462 



THE GRAMMAR OF SCIENCE 



only to measure the intensity of heredity between both 

 parents and younger and elder children. This has been 

 tried for stature with the following results :^ — 



The differences for sons are quite insensible ; for 

 daughters they are more irregular, but what is quite clear 

 is that there is no increase in the hereditary influence of 

 the father, or decrease in that of the mother, as we pass 

 from elder to younger children. It is rather the reverse. 

 In this, the only case so far as I am aware in which the 

 matter has been definitely investigated, there is thus no 

 evidence of any steady telegonic influence. The possibility 

 of an abnormal and infrequent preservation of the gametes 

 of an earlier male can hardly be negatived by isolated 

 experiments on zebras and horses. Should it occur once 

 in a hundred trials we are hardly likely just to hit upon 

 the successful instance. 



^ 9. — On t/te hiheritance of Fertility. Genetic Selection 



We have seen the enormous importance for the theory 

 of evolution of the existence of differential fertility 

 (pp. 414, 423). We must now consider the crucial prob- 

 lem of whether fertility is or is not inherited. Is fertility 

 only settled by the environment, or are differences in 

 fertility genetic variations, and so inherited like other 

 characters ? In order to solve this problem we must 

 take individuals living under sensibly the same environ- 

 ment, and treating fertility as any other character form 

 a correlation table (see p. 394) for its value in pairs of 

 relatives. The measurement of an annual fertility, say, 



^ As to these rather high values see footnote, p. 457. 



