 There is a difference in emphasis between the two approaches in that the replicator/interactor approach focuses on the entities forming the population, while the classical approach provides a population description of evolutionary change. Another difference between the two approaches is that under the classical approach, replication is not required for evolution by natural selection to occur. In fact, as long as heritability is positive, and the two other conditions are satisfied, evolution by natural selection can occur (but will not necessarily do so, cf. Godfrey-Smith 2009: 25). An abstract definition of heritability (\(h^2\))—although by no means fully general (see Bourrat 2015a, 2022)—is that it represents the slope of the regression of average offspring character on parent or mid-parent (in case of sexual species) character [see the entry on  heritability].  Given that a positive heritability does not entail replication of character between parent and offspring, but is rather a special case in which heritability would be exactly 1 in the absence of environmental variation, the replicator/interactor perspective is subsumed by the classical approach. Godfrey-Smith concurs: