Research indicates that, by human measures for intelligence, dolphins are the second-most intelligent species on the planet. MRI scans show that dolphins are self-aware, and other research suggests that the marine mammals have a special vulnerability for suffering and trauma.
Dolphins have very highly developed brains, which are of an impressive size relative to the size of their bodies. The neocortex of a dolphin is notably expanded relative to other species, which suggests that dolphins are capable of higher-order thinking and advanced processing of emotions. Dolphins are also capable of understanding symbolic systems of communication and of comprehending abstract concepts, both of which are particularly human-like.