. ORGANIC EVOLUTION 57 



legerdemain to show why the sloths are confined 

 to South America and the monotremes to Australia 

 and its islands. The reindeer of northern Europe 

 and Asia, and the elk and caribou of Arctic 

 America, are so much alike they must have 

 descended from a common ancestry, and been 

 developed into distinct species since the separation 

 of North America and Eurasia. The same thing 

 is probably also true of the puma and jaguar, who 

 inhabit the middle latitudes of the New World, 

 and the lien, tiger, and leopard, occupying like 

 latitudes of the Old World. They all belong to 

 the cat family, and represent divergences from 

 a common feline type of structure. The camel 

 does not exist normally outside of northern Africa 

 and central and western Asia. And when the 

 camel-like llama of South America first became 

 known to zoologists, it was a problem how this 

 creature could have become separated so far from 

 the apparent origin of the camel family. But 

 since then fossil camels have been found all over 

 both North and South America. And it has even 

 been suspected that perhaps America was the 

 original home of the camel, and that, like the 

 horse, the camel migrated to the eastern hemi- 

 sphere at a time when the eastern and western 

 land masses were connected. The foxes, hares, 

 and other mammals of the upper Alps, also many 

 Alpine plants, are like those of the Arctic regions. 

 The most probable explanation of these resem- 

 blances is that these Alpine species climbed up 

 into these inhospitable altitudes, and were left 



