Chapters 6 and 7 - Chapters 6 and 7 Hominin Characteristics...

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Chapters 6 and 7 Hominin Characteristics Features of mosaic evolution in hominins (defining features of the hominin line?) Causes and effects of increase in brain size? • Compared to other primates, human children have long period of dependency during which brain and skulls grow dramatically • Larger skulls demand larger birth canals, but requirements of bipedalism imposes limits on expansion of human pelvic opening • If opening is too large, pelvis doesn’t provide sufficient support for trunk→locomotion suffers; posture problems develop • If birth canal is too narrow, mother and child may die • Due to natural selection • Balance between structural demands of upright posture and tendency toward increased brain size • Birth of immature and dependent children whose brains and skulls grow dramatically after birth Causes and effects of bipedality • Key feature differentiating early hominins from apes • Began more than 5 million years ago • Adaptation to open grassland or savanna habitat • Advantages: • Ability to see over long grass • Carry items back to home base • Reduce body’s exposure to solar radiation • Preceded expansion of hominin brain • Preserved enough apelike anatomy to remain good climbers • Environmental causes • During late Miocene, global climate became cooler and drier, grasslands in Sub-Saharan Africa expanded • Rain forests contracted, shrinking habitat available to arboreal primates • Geological shift deepened Rift Valley→sinking of valley created mountains • Land west of valley humid and arboreal, while land east was arid and dominated by savanna • Common ancestors of hominins and chimpanzees divided and those in the humid west became chimpanzee family, while those in the east forced to change • Eastern primates (those that became hominins) ventured more into open country for food and retreating to trees to escape predators at night • To move more efficiently, and to keep lookout for food and predators, started walking on two legs
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• Adaptation enhanced chance of survival and genes favoring this stance were passed on • Possible that intense tropical heat of savanna too stressful • Most savanna dwelling animals have built-in ways to protect brains from overheating but humans don’t and early hominins most likely didn’t either • Early hominins may have stood up to cool off • 60% less exposure to solar radiation • upright body allowed people to catch cooler breeze Basic early hominin chronology/ taxonomy (know the basic order of appearance, not exact dates). When does it begin? When does the Homo genus appear? • Hominin is used to designate human line after its split from ancestral
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Chapters 6 and 7 - Chapters 6 and 7 Hominin Characteristics...

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