Bipedalism is a form of terrestrial locomotion where a life form moves by means of its two rear limbs, or legs. A animal that moves in a bipedal manner is known as a biped, meaning “two feet” (from the Latin bi for “two” and ped for “foot”). Examples of bipedal movements include walking, running, or hopping, on two appendages (typically legs). Bipedalism is not unique to human beings, though our particular type of it is.
Bipedalism evolved well ahead of the human brain or the development of stone tools. Many diverse explanations have been presented to account for the evolution of upright walking. A number of the hypotheses consist of: (1) freeing the hands, which was beneficial for hauling food or tools; (2) better vision, in particular to see over high grass; (3) reducing the body’s exposure to hot sun, which allowed improved cooling throughout the day in an open landscape; (4) hunting or weapon use, which was much easier with upright posture; and (5) feeding from bushes and low hanging branches, which was easier when standing and moving upright amid closely spaced bushes.
Although none of these hypotheses in particular has had overwhelming support, recent study of chimpanzees favors the last one. Chimps move about on two legs most often when feeding on the ground from bushes and low hanging branches.
Bipedalism is nearly exclusively found in terrestrial animals, though at least two types of octopus walk bipedally on the ocean floor using two of their arms, allowing the left over arms to be used to disguise the octopus as a mat of algae or a floating coconut.