EXPERIMENTS ON SEX RECOGNITION AND THE 



PROBLEM OF SEXUAL SELECTION 



IN DROSOPHILA 



A. H. STURTEVANT 

 Columbia University 



Much has been written on the subject of sexual selection 

 since Darwin first developed the theory, and many remarkable 

 observations have been recorded. There has, however, been 

 very little experimental work in this field. Darwin and those 

 who have followed him have obtained much of their evidence 

 from the insects, and within this group some of the most striking 

 cases of elaborate mating habits have been reported in the 

 Diptera, and here too there is to be found a most remarkable 

 array of secondary sexual characters. Perhaps the most extreme 

 case is that of the Elaphomyia described by Wallace, in which 

 the male has long, hornlike processes arising from his head, 

 which are absent in the female. The families of Platypezidae, 

 Dolichopodidae, and Empididae are especially rich in secondary 

 sexual characters, which occur in the legs, wings, antennae, 

 face, or other parts. In the two latter families some very curious 

 observations on mating habits have been recorded (see especi- 

 ally 'Poulton's account ('13) of Hamm's work on Empididae). 1 



Some of the best experimental evidence in favor of sexual 

 selection is that obtained by Lutz (1911), who worked with an* 

 abnormal wing venation in Drosophila ampelophila which he 

 found to be strongly selected against. To Dr. Lutz is due the 

 suggestion that the mutants in this fly obtained by Morgan 

 would form excellent material for the study of the problem. 

 The method of some of the experiments was also suggested by 

 Lutz. I took up the matter at the suggestion of Professor 

 Morgan, to whom I am greatly indebted for most of the material 

 and for his encouragement and criticisms. Several discussions 

 of the matter with Dr. Lutz have also been very helpful. Some 



1 1 have myself observed courtship in a few Dolichopodidae and in a number of 

 other Diptera. These observations will be published in full later. 



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