Published online by Cambridge University Press: 15 May 2009
It has been already shown by Darwin and others that reproduction is a function of environment and that unfavourable conditions of life are likely to increase the number of seeds formed or offspring produced; hence so many are reproduced that the chance of the species being perpetuated is maintained, despite the unfavourable conditions for survival. To extend this idea, and say that a dying species tends to reproduce faster than one actively evolving, is a suggestion worthy of enquiry. It has been argued that the varying birth rates in man may to some extent reflect the future biological possibilities of his race. In so far as all environments are really functions of time, or, to put it another way, we measure the nature of an environment by the length of time it takes to produce a certain result, it is quite a natural sequence to consider the effect of time, that is, age on fertility. Dr Matthews Duncan and others have dealt with the immediate effect of time, that is personal age, and the question of the transmitted effect, if any, remains to be considered. If the idea that a species which is dying out tends to reproduce more rapidly, holds good for man, then our previous finding, that the later born do not on the average live so long as the earlier born, would suggest that they might possess as compensation an enhanced fertility. To solve this problem we must correlate the number of offspring produced by each unit with the age of the parents when he or she was born, the reproductive period being made constant.