WE will now turn to the consideration of another element which
determines the physical type of man. Although we have seen that
environment, particularly domestication, has a far-reaching influence
upon the bodily form of the races of man, these influences are of a
quite secondary character when compared to the far-reaching influence of
heredity. Even granting the greatest possible amount of influence to
environment, it is readily seen that all the essential traits of man are
due primarily to heredity. The descendants of the negro will always be
negroes; the descendants of the whites, whites; and we may go even
considerably further, and may recognize that the essential detailed
characteristics of a type will always be reproduced in the descendants,
although they may be modified to a considerable extent by the influence
of environment. I am inclined to believe that the influence of
environment is of such a character, that, although the same race may
assume a different type when removed from one environment to another, it
will revert to its old type when replaced in its old environment. This
point has not been proved by actual anthropological evidence; but it
seems reasonable to make this assumption by analogy with what we know of
the behavior of plants and animals. It would, of course, be highly
desirable to clear up this question by appropriate investigations.
In order to obtain a clearer understanding of the racial problem, it
seems necessary to describe more definitely the characteristics of
heredity. In the discussion of modern anthropology, two theories have
been advocated relating to the manner in which parental traits are
inherited by children. Francis Galton and his adherents have assumed
that the form of the body of an individual is determined by the racial
type to which the parents belong, modified, however, by the tendency of
reversion to a type intermediate between the special variations
presented by the parents. When, for instance, the father of an
individual is unusually tall, his mother somewhat taller than the
average, it is assumed that the tendency of the children would be to
develop a stature which is somewhat near the general type, but at the
same time dependent upon the intermediate value located between the
stature of the mother and that of the father. On the other hand, the
development of the Mendelian doctrine (Lock, Bateson) of heredity has
led other investigators to assume that the offspring of two distinct
types may be a mixed type, but that his descendants will tend to revert
either to one parental type or to the other, or that one of the parental
types may dominate over the influence of the other parental type.
Investigations relating to this problem are not very numerous; but, on
the whole, it would appear that the results so far obtained are in favor
rather of a modified form of Mendelian inheritance than of an
inheritance characterized by reversion of the children to a middle type
between the parents, or to a type dependent upon such a middle type.
A number of years ago I had an opportunity to investigate a considerable
number of Indian half-bloods; that is to say, of descendants of Indian
mothers and white fathers. The most characteristic difference between
the American Indian race and the European race, so far as these
differences can be expressed in metrical form, is found in the width of
the face. An extensive series of measurements of width of face made
among half-bloods showed conclusively that the width of face does not
tend to range around a certain intermediate value located between the
width of face of the white race and that of the Indian race, but there
was a decided tendency in the children to resemble either the Indian
race or the white race; in other words, that feature of Mendelian
inheritance which brings about the occurrence of mixed characteristics
in the first hybrid generation was not found, but instead of this a
decided tendency of reversion to either type, and to comparative rarity
of intermediate forms. The results seem also to indicate that the Indian
form in this mixture seems to dominate over the white form, but not in
the Mendelian sense, which would require the presence of dominant
features in a certain definite number of individuals, but only in the
sense that the Indian type was a little more frequent than the European
type, with the effect that the average width of face of the whole series
was a little nearer to the Indian group than to the white group.
While this single observation is not by any means sufficient to
determine fully the characteristic traits of heredity which govern the
phenomenon in question, they indicate decidedly and beyond cavil that,
in this case at least, we find what has been called by Karl Pearson
“alternating inheritance.” It is worth remarking that not all the
features of the body of the half-blood Indian exhibit the same tendency;
that, for instance, in the case of stature, a general increase in the
stature of the mixed people over that of the pure races may be observed.
Attention has been called by Felix von Luschan to a similar phenomenon
which occurs in the mixed population of southern Asia Minor, where he
believes to have found an alternating inheritance of the head-form,
particularly of the proportions between width and length of head; some
of the people retaining the short, high head-forms of the Armenoid type
of the interior of Asia Minor, while the others have the long, low head
of the Semites of Syria.
For a clear understanding of the laws of heredity, it seems important to
know whether a similar alternating inheritance occurs in marriages of
members of the same type. I have been enabled to investigate this
question by a study of the East European Hebrews living in New York. A
simple consideration shows, that, if the children tend to follow a type
intermediate between the type of their parents, then the children of one
family will show the same degree of resemblance among themselves, no
matter how great the difference between the parents; for, if they simply
tend to reproduce a middle type, it would not make any difference
whether the mother is excessively short and the father excessively tall,
or whether both parents are of middle stature. In both of these cases
the intermediate value would be the same, and we should therefore expect
that the effect upon the children would be the same. If, on the other
hand, there is any kind of alternation in inheritance, the effect upon
the family would be quite different. We should expect, in a family of
which both parents are near the typical average, to find the children
also to be near this average. On the other hand, if the mother is
excessively short and the father excessively tall, we should expect some
of the children to follow the mother in regard to shortness of stature,
others to follow the father in regard to tallness. It will therefore be
seen that in the case of alternating inheritance, we must expect an
increased variability among the children. The compilation of material
obtained from several thousand families shows very definitely that the
variability among children both of whose parents belong to the same
racial type, even to the same local type, increases quite considerably
with the increased difference of the parents; so that we may assume a
decided tendency to alternating inheritance in these cases. There is,
however, no evidence whatever of the dominance of one type over another.
Quite a number of investigations have been made in relation to the
intensity of heredity of parents and of grandparents; and,
notwithstanding the uncertainty of the quantitative result, it seems
reasonably certain that the intensity of heredity for each parent may be
expressed by the value of about one-third (Pearson, Boas). It is
somewhat difficult to explain clearly the significance of this value. I
may, however, briefly indicate it in the following manner. Provided the
mother differs in her stature by an amount of 9 cm. from the racial
norm,—for instance, if she is 9 cm. taller than the average
individual,—then we may expect the child to be one-third of 9 cm., or 3
cm., above the average. It will thus be seen that if both parents differ
in the same direction from the average, the effect of both will be
cumulative; and if both differ from the average of their people by the
same amount, the joint effect of the two parents may be expressed by the
coefficient of about two-thirds. In case, for instance, both father and
mother should be 9 cm. above the type average, we should expect the
child to be about two-thirds of 9 cm., or 6 cm., above the average.
Although definite information on the amount of heredity of previous
generations is not yet available, the probability seems to be that the
grandparents have jointly an influence of about two-ninths, the
great-grandparents jointly of about two twenty-sevenths, etc., upon the
offspring.
When we study these problems according to statistical theories, and take
into consideration the observations on the resemblance of brothers and
sisters, it can be shown that the theory of alternating inheritance
cannot be taken too literally; for, if there were an absolute reversion
of any one trait to pure ancestral types, we might say that the
probability would be very small that two brothers should happen to
repeat the bodily form of the same ancestor, because the number of
ancestors in remote generations is very large. In other words, there
must be an additional cause of resemblance between brothers and sisters.
It is possible to show, that in case the inheritance has the strength
denoted before, and if bodily form of a certain generation were due only
to alternating inheritance acting from parents, grandparents,
great-grandparents, and so on, and directly upon the generation in
question, and without an occurrence of the same individuals in various
places in the line of ancestors, then the resemblance between brothers
and sisters, or, as we say, between the members of a fraternity, would
result in a degree of resemblance which is much lower than the one
actually observed. When the total number of ancestors is small, the
recurrence of the same forms would become more probable, and the
similarity of the series would increase. On the whole, the data seem to
be best explained if we assume that there is not only alternating
inheritance, but also a direct dependence upon the combination of the
two parental types.
I should like to repeat here that these results have not been obtained
with absolute certainty, and that it seems improbable that the laws of
heredity in regard to various ancestral traits are the same. I do not
enter into a discussion of the question of in how far these traits
follow the laws of Mendelian inheritance,—a question that cannot be
answered definitely at the present time (Davenport).
These problems have a fundamental importance for a clearer
interpretation of the conditions which prevail in the form of local
types of man.
In a large population which is as little stable in its habits as that of
modern Europe and modern America, the number of ancestors of a single
person increases very rapidly, the number of parents being two; of
grandparents, four; of great-grandparents, eight; the theoretical number
of ancestors twenty generations back would be over a million, or, more
accurately, 1,048,576. Twenty generations represent, according to the
rate of increase of modern times, about seven hundred years; according
to the rate of increase of older times, about four hundred years as a
minimum. These figures would apply to the series of generations
represented by first-born males; for first-born females the respective
numbers would be about five hundred years and three hundred and fifty
years. If we consider, however, the actual descent of families,
including individuals later born, we might perhaps assume that twenty
generations in Europe would represent from eight hundred to nine hundred
years, and among primitive peoples perhaps only little less, since in
former times the differences between the rapidity of successive
generations in Europe and among primitive peoples was not very great.
This makes it obvious that it is entirely impossible that as great a
number of ancestors as the theory requires can have contributed to the
development of the individuals of the present generation. The reason for
this is plain. Owing to intermarriages between the same families, large
numbers of ancestors will be duplicated in different paternal and
maternal lines; and in this way the real ancestry of each individual
appears to be much more complex than the purely arithmetical treatment
would suggest. The calculation for the ancestor table of the German
Emperor, for instance, is instructive. According to O. Lorenz, the
numbers of his ancestors in successive generations were as follows:—
═════════════════════╤═══════════╤═══════════
GENERATION │THEORETICAL│ ACTUAL
│ NUMBER │ NUMBER
─────────────────────┼───────────┼───────────
I │ 2│ 2
II │ 4│ 4
III │ 8│ 8
IV │ 16│ 14
V │ 32│ 24
VI │ 64│ 44
VII │ 128│ 74
VIII │ 256│ 116[2]
IX │ 512│ 177[2]
X │ 1024│ 256[2]
XI │ 2048│ 342[2]
XII │ 4096│ 533[2]
═════════════════════╧═══════════╧═══════════