Is Animalism Undermined by Conjoined Twinning Cases?

Animalism claims that we are animals, i.e. biological organisms of the primate species Homo sapiens. If there is a case in which the number of persons differs from the number of organisms, then animalism is false. Timothy Campbell and Jeff McMahan hold that there are, at least, two such cases: the dicephalus and the cephalopagus conjoined twinning cases. Recently, Eric Olson argued that either Campbell and McMahan's arguments assume the point at issue, rely on undefended assumptions, or constitute paradigmatic anti-animalist claims. After characterising animalism, we address Campbell and McMahan's arguments and Olson's replies. We endorse Olson's first general objection and reject the second and third, nonetheless concluding that animalism isn't undermined by conjoined twinning cases.