...each living creature is said to be alive and to be the same individual-- as for example someone is said to be the same person from when he is a child until he comes to be an old man. And yet, if he's called the same, that's despite the fact that he's never made up from the same things, but is always being renewed, and losing what he had before, whether it's hair, or flesh, or bones, or blood, in fact the whole body. And don't suppose that this is just true in the case of the body; in the case of the soul, too, its traits, habits, opinions, desires, pleasures, pains, fears-- none of these things is ever the same in any individual, but some are coming into existence, others passing away.

Plato