Primates have really big brains relative to their body size if you compare them to other animals, even other mammals. The sheet of cells that forms the outer layer of mammal brains (the neocortex) is greatly enlarged. This neocortex is the newest part of the brain to evolve, and beneath it is a primitive brain similar to a reptile's brain (the medulla). As the center for memory, creative thinking, spatial reasoning, language, and conscious thought, the neocortex is what makes primates smart. A human being has the highest ratio of neocortex to medulla of any animal. Much of primate intelligence comes to play in social and learning behavior. Scientists believe the extreme development of the neocortex may be an adaptation for the advanced cooperation (e.g. for hunting) that takes place in primate societies. Sustained social interactions require that primates remember a lot of information about each other.

Mammals have a unique arrangement of a lower jaw directly hinged to the skull. The upper jaw is fixed, while the lower jaw is movable. A powerful bite results which, coupled with specialized teeth, allows mammals to eat a diversity of foods. Straight-edged incisor teeth at the front of the jaw are for cutting and gnawing. Pointed, canine teeth on the sides can grab and tear meat. Flat, broad molars are used to grind or crush plants or shelled animals. Mammals tend to have more than one type of tooth (heterodont dentition), with the mix depending on diet. Meat-eaters have sharp incisors and canines plus slicing molars; mammals who eat tough plants have duller incisors and canines, but large, ridged molars. All types of mammal teeth are replaced once or never during a mammal's lifetime. A coating of enamel, the hardest material found in a mammal's body, makes teeth built to last.