92 ANALYSIS OF THE FOUR PRINCIPLES. 



Having suspended laying eggs for a few days, the hen might devote 

 herself faithfully to setting on a nest full of eggs needing warmth for 

 hatching; but before the chicks were ready to appear, the necessity 

 would return for giving herself to laying eggs. In a state of nature 

 such an unbalanced development of the powers that should cooperate 

 in the process of reproduction could never have become so marked ; 

 for the one-sided development of any individual causing it to pro- 

 duce even a few eggs or young in excess of the normal number would 

 in some degree impair its power of leaving successful offspring. The 

 failure of such individuals to leave their full proportion of offspring, 

 and the effect of this failure on the race, I describe as the action 

 of filio-parental selection setting limits to the range within which 

 fecundal selection may act. 



1 1 . Fecundal Selection in Human Races. 



One of the most striking examples of the loss of fertility, and of the 

 gradual extinction that follows, is found in the experience of the Poly- 

 nesians since their contact with Europeans. In but few of the islands 

 of the Pacific have the aborigines been displaced by conflict of arms 

 or by industrial competition. The great cause of their disappear- 

 ance, during the earlier periods of intercourse was their inability to 

 cope with the microbes of measles, smallpox, leprosy, and other dis- 

 eases, unknown to them before the arrival of Europeans and Chinese. 

 But in many groups of these islands, and especially in Hawaii, that 

 stage of disadvantage is now largely past, through the protection 

 gained from Western science. Still the steady decrease in numbers 

 continues, for the birth rate is not sufficient to meet the natural rate 

 of mortality. And there is no reason to attribute this small birth 

 rate to poverty or to prudential selection. Whatever the antecedent 

 causes may have been, the present condition is failure to meet the 

 demands of fecundal selection. 



The nature of the deficiency is more fully realized when the decrease 

 of the Polynesian race in their original home is compared with the 

 increase of the African race in North and South America. 



12. Statistical Methods in the Study of Fertility. 



Karl Pearson has within a few years published several interesting 

 discussions on the subject of fertility as a factor in the evolution of 

 civilized man,* in which he has reached by statistical methods some 



* See "Chances of Death and Other Studies in Evolution," Chapter III, entitled 

 "Reproductive Selection," published by Edward Arnold, London and New York, 

 1897; also "The Grammar of Science," second edition, published by A. C. Black, 

 London, 1900; in the sections devoted to reproductive or genetic selection. 



