112 SECTIONAL ADDRESSES 



of sex differences in mortality have to be considered : (i) sex-linked 

 lethals, (2) sex-limitation of defects and derangements, and (3) sex- 

 dimorphic physiological and endocrinological differences. It seems 

 probable that sex-linked lethals play only a minor part and that the defects 

 and derangements that have come to be manifested only or more completely 

 in the male owing to his relative unimportance in respect of propagation, 

 constitute the major cause, though as yet too little is known of sex differ- 

 ences in respect of hormones and their effects to permit us to regard these 

 as unimportant. For your pleasure and my own I have attempted to 

 construct a thought-model of a genetic mechanism that could yield what 

 I have called an optimum reproductive sex ratio ranging as this may 

 from equality to the grossest inequality. I have tried to reconcile the 

 views of the geneticist and of the physiologist out of whose disputations 

 has emerged a clear recognition of the need for a closer collaboration. 

 I have shown, I hope, that the problem of the human sex ratio must be 

 studied not only in the office of the statistician but also in the laboratory 

 of the experimental biologist and in the open country, and I have stressed 

 the view that out of the secondary sex ratio can be fashioned an instrument 

 of precision by the use of which a human society may measure the quality 

 of its structure. 



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