A Lot Goes on Inside a Fish
Peter Godfrey-Smith:
Fish will count objects in experimental tasks. They use counting as a last resort, apparently, using other clues if they can, but the same is true of dolphins and people. Fish have learned to discriminate different styles of music – blues from classical – and could extrapolate from one blues artist to another; they were not learning the quirks of one performer. This is a quite abstract feat of pattern-recognition. A lot goes on inside a fish. … Why, then did fish (or some of them) become so smart? The question must first be asked the right way. The wrong way to ask it is: “Why do fish need to be smart?” This is not a question of need, but of relative advantage. If you are a fish, can you do a bit better than others in your population if you are a bit smarter, especially given the costs of building and running a larger brain? If you can indeed do better, what gives rise to this advantage? Much of the answer seems to be that fish, even more than seems immediately apparent, are gregarious animals. They are continually interacting with others. Social interaction creates a complex environment for an animal, and is very often a driver of the evolution of intelligence. This principle was originally developed for primates, where especially large brains are found in the more social species, but it has a broader application, and fish look like a likely case.
Metazoa: Animal Life and the Birth of the Mind, p. 178.