MAN AND MANKIND 



power, the equilibria of races and classes in man have always been 

 unstable throughout his history. Secondarily, too, these changes 

 have brouglit logarithmic increase in the total population of the 

 world, which has approximately multiplied itself by ten in each of 

 the last four periods of a hundred generations. It is, however, not 

 merely these cultural and numerical changes (leading to conquests 

 and migrations) that have upset the equilibria of races and classes 

 in human history. All such groups are inherently impermanent 

 owing to the increasing homogeneity and consequent lack of 

 flexibility produced by inbreeding within them. 



The largest inbreeding experiment ever carried out is that of the 

 caste system of India. The caste system breaks up the Hindu com- 

 munity, according to the Indian census, into some 2,300 mating 

 groups. These are of sizes varying from a few hundreds to a few 

 hundred thousands, and of ages varying from i to 50 generations. 

 They differ also in exclusiveness, which in general is increased by the 

 operation of the census itself, and through the imitation of Hindus 

 by Muslims. The remarkable position, however, is often reached 

 that, when all the persons are excluded who are too closely related 

 to marry and also all those who are too remotely related, that is 

 outside the caste, no one but a first cousin is left, and for a woman 

 sometimes only a fraction of that. This must give a very great 

 stability to the flow of variability discussed in our earher chapters. 

 The situation is the opposite of that where outbreeding is suddenly 

 followed by inbreeding. 



With Hinduism, such diffusion as occurs between castes is chiefly 

 by social demotion or out-casting. The social promotion which 

 is characteristic of European systems is available only for women. 

 The whole system can be maintained only by religious conviction, 

 and it shows its effect in reducing the flexibility and initiative of the 

 peoples concerned and of their culture (Fig. 87). 



Where inbreeding is combined with geographical isolation 

 another effect is to produce a homogeneous susceptibility to diseases 

 from which the community has been sheltered. The sudden break- 

 down of this sheltering has been characteristic of the opening up 

 of backward countries since the great navigations. Its consequences 

 are well known. Large groups, like the old world population which 

 received syphilis from America in 1492, recovered from the first 



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