 The diachronic identity of an organism, its capacity to remain the same despite transformations, has puzzled philosophers since ancient Greece. Aristotle postulated the existence of immutable forms, that, being distinct from fluctuating matter, ensure the continued identity of living creatures (Categories, 3b22–33; Metaphysics, Book D).  Dissatisfied with this solution, Locke proposed that temporal identity of animals and plants is not ensured by their unvarying forms, but rather by the continuity of their lived life (Locke 1689, II.27.4 and II.27.8; Kaufman 2016). In the context of contemporary philosophy of biology, the importance of continuous identity was emphasized by Hull who argued that species lack essences and thus should be considered historical individuals with their own inner coherence and persistence conditions not unlike those of other living creatures (Hull 1978). He assumed that these persistence conditions are provided by continuity of changes in biological organization of these individuals so that only an abrupt disruption could cause a loss or change of identity (Hull 1992; Hull 1978: 355).  This latter perspective has recently been adopted by advocates of animalism, who argue that continuity of physiological processes (organic animalism) or maintenance of characteristic structural organization (somatic animalism) are necessary for diachronic identity (Olson 1997; van Inwagen 1990; Mackie 1999; see the entry on  animalism).