CHAP, vn EVOLUTION IN DARWIN 71 



by trial and error is the most tedious method possi- 

 ble. If at every cross-roads I have to follow each 

 track in turn, taking them as they come, going on in 

 each case to the next town before I can learn whether 

 I am on the right road, if I am wrong, coming 

 back from the town to my cross-roads and trying the 

 next track till I find a town upon it, and so forth and 

 so forth plainly, it may take me all my days to 

 work my way to my chosen destination. 



Darwin's theory, however, includes other elements 

 besides natural selection ; and these, if reliable, seem 

 to point to agencies which would accelerate the pro- 

 cess of evolution. One addition which Darwin pro- 

 posed to his doctrine was sexual selection. " None 

 but the brave deserves the fair" that is half the 

 new doctrine. For sexual selection is believed to ex- 

 ist in two forms: first, when the males fight with 

 each other for the privilege of access to the females, 

 as in the case of lions or stags ; secondly, when the 

 males vie with each other in aesthetic attractiveness, 

 as Darwin supposed to be the case with birds, and as 

 a larger number of observers believe to be demon- 

 strated in the case of certain insects. The assump- 

 tion appears to be that the unsuccessful males remain 

 almost or altogether sterile by force of circum- 

 stances; accordingly, a criticism passed by Wallace 

 upon Darwin's theory of a sexual selection in the 

 case of birds is to the effect that, apparently, even 

 the least beautiful of male birds finds a mate sooner 

 or later during the pairing season ; that the inferior 

 forms leave offspring as well as the superior forms ; 

 that accordingly no selection between different forms 

 is due to the imperfect rivalries of courtship. It 



