Sex Rat/0 of ail Aranead 451 



preserve, ceteris paribus^ those races in which the females are 

 either most reproductive or else most caretaking of their young, 

 and in which there is at the same time a sufficiency of males to 

 insure the needed fertilization of the eggs. Within a given species 

 the male ratio would be subject to individual variation: some 

 females would produce a preponderanceof males, othersof females. 

 In the breeding area of such a species different groups of individ- 

 uals would come to show different male ratios, just according to 

 the productive peculiarities of their females, and in agreement with 

 what we understand of the action of segregation or physiological 

 selection in general. There would be groups with an unneces- 

 sarily large male ratio, others with the male ratio injuriously 

 small, others with the male ratio just rightly proportioned to the 

 number of females to be impregnated. An excessively high male 

 ratio would be a waste of males, and too low a male ratio a waste 

 of eggs because then all the eggs could not become fertilized; in 

 both these cases there would be an overplus of individuals that 

 would not be of service in procreation. Accordingly, selection 

 would preserve such groups of individuals in which the male 

 ratio is most nicely proportioned, most closely proportioned, to 

 the number of females needing to be impregnated. It would pre- 

 serve them because they would leave the most offspring. The 

 other segregations of individuals would become eliminated because 

 they include a waste of energies and individuals. Selection and 

 segregation would certainly be efficient factors, while it is more 

 doubtful whether heredity would also play a part. 



What the male ratio would be in a particular species would 

 vary with different conditions, and particularly with differences 

 in the mode of life of the sexes. Where the sexes are most alike 

 in general habits of life, where internal impregnation of the female 

 is necessary and where the male cannot impregnate more than one 

 female, the proportion of the sexes would be most equal. Where 

 the males are physically quite as strong or even stronger than the 

 females, and where the male has the habit of impregnating several 

 females, it might be that the male ratio would sink below i ; 

 whether polygamous gregarious species should be reckoned here we 

 cannot say offhand, for the number of males born should be higher 



