Proportion of Sexes produced by Whites and Coloured Peoples. 33 



the Mendelians will make it so ; at present, perhaps, all that can be said 

 regarding mammals is that the evidence available is in favour of the view 

 that the ovum determines the sex of the offspring in these animals. 



[Now a female mammal produces only a limited number of her ovarian ova 

 during her life, others degenerate and are absorbed, in fact, some ovarian ova 

 survive at the expense of others and it would appear that this process goes 

 on with more or less activity at different times. Thus there is a struggle for 

 existence and a process of selection going on in the mammalian ovary, and 

 this is a very important fact, for the projection into the ovary itself of forces 

 which are undeniably produced by extraneous conditions shows that such 

 conditions must to some extent influence the output of the ovary. 



A wealth of evidence has been adduced by many observers to show that 

 M. and F. larvae are very differently affected by different foods and different 

 climatic conditions, and this evidence is overwhelmingly in favour of the view 

 that F. larvae require more nourishment, more favourable conditions, than do 

 M. larvae for their development. But if this is true for larvae it is surely true 

 also for ovarian ova, and the conclusion may be confidently drawn, that the 

 selection of M. or F. ovarian ova, for production, is liable to be influenced by 

 the food supplied to the ovary by the mother and therefore by the conditions 

 of metabolic activity she experiences. 



As all breeders know, the breeding power of an animal is in direct relation 

 to its metabolic activity, and the metabolic activity of a mother is 

 undoubtedly affected by the food supplied and the climatic conditions she 

 experiences ; thus it would appear that extraneous conditions must exert 

 influence on the proportion of the sexes produced by all animals in which a 

 struggle for existence takes place among the ova in her ovary. 



This view, it appears to me, explains a variety of facts winch have been 

 judged to be contradictory, and brings into line the results of many observa- 

 tions which have hitherto been supposed to favour now one, now another, 

 quite different theory. For instance, all the contradictory evidence I have 

 examined regarding the effect on the sex ratio of the ages of the parents and 

 the times of conception, may be so accounted for, while upon the phenomena 

 concerning sex ratio observed in consequence of crossing or of in-breeding, a 

 new light is thrown which will, I think, go far to show adequate reason for 

 the results obtained for mammals. It must not be supposed that I attribute 

 the proportion of the sexes produced to these agencies alone ; there can be no 

 doubt, in my opinion, that heredity is the main force at work, but it is 

 incontrovertible that variations in that proportion constantly occur, and I 

 maintain that these variations cannot be accounted for by any law of 

 heredity and are referable to those extraneous forces which act as selective 



VOL. LXXXI. — B. D 



