64 THE GENETIC AND THE OPERATIVE EVIDENCE 



a firm foundation for a scientific study of the subject. It is equally 

 important that critical evidence be obtained in regard to the effect on 

 the female of males of different types in competition. The instinctive 

 reactions of animals in these respects, their first reaction, the asso- 

 ciations that may or may not result, are practically an open field for 

 investigation. The entire equipment of human psychology of the in- 

 trospective school, that has been appealed to for help in a situation 

 itself little understood, reads often more like fiction than like science. 



So far as one branch of the subject goes — the possible interpretation 

 of ornamentation in the male — there seem to be two ways at least in 

 which the subject calls for immediate investigation: First, if it can be 

 shown that, other things being equal, a more adorned male rouses the 

 female to prompter mating, it may be inferred with some probability 

 that in the long run such conduct would lead to the establishment of 

 the more effective individual, but this would not be true unless the 

 males mate, as a rule, more than once, for any advantage that might 

 accrue to a more ornamented male would not affect the course of evolu- 

 tion of the species if every other male found a mate too. Second, if it 

 could be shown that the special ornamentation of the male is only one 

 of several effects of a gene whose main effect is in some other direction, 

 then the advantage gained through natural selection in this other 

 direction would carry in its wake the advance in ornamentation, and if 

 the change affects one sex more than the other, owing to the difference 

 in the genetic complex of the two sexes, it would be called a secondary 

 sexual character. 



A. Evidence from Mammals. 



Owing to the differences in the secondary sexual characters of dif- 

 ferent breeds of sheep, we have more genetic information about such 

 characters in this group than in other groups of mammals. For- 

 tunately, also, in some of the breeds both castration and ovariotomy 

 have been performed, and consequencely we are in position to utilize 

 both sources of information for interpreting the situation. In certain 

 breeds both males and females have horns (Dorsets), in which case the 

 horns of the male are larger than those of the female. In other breeds 

 neither males nor females have horns (Suffolks). In still other breeds 

 the males have horns and the females are hornless (Merinos and Herd- 

 wicks). The clearest evidence that we have, both genetic and opera- 

 tive, is that obtained by Woods, as reported by Bateson, in which 

 horned (Dorsets) and hornless (Suffolks) breeds were crossed. In the 

 Dorsets, where both sexes have horns, those of the male are larger than 

 those in the female. When the young male is castrated the horns 

 develop, but only as far as in the female. It appears, therefore, that 

 the presence of the testis, probably through some secretion from it, 



