 Pierrick Bourrat (2018) offers an alternative response to Reisman and Forber; he implies that Reisman and Forber (2005) have overlooked Woodward’s criterion of invariance when they invoke the manipulability account in support of drift as a population-level cause.  Invariance in an intervention, Bourrat states, “measures the extent to which a relationship between two variables satisfying the manipulation condition remains stable or unchanged as various other changes are made in the background of this relationship” (2018: 162), and, again invoking Woodward, he asserts that causal relationships that are more invariant provide better explanations. But, Bourrat argues, causal explanations in terms of individual-level variables are more invariant under intervention than causal explanations in terms of population-level variables, and thus should be preferred for that reason. In other words, similar to Bouchard and Rosenberg (2004) who are briefly mentioned above, Bourrat defends a causalist position, but at the level of individuals rather than at the level of populations. However, Bourrat does concede that it is reasonable to conceive of drift and natural selection as population-level causes when they depend on indeterministic events, as well as for some cases of frequency-dependent selection. Moreover, Bourrat does not discuss Clatterbuck’s (2015) alternative and arguably superior understanding of the relevant manipulation for drift; had he done so, it is not clear that his claim for the superiority of individual-level causal explanations with respect to drift would follow. Again, though, these are disagreements within the causalist camp.