212 Cofichision. 



struggle between fluctuations, the latter between muta- 

 tions. In the former case those that survive are the in- 

 dividuals which find conditions favorable to them — that 

 is to say, as a rule, the strongest individuals. It is by this 

 process that local races arise, and by it that acclimatiza- 

 tion is rendered possible. If the new conditions of life 

 are relaxed, the adapted race reverts to the form from 

 which it sprang. 



The natural selection of newly arisen elementary spe- 

 cies in the struggle for existence is an entirely different 

 matter. They arise suddenly and without any obvious 

 cause; they increase and multiply because the new char- 

 acters are inherited. When this increase leads to a 

 struggle for existence the weaker succumb and are elim- 

 inated. According as the young or the parent form is 

 l)etter fitted to the environment wmII the one or the other 

 of them survive. Species no more arise as the result of 

 this struggle for existence, than they do as the result of 

 the struggle between the variants of one and the same 

 type — though for different reasons in the two cases. In 

 order that species may engage in competition with one 

 another it is evidently an essential condition that they 

 should already be in existence ; the struggle only decides 

 which of them shall survive and which shall disappear. 



It is evident moreover that this ''elimination of spe- 

 cies" must have weeded out many more than it has pre- 

 served. 



In a word, from the standpoint of the theory of muta- 

 tion it is clear that the role played by natural selection 

 in the origin of species is a destructive, and not a con- 

 structive one. 



5. Herbert Spencer's well-known expression : ''The 

 survival of the fittest" may mean one of two things : 



