 For this reason, the species Homo sapiens, like every other species taxon, must meet a historical or genealogical condition. (For pluralistic objections to even this condition, see Kitcher 1984: 320ff.; Dupré 1993: 49f.) This condition is best expressed as a segment of a population-level phylogenetic tree, where such trees represent ancestor-descendent series (Hull 1978: 349; de Queiroz 1999: 50ff.; 2005). Species, as the point is often put, are historical entities, rather than kinds or classes (Hull 1978: 338ff.; 1984: 19). The fact that species are not only temporally, but also spatially restricted has also led to the stronger claim that they are individuals (Ghiselin 1974; 1997: 14ff.; Hull 1978: 338). If this is correct, then organisms are not members, but parts of species taxa. Independently of whether this claim is true for all biological species, Homo sapiens is a good candidate for a species that belongs to the category individual. This is because the species is characterised not only by spatiotemporal continuity, but also by causal processes that account for the coherence between its component parts. These processes plausibly include not only interbreeding, but also conspecific recognition and particular forms of communication (Richards 2010: 158ff., 218).