" Animal rights theory seeks to move at least some nonhumans from the “thing” side of the “person / thing” dualism over to the “person” side. There are at least two reasons to offer in favor of this move. First, there is no characteristic or set of characteristics that is possessed by all humans (whom we regard as persons) that is not possessed by at least some animals. To put the matter a different way, those who support animal exploitation argue that animals are qualitatively different from humans so animals can be kept on the “thing” side of the “person / thing” dualism; animal rights advocates argue that there is no such difference because at least some nonhumans will possess the supposedly “exclusive” characteristic while some humans will not possess the characteristic. Nor is it enough to argue that species difference is itself morally relevant; after all, to rely on species alone as morally relevant is to assume what needs to be proved by those who hold such a view, and is morally indistinguishable from using race, sex, sexual orientation, or ability to determine membership in the moral community of persons. In other words, there is no reason to exclude animals from the progressive concept of personhood that has been developed. "

― Gary L. Francione , Animals as Persons: Essays on the Abolition of Animal Exploitation