V. 



THE THEORY OF DEVELOPMENT BY 

 NATURAL SELECTION. 1 



Just fifty-eight years ago Charles Darwin published 

 The Origin of Species ; and it may confidently be said 

 that no book which appeared during the last century 

 has had so great an influence on human thought and 

 human action. The time of its publication coincided 

 not only with great advances in physics and chemistry, 

 but with an enthusiastic attempt among the younger 

 and more progressive physiologists to reach physical 

 and chemical explanations of the phenomena of life — 

 in fact, to convert biology into a department of applied 

 physics and chemistry. The doctrine of natural selection 

 at once became a part of this movement, and has been 

 generally accepted as one of the main supports of the 

 mechanistic theory of life. 



The latter theory has been dominant among physio- 

 logists for more than half a century, and has been of 

 great service in the development of physiology. But 

 it has now, I think, served its purpose, and is outworn, 

 though still what may be called the orthodox theory 

 among physiologists. What I wish to do to-night is, 



1 A lecture delivered at the Birmingham ami Midland [nstitute, 

 December 10, 1917. 



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