214 THE EEGULATION OF NUMBERS 



characteristics of these factors are noteworthy. The effect they 

 have upon the hmitation of increase is incidental ; it is the chance 

 accompaniment of the practice of certain customs or of certain 

 habits. In the second place the working of any single factor, so 

 far as it reduces fertility or increases ehmination, is fairly regular ; 

 in any primitive race at any given time such habits as prolonged 

 lactation and early intercourse, when they occur, cause a certain 

 definite reduction of fertility ; and such customs as those of war 

 and those connected with the upbringing of children cause a certain 

 definite amount of ehmination. The nature of the factors present 

 and the degree of their incidence varies considerably from race to 

 race, but it follows from what has been said above that in any 

 primitive race over a considerable length of time the amount by 

 which fertility is decreased and the amount of elimination which 

 is caused remain fairly constant. 



There is another class of factors the primary and not the inci- 

 ental function of which it is either to reduce fertihty or to cause 

 elimination. These factors are prolonged abstention from inter- 

 course, abortion, and infanticide. The view put forward here is 

 l^that normally in every primitive race one or more of these customs 

 are in use, and that the degree to which they are practised is such 

 that there is an approach to the optimum number. With regard 

 to this view we may first deal with the question as to the prevalence 

 of these customs. We may then refer to the evidence as to the 

 nature and origin of these practices. We shall then be in a position 

 to ask how it may be supposed that they are so practised as to 

 bring about that amount of restriction of increase which will result 

 in an approach to the optimum number being made. 



7. The evidence regarding the practice of these customs — 

 prolonged abstention from intercourse, abortion, and infanticide — 

 has already been given in the last two chapters. This evidence is 

 also summed up in the Appendix to which the reader is invited to 

 turn. No attempt has been made to conduct an exhaustive 

 inquiry ; but it is claimed that there is ample evidence of the 

 widespread prevalence of one or more of these practices. There is 

 no indication of the correlation of any one practice with any one 

 economic stage. As far as the evidence goes, any practice may be 

 in use in any economic stage. To the meaning of this we shall 

 refer later. It is further claimed that, when the influence of contact 

 with Europeans is taken into account, the evidence of the existence 



