MAN AND MANKIND 



sliock and gradually increased by selection their capacity for resis- 

 tance. Small groups, like the South Sea and Andaman islanders, 

 rapidly succumbed to diseases like measles, to which larger and 

 more exposed populations had become resistant. Such small 

 populations are often wiped out in this way. Highly fitted to 

 their previous conditions, they are not flexible enough to survive 

 the change. 



The great alternations of inbreeding and outbreeding, which 

 destroy old races and their empires, and establish new ones, have 

 the same effect on the smaller groups within them. Every nation 

 is subdivided into economic and cultural groups which w^e call 

 classes. The classes adapt themselves continually to special functions 

 in a changing society. The most important of these (whose function 

 is also changing with changes in the means of production) is the 

 governing class. All governing classes have the aim and the ability 

 to remove themselves from the pressure of natural selection. But 

 the mating systems they favour lie between the usual extremes. 

 Governing classes which adhere to the most exclusive inbreeding 

 are always overthrown through lack of genetic flexibility when 

 conditions change, either from inside or outside their empire. 

 Governing classes which allow of a social osmosis, a not too limited 

 diffusion by intermarriage like that in Rome under the Empire, 

 often succeed in surviving, with appropriate dilution, very drastic 

 cultural changes. 



Those who favour the opposite extreme to an Indian caste system, 

 an indifferent, classless unadapted heterogeneity of the whole of the 

 community may look to polygamous societies for an example of 

 how it works. One of these appears as a convenient control in the 

 Mohammedan population of India. Polygamy can never be effective 

 except for a wealthy governing or conquering group. But such 

 a group cannot be a class in a strict hereditary sense since polygamy 

 implies recruitment or dilution from below, or from the outside, 

 on a vast scale in every generation. Moreover the governing group 

 propagates itself from women selected for their value as individuals 

 in a harem, and not for their parentage or their position in society. 

 It seems to be this method which permitted the explosive growth 

 of Islam by a series of unprecedented conquests over a period of 

 1,000 years. But each explosion has been followed by a somewhat 



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