Due to the forward orientation of their large eyes, the primates have stereoscopic sight, allowing them to estimate distances. This comes in handy while climbing and leaping from one branch to another. They can also see colours that several animals cannot see. This way, they see whether fruits are ripe and can recognize different flowers, fruits and leaves. This capacity to distinguish colours can also be important during the mating season.
Nearly all primates will spend their entire life as part of a social group. One of the most important advantages of this is safety. All eyes and ears are directed towards finding potential predators. This is particularly important for young animals because they may depend on their parents and other members of the group for a longer period.