Bipedal locomotion is an ability of an organism to move by using its two feet and two legs in an upright position. An animal that uses this type of locomotion is known as a biped, meaning “two feet”. Biped came from the Latin words “bis”, which means “double” and “pes”, which means “foot”. Bipedal locomotion involves not only walking but also running, hopping, galloping, and other movements by using two feet in an upright position. Human beings are considered to be the only kind of mammal to move on two legs in an upright position at all times. Ardipithecus ramidus is known as the earliest bipedal ancestor who existed 4.4 million years ago.