... particles, of which an object is composed, have altered. Obviously, with a living organism this never occurs since parts are continually being lost or renewed. So sameness of physical substance won't be a useful criterion for determining personal identity over time since no living human being ever maintains precisely the same physical constituents from moment to moment. For Locke a 'man' is a particular biological organism: a member of the species Homo Sapiens. A man is like an oak tree or a horse in this respect. A huge spreading oak tree is still the same oak it was twenty years ago, despite having doubled in size and shed its leaves twenty times. It is not the same substance, but it is the same oak, in virtue of the continued function of its living parts. In the same way, I am the same man I was ten years ago, despite both physical ...

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