444 TKADITION AND HEREDITY 



it is nearly cut off from the rest of Africa by desert, being connected 

 with the remainder of the continent only by the valley of the Nile 

 which in its middle regions is almost barren while its upper reaches 

 pass through huge tracts of marsh and swamp. As we approach 

 the south of Africa we come to what in primitive times was 

 a blind alley. So, too, in whatever direction We pass outwards 

 from the heart of Eur-Asia, whether we cross the sea to Australia 

 or travel to the eastern or western boundaries of the Eur- Asiatic 

 land mass, we reach regions where, on account of what we may 

 call their location and of other factors such as the presence of 

 forest or jungle or on account of the configuration of their sur* 

 faces, contact is not favoured. We must in addition bear in mind 

 that it is the central region which is the most richly endowed 

 as far as fertility is concerned. 



We may remember that there was another factor to which 

 as a stimulus to the formation of skill and to the transmission 

 and storing of tradition we found reason to attach great impor- 

 tance namely, the replacement of the segmentary by the organic 

 type of social organization. This great change took place in the 

 Eur- Asiatic region and must be traced indirectly to the charac- 

 teristics of that region as a whole. For we found that, before such 

 a change could come about, a growth in the volume of population 

 was necessary, and growth in volume is directly dependent upon 

 fertility and all other elements in the surroundings which favour 

 the increase of skill. 



8. There is, therefore, at the least a very remarkable corre- 

 spondence between the outstanding events of history since the 

 opening of the first period and the distribution in space and time 

 of the chief factors which influence, tradition. We may set 

 events in America up to the time of the discovery against events 

 in the rest of the world. We do not know with what degree of 

 skill the original emigrants were armed ; but since, generally 

 speaking, the fertility of America relative to skill in hunting and 

 fishing is not, if at all, inferior to fertility elsewhere, we have no 

 reason to imagine that progress in the first period would be 

 less rapid than elsewhere. Again the presence, though not in 

 great variety, of easily cultivatable plants would facilitate much 

 as elsewhere the transition to the most primitive form of agricul- 

 ture. But the poverty in cereals and animals fit for domestication 

 and the absence of milch animals indicate an environment which, 



