 One of the two chief uses of the notion of natural selection is as an interpretation of one or another quantity in formal models of evolutionary processes; this is the focused sense distinguished above. Two different quantities are called selection in different formal models widely discussed by philosophers. On the one hand, fitness coefficients are said to quantify selection in type recursion models of selection; the \(w\)’s in the above genotypic selection model are fitness coefficients. This is standard textbook usage (Rice 2004; Hedrick 2011). The recursive structure of these models is important. They can be used to infer how a system will behave into the future (though of course only if causes of the variables in the system do not change their values in dynamically-relevant ways that are not explicitly modeled in the recursive equations). At their simplest, type recursions make system dynamics a function of fitness coefficients weighting type frequencies/numbers together with effective population size (quantifying drift), as in the genotypic selection model discussed above. More complex variants of type recursions include frequency-dependent selection models, for cases in which population members’ fitness is a function of the type frequency variables; density-dependent selection models, for cases in which fitness is a function of population size; spatially and temporally variable selection models, for cases in which fitness varies as a function of a varying environmental variable that interacts with type differences, and many more. Writers working with type recursion models have developed explicit interpretations of their theoretical terms, including the fitness variables quantifying selection. So, for instance, Beatty and Millstein defend the view that the fitness coefficients representing selection in type recursions should be understood as modeling a discriminate sampling process, while drift, controlled by effective population size, should be understood as indiscriminate sampling (Beatty 1992; Millstein 2002).