 A third option, like the previous one, assumes that biologists have looked long enough for the unifying feature of species. In that search, biology has learned that there are different types of lineages called ‘species.’ But proponents (Ereshefsky 1998) of this option do not opt for a disjunctive definition of ‘species.’ According to this option, we should doubt the very existence of the category species. Those lineages we call ‘species’ vary in their patterns and processes. Furthermore, the distinction between species and other types of taxa is riddled with vagueness. Consequently, we should doubt whether the term ‘species’ refers to a real category in nature.