THE SIZE OF AMERICAN FAMILIES. 69 



to 1, 2 and 3. But we can not then account for the great number of 

 zeros in the early decades, nor for the way in which the reduction of 

 the variability occurs. Again it might be thought that there has been 

 a growing reluctance to have families over a certain size, a reluctance 

 that becomes more and more intense in the case of large sizes. But it 

 is impossible to find any scale for the increase of this reluctance such 

 that by assigning more and more individuals to the reluctant class we 

 can derive a series of distributions by decades at all like those actually 

 found. 



Of course if we postulate both a lowering with time of the size to 

 which families are restricted and a sliding scale of reluctance that also 

 varies with time we can account for the observed facts. Such a h}'- 

 pothesis is, however, suspicious because of its complexity and apparent 

 artificiality. I do not deny that it may be true, but until we find some 

 further support for it, we are bound so far as the observed facts go to 

 prefer the vera causa which explains the observations with perfect sim- 

 plicity, and to attribute the numerical degeneration of our group to a 

 real decrease in fertility. 



So far as our general mental prepossessions go, however, a real 

 decrease in fertility seems at first sight a preposterous doctrine. One 

 can well imagine the sneer of the physician whose experience empha- 

 sizes the frequency of restriction and the pitying smile of the biologist 

 who discerns that a progressive decrease in fertility of a species is a 

 flat contradiction of the doctrine of natural selection. 'Play on with 

 your statistical hair-splitting,' they would say, 'Nothing that you find 

 will disturb our beliefs. We know better.' 



But I venture to assert that the experiences of metropolitan physi- 

 cians will not serve to prophecy the social psychology of the species we 

 have studied, that their opinions may here be as wide of the mark as 

 the common belief that unwillingness is the main cause of the failure 

 of the women of the better classes to nurse their children. As to the 

 contradiction of natural selection, I may suggest that the existence, 

 amount and results of the elimination of types by their failure to pro- 

 duce their kind is after all a problem which only statistical inquiries 

 can settle and that if the doctrine is to be used as an excuse for evad- 

 ing certain obvious facts in human history it is perhaps time that it 

 should be questioned. 



The issue is clear. The more fertile members of a race produce 

 of course a larger measure of the next generation than do the less fer- 

 tile. So also do their children, if fertility is inherited. There should 

 then, according to present-day biology, be a quantitative evolution of 

 fertility. Absolute sterility would needs be the first trait to be elim- 

 inated from a species. It should have disappeared from the human 

 stock seons asro. And so long as there are variations in fertility and 



