Abstract

According to a traditional view, humans are superior to their non-human terrestrial companions because they alone are “rational animals.” Although the traditional view is presupposed by our social and legal institutions, it has been called into question by modern science: Darwin himself claimed that humans differ in degree rather than in kind from animals, and recent discoveries in comparative animal cognition have seemed to confirm Darwin's assertion. Sustaining the traditional view in light of these discoveries calls out for a careful comparison of the human mind with its precursors, the vertebrate mind and the mammalian mind. Psychological capacities shared across the animal kingdom are repurposed in humans, rendering humans uniquely capable of rationality. To be rational is to respond appropriately to value. Humans as such are not rational animals, but have the potential to become rational animals. This potential marks a morally relevant difference in kind between humans and non-human animals.