210 OUTLINES OF EVOLUTIONARY BIOLOGY 



certain reasons into which we cannot enter in this place, but it 

 may be taken as a substantially correct expression of the results 

 obtained by biometrical inquiry. If we remember that Galton's 

 Law merely expresses the average results which may be antici- 

 pated from the interbreeding of a large population, in which 

 hybridization probably plays a very small part, it does not appear 

 in any way antagonistic to the Mendelian theory. It is of course 

 not applicable to individual cases of hybridization, where we are 

 concerned, not with small variations in the same characters, but 

 with the permutations and combinations of alternative character 

 units. 



Intimately bound up with Galton's Law of Inheritance is 

 another important generalization known as the Law of Filial 

 Regression, which we owe to the same distinguished philosopher. 

 The law of ancestral inheritance teaches us that on an average 

 the individual derives half its characteristics from its immediate 

 parents and the remaining half from its more remote ancestry. 

 If the immediate parents, or one of them, happen to depart from 

 the average condition of the race in respect of any character 

 there will be a tendency on the part of the offspring to inherit 

 the deviation in question ; but not to the same extent, for the 

 influence of the more remote ancestry will tend to counteract 

 that of the parents and cause a partial return or regression 

 towards mediocrity. As a result of his statistical investiga- 

 tions Galton estimated that the offspring of parents exhibiting 

 a marked deviation from the average would tend to inherit that 

 deviation to the extent of only one-third of its magnitude in the 

 parents (the mean of the two parental deviations being taken as 

 the standard of comparison). In the w r ords of Professor Karl 

 Pearson, " It is the heavy weight of this mediocre ancestry which 

 causes the son of an exceptional father to regress towards the 

 general population mean ; it is the balance of this sturdy common - 

 placeness which enables the son of a degenerate father to escape 

 the whole burden of the parental ill. Among mankind we trust 

 largely for our exceptional men to extreme variations occurring 

 among the commonplace, but ... if we could remove the 

 drag of the mediocre element in ancestry, were it only for a few 

 generations, we should sensibly eliminate regression or create a 

 stock of exceptional men." l 



1 Grammar of Science, 1900, pp. 456457. 



