Back vertebrae for the spinal cord narrowing

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back) vertebrae for the spinal cord, narrowing considerably further down - the nerves that fill this additional space mostly go to the chest cavity - may have to do with fine control of breathing needed for modern speech - H. ergaster lacked the wider space for these extra nerves, so it presumably could not control its breathing as well - so maybe it could not make controlled speech sounds the way modern humans do - H. ergaster was fully committed to being a biped on the ground, unlike the earlier hominins that retained features for living in trees - no longer had the long arms of the earlier hominins - long arms are good for moving in trees, but are not needed by a biped - instead, had long legs relative to torso and arms - long legs make for a much more efficient terrestrial biped - because longer strides waste less energy per mile - but long legs make a quadrupedal stance almost impossible - so good bipeds give up the ability to walk quadrupedally on branches or the ground - narrow shoulders compared to earlier hominins and other apes - like modern humans - again, reducing a feature that helps with moving through trees - narrow hips relative to new, taller stature - narrow hips make for more efficient bipedalism - less energy expended tensing abductor muscles to hold pelvis horizontal, because the hip joint is closer to the centerline – better leverage - less energy expended accelerating the body to one side, then the other, to move weight more over the hip joint - H. ergaster may have been the first hominin able to run (or jog) long distances - allowing them to chase a wounded animal for days, as modern low-tech hunters do
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Intro to Biological Anthro F 2011 / Owen: Homo but not quite us p. 3 - an inefficient biped would lose a lot of these potential kills - Overall, fully modern body size - WT 15000 was 5’ 4” tall as a 12-year-old - estimated to have been heading for about 6’ tall as an adult - extremely robust bones and strong muscles - H. ergaste r was only slightly more sexually dimorphic than modern humans are - suggesting greatly reduced male-male competition - maybe monogamous mating strategy, like modern humans? - H. ergaster apparently had longer juvenile development than earlier hominins - growth rings in tooth enamel suggest a rate of juvenile development about half-way between that of australopithecines and modern humans - suggests more time for brain development and learning - that is, H. ergaster did not have a significantly larger brain relative to its body (especially at first), but it had extended the period in which that brain was most able to learn complex behaviors - H. ergaster was the first hominin to spread out of Africa - numerous individuals found at Dmanisi, Georgia - at 1.7 mya, only 0.1 mya after the earliest H. ergaster known in Africa - earlier hominins made “mode 1” Oldowan tools - basically, just cobbles with some flakes broken off in no obviously intended shape - and the resulting flakes - the earliest H. ergaster (1.8 mya) apparently also made only “mode 1” tools - but quickly, by 1.6 mya, H. ergaster
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