The diagram compares the skeletal features of two human ancestors, Australopithecus afarensis and Homo erectus, and shows how their bodies were adapted to different ways of moving.
Overall, Australopithecus afarensis had a body suited to both walking and climbing trees, whereas Homo erectus was clearly adapted for efficient walking and long-distance running.
In terms of the upper body, Australopithecus afarensis had an unbalanced head with a long snout, high and narrow shoulders, and a wide chest. By contrast, Homo erectus had a more balanced head with a shorter snout, lower and wider shoulders, and a narrower chest. The waist of Homo erectus was also taller and narrower.
Looking at the limbs and lower body, Australopithecus afarensis had long forearms, a small gluteus maximus, and a long femoral neck. In contrast, Homo erectus had shorter forearms, a much larger gluteus maximus and a shorter femoral neck. Furthermore, Homo erectus possessed larger hip, knee and ankle joints, a longer Achilles tendon, an enlarged heel bone and a stabilized foot arch, while Australopithecus afarensis had smaller joints, longer toes and only a partial foot arch.