Biology-Lecture 4 Chapter 8-Early Hominins Oct 3 2008

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23 Aug 2010
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10-03-08
Chapter 8: Early Hominins
y Australopithecus: genus of Pliocene and Pleistocene hominins
y Homo: genus to which modern human beings and their ancestors belong
Trends in Hominin Evolution
y Development of bipedal locomotion (walking on 2 legs)
y Expansion of brain, modification of the female pelvis (allow bigger brained babies to be
born), reduction of face, teeth, jaw
y Extended period of infant/child dependency, increased reliance on meat
Bipedalism
y Slow/quickly?- sparse fossil records
y Miocene anthropoids- capable of assuming upright position
y Bipedal- Africa (16 -11 MYA)- changing environment: tropical forests-> open country
y Open country favored ground living
y Bipedalism: adaptive response to life amid the tall grasses of savannahs (spot predators)
y Better dispersion of body heat
y Allowing hands to be free while legs moving (carrying food etc)
y Efficiently harvest small seeds and nuts because both hands could be used to pick up food
and move it directly to the mouth
y Use and make tools/weapons that they could carry with them as they moved about (hunting-
teeth/jaw not strong enough)
y (-)= harder to overcome gravity to supply blood to brain, weight of body above pelvis and
lower limbs- puts greater stress on hips, lower back, knees, feet, (even greater for
pregnant/nursing females)
y Changes in ape skeleton
y Foramen Magnum: the hole in the base of the skull through which the spinal cord passes en
route to the brain
y Pelvis is bowl shaped, has different set of muscles attach to femurs (move legs forward),
support internal organs, lowers the bodys centre of gravity
y Legs- angle inward toward one another (move legs forward/maintain centre of gravity)
y Feet- enlarged group ankle bones forming robust heel that can withstand the substantial
forces placed on them as a result of habitual Bipedalism
y Also have arch (absorbs locomotion force)
Expansion of the Brain
y Bipedalism evolved 1st-> development of brain
y Homo Habilis: early species belonging to our genus, Homo, with cranial capacities averaging
about 630-640 cc, about 50% of the brain capacity of modern humans (2 MYA)
y Homo Erectus: the first hominin species to be widely distributed in the Old World. The
earliest finds are possible 1.8 MYO. The brain (averaging 895-1040 cc) was larger than that
found in any smaller than the average brain of a modern human
y Stone tool making-> favored bigger-brained individuals because the had motor and
conceptual skills that enabled them to be better tool makers
y Expansion of brain-> hunting, increase lifespan, and language
Reduction of the Face, Teeth, and Jaw
y After 2 million years
y Diet- plants, seeds roots, tubers
y Staring to eat foods easier to chew (not needing such large/strong features)->
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