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This dimorphism has been seen as an evolutionary adaptation of females to bear lumbar load better during pregnancy , an adaptation that non-bipedal primates would not need to make. This idea, labelled "the wading hypothesis",  was originally suggested by the Oxford marine biologist Alister Hardy. Gordon Hewes suggested that the carrying of meat "over considerable distances" Hewes These apes may have once been bipedal, but then lost this ability when they were forced back into an arboreal habitat, presumably by those australopithecines from whom eventually evolved hominins. A feedback mechanism from the advantages of bipedality in hot and open habitats would then in turn make a forest preadaptation solidify as a permanent state. Peter Wheeler, a professor of evolutionary biology, proposes that bipedalism raises the amount of body surface area higher above the ground which results in a reduction in heat gain and helps heat dissipation. Analysis and interpretations of Ardipithecus reveal that this hypothesis needs modification to consider that the forest and woodland environmental preadaptation of early-stage hominid bipedalism preceded further refinement of bipedalism by the pressure of natural selection. In addition to the change in shoulder stability, changing locomotion would have increased the demand for shoulder mobility, which would have propelled the evolution of bipedalism forward. Among most monogamous primates, males and females are about the same size. It is also proposed that one cause of Neanderthal extinction was a less efficient running. Wheeler's "The evolution of bipedality and loss of functional body hair in hominids", that a possible advantage of bipedalism in the savanna was reducing the amount of surface area of the body exposed to the sun, helping regulate body temperature. November Learn how and when to remove this template message The postural feeding hypothesis has been recently supported by Dr. Ancient pollen found in the soil in the locations in which these fossils were found suggest that the area used to be much more wet and covered in thick vegetation and has only recently become the arid desert it is now.
Modern monogamous primates such as gibbons tend to be also territorial, but fossil evidence indicates that Australopithecus afarensis lived in large groups. Peter Wheeler, a professor of evolutionary biology, proposes that bipedalism raises the amount of body surface area higher above the ground which results in a reduction in heat gain and helps heat dissipation. A feedback mechanism from the advantages of bipedality in hot and open habitats would then in turn make a forest preadaptation solidify as a permanent state. Also, Hunt's hypotheses states that these movements coevolved with chimpanzee arm-hanging, as this movement was very effective and efficient in harvesting food. Why were the earliest hominins partially bipedal 2. Human skeletal changes due to bipedalism There are at least twelve distinct hypotheses as to how and why bipedalism evolved in humans, and also some debate as to when. Thus the male would leave his mate and offspring to search for food and return carrying the food in his arms walking on his legs. It is also proposed that one cause of Neanderthal extinction was a less efficient running. Other behavioural models[ edit ] There are a variety of ideas which promote a specific change in behaviour as the key driver for the evolution of hominid bipedalism. That is sexual dimorphism is minimal, and other studies have suggested that Australopithecus afarensis males were nearly twice the weight of females. According to this model, hominids were trying to stay as visible and as loud as possible all the time. Humans and orangutans are both unique to a bipedal reactive adaptation when climbing on thin branches, in which they have increased hip and knee extension in relation to the diameter of the branch, which can increase an arboreal feeding range and can be attributed to a convergent evolution of bipedalism evolving in arboreal environments. This model is supported by the reduction "feminization" of the male canine teeth in early hominids such as Sahelanthropus tchadensis  and Ardipithecus ramidus ,  which along with low body size dimorphism in Ardipithecus  and Australopithecus,  suggests a reduction in inter-male antagonistic behavior in early hominids. For this reason, Hunt argues that bipedalism evolved more as a terrestrial feeding posture than as a walking posture. The theory suggests that early hominids were forced to adapt to bipedal locomotion on the open savanna after they left the trees. And it has even been suggested e. According to Richard Dawkins in his book " The Ancestor's Tale ", chimps and bonobos are descended from Australopithecus gracile type species while gorillas are descended from Paranthropus. This dimorphism has been seen as an evolutionary adaptation of females to bear lumbar load better during pregnancy , an adaptation that non-bipedal primates would not need to make. In the face of long inter-birth intervals and low reproductive rates typical of the apes, early hominids engaged in pair-bonding that enabled greater parental effort directed towards rearing offspring. When analyzing fossil anatomy, Australopithecus afarensis has very similar features of the hand and shoulder to the chimpanzee, which indicates hanging arms. Unsourced material may be challenged and removed. However, while both gibbons and hominids have reduced canine sexual dimorphism, female gibbons enlarge 'masculinize' their canines so they can actively share in the defense of their home territory. The convenience of the savanna-based theory caused this point to be overlooked for over a hundred years. Wheeler's "The evolution of bipedality and loss of functional body hair in hominids", that a possible advantage of bipedalism in the savanna was reducing the amount of surface area of the body exposed to the sun, helping regulate body temperature. Lovejoy proposes that male provisioning of food would improve the offspring survivorship and increase the pair's reproductive rate.
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