2i8 Evolution and Adaptation 



ii. It is baffling to find Darwin resorting to the Lamarck- 

 ian explanation in those cases in which the improbability of 

 the hypothesis of sexual selection is manifest. If either prin- 

 ciple is true, we should expect it to apply to all phenomena of 

 the same sort ; yet Darwin makes use of the Lamarckian 

 principle, in the hypothesis of sexual selection, only when 

 difficulties arise. 



12. In attempting to explain the development of the musi- 

 cal sense in man, it is clear that the hypothesis of sexual 

 selection fails to give a satisfactory explanation. To suppose 

 that the genius of a Beethoven or of a Mozart could have 

 been the result of a process of sexual selection is too absurd 

 to discuss. Neither the power of appreciation nor of expres- 

 sion in music could possibly have been the outcome of such a 

 process, and it does not materially help the problem to refer 

 it back to a troop of monkeys making the woods hideous 

 with their cries. 



We come now to some of the special cases to which Dar- 

 win's hypothesis has been applied. 



13. In one case at least, it is stated that a bird living on 

 the ground might have acquired the color of the upper sur- 

 face of the body through natural selection, while the under 

 surface of the males of the same species might have become 

 ornamented through the action of sexual selection. Thus in 

 one and the same individual the two processes are supposed 

 to have been at work, and it does not lessen the difficulty very 

 much by supposing the two processes to have been carried 

 out at different times, because it is evident that what had 

 been gained at one time by one process might become lost 

 while the color of certain parts was being acquired through 

 the other process. 



14. Darwin points out that "the plumage of certain birds 

 goes on increasing in beauty during many years after they 

 are fully mature," as in the peacock, and in some of the birds 

 of paradise, and with the plumes and crests of some herons. 



