Reprinted from the Journal of the Washington Academy of Sciences 

 Vol. VII, No. 11, June 4, 1917 



GENETICS. — The control of the sex ratio. 1 Oscar Riddle, 

 Department of Experimental Evolution, Cold Spring Har- 

 bor, New York. 



No better way to introduce a discussion of the present sub- 

 ject has occurred to me than to avail myself of the words — 

 written less than three years ago — with which Professor Don- 

 caster begins his very excellent book on The Determination of 

 Sex: 



The question "Is it a boy or a girl?" is perhaps the first which is 

 generally asked about the majority of mankind during the earliest 

 hours of their independent existence; and the query "Will it be a 

 boy or a girl?" must equally often be in the mind, even if it is less 

 frequently expressed in words. This second question raises one of 

 the most widely discussed problems of biology, that of the causes 

 which determine whether any individual shall be male or female, and 

 it suggests the still deeper question, "Why should there be male and 

 female at all?" The problem of the nature and cause of Sex ranks 

 in interest with that of the nature and origin of Life, and it may be 

 that neither can be completely solved apart from the other. Not- 

 withstanding the immense amount of brilliant speculation and re- 

 search which has been devoted to the fundamental problem of Life, 

 it must be admitted that hitherto no satisfactory solution has been 

 found, and in some respects the question of Sex is equally obscure. 

 Hardly any other problem has aroused so much speculation, and about 

 few has there been such great divergence of opinion. In one direction, 

 however, the last few years have seen a considerable advance, and 

 we now know at least something of the causes which lead to the pro- 

 duction of one or the other sex, although of the manner in which these 

 causes act our ignorance is still profound. 



It is but a short step from the question "Is it a boy or a girl?" to 

 the further question "Why is it a girl instead of a boy?" and yet until 

 recently the answer to this latter question seemed hopelessly beyond 

 our grasp, and even now, although some indications of an answer 

 can be given, they do not touch the deeper problems of the real nature 

 of sex. It is a remarkable thing that apart from the fundamental 

 attributes of living matter — irritability, assimilation, growth, and so, 

 forth — no single character is so widely distributed as sex; it occurs in 

 some form in every large group of animals and plants, from the highest 

 to the lowest, and yet of its true nature and meaning we have hardly 

 a suspicion. Other widely distributed characters have obvious func- 

 tions; of the real function of sex we know nothing, and in the rare 

 cases where it seems to have disappeared, the organism thrives to all 



1 A lecture delivered before the Washington Academy of Sciences, March 29, 

 1917, 



