HYBRIDIZATION 
Altho we have evidence that new species most often origi- 
nate thru mutation and subsequent isolation, the possibility 
still remains that species may on occasion have hybrid origins. 
Mendelian hybrids in the midst of populations in which muta- 
tions have occurred have already been described in this paper 
(pp. 49, 53), with the suggestion that such hybrids are sub- 
merged, or that they give rise to local variations of the origi- 
nal population, or that they may after considerable time 
change the complexion of the old species and thus give rise 
to a new species. But the question is raised whether hybrid 
individuals originating from interspecific crosses may give 
rise to a third species without the replacement of either of 
the parental stocks. 
Jeffrey’s charge (1925-1928) that Drosophila melanogaster 
has had a hybrid origin pertains to the product of inter-spe- 
cific hybridization; the geneticists have considered the criti- 
cism unimportant probably because they have in mind such 
Mendelian races or mutant individuals as may readily be ad- 
mitted to have entered into the constitution of probably every 
species. The real issue is evidently that which Lotsy (1916), 
Jeffrey, and many others have had in mind, but the solution 
must depend upon a knowledge of hybrids and species in na- 
ture, as well as upon the more cryptic means which Jeffrey 
would employ. 
Everyone who has studied a large group of closely related 
species in the field knows that hybrid individuals of apparently 
inter-specific origin are not uncommon in the transition areas 
that usually occur between related faunas and floras, especially 
in the relatively uniform eastern two-thirds of the United 
States. The recognition of these individuals as hybrids de- 
pends, of course, upon the recognition of combinations of 
characters typical of Mendelian heredity, and of such graded 
series as we would be led to expect from crosses in which 
many of the characters were controlled by multiple factors in 
heredity. Further than that, we may expect that hybrids will 
occur within or between the areas occupied by the two hy- 
bridizing species. 
On the above bases, hybrid populations are recognizable 
among the Cynipidae of the northern half of the Lower Penin- 
( 55 ) 
