Almost all living primates have prehensile hands and feet, and most have five digits on these appendages, including opposable thumbs. With their hands and feet, many primates are able to perform different types of grips, whether holding food, or grabbing onto branches or trunks to hold on. Humans are the exception as their feet, while still pentadactyl, are not prehensile. The hands are particularly sensitive, adding to the sense of touch. Like many of the other defining characteristics of primates, these features add to the ability to live in trees successfully and efficiently.
Unlike many other mammals, primates have particularly flexible and limber shoulders and hip joints. The shoulders help them to have overarm movement, ideal for swinging through trees and being able to climb up and down quickly. Their hips are just as mobile, allowing them greater range of motion in their legs. These characteristics also evolved to aid in the primates' primarily arboreal lifestyle.
The brains of primates often is one of the most distinguishable characteristics from other types of mammals or animals. The olfactory region in primates has been reduced greatly in most species, such as humans, and the cerebrum expanded to accept the order's increasing reliance on sight and social behaviors. The areas of the brain that correlate with eye-hand coordination and stereoscopic vision are particularly large compared to other mammals.
Other primate characteristics include having a nail on the first digit although, in many cases, each digit has a nail instead of a claw. Primates also possess a clavicle, or collarbone. All primates exhibit the tendency to be erect; this trait is visible when even quadrapedal primates sit or stand. Most species also occasionally exhibit bipedalism, or standing on the two hind legs like humans.
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