THE INDIVIDUAL AND THE SPECIES 



191 



tendency to revert to the value from which it arose. 

 Let the observed variabiHty of stature in a human 

 population be represented by the frequency distribu- 

 tion A , and let the individuals at A^^ — that is, those in 

 which the stature was greater than the mean by the 

 deviation ON — intermarry. It might then happen 

 that the variability of the offspring of these unions 

 would be represented by the frequency distribution 

 B, in which the value of the mean is also that of the 

 stock, at N, from which the race originated. It does 



i- 



f 



■ j: 



■\- 



-^e 



B 



Fig. 22. 



-Mean 



not matter now from what variants in B a progeny 

 of the third generation arises : the mean height of 

 the latter will be that of the pure race. In this case 

 the individuals from which the pure race originated 

 (those d± N m A) have exhibited a mutation. The 

 stature of the individuals of this new race will continue 

 to exhibit fluctuating variations, and the range of this 

 variability may be as much as that of the stock from 

 which it arose, hut the mean stature of the new race will 

 continue to be that of the original mutants. 



It is well known that de Vries himself considered 

 fluctuating variations and mutations as something 

 quite different. The former he considered as nothing 



