There has been considerable debate in both biology and philosophy about which entities undergo natural selection and what it is that fits them for that role. The term replicator, originally introduced by Dawkins, is used to refer to any entity of which copies are made. The focus of discussions about replicators concerns just which organic entities actually meet the definition of replicator. Group Selection George Williams's famous near-deathblow to group panselectionism was, oddly enough, about benefit. Ambiguities about the definition of a unit of selection have also snarled the debate about selection processes at the species level. One may understandably think that Dawkins is interested in the replicator question because he claims that the unit of selection ought to be the replicator. Dawkins had particular problems with his treatment of the interactor. The pluralists seem to be arguing against the utility of the notion of the interactor in studying the selection process.