WEEK 12 BIPEDALISM Flashcards
What was the tool and weapons hypothesis?
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
What are the weaknesses in the tools and weapons hypothesis?
- 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
What is the thermoregulation and efficiency hypotheses?
‘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
What are the weaknesses in the thermoregulation and efficiency hypothesis?
- 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)
What are the sexual selection and mating strategies hypotheses?
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
What are the weaknesses in the sexual selection and mating strategies hypotheses?
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.
What is the seed and nut gathering hypothesis and small feeding hypothesis?
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)
What are the weaknesses with the seed and nut gathering hyp?
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
What is the postural feeding hypothesis?
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
What are the weaknesses in the postural feeding hypothesis?
Posture alone is too weak to be a selection pressure
Also bipedal threat displays are a precursor to bipedal locomotion
What is the ecological influences visual surveillance hypotheses?
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
What are the weaknesses in this hypothesis?
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
What is vertical clinging and leaping?
Arborial species that can move between separate trees or b/w tree trunks
What is arboreal quadrupedalism?
More suitable for movements on continuous network of branches (less hazardous than leaping)
What is terrestrial quadrupedalism?
Primate can move rapidly on ground