128 EVOLUTION AND GENETICS 



tinned selection in the same direction may seem to 

 imply that the range of variation shown by the off- 

 spring of a given individual about that type of indi- 

 vidual would be as wide as the range shown by the 

 original population, but Galton's work first made 

 clear that this is not the case in a general or mixed 

 population. If the offspring of individuals did con- 

 tinue to show as wide a range of variability about the 

 new average as did the original population, then it 

 would follow that selection could slide successive 

 generations along in the direction of selection. 



Darwin himself was extraordinarilv careful, how- 

 ever, in the statements he made in this connection, and 

 it is rather by implication than by actual reference 

 that one can ascribe this meaning to his views. Some 

 of his contemporaries and many of his followers, 

 however, appear to have accepted this sliding scale 

 interpretation as the cardinal doctrine of evolution. 

 And in this connection we should not forget that just 

 this sort of process was supposed to take place in the 

 inheritance of use and disuse. What is gained in one 

 generation forms the basis for further gains in the 

 next generation. Now, Darwin not only believed 

 that acquired characters are inherited but turned 

 more and more to this explanation in his later writ- 

 ings. Let us, however, not make too much of the 

 matter; for it is not so important to find out whether 

 Darwin's ideas were as definite on this point as our 

 own as it is to make sure that oiu* own ideas are clear 



