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CHAPTER II 

 THE HEREDITARY BASIS 



"The experimental study of heredity, development and evolution 

 in forms of Hfe below man must certainly increase our knowledge of 

 and our control over these processes in the human race. If human 

 heredity, development and evolution may be controlled to even a 

 slight extent we may expect that sooner or later the human race will 

 be changed for the better." — E. G. Conkhn, Heredity and Environment 

 in the Development of Men. 



Before entering upon a discussion of the complex biological 

 problem of the evolution of man, it may be useful to touch briefly 

 upon some of the main principles which are observed to hold 

 true for the transmission of hereditary traits. The establishment 

 of the doctrine of evolution naturally lent a great impetus to 

 the study of heredity and the complementary topic of variation. 

 The search for the causes of evolution would be greatly aided by 

 a knowledge of the principles or laws according to which variations 

 in organisms arise and are transmitted to subsequent generations. 

 No one appreciated this fact more than Mr. Darwin as is evinced 

 not only by several chapters in the Origin of Species, but espe- 

 cially by his great work on the Variatiofi of Animals and Plants 

 under Domestication. It was his conviction that the key to the 

 method of evolution lay in the close and careful study of variation 

 that led to the vast amount of observation and experiment w^hich 

 Darwin devoted to this subject. The ingenious theory of pan- 

 genesis by which Darwin attempted to give a provisional explana- 

 tion not only of inheritance, but of many phenomena of variation 

 as well, shows how thoroughly he appreciated the fundamental 

 importance of true insight into these processes. 



Darwin considered his doctrine of pangenesis as a provisional 

 hypothesis, a tentative theoretic formulation of a principle which 

 would introduce some order into what was then a chaos of empiri- 



II 



