VI. Mathematical contributions to the theory of evolution. —VI. Genetic (reproductive) selection: Inheritance of fertility in man, and of fecundity in thoroughbred racehorses

Abstract

I understand by a factor of evolution any source of progressive change in the constants—mean values, variabilities, correlations—which suffice to define an organ or character, or the interrelations of a group of organs or characters, at any stage in any form of life. To demonstrate the existence of such a factor we require to show more than the plausibility of its effectiveness, we need that a numerical measure of the changes in the organic constants shall be obtained from actual statistical data. These data must be of sufficient extent to render the numerical determinations large as compared with their probable errors. In a “Note on Reproductive Selection,” published in the ‘Roy. Soc. Proc.,’ vol. 59, p. 301, I have pointed out that if fertility be inherited or if it be correlated with any inherited character—those who are thoroughly conversant with the theory of correlation will recognise that these two things are not the same—then we have a source of progressive change, a vera causa of evolution. I then termed this factor of evolution Reproductive Selection . As the term lias been objected to, I have adopted Genetic Selection as an alternative. I mean by this term the influence of different grades of reproductivity in producing change in the predominant type.