Evolution of bipedalism part 1

Question 1

What are three types of bipedalism and define them.

Answer 1

Facultative bipedalism: Temporal basis -> to perform a particular function.

Habitual bipedalism: regular basis -> but not the only form of locomotion.

Obligate bipedalism: For hominins, bipedalism is only type of terrestrial locomotion -> other forms of locomotion on ground are not possible.

Question 2

Name the steps of the walking: gait cycle, and describe briefly what happens in each phase.

Answer 2

Mnemonic for all steps: 
He
Looks
More
Tired
Proposing 
In
Twitter

(A: Heel Strike, initial contact). Knees fully extend -> foot dorsiflexes -> results in heel striking ground before rest of foot.

force is transmitted through substrate along lateral border.

Foot plantarflexes (B, loading response, foot flat).

C. (Midstance) Eventually reaching midstance phase (pt where body is directly over weight bearing foot. )

D. Terminal stance (heel off): Body carries forward momentum over leg, at which pt, force moves medially over ball of foot. At which pt, strong muscular contraction of plantar flexor results in ball of foot pushing against ground, eventually lifting away from it as body continues to move forward. 

E. Pre-swing (toe off): This action finishes with final push of big toe, known as toe off 

F. Initial and mid-swing: Leg is now off the ground and in swing phase with knee and hip bent. 

G. Terminal swing: Swings forward to make next heel strike.

Question 3

Can chimpanzees walk on hindlimbs? Does it need less or more energy than humans to do this?

Answer 3

• Yes, for carrying objects with hand

- More

Question 4

Do gibbons use their long forelimbs for balancing when walking?

Answer 4

Yes.

Question 5

Can gibbons move bipedally faster than apes and humans?

Answer 5

• Yes

- at speech which humans have to start running.

Question 6

Do gibbons and siamangs live on ground or trees?

Answer 6

• Trees (arboreal)

Question 7

What type of motion do gibbons and siamangs move in trees?

Answer 7

-  Brachiation (swinging from tree to tree using forelimbs) 
Suspensory behaviour (hanging below trees).

Question 8

Do gibbons and siamangs have long or short hind limbs?

Answer 8

Have long forelimbs and short hind limbs.

Question 9

Compare the shoulders of gibbons and siamangs to humans, what is the function of this?

Answer 9

Shoulders are placed more dorsolateral (are more up and to the side) -> allow for greater range of motion.

Question 10

Compare the locomotion of great apes; Orangutans, gorillas and, bonobos and chimpanzees.

Answer 10

look on slide 8.

Question 11

Compare various hand positions in primates. Which species it is common in (if any), mechanism of hand when it makes contact:

Answer 11

Palmigrade hand:

- Most common hand posture. 
- Fingers and hand contact substrate. 
- Characterises arboreal quadrupedal; facilitates grasping. 

Digitigrade hand:

- Palm of hand is elevated and contact with ground occurs through middle and distal phalanx. 
- Most common in terrestrial quadrupedal primates such as baboons. 

Knuckle-walking hand:
- Hand is pronated (
turn or hold (a hand, foot, or limb) so that the palm or sole is facing downwards or inwards) and middle phalanx is in contact with ground -> reduced bending load on fingers
- Found in african apes, chimpanzee, bonobos and gorillas.

Suspensory grasp:

- Proximal phalanges above support, middle and distal phalanges make contact on side and near bottom of support, metacarpal not in support, thumb is of little importance. 
- Observed in gibbons, siamang, new world monkey species.