Hominid evolution

Question 1

Primates

Answer 1

order, lemurs lorises tarsiers monkeys apes humans

Question 2

hominid

Answer 2

members of the hominidae family, great apes and humans

Question 3

hominin

Answer 3

member of tribe hominini, humans both alive and extinct

Question 4

brain

Answer 4

Increased size of brain relative to body
- cranial capacity –> volume of cranium, determined by endocast

Increased number of convolutions of cerebrum –> increase surface area of the brain

Cerebral cortex making up larger portion of brain, enlargement of frontal lobe surface area
- rely on vision to move about, locate and manipulate food produces a large amount of complex sensory information to be processed and stored
- tool making, involves a predetermined image of what the completed tool looks like
- changes in behaviour to meet a wide array of env problems

Question 5

digits

Answer 5

Pentadactyl - 5 digits on each limb, able to move independently of one another with increasing mobility

increasing effectiveness of opposability of thumn, able to use thumb to touch the tips of the rest of the digits on the hand

nails instead of claws

friction ridges to increase grip between ends of fingers and objects

prehensile, capable of grasping, wrap digits around branches of trees
- power grip : fingers and thumb apply force to the palm
- precision grip: manipulate small objects using tips of fingers and thumb

Question 6

prognathism

Answer 6

having a protruding jaw
- reduced sense of smell, reduction in size of snout, flatter face
- only nose protrudes in humans
- more of skull used for housing brain, brow is vertical and lacks prominent brow ridges, snout also shortens

Question 7

dentition

Answer 7

dental formula: number of each type of teeth in 1/4 of the jaw
reduced to become 2123 due to smaller prognathism
large canines project beyond level of other teeth
diastema between upper 2nd inscisor and upper canine to accomodate large lower canine
4 cusp to 5 cusp molar evolved due to predominantly fruit diet

dental arcade: shape made by the rows of teeth in the upper jaw
parabolic instead of U shaped due to decreased prognathism

Question 8

bipedalism - foramen magnum

Answer 8

located centrally in base of cranium, but further back in apes and earlier ancestors
gradually moved forwards to become more central, allows skull to balance on top of vertebral column
weight of skull carried by vertebral column, large neck muscles not required to hold head in position

Question 9

bipedalism - prognathism

Answer 9

reduced prognathism, small and non projecting jaw bone enables skull to balance on top of vertebral column
weight in front of the foramen magnum approx equal to the weight behind it

Question 10

bipedalism - curvature of spinal column

Answer 10

C shaped to S shaped spinal column, improves balance of the body in the upright position
created by lumbar vertebrae wedge shaped from front to back, forming a forward jutting curve
cervical curve in neck brings vertebral column directly under CG in the skull

Question 11

Bipedalism - pelvis

Answer 11

Apes - narrow and long, Humans - bowl shaped
- holds abdominal organs when standing upright, increased stability for bipedal locomotion, supports foetus during pregnancy
- sacrum wider, wider base for support
- femurs attached far apart, contribute to carrying angle
- broad hip bones allow attachment for large buttock muscles to move the legs and keep body erect
- broader pelvis, weight transferred directly to the legs, stability when walking upright

Question 12

bipedalism - femur

Answer 12

• large head of femur fits into acetabulum, contributing to carrying angle
• converge towards knees, forming an angle to the vertical (carrying angle)
• weight distribution remains close to the central axis of body when walking
• increasd stability, allowing for striding gait instead of swinging from side to side
• apes have a smaller carrying angle, femurs are not converging inwards as much, less stability.

Question 13

bipedalism - knee

Answer 13

• 2 part hinge joint, weight transmitted to outer hinge, larger and stronger than inner hinge
• CG falls through a line just in front of knees
• knee prevents leg from bending backwards because ligaments in knees resist this, no energy needed to support body in standing position
• degree of knee movement in humans is less than in apes, designed to provide strength

Question 14

bipedalism - legs

Answer 14

• longer than arms, low CG, more stable, increase length of stride
• carrying angle, weight of body close to central axis
• ankle(talus), tarsals, metatarsals, phalanges via arches in foot

Question 15

bipedalism - foot

Answer 15

• large heel bone and aligned big toe form a pedestal on which the body is supported on
• 2 longitudinal, 1 transverse arch, perfectly bipedal
• arch absorbs energy when foot comes down, enabling foot to be pushed up again
• allows for striding gait

Question 16

bipedalism - muscle tone

Answer 16

partial contraction of skeletal muscles to support spine hip knee and anklet

Question 17

striding gait

Answer 17

walking upright in such a way that the hip and knee are fully straightened

Question 18

how a foot walks

Answer 18

heel –> along outside foot–> ball of foot –> across ball of foot –> big toe

Question 19

walking

Answer 19

trunk rotates around pelvis, arms swing to compensate for natural rotation of body

Question 20

advantages of bipedalism

Answer 20

• more energy efficient way of moving
• leaves hands free to use tools or carry children
• achieve greater height, see further
• less of body exposed to sunlight, less chance of overheating
• increase exposure to breezes, increase cooling mechanisms

Question 21

how does carrying angle allow striding gait

Answer 21

close to central axis of body, weight of body is over feet at all times, body able to rotate about the lower leg and foot, centre weight distribution over foot, body does not sway side to side when walking

Question 22

endocast

Answer 22

impression of inside of skull made of a solid material
give a model of the brain, showing the size and shape of the brain surface, including any convolutions