522 THE THEORY OF EVOLUTION 



could be cited, all showing that the evolutionary theory gives 

 meaning to the geographical distribution in special types of animals. 

 In many cases it is possible to explain the peculiarities of a whole 

 fauna, which is the name applied to the animal population of any 

 particular locality, by the extension of a similar line of reasoning. 

 Island life is an illustration. There are, geologically speaking, two 

 types of islands in the ocean: continental islands, like the British 

 Isles and our own Long Island; and oceanic islands, like the 

 Azores, Bermuda, and the Hawaiian Islands. The former are not 

 far from continents, of which they seem to have been once a part; 

 the latter are islands that have appeared in the ocean without pre- 

 vious connection with any continent, or surviving elevations of 

 continents that have existed in the past but have never been united 

 with the well-known continental areas. The faunas that are 

 found upon these two types of islands bear out the theories of their 

 geologic origin and of the origin of faunas by evolutionary processes. 

 Without going into details, it may be said that the native fauna of 

 the British Isles is like that of northwestern Europe, because these 

 islands were recently part of the neighboring continent. The native 

 fauna of the Hawaiian Islands, on the other hand, is an odd mixture 

 and unlike that of any continent, because these islands have had no 

 recent connection with any continent and were presumably popu- 

 lated by animals and plants Ijrought to them by chance, on floating 

 objects or otherwise. Only from some such parentage could such 

 bizarre combinations be expected to originate as occur on oceanic 

 islands. Again, the continent of Australia has a fauna very dif- 

 ferent from that of Asia, because the two have been so long 

 separated. Eurasia, Africa, and North America have similar 

 mammalian faunas, because of former connections across Bering 

 Sea and Greenland. As elsewhere, the argument is that the facts 

 find a more reasonable explanation in the theory of evolution than 

 in any other theory. 



Evidence from Physiology 



General Physiology. — The similarity of the great physiological 

 functions of metabolism, irritability, and reproduction is addi- 

 tional evidence for evolution. Since all forms of animal life agree 

 in these fundamental processes, one may reasonably suppose that 

 all have descended from an ancestral protoplasm which functioned 

 in this manner. Taken alone, this general uniformity of functions 



