Length at Birth 5.8 to 6.5
Length of Limb Bones 4.5 to 5.5
Cephalic Index 3.7 to 4.8
Skull Capacity 7.0 to 8.0
Weight (University Students) 10.0 to 11.0
Weight at Birth 14.2 to 15.7
Weight of Brain 7.0 to 10.6
Weight of Heart 17.4 to 20.7
Weight of Liver 14.3 to 22.2
Weight of Kidney 16.8 to 22.5
Lung Capacity 16.6 to 20.4
Squeeze of Hand 13.4 to 21.4
Strength of Pull 15.0 to 22.6
Swiftness of Blow 17.1 to 19.4
Dermal Sensitivity 35.7 to 45.7
Keenness of Eyesight 28.7 to 34.7
It is not so easy to answer the question whether mutations or true
variations are occurring frequently in the human species. Usually it
is impossible to distinguish between an extreme fluctuation and a true
variation without experimental test and the observation of the
behavior of the varying trait through several generations. In most
instances this has been impossible with human beings. From collateral
evidence it seems quite probable that man is mutating with
considerable frequency, especially with respect to psychic traits.
The evolution of the race could be directed more easily and permanent
results attained more rapidly through taking advantage of valuable
mutations than in any other way. A race truly desiring to progress
would foster carefully anything resembling mutation in a favorable
direction. As a matter of fact, however, our social custom leads us to
look with disfavor upon most youthful traits that seem unusual or out
of the ordinary. It would be difficult to devise a system of
"education" which could more effectively repress than does our own the
development of unusual mental traits. In this connection "abnormal" or
"eccentric" may often mean a mutation in a profitable direction, a
getting away from the average of mediocrity in the direction of
improvement.
It is clear that we have the raw materials for race improvement. There
are some individuals with more and some with less than the average in
any respect--physical, mental, moral. The average of a whole social
group can be shifted by subtraction at one end or addition at the
other, or more easily and more effectively by both together. In order
to raise the general average of the value of any of these traits it
is not necessary to strive to exceed the known maximum value in any
respect. The study of the "pure line," as mentioned above, shows that
this may for a long time remain impossible, or at any rate difficult,
pending the appearance of a mutation in a favorable direction. We can,
however, raise the general average of physical strength or of mental
or moral ability by increasing the relative number of individuals in
the upper groups or by diminishing the number in the lower groups,
most easily of course and most effectively by doing both of these
things. By increasing the numbers composing the lines which form the
upper elements of a social group we not only add immensely to the
total value of the group but we do actually change somewhat the
general average. On the other hand numerical increase in the lines in
the lower part of the group will actually lower the average of the
whole, though it does not actually affect the number of individuals in
the more able and valuable classes.
Another consideration is of great importance here. The average is
affected only slightly by the change of individuals from class to
class near the average. But the shifting of even one or two per cent
of the individuals into or out of extreme positions has a very marked
effect upon the character of the total group and upon the average. In
the life of the State the character of the general average of the
citizens is of the greatest importance, and comparatively small
deviations in the average of civic worth may mean much as regards the
history of a democracy. Of course the average individuals in a social
group may not be those of greatest influence; even when taken all
together they may not determine the trend of the life of the society;
but that does not alter the essential fact that the condition of the
average of the population is of very great moment to a democratic
state.
Many of our social endeavors to-day serve in effect to raise
individuals from one of the lower groups up to or toward the average.
Millions of dollars and an incalculable amount of time and energy are
spent annually in striving to accomplish this kind of result. How
immeasurably greater would be the benefit to society if the same
amount of energy and money were spent in moving individuals from the
middle classes on up toward the higher. In the development of our
societies we need to use every possible means to carry individuals
from positions near the average to positions above the average, and
the farther this remove is above the average both in its starting
point and its stopping point, the better for the social group.
Elevation from mediocrity to superiority has far greater effect upon
the social constitution than has elevation from inferiority to
mediocrity.
As the Whethams have written recently: "Of late years, the duty of the
State to support the falling and fallen has been so much emphasized
that its still more important duty to the able and competent has been
obscured. Yet it is they who are the real national asset of worth, and
it is essential to secure that their action should not be hampered,
and their value sterilized, by the jealousy and obstruction of the
social failures, and of others whom pity for the failures has blinded.
Mankind has been shrewdly divided into those who do things and those
who must get out of the way while things are being done, and if the
latter class do not recognize their true function in life, they
themselves will suffer the most. The incompetent have to be supported
partially or wholly by the competent, and, even for their own good,
it would be worth while for the incompetent to encourage the freedom
of action and the preponderant reproduction of the abler and more
successful stocks. It is only where such stocks abound that the nation
is able to support and carry along the heavy load of incompetence kept
alive by modern civilization."
In discussing the general subject of variation and variability in
this connection, we must take always into account the biological
distinction between variation and functional modification, between
innate and acquired traits. Only the former are of real and primary
value in evolution. The distinction is familiar and we cannot dwell
upon it here; but it is of particular importance in dealing with
social improvement and we shall return to it in the next chapter.
Many "social variations" are in reality not variations at all, but
modifications; although these may be of the greatest value to the
individual modified, they are artificial things without permanent
value to the race. So many of the distinguishing personal traits are
the results of nurture rather than of nature. They represent the
result of the incidence of special factors in the environment. It is
extremely difficult and at times impossible to distinguish between
variations and modifications in adult characters, but in general the
distinction is usually clear upon careful analysis.
The changing of the innate characters of the human race is a slow
process, depending chiefly upon the advantage taken of the appearance
of real mutational variations. On the other hand, it is comparatively
easy to improve the condition of the individual by improving his
environing conditions--cleaning him, educating him, leading him to
higher ideals in his physical and mental and moral life. But as this
is easy, so it is impermanent. All this is modificational and has no
influence upon the stock. This is not opposed by the Eugenist; it
simply is no part of his province, for its effect is not racial. By
releasing a deforming pressure it may permit the individual to come
back to his real structurally determined condition, but the
structural condition itself is not thus affected. It is temporary and
must be done over with each generation, or on account of the
unfortunate habit of "backsliding," even at intervals shorter than
that of a generation.
* * * * *
Let us now turn to another phase of our subject and consider the
biological methods of the description and measurement of heredity, as
a preliminary to our next chapter in which we shall discuss the
bearings of the facts of human heredity upon the possibility of the
formation of a permanently improved human breed.
The fact of heredity is one of the most familiar and patent things
about organisms. "Do men gather grapes of thorns or figs of thistles?"
For we may define heredity as the fact of general resemblance between
parent and offspring. This simple definition is disappointing to many
persons. "Heredity" is so often supposed popularly to refer only to
some occasional, striking, and unusual similarity within a family
respecting certain traits or peculiarities. Very often the idea of
heredity seems shrouded in mystery: it is some uncanny relation which
explains peculiarities and helps the novelist out of difficulties, but
is itself inexplicable. In truth, however, the fact that a boy, like
his father, has a head and a heart and hands and feet, physical traits
characteristic of the human species, that he begins to walk and talk
and shave at about the same age as his father did--all this is the
fact of heredity. The fact that guinea pigs produce guinea pigs and
not rabbits is the fact of heredity. Often it is true that this
resemblance is strikingly particular. All know of family traits; we
may have our father's eyes or nose, our mother's hair or disposition,
a grandfather's determination or a grandmother's patience. But these
particular individual resemblances are no more and no less
illustrations of heredity than the fact that on the whole children are
more like their parents than like other human beings.
The subject of heredity is of supreme importance in the practice of
Eugenics. The facts of no other department of biological inquiry are
of equal value, and at the same time there is probably no biological
subject regarding which there is so much misunderstanding. Of the
many phases of this extremely fascinating subject there are chiefly
two with which we are particularly concerned as Eugenists. These are
the questions: first, how completely are all the distinguishing traits
of either or both parents represented in the offspring; and, second,
how completely is each trait inherited that is inherited at all? In
other words, what we are chiefly interested to know, as bearing upon
the subject in hand, is whether all or only some of the
characteristics of our parents are heritable, and whether the
offspring show each inherited trait with the same intensity shown in
the parent, or more, or less.
One of the leading British students of heredity has said that no one
should undertake the study of this subject unless he can instantly
detect and explain the fallacy involved in the familiar conundrum,
"Why do white sheep eat more than black ones?" It is perhaps the
elasticity of our language that makes possible the mental confusion
involved in this question, but yet it is certainly true that we do
tend to confuse individual and statistical statements. We must
remember, in connection with this subject particularly, that an
individual may belong to a group without representing it, and that
within a group there are many more individuals with average than with
exceptional characteristics. The mediocre is common, the extremes are
rare. And yet an unusual individual may really be an outlying member
of a normal group.
In describing the facts of hereditary resemblance between successive
generations two formulas are available. One deals ostensibly with the
individual--the Mendelian formula: the other deals with the group--the
statistical formula. It seems entirely probable that these are not
formulas for describing two essentially different processes or forms
of heredity, but that in reality these are two ways of describing the
same facts seen from two different points of view. The Mendelian
formula regards each individual separately and describes its heredity
thus. The statistical formula regards the whole group as the unit and
considers the individual not as such, but as one of the crowd,
concerning which statements can be made only in terms of averages and
probabilities; black sheep and white. Of these two formulas the
Mendelian is obviously of much the greater importance on account of
its more exact, more particular character; its greater definiteness
gives it a value in the treatment of eugenic problems that statistical
statements must inherently lack. While much has been written of late
regarding the Mendelian formula of heredity, we shall find it
profitable to repeat here its general outlines and to recall a few of
the essential features of this important law that we shall make much
use of later.
Let us have a concrete illustration. One of the simplest cases is that
of the heredity of color in the Andalusian fowl which has been so
clearly described by Bateson. There are two established color
varieties of this fowl, one with a great deal of black and one that is
white with some black markings or "splashes"; for convenience we may
refer to these as the black and white varieties respectively. Each of
these breeds true by itself. Black mated with black produce none but
black offspring, white mated with white produce none but white
offspring. Crossing black and white, however, results in the
production of fowls with a sort of grayish color, called "blue" by the
fancier, though in reality it is a fine mixture of black and white. At
first sight we seem to have a gray hybrid race through the mixture of
the black and the white races. Not so: for if we continue to breed
successive generations from these blue hybrid fowls we get three
differently colored forms. Some will be blue like the parents, some
black like one grandparent, some white like the other grandparent. Not
only this but we get certain definite proportions among these three
classes of descendants. Of the total number of the immediate offspring
of the hybrid blues, approximately one half will be blue like the
parents, approximately one fourth black, and one fourth white like
each of the grandparents. Now comes the most important fact of all.
These blacks, bred together produce only blacks, the whites similarly
produce only whites; the blues, on the other hand, when bred together
produce progeny sorting into the same original classes and in the same
proportions as were produced by the blues of the original hybrid
generation. Their blacks and whites each breed true, their blues
repeat the history of the preceding blues. No race of the hybrid
character can be established: blues always produce blacks and whites,
as well as blues. A summary of this history in graphic and
diagrammatic form is given in Fig. 7.
[Illustration: FIG. 7.--Diagram showing the course of color
heredity in the Andalusian fowl, in which one color does not
completely dominate another. _P_, parental generation. The
offspring of this cross constitute _F1_, the first filial
or hybrid generation. _F2_, the second filial generation.
Bottom row, third filial generation.]
This law of heredity was first discovered about forty-five years ago
by Gregor Mendel, working with peas in the garden of the Augustinian
monastery in Bruenn, Austria. His work curiously failed to arouse the
interest of contemporary scientists and his results were soon
completely lost sight of. The independent rediscovery of Mendel's
formulas of heredity, about ten years ago, was probably the most
important event in the history of biology and evolution since the
publication of "The Origin of Species."
In most cases of Mendelian heredity the progeny are less easily
classified than in the case above, because the hybrid individuals
resemble one or the other of the parents, quite or very closely. For
instance the crossing of the black and white varieties of guinea pigs
gives hybrids that are all black like one parent. That is, when the
black and white characters are brought together these do not appear to
blend into a gray or "blue," as in the case of the Andalusian fowl,
but one character alone appears; the black seems to cover up or wipe
out the white. This illustrates the frequent phenomenon of
_dominance_; one of the two contrasting characters, in this case the
black color is said to dominate over the other and the two traits are
described as _dominant_ and _recessive_ respectively. Fig. 8 gives a
graphic representation of the history of such a cross. When the black
looking hybrids are crossed together the progeny fall into but two
groups, one resembling each of the grandparental forms. Three fourths
of the progeny now resemble superficially the hybrid form and at the
same time one of the grandparents--the dominating black form, while
the remaining fourth resembles the other white grandparent. However,
we know that the black three fourths do not in reality constitute a
homogeneous class but that this includes two distinct groups; one
group of one fourth of the whole number of progeny (i. e., one third
of all the blacks) are truly black like their black grandparents and
in successive generations will, if bred together, produce none but
blacks of the same character, i. e., pure blacks: the remaining two
fourths of the whole number of progeny (two thirds of all the blacks)
in this generation are actually hybrids and in the next generation, if
bred together, will give the same proportions of the two colors as
were found in the whole of the present generation, i. e., three
fourths black, one fourth white. Of these the whites always produce
whites, the blacks always produce blacks and whites in the approximate
proportions of 3:1; a certain proportion of these--one third (one
fourth of the whole generation) always remain blacks, the other two
thirds (one half of the whole generation) again produce blacks and
whites. In such cases as this where the phenomenon of dominance
appears, and this is the usual course of events, it is impossible to
say which individuals _are_ the hybrids. Only after their progeny are
studied can we say which _were_ the hybrids.
[Illustration: FIG. 8.--Diagram showing the course of color
heredity in the guinea pig, in which one color (black)
completely dominates another (white). Reference letters as
in Fig. 7.]
In the crossing of the black and white Andalusian fowls described
above the phenomenon of dominance does not appear; when the two color
characters are brought into a single individual neither appears alone,
neither overcomes nor is overcome by the other. In the crossing of the
black and white guinea pigs dominance is complete; when the two color
characters are brought into a single individual only one color
appears, the second becomes recessive, that is, it remains present as
we know from the later history of such hybrids, but it is not visibly
indicated. Besides the Andalusian fowls there are known several other
instances of the absence of dominance and there are many cases where
dominance is incomplete, i. e., where one character merely tends to
dominate the other. And in a few instances dominance is irregular,
i. e., sometimes one character dominates, at other times or under
other circumstances it does not, as with certain forms of the comb or
the feathering of the legs in the common fowl, or with the presence of
an extra toe in the domestic cat, the rabbit, and guinea pig. And
even in those cases where dominance is said to be complete the trained
eye of the breeder can frequently distinguish between the hybrid and
the pure bred dominant individuals. The phenomenon of dominance,
therefore, is not an essential of the Mendelian theory although it is
a frequent, we may say usual, relation.
It does not come within our province to attempt an explanation of this
formula of heredity by describing some of the more fundamental
conditions upon which it depends. In fact, no complete explanation is
yet possible, although several explanatory hypotheses have been
suggested. We may outline briefly that which seems the most
satisfactory in that it serves to account for most of the facts in
Mendelian heredity in a comparatively simple manner. The germ of an
organism, we have seen, somehow contains dispositions of materials
which primarily determine the characteristics of the organism
developed from that germ. To these dispositions or configurations the
term of "determiners" has been applied. In a pure variety like the
black Andalusians, all the germ cells of each fowl are alike in
having this determiner for black color. When two such fowls are mated
together their descendants will result from the fusion of two germ
cells, _each_ containing the determiner for black color; that is, the
germ of the new individual comes to have a double determiner, one from
each parent, for this trait. In the white variety all the germ cells
are alike in _lacking_ this determiner; blackness is entirely absent
and all their descendants are formed from germ cells entirely without
black determiners. When the single germ cell of a black fowl with its
single black determiner is fertilized by a germ cell from a white fowl
without any determiner for black the resulting hybrid has a color
produced by only a single determiner, that from the black parent, and
in this case the blackness is not as fully expressed because produced
by only this single determiner and the fowl appears gray or "blue";
that is, the black produced by a single determiner is in this case not
as black as that produced by the double determiner. Now of course this
hybrid fowl forms germ cells containing determiners for color, but
these cells, instead of being all alike and with semi-black
determiners corresponding with the semi-black characteristics of the
individual, are of two different kinds--some are like those of each of
the grandparents which fused to give origin to the parent forms, and
these are formed in approximately equal numbers--one half with the
black determiner, one half without it. When two such fowls are bred
together the chances are equal for certain combinations of germ cells;
the chances are equal that the "black" or "white" germ cell of the one
individual shall meet and conjugate with the "black" or "white" germ
cell of the other individual. The result may be expressed
algebraically as follows, using the letters _B_ and _W_ to indicate
respectively germ cells with and without the black color determiner.
Germ cells of first parent _B_ + _W_
Germ cells of second parent _B_ + _W_
-------------
_BB_ + _BW_
_BW_ + _WW_
-----------------
Combinations in the germ of the offspring _1BB_ + _2BW_ + _1WW_
That is, one fourth are pure black (_BB_), one fourth pure white
(_WW_), and the remaining half are hybrids, black and white (_BW_).
The pure blacks again form germ cells, all possessing the determiner
for blackness; the pure whites form germ cells all lacking the
determiner for blackness; the hybrid blues produce again equal numbers
of germ cells possessing and lacking the determiner for blackness. The
relation of the germ cells and the organisms forming them and
developing from them is shown in the diagram in Fig. 9.
In the more common cases where the phenomenon of dominance appears, as
in the guinea pig, this is explained by saying that here a single
determiner for blackness is somehow sufficient to produce the color.
In such cases the black color observed may result either from a single
(_BW_) or from a double (_BB_) black determiner in the germ which
forms the organism. Only when the black determiner is entirely absent
(_WW_) does the white color appear in the developed organism and the
individual is then said to exhibit the recessive characteristic.