THE EVIDENCE FOR ORGANIC EVOLUTION 



521 



but it becomes intelligible when we examine the geologic distribu- 

 tion (Fig. 280). As shown by the fossil record, camels originated 

 as a family of hoofed animals in North America, where they 

 flourished from the Eocene to the end of the Pliocene epoch. 

 During the Pliocene they migrated, on the one hand to South 

 America, and on the other to Asia by way of a former land con^ 



Fig. 280. — Evolution of the camel familj- from Eocene Period of early- 

 Tertiary (c/. Time-scales, Figs. 259 and 276). 



(Figiires from Scott, "Theory of Evolution," copyright, 1917, by The Macmillan Co., 

 printed by permission.) 



nection in the Bering Sea region. The extinction of the North 

 American forms at the close of the Pliocene left representatives in 

 South America and Asia from which existing species have 

 descended. The seemingly inexplicable separation of the two 

 branches of the family thus finds an explanation in terms of evolu- 

 tion and the past migrations of animals. Numerous examples 



