 Importantly, though, one can claim that death is a natural kind without accepting any kind of essentialism. An alternative to the essentialist conception is the homeostatic property cluster theory of natural kinds (Millikan 1999). On this view, natural kinds do not, or at least need not, share essential properties. They are comprised by members sharing a stable cluster of similarities, which are brought about by “homeostatic causal mechanisms” (such as, in the case of species, common developmental programs and selective pressures). On this view, X (e.g., a fetus) might be a member of a natural kind (e.g., our species) despite lacking one of the properties (e.g., the potential for rationality) among the cluster of similarities. Death and its opposite, life, might similarly be natural kinds lacking essences, each kind being associated with a cluster of properties that tend to go together and support one another without being necessarily coinstantiated (see, e.g., Chiong 2005). If so, death cannot be defined in a set of necessary and sufficient conditions—in which case no such definition can justify a particular standard.