Sexual and Artificial Selection. 115 



CHAPTER XVII. 



SEXUAL, AND ARTIFICIAL SELECTION. 



It has been stated that the prevertebrate types in the ancestral line 

 to which our race belongs were hermaphrodite. The first differentia- 

 tion into male and female occurred in an animal equivalent to the Am- 

 phioxus, and consisted of a differentiation of the reproductive organs 

 only, which being internal left the male and female indistinguishable. 

 The female ova and the male spermatozoa being thrown into the water 

 found each other without care or intervention from the parents. But in 

 the course of evolution there came about a condition of things in which 

 greater certainty in the impregnation of the ova became essential, the 

 number of the ova diminishing with the increase in the race develop- 

 ment and with the certainty of the impregnation and safety of egg 

 when impregnated. When the impregnation of the ova became internal 

 in the body of the female, as in reptiles and mammals, a choice or se- 

 lection of males became possible. Especially is that the case when the 

 services of the male are not required in the care of the young, for then 

 polygamy is possible and a single male may mate with several females 

 to the exclusion of several males. The selection of this single mate is 

 sometimes made by the females interested, but more often is settled by 

 contest among the males, the largest, most vigorous and active usually 

 coming out ahead, and becoming the father of the next generation. 

 This sort of selection will tend to the general improvement of the race 

 in both sexes, since the qualities of both parents are transmitted to both 

 the male and female offspring. Nevertheless there are qualities which 

 transmiss ible through either sex, only appear and are developed in one. 

 Obviously the exclusively male qualities will appear only in the male 

 offspring and the female in female offspring. But along with these are 

 collateral and parallel developments that follow sex more or less closely 

 and only appear in the proper sex. This law of collateral development 

 will be mentioned further on. By it the qualities of courage and pug- 

 nacity, and the accompanying size, strength and anatomical peculiarities 

 by which the males are selected to be parents, are inherited by the male 

 offspring. The infinite repetition of this selective process accumulating 

 masculine advantages, without a parallel competition among the females, 

 amply accounts for the difference in size and strength between the two 

 sexes throughout the mammalian class, especially the polygamists of the 

 class ; also for the superior development in the males of such weapons 

 of war as spurs and horns, and such aids to defense as the mane of the 

 male lion and the shoulder pad of the boar. According to Darwin the 

 male alligator and salmon contend for the possession of the female. 



