TEADITION AND HEKEDITY 443 



to speak. The absence of all mammals, with the exception of 

 marsupials, from AustraUa is well known, and the handicap 

 resulting therefrom is obvious. There are, however, certain 

 broad facts with regard to fertility and geographical configuration 

 to which attention may be drawn here. With respect to the 

 fertility of tropical regions in general there are two facts of 

 importance. For the most part cereals are absent, and it is chiefly 

 trees and roots among indigenous plants which lend themselves 

 to domestication. Arboriculture and root-culture, however, do 

 not in many respects give as good a return as does the culture 

 of cereals. Further, fruits and roots cannot be stored as a rule ; 

 their food value is not high, and in many ways the problems 

 presented by the cultivation of roots and trees do not afford 

 anything like the same stimulus to skill or require anything like 

 the same advance in social organization and in settled and 

 regulated conditions of life as does the cultivation of cereals. 

 Again, in the general make-up of tropical conditions there is 

 frequently an element of destructiveness. The rapidity with 

 which in tropical Africa products of human handiwork are 

 destroyed is well known, and to a greater or less degree some- 

 thing of the kind is a feature of all tropical regions. 



7. Turning to geographical conditions in general as favouring 

 or hindering contact we find America isolated and, as a land 

 mass taken by itself, practically divided into two parts in which 

 the conditions do not markedly favour contact — especially 

 contact between different economic systems in close proximity. 

 The remaining land masses may be thought of as radiating out 

 from one centre. The central area is not only in general favourably 

 located, but is in itself so formed as to favour contact. The 

 diversity of its surface, the inland seas, the steppes, plateaux, 

 mountain uplands, plains, and river valleys render it in this 

 respect richly endowed. Forests were less of a barrier to contact 

 in this region than elsewhere, and in this respect Western Asia 

 was better situated than Europe. Tropical forests and jungles 

 form far more serious barriers than do forests in temperate regions, 

 and the discovery of the use of metals is of less effect in reducing 

 the hindrances due to this barrier in tropical than in temperate 

 countries. Looking at the tracts of land which radiate out from 

 this centre we see how isolated is the greater part of Africa. 

 Egypt is indeed almost a part of the Western Asiatic region, but 



