Kinsey: Gall Wasp Genus Cynips 
57 
forids might finally achieve a thoro exchange of genes thru- 
out the whole of the population. Then a sample taken from 
any part of the range would vary within the same wide but 
uniform limits typical of every other sample of the population. 
It would then satisfy our concept of a species, for it would 
have a common heredity. 
It is this problem, the attainment of homogeneity out of a 
hybrid population, that has become the immigration problem 
of the American people in the last half-century. Whether 
homogeneity is a biologic virtue or not, the statesmen have 
shown themselves good taxonomists in their insistence that 
we cannot become a true species until barriers are erected 
to protect us from continued contributions of parental stock. 
Whether in peoples or insects, the melting pot cannot blend 
diverse materials that pour in too rapidly. 
Now it becomes obvious why hybrid populations cannot 
often give rise to new species. Such inter-specific hybrids 
must usually arise in limited areas between the parental 
species. As long as the area is limited and the parents are 
close at hand, the hybrids will continue to be hybrids of every 
shade and extreme and intermediate combination of parental 
characters. On theoretic grounds, it would appear that 
hybrids may become species only when geographically removed 
or in some other way isolated from the parental stock. These 
circumstances would seem so rare that we cannot believe that 
hybrids account for the origin of many of the species with 
which we are acquainted in the field today. 
And yet, there is one group of species among the Cynipidae 
which would seem to have had hybrid origin. These species 
occupy that very portion of the northeastern United States 
in which so many of our biologic studies have been pursued. 
Cynips erinacei , to which repeated reference has already been 
made, is the most certain of these cases in the genus Cynips. 
Erinacei, it will be recalled, is a highly variable species 
occupying about 500,000 square miles of the area which we 
have just defined. It is unique among Cynips in the extent of 
its individual variation. The extreme individuals of the group 
have previously been considered representatives of two dis- 
tinct species, but the specific unity of erinacei is affirmed by 
the existence of every type of intergrade between these 
extreme individuals, and by the occurrence of all these varia- 
