168 Heredity. 



A secondary sexual character is a peculiarity which 

 is not directly concerned in the reproductive process, 

 although it is normally either confined to one sex, or 

 else is much more developed in one sex than it is in the 

 other. The presence of a beard is a secondary sexual 

 character of man; the comb, wattles, spurs and brilliant 

 plumage of the domestic cock, the horns of a stag, the 

 tusks of an elephant, the mane of a lion, or the brilliant 

 plumage of the peacock or of the drake, are all of them 

 examples of this sort of organs, for they are either con- 

 fined to one sex, or else they are much more conspic- 

 uous and important in one sex than they are in the other. 



They furnish, like hybrids, a means of disentangling 

 or analyzing to some extent the influence of the two 

 sexes in heredity, and I hope to show in this and the fol- 

 lowing chapters that they furnish evidence to prove 



1. That in most animals with separate sexes the males 

 of allied species differ more than the females from the 

 ancestral type. 



2. That organs which are confined to males or are of 

 more importance or are more perfectly developed in them 

 than in the females, are much more likely to give rise to 

 hereditary modifications than parts which are confined 

 to or are most developed in females. 



3. That a part which is confined to or is most de- 

 veloped in males is more likely than a similar female 

 part to vary. 



4. That males are, as a rule, more variable than 

 females. 



5. That the male leads and the female follows in the 

 evolution of new races. 



There are two criteria which are of great use in the 

 attempt to trace the path which a species has followed 

 in its evolution. One of these is by comparison of a 



