218 Evolution and Adaptation 
11. 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 tefer 
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. 
