 Barker also attacks species pluralism from a different angle. In the pluralist’s argument there is the assumption that the three main types of species lineages are basal lineages. ‘Basal’ here means they are the smallest lineages on the Tree of Life that are recognized by the Linnaean Hierarchy of biological classification. (Recall that hierarchy: species are the smallest units of classification followed by more inclusive units such as genus, family, order, and so on.) Barker argues that species pluralists unknowingly make an assumption that goes against their attempt to establish species pluralism. Namely, they assume the three types of species taxa that pluralists refer to (interbreeding species lineages, ecological species lineages, and phylogenetic species lineages) have an important similarity – they are all basal lineages in the Linnaean Hierarchy. If that is the case, then these different types of species lineages have something in common – they are all basal lineages. So, species pluralists are wrong to assert that there are three types of species lineages that lack a biologically important commonality.