We can generate a puzzle concerning identity by combining two plausible assumptions and one strong temptation. I shall consider these in order.
The first assumption is often ignored, at least by implication, but it is something which seems obviously to be the case, namely, that we human beings are animals—comparatively complex animals by the standards that hold for our planet, perhaps, but animals nonetheless. For such animals the conditions for individuation are no more complex than they are for any other animal, or, at least, for any other mammal. There are problems, of a sort, for Siamese twins, real or conceptual, and there may be individuation problems of one kind or another kind for various animals, including humans, during the reproductive cycle, as well as classification problems concerning what John Locke wanted to teach us all not to consider monsters. Still, by and large, the question is a simple one. Animals are born and they die, and, in general, there is not too much theoretical puzzlement over their world lines. Between any given birth and its corresponding death there is precisely one such line. Thus, I shall take our animality for granted. I do not know if the puzzle I pose would still arise on other accounts or not. As there are no coherent alternative accounts around, the question is a fairly academic one.