Wallace became a full-time naturalist in 1848, the year when he and Bates set out on their journey to South America. Wallace was twenty-five at the time and over half of his life had been spent in various parts of Wales, the land of his birth. Commentators have tended to gloss over or ignore any formative influences from this early period of his life or even to dismiss them as non-existent. This is surprising as it was during the eight or so years in Wales leading up to 1848 that Wallace's interest in natural history emerged. ‘The importance of this early period in Wallace's life can scarcely be over-emphasized’ wrote Durant in his account of the development of the Wallace personality, but he omitted any specific reference to the significance of the early period in Wales. Those seeking a simple unitary cause for Wallace's conversion to natural history usually locate this in his visit to Leicester in 1844 and his meeting there with H. W. Bates. ‘The odyssey began … in 1844, in Leicester’ wrote Brooks, adding that ‘the more remote parts of … southern Wales had offered little reading material…’ This, and similar claims, are presumably founded primarily on Wallace's belief—expressed sixty years later—that it was at Leicester that he first familiarized himself with Malthus' Essay on the Principles of Population and Humboldt's Personal Narrative of Travels in South America. There is, however, evidence that Wallace was probably familiar with at least one of these books some time before his visit to Leicester and that it was during his period in southern Wales that his interest in natural history emerged and developed.

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.