CHAPTER X 

 ZOOGEOGRAPHICAL REGIONS 



We have now surveyed those natural regions of the 

 earth described in the Introduction, and have noted 

 their more important occupants, and the adaptations 

 which these show to their particular habitats. In the 

 course of these descriptions it has become obvious that 

 what may be called the raw material upon which 

 adaptation has worked is not the same in all parts of 

 the globe. We have found that animals inhabiting 

 dense forest generally show certain arboreal adaptations, 

 such as the prehensile tail, the opposable thumb and 

 great toe, and so forth, found wherever the forest 

 occurs. But in New Guinea, for example, certain 

 kangaroos have taken to the trees and become arboreal ; 

 in Madagascar lemurs swarm in the forests ; in South 

 America particular kinds of monkeys, the opossums, 

 and the sloths, as well as other animals, people the 

 selvas, and so on. In other words, each isolated forest, 

 or other area, has its own types of adapted animals. 



The only possible explanation of these conditions is 

 the hypothesis that the specialized forms in each 

 separate region have been evolved from pre-existing 

 unspecialized forms inhabiting the region. In South 

 America we find fossil representatives of ground sloths. 

 These have long since become extinct, and the exist- 

 ing sloths have apparently been saved from a hke 

 fate by the acquisition of marked arboreal characters, 

 which protect them from many possible enemies. In 

 the continent of Australia, and parts of the adjacent 



