332 STATISTICAL STUDY OF INHERITANCE 



mena which are often misinterpreted as reversions, and Mendelian 

 experiments [q.v) have still further reduced the number of 

 alleged cases. 



By statistical methods Pearson has sought to ascertain how 

 far the inheritance of the duration of life extends, and has reached 

 the important conclusion that in a large percentage of cases 

 there is evidence in the death-rate that discriminate selection is 

 at work. It is no longer possible to say of natural selection, 

 as Lord Salisbury did in 1894, that " no man, so far as 

 we know, has seen it at work." "It is at work, and at work 

 among civilised men, where intra-group struggle — i.e. auto- 

 generic selection — is largely suspended, with an intensity of a 

 most substantial kind. Of the existence of natural selection 

 there can be no doubt ; we require careful experiments and 

 observation to indicate the rapidity of its action. In a few 

 years we may hope no longer to hear natural selection spoken 

 of as hypothetical, but rather to listen to a statement of its 

 quantitative measure for various organisms under divers en- 

 vironments " [Grammar of Science, p. 500). 



§ 7. Application to Individual Cases. 



Galton suggested in a cautious way, when he formulated his 

 Law, that it might be applicable to the individual, and many 

 have run away with the idea that Galton's Law means that an 

 individual inheritance is made up of contributions ^ parental, 

 J grandparental, | great-grandparental, and so on. But this 

 application to the individual is very rarely justified, and, in any 

 case, it is a distinct idea. Darbishire (1906) proposes to distin- 

 guish from Galton's Law what he calls the Law of Diminishing 

 Individual Contribution, which may be stated thus : " The germ 

 plasm of an individual contains contributions from all of its 

 progenitors ; the amount of the contr-ibutions being large in 

 proportion as the progenitor is near — i.e., large in the case of the 



