88  Upright gait
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The upright gait of humans involves concurrent occurrence of the following anatomic features: stretched knee and hip joint, cervical spine joined to the head at a point centred beneath it (instead of at the back as in apes), flat face, improved organ of equilibrium, straight back, foot with raised instep, a strong big toe and brain functions facilitating an upright gait. Each of these features would have required the simultaneous occurrence of several thousand correct and perfectly-adapted mutations in the genome, a sheer unthinkable scenario.


Unique features of human upright gait:

The human foot is formed to the best advantage for the upright gait. It forms a flat arch between the ball and heel. This facilitates better balancing on uneven terrain. The foot has twenty-six bones as well as many muscles and tendons that give it the flexibility it needs to make walking function well. Thanks to the foot’s arched instep, it can absorb the impact of walking and running. Apes, on the other hand, have hand-like feet that make it easier to grasp branches, but harder to walk.

The big toe of the human foot is particularly strong. It lies parallel to the other toes. At every step, the big toe provides the final abetting. The big toe must be particularly strong to keep the body under control when walking. In apes, on the other hand, the big toe is splayed, enabling it to grasp and hold a branch readily.

The human knee joint makes it possible to extend the legs until they are straight. In the upright position, the knee joint assumes an extended and locked position that relieves the muscles while in standing position. Apes cannot extend their knee joints completely, forcing them to walk with bent legs, a very tiring affair. Scott F. Dye, M.D. wrote the following passage on the uniqueness of the human knee, “Despite the general similarity of the knee among all tetrapods (land vertebrates), none of them provides an ideal model for the human knee” (1).

Human legs are about half as long as the entire body, making it possible to walk or run long distances. The legs of apes, on the other hand, make up only about one-third of the length of the body, so that these animals tire more quickly from walking. A chimpanzee is unable to stretch its legs out straight when standing and finds the upright position very strenuous. Its face is then turned upwards so that it must bend over to look ahead. In apes, the spine is joined to the back of the head, in humans to the bottom of the head. This means apes can look straight ahead readily when they move on all fours, but not when they stand upright. A small human child crawling on all fours has to expend considerable effort to hold its head up in order to look straight ahead.

The hip joints of the human body make it possible to move the femoral bones into a vertical position. This is not possible for apes. The human femur (thigh bone) is constructed so as to allow the knees and feet to be close together when standing. The position of the feet near the centre of gravity of a standing person makes for the greatest possible degree of stability for walking and running. While we walk or run, the body is carried alternately by one foot at a time and would therefore tend to tip over if the centre of gravity were too far outside the load bearing foot. The femurs of apes, on the other hand, are straight, so that the knees are farther apart. That is the reason apes sway from side to side so much when they attempt to walk upright.

The straight back of humans positions the head directly above the hips when a person is standing. Apes have a bent back and must therefore use their hands for support to keep themselves from falling over. The human spine is slightly S-shaped, whereas the spine in apes has a shape of a C. The ape spine is relaxed when the animal walks on all fours. In humans, the spine is relaxed when we walk upright. Any transitional forms would have had to bear an unfavourable load. In this connection, it is interesting to note that present aboriginal groups have a healthy upright gait. The only creatures that in some cases go through life with a bent posture are civilized urban humans.

The flat face of humans makes it possible for us to see what is right in front of us. The chimpanzee, on the other hand, has eyes set farther back in its head and a protruding chin, making it unable to see an obstacle right in front when walking upright. The ape’s head is lower when he walks on all fours, thus enabling it to see the obstacles.

The organ of balance in the human ear is designed to master the vertical spatial dimension in particular. In apes, on the other hand, the capacity to balance in the anterior vertical dimension is much less pronounced (2). When walking on all fours, apes are normally already balanced by the four contact points. Apes cannot walk on their toes or stand on one leg. 
 
Facial expression is an important part of human communication. We may not always be conscious of the fact, but we actually keep a constant eye on the facial expressions of the persons within our field of view. We try to guess their thoughts and reactions. Many of our own reactions are influenced by the facial expressions of others. For example, when we see someone with a sad face, we ask why. Apes have relatively few facial muscles and can only change their facial expression within narrow limits.

The human vocal organ is conceived for the exchange of information using a language. Apes produce vocalizations using a different construction. The human larynx lies deeper in the throat, giving the tongue more room to move. This makes it possible to produce more vowels. In apes, the larynx lies much higher, making production of precise sounds impossible. The human oral cavity is also acoustically advantageous.

The ability to speak depends on a corresponding part of the brain that controls the muscles used in speech and processes the signals received by the aural sense so as to make them comprehensible. This brain region is lacking in apes.
 
The human brain is much larger than the ape brain. The human brain contains about 100 billion neurones, each of which has about 1,000 interconnections to other neurones. Counting the number of connections to the cerebral cortex at the rate of one connection per second would take 3.2 million years.

The ability to think is what makes a human being human. He is self-aware and creative. The human brain has the unique ability to recognize beauty. The left half of the brain contains the centre for processing and producing language and the right half contains the centre for making and perceiving music. No other creature has an “ear for music.”



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References:

(1) Scott F. Dye, M.D., An evolutionary perspective of the knee, Journal of bone and joint surgery, 69A, 1987, pages 976–983.
(2) Labyrinth and aufrechter Gang, factum Mai 1995, pages 17–21.
 
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