LIKE life itself, the mind first emerged in Earth’s oceans. What is less well appreciated is that it evolved there in at least two distinct ways. One sentient branch of the tree of life is descended from the animals that crawled onto dry land hundreds of millions of years ago. It comprises humans and other mammals, and birds. The other branch remained water-bound and eventually produced another collection of creatures possessing higher intelligence: the cephalopods, a class of animals that includes squid, cuttlefish and octopus, probably the smartest of them all. In “Other Minds”, Peter Godfrey-Smith, a philosopher, skilfully combines science, philosophy and his experiences of swimming among these tentacled beasts to illuminate the origin and nature of consciousness.