Primates are an order of mammals that includes humans, apes, monkeys, lemurs, lorises and tarsiers. They show several distinctive characteristics that distinguish them from other mammals. Most primates possess grasping hands and feet, with nails instead of claws on most digits. The first digit is often opposable, allowing effective grasping and manipulation of objects. Their fingertips commonly have sensitive tactile pads and fingerprints. The eyes are directed forward, producing binocular and stereoscopic vision, which is particularly useful for judging distance during climbing and movement through trees. Primates generally have a well-developed brain, especially the cerebral cortex, and show considerable learning ability, memory and behavioural flexibility. They usually have relatively long gestation and infancy, prolonged parental care, and complex social behaviour. The limbs of primates are generally adapted for climbing, grasping and varied forms of locomotion. The shoulder joint is highly mobile, particularly in apes, while the clavicle is well developed. Primates usually have a generalized dental pattern, although the number and form of teeth vary among groups. The presence of three types of teeth—incisors, canines and cheek teeth—allows them to