CHAPTER XVIII 



THE DETERMINATION OF SEX 

 SECTION I THEORIES 



The desire to control the sex, or at least to predict what it 

 will be, is a very old and a very common one. There are 

 apparently about as many theories purporting to cover the case 

 as human ingenuity has been able to devise (more than five 

 hundred are now known), 1 and as there is but one alternative in 

 the case, any theory, no matter how absurd, is certain, under the 

 law of probabilities, to come true half the time. Some of the 

 principal theories that have gained popular credence, and which, 

 so far as present knowledge goes, contain no basis of truth, are 

 the following : 



1. That one testicle is naturally male, the other female, and 

 that the sex will depend upon the source of the particular sper- 

 matozoon taking part in fertilization. Disproved by the fact 

 that males with but one testicle are yet able to sire both sexes. 



2. That successive ova are alternately male and female, so 

 that naturally the sexes would be evenly distributed, and all 

 that is needed to produce sex at will is to choose the proper 

 heat for service ; that is to say, if the last young were a female, 

 then service at the first, third, fifth, etc., heats thereafter would 

 produce males, and at the second, fourth, sixth, etc., heats would 

 result in females. Disproved in the same way as is the first 

 theory ; that is to say, females with but one ovary produce 

 both sexes, and the same sex is repeated indefinitely, with no 

 alternation in heats. 



3. That the stronger personality, especially in a sexual sense, 

 will impress its sex upon the offspring. Disproved by the fact 

 that parents of both sorts produce both sexes freely, and by the 

 further fact that in general sires are better bred and stronger 



1 Geddes and Thomson, Evolution of Sex, p. 35. 

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