All these deal with being bipedal:
FINE BALANCE: Requires a fine sense of balance.
The inner ear has a network of fluid-filled canals which contain sensors which are sensitive to movement
and gravity. The sensors consist of fine hairs which send out signals to indicate direction and speed. Humans have a
more complex inner ear design than
FLAT FACE: So their eyes have a field of view
which extends down to the ground in front of the feet.
UPRIGHT SKULL: the position at which the spinal
cord enters the skull. In humans it is located at the bottom of the skull. This means the most natural
position for the head is looking
forward in the upright position.
STRAIGHT BACK: This is ideal for upright
posture because the torso and head are directly above the hips in the standing position. Apes have a curved
FULLY EXTENDABLE FEMUR BONES: When looking from
the front humans have femur bones which are
angled inwards as they come down from the hip. This has the effect of making
the knees and feet closer together. Having
feet closer together keeps the feet nearly under the center of the body and
gives stability during walking and running.
During walking and running the body is supported by one leg at any instant and so the body can topple over if the legs are
not right under the body. If the feet were not close together then the body would be thrown from side to
FULLY EXTENDABLE KNEE JOINTS:
VERY LONG LEGS: The length of human legs is
about half the total body. This makes it possible to walk and run for long distances with relative ease. In
contrast, apes are only about a third.
ARCHED FEET: The human foot is arched between
the ball of the foot and the toes. The foot has around 26 bones and many muscles and ligaments, tendons and nerves so the
foot can flex between the heel and the
ball. The arched structure of the foot makes it easy for a person to press
down on the ball for the foot which is
important for balance and control. This ability is also important for
movements such as standing on tiptoe,
running and turning. It also helps absorb shocks during walking and running.
In contrast the feet and hands of apes are
like hands suited for grasping.
STRONG BIG TOES: This feature is important for
walking and running. For each step, the final push from the ground comes from the big toe. In order to
propel the body forwards in a controlled manner, the big toe must be very strong. Apes have a toe designed
for grasping. They cannot make a firm push from their big toe.
Image Source: (Fair Use)
Miller and Levine, Prentice Hall Biology, 2008,