X 



HEREDITY AND VARIATION 1 



HEREDITY and variation are the two facts with- 

 out which organic evolution would be impossible. 

 Since Darwin's work, which somewhat obscured 

 the initial questions that they raise, but demon- 

 strated their stupendous consequences, biologists 

 have spent much labor in discussing the causes and 

 conditions of the two facts, that like tends to be- 

 get like, but that like does not beget exactly like. 

 The subject is worthy of study, for it is evident 

 that without variation there could be no differentia- 

 tion of species ; while without inheritance of varia- 

 tions no differentiation could survive for more 

 than one generation. Natural selection presup- 

 poses variation, and now we have ceased to doubt 

 that natural selection is a fact, biologists are 

 going back to the beginning and studying that 

 factor from which attention was long diverted by 

 the influence of Darwin's masterpiece. 



Some forty years ago the Abb6 Mendel took 



1 The best popular text-book on heredity with which I am 

 acquainted is Mr. Archdall Reid's recently published Principles 

 of Heredity (Chapman and Hall). 

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