The increasing attention which has been given to social history of science and to the sociological analysis of scientific activity has resulted in a renewed interest in scientific controversies. Furthermore, the rejection of the presentist view of history, according to which those contestants who took what we can identify, with the benefit of modern knowledge, as the ‘right’ stand in a controversy, were right and their opponents were ‘wrong’, left the subject of scientific controversies with many questions. What determines their emergence, course and resolution? When Froggatt and Nevin wrote on the Bio-metric-Mendelian controversy in 1971 they called their article ‘descriptive rather than interpretative’, so they avoided the very questions we would like to ask. Provine, in the same year, concentrated on the strong personalities of the contestants, their clashes, and the scientific arguments in play. But in 1975 Mackenzie and Barnes argued that the controversy could not be accounted for unless recourse was had to sociological factors. Their view has become widely known and figured prominently in 1982 in Steven Shapin's recital of the empirical achievements of the application of the sociological approach. I have returned to this subject because I do not yet feel altogether convinced by Mackenzie and Barnes' analysis. Even if their analysis of the controversy between Pearson and Bateson be accepted, it is not so obvious how effectively it can be used to explain the controversy between Weldon and Bateson, and I am not confident that it is adequate for an understanding of the evolution of their differing views of the mechanism of evolution.