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REASONS:
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While there are many proposed reasons for the causes of bipedalism, this website will focus on five: the Upright Provider, the Upright Scavenger, the Efficient Walker, the Decreased Aggression, and the Social Expansionist.
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| The Upright Provider theory is proposed by Owen Lovejoy. The theory states that bipedal locomotion was selected to allow males to have the ability to carry food for their females and offspring back at a camp or village. Lovejoy builds his theory on a comparison to modern chimps. He notes that the existence of polygamy among chimps and thus the reduced survival rate of offspring due to the lack of attention by males. He believes that the lack of knowing who is the genetic father of the offspring causes males to not care for young. With the development of monogamy, this uncertainty is removed. With a certainty of fathership, males can assure the passing of their genetic material by simply providing food for female and the offspring sired with her. This is only made efficiently possible by the freeing up of the arms and hands to carry materials; thus the development of bipedalism. However, many opponents attack this theory citing the lack of sexual fidelity among modern hunter gather groups.
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.uPRIGHT PROVIDEr.
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(Upright Scavenger)
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The Upright Scavenger theory is proposed by Pat Shipman. By examining remains of animal bones with an electron microscope, Shipman noted the presence of stone tool markings after the creation of markings made earlier by predators and scavengers. Thus, she concluded that early hominids were scavengers. She believes that bipedalism was selected to allow for the greater coverage of land in search of scavengable carcasses as well as the ability to remove scavenged material from a kill site to a safer location where they cound be eaten more safely. In addition, bipedalism allowed for the use of stone tools to more efficiently remove meat and marrow from bones.
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| The Efficient Walker theory is proposed by Henry McHenry and Peter Rodman. McHenry and Rodman compared the efficiency of chimpanzees walking on two versus four legs. They found that two legged locomotion was far more efficient. They concluded that bipedalism was selected simply because it allowed for a father range of travel for hominids. As the Miocene forests decreased and hominids were forced into the savannas, bipedalism allowed for greater access to resources.
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Efficient Walker
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The Decreased Aggression theory is proposed by Nina G. Jablonski and George Chaplin. Published in the April 1993 issue of Journal of Human Evolution, this theory proposes that due to the increased scarcity of resources during the late Miocene there was an increased competition among hominids. In order coexist with the decrease in resources, Jablonski and Chaplin believe there were two feasible solutions: decreased social group size or increased mobility for greater access to resources. Noting the behavior among modern gorillas and the tendency for violence among and within social groups for resources, Jablonski and Chaplin believe that bipedalism allowed for greater access to resourcs and thus decreased conflicts among and within social groups of early hominids. With the decrease of social conflict among groups, the spread of humans throughout Africa became feasible.
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| The Social Expansionist theory is proposed by Lynne A. Isbell and Truman P. Young. The theory was published in the Journal of Human Evolution, May 1996. Isblee and Young believe that due to the reduced resources of the late Miocene, there were two feasible options for hominid species: reduce social group size or increase access to resources. Bipedalism was chosen to allow for greater access to resources. This allowed for the maintenance of larger social groups which would be better able to defend themselves against other groups of hominids or creatures. With the larger social groups, social interaction was developed further creating bonds and group strength.
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°Social Expansionist°
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In lumine Tuo videbimus lumen...
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While each of these theories is quite plausible, not all of them can be correct. The lack of substantial evidence with regards to social interaction, dietary habits, and migratory patterns makes many theories founded on fragmentary bits an pieces of hominid remains. Until further evidence discovered, one theory may be as good as the next.
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