 Another potential problem is how the General Lineage Concept distinguishes species from higher taxa. According to de Queiroz, species are single lineages whereas higher taxa are clades of multiple lineages. What, then, distinguishes a single lineage from a branch with multiple lineages according to the General Lineage Concept? De Queiroz (2005, 1265) writes that the General Lineage Concept does not need to cite the secondary properties mentioned in other species concepts to answer this. However, de Queiroz offers no alternative criteria for determining when a single lineage becomes a branch of multiple lineages. Moreover, the secondary properties of other species concepts are commonly used to make that determination. Therein lies a potential problem with the General Lineage Concept’s attempt to unify the species category. According to the General Lineage Concept, species are lineages. But to determine what is a lineage we must turn to other species concepts, and in doing so the heterogeneity of the species category rears its head again. De Queiroz attempts to unify the species category by asserting that all and only lineages are species. But that just masks the heterogeneity of the species category because what constitutes a lineage has multiple answers, and those answers vary according to which species concept one adopts.