R. A. Fisher on J. A. Cobb’s The problem of the sex-ratio

Abstract

The logic of the rarer-sex effect, concerning how natural selection acts to balance the sex ratio among newborns, was long supposed to have originated with Ronald Aylmer Fisher in his 1930 book The genetical theory of natural selection. However, the principle is now understood to have originated with John Austin Cobb in his 1914 paper The problem of the sex-ratio. Fisher did not provide a citation of Cobb’s sex-ratio paper, and it has been unclear whether he was aware of its existence. Here, I show that Fisher was indeed aware of Cobb’s paper in 1930, as revealed by his having cited it elsewhere that same year. Fisher’s willingness to highlight Cobb’s sex-ratio work lends support to the view that his failure to mention it in his book reflects the lax citation standards of the time rather than an attempt to deceive readers as to the provenance of the rarer-sex effect.