14 EVOLUTION AND GENETICS 



factors. Living matter was stopped down, so to 

 s]3eak, at the beginning of the world. As the stops 

 are lost, new things emerge. The germinal material 

 has changed only in that it has become simpler. 



Natural Selection 



DARWIN 



Of the four great historical sj^eculations about 

 evolution, the doctrine of Xatural Selection of Dar- 

 win and Wallace has met with the most widespread 

 acceptance. Later the theory will be examined more 

 critically. Here only its broadest aspects will be 

 considered. 



Darwin appealed to chance variations as supply- 

 ing evolution with the material on which natural se- 

 lection works. If we accept, for the moment, this 

 statement as the cardinal doctrine of natural selec- 

 tion it may appear that evolution is due, ( 1 ) not to 

 an orderly response of the organism to its environ- 

 ment, (2) not in the main to the adjustment of the 

 animal through the use or disuse of its parts, (3) 

 not to any innate non-physical principle of living 

 material itself, and (4) above all not to purpose 

 either from within or from without. Darwin made 

 quite clear what he meant by chance. By chance he 

 did not mean that the variations were not causal. 

 On the contrary he taught that in science we mean 

 by chance only that the particular combination of 

 causes that bring about a variation is not known. 



