THE FACTORS WHICH DETERMINE SEX 685 



unfavourable ones towards the development of males, and certain of 

 the evidence referred to above (p. 662) has been cited by them in 

 support of this hypothesis. The normal female metabolism is said 

 to be relatively anabolic, while the greater activity of the male is 

 held to indicate a preponderance of katabolic conditions. Conse- 

 quently the generalisation is reached that abundant or rich nutrition 

 (or any other favourable circumstance) tends to induce an anabolic 

 habit, and so favours the development of females; and conversely, 

 that deficiency of the necessary food supply (or any adverse 

 circumstance) leads to a katabolic condition of life, and so causes 

 the production of males. According to this idea, the organism is 

 at first "sexually indifferent," the sex becoming established at 

 varying periods of development in different animals according to 

 the circumstances. Thomson has subsequently admitted that some of 

 the evidence which was formerly adduced in support of this view 

 has been invalidated, since in a very large number of animals sex 

 appears to be fixed in the fertilised ovum or earlier, and con- 

 sequently subsequent conditions of nutrition ordinarily play no 

 part in determining the relative proportion of males and females. 

 But Thomson is still disposed to lay stress on the connection 

 between sex and metabolism, believing that the determinants for 

 each of the sexual characteristics (both male and female) are present 

 in all ova and in all sperms, and that their liberation or latency 

 depends on a bias towards egg- production or sperm-production. 

 The so-called contrasted peculiarities of the two sexes are due in 

 certain cases "to internal physiological conditions which give the 

 same primordium two different expressions, much less different than 

 they seem." l 



Riddle 2 has elaborated a theory of sex- determination which is 

 somewhat similar to that of Geddes and Thomson ; but Riddle's 

 view is based on experimental evidence obtained from a prolonged 

 study of sex-phenomena in doves and pigeons. This investigator 

 interprets sexual differentiation as the expression of quantitative 

 differences in the rate of protoplasmic activity, the more active 

 metabolism being associated with a production of males, and the 

 less active with females. The theory is elaborately worked out, and 

 it is shown that much of the accumulated evidence on this question 

 supports (e.g. see above, p. 668) the view that the preponderance of 



1 Thomson, Heredity, London, 1908. 



2 Riddle, " The Determination of Sex and its Experimental Control," Bull. 

 Aimer. Acad. Med., vol. xv., 1914. "Sex-control and Known Correlations in 

 Pigeons," Amer. Nat., vol. 1., 1916. "A Quantitative Basis of Sex, etc.," Science, 

 vol. xxxix., 1914. " The Theory of Sex, etc.," Science, vol. xlvi., 1917. " A Note 

 on Social Aspects of New Data on the Biology of Sex," Jour. National Inst. of 

 Social Sciences, 1915. See also Jennings, Riddle, and Castle, Lectures on Heredity, 

 Washington, 1917. 



