CHAPTER II 
THE HEREDITARY BASIS 
“The experimental study of heredity, development and evolution 
in forms of life 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. Conklin, 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 Variation 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 which 
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- 
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