324 NATURAL SCIENCE. may, 



changes from wives to daughters (0-25" and 0'O44") are, in the only 

 statistics at present available, far more considerable than the above 

 values ; but it must be remembered that other causes than repro- 

 ductive selection are at work, such as shrinkage with age and the 

 greater physical training of the young women of to-day. 



(5) I have only been able to measure, so far, the actual value of 

 the correlation between fertility and any organ in the case of stature 

 in women. It would, doubtless, be more sensible in other cases, e.g., 

 pelvic measurements. But there are certain considerations which 

 may be referred to here, and which will suggest how important — at 

 any rate in the case of man — it is to take into consideration the 

 influence of reproductive selection. 



From considering the fertility of man, in England and in Denmark, 

 I conclude that 25 per cent, of the mated population produce one- 

 half the next generation. This is the gross fertility. Allowing for 

 the selective death-rate — which I knew only for Denmark — 27 per cent, 

 of the mated population produced half the next generation. In 

 other words, although natural selection tends to counteract repro- 

 ductive selection by a death-rate which, it may be shown, rises 

 continuously and uniformly with increased fertility, yet, in the case 

 of civilised man, it is totally ineffectual as against reproductive 

 selection. If we allow for the portion of the population which 

 remains unmarried, we are well within the mark if we say that less 

 than 25 per cent, of one generation produce more than half of the 

 next generation. Correlation, therefore, between fertility and any 

 mental or physical characteristic must work a progressive change. 



We know that there are very considerable race and class 

 differences in the matter of fertility. It is very difficult to understand 

 how these could have arisen by the action of natural selection com- 

 bined with heredity, unless either (i) fertility be inherited, or (2) 

 fertility and some inherited mental or physical characteristic be corre- 

 lated. But either (i) or (2) involves reproductive selection. We 

 have seen that there is evidence of correlation between the stature of 

 women and their fertility. There is also evidence of a correlation 

 between fertility and class. Taking Copenhagen, for which alone we 

 have satisfactory class-fertility statistics, it is possible to show : — 



(i) That the gross fertility of the artisan is more than the gross 



fertility of the professional classes, 

 (ii) That the net fertility of the artisan is less than the net 



fertility of the professional classes. 



Thus natural selection, at first sight, checks reproductive selection, 

 greater fertility connoting a greater death rate ; but we find : — 



(iii) That the marriage rate of the artisan is so much higher than 

 the marriage rate of the professional classes that the per- 

 centage fertility of the former considerably exceeds that of 

 the latter. 



