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Lessons > Step by Step: The Evolution of Bipedalism
 

Introduction to Bipedalism: What is Bipedalism

A human skeleton (standing in anatomical position) demonstrating bipedalism, and a chimpanzee skeleton (knuckle walking in anatomical position) demonstrating quadrupedalism.

Bipedalism refers to locomotion (e.g., walking, jogging, running, etc.) on two legs. It is not uncommon to see animals standing or walking on two legs, but only a few animals practice bipedalism as a consistent means of locomotion. Most other animals, including chimpanzees and gorillas, practice a form of locomotion called facultative bipedalism, a type of bipedalism assumed on a temporary basis in order to perform a particular function. For example, it was recently discovered that octopodes sometime walk bipedally1 in order to camouflage themselves from predators. Using six limbs piled on the top of their head, an octopus assumes the shape of a drifting plant, and then uses its two remaining limbs to literally walk away. As for quadrupeds (animals that move on four limbs), it is not uncommon to see antelope standing on their hind limbs while using their forelimbs to support themselves when reaching for food in high branches. Chimpanzees have been documented walking on two legs in order to carry things with their hands.

Habitual bipedalism is relatively rare. This is the form of bipedalism that is assumed as a regular (i.e., habitual) means of locomotion. Today, only humans and birds demonstrate habitual bipedalism. However, many early hominins (i.e., a classification term that includes modern humans and all their bipedal fossil relatives) show a combination of characteristics that indicate both habitual bipedalism and some arboreal behavior.