What is Selected 



351 



quality of the race move in the direction selected, but that 

 the range of variation would also move in the same direction 

 in each successive generation (see Fig. 90) . Galton had 

 already shown from his measurements that this does not take 



Fig. 90. Darwin's Assumption 



The theory of natural selection, supported 

 In part by experience with artificial selection, 

 assumes that if from a mixed population, A, in- 

 dividuals are selected near one extreme of the 

 range of variations, these will give rise to a 

 group, B, that fluctuates about a new mean cor- 

 responding to the character of the selected 

 parents. If the process is repeated, the mode 

 and the range in the following generation, C, 

 will have shifted still further in the direction 

 of the selection, and so on indefinitely. After 

 a number of generations, the descendants, D, 

 of the original population will present charac- 

 teristics definitely beyond the ancestral range 

 of fluctuations. Pure-line experiments in 

 breeding have not supported this view. 



