ARGUMENTS FOR EVOLUTION 5 



ing age of the rocks that contain their fossils, 

 and that during the remotest geological age 

 from which relics of life have come down to us, 

 no animal existed so highly developed as a fish. 

 The growth of the embryos of the higher animals 

 presents phases that appear to illustrate by 

 repetition the course of their progenitors' develop- 

 ment up the animal kingdom, exhibiting in transi- 

 tory stages the likenesses of adult forms that have 

 become extinct. The human embryo, for instance, 

 at one stage of its growth, is actually equipped with 

 gill-clefts, such as those through which fish pass the 

 water that gives oxygen to their blood. Useless 

 organs survive which can only be relics of an 

 outgrown constitution. There are rudiments of 

 hind legs in whales and boa- constrictors. Monkeys 

 have pointed ears, and from time to time children 

 are born possessing them. We all retain muscles 

 for moving the ears, although very few can use 

 them. And every baby confesses its kinship with 

 the monkeys by the disproportionate strength 

 of its arm muscles a necessary endowment in the 

 days when mothers sprang about the branches of 

 an arboreal home. The peculiar character of the 

 animals and plants of oceanic islands indicates 

 very forcibly that species have originated by 

 development, and that, remote from outside 

 influences, they have undergone changes along 

 special lines of their own. That differences, as 

 marked as those which distinguish one species 

 from another, can come about by development is 

 proved by the varied forms of our domesticated 

 animals : admitting that a Pekinese is akin to a 

 bulldog, we cannot deny that there may be 

 blood relationship between the horse and the 

 donkey. We may be unwilling to believe that 

 man is the last shoot of a genealogical tree that 

 extends down the length of the animal kingdom. 



