The Making of Species 



In either of these circumstances natural selection 

 will be an inhibitory force, for if the normal 

 organism is perfectly adapted to its environment, 

 all variations from the type must be unfavour- 

 able, and natural selection will weed out the 

 individuals that display them. No careful 

 student of nature can maintain, either that all 

 animals are perfectly adapted to their environ- 

 ment, or that this never changes. Hence those 

 who deny that natural selection is a factor in the 

 making of species, assume the second set of con- 

 ditions, that species develop in certain fixed 

 directions, being impelled either by internal or 

 external forces. How far these ideas are founded 

 on fact we shall endeavour to determine when 

 speaking of variation. It must suffice at present 

 to say that even if any of these views of ortho- 

 genesis be established, natural selection will have, 

 so to speak, a casting vote, it will decide which 

 series of species developing along preordained 

 lines shall survive and which shall not survive. 



Thus we reach by a different line of argument 

 the conclusion we arrived at in the last chapter : 

 namely, there is no room for doubt that natural 

 selection is a factor in the making of species. 



We must now pass on to the second class of 

 objections, those which are urged against the all- 

 sufficiency of natural selection. So numerous 

 are these that it is not feasible to consider them 

 all. A brief notice of the more important ones 



34 



