Index• Definition• The Australopithecus• Changes in the body • The Foto • The Hip • The knee • The Human Skull
The Australopithecus• The Australopithecus represent the oldest hominid fossils.• The first Australopithecus only measure about one meter high. It had, long simetrical arms, and his pelvis, backbone and legs showed that ti was qualified of bipedalism.• This si the first feature of the human arce that we are bale to recognize in our ascendants.
Definition• Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped, meaning "two feet"• It gives a celar benefit, leaves free the arms and hands when walking, that can be used in other actions. It also increases the visual field in open areas with high grass.
Differences• There are some diferences between human and chimpanzee bipedalism: • Chimpanzees are unable to extend their knee-joints to produce a straight leg in the stance phase. • Muscular power has to be exerted to support the body. • The constantly flexed position of the chimpanzee leg also mean there is no toe off and heel strike in the swing phase.
The Foot• The human foot evolved to act as a platform to support the entire weight of the body, rather than acting as a structure, as it did in early hominids. Humans therefore have smaller toes than their bipedal ancestors.• 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 while a human foot transmits weight from the heel, along the outside of the foot, across the ball of the foot and finally through the big toe.• This transference of weight contributes to energy conservation during locomotion.
The Hip• Modern human hip joints are larger than in our ancestral species for the better support of the greater amount of body weight passing through them, as well as having a shorter, broader shape.• This change in the shape brought the vertebral column closer to the hip joint, providing a stable base for support of the trunk while walking upright.• Also as bipedal walking requires humans 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 in balancing.
The Knee• Human knee joints are enlarged for the same reason as the hip ,for the better support in 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”.• Double knee action decreases energy lost by vertical movement of the center of gravity. Humans walk with their knees kept straight and the thighs bent inward so that the knees are almost directly under the body, rather than out to the side, as is the case in ancestral hominids. This also helps balance increase.
The Human Skull• The human skull is balanced on the vertebral column: The foramen magnum is located under the skull, which puts much of the weight of the head behind the spine.• Also, the flat human face helps to maintain balance. Because of this, the erect position of the head is possible without the prominent bone and the strong muscular attachments found in. As a result, in humans the muscles of the forehead (the occipitofrontalis) are only used for facial expressions.