116 Dynamic Theory. 



Among the most remarkable examples of sexual selection are the 

 seals, in most of which there is great disproportion in the size of the 

 sexes. In the Falkland Otary or Fur Seal of commerce the full grown 

 male according to Weddell measures six feet, nine inches in length and 

 the female only three feet, six inches. ll lt is polygamous in the pro- 

 portion of one male to twenty females." 1 The Inia, a Cetacean mam- 

 mal is also remarkable for the disparity of sexes, a female measuring 

 about seven feet in length and a male about fourteen. 2 The female 

 orang is smaller and the female gorilla is much smaller than the male. 

 The disparity of the sexes in our own race is due in the first instance to 

 the practice of polygamy just as in the case of other mammals. 



Among some animals the females exercise an elective power over the 

 males based upon the attractive personal qualities of the latter. This is 

 true especially of birds, and no doubt the peculiar and generally superior 

 plumage and singing qualities of the male over the female birds is due 

 to the infinite accumulations of feminine preferences. The inequality be- 

 tween the sexes is therefore a necessary consequence of that division of 

 labor by which the ovary and its products were assigned to the keeping 

 of one individual and the testis and its products to another. And such 

 division of labor and the differentiation of parts to suit its performance 

 is as we shall see, the sum and essence of evolution. 



Different races of animals exercise upon one another very considerable 

 powers of selection. Geology shows that there has always been some 

 one dominant race at the head of the animal kingdom. The dominant 

 race has been superior to the others in power, has exterminated those of 

 them that were rivals, fed upon others suitable for food and caused all 

 with which it came into contact to assume new modes of defense and 

 habits of life. The accession to power of a new dominant race has al- 

 ways been followed by a dwindling in the number and generally in the 

 size, power and importance of the preceding dominant race. Thus the 

 accession of the Cephalopod Orthoceras in the Silurian times was fol- 

 lowed by the dwindling and disappearance of the Trilobite, which had 

 been the ruling race. The Orthoceras retired and took a subordinate 

 place when the vertebrate Selachians came upon the scene. 



In Mesozoic times the great Saurian reptiles became the dominating 

 types and the seat of the dominion of the earth was .gradually transferred 

 from the sea to the land. The great Saurians retired on the accession 

 of the land mammals, the Elephant, the Stag, the Bison, and the great 

 Carnivores, and these in turn have given way before man. Aside from 

 or in addition to the primary action of the general forces of nature in 

 developing these new types and in giving a backset to the old ones this 

 secondary action of the types upon one another is of very great import- 



1 Cuvier Animal Kingdom, P. 87. 2 (Juvier 136. 



