Final answer:
Human bipedalism is more energetically efficient than quadrupedalism, due to anatomical adaptations such as the valgus angle, longer leg structures, and arched feet. These features have likely evolved due to the benefits they provided for our hunter-gatherer ancestors, and are supported by the human body's metabolic efficiency in converting food into energy.
Step-by-step explanation:
Studies have shown that human bipedalism is more energetically efficient than quadrupedalism or bent-hip, bent-knee bipedalism. Early hominins such as Homo erectus exhibited anatomical features that favored this efficiency, including a broader pelvis, longer legs, and arched feet, along with a distinctive inward angle of the femur known as the valgus angle. These adaptations positioned the knees and feet under the center of the pelvis, aiding in balance and energy-efficient locomotion.
The angling of the femur, the development of spinal curves to balance the upper body's weight, and the evolution of foot arches contributed significantly to the success of bipedalism. These adaptations potentially offered advantages such as freeing hands for carrying tools, food, or offspring and improving energy efficiency in the context of gathering-hunting lifestyles practiced by ancestors for over two million years.
Furthermore, human metabolism converts the chemical energy from food into mechanical work with an efficiency of 20-25%, and bipedalism helps maintain body temperature by exposing more of the body's surface for thermoregulation. These factors contribute to the hypothesis that bipedalism evolved as an adaptation to a savanna habitat, as proposed by the savanna hypothesis.