THE EEGULATION OP NUMBEES 223 



of the difficulty of transporting and of suckling more than one 

 child at a time. Abstention from intercourse arises as a taboo. 

 The problem we have to face is how these practices could come 

 to be of the necessary intensity. Now men and groups of men are 

 naturally selected on account of the customs they practise just 

 as they are selected on account of their mental and physical 

 characters. Those groups practising the most advantageous 

 customs will have an advantage in the constant struggle between 

 adjacent groups over those that practise less advantageous 

 customs. Few customs can be more advantageous than those 

 which limit the number of a group to the desirable number, and 

 there is no difficulty in understanding how — once any of these three 

 customs had originated — it would by a process of natural selection 

 come to be so practised that it would produce an approximation 

 to the desirable number. There would grow up an idea that it was 

 the right thing to bring up a certain limited number of children, 

 and the limitation of the family would be enforced by convention. 



Though, however, adjustment is understandable as the result 

 of a natural selection of customs, the evidence shows that there is 

 even among the most primitive race^ at times at least some 

 dehberation as to whether a child shall be allowed to live. In the 

 more advanced races there is increasing evidence of deliberation. 

 It cannot be supposed that in deliberation of this kind there is any 

 grasp of the true position regarding the importance of the optimum 

 number, but it may be supposed that under these circumstances 

 the actual position at the moment as to whether there are too many 

 or too few in the group does weigh when taking the decision. To 

 all members of such a group, confined as they are within the 

 knowledge of them all to a limited area, the disadvantages of too 

 many mouths must be obvious. Therefore even among the more 

 primitive races there may be some semi-conscious adjustment of 

 numbers by means of one of these methods. However this may be, 

 it is clear that, even if there is no semi-conscious deliberation 

 among the lower groups, there is to some extent an automatic 

 adjustment to the needs of the moment. Suppose disease or 

 severe weather, for instance, to produce a higher rate of infant 

 mortality, then abortion and infanticide, inasmuch as they are 

 practised because of the difficulty of transporting more than one 

 child, will be less practised, 



10. Leaving aside for the moment the evidence that an approxi- 



