  Kant was interested not only in the inanimate bodies studied by physics, but also in living organisms, which he viewed as deserving of additional philosophical scrutiny due to their special status, for two reasons. First, the symmetries and regularities of their structure and workings make them “in the highest degree contingent” (5: 360) and “mechanically inexplicable.” Second, organisms come from their own kind; grow their own functional parts, or organs, and repair them if they become damaged; and do in general exhibit homeostasis. These facts about them prompt Kant to claim that an organism is “cause and effect of itself” (5: 370). In a sense, a living entity is self-caused, and indeed by a causality that we can grasp solely “under the idea of purposes as a principle” (5: 383). Organisms, in other words, are “natural purposes,” or naturally occurring ensembles of parts purposefully fitted and working in unity.