 As reviewed above, one example from their own writing comes from the treatment of the t-allele case, a universally recognized case of three levels of selection operating simultaneously on a single allele. Right before the t-allele case, a suggestion is offered that a Williams’s type analysis could be based on an application of Lloyd’s additivity criterion for identifying interactors, which is strictly hierarchical (Waters 1991: 563; Lloyd [1988] 1994: Ch. 5). Thus, the pluralist suggestion is to borrow a method for identifying potential higher-level interactors in order to determine the genic environments and thus to have more adequate genic level models. Similarly, other pluralists resort to a traditional approach to identifying interactors in order to make their genic models work. It had earlier been proposed that the statistical idea of screening off be used to identify which levels of entities are causally effective in the selection process; i.e., it is a method used to isolate interactors (Brandon 1982). But some pluralists propose using screening off to identify layers of allelic environments, and also show how Sober’s probabilistic causal account could be used for a genic account (Sterelny &amp; Kitcher 1988: 354).