 Godfrey-Smith (2009; see also Godfrey-Smith 2000b; Griesemer 2005) contrasts the replicator/interactor approach to natural selection with a more classical approach. This latter approach is usually given as a “recipe” for evolution by natural selection, to use Godfrey-Smith’s terminology (see also Brandon 1990: 3.1). Ever since Darwin, a number of authors have proposed that for evolution by natural selection to occur, three conditions or ingredients are necessary. A population should exhibit (1) variation that (2) leads to differences in fitness between the entities forming the population [see the entry on  fitness],  (3) which are heritable (reviewed in Godfrey-Smith 2007). The most famous version of these recipes is that provided by Lewontin (1970).