WEEK 12 BIPEDALISM

Question 1

What was the tool and weapons hypothesis?

Answer 1

That bipedalism evolved to allow tool and weapon contruction

• Some people thought that tool use was a selection pressure
• some poeple thought that it freed hands to carry other things such as infants
• carrying food to home base to provide for mates was also proposed- upright posture
• hunting was also thought to allow for bipedalism and from that more accurate hunting and long distance walking

Question 2

What are the weaknesses in the tools and weapons hypothesis?

Answer 2

• evidence of bipedal locomotion was well before (1.5 mya) stone tools were made)- so tool use could not have been a cause for bipedalism (selection pressure)
• No other primate infants need help clinging to mother whereas humans do need help so the hands wouldn’t be freed up
• Hunting wasn’t practiced until AFTER bipedalism

Question 3

What is the thermoregulation and efficiency hypotheses?

Answer 3

‘keeping cool in hot equitorial environments drove bipedalism by reducing S.A to body exposed to the sun (UV radiation) at NOON (12pm) and by placing the body into cool breezes when bipedal’

• hominin standing upright would apparently absorb 60% less heat at midday
• reduced rates of overheating would allow them to go further to collect food without increased water intake
• bipedalism has been shown to be more efficient than quadrapedalism for WALKING

Question 4

What are the weaknesses in the thermoregulation and efficiency hypothesis?

Answer 4

• Long ditance foraging unlikely for early hominins
• Adaptation to bipedalism may have occurerd in woodlands not savanna (this would provide shade from sun)
• If hominins were in very tall grassland, that would also provide shade from sun
• It is rare for early hominins to hunt/forage at midday (when sun is hot)

Question 5

What are the sexual selection and mating strategies hypotheses?

Answer 5

Bipedalism arose because it had mating benefits on hominins that walked upright -males that obtained food/supploes and carried it (selection pressure)

• Also some evidence of sexual dimporphism
• 1993 proposed that bipedalism would’ve assisted males in bipedal displays to show dominance over female- this could be more impressive for female and lead to more reproduction
• slow reproductive rate of hominins would have lead to our extinction if we didnt find a way of increasing reproduction
• monogamy increased infant survival rates
• males carrying food and sticking around more for the female shortening time between births and more reproduction

Question 6

What are the weaknesses in the sexual selection and mating strategies hypotheses?

Answer 6

Bipedality arose well before hominins moved to grassland habitats
- Early hominins may have been sexually promiscuous as they were dimorphic-although still debates about whether early humans were dimorphic.

Question 7

What is the seed and nut gathering hypothesis and small feeding hypothesis?

Answer 7

SEED AND NUT: Early hominins stood up erect to gather grass seeds to eat and sufficient intake rewuired two hands to grab the seeds
SMALL FEEDING: When trees are packed closely together, bipedal shuffling uses less energy than repeatedly raising and lowering the torso to walk quadrupedal (can explain increase in biped freq)

Question 8

What are the weaknesses with the seed and nut gathering hyp?

Answer 8

Grasses can be pulled over and harvested without bipedalism

• hominin habitat was most likely woodland or forest rather than grassland
• dental analysis suggested diet of fruits rather than seeds

Question 9

What is the postural feeding hypothesis?

Answer 9

hunting bipedal movements may have evolved into regular habits because they were convenient for obtaining food and keeping balance

• chimps are only bipedal when feeding so it is argued that bipedalism evolved as a feeding technique rather than a walking one
• Adaptations in australopithecus were related to similar postural feeding habits (by head and shoulder features)- hip and hind limb indicated bipedalism

Question 10

What are the weaknesses in the postural feeding hypothesis?

Answer 10

Posture alone is too weak to be a selection pressure

Also bipedal threat displays are a precursor to bipedal locomotion

Question 11

What is the ecological influences visual surveillance hypotheses?

Answer 11

involved with changes from end of miocene to beginning of pleisocene

• bipedalism strongly corellates eith cooler and dryer conditions and increase in more open grassland habitats
• Forested environemnts were replaced by mosaic (bushland, open areas, grassland) environment
• changes in the environment meant a change in food acquiring behaviour due to food sources changing
• they had to either range further for food or changfe activity patterns (such as terrestrial travel) - therefore emergence of bipedalism

Question 12

What are the weaknesses in this hypothesis?

Answer 12

How come such enormous anatomical changes that allowed bipedalism took place?

• Seeing over tall grass is not something that requires drastic anatomical changes is it??
• Bipedalism was used to scare and intimidate others but if it was used more often then it would just be less effective

Question 13

What is vertical clinging and leaping?

Answer 13

Arborial species that can move between separate trees or b/w tree trunks

Question 14

What is arboreal quadrupedalism?

Answer 14

More suitable for movements on continuous network of branches (less hazardous than leaping)

Question 15

What is terrestrial quadrupedalism?

Answer 15

Primate can move rapidly on ground

Question 16

What is suspensory behaviour (brachiation)?

Answer 16

Allows larger species to spread weight among small supports and to aovid problem of balancing weight above a support

Question 17

What is bipedalism?

Answer 17

Allows species to travel on a continuous level area whilst freeing hands for other tasks

Question 18

What is the intermembranal index and what is it roughly correlated with?

Answer 18

Measure of the relative limb proportions; (humerus + radius length)/ (femur + tibia legnth) *100
Roughly correlated with locomotor habits

Question 19

What was the I.I for suspensory primates?

Answer 19

longer forelimbs than hind limbs therefore higher I.I

Question 20

What was the I.I for leapers and bipedal humans?

Answer 20

Longer hindlimbs than forelimbs so lower inermembranal index

Question 21

What is the I.I for quadrupedal primates?

Answer 21

Forelimbs and hindlimbs roughly same size so I.I close to 100

Question 22

What is the humerofemoral index and what does it relate to?

Answer 22

(Humerus length)/(femur length)*100
Relates to overall bosy proportion
- the higher the value, the longer the arms and more likely primate is arboreal
(Lucy is intermediate b/w modern humans and chimpanzees)

Question 23

What was surprising about the discovery of Salenthropous?

Answer 23

Mixed characteristics of apes and homo erectus

- Hominin was found 6-7 million years ago but the next closest one was found 4 million years ago .
- Most of hominins have been found in the rift valleys (isolation) 
- Discovered in forest rather than open habitat (like Savana)

Question 24

Why do some people belive it was just an ape?

Answer 24

• Dentition is hybrid
  
  • Cranial capacity very small-similar to chimpanzee
  • Position of foramen magnum is intermediate

Question 25

What are features indicative of bipedalism?

Answer 25

Bicondular angle, large and robust calcaneus, non opposable big toe, S shaped spine from secondary curvatures, foramen magnum placed more inferiorly, horizontal nuchal plane, shorter forelimbs than hind limbs

Question 26

How come being bipedal is efficient?

Answer 26

Bipedalism is efficient as centre of gravity is over legs reducing the energy needed to balance.

Question 27

Is bipedal walking more efficient than non bipedal?

Answer 27

Yes aparently it is but not running-although bipedal locomotion and quidrupedal locomotion apparently have no difference in terms of wefficiency (contradicaiton :/)

Question 28

What are some features of Australopithecus Aferensis?

Answer 28

smaller femoral head and larger femoral neck than homo, distal tibia articular surface is oriented relatively inferior (as in modern humans) inflexible midfoot but more flexible than human feet.

Question 29

What makes the head balanced?

Answer 29

foramen magnum and atlanto-occipital joint positioned further forward than other parts of skull (due to relativley shorter basiooccipital, more flexed cranial base and expansion of the brain

Question 30

What do secondary curvatures help with?

Answer 30

Bringing the centre of mass anteriorly, closer to the midline of body above feet

Question 31

What is shape of the pelvis in a bpied?

Answer 31

Basin shaped (short broad ilium) - modern human pelvis has relativley larger hip joints and larger pelvic outlet compared to Australopiths or modern apes.