Natural History 483 



back" made by certain creatures with a constitutional peculiarity; 

 other mammals meet the winter in other ways. 



13 



Sex Dimorphism 



The contrasts between lion and lioness, between stag and 

 hind, are familiar. They illustrate what is technically called sex 

 dimorphism, i.e., a marked structural difference between male and 

 female. The contrasted characters are called secondary sex 

 characters, to distinguish them from primary sex characters, which 

 have to do more or less directly with the reproductive function 

 itself. The males are sometimes equipped with decorations the 

 manes of lion and bison, the beards of certain goats, the crests 

 along the back of some antelopes, and the dewlaps of bulls. Or 

 they may have weapons which are either absent in the females 

 or represented in less exuberant development. Thus antlers are 

 restricted to the males except in the case of the reindeer ; the horns 

 of bull and ram may be much larger than those of cow and ewe ; 

 the male narwhal has a spear-like tusk which is not developed in 

 the female. There may also be differences in colour and in odour. 



Darwin suggested that when the males fought for the posses- 

 sion of the females, as stags and antelopes do, the males with 

 better weapons would prevail. As they would therefore have most 

 success in leaving progeny, their strong qualities would gradually 

 become racial characters; the males with poor weapons would be 

 sifted out. In regard to sex decorations he suggested that the 

 females would be most interested in, and would give the preference 

 in mating to, the more handsome males, and that the race would 

 therefore evolve in the direction of increased decorativeness. This 

 is, in brief, Darwin's theory of sex selection, which is discussed in 

 the article, "How Darwinism Stands To-day." But one point 

 must be noticed here. If the quality of having strong weapons or 

 of having handsome decorations is hereditarily transmissible, why 

 does it not appear in the female as well as in the male offspring? 



