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. Ina state of nature 
such an unbalanced development of the powers that should codperate 
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 afew 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. 
11. 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 ITI, 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. 
