348 ACTION OF NATURAL SELECTION 



and the youngest the worst. We may perhaps look 

 upon this decrease of vitality as the direct result of the 

 diminished vigour of the parents at the time of con- 

 ception, and of the mother during the period of intra- 

 uterine development. If this is actually the case, then 

 we ought to find that the expectation of life is more 

 closely correlated with the age of the mother at the 

 time of conception than with that of the father. 



Again Miss Beeton, in conjunction with Mr. G. U. 

 Yule and Professor Pearson,* have found that there is 

 a direct correlation between the duration of life in 

 parents, and the number of children borne by them. 

 It was found that fertility was correlated with 

 longevity even in parents of 50 years and upwards, 

 when the fecund period is passed, though the correla- 

 tion is not by any means so close as in parents under 

 50. 



For instance, American mothers dying at 25 had on 

 an average 2.2 children; those at 35, 4 children; and 

 those at 50, 5.7 children: but mothers dying at TO had 

 on an average 6.8 children, and those at 90, no less 

 than 7.6 children. With English mothers dying at 50 

 years and over, the increased fertility is not so marked, 

 and it becomes slightly diminished in those living over 

 75 years. Similarly also with English fathers the re- 

 lation of fertility to longevity is less marked than in 

 the case of American fathers. 



All these data mav undoubtedly be taken to indi- 



e/ * 



cate, therefore, that longevity is inherited in man, and 

 as long life means a healthier and stronger constitu- 

 tion, it is natural to find that it also betokens increased 

 *Proc. Roy. Soc., Ixvii. p. 159, 1900. 



