This paper traces the background to R. A. Fisher's multi-factorial theory of inheritance. It is argued that the traditional account is incomplete, and that Karl Pearson's well-known pre-Fisherian objections to the theory were in fact overcome by Pearson himself. It is further argued that Pearson's stated reasons for not accepting his own achievement has to be seen as a rationalization, standing in for deeper-seated metaphysical objections to the Mendelian paradigm of a type not readily discussed in a formal scientific paper. (...) The apparent, post-Fisherian, continued acceptance of Pearson's objections is presented as an interesting problem for the historian and sociologist. (shrink)

The debate between the Mendelians and the (largely Darwinian) biometricians has been referred to by R. A. Fisher as ‘one of the most needless controversies in the history of science’ and by David Hull as ‘an explicable embarrassment’. The literature on this topic consists mainly of explaining why the controversy occurred and what factors prevented it from being resolved. Regrettably, little or no mention is made of the issues that figured in its resolution. This paper deals with the latter topic (...) and in doing so reorients the focus of the debate as one between Karl Pearson and R. A. Fisher rather than between the biometricians and the Mendelians. One reason for this reorientation is that Pearson's own work in 1904 and 1909 suggested that Mendelism and biometry could, to some extent, be made compatible, yet he remained steadfast in his rejection of Mendelism. The interesting question then is why Fisher, who was also a proponent of biometric methods, was able to synthesise the two traditions in a way that Pearson either could not or would not. My answer to this question involves an analysis of the ways in which different kinds of assumptions were used in modelling Mendelian populations. I argue that it is these assumptions, which lay behind the statistical techniques of Pearson and Fisher, that can be isolated as the source of Pearson's rejection of Mendelism and Fisher's success in the synthesis. (shrink)