As a first-year medical student, I lived near a veterinary program. The comparison often made—by both med and vet students, as well as community members—was that med students studied humans, whereas vet students studied everything else. Of course, in its practical aim, medicine is exclusively about people. We undergo a serious study of human biology so as to meet the responsibility of caring for other human beings, and the central challenge of medicine is matching that knowledge to the unique experiences of our patients. We should be careful, however, not to underestimate the importance of non-human life for that purpose. As a scientific endeavor, human medicine is predicated on knowledge of many different types of living things, whether we consider the ecology of our bodies or the pharmacology of our cures. Moreover, the humility of its practitioners stems from recognizing the mutual dependence of human life and the rest of the biosphere. In short, medicine is a multi-species affair.