vi THE DOMESTIC LIFE OF ANIMALS 103 



mammals woo chiefly by force ; the birds are often 

 moved to love by beauty, and mates often live in pro- 

 longed partnership with mutual delight and helpfulness. 

 Sixty years before Darwin elaborated his theory of 

 sexual selection, according to which males have grown 

 more attractive because the most captivating suitors 

 were most successful in love, the ornithologist Bechstein 

 noted how the female canary or finch would choose the 

 best singer among a crowd of suitors ; and it is still a 

 tenable theory that the female's choice of the most 

 musical or the most handsome or the most exciting has 

 been a factor in progress. Wallace, on the contrary, 

 maintained that the females are plainly dressed because 

 of the elimination of the conspicuous during incubation, 

 and denied that there is effective selection in courtship. 

 It may be that masculine characteristics, arising to begin 

 with as germinal variations in males, are congruent with 

 maleness, and do not emerge in individual development 

 except in what one may call a male soil. And similarly 

 for feminine peculiarities, which are usually more nega- 

 tive. 



Compared with the lion's thunder, the elephant's trum- 

 peting, or the stag's resonant bass, and the might which 

 lies behind these, or with the warble of the nightingale, 

 the carol of the thrush, the lark's blithe lay, or the mock- 

 ing-bird's nocturne, and the emotional wealth which 

 these express, the challenges and calls of love among 

 other classes of animals are apt to seem lacking in force 

 or beauty. But our human judgment affords no sure 

 criterion. The frogs and toads, which lead on an 

 average a somewhat sluggish life, wake up at pairing 

 time, and croak according to their strength. Vocal 

 powers are sometimes confined to the males, which may 

 be furnished with two resonating sacs at the back of the 

 mouth. It is a verv interesting fact that the voices of 



*/ 



the different species of frogs and toads are quite charac- 

 teristic. 



Of the mating of fishes we know little, but there are 

 some well-known cases alike of display and of tourna- 

 ment. The stickleback fights with his rivals, leads his 



