58 STUDIES IN EVOLUTION 



Ruminata there are species without horns, other species with 

 horns in both sexes, and still others with horns only in the 

 male. In the wild state the presence or absence of horns 

 and their character in any particular species seem to be well 

 established, but in domesticated forms the greatest variety 

 is found. Among domesticated cattle, presumably of one 

 species originally, varieties are found without horns, and 

 others with horns showing all degrees of twisting and 

 length. 



By protecting cattle from enemies, by forcing them into 

 changed environment, and by varying amounts of nutrition, 

 man has evidently brought the original stock into a condition 

 of free variation. This state has been made use of in the 

 production of endless varieties by selection and cross-breeding. 



Darwin^* accounts for the sexual selection affecting the 

 growth of the antlers in the Deer as due to excess in the 

 number of male individuals, and their struggles for supremacy 

 in the possession of a mate. The antlers at the breeding 

 season are strong and solid, and are therefore at their 

 maximum of efficiency in each individual. They are shed 

 at or before the time the young are born. Previous to the 

 growth and maturity of the new antlers, the young are so 

 far advanced as to be able to avoid being killed by the adult 

 males. Furthermore, Darwin suggests that the excessive 

 development of antlers into palmate and arborescent forms 

 was probably an ornamental character attractive to the 

 females. These complicated antlers not being the most 

 efficient weapons, the fighting proclivities of the males would 

 tend to favor the individuals with simple antlers, and to 

 repress the more differentiated forms. Thus the two in- 

 fluences would be opposed to each other, though not necessarily 

 equal. The law of the multiplication of effects may also 

 have some force, since it may carry a structure beyond the 

 bounds of efficiency. Even in one of the oldest horned 

 mammals, the Protoceras *^ of the Miocene Tertiary, a great 

 difference is seen in the horns of the two sexes. The female 

 has little nodes or tubercles, which in the male rise to the 



