Primate Heritage:

Man belongs to a group of  animals called mammals which are different  from other animal groups in possessing hair, and milk producing mammary glands, among other things. Mammals can be further divided into smaller groups or 'orders'  on the basis of 4fferences within the group. 'Primates',  the order to which man belongs, alongwith apes and monkeys, were active during the night, that  is, they were nocturnal in the beginning of  their evolution. These animals were insect-eaters  and lived on trees. This combination of  feeding on insects, while being suspended on branches and  

twigs, led the primates to develop some important adaptations. The hand, underwent several changes. The thumb became opposable, that is, it closes to meet the finger tips which aided in holding the prey. Sensitive fingers developed, having nails rather than claws. Eye sockets were shifted to the front of the head, providing  the primates a better vision and keen ability for judging distance. These striking adaptations in  the primates gave rise to large sized forms, which adopted a diurnal life style, i.e. they were active during the day. Their diet included plant food like leaves and fruits. The origin of monkeys and apes took these adaptations  to even higher levels. Possession of sensitive finger tips became of  even greater importance, as the ripeness of  fruits could be judged better by  touch than by sight. Apes move beneath the branches, suspended by  long agile arms rather than walking along them. This involves a relatively upright posture, and their hips became a part of  this kind of movement. Even when  they move on the ground, apes ockasionally walk as bipeds, i.e., on two feet. It may be an awkward walk with short steps and swaying motion, but  it is two footed. nonetheless. Changes in the skull and back~bone  help in the upright posture. And the way the heart, lungs and other body organs are suspended in the abdomen differs from that of  conventionally four footed animals.