60 



STUDIES IN EVOLUTION 



45 



46 



enormous horns. These two forms of male are called "low" 

 and "high" males, respectively. Among the males sim- 

 ilar dimorphism in respect to size and length of horns 

 occurs in Xylotrupes gideon, and in the stag beetle (^Luca- 

 nus cervus, L. titamis, L. daind). 



In many of these cases the horns 

 are evidently protective, and not de- 

 veloped through the selective influ- 

 ences of the female. In such cases 

 the habits of the male are supposedly 

 different from those of the female. 

 Thus Wallace "'^ suggests that the 

 horned males of the coleopterid fam- 

 ilies Copridse and Dynastidse fly 

 about more, as is commonly the case 

 with male insects, and that the 

 horns are an efficient protection 

 against insectivorous birds. These 

 interpretations clearly do not come 

 under the definition of sexual selec- 

 tion as restricted to the choice of 

 either sex. Beauty, voice, or strength may influence the 

 selection of a mate by the opposite sex, but when the habits 

 of the sexes are different, and certain characters arise in 

 response to this change, the explanation is then really found 

 in the law of adaptation or physical selection. 



FiGDRE 45. — Profile of 

 head of Chamceleon Oweni ; 

 male. |. 



Figure 46. — Female of 

 the same species. \. (After 

 Darwiu.) 



V. Secondarily from mimetic iiifluences. (A5, B4.) 



Natural selection may aid in furthering and preserving a 

 spinose organism after the spines have originated through 

 any primary cause. One aspect of this influence may be 

 treated under the head of mimicry. If, by their resemblance 

 in form, color, or voice, any characters are similar to char- 

 acters present in the surroundings of the animal, and afford 

 a means of protection or are useful, they may be considered 

 as mimetic in the broadest sense of the term. Mimicry is 



