^2^ EVOLUTION, HEREDITY, EUGENICS 



One of the earliest known theories of sex determination, first put 

 forth by Aristotle, is based on the alternate functioning of the ovaries 

 and on evidence from pregnancies after one ovary has been removed. 

 The right ovary is supposed to produce eggs that develop into males. 

 Experiments with mammals and statistics from hospitals prove this 

 theory worthless. The age and vigor of the parents have also been 

 shown to be of no importance. 



In cattle, Thury, Russell and later Raymond Pearl have pro- 

 duced considerable evidence to prove that matings which take place 

 at the beginning of heat produce a preponderance oi females, while 

 those taking place in the period of heat produce males. In pigeons 

 the eggs produced in the early part of the breeding season will 

 develop into males, while those from the latter part of the breeding 

 season develop \x\to females. Whitman and Riddle have brought 

 out this fact most clearly. 



Riddle believes that sex is a quantitative modifiable character. 

 The males have a higher rate of metabolism, than the females. He 

 concludes ^'^ that from the egg-stage onward through embryonic and 

 adult life the oxidizing powers of the male tend to exceed those of 

 the female, and that it is this tendency which ultimately decides 

 whether male or female shall develop. According to Riddle the two 

 diverse chromosome combinations which ordinarily determine sex 

 really accomplish this by thus providing an " internal genetic pull 

 toward a lower or a higher metabolic rate." This genetic tendency 

 can, however, be overridden by means which specifically establish 

 an opposed rate of metabolism over prolonged periods, particularly 

 over early and critical periods in the differentiation of sex. 



As Riddle has pointed out (Science, 1927. vol. 65, page 139), 

 Goldschmidt (Science, 1926, n. s., vol. 64, page 299) has made no 

 reference to the earlier work of Riddle when (Science, 191 2, n. s., 

 vol. 35, page 462) he first gave evidence for his quantitative theory 

 of sex. Riddle gladly credits Goldschmidt with the discovery that 

 the genes influencing sexuality in the autosomes were not of equal 

 potency in certain races of moths (see Goldschmidt's Enzyme 

 Theory, page 534). 



Certain Germans, including Pryll, Zolner, Ismer and Siegel, 

 published papers during the Great War, indicating that earlier ova 

 develop into males while the later, more mature and possibly better 



1^ Riddle, O. 1916. Sex control and known correlations in pigeons. Amer. Nat., 

 vol. 50, pp. 385-410. 



