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Adaptations to Hominid Bipedal Walking (basic list)
- 1) forward placed foramen magnum
- 2) sigmoid or S curved vertebral column
- 3) increased capacity for lumbar lordosis in females
- 4) short, broad posteriorly tilted pelvis
- 5) elongation of lower limb (femur particularly)
- 6) angled medially femur (allows knee to lie in midline of body, has larger medial condyle)
- 7) strong abductor muscles
- 8) locking knee
- 9) enlarged and aligned big toe
- 10) arched foot to act like spring
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Forward placed foramen magnum
-centers the cranium over the vertebral column, allows maintenance of erect posture
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Sigmoid Curved vertebral column
- -also comes with narrower ribcage
- -centers weight over pelvis
- -4 curves
- -2 primary (present at birth)
- -2 secondary (develop as infants/toddlers as we become bipedal)
- -anterior curves
- --cervical(secondary)
- --lumbar(primary)
- -posterior curves
- --thoracic(secondary)
- --pelvic/sacral(primary)
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Lumbar Lordosis
- -allows lumbar vertebrae to become more dorsally wedged in females when pregnant
- -surface are of vertebral facets are about 14% larger in females
- -superior articular facets are oriented more coronally to resist fetal load
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Short Broad pelvis
- -posteriorly tilted pelvis
- -particularly the ilium
- -supports weight better
- -allows vertical orientation of trunk
- -anchors pelvic and leg muscles
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Abductor Muscles
- -gluteus minimus and gluteus medius
- -used to counteract the inward torque of the torso when supporting body weight on one leg
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Locking Knee
-allows full joint extension and better GAIT
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Enlarged Hallux
- -enables foot to completely support body weight
- -loss of pedal prehension, still ape foot
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Bipedal running (list of adaptations)
- -endurance runners (uncommon amongst quadrupedal animals)
- 1) long spring like tendons
- 2) long legs relative to body mass
- 3) larger joint surfaces
- 4) enlarged gluteus maximus
- 5) long and narrow waist
- 6) free rotation of head compared to chest
- 7) wide shoulders
- 8) occipital projection for muscle attachment
- 9) obligate oral breathing
- 10) effective sweating
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Tendons for running
- -long and spring like
- -short muscle fascicles save up to 50% of metabolic cost of running
- -ex achilles tendon first found in Homo erectus
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Where are longer legs for running first found
-Homo erectus
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Joint surface enlargement
- -specific for running
- -Homo have larger lower joint surfaces
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Enlarged gluteus maximus
- -adaptation for running
- -first true buttocks
- -not engaged when walking, only when running
- -stabilizes the trunk on planted foot and to decelerate leg swing on other foot
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Elongated and narrow waist
- -allows counter rotation of hips compared to trunk
- -fully developed in Homo erectus, partially found in australopithecines
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Independent head movement
- -allows you to keep your head on straight as the rest of your torso rotates to counteract the rotation of your hips
- -fully developed in homo erecuts
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Wide shoulders
- -enhancement for running
- -allows swinging of arms to counter rotate the hips
- -characteristic of Homo
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Theories for Bipedal evolution
- -carrying model- began because we needed to transport scarce resources
- -vigilance model- stand up to see predators
- -heat stress model-decrease surface area facing sun
- -energy efficiency model- we are more efficient bipedally than chimps at 4 legs
- -foraging/harvest model-stand up to reach stuff in trees
- -display model-to assert intimidation for predators or sexual needs
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Adaptations for hominid language
- -hemispheric specialization of the brain (left for language and symbol use)
- -broca's area- speech production (present in australopithecines)
- -wernickes area- language comprehension (homo habilis)
- -enlarged thoracic vertebral canal(more control over breathing, neanderthals)
- -flexed basicranium- bends and lengthens the pharynx, lowers the larynx allows broad range of sounds(H erectus)
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Increasing Hominid Brain Size
- -increasing size and complexity starting with Homo
- -slower infant maturation(high parental investment)
- -transmission of culture
- -tool use and manufacture
- -increasing social complexity
- -resource distribution
- -environmental challenges
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Hominid Dentition
- -obviously changing dental formulas
- -wider and more parabolic dental arcades
- -thicker enamel (compared to quadrupedal apes)
- -reduced canines with no/smaller diastema
- -larger posterior and smaller anterior teeth
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Neoteny
- -where adults of a species retain a trait that was only previously found in the juvenile forms
- -adult human foramen magnum placement similar to juvenile chimps placement, but adult chimps is much farther back
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2 Different Skeletal Classification
- -cranial vs postcranial
- -axial vs appendicular
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Two types of bone tissue
- -compact or cortical bone
- -cancellous, trabecular or spongy bone
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Cortical Bone
- -compact bone
- -hard, dense external layer of bone
- -bulk of long bone shafts
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Cancellous Bone
- -trabecular or spongy bone
- -20% of skeletons mass, but 10x surface area
- -inner lattice work of branching bony spicules provide strength without mass
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Obligate Behaviours of hominids
- -bipedal locomotion (which came about millions of years before an increase in brain size)
- -non honing chewing
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Textbook Bipedal Hypotheses
- -patchy forest-had to move long distances with no trees so it came about easily
- -provisioning-males needed to carry food to females so they could care for more infants at a time
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