One concept of personal persistence over time is simply to have continuous bodily existence.[8] However, as the Ship of Theseus problem illustrates, even for inanimate objects there are difficulties in determining whether one physical body at one time is the same thing as a physical body at another time. With humans, over time our bodies age and grow, losing and gaining matter, and over sufficient years will not consist of most of the matter they once consisted of. It is thus problematic to ground persistence of personal identity over time in the continuous existence of our bodies. Nevertheless, this approach has its supporters which define humans as a biological organism and asserts the proposition that a psychological relation is not necessary for personal continuity.[note 8] This personal identity ontology assumes the relational theory[9] of life-sustaining processes instead of bodily continuity.
Derek Parfit presents a thought experiment designed to bring out intuitions about the corporeal continuity. This thought experiment discusses cases in which a person is teletransported from Earth to Mars.[note 9] Ultimately, the inability to specify where on a spectrum does the transmitted person stop being identical to the initial person on Earth appears to show that having a numerically identical physical body is not the criterion for personal identity