 Another response to species pluralism is de Queiroz’s (1999, 2005, 2007) General Lineage Concept. De Queiroz suggests that despite differences among various species concepts, all such concepts agree on one thing: species are “separately evolving metapopulation lineages” (2005, 1263). De Queiroz writes that this conception of species is the “single, more general, concept of species” that reconciles all other species concepts (2007, 880). What is the relationship between the General Lineage Concept and those concepts? De Queiroz suggests that the General Lineage Concept provides the necessary criterion for being a species. The properties that other species concepts disagree over, for example, a lineage’s occupying a unique niche, being monophyletic, or being reproductively isolated, are contingent properties of species. They are “secondary” properties of species (de Queiroz 2005, 1264). All species taxa must be metapopulation lineages, but they can vary in their secondary properties. De Queiroz contrasts the necessary property of species from their secondary properties in another way. Whereas the necessary property cited by the General Species Concept captures the fundamental nature of species, the secondary properties of species are merely “operational criteria” (2007, 882) for “inferring the boundaries and numbers of species” (2005, 264). According to de Queiroz, disagreements among other species concepts merely concern operational and evidential issues. Proponents of other species concepts are confusing “methodological” disagreements with “conceptual” ones (de Queiroz 2005, 1267).