SECTION D.— ZOOLOGY. 



THE SEX RATIO 



ADDRESS BY 



PROF. F. A. E. CREW, D.Sc, 



PRESIDENT OF THE SECTION. 



Of the thousands of zoological papers that appear in the course of a year 

 few surpass in interest the Statistical Review of the Registrar-General. 

 Its pages are crowded with irresistible invitations to thought, and nowhere 

 else can be encountered greater incentives to further inquiry through 

 observation and experimentation. Its title and address do not disguise 

 its real nature, for it deals with phenomena that are essentially zoological — 

 with growth, multiplication, natality and mortality in an animal population, 

 and with the results of the interplay of living animal and varying environ- 

 ment. It is, in fact, a progress report of a vast and exciting zoological 

 experiment which we are conducting, scientifically or otherwise, with 

 ourselves as the experimental material. For this reason alone it commands 

 the attention of the zoologist. 



But there is another and even more cogent reason why we should 

 study this Review. Many of the data presented therein can be inter- 

 preted correctly only by such as can bring to their examination knowledge 

 derived from a comparative study of a number of different living forms. 

 Much concerning man must remain incomprehensible until the answers 

 to our questions are sought amongst the structures and behaviours of 

 other and sometimes quite lowly animals. 



An excellent illustration of this contention is provided by the figures 

 in this Review which relate to the human sex ratio. Nothing is 

 easier than to demonstrate that for an understanding of the somewhat 

 startling and certainly intriguing facts concerning the relative numerical 

 proportions of the sexes in a human population we are inevitably forced 

 to make a comparative survey of the sex ratio amongst other mammals, 

 birds and insects, wild and domesticated, both in the open and under 

 the controlled conditions of experimentation. In this matter of the sex 

 ratio, to know only man is to understand nothing. 



This subject of the numerical proportions of the sexes in a population 

 is of such obvious interest to the naturalist, the sociologist, the economist 

 amongst others, that it is not surprising to find that to it considerable 

 attention has been paid. But so complicated are the problems that cluster 

 round it that even yet our understanding of the significance of the sex 

 ratio is still very incomplete. It will be remembered that Darwin (1871), 

 in discussing the influence of natural selection on the sex ratio, made the 



