CHAPTER V 

 MUTATIONS 



THERE is endless dissimilarity in nature. No two 

 plants and no two animals are exactly alike. There are 

 more plants and animals than can find a place in which 

 to live and thrive. There results a struggle for existence. 

 Those animals or plants which, by virtue of the individual 

 differences or peculiarities, are best fitted to the condi- 

 tions in which they are placed, survive in this struggle 

 for existence. They are " selected to live." Those that 

 survive, propagate their peculiarities. By virtue of 

 continued variation, and of continued selection along a 

 certain line, the peculiarities may become augmented; 

 finally the gulf of separation from the parental stem 

 becomes great, and what we call a new species has origi- 

 nated. 



Evolutionary theories of Darwin and de Vries. This, 

 in epitome, is the philosophy of Darwin in respect to evolu- 

 tion of organic forms. It contains the well-known postu- 

 late of natural selection, the principle that we know as 

 Darwinism. This principle has had more adherents 

 than any other hypothesis of the process of evolution. 

 All recent hypotheses in some way relate to it. A number 

 of them modify it, and some dispute it. The most pro- 

 nounced counter-hypothesis is also the newest. It is that 



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