The Gall Wasp Genus Cynips
PART I. THE ORIGIN OF SPECIES
Among the diverse aspects of the so-called species problem, there is none that has received more unsatisfactory treatment than the study of species. The data of morphology and paleontology have given us information on the origin of orders and classes and phyla, and the geneticists and cytologists have contributed a brilliant interpretation of the mechanism which accounts for the similarities and, ipso facto, for the differences between individuals of successive generations; but comparative studies of species, first-hand contacts in the field with thousands of individuals of hundreds of related species, the careful examination of these individuals with .modern laboratory facilities, and the correlation of such studies with the findings of genetics, cytology, and the other sciences—in short, the thoro taxonomic study of species has only occasionally been accomplished.
Our present account of the gall wasp genus Cynips is offered as an intensive study of 93 species of a phylogenetically natural group. It has been possible to translate so much of the story because the genus is a highly specialized unit of such recent (Oligocene or Miocene) origin that there are no serious gaps in the record as we find it today. The galls produced by these wasps are direct measures of one of the physiologic capacities of the insects, and thus afford an opportunity for the study of physiologic as well as morphologic variation within the group. The precise restriction of each species to particular hosts gives us an opportunity to analyze the relation of isolation to the origin of species, and the relatively poor means of locomotion of most of the gall wasps accounts for considerable geographic variation with its further emphasis on isolation. The existence of 42 subapterous forms in the genus has afforded an unexpected opportunity to show the relation of mutation to the origin of species. All of these items contribute to the utility of these insects for the study of the general problem of evolution. Whether species in the genus Cynips present a fair picture of species in general can
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