bipedal

Bipedal describes locomotion or posture that uses two legs for support and propulsion. The term can refer to a species whose habitual movement is on two feet, as well as to organisms or individuals that can walk on two legs but do so only occasionally or under certain conditions. It is most commonly associated with humans, who are obligate bipeds in daily life.

Anatomy and mechanics of bipedal locomotion involve maintaining balance and propulsion with the legs in an upright posture. In habitual bipeds, the pelvis is shortened and broadened, the femur angles inward to place the knees under the torso, and the spine forms an S-shaped curve for vertical balance. The feet usually have arches and a non-grasping big toe, features that support efficient forward propulsion and weight transfer from heel to toe during the walking cycle.

Evolution and diversity: Bipedalism has evolved in multiple lineages and is studied most intensively in human evolution. The best-known evidence suggests that habitual bipedality appeared among early hominins around 3 to 6 million years ago, with later species such as Homo erectus showing more efficient long-distance walking. Theories about its advantages include energy efficiency for travel, the ability to carry objects (including offspring) while walking, improved field of view, and thermoregulation in open environments.

Variants and applications: Some birds are obligate bipeds, while certain mammals and reptiles can adopt two-legged locomotion under specific circumstances. Beyond biology, bipedalism is a central concept in robotics, computer animation, and biomechanics, where two-legged design emphasizes balance, stability, and control on varied surfaces.