 The theory of definition developed in Aristotle’s logical works assigns entities to a genus and distinguishes them from other members of the genus, i.e., from other “species”, by their differentiae (Topics 103b). The procedure is descended from the “method of division” of Plato, who provides a crude example as applied to humans, when he has the Eleatic Stranger in the Statesman characterise them as featherless bipeds (266e). Hull and many scholars in his wake (Dupré 2001: 102f.) have claimed that this simple schema for picking out essential conditions for species membership had a seriously deleterious effect on biological taxonomy until Darwin (cf. Winsor 2006).