 Given the observation that we should cite both genealogy and developmental mechanisms to understand why zebras have stripes, should we infer, as Devitt does, that the taxon Zebra has an intrinsic essence? Some argue ‘no’ (Ereshefsky 2010a). Biologists explain the characters of organisms by citing other characters, without the added metaphysical claim that a character cited in an explanans is essential for membership in a taxon. Consider how a biologist explains the occurrence of stripes in a zebra. In its embryonic state, a zebra has an ontogenetic mechanism that causes it to develop stripes. That developmental mechanism is neither necessary nor sufficient for membership in Zebra. Some zebras lack that mechanism. Moreover, the developmental mechanism that causes stripes in zebras causes stripes in a variety of mammals, including cats. Generally, the intrinsic properties that cause organismic traits do not coincide with taxonomic boundaries: they cross-cut such boundaries. The belief that such intrinsic properties are essential for taxon membership is not part of biological theory.