BREEDING SYSTEMS 



intellectual control. Thus the whole of mankind consists of groups 

 which arc separated by race, language, general culture and economic 

 status. Between these groups mating is discouraged. Within them, 

 therefore, inbreeding is encouraged. At the same time extreme 

 inbreeding is discouraged almost universally by the prohibition of 

 incest. The rare exceptions to this rule are of great interest and 

 are of many different kinds and degrees according to whether they 

 occur in a homogeneous group, as in the Royal Families where 

 inbreeding was sometimes but not usually cumulative, or in an 

 extremely heterogeneous group like the populations of the islands 

 already mentioned. 



Inbreeding, to the degree described elsewhere as incest, and 

 existing as a continuous social habit, probably survives only in a 

 few primitive tribes of southern Asia. One of its most interesting 

 forms was in the Emadan tribe of Malabar in which the father of a 

 family habitually took his eldest daughter as his second wife. Such 

 a system probably represents a dying vestige of earlier inbreeding 

 systems which have been killed wherever, as in Australia, migration 

 and conquest are easy, by the diffusion of more successful systems 

 of outbreeding, often carrying with them diseases which inbred 

 populations, as we shall see, are not flexible enough to resist. 



Here we are assuming that natural selection will operate on 

 breeding systems which are culturally determined and not therefore 

 directly under genetic control. This is an assumption required only 

 in the field of human genetics, but it has serious implications for 

 the evolution of man. 



The succession of outbreeding by inbreeding causes human society 

 to be continually breaking up into small groups, races and tribes, 

 castes and classes. These groups resemble the races of animals and 

 plants except in one important particular : they are consciously made 

 by man himself and not by external or genetic accidents. Throughout 

 history these groups are as continually being broken down by man's 

 own activities, by conquest, slavery, conversion, and mere migra- 

 tion. There is, therefore, an alternation of inbreeding and out- 

 breeding of a rapidity unknown in any other organism and 

 successively favouring fitness and flexibility, the rises and falls of 

 races and classes. 



Owing to the rapid changes in his cultural capacity and economic 



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