EVOLUTION THE MASTER-KEY 



called natural selection. This principle Spencer 

 more happily styled the "survival of the fittest." 

 We must inquire whether it really exists, and, if so, 

 whether it is all-important, as Weismann and the 

 neo-Darwinians assert, but as Darwin himself did 

 not assert; or whether it is merely one of the 

 most important of the factors of organic evolu- 

 tion. 



Similarly we must discuss sexual selection, 

 which Darwin described at such length and with 

 such characteristic completeness in his Descent of 

 Man, published in 1871, twelve years after the 

 epoch-making work of 1859. Here we shall find, 

 as in every other instance, that recent work has 

 supplemented that of the great pioneers. In 

 regard to sexual selection, for instance, we shall 

 be able to adduce the conclusions reached by 

 that new method of biological study which was 

 founded by Francis Galton, the illustrious cousin 

 of Charles Darwin, and which his foremost follow- 

 er, Professor Karl Pearson, of University College, 

 London, has called biometrics or biometry. The 

 essence of biometry is the application of exact 

 mathematical methods, and the most carefully 

 controlled statistical inquiry, to the problems of 

 life. We shall find that the principle of sexual 

 selection has been greatly supported and extended 

 through the discovery by the biometricians, of the 

 principle of homo gamy, which asserts that, through- 

 out the entire realm of living matter, like tends 

 to mate with like. This principle has doubtless 

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