EVOLUTION OF PHYSICAL CHAKACTEKS 379 



of the married population provide 75 per cent, of the next 

 generation. It thus becomes most important to determine whether 

 the various sections of the population are innately different as 

 regards their physical characters. Largely owing to our ignorance 

 respecting the direct influence of the environment, it is not 

 possible to arrive at present at any precise answer. But there 

 can be little doubt that on the whole the most fertile sections 

 of the population are the less physically fit sections. 



It is necessary, however, to view these facts in their proper 

 perspective. Though differential fertility of this kind may have 

 been at work among some of the ancient empires in their later 

 years, it is chiefly a very modern phenomenon characteristic of 

 modern European countries and their derivatives only within the 

 last fifty years. Therefore, however important a problem it may 

 be for modern communities, it is a factor which has had but 

 little effect on human history as a whole. It may be noticed 

 that restriction of increase is not the only form of reproductive 

 selection in modern communities. Sexual selection is also at 

 work. 1 



6. Such has been the direction in which, through selection and 

 differential fertility within races, changes have taken place. But 

 changes also take place through the conflict of races, and the nature 

 of these changes demands some notice. Warfare plays a part in 

 the normal existence of nearly all primitive races. It is some- 

 times, as among the American Indians, a bloodthirsty affair, but 

 more often than not it is a relatively unimportant cause of 

 elimination. It is not easy to arrive at any conclusion regarding 

 the results of warfare as an agent of selection. Upon the whole, 

 among primitive races, so far as physical characters are concerned, 

 there is probably a tendency towards the preservation of the 

 physically strong and fit. But it has to be remembered that 

 missile weapons were early introduced, and that, as Thucydides 

 remarked, missile weapons kill the strong man in the prime of 

 life as well as the weak. Again, success in warfare very largely 

 depends upon characters other than physical such as the 

 possession of skill. All that can be said with certainty is that 

 in the first and second periods warfare was not a cause of elimina- 

 tion of the fit which it has come to be in the third period. This 

 latter fact has been lately brought home to the civilized nations 



1 See Popenoe and Johnson, loc. cit., ch. xi. 



