THEORY OF EVOLUTION 37 



ture I intend to examine this theory critically. 

 Here we are concerned only with its broadest 

 aspects. 



Darwin appealed to chance variatious as 

 supplying evolution with the material on which 

 natural selection works. If we accept, for the 

 moment, this statement as the cardinal doctrine 

 of natural selection it may appear that evolu- 

 tion is due, (1) not to an orderly response of 

 the organism to its environment, (2) not 

 in the main to the a<^tivities of the animal 

 through the use or disuse of its parts, (3) not 

 to any innate principle of living material itself, 

 and (4) above all not to ])in-pose either from 

 within or from without. Darwin made quite 

 clear what he meant bv chance. Bv chance he 

 did not mean that the variations were not 

 causal. On the contrary he taught that in 

 Science we mean by chance only tliat the par- 

 ticular combination of causes that bring about 

 a variation are not known. They are accidents, 

 it is true, })ut they are causal accidents. 



In his famous book on "Animals and Plants 

 under Domestication", Darwin dwells at great 

 length on the nature of the conditions that 



