CHAPTER II 



THE SCIENTIFIC STUDY OF VARIATION AND HEREDITY 



Before we pass to the problems of variation and 

 heredity in man, it is necessary to trace the progress of 

 our knowledge of those problems in the lower animals, 

 and in the vegetable kingdom. Here experiment is 

 possible, and consequently more definite results have 

 been reached. With these results in mind, it is easier 

 and more instructive to examine the purely observa- 

 tional information that is available about mankind than 

 it would be without such guides. 



In the subject as left by Darwin, the greatest need 

 was further light on the variations and mutations 

 necessary for natural selection to have something 

 to work upon. Two possibilities were recognised. 

 Selection might act on the small variations found 

 among the individuals of a species otherwise homo- 

 geneous — on the greater speed of an antelope with 

 legs an inch longer than the average of his kind ; or 

 large, discontinuous variations might arise, and the 

 *' sports" or individuals possessing them might make 

 large steps towards forming new species at once, if 

 the variations were favourable to survival. 



Although Darwin recognised that " sports " had 



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