CHAPTER VI 



THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 



To every one who has paid the slightest attention to the 

 subject, it is a familiar fact that different parts of the earth 

 have different animals ; school-children learn from their 

 geographies that kangaroos are found in Australia, the Hippo- 

 potamus in Africa, the Tiger in southern Asia, armadillos and 

 llamas in South America. These examples are all taken 

 from distant lands, yet the zoological difference between two 

 given land-areas is by no means proportional to the distance 

 between them. An Englishman landing in Japan finds him- 

 self surrounded by animals and plants very like and often iden- 

 tical with those which he left at home, while the narrow Strait 

 of Lombok, east of Java, separates two profoundly different 

 regions. In crossing Mexico from east to west, the traveller 

 meets very different animals in closely adjacent areas ; and, 

 at first sight, the arrangement of animals appears to be so 

 capricious as to admit of no formulation in general laws. 



In pre-Darwinian times, when it was the almost universal 

 belief that each species had been separately created and was 

 exactly fitted to the region which it inhabits, no explanation 

 of the geographical arrangement of animals was possible, but 

 the acceptance of the theory of evolution demanded that such 

 an explanation should be found. A failure to devise any ra- 

 tional and satisfactory account of the geography of animal 

 life would be a fatal weakness in the evolutionary theory, hence 

 the facts of distribution were subjected to a renewed and search- 

 ing analysis as one of the best means of critically testing the 

 new doctrine. Not that the subject had received no attention 



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