Quite fundamental to any understanding of animal behaviour is the
distinction so clearly drawn by Sir Ray Lankester between the
"little-brain" type, rich in inborn or instinctive capacities, but
relatively slow to learn, and the "big-brain" type, with a relatively
poor endowment of specialised instincts, but with great educability. The
"little-brain" type finds its climax in ants and bees; the "big-brain"
type in horses and dogs, elephants and monkeys. And of all animals
monkeys are the quickest to learn, if we use the word "learn" to mean
the formation of useful associations between this and that, between a
given sense-presentation and a particular piece of behaviour.