 Let us recall what the interactor question in the units of selection debate amounts to: What levels of entities interact with their environments through their traits in such a way that it makes a difference to replicator success? As mentioned before, there has been much discussion in the literature about how to delineate and locate interactors among multilayered processes of selection. Each of these suggestions leads to slightly different results and different problems and limitations, but each also takes the notion of the interactor seriously as a necessary component to understanding a selection process.