NATURAL SELECTION 33 



arrangement, and this arrangement is constant for the 

 species. They are, then, true specific characters. Of what 

 possible use can these minute ridges and furrows upon the 

 shell, or the particular arrangement of skeletal spicules, be 

 to these little plants and animals ; or why are they more 

 useful if regularly arranged according to a particular pat- 

 tern ; or why is it important that each species should have a 

 pattern peculiarly its own ? We cannot satisfactorily answer 

 these questions. We know comparatively little about the 

 details of the life of these species. If we knew more it is 

 possible the explanation of these skeletal characters might 

 appear and we see that they are useful. Much of our 

 inability to show the utility of the apparently useless char- 

 acters of animals and plants is probably due to our ignorance 

 of the life habit of these organisms. 



Yet we may, for the present, grant that certain struc- 

 tures and habits are useless. We must, however, remem- 

 ber that natural selection is not the only factor of evolu- 

 tion, and that, while it develops directly none but useful 

 characters, the other factors give rise to characters that are 

 not necessarily useful. This point will come out more 

 clearly after we have described the action of these other 

 factors. 



But, setting this point aside, natural selection may indi- 

 rectly give rise to features of organization or disposition 

 that are not useful to their possessors. An organism is a 

 very complex thing, with its parts most intimately related to 

 each other. No single structure in the body is independent 

 of the rest. One part acts upon another in ways most 

 remarkable. The intimacy of this interrelation of parts and 

 the complex way in which they react upon and influence 



