The morphological alterations to the human skeleton that have occurred since the first bipedal hominid include changes in foot bone arrangement and size,hip size and shape,knee size,leg length and vertebral column shape and orientation.
Foot:the human foot has been redesigned to act as a platform to support the entire weight of the body,rather than acting as a grasping structure.as it did in early hominids.humans therefore have smaller toes than their bipedal ancestors.this includes a non opposable hallux(big toe),which is relocated in line with the other toes.moreover humans have a foot arch rather than flat feet.when non human hominids walk upright weight is transmitted from the heel along the outside of the foot and then through the middle toes.conversely a human foot transmits weight fromthe heel along the outside of the foot across the ball of the foot and finally through the big toe;this transferance of weight contributes to energy conservation during locomotion.
Hip:modern human hip joints are larger than quadrupedal ancestral species to better support the greater amount of body weight passing through them,as well as a shorter broader shape.this alteration in shape brought the vertebral column closer to the hip joint.providing a stable base for support of the trunk while walking upright.also because bipedal walking requires human to balance on a relatively unstable ball and socket joint the placement of the vertebral column closer to the hip joint allows humans to invest less muscular effort to balance.the shape change of the hip may have led to the decrease in the degree of hip extension an energy efficient adaptation.
Knee:Human knee joints are enlarged for the same reason as the hip-to better support an increased amount of body weight.the degree of knee extension has decreased.the changing pattern of the knee joint angle of humans shows a small extension peak called the double knee action in the mid stance phase.double knee action decreases energy lost by vertical movement of the centre of gravity.humans walk with their knees kept straight and the thighs went inward so that knees are almost directly under the body,rather than out of the side,as is the case with ancestral hominids.this type of gait also increases balances.
Limbs:an increase in leg length since the evolution of bipedalism changed how leg muscles functioned in upright gait. in humans, the push in walking comes from the leg muscles acting at the ankle.a longer leg allows the use of the natural swing of the limb so that when walking humans do not need to use the muscles to swing the other leg forward for the next step.as a consequence as the human forelimbs are not needed for locomotion.they are instead optimized for carrying holding and manipulating objects with graet precisions.
Skull:the human skull is balanced on the vertebral column:the foramen magnum is located inferioraly under the skull which puts much of the weight of the head behind the spine.the flat human face help maintaining the balance on the occipital condyles. because of this arrangement the erect position of the head is possible without the prominent supraorbital ridges and the strong molecular attachment found in.
Vertebral column:the vertebral column of humans takes a forward bend in the lumber region and a backward bend in the thoracic region.without the lumber curve, the vertebral column would always lean forward, a position that requires much more muscular effort for bipedal animals. with a forward bend humans use less muscular effort to stand and walk upright.together the lumber and throcacic curves bring the body center of gravity directly over the feet, also the degree of body erection is significantly smaller to conserve energy.