Homo erectus: Adaptation
This state of affairs lasted for a very long time, probably as much as three million years. Slowly, generation after generation, the bodies of one line of ape-men became better adapted to the plains-living life. The feet became more suited to running, lost their ability to grasp and acquired a slight arch. The hips changed, the joint moved towards the centre of the pelvis to balance the upright torso, and the pelvis itself became more bowl-shaped and broader to provide a base for the strong muscles running between the pelvis and spine that were needed to hold the belly in its new upright position. The spine developed a slight curve so that the weight of the upper part of the body was better centred. Most importantly, the skull changed, the jaw became smaller and the forehead more domed. The brain of the first ape-men was similar to that of a gorilla, around 500 cubic centimetres, but by this time had doubled in size and these ape-men had grown to a height of over a metre and a half and were called Homo erectus, Upright Man.