The diagram compares the skeletal structures of two early human ancestors, Australopithecus afarensis and Homo erectus.
Overall, while Australopithecus afarensis shows physical traits suited for both walking and climbing, Homo erectus developed a more advanced structure optimized for running and endurance walking.
The first species, Australopithecus afarensis, had an unbalanced head with a long snout, high and narrow shoulders, and a wide chest. Its short, wide waist and long forearms suggest strong climbing abilities. In addition, this ancestor had relatively small hip, knee, and ankle joints, as well as long toes and a partial foot arch, which limited its stability during running.
By contrast, Homo erectus possessed a balanced head with a short snout and a narrow chest. Its low, wide shoulders and tall, narrow waist indicate efficient movement suited for endurance running. Furthermore, its large joints, long Achilles tendon, and stabilized foot arch, along with short toes and an enlarged heelbone, reflect a fully adapted bipedal structure designed for long-distance travel.