 A number of other philosophers have sought to challenge the statisticalists’ claim that drift is not a force. For example, Stephens (2004) defends the claim that drift is both a force and a cause. He asserts that if we understand drift properly as a process of indiscriminate sampling (instead of as an outcome, as the statisticalists do), we can see that it is a force, but that in a population of a given size it always has the same force, regardless of whether there is a large or a small deviation from expectation. (It may be that Sober’s inadvertent vagueness in his 1984 book on the process/outcome question contributed to the confusion, since the statisticalists were responding to Sober). He clarifies that, “because drift is a probabilistic cause, the same causal force can have two different outcomes” (Stephens 2004: 557; emphasis in original). Stephens further defends the claim that drift can be understood as a force or a cause by arguing (contra Matthen and Ariew) that drift does have a direction, namely, eliminating heterozygosity; that it can “make a difference” by affecting the probability of evolutionary change (more in small populations, less in large); and that we can cogently speak of the relative importance of drift in an ensemble of populations or in a population, albeit not at the level of individuals (see Walsh 2007 for a response to Stephens 2004, 2010 and Gildenhuys 2014 for a response to his response).