DIFFERENTIAL FECUNDITY 



How Various Races of the United States Are Altering Their Relative Positions- 

 Native Americans Dying Out in New England — Whites Supplanting 

 Negroes in the South — Influence of Cities on the Birth-Rate.^ 



Walter F. Willcox, 

 Professor of Economics and Statistics, Cornell University, Ithaca, N. Y. 



HAVING been honored with an 

 invitation to address you upon 

 the subject of "differential 

 fecundity as one of the causes 

 of the need for race betterment," I have 

 felt it both a privilege and a duty to 

 accept the invitation. 



At the start it is well to define 

 fecundity. This is the more necessary 

 because the definition used in biology 

 and medicine differs somewhat from that 

 used in statistics. The definition pro- 

 pounded by Professor Raymond Pearl 

 in his paper before the First Inter- 

 national Eugenics Congress at London 

 in 1912 was as follows: "the innate 

 potential reproductive capacity of the 

 individual organism as denoted by its 

 ability to form and separate from the 

 body mature germ cells." For human 

 statistics this definition is inapplicable 

 and useless. Statistics disregards poten- 

 tial as distinguished from actual or 

 realized fecundity and makes fecundity 

 a characteristic, not of men or women, 

 husbands or wives, but of marriages. 

 For present purposes, then, it is a 

 term applied to marriages which have 

 proved fruitful in the birth of at least 

 one child, and is thus the opposite of 

 sterility. 



In some technical discussions a dis- 

 tinction is drawn between fecundity and 

 fertility, the former being applied indis- 

 criminately to every marriage which has 

 resulted in the birth of a child, the latter 

 taking into account also the number of 

 children born to the marriage. If we 

 were to accept this distinction, two 

 marriages, to one of which a single 

 child had been born, and to the other 



of which six children had been born, 

 would be equally fecund, for fecundity 

 has no degrees, but the marriage which 

 had resulted in six children would be 

 more fertile than the other. In the 

 present paper, which must be general 

 in character, the distinction between 

 fecundity and fertility will be ignored. 

 For our purposes, fecundity means the 

 yield of living births in any population 

 group in a unit of time, usually a year. 

 This yield can seldom be effectively 

 stated as a total niunber of births, for 

 such a number ignores variations in the 

 size of the group which produces it. To 

 avoid this difficulty fecundity is stated 

 ordinarily as a proportion or ratio, 

 called the birth rate. 



WHAT DIFFERENTIAL MEANS. 



The word differential also must detain 

 us a moment. The differences which it 

 implies are differences in the fecundity 

 of various population groups and, in 

 consequence, differences in the rates at 

 which these groups perpetuate them- 

 selves and multiply by nature's pro- 

 cesses of birth and death. The real 

 things to be compared are the rates of 

 increase or of decrease resulting from 

 the balance between these natural pro- 

 cesses. The birth rate or fecundity gives 

 only one term when what is wanted is 

 the difference between two terms, the 

 birth rate and the death rate. A popu- 

 lation group may increase either by 

 excess of births over deaths, by excess 

 of immigration over emigration, or by 

 various combinations of these two kinds 

 of change reinforcing or antagonizing 

 each other. An increase by excess of 



^Address delivered before the First National Conference for Race Betterment. Battle Creek, 

 Mich., January 10, 1914. 



141 



