358 
From the point of view here suggested 
the most interesting ethnic questions 
are: first, those concerning the ability 
of any human stock to survive in the 
competition, and second in regard to 
the character of the contribution of any 
surviving race to the ultimate human 
race and its effect upon the ultimate 
race. To the biologist such social 
problems as immigration and inter- 
nationalism, while timely and important 
today, seem very transient. 
Thus far we have mentioned only long 
familiar factors of evolution. There 
has been some change of emphasis in 
these fields, but no new discovery. 
In the field of heredity, on the other 
hand, there has been discovery, and a 
new science—genetics—has been born, 
We have found that there are two 
fundamentally distinct types of varia- 
tion—the first producing new qualities 
that are not transmitted in breeding, 
and the second producing characters 
that persist and breed true. The latter 
are mutations and are the material with 
which evolution deals. The transient, 
unstable type of variation is but shifting 
sand and gives no foundation for the 
erection of any superstructure of evolu- 
tion. 
TWO KINDS OF VARIATIONS 
In discussions of these relatively new 
phases of the science of heredity there 
has been undue emphasis upon some of 
the less vital features. It is true that 
the changes produced by mutation 
(variation of the ‘stable type) are 
generally somewhat greater than are the 
changes seen in fluctuating, unstable 
variation, but this distinction is not 
universal nor really of much moment. 
It is the heritability or non-heritability 
of any newly acquired quality that is 
of fundamental interest. The usual 
British terminology, which calls the 
non-heritable variations continuous and 
the heritable discontinuous, emphasizes 
the minor fact that the former are 
usually slight and the latter greater in 
amount. It seems far better to call 
them unstable and stable, emphasizing 
The Journal of Heredity 
thus their most fundamental quality of 
non-heritability or heritability. 
Not only have we learned this great 
distinction between heritable and non- 
heritable qualities—we have also found 
out a few fundamentally important 
things about the manner of inheritance 
of the heritable qualities, of the way 
they behave in inheritance. We think 
we know that the resemblance between 
parent and child is not a vague general 
resemblance, that the child does not 
inherit resemblance to either parent as 
a whole or a sort of fused resemblance 
to both, but rather that he inherits 
particular qualities, or to be more 
accurate, inherits a series of determiners 
each of which is related to the develop- 
ment of a particular quality. We think 
too that we have found satisfactory 
evidence that in general the child carries 
two determiners for each heritable qual- 
ity, one received from the father, another 
from the mother.’ We are beginning 
to learn something of the interrelation 
and interaction of the two determiners 
of each pair within the body of the child, 
and especially we think we know some 
fundamentally important features of 
their behavior in connection with the 
process of fertilization, which starts a 
new individual in life. 
This is not the place to discuss the 
phenomena of genetics in any detail. 
Suffice it to say that inheritance is not 
vague but definite, not general but 
particular. Stature is not inherited but 
rather the child receives from its two 
parents a whole double series of deter- 
miners which guide the development in 
a number of particular ways affecting 
stature. Brown eyes are not inherited, 
but rather apparently two pairs of 
determiners, each pair for a distinct 
pigment, whose combination produces 
a brown iris. Brown hair, red _ hair, 
flaxen hair, is not inherited as a whole, 
but rather there seem to be two pairs 
of hair pigment determiners which 
when present in full activity produce 
even so-called black hair, and the 
absence or perhaps the relative inac- 
tivity of one or more of these pigment 
’ One or occasionally both determiners of a pair may be absent, the quality itself being in the 
first instance less developed and in the second instance wholly absent. 
