E.— GEOGRAPHY. 07 



which the members of u coiumunily disjjlay, llie tools which they use, 

 the kind of Icnowledge which they a.ccuinulate, tlieir modes of organisa- 

 tion, their type of material wealth, their traditions and ideals, which 

 show the environmental imprint most closely, far more closely than 

 the colom" of their skins oi- tlie shape of their heads. 



But when and how ditl the change in the two modes of response 

 come about? To answer this question let us recall what has been 

 already said as to the importance of fixation and isolation in the case 

 of animals. The surface of the earth is almost infinitely diverse, and 

 what the biologists call natural barriers, the major barriers like deserts, 

 seas and mountain chains, or the minor ones produced by the transition 

 ffom one type of plant formation to another — e.g. from the forested 

 river valley to the grass-co'vered upland — separate different types of 

 environment, and form obstacles to the distribution of most land 

 animals. There must have been a time when groups of men, no less 

 tilian the pigs in the foresti or the asses on the steppe, were firmly 

 gripped by the physical conditions, were isolated from other gi'oups, 

 forced to become fitted by structm-e and habit for a pai'ticular set of 

 conditions, or to die out. But with his growing intelligence man 

 escaped from this u'on grip, learnt to make virtually eveiy part of the 

 surface yield enough for survival, proved capable O'f overcoming every 

 kind of natm'al barrier. When this occuiTed the old mechanism of 

 adaptation largely — though not completely — ceased to work. Evolution 

 then might have ceased also, man might have become specially fitted to 

 no environment because fitted for all, if the factors of fixation and 

 isolation had not, in quite a different fashion, obtained a new hold. 



He ceased, save in relatively few parts of the earth's surface, to 

 be a continuous wanderer. He settled down afresh on particular parts 

 of it, and there learnt to use his increasingly complex brain not only 

 in utilising to their full the natural resources, but also in modifying the 

 local conditions so that new resources became available. In other 

 words, I wish to suggest that the cultivation' of the soil was the great 

 agent in ensuring the new type of fixation to a particular area which 

 once again made evolution possible. But evolution now took the form 

 of increasing development of communal life, or, in other words, the 

 growth of what we call civilisation is the precise equivalent of specific 

 differences in plant or animal. 



Further, just as, in the case of the animal, isolation is necessary 

 before an incipient species can become fixed, so in the case of human 

 conununities a measure of protection from the inhabitants of neigh- 

 booming areas — a measure, that is, of isolation — is essential before 

 civilisation can develop. 



Again, in the case alike of plants and animals we know that where 

 the local conditions are such that the incipient species is limited to a 

 very narrow area, there highly specialised forms of adaptation may 

 occur, as they do, for example, on many islands, or in isolated mountain 

 chains ; but that specialised type of development is associated with the 

 loss of the capacity to vary, to acquire adaptations fitting the organism 

 for a wider area. So in the case of human communities, where the 

 isolation is too complete the power of adaptation tends to be lost, 

 and such groups, though their civilisation may, along its own lines, 



