TKADITION AND HEKEDITY 445 



relative to conditions in Western Asia, offers far less stimulus to 

 progress. Further the general configuration of the land does not 

 favour contact as in the latter region. Nevertheless considerable 

 progress in cereal culture and in the domestication of animals 

 had been made, and in Mexico and Peru, where the presence of 

 lakes, the absence of formidable barriers, and the diversity of 

 surroundings offered by the proximity of high and low land 

 rendered contact most effective, there had grown up societies 

 with a relatively high level of skill. But America had" lagged 

 behind Eur-Asia, and the degree to which this was so is only what 

 would be expected if we suppose that the innate capacity 

 of the inhabitants of both regions was once approximately equal 

 and that, while some had wandered into less favourable surround- 

 ings, others had remained in or migrated to more favourable 

 surroundings. It is at least clear that if we do set the general 

 trend of events in America against events in Eur-Asia there is 

 nothing incompatible with the theory that the constitution of the 

 environment can account in the main for the differences in the 

 growth and accumulation of skill. 



Putting America aside, the same may be said of events elsewhere. 

 The rich endowment of Western Asia has been emphasized, and this 

 region appears to have been the centre of progress in the first 

 period and was most certainly so in the second and during the 

 earlier part of the third period. Everything leads us to suppose 

 that at any given timet up to a comparatively recent date the 

 level of skill was higher in this region than elsewhere. From time 

 to time waves of migration spread outwards most often appar- 

 ently into Europe and less often into Africa and Oceania carrying 

 with them a degree of skill so much higher than that existing in 

 the outlying areas that an abrupt transition to another culture 

 took place accompanied by varying degrees of extermination of, 

 and mixture with, the races situated there. If we bear in mind the 

 endowment of, and general conditions in, Africa and Oceania, 

 the trend of events in these regions is again comprehensible on the 

 same principles as those indicated above. It may also be observed 

 that the principle of the shifting of the centre of progress owing to 

 the change in relative fertility may be seen at work in Western 

 Asia. At a certain period, for instance, after a particular degree 

 of civilization had been reached, the great river valleys of the Nile 

 and of the Tigris and the Euphrates, which formerly had been 



