 Questions about interactors focus on the description of the selection process itself, that is, on the interaction between an entity, that entity’s traits and environment, and on how this interaction produces evolution; they do not focus on the outcome of this process (see Wade 1977; Vrba &amp; Gould 1986). The interaction between some interactor at a certain level and its environment is assumed to be mediated by “traits” that affect the interactor’s expected survival and reproductive success. Here, the interactor is possibly at any level of biological organization, including a group, a kin-group, an organism, a gamete, a chromosome, or a gene. Some portion of the expected fitness of the interactor is directly correlated with the value of the trait in question. The expected fitness of the interactor is commonly expressed in terms of genotypic fitness parameters, that is, in terms of the fitness of combinations of replicators. Hence, interactor success is most often reflected in and counted through, replicator success, either through simple summation of the fitnesses of their traits, or some more complicated relation. Several methods are available for expressing the correlation between interactor trait and (genotypic or genic) fitness, including partial regression, variances, and  covariances.[2]