The diagram illustrates two different skeleton systems of human ancestors.
From an overall perspective, it can be observed that the two ancient human species’ skeletal systems evolved in relation to their predominant physical movements. Specifically, the Australopithecus afarensis are generally larger in their stature as compared to the Homo erectus.
Starting with the Australopithecus afarensis, the skeletal structure of this species evolves to serve the function of walking and tree climbing. The first skeleton contains an unbalanced head due to its long snout. A wide chest with a short waist explains why this human ancestor seems to be considerably huge in terms of build. Moreover, as tree climbers, their forearms are considered long, leading to a bulky hand proportion. The lower body is meant for walking as evident in the short achilles tendon, small heel bones, and long toes.
In comparison, the anatomy of the Homo erectus facilitates walking and endurance running. A more balanced head with a shorter snout can be observed in this species, which shows a stark contrast to that of the Australopithecus afarensis. While their counterpart’s shoulders are higher and narrower, Homo erectus’ shoulders are lower and wider as they are runners. Additionally, their chests are tall and narrow as opposed to the Australopithecus afarensis’ significantly wider chests along and shorter waists. Besides their anatomical differences in the upper body, the endurance runner contains a longer Achilles tendon and shorter toes than the previous species.