370 castle: role of selection in evolution 



nature, that is, in a state of affairs not actively controlled by- 

 man, those creatures survive which are 'best adapted to their 

 surroundings. This is what Darwin meant by "natural selec- 

 tion." Among organisms under the immediate control of man, 

 as the cultivated plants and domesticated animals, where the 

 determination of what individuals shall become parents rests 

 with man, Darwin recognized the occurrence of "artificial 

 selection." 



Any legitimate attack on Darwin's views of selection must 

 deal either with natural selection or with artificial selection. 

 But when "Darwinian selection" is mentioned as a term of 

 reproach, the attack is really directed neither against natural 

 selection nor against artificial selection, nor against any other 

 conceivable form of selection, but against one of Darwin's views 

 as to the nature of variability. Darwin recognized two sorts of 

 heritable variations, (1) those which are purely quantitative, 

 plus or minus, as compared with the prevailing racial condition, 

 and (2) those which are wholly different from the prevailing 

 condition. The former we may call "fluctuations," adopting 

 the convenient term of DeVries. The latter Darwin often 

 called "sports." Bateson has called them discontinuous varia- 

 tions, and DeVries calls them mutations. Darwin believed that 

 evolution might result either from the systematic and repeated 

 selection of fluctuations or from the propagation of sports. 

 DeVries doubts whether the systematic selection of fluctuations 

 amounts to much in an evolutionary way, and Johannsen has 

 denied to it any evolutionary effect whatever, on the ground 

 that fluctuations are not inherited. Darwin assigned to the selec- 

 tion of fluctuations a major part in evolution, DeVries assigned to 

 it a minor part, and Johannsen allows it no part in evolution. 

 As regards sports, Darwin assigned to their selection a minor 

 part in evolution (chiefly among cultivated plants and domestic 

 animals); DeVries ascribed to a particular kind of sports (his 

 "mutations") a major part in evolution; and Johannsen ascribes 

 an exclusive part in evolution to a type of variation which 

 would include both Darwin's sports and DeVries' mutations 

 and then some. Johannsen has indeed made a new classification 



