94 SEXUAL DIMORPHISM 



general tendency of all unisexual characters ultimately to 

 become common to both sexes. It is possible that unisexual 

 characters originally developed by special stimulations related 

 to reproduction, tend sooner or later to be inherited in 

 common by all individuals of the species, that considered in 

 relation to periods of evolution their sexual limitation is only 

 temporary. This view would be in harmony with many cases 

 besides that of the reindeer. The latter species would there- 

 fore have acquired horns at an earlier period than other deer, 

 and have thus got to a later stage in their evolution. 



This view is in direct opposition to that of Mr. Gordon 

 Cameron, and to some extent in agreement with that of Mr. 

 Lydekker. 1 The former author considers that the possession 

 of defensive weapons, whether cranial or dental, by both sexes, 

 was a primitive character, and concludes that therefore 

 Rangifer represents the oldest line of antlered deer, from 

 which the dimorphic forms have diverged. Mr. Lydekker, on 

 the other hand, points out that in the Bovidre it is mostly in 

 the specialised and modern forms that the females, if horned 

 at all, bear large horns, that in the gazelles and their allies, 

 which are an ancient group dating back to the Miocene, 

 generally the males only are horned, and that in the extinct 

 Cervine genus Dremotherium of the Miocene, some specimens, 

 probably the females, are hornless. In my own opinion the 

 conclusion to be drawn is that whatever the geological age of 

 the species or genus, the possession of horns, or other secondary 

 sexual character generally confined to the males, by both 

 sexes, is a recently acquired character. Palaeontology tells 

 us that the earliest deer possessed no antlers at all, and as 

 species in these were already differentiated, it is not certain 

 that all antlered deer are descended from one original antlered 

 species. It is thus possible that antlers were acquired separ- 

 ately in distinct lines of descent, in consequence of the same 



1 Deer of All Lands, 1898, p. 35. 



