Members of the animal kingdom’s intelligentsia tend to be sociable; indeed, the need to remember and manage a complex network of relationships might have helped drive the evolution of their brains. Smart animals also tend to be long-lived, since a large brain both takes a long time to grow and helps an animal avoid danger. Apes, elephants, whales and dolphins, crows and other corvids, parrots: They all share these traits.

Cephalopods do not.