Page:The Gall Wasp Genus Cynips.pdf/61

 HYBRIDIZATION

we have evidence that new species most often originate 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 mutations have occurred have already been described in this paper (pp. 49, 53), with the suggestion that such hybrids are submerged, or that they give rise to local variations of the original 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-specific hybridization; the geneticists have considered the criticism unimportant probably because they have in mind such Mendelian races or mutant individuals' as may readily be admitted 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 nature, 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 depends, 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 hybridizing species.

On the above bases, hybrid populations are recognizable among the Cynipidae of the northern half of the Lower (55)