1G<; M;^ M. Beeton, Mr. (I. I'. Yule, ami I'r-.f. K. 1'. arson. 



((injured with the physique which tends to longevity has an effect 

 on fertility of about 5 or 6 to 1. 



(iii.) Weismann has suggested that it may be an advantage to a species 

 that its duration of life should l>e shortened. This is not, & priori, con- 

 firmed for the case of man in the American series : the longer the 

 parents live the greater the number of their offspring. But if we can 

 lay any stress on the bend-in for the English mothers, and on the 

 similar but less marked tendency for the English fathers, we might 

 argue that reproductive selection was possibly in England working 

 against extreme longevity, although favouring parents living till 65 or 

 70. Indeed those who rush rapidly to brilliant but not over-stable 

 conclusions might emphasise Weismann's views by showing how in an 

 old community, with much greater pressure on the material resources, 

 there is a tendency to reduce the fertility of the long-lived parents ; 

 while in a new community, with plenty of food and occupation for all, 

 the longest-lived parents are the most fertile ! However, all that we 

 can safely say is that there is a marked difference between English and 

 American parents, and that this distinguishing characteristic is almost 

 equally visible if we take opposite sexes of such diverse classes as English 

 Friends and English country gentlemen. We would leave to further 

 investigations its true interpretation. 



6. Admitting a substantial correlation between length of life and 

 fertility, it is of great interest to investigate what effect, other things 

 being equal,* reproductive selection would have in modifying the 

 duration of life. 



The following table gives the mean length of life of parents taken 

 singly and of parents weighted with their offspring : 



Table IV. Mean Duration of Life of Parents in Years. 



Now these are substantial differences even in the case of the English 

 parents (II and IV), but they are very large differences in the case of the 

 American parents (I and III). If we suppose no assortative mating on 

 the basis of characters tending towards longevity, then it is easy to 



* Omitting, for example, the effect of natural selection as evidenced possibly in 

 a greater death-rate in large families, &c. 



