The literature of bioethics suffers from two serious problems. (1) Most authors are unable to take seriously both the rights of the great apes and of severely disabled human infants. Rationalism—moral status rests on rational capacities—wrongly assigns a higher moral status to the great apes than to all severely disabled human infants with less rational capacities than the great apes. Anthropocentrism—moral status depends on membership in the human species—falsely grants all humans a higher moral status than the great apes. Animalism—moral (...) status is dependent on the ability to suffer—mistakenly equates the moral status of humans and most animals. (2) The concept person is widely used for justificatory purposes, but it seems that it cannot play such a role. It seems that it is either redundant or unable to play any justificatory role. I argue that we can solve the second problem by understanding person as a thick evaluative concept. This then enables us to justify assigning a higher moral status to the great apes than to simple animals: the great apes are persons. To solve the first problem, I argue that certain severely disabled infants have a higher moral status than the great apes because they are dependent upon human relationships for their well-being. Only very limited abilities are required for such relationships, and the question who is capable of them must be based on thick evaluative concepts. Thus, it turns out that to make progress in bioethics we must assign thick evaluative concepts a central role. (shrink)