Chpts. 17, 18 & 19 Flashcards Preview

Human Bio- Sem 2 > Chpts. 17, 18 & 19 > Flashcards

Flashcards in Chpts. 17, 18 & 19 Deck (16):

Trends in primates from most primitive to most advanced- explain hands

M.P- very little opposability on the first digit
M.A- highly mobile first digit, nails not claws

Precision grip
Able to manipulate objects


Trends in primates from most primitive to most advanced- explain feet

M.P- highly mobile first digit
M.A- very little opposability on first digit

Evolution to upright stance means hands were free for holding objects and tools


Trends in primates from most primitive to most advanced- explain eyesight and smell

M.P- eyes more towards side of head and good sense of smell (prognathic snout)
M.A- forward facing eyes, 120 degree vision overlap for 3D vision, less focus on smell (reduced prognathism)

Better for judging depth and distance
Human ancestors needed to see long distance in open country side


Explain evolution of Formen magnum

Foramen magnum is a hole in skull where brain joins the spinal cord
Humans=located centrally underneath skull so skull can balance on vertebral canal
In quadrupedals it is located more to the back

Apes also need large neck muscles to hold head unlike humans


Explain evolution of curvature of the spine

Humans have double curvature giving spine an S shape that contributes to upright stance, apes have C shape
Vertebrae in lower is wedged shaped to form a forward jutting curve= improves balance in upright position/ enables neck to balance on spine/ brings vertebral column directly under centre of gravity of the skull


Explain evolution of the jaw

Apes have protruding jaw, humans have a flatter jaw
Helps skull balance on spine -- weight in front of foramen magnum equal to weight behind -- achieved with little muscular effort


Explain evolution of pelvis

Humans- pelvis is bowl shaped and shorter from top to bottom, whilst broader in apes
Bowl shape supports abdominal organs when standing erect and support developing foetus in pregnancy


Explain evolution of carrying angle

Femur angled toward knee, is is the reverse in apes
Ensures weight distribution remains close to central axis of the body
Allows stability when walking so body can be rotated about the lower leg and foot
Each footstep can follow more-or-less a straight line
Humans won't sway side to side like apes (striding gait)


Explain evolution of knee structure

Transmission of body weight goes from femur to knee
Knee= two part hinge joint with one hinge on either side of ligaments in middle of joint
Outer hinge larger and stronger although body weight tends to fall through line just in front of leg, centre of gravity tends to fall through line in front of knees--> force tries to bend knee back but is resisted by ligaments making up knee joint
Natural resistance caused by joint that requires no energy to support body in upright position


Explain evolution of feet

Foot lost grasping ability (prehensility)--> most noticeable in big toe which is large and aligned with other toes, in humans
Metatarsals shaped to form longitudinal arch running front to back and a transverse arch that is only unique to humans and allows perfect bipedal locomotion


Explain evolution of centre of gravity

Human legs are longer than arms which increases length of walking stride and lowers centre of gravity
Centre of gravity is the point at which all body weight is concentrated
1/2 humans total height comes from legs, whilst 1/3 total height in apes comes from legs
Centre of gravity in apes in further up
Apes= chest level, humans=pelvis level
Is allows stability when walking bipedally or when standing erect


Advantages and disadvantages of bipedalism

A: frees up hands for other uses (carrying food or tools), can see further in distance (not hunched over), improved cooling of the body, higher reach with picking fruit off trees, increased size to deter predators

D: can no longer use feet for climbing or grasping to climb trees and get away from predators, slower moving compared to some quadrupedeals, difficult to maintain body temp in cold climates


Explain evolution of muscle tone

The partial contraction of skeletal muscles, this is what keeps the head erect
Sustained muscle tone is evident in muscles that support upright stance - in humans this is muscles that bring about movement of spine, hip, knee, ankle, abdominal muscles


Explain striding gait

Hip and knee fully straightened when walking upright
Human foot evolved to weight bearing appendage rather than grasping one - body propelled by big toe
When waking, trunk rotates about pelvis
Forward swinging of arms compensates for this rotation
Arm swing keeps shoulders at right angles to travel direction and reduces energy expended


Explain cerebral cortex

Human brain on average is 1350cm3
Apes range from 400-500cm3
Size difference due to cerebrum


Why did a chin evolve and decreased brow ridges

Chin- increased tongue movement for speech

Brow ridges- eyes protected by forehead instead, allows for increased cranial capacity (frontal lobe)