Bipedalism, or erect bipedalism
, is the defining feature of hominid
s. It is the locomotor
pattern in which the body is maintained in an upright position on two legs, while moving by means of a heel-toe slide.
Animals that do not walk on two legs have straight spines
, while humans have an S-shaped spine to center the bodyweight over the feet. The locking knee joint
found in humans also helps make it easier to stand upright, while other primates
do not have this attribute.