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ANT203 - 31 January 2012 .pdf

Course Code
Xueda Song

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Bipedalism and Early Hominins
recall: mosaic evolution
derived and primitive traits
cranial (encephalization, diet)
post-cranial (bipedalism)
the bipedal adaptation
earliest hominins from Africa around 6 mya onwards
most became extinct - why? direct ancestors?
bipedal adaptation suggests most dramatic changes occurred in the pelvis
recall early feet: well-developed arches, considerable flexibility in the ankle (suggesting
climbing), adducted big toe
more rigid / tightly joined tarsal bones = more stability, less flexibility
pre-bipedalism: why be arboreal?
food, safety (esp. at night)
this explains why early hominins would have kept some arboreal characteristics
see anatomical features associated with bipedalism
why did hominins become bipedal?
carrying (objects, tools, weapons, infants), proposed by Darwin
upright posture frees arms to cary objects or offspring
bipedalism allowed for carrying of weapons, more accurate throwing of
certain weapons, and improved long-distance walking
systematic hunting is now thought not to have been practiced until after the
origin of bipedal hominins
seed and nut gathering
feeding on seeds and nuts occurred while standing upright
model initially drawn from analogy with gelada baboons
feeding from bushes
upright posture provided access to seeds, berries, etc. in lower branches;
analogous to adaptation seen in some specialized antelope
climbing adaptation already existed as prior ancestral trait in earliest
hominins (i.e. bush and tree feeding was established before bipedal
adaptation), so this hypothesis is unlikely
vertical posture exposes less of the body to direct sun increased distance
from ground facilitates cooling by increased exposure to breezes
works best for animals active midday on savanna; adaptation to bipedalism
may have initially occurred in woodlands, not on savanna
visual surveillance
standing up provided better view of surrounding countryside (view of
potential predators as well as other group members)
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