364 THE POPULAR SCIENCE MONTHLY 



THE INHERITANCE OF FECUNDITY 1 



By Db. RAYMOND PEARL 



MAINE AGRICULTURAL EXPERIMENT STATION 



A THOROUGH and searching investigation of two great biological 

 problems is a necessary prerequisite to any substantial advance 

 of the science of eugenics. These problems are: 



1. The mode of inheritance of human characters and traits of all 

 kinds. 



2. The physiology of reproduction in man, particularly with refer- 

 ence to human fecundity and fertility. 



The progressive decline of the birth-rate in all, or nearly all, civil- 

 ized countries is an obvious and impressive fact. Equally obvious and 

 much more disturbing is the fact that this decline is differential. Gen- 

 erally it is true that those racial stocks which by common agreement 

 are of high, if not the highest value, to the state or nation, are precisely 

 the ones where the decline in reproduction rate has been most marked. 



The causes concerned in the production of these results are without 

 question exceedingly complex and difficult, if not impossible, of com- 

 plete analysis. But of one thing we may be certain; somewhere in the 

 complex of causes is included the biological factor as one element. 

 Fecundity and fertility are physiological characters of the organism, 

 subject to variation and capable of being inherited, just in the same 

 manner as structural characters. We must be in possession of definite 

 information regarding the physiology of fecundity and fertility, before 

 it will be possible to make safe and sure advance in the social and 

 eugenic analysis of matters involving these factors, such as, for example, 

 the declining birth-ra*te. 



The basic eugenic significance of that characteristic of organisms 

 termed fecundity furnishes sufficient justification, I hope, for bringing 

 to the attention of this Congress certain results regarding fecundity in 

 one of the lower animals, namely the domestic fowl. In some particu- 

 lars the results are, I believe, novel. They indicate, for the first time, 

 the precise mode by which this complex physiological character fecun- 

 dity is inherited. It will be the purpose of this paper to present — 

 necessarily very briefly and without the detailed supporting evidence — 

 the essential results of a study of fecundity in poultry, pointing out at 

 the end some possible eugenic bearings of the results: 2 



1 This paper was read at the First International Eugenics Congress, held 

 in London, July 24-30, 1912. 



2 The results set forth below were first presented at the meeting of the 

 American Society of Naturalists at Princeton, N. J., in December, 1911. A 



