Conjoined twins share no parts

Dicephalus conjoined twins, conjoined twins fused below the neck, pose a unique problem for animalism, the view that each of us is identical to a living human organism. If dicephalus twins are, or share, the same human organism, then at least some of us are not numerically identical to living human organisms. Some animalists have responded by arguing that dicephalus twins are numerically distinct but overlapping human organisms. Another option is to say that dicephalus twins are merely conjoined: they are intimately connected with one another, but they do not overlap or share any of their parts. In this paper, I argue that there are both metaphysical and practical or ethical considerations that weigh in favor of the non-overlapping option. Animalists who already have good reason to think that there are two living human organisms in a case of dicephalus twins should prefer the non-overlapping option to the overlapping option.