CHANGES TO MOBILITY, STANCE AND LOCOMOTION

what are the advantages of bipedalism?

• more energy efficient (than quadrupedalism)

• leaves hands free to use tools/ carry items

• upright stance= greater height= can see further

• upright stance= less of body exposed to sunlight

• upright stance= exposes more of the body to breezes, enhancing cooling mechanisms

what are the advantages of mobility of digits (being pentadactyl)

• pentadactyl= 5 digits on each limb

• high level of mobility (adaptation to being arboreal) where prehensile (ability to grasp) digits are essential for climbing and clinging to branches

what is prehensility?

the ability to grasp something

what is opposability and why did we lose this in our feet?

• can move the first digit of the hands (thumb) to touch each of the other digits

• we became bipedal= the foot became weightbearing

how did the use of the hand change from non-human primates to humans

NON-HUMAN PRIMATES:

• long, curved fingers

• short, opposable thumbs

• robust, but flexible wrist joints

• this allowed for brachiation

  HUMANS:

• thumbs become longer

• increased opposability of thumb

• short, broad palm

• no need for brachiation= drives change

what is precision grip and why did humans develop this?

• due to the prehensility of the hand

• requires the use of an opposable thumb

• enables fine motor usage of objects (e.g. grasping pens)

what is power grip?

actions where the thumb and finger apply force to the thumb

how do humans walk?

bipedally with a striding gait

what is the foramen magnum?

(foramen= hole/passage, magnum= large)

• the hole in the skull where the spinal cord joins the brain

how has the foramen magnum changed and why?

• moved forward to become more central

• allows skull to balance on top of the vertebral column

  apes= closer to back of skull, need large neck muscles to hold their head in position

  humans= central, weight borne by the vertebral column (so don’t need larger neck muscles)

how has the curvature of the spine changed and why?

• changed to allow for upright position

• apes= smooth, C shaped curve

• Homo sapiens= double curvature, or S shaped curve

how is the double curvature achieved?

• vertebrae in lower (lumbar) region are wedge shaped from front to back

• forms a forward jutting curve in lower region

• cervical curve in neck brings vertebral column directly under the center of gravity in skull

what are the advantages of the double curvature in the spine?

• s-shaped improves balance in standing position

• enables the head to balance on the vertebral column

how do human and non-human primates pelvises differ?

HUMANS:

• broader

• hip sockets wide apart= allows femurs to angle towards the knee

• allows attachment allowing larger gluteal muscles to attach= enabling bipedal locomotion and upright stance

• shorter from top to bottom= lowering center of gravity and providing stability for bipedalism

• bowl shaped= supports abdominal organs when standing, provides greater stability for bipedalism, supports developing foetus in pregnancy

• (female pelvis more broad than males to allow passage of infant during childbirth)

• **non-human primates are the opposite of this

what is the carrying angle like in humans?

• head of femur fits into acetabulum (hip sockets) of the pelvis

• sockets are wide apart due to the broadness of hips

• femurs converge (angle) towards the knees

• forms an angle to the vertical called the carrying angle

• keeps weight distribution close to central axis of the body which provides greater stability for bipedal locomotion

how do humans walk with a striding gait?

• enables placing one foot in front of the other

• footsteps follows a straight line

• hip and knee fully extend

• humans have a striding gait rather than swaying side to side like apes (who don’t have these adaptations)

how is weight transmitted through the foot?

weight transmitted from the heel, along the outside of the foot, across the ball of the foot then propelled by the big toe= reason for losing opposability of the big toe

what is the knee like in humans?

• STRUCTURE:

• the lateral (outer) condyles are larger and stronger than the medial (inner) condyles

• due to their role in weight bearing and stabilisation in bipedal locomotion

• CENTRE OF GRAVITY:

• slightly in front of the knee

• ligaments resist force trying to bend knee backwards

• this means no energy is used to support body in erect standing position