 It is evolution that confers on this distinction its particular form and importance. The variation among organismic traits, without which there would be no evolution, has its decisive effects at the level of populations. These are groups of organisms that in some way cohere at a time in spite of the variation of traits among the component organisms. It is population-level groupings, taxa, not organisms, that evolve and it is taxa, such as species, that provide the organisms that belong to them with genetic resources (Ghiselin 1987: 141). The species Homo sapiens appears to be a metapopulation that coheres at least in part because of the gene flow between its component organisms brought about by interbreeding (cf. Ereshefsky 1991: 96ff.). Hence, according to evolutionary theory, Homo sapiens is plausibly a higher-level entity—a unit of evolution—consisting of the lower-level entities that are individual human beings. The two questions phrased in terms of “human nature” thus concern the conditions for individuation of the population-level entity and the conditions under which organisms are components of that entity.