is. j PALEONTOLOGY AND EVOLUTION. 297 



Glacial epoch, during which the excessive cold, to say 

 nothing of depression and ice-covering, must have almost 

 depopulated all the northern parts of Arctogaea, destroy 

 ing all the higher mammalian forms, except those which, 

 like the Elephant and Ehinoceros, could adjust their 

 coats to the altered conditions. Even these must have 

 been driven away from the greater part of the area ; only 

 those Miocene mammals which had passed into Hin- 

 dostan and into South Africa would escape decimation 

 by such changes in the physical geography of Arctogaea. 

 And when the northern hemisphere passed into its 

 present condition, these lost tribes of the Miocene Fauna 

 were hemmed by the Himalayas, the Sahara, the Eed Sea, 

 and the Arabian deserts, within their present boundaries. 

 Now, on the hypothesis of evolution, there is no sort 

 of difficulty in admitting that the differences between the 

 Miocene forms of the mammalian Fauna and those which 

 exist at present are the results of gradual modification ; 

 and, since such differences in distribution as obtain are 

 readily explained by the changes which have taken place 

 in the physical geography of the world since the Miocene 

 epoch, it is clear that the result of the comparison of the 

 Miocene and present Faunae is distinctly in favour of 

 evolution. Indeed I may go further. I may say that 

 the hypothesis of evolution explains the facts of Miocene, 

 Pliocene, and Recent distribution, and that no other 

 supposition even pretends to account for them. It is, 

 indeed, a conceivable supposition that every species of 

 Khinoceros and every species of Hysena, in the long 

 succession of forms between the Miocene and the present 

 species, was separately constructed out of dust, or out 

 of nothing, by supernatural power ; but until I receive 

 distinct evidence of the fact, I refuse to run the risk of 

 insulting any sane man by supposing that he seriously 

 holds such a notion. 



