Bipedalism

Bipedalism is locomotion on two legs. It occurs in humans and other animals, either habitually or for particular activities.

Human gait: The repeating pattern of motions used during human walking. Walking alternates support between the legs while keeping the body balanced over each step.
Human evolution: The evolutionary history of humans and their ancestors. Bipedalism arose early in the human lineage, before many later human traits.
Human running: A form of human locomotion in which both feet periodically leave the ground. Running uses the same two-legged body plan but differs from walking in its airborne phases.
Quadrupedalism: Locomotion using four limbs for support or movement. Four-limbed movement generally offers a broader support base than bipedal locomotion.
Center of mass: The point representing the average position of an object's mass. Bipedal steps continually shift the body's center of mass over its supporting foot.
Sahelanthropus tchadensis: An extinct hominin species known from fossils dated to roughly seven million years ago. Its skull anatomy has been used to investigate the earliest possible evidence of bipedalism.
Bird locomotion: The ways birds move, including walking, running, hopping, and flying. Birds use two legs for terrestrial movement despite a very different body plan.
Knuckle-walking: A form of quadrupedal locomotion in which an animal supports its forelimbs on the knuckles. Chimpanzees and gorillas combine knuckle-walking with occasional upright movement.
Balance (ability): The ability to maintain or recover a stable body position. Bipedal locomotion depends on controlling balance over a narrow base of support.
Australopithecus afarensis: An extinct East African hominin species that lived about 3.9 to 2.9 million years ago. Its skeleton and footprints show that habitual bipedalism was established by its time.

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