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ANTHR 101 CH 6-7

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Francois Larose

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Anthropology 101 (2 Midterm – Chapters 6 – 10) Chapter 6: The First Hominids and the Emergence of Homo The Evolution of Bipedal Locomotion  Bipedal locomotion: walking on two legs  Don’t know whether bipedalism developed quickly or gradually, because the fossil record for the period between 8 million and 4 million years ago is very skimpy  Miocene anthropoids were capable of assuming an upright posture  Eg. Brachiation o swinging by arms through the trees puts an animal in an upright position o climbing up and down trees with grasping hands and feet  Bipedal hominids emerged in Africa, according to fossil records  The new, more open country probably favoured characteristics adapted to ground living in some primates as well as other animals Theories for the Evolution of Bipedalism  Bipedalism was adaptive for life amid the tall grasses of the savannas o An erect posture may have made it easier to spot ground predators as well as potential prey  Recent evidence shows that where early hominids lived in East Africa was not predominantly savanna, instead seemed to have been a mix of woodland and open country  Gordon Hewes emphasized the importance of carrying hunted or scavenged meat  The ability to carry any food to a place safe from predators may have been one of the more important advantages of bipedalism  If males go out and get the food for the females and babies, then the females would save energy to produce and care for more babies  Clifford Jolly argued that bipedalism would have allowed early hominids to efficiently harvest small seeds and nuts o Both hands could pick up food and move it directly to the mouth  In the changing environments of East Africa, an advantage in foraging for small seeds and nuts proved important for survival (favoured by natural selection)  Bipedalism might have also have been favoured by natural selection o Available hands can be used to make tools and carry them  David Pilbeam suggested that tool use by the more open-country primates increased the number and amount of plant foods they could eat  Tools were used to kill and butcher animals  Weapons against predators  Some anthropologists question this idea of bipedalism and tools o First evidence of tools appears more than 2 mil years after bipedalism  Bipedalism is more effective for long distance  Bipedalism was also favoured to regulate body temperature o Bipedal posture limits the area of the body directly exposed to the sun o Facilitate convective heat loss by allowing heat to rise up and away from the body rather than being trapped inside it o Reduced heat stress in the warming environments of East Africa The “Costs” of Bipedalism  Bipedalism makes it harder to overcome gracity to supply the brain with sufficient blood  Stressed on the lower body are even greater for pregnant and nursing females who carry babies  The ancestral ape skeleton had to be modified and the major changed that allowed the early hominids to become fully bipedal  Foramen magnum: where the spinal column enters the skull at the bottom through this hole  Ape pelvises are long and flat, forming a bony plate in the lower back to which the leg muscles attach  In Bipedal hominids, the pelvis is bowl-shaped, which supports the internal organs and also lowers the body’s center of gravity, allowing better balance on legs  Hominid pelvis provides a different set of muscle attachments and shifts the orientation of the femurs from the side of the pelvis to the front o Allow them to move their legs forward in a bipedal stride o Apes move their legs forward by shifting their pelvis from side to side  Bipedal hominid legs angle inward toward one another o Helps move our legs forward and maintain a center of gravity in the midline of our bodies  The feet of bipedal hominids have two major changes compared to those of apes 1. Have an enlarged group of ankle bones forming a robust heel 2. Have an arch, which also aids in absorbing the forces endured by the feet during bipedal locomotion The Transition from Hominoids to Hominids  Sahelanthropus tchadensis: a primate that lived on the shores of the lake o Represented by an almost complete skull, has unique mix of hominid and hominoid traits  Orrorin tugenensis: bipedal; consists of 19 specimens of jaw, teeth, finger, arm, and leg bones, and top of femur o 5.8-6 mil years – turn out to be the earliest hominid  Tim White and a team of researchers surveyed a 4.4 mil year old fossil deposit at Aramis, Ethiopia o Discovered 17 fossils of what may be the earliest hominid, Ardipithecus ramidus  Ardipithecus ramidus has a combination of bipedal locomotion and an overall hominidlike skeleton o Relatively small cheek teeth with thin enamel and large canines o Arms are hominid-like, base of its skull shows foramen magnum o Feet adapted to bipedalism Australopithecus: The First Definite Hominid  Small canines, flat and thickly enameled molars, and a parabolic dental arch  Fully bipedal  Seem to be capable of climbing and moving in trees, judging by arm vs leg length Gracile Australopithecines  Have smaller dentition and lighter facial and dental musculature Australopithecus anamensis  Earliest species, between 3.9-4.2 mil years ago  Northern Kenya  Small bipedal hominid with teeth similar to those of later A. afarensis  More controversial specimen ha
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