PREFACE 



^HE third reprinting of the Vanuxeni Lectures 

 . for 1915-16, entitled A Critique of the Theory 

 of Evolution, having been exhausted, the pubhshers 

 have asked for a revised edition. The revision is no 

 less an attemj^t at a critique of the evolution theory 

 than its predecessor, but, as the change in title sug- 

 gests, greater attention is here paid to one of the 

 most debated questions among evolutionists today, 

 namely, the bearing of the recent discoveries in 

 genetics and in mutation on the theory of evolution. 



While in a general way Darwin's theory of Natu- 

 ral Selection is independent of the origin of the new 

 variations that furnish it with its materials, yet the 

 scientific formulation of the theory is intimately con- 

 nected with the origin and inheritance of suitable vari- 

 ations. For instance, if most of the observed variabil- 

 ity of animals and plants were due directly to the 

 environment, and if the effects thus brought about 

 were not inherited, such variability could no longer 

 be appealed to as material for natural selection. 



Again, if the variations that aj^pear as mutants are 

 alwaj^s defective types, they could not, even though 

 they are inherited, be appealed to as furnishing ma- 

 terial for progressive evolution. 



