Human Bio- Evidence for evolution

characteristics of the skull to show evolution

cerebrum/cerebral cortex, brow ridges, number/shape of teeth, prognathism

describe how the cerebrum and cerebral cortex has changed in humans

• Cerebral cortex (layer around the outside) is larger

• this results in higher functions, higher ability of vision, memory, manipulative ability, a higher amount of convolutions which increases surface area=ability to carry out higher functions

• there is an increased size of the frontal lobe which increases the development of behavior, communication and planning and increases cranial capacity

• the increase of brain function allows for development of communication skills, social skills, planning forethought, and use of tools.

describe how the cerebrum and cerebral cortex has changed in Apes

• cerebral cortex is smaller

• this means it has decreased functions, lower ability of vision, memory, reasoning, manipulative ability, a decreased convoluted area which decreases surface area= decreased ability to carry out higher functions.

• decreased size of frontal lobe= less development of behavior, communication, and planning and a decreased cranial capacity.

• this is because apes were originally arboreal tree dwelling) so only need to be able to process visual info, make decisions, respond to stimuli and coordinate movement

describe how brow ridges have changed in humans

• we have no distinct brow ridges

• this is due to the size of the frontal lobe increasing so brain occupies a larger space

• front of cranium extends forward which reduces brow ridge

describe how brow ridges has changed in apes

• less prominent brow ridges

• this is due to frontal lobe not being fully developed so less space is occupied by brain

• cranium doesn’t extend forward so ridges become more visible

describe how the shape and number of teeth have changed in humans

• format= incisors: canines: premolars: molar

• 2:1:2:3 (8 in ¼, 32 total)

• mouth is more parabola shaped

• Canines: are even/ flatter to incisors, and they don’t project so no need for diastema

• Molars: have 4 cusps on upper and 5 on lower to adapt to fruit diet

• decreased number and size of teeth due to decreased face size so its easier to balance skull.

describe how the shape and size of teeth have changed in apes

• format= incisors: canines: premolars: molar

• 2:1:2:3 (8 in ¼, 32 total)

• U shaped mouth

• canines: are sharp, pointed, and large so require a diastema to close jaw

• molars: have 3 cusps

• increased size of teeth is due to large face and no need to balance skull.

how has prognathism changed in humans

• less prognathism

• this increases the balance of the skull

• tooth size decreasing flattens face

• this causes nose to be prominent

• leads to development of chin

how has prognathism changed in humans

• increased prognathism

• decreases balance which isnt needed

• its more prominent due to tooth size

• no nose

• no chin

advantages of bipedalism

• more energy efficient movement than quadrapedalism

• leaves hands free to use tools

• upright= greater height so can see further

• upright=less body exposed to sun

• upright=more body exposed to breeze to enhance cooling mechanisms

what are the changes to mobility, stance and locomotion

bipedalism, mobility of digits, opposability, use of hands

how has the mobility of digits changed

• humans are now pentadactyl (5 digits) which allows for a high level of mobility

• apes are prehensile (ability to grasp) digits which is essential for being able to climb and clinging to trees showing how they were adapted to brachiation

• we also now have opposable thumbs

how has opposability changed

• we have opposable thumbs (can move thumb to touch each individual other digit)

• primates have opposable big toes

• we lost opposability due to change in function to become weight bearing with bipedalism

• flat nails help with opposability compared to claws which limit prehensability

how has the use of hands changed in humans

• thumb becomes longer

• increased opposability of big thumb

• short, broard palm

• this allows for precision of grip due to prehensility of hand and requires use of opposable thumbs which enables fine motor use of objects

• also allows power grip where thumbs and fingers apply force to palm

how has the use of hands changed in apes

• long curved fingers

• short opposable thumbs

• robust but flexible wrist joints

• allows for brachiation and swinging through trees.

what are the main features to allow for bipedalism

foramen magnus, curvature of spine, pelvis, carrying angle//striding gait, knee, foot, center of gravity, muscle tone.

how does the foramen magnus differ from humans and primates and how does it effect bipedalism

Humans:
- evolves to be more central
- allows weight to be surrounded by vertebral column so no large muscles are required to hold up head
- allows skull to balance on top of skull

Primates
- is closer to back of skull
- as large muscles are needed to hold head in position when on all fours
- it is more towards the back of the skull

how does the curvature of the spine differ from humans and primates and how does it effect bipedalism

humans
- double curve of the spine/s shape
- this allows upright position
- its achieved by wedge shaped vertebrae in lumber which forms a forward jut in lower region
- cervical curvature in neck brings vertebral column directly under center of gravity of skull
- this improves balance, enables head to balance om vertebral column.

Primates:
- c shape curve

how does the pelvis differ from humans and primates and how does it effect bipedalism

Humans:
- broard pelvis

• hip sockets wide apart which allow femurs angle to knee

• allows attachment of large glute muscles to allow bipedal locomotion and stance.

-shorter top to bottom which allows a lower COG making us more stable

- bowl shaped: pelvis is more broard in females to allow for childbirth

+ LINK TO CARRYING ANGLE +

Apes:

- narrower pelvis

- longer top to bottom

+ LINK TO CARRYING ANGLE +

how does the carrying angle and striding gait differ from humans and primates and how does it effect bipedalism

Humans:

- head of femur fits into acetabulum

- sockets are wide apart due to broard hips

- this converges femur to knees which forms a carrying angle

- this keeps weight distributed close to central axis of body which increases stability

- it enables to walk with a striding gait

• one foot infront of the other

• footsteps follow in a straight line

• hip and knee fully extend

-weight is distributed across from heel, across the ball of foot, then projected by big toe

- this is the reason why we lose opposability for bog toe

Apes:

- sway side to side as they cant put one foot infront of other

- weight is distributed on side of leg

- femur has no converge

- no angle due to narrow hips

- weight is distributed away from central axis

how does the knee differ from humans and primates and how does it effect bipedalism

humans

• lateral/outer condyles are larger and stronger than medial

• this is due to their role in weight bearing and stablilisation in locomotion of bipedalism

• COG becomes slightly infront of knee

• ligaments resist knee bending backwards

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

how does the foot differ from humans and primates and how does it effect bipedalism

humans

• lost prehensibility due to change in function to become weight bearing

• Big toe: larger, aligned to other toes, no opposability

• robust calcaneus with aligned big toe create pedestal to support stance

• metatarsals: shaped to form 2 arches (longitudinal and and transversal) which contribute to bipedal locomotion

Primates:

• big toe: small, not aligned with other toes, has opposability

• has prehensibility to allow grasping

• only has longitudinal arch

how does the center of gravity differ from humans and primates and how does it effect bipedalism

humans:

• legs are longer than arms

• they are roughly half the height

• it increases the length of the stride and lowers the COG to level of pelvis

• this provides stability when moving/standing

Primates:

• legs are a third of height

• results in a higher COG closer to chest

• it decreases ability to stand upright

how does the muscle tone differ from humans and primates and how does it effect bipedalism

humans:

• particularly contracted skeletal muscles skeletal muscle are essential for maintaining upright stance

• muscles in back of neck are partially contracted to ensure head remains up

• muscles in abdomen, hips, knee and ankle hold position.