,
strabismus, plagio-cephaly, hydrocephaly, dental malformation, etc.,
showed a large number of alcoholics and epileptics.
The explanation of the pernicious consequences to the psycho-physical
characters of the children of parents too young or too advanced in age
does not present much difficulty.
At the younger period the organism is still in process of formation;
the incomplete development of the skeleton, as of all the other organs,
continually absorbs a mass of plastic materials necessary to the
formation of offspring. So we may consider that the faults of children
born of too young parents are due to an incomplete development because
of the insufficiency of plastic material.
We must, on the other hand, seek in the conditions which accompany old
age for the reason why it has a disastrous influence on the vitality of
the germinal elements of the parents and predisposes the descendants to
various forms of physical and moral degeneracy.
During this period we have in the tissues, instead of a development
and renewal of protoplasm, the tendency to an accumulation of fat;
and in the whole organism, chiefly in the tissues of the arterial
system, we find the tendency to a deposit in their structure of an
amorphous substance which converts the supple elastic canals into rigid
tubes; and from this a general slowing up of the organic functions
(circulation, oxidation, secretion) results; the blood, not reaching
the degree of elaboration which it possessed before, acquires a greater
acidity, and cannot by the ordinary excretory channels so quickly get
rid of the catabolic products with which it is charged.
By reason of these conditions the organism of older people undergoes
a sort of slow and gradual intoxication, which, at the same time as
it shows itself in the individual by the gradual languishing of all
his functions, influences in a disastrous manner the germs which
develop within him, and predisposes them to become beings condemned to
degeneracy.
Consequently this cause of degeneracy enters the general category of
intoxications.
GENETICS AND EUGENICS.
(Abstract.)
By R. C. Punnett,
_Professor of Biology, Cambridge_.
To the student of genetics, man, like any other animal, is material for
working out the manner in which characters, whether physical or mental,
are transmitted from one generation to the next. Viewed in this way he
must be regarded as unpromising, not only from the small size of his
families, the time consumed in their production, and the long period of
immaturity, but also because full experimental control is here out of
the question. For these reasons man is of interest to the student of
genetics, chiefly in so far as he presents problems in heredity which
are rarely to be found in other species, and can only be studied at
present in man himself. The aim of the Eugenist, on the other hand, is
to control human mating in order to obtain the largest proportion of
individuals he considers best fitted to the form of society which he
affects. It is evident that to do this effectually he must have precise
knowledge of the manner in which transmission of characters occurs,
and more especially of those with which he particularly wishes to
deal. Precise knowledge is at present available in man for relatively
few characters; and those characters, such as eye-colour, and certain
somewhat rare deformities, are not the kind on which the Eugenist lays
great stress. The one instance of eugenic importance that could be
brought under immediate control is that of feeble-mindedness. Speaking
generally, the available evidence suggests that it is a case of simple
Mendelian inheritance. Occasional exceptions occur, but there is every
reason to expect that a policy of strict segregation would rapidly
bring about the elimination of this character.
There is reason to suppose that many human qualities are more
complicated in their transmission, and it is probable that certain
phenomena now being studied in plants and animals will throw definite
light upon man. Though characters are frequently transmitted on the
Mendelian scheme quite independently of one another, there are cases
known in which they are linked up more or less completely in the germ
cells with the determinant of a particular sex. Sex-limited inheritance
of this nature has been carefully worked out in particular cases in
Lepidoptera and poultry. As yet there is much to be learnt in this
direction, and further progress may be expected to lead eventually to
a precise knowledge of the mode of transmission of many human defects,
such as colour-blindness and hæmophilia. It is not unlikely that a
similar mode of transmission will be found to hold good for many human
characters usually classed as normal.
Another set of phenomena which will probably be found of importance in
the heredity of man are those included under the terms "coupling" and
"repulsion." Characters, each exhibiting simple Mendelian segregation,
may become linked together more or less completely in the process of
heredity, or the reverse may occur. Our knowledge of these phenomena
is at present almost completely confined to cases in plants, but
evidence is beginning to be obtained for their occurrence in animals.
It is not unlikely that they will be found to play a considerable part
in human heredity. For one of the most noticeable things about man
is the frequency with which children resemble one or other parent to
the seemingly almost complete exclusion of the other. In view of the
mongrelisation of the human race, the frequency of these cases is very
remarkable, and can hardly fail to suggest that some sort of coupling
between characters plays a large part in human heredity.
Except in very few cases, our knowledge of heredity in man is at
present far too slight and too uncertain to base legislation upon.
On the other hand, experience derived from plants and animals has
shewn that problems of considerable complexity can be unravelled by
the experimental method, and the characters concerned brought under
control. Though the direct method is hardly feasible in man, much
may yet be learnt by collecting accurate pedigrees and comparing
them with standard cases worked out in other animals. But it must be
clearly recognised that the collection of such pedigrees is an arduous
undertaking demanding high critical ability, and only to be carried out
satisfactorily by those who have been trained in and are alive to the
trend of genetic research.