76 EVOLUTION AND ANIMAL LIFE 



successful in this struggle which are the strongest and best 

 armed or equipped for battle among themselves, or which are 

 most acceptable by reason of ornament or other attractiveness 

 to the females. In the former case mating with a certain 

 female depends upon overcoming in fight the other suitors, the 

 female being the passive reward of the victor; in the second case 

 the female is presumed to exercise a choice, this choice depend- 

 ing upon the attractiveness of the male (due to color, pattern, 

 plumes, processes, odor, song, etc.). The actual fighting among 

 males, and the winning of the females by the victor is an ob- 

 served fact in the life of numerous animal species. But a spe- 

 cial sexual selection theory is hardly necessary to explain the 

 development of the fighting equipment, antlers, spurs, claws, 

 tusks, etc. This fighting array of the male is simply a special 

 phase of the already recognized intraspecific struggle; it is not a 

 fight for room or food, but for the chance to mate. But this 

 chance often depends on the issue of a life and death struggle. 

 Natural selection would thus account for the development of 

 the weapons for this purpose. 



For the development, however, of such secondary equal char- 

 acters as ornament, whether of special plumage, color, .pattern, or 

 processes, and song, and special odors, and "love dancing," the 

 natural selection theory can in no way account; the theory of 

 sexual selection was the logical and necessary auxiliary theory, 

 and when first proposed it met with quick and wide acceptance. 

 Wallace in particular took up the theory and applied it to ex- 

 plain many cases of remarkable plumage and pattern develop- 

 ment among birds. Later, as he analyzed more carefully his 

 cases, and those proposed by others, he became doubtful, and 

 finally wholly skeptical as to the theory. 



The theory as proposed by Darwin was based on the follow- 

 ing general assumptions, for the proof of each of which various 

 illustrations were adduced. First, many secondary sexual 

 characters are not explicable by natural selection; they are not 

 useful in the struggle for life. Second, the males seek the 

 females for the sake of pairing. Third, the males are more 

 abundant than the females. Fourth, in many cases there is a 

 struggle among the males for the possession of the females. 

 Fifth, in many other cases the females choose, in general, those 

 males specially distinguished by more brilliant colors, more 

 conspicuous ornaments, or other attractive characters. Sixth, 



