THE " SEXUAL SEASON *' OF MAMMALS. 39 



peoples who occupy a low position in the scale of civilisation, 

 but there is also evidence that the latter produce smaller 

 families. 



In some cases this is ascribed to the practice of infant 

 marriage, to the strain of child-bearing on a mother who 

 requires for herself all the nourishment she is capable of 

 assimilating ; but comparatively small families are usual in 

 many savage peoples whose women do not become mothers 

 at a very early age (Westermarck, 1891). 



In these cases the result is probably due not only to pro- 

 longed lactation, or to infant mortality, but to inability to 

 produce more children ; for, as the practice of polygamy 

 shows, the advantage of large families is fully recognised, 

 and each individual woman will be required to reproduce as 

 frequently as possible. 



It would seem highly probable, therefore, that the repro- 

 ductive power of man has increased with civilisation, precisely 

 as it may be increased in the lower animals by domestication; 

 that the effect of a regular supply of good food, together 

 with all the other stimulating factors available and exercised 

 in modern civilised communities, has resulted in such great 

 activity of the generative organs, and so great an increase in 

 the supply of the reproductive elements, that conception in 

 the healthy human female may be said to be possible almost 

 at any time during the reproductive pei'iod. 



We have come to believe that it is to the regular monthly 

 menstrual periods, which the human female generally ex- 

 periences, that this great reproductive power is due. But 

 the evidence of a regular menstruation with a limited con- 

 ception period in monkeys, shows that this is certainly not 

 so. As in monkeys, so in man, these two functions are not 

 necessarily equally developed. 



I think it may fairly be stated that an increase in the 

 frequency of menstruation is not necessarily a sign of an 

 increased power of reproduction among women, and that 

 there is no indication that women who menstruate every two 

 or three weeks are more prolific than those who menstruate 



