THE ARGUMENT FROM PALEONTOLOGY 73 



renders it impossible that identical conditions could 

 have been acquired twice independently. The 

 fact that the two groups of camels agree in a large 

 number of points, in which they differ from all other 

 animals of the same class, must be taken as a proof 

 of near blood-relationship. 



Near blood-relationship means common origin — 

 i.e., one of the two groups of camels must be 

 descended from the other, or both groups must be 

 descended from some common ancestors, which were 

 already camels. In other words, either the new- 

 world camels must be descended from the old-world 

 camels, or vice versa; or both must be descended 

 from camels that formerly lived elsewhere, but are 

 now extinct. 



Our problem is now becoming more clearly 

 denned, and we have to consider the means of 

 migration of mammals. The only means of migra- 

 tion is by walking ; for although most of them can 

 swim, it is only for short distances, and it is doubtful 

 whether any land mammal can swim across an arm 

 of sea fifty miles wide. Captain Webb's swim across 

 the Channel has perhaps never been beaten by a 

 land mammal. The practical proof of the efficacy 

 of the sea as a barrier to migration is seen in the 

 fact of the absence in most oceanic islands of indi- 

 genous mammals, except bats. To put it in plain 

 words, if mammals are to get from one place to 

 another, they must walk. 



The only explanation possible is through fossils, 

 which thus have a new interest, depending on what 

 parts of the earth we find them in. The evidence 



