SECONDARY SEXUAL DIFFERENCES 199 



It is evident that useless horns, such as those of 

 the Oryx leucoryx and other antelopes, cannot be 

 accounted for by natural selection. It is also evident, 

 I think, that sexual selection cannot account for their 

 evolution. Among some antelopes the males alone 

 have horns, and among others both sexes have them. 



We find the same difficulties here as in the evolu- 

 tion of deers' horns — namely, the long period during 

 which they were rudimentary and during which no 

 kind of selection will account for their preservation, 

 followed by a second period during which they were 

 useful, and then a third period during which they are 

 useless. The first and third periods cannot be ac- 

 counted for. If we assume that the third period — the 

 period of uselessness — has been produced by sexual 

 selection, we have a theory without facts to support 

 it. Sexual selection, in this case, was opposed to and 

 prevailed over natural selection to the disadvantage 

 of the species, by converting useful into useless horns. 

 Considering the dangers to which these animals are 

 exposed, such an assumption is not justified 



I think that the protection of most deer and ante- 

 lopes is, and has always been, their fleetness, and not, 

 to any great extent, their horns — that by the latter 

 they have sometimes been rendered more helpless. I 

 regard their horns as, for the most part, ornaments, 

 and I see no theory by which their evolution can be 

 satisfactorily explained. 



Mr. Darwin refers to various chameleons, the males 

 of which have appendages on the head, of which the 

 females are nearly or entirely destitute. The male of 

 the Chameleon Owenii " bears on his snout and fore- 

 head three curious horns, of which the female has not 

 a trace. These horns consist of an excrescence of 

 bone covered with a smooth sheath, forming part of 

 the general integument of the body, so that they are 



