 While the arguments just considered suggest a microstructural essence for the chemical and physical kinds considered, they do not have the consequence that every natural kind must have a microstructural essence. Kripke regards material individuals as having historical essences. In the light of cladism in biology, one may regard biological taxa as having historical essences also, and this is consistent with the general picture given to us by Kripke and Putnam, even if they themselves once thought that biological kinds had microstructural essences (McGinn 1976; Kornblith 1993, 111; LaPorte 2004, 64). Cladism is the most commonly accepted system of biological classification that groups organisms according to their shared phylogenetic ancestry. Cladism has replaced the Linnean hierarchical system of biological classification where organisms were grouped according to their shared morphological characteristics (see Section 2.1 below).