 However, notice that the fourth drift “phenomenon” that Walsh, Lewens, and Ariew identify isn’t really a phenomenon. Rather, it refers to a model from population genetics, the Hardy-Weinberg model, and predictions based on that model. It is true that as a consequence of the model, there would be no deviation from fitness expectations with an idealized infinite population (if we make some philosophical assumptions about what happens in infinity; Sober (1984) raises questions about these assumptions), but that there would likely be such deviations with a finite population. But this is a purely mathematical approach. The purely mathematical approach doesn’t ask what phenomena the model is supposed to be modeling and why it is that finite populations are of interest. There is also no explanation of why a Hardy-Weinberg model with an assumption of finite population size should count as drift; perhaps this is because of a philosophical tradition of referring to this as drift (e.g., some parts of Sober 1984 read that way), or perhaps it is because of the previously-noted longstanding association between drift and small population sizes. In contrast, on the Causal Process Account of Drift, drift would occur even in infinite populations as long as there is indiscriminate sampling; drift-like outcomes (deviation from fitness expectations) are not required.