396 ANNUAL REPORT SMITHSONIAN INSTITUTION, 192 8 



learned that the opposite process is actively going on; that is, that 

 some mammals are now extending their ranges. In the northeastern 

 United States cottontail rabbits are moving northward and eastward ; 

 coyotes, in spite of organized campaigns for their extermination, are 

 spreading toward the north in Canada and Alaska and possibly 

 toward the east in the United States; even the slow armadillo has 

 pushed the limits of his territory northward across the State of 

 Texas during the memory of men now living. 



All of this shows that the species of mammals, like the lands on 

 which they live, are never still. Life moves about on the surface 

 of the earth in just the same way that this surface is continually 

 moving — being raised, worn down, wetted, dried, covered, denuded, 

 heated, cooled. The geographical distribution of mammals to-day 

 is the result of a long series of wanderings. Something of the his- 

 tory of the earth's land masses can therefore be inferred from the 

 characteristics of the mammals which inhabit them. The striking 

 peculiarities which distinguish the pouched kangaroos and the egg- 

 laying duckbills of Australia from all the mammals known to occur 

 elsewhere point unmistakably to a long geographical isolation of 

 Australia; the similarity of the bears, wolves, hares, and ground 

 squirrels of Alaska to those of eastern Asia points to a very recent 

 land connection between these most nearly contiguous portions of 

 the eastern and western worlds. 



Man in the early stages of his development, before the discovery 

 of artificial means for overcoming natural obstacles, was probably 

 subject to much the same limitations as other mammals. When 

 seaworthy boats were unknown he must have sought ancient land 

 connections to enable him to travel from island to island and irom 

 continent to continent in precisely the same manner that elephants 

 and horses sought these natural highways. Hence an adequate 

 knowledge of the migration routes by which mammals have arrived 

 at their present homelands ought to throw light on the subject of 

 prehistoric human dispersal. 



The great problems now facing mammalogy may therefore be 

 summed up by the words: Description, distribution, relationship, 

 history. Description is the fundamental work on which all subse- 

 quent structures must rest. To attempt the study of distribution, 

 of relationships, of history, or of the exact economic value of mam- 

 mals, without a previous accurate knowledge of the different kinds 

 would be as futile as to attempt to run a railway into a new country 

 without first surveying the land to be traversed. 



