 Kitcher’s pluralism is more circumspect: it limits species concepts to those that are legitimized by theoretical biology. Still, one might worry that Kitcher’s form of pluralism is too liberal. Kitcher’s pluralism allows that some species are spatiotemporally continuous entities (individuals), while other species may be spatiotemporally unrestricted entities (natural kinds). As we saw in Section 2.1, Hull’s evolutionary unit argument states that within the purview of evolutionary biology, species must be individuals. Kitcher’s pluralism does not satisfy this requirement. If one assumes that ‘species’ is a theoretical term in evolutionary theory and that species are individuals, then Kitcher’s pluralism is too inclusive.