The diagrams compare the skeletal structures of two ancestors of modern humans, namely Australopithecus afarensis and Homo erectus. Overall, it can be seen that the former was more adapted to tree climbing, while the latter developed features suitable for long-distance walking and running.
Australopithecus had an unbalanced head with a long snout, high and narrow shoulders, and a wide chest. In addition, its waist was short and wide, and the forearms and femoral neck were relatively long. Its hip, knee, and ankle joints were small, and the feet were characterized by a partial arch, long toes, and a small heel bone, all of which suggest climbing ability.
In contrast, Homo erectus had a balanced head with a short snout, low and wide shoulders, and a narrower chest. Its waist was tall and narrow, and the forearms were short. Furthermore, this ancestor possessed larger hip and ankle joints, a long Achilles tendon, and an enlarged heel bone. The foot was more stabilized with shorter toes, making the species more suitable for endurance running.