The diagram illustrates the skeletal systems of two ancestors of modern humans, including , Australopithecus afarensis and Homo erectus.
Overall, it can be seen that both skeletal systems have different physical changes, especially head, shoulders, chest, waist, forearm, toes and femoral neck.
Looking ahead, Australopithecus afarensis ancestor had unbalanced head and high, narrow shoulders, while Homo erectus ancestor had balanced head and low, wide shoulders. Moreover, tree climber had wide chest and short, wide waist, whereas endurance runner had narrow chest and tall, narrow waist.
In detail, Australopithecus afarensis had long forearm, long toss and partial foot arch. Although, Homo erectus had short forearm, short toes and stabilized foot arch. Furthermore, former ancestor has small heelbone, long femoral neck and short achilles tendon. Nevetherless, later ancestor had enlarged heelbone, short femoral neck and long achilles tendon. Additionally, tree climber had small gluteus maximus, hip, knee and ankle joints. However, endurance runner had large ones.