Data for the Problem of Evolution in Man. 159 



" Data for the Problem of Evolution in Man. V. On the Cor- 

 relation between Duration of Life and the Number of 

 Offspring." By Miss M. BEETON, G. U. YULE, and KARL 

 PEARSON, F.R.S., University College, London. Eeceived 

 April 19, Read June 14, 1900. 



1. According to the Darwinian theory of evolution the members of 

 a community less fitted to their environment are removed by death. 

 But this process of natural selection would not permanently modify a 

 race, if the members thus removed were able before death to pro- 

 pagate their species in average numbers. It then becomes an important 

 question to ascertain how far duration of life is related to fertility. In 

 the case of many insects death can interfere only with their single 

 chance of offspring ; they live or not for their one breeding season 

 only.* A similar statement holds good with regard to annual and 

 biennial plants. In such cases there might still be a correlation between 

 duration of life and fertility, but it would be of the indirect character, 

 which we actually find in the case of men and women living beyond 

 sixty years of age a long life means better physique, and better 

 physique increased fertility. On the other hand, there is a direct 

 correlation of fertility and duration of life in the case of those animals 

 which generally survive a number of breeding seasons, and it is this 

 correlation which we had at first in view when investigating the 

 influence of duration of life on fertility in man. The discovery of the 

 indirect factor in the correlation referred to above was therefore a 

 point of much interest. For it seems to show that the physique fittest 

 to survive is really the physique which is in itself (and independently 

 of the duration of life) most fecund. 



In continuing our study of the inheritance of longevity,! it occurred 

 to us that it would be possible at the same time as extracting data for 

 duration of life to extract data bearing on the size of the family. 

 Accordingly Miss M. Beeton, in working upon family histories, made 

 records of this additional character. Meanwhile Mr. G. U. Yule, who 

 had been independently at work on this very point, drew my attention 

 again to the matter in connection with a passage in the ' Grammar of 

 Science.'^ We agreed to unite our material, and the result is the 

 following joint paper. 



* Of course longer life may denote greater chance of male or female meeting 

 female or male, but in this case we have not a graduated fertility, the individual 

 is or is not once fertile. 



t ' Roy. Soc. Proc.,' vol. 65, p. 290. 



Second edition, p. 445. 



We have also to very heartily thank Mr. L. N. Filon, M.A., and Mr. K. 

 Tressler for aid in the calculations and in the preparation of diagrams. 



VOL. LXVII. N 



