 Perhaps they share a common property that renders them species. If one adopts the thesis that all species are genealogical lineages, then a common feature of species is their being lineages. However, this feature is also shared by other types of taxa in the Linnaean Hierarchy. From an evolutionary perspective, all taxa, whether they be species, genera, or tribes, are genealogical lineages. We need to locate a feature that is not only common in species but also distinguishes species from other types of taxa.