| Walking upright made human body and human society began to evolve by a unique path. Bepedalism is the symbol of human origin, and it is the core problem of human evolution.How did bipedalism originated and how was it evolved? This is a question remains unsolved. In order to make a reasonable explanation, researchers proposed even more than 30 kinds of potheses. Unfortunately, most of them are lack of persuasion. Here, we give a new reasonable hypothesis from biological dynamics. We think that the locomotion mode of two-arm brachiation is the transition of human bipedalism based on the analisis of many similarities of this two locomotion mode.In this dissertation two-arm brachiation is suggested as a mode of locomotion used frequently by ancient human. It was proven that, in order to gain the highest swing efficiency, the upper limbs should be shorter than the lower limbs, and all kinds of quadruped mode are of lower efficiency for human, due to their special body structure. On the other hand, two-arm brachiation would straighten the joints of the hips and the knees, as well as the whole bodies of ancient human, which made ancient human walk upright. During continuous two-arm brachiation the body of ancient human was stretched continuously by gravity and the centrifugal force, which can account for a lot of characteristics of the body structure of human.Based on the conjecture of two-arm brachiation and the corresponding mechanics analysis, we would try to explain the origin of bipedalism, the evolution of human, and many main characteristics of the body structure of Australopithecine, which also be supported by the human bone fossils. The stress analysis of human body model shows semi-erect posture is actually a very unstable mechanical structure. So, maybe it was very hard to stand up directly for ancient human.This dissertation try to explain the relationship between human skeleton evolution and two-arm swing with the help of ancient human fossils and we measured the modern human body length ratio to verify the theoretical predictions of this dissertation.We would try to answer the following interesting questions by analysis related mechanical models:(1) Why human bodies are so slim compared with other great apes?(2) Why human’s upper limbs are shorter than the lower ones, and human’s trunks are shorter than upper limbs?(3) Why our thumbs are very long, but our palms are so short?(4) Why human has a long neck?(5) Why our chests and shoulders are so broad?(6) Why our scapulas sit parallel to the back, but the scapulas of other apes are obliquely located on two sides?(7) Why Australopithecine have a long flexible waist? Some ancient fossils may have 6 vertebra lumbar vertebrae(fossil STS14), even their thoracic and sacral vertebrae show functions of lumbar vertebrae.(8) Why human’s spine has so many curves?(9) The Australopithecus infants’ brains are much smaller than modern human infants, but the pelvis of Australopithecus are wider than that of modern human. Why Australopithecus needed such a wide pelvis if not because of the pressure of birth and walking?(10) Fossils show that human feet had arches 3.6 million years ago. How sis the arches evolve when ancient human still spent most time on trees?(11) Our big toes are parallel to the others, is it evolved by walking?(12) It is known that there is a long period of hunting history during the evolution of human. As a bipedal creature, our ancestors were much weaker and slower than most big animas, how could our ancestors hunt other animas and run a long distance?(13) Is it easy to evolve bipedalism from semi-bipedalism?Based on the mechanical analysis in this dissertation it is suggested that the human behavior of walking upright should be evolved on the trees with the help of gravity rather than against gravity on the ground. |
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