Bipedalism and characteristics of humans vs apes

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29 Terms

1

what is the defining characteristic of hominins

bipedalism

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2

what does bipedalism mean

a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs

  • habitually walking on two legs

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3

how is bipedalism significant in human evolution

it’s likely that it was the main driving force for subsequent hominin evolution

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4

what is the most important advantage of bipedalism

it freed the hands to carry out a variety of functions therefore:

  • bipedalism freed the hands for purposes that would make a large brain particularly advantageous

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5

what functions did freeing hands aid in

  • carrying foods

  • tools

  • weapons

  • babies

  • picking fruit and other foods

  • wielding weapons

  • manufacture of tools

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6

what other advantages did bipedalism allow

  • greater height → look above grass to see predators, find food, locate shelter + appear more intimidating

  • energy efficient → walking long distances, less energy used walking on two legs compared to knuckle walking on four limbs

  • too keep cool in hot savannah → less body surface in direct sunlight + increased airflow around body

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7

disadvantages of bipedalism

  • moving more slowly

  • less stable on two feet than on four

  • smaller pelvis → disadvantage for females and birthing young

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8

why are quadrupeds more stable that bipedal

  • a body is balanced when the centre of gravity falls within the base of support

  • quadrupedal organisms have a wide base of support (four legs) whereas bipedal organisms have a narrower base of support (two legs)

  • therefore any changes in skeletal structure that maintains centre of gravity inside the body and thus balance will be selected for

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9

what is the foramen magnum

the hole where the spinal cord exits the brain

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10

where is the foramen magnum in humans

it’s near the centre of the skull → which allows the skull to balance on top of the spine

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11

where is the foramen magnum in apes

it’s located at the rear of the skull → the skull projects forward and requires strong neck muscles to support it

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12

how does the position of the foramen magnum relate to the nuchal crest size in humans and apes

  • in human the centred skull does not require strong muscles to hold in place

  • thus little energy is required to support the skull

  • therefore the nuchal crest is greatly reduced in humans compared to apes as there skull projects forward

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13

what is nuchal crest

where the neck muscles are attached

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14

what kind of shape spines do humans have

a S-shaped spine

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15

why do humans have a S-shaped spine

  • to act as a shock absorber

  • keep the body weight above the hip joints for upright movement

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16

what shape spines do apes have

C-shaped spines

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17

why do apes have C-shaped spines

  • the slight curve counterbalances the downward force of organs and chest

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18

ribcage characteristics of humans

  • flattened front to back

  • centre of gravity body is close to the spine

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19

ribcage characteristics of apes

  • flattened side to side

  • making it more funnel-shaped to accomodate the large gut → herbivore

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20

pelvis characteristics of humans

  • short and wide → bowl shaped

  • to reduce stress of upper body weight on hips

  • to support internal organs

  • strong bones support the muscles that move the legs when walking

  • wide pelvis allows babies with large skulls to be born

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21

pelvis characteristics of apes

  • long and narrow → provide large surface area

  • needed for the attachment of the leg muscles

  • shape does not allow a passage suitable for the birthing of a large brained infant

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22

femur characteristics of humans

  • long and angled/curved in

  • large valgus angle → cause knees to be almost directly under the centre of the pelvis so body weight is centred through middle of pelvis when walking

  • buttress knees → prevent sideways titling of the lower leg when walking + wider surface area so less pressure and can support weight over large area without dislocation

  • can fully extend legs

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23

femur characteristics of apes

  • femur is curved out

  • small to no valgus angle → legs hang vertically from the hips which facilitates brachiation when apes are moving through trees

  • shorter and no buttress knee

  • cannot fully extend their legs

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24

feet characteristics of humans

  • toes are straight

  • foot has an arch → act as shock absorber when walking/running + act as spring to walk efficiently and save energy

  • big toe points forward → pivot point

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25

feet characteristics of apes

  • flat foot → grip and wrap around things

  • big toe goes sideways and is opposable → grip things eg. grasping trees

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26

what were the two major developments from bipedalism freeing the forelimbs of early hominins

  1. stone tool technology → allowed hominins to be better able to kill prey, cut up carcasses, process meat (pound to soften it)

  2. controlled use of fine → enabled cooking

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27

which is the enabling of cooking so vital in the evolution of early hominins

  • cooking makes food easier to ingest

  • physically break down and digest food so less energy is required to process the food + nutrients in the food can be accessed quicker

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28

overall bipedalism affect on evolution of hominins

  • bipedalism resulted in hands being freed to handle objects

  • which eventually included making and using stone tools

  • hunting became more effective + more meat was added to diet

  • meat supplied more protein and fats to grow the brain, resulting in an increased brain size and development

  • cooking began and released more nutrients from food

  • addition of fish from cooking populations added further protein to the diet

  • brain increased in size and complexity and so did learning and communication

  • resulted in improved hunting and tool technology

  • which both increased amount of fat and protein in the diet and a further increase in brain development

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29

positive feedback loop of bipedalism in hominin biological and cultural evolution

bipedalism → manipulative hands → improved diet → bran development → increased ability to think, learn, communicaton → improved diet → improved survival chances

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