Was Jekyll Hyde?

Many philosophers say that two or more people or thinking beings could share a single human being in a split-personality case, if only the personalities were sufficiently independent and individually well integrated. I argue that this view is incompatible with our being material things, and conclude that there could never be two or more people in a split-personality case. This refutes the view, almost universally held, that facts about mental unity and disunity determine how many people there are. I suggest that the number of human people is simply the number of appropriately endowed human animals.