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The diagram compares the skeletal systems of two human ancestors, Australopithecus afarensis and Homo erectus, illustrating their physical adaptations to different modes of locomotion such as walking, climbing, and running.
Overall, Australopithecus afarensis displays skeletal features suited for both walking and tree climbing, characterized by a more primitive structure. In contrast, Homo erectus exhibits significant advancements in skeletal anatomy, optimized for walking and endurance running, particularly due to its stabilized foot structure and larger joints.
Australopithecus afarensis is depicted as having an unbalanced head with a long snout and high, narrow shoulders, which likely limited its ability to walk efficiently. Its chest is notably wide, and the waist is short and broad, suggesting a compact frame. The limbs further reflect its climbing adaptations, with long forearms and small hip, knee, and ankle joints, which would have reduced walking efficiency. Additionally, its feet are designed with long toes and a partial foot arch, which emphasize a reliance on gripping rather than stable bipedal motion.
In comparison, Homo erectus demonstrates an evolved skeletal system ideal for endurance running and efficient walking. It has a balanced head with a short snout and low, wide shoulders, providing stability during motion. The chest is narrow, and the waist is tall and narrow, further supporting long-distance running. Its legs and feet show significant advancements, including large hip, knee, and ankle joints, an enlarged heel bone, and a stabilized foot arch. Additionally, the presence of short toes enhances its ability to sustain efficient bipedal locomotion. These features are complemented by its large gluteal muscles (not shown in the diagram), which enhance running performance.
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