Diverse Modes of Selection 141 



Flora and fauna are sieves to one another, and both 

 show continually changing patterns. Perhaps we 

 should recognize a special kind of sieve where there 

 is something in the way of gregarious or social life, 

 for the members are sifted according to their capacity 

 for "give and take" and for "playing the game." 

 Moreover, under the shelter of society there is a pos- 

 sibility of new departures which would be speedily 

 eliminated by the sieves which apply to ordinary, 

 more or less individualistic, life. At different levels of 

 animal society there will be a different pattern of 

 sieve. 



Perhaps this is the place for special recognition of 

 the sieve of courtship, to which Darwin attached so 

 much importance. We refer not so much to cases 

 where rival males fight with one another, like the 

 stags in the forest glade ; we are thinking more of the 

 indubitable cases where the female animal holds the 

 sieve and exhibits something like choice. Here again 

 the meshes evolve, becoming finer and finer as aesthetic 

 and other psychical considerations begin to tell. In 

 preferential mating there is certainly an evolving 

 sieve. 



It is not necessary to give more illustrations, for 

 we have said enough to suggest the complexity of 

 Nature's sifting and what seems to us the very im- 

 portant idea that there has been in the course of ages 

 an evolution of sieves as well as an evolution of the 

 material to be sifted. Sometimes, no doubt, the width 

 of the mesh has been increased, not decreased, and the 

 result has been the survival of flabby and degenerate 



