68 PRODUCTION OF NATIONALITY 



divergent modification, whether the forces at work 

 be those that can be referred to the principle of 

 natural selection, or whether they are to be attri- 

 buted chiefly to the direct influence of the circum- 

 ambient media. If a group, consisting of members 

 originally similar, be divided into two isolated groups, 

 the combination of the circumambient media is 

 certain to differ in the two cases, and thus, partly 

 by selection, partly by repeated action in each 

 generation, the isolated divisions will be moulded in 

 different directions. 



Geographical separation is the most direct form 

 of isolation, and much of the work of Darwin, 

 Wallace and their successors has been directed 

 towards tracing how changes of level have raised 

 scattered islands into archipelagoes, archipelagoes 

 into continents, have joined and separated conti- 

 nents, have degraded them again into islands, so 

 shuffling, redealing and shuffling again the species 

 of animals and plants. They have discussed the 

 effect of the barriers presented by arms of the sea, 

 by rivers and mountain chains, by forests and 

 deserts. The mere fact that nations occupy different 

 geographical areas brings about a relative isolation 

 of the peoples, for most individuals of modern popu- 

 lations are as surely fixed to their native soil as 

 rooted plants and slow-moving animals. At first 

 sight it would seem as if modern man, with his 

 greater powers of prevision, intelligence and mechani- 

 cal locomotion must be free from the limits of geo- 

 graphy. But it is not so. An animal or a savage 

 has only the convenience of the moment to tie him 

 to any spot, and as his world is little more than 



