 However, the Causal Process Account of Drift has not gone unchallenged. Robert Brandon (2005) argues that it “does not map well onto the ways biologists differentiate drift from selection” (2005: 156), that selection and drift are the same process (i.e., sampling), and that the large majority of biological cases are not cases of indiscriminate sampling. He maintains that “Drift is any deviation from the expected levels of reproduction due to sampling error” whereas “Selection is differential reproduction that is due to (and in accord with) expected differences in reproductive success” (2005: 168–9). These definitions include both process and outcome. Millstein (2005) responds to each of these challenges and defends her view over his. For the purposes of this essay, it is important to note, as Millstein (2005) acknowledges, that Brandon is certainly correct in his descriptive claim that many biologists incorporate both process and outcome in their definitions of drift (see Millstein, Skipper, and Dietrich (2009) for examples). Indeed, the plurality of definitions of drift offered by contemporary biologists—some process-oriented, some outcome-oriented, some both, and some alternating within the same work—gives rise to the need for philosophical analysis, even if the result, in the end, is to accept that pluralism. The Causal Process Account of Drift is making a prescriptive claim on the grounds of 1) increased clarity, 2) the ability to conceptually differentiate biologically very different phenomena, such as selection in a fluctuating environment from fluctuating gene frequencies due to indiscriminate sampling, which have the same outcomes, while 3) maintaining a grounding in biological practice and (some) biological usage.