Hands

Evolution

The prehensile hands and feet of primatesevolved from the mobile hands of semi-arborealtree shrews that lived about 60 million years ago. This development has been accompanied by important changes in the brain and the relocation of the eyes to the front of the face, together allowing the muscle control and stereoscopic vision necessary for controlled grasping. This grasping, also known as power grip, is supplemented by the precision grip between the thumb and the distal finger pads made possible by the opposable thumbs. Hominidae (great apes including humans) acquired an erect bipedal posture about 3.6 million years ago, which freed the hands from the task of locomotion and paved the way for the precision and range of motion in human hands. Functional analyses of the features unique to the hand of modern humans have shown that they are consistent with the stresses and requirements associated with the effective use of Paleolithic stone tools. It is possible that the refinement of the bipedal posture in the earliest hominids evolved to facilitate the use of the trunk as leverage in accelerating the hand.