n mammals, as in other animals, intelligence is linked to the size and structure of the brain. The brains of mammals and other vertebrates are divided into three parts—the hindbrain, midbrain, and forebrain (see Brain: Evolution of the Brain). The hindbrain deals mainly with essential body processes, such as breathing, while the midbrain receives and coordinates sensory and motor impulses. The forebrain integrates and processes information, enabling an animal to make decisions and respond to the world around it. In mammals, the forebrain is highly developed and it has a folded surface that enables it to contain millions of interconnected neurons, or nerve cells.

In mammals, behavior is also acquired by imitation. If one animal in a group stumbles on a new way of doing something, others may follow the example. This kind of behavior can be seen in many animals, from dogs to dolphins, but it is particularly well developed in primates. Learning by imitation has been observed in chimpanzees and also in some species of monkeys. In one famous case, scientists fed sweet potatoes to a group of Japanese macaques living on a small offshore island. One animal discovered that the food could be cleaned by washing it in the sea, and after several years, all the adult macaques had adopted this cleaning routine.

A key feature of this kind of learned behavior is that it can be passed on from one generation to another, allowing succeeding generations to benefit from the experiences of earlier ones. This kind of learning played a key part in human evolution, and has since become one of the outstanding features of our species.

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