Chapter X 



NATURAL SELECTION AND 

 EVOLUTION 



Darwin's Theory of Natural Selection still liolds 

 today first place in every discussion of evolution, and 

 for this reason the theory calls for careful scrutiny ; 

 for it is not difficult to show that the expression 

 "natural selection" is to many men a metaphor that 

 carries many meanings, and sometimes different 

 meanings to different men. While I heartily agree 

 with my fellow biologists in ascribing to Darwin 

 himself, and to his work, the first place in evolutionary 

 philosophy, yet recognition of this claim should not 

 deter us from a careful analysis of the situation in 

 the light of all that has been done since Darwin's 

 time. 



The Theory of Natural Selection 



In his famous book on the Origin of Sjjecies, Dar- 

 win tried to do two things: first, to show that the 

 theory of evolution furnishes an adequate explana- 

 tion of the facts. No such great body of evidence had 

 ever been brought together before, and it convinced 

 most thinking men that the theory of evolution of 

 living things furnished a rational explanation of what 

 is known about their relationships and past history. 



Darwin also proposed several theories as to how 



