 The third school of thought regarding the ontology of race is racial population naturalism. This camp suggests that, although racial naturalism falsely attributed cultural, mental, and physical characters to discrete racial groups, it is possible that genetically significant biological groupings could exist that would merit the term races. Importantly, these biological racial groupings would not be essentialist or discrete: there is no set of genetic or other biological traits that all and only all members of a racial group share that would then provide a natural biological boundary between racial groups. Thus, these thinkers confirm the strong scientific consensus that discrete, essentialist races do not exist. However, the criteria of discreteness and essentialism would also invalidate distinctions between non-human species, such as lions and tigers. As Philip Kitcher puts it, “there is no…genetic feature…that separates one species of mosquito or mushroom from another” (Kitcher 2007, 294–296; Cf. Mallon 2007, 146–168). Rather, biological species are differentiated by reproductive isolation, which is relative, not absolute (since hybrids sometimes appear in nature); which may have non-genetic causes (e.g., geographic separation and incompatible reproduction periods or rituals); which may generate statistically significant if not uniform genetic differences; and which may express distinct phenotypes. In effect, if the failure to satisfy the condition of discreteness and essentialism requires jettisoning the concept of race, then it also requires jettisoning the concept of biological species. But because the biological species concept remains epistemologically useful, some biologists and philosophers use it to defend a racial ontology that is “biologically informed but non-essentialist,” one that is vague, non-discrete, and related to genetics, genealogy, geography, and phenotype (Sesardic 2010, 146).