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Introduction to Evolution and Genetics > Evolution of the skull and cranium > Flashcards

Evolution of the skull and cranium Flashcards

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Biology 101 flashcards
1
Q

What is the cranium?

A

The cranium is part of the skull that holds and protects the brain (also called the cranial vault)

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2
Q

What is the cranium composed of?

A

The cranium comprises eight plate-like bones that fit together at joints called sutures and various other bones.

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3
Q

What bones are located in the cranium?

A

Bones located in the cranium are:
* Frontal
* Parietal (X2)
* Occipital
* Temporal (X2)
* Ethmoid
* Sphenoid.

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4
Q

What is the front of the skull composed of?

A

Front of the skull also includes 14 facial bones that form the lower front of the skull.
* Nasal conchae (x2)
* Lacrimal Bones (x2)
* Mandible
* Maxilla (x2)
* Nasal Bones (x2)
* Palatine Bones (x2)
* Vomer
* Zygomatic Bones (x2)

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5
Q

What is the cranium also called?

A

The cranial vault.

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6
Q

WHat are the further features of the skull?

A

Processes
Sinuses
Foramina (singular foramen)

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7
Q

What is the function of the processes?

A

Processes – areas where the bones have extra material for attachment of muscles and ligaments

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8
Q

What are the function of the sinuses?

A

Sinuses – empty spaces in the bones that make the skull lighter.

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9
Q

What are the function of the foramina (singular foramen)?

A

holes in the bones through which nerves and blood vessels pass.
Also connects spine and brain.

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10
Q

What are the cranium and facial bones the foundation for?

A

The cranium and the facial bones are the foundation for the soft tissues of the face.

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11
Q

Explain the foundation of reconstructing soft tissues.

A
  • The cranium and the facial bones are the foundation for the soft tissues of the face.
  • Much of the external visible appearance consequently depends on the shape and qualities of these bones.
  • This provides the basis for facial reconstructions.
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12
Q

Proportions of the skull have…

A

…changed throughout human evolution.

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13
Q

Give two clear examples of skull anatomy changing.

A
  • Decrease in the size of the jaws, jaw muscles and teeth
  • Increase in the size of the brain case.
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14
Q

How has the overall shape of the skull changed?

A
  • The skull became taller
  • Has fewer redges for muscle attachment
  • Has a reduced zygomatic arch
  • Has a shorter jaw and face (less prognathous)
  • Has a more vertical forehead to accommodate the development of the forebrain.
  • A decreased need for powerful neck muscles.
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15
Q

What happens to the brain, jaw and teeth throughout evolution?

A

Over time, the brain gets larger, and the jaw and teeth get smaller throughout evolution.

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16
Q

How can brain size be estimated?

A

Brain size can be estimated from the internal volume of fossil skulls.

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17
Q

How did brain size of hominins change as they evolved?

A

As hominins evolved, brain size increased dramatically, but this doesn’t occur until around 3 million years ago

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18
Q

What were the brains of A.afarensis comparable to?

A

The brains of A.afarensis (3.9 – 3.2 million years ago) were comparable to that of a modern chimpanzee (380-400 cc), hence they were only as smart or slightly smarter than the modern chimpanzee, even though their behaviour closely resembles that of modern humans.

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19
Q

What is the general change in skull anatomy throughout evolution?

A

Front of skull becomes flatter.

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20
Q

What is the general brain change over time throughout evolution?

A

Brain gets larger

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21
Q

How did jaw and teeth generally change throughout evolution?

A

Jaw and teeth got smaller

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22
Q

What is the brain size of early H. erectus?

A

900cm^3 (1.7 - 1.0 Mya)

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23
Q

What is the brain size of later H. erectus?

A

1200 cm^3 (0.5 Mya)

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24
Q

What is the brain size of H. sapiens?

A

1400 cm3

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25
Q

Most of the evolutionary increase in brain size appears to have taken place with…

A

…H. erectus with a second increase to H. sapiens

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26
Q

Is the increase in brain size progressive or punctuated?

A

Whether the increase was progressive or punctuated is still debated.

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27
Q

How is the change in brain size from Australopithecus to H. habilis described?

A

The change in brain size from Australopithecus to H. habilis and early H. erectus is substantial and cannot be accounted for simply in terms of increased body size (although some argue this).

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28
Q

Why cant increase in brain size be accounted for simply in terms of increased body size?

A

From the appearance of H. erectus ~1.7 Mya. to the present, there has been little change in body size yet brain size has nearly doubled from ~800 cm3 to 1500 cm3.

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29
Q

What correlates with brain size?

A

When corrected for body size, ‘intelligence’ correlates very roughly with brain size.

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30
Q

How is intelligence and cognitive ability of a species calculated/estimated?

A

Encephalisation quotient (or encephalisation index) is based on brain size in relation to body mass.

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31
Q

What are the two most relevant aspects of the brain?

A

1) Brain size and surface features (fissures and convolutions)

2) Regions

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32
Q

How much did the brain increase in 3.5 million years?

A

Four-fold increase in size over 3.5 Ma

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33
Q

Whats the function of the frontal lobe?

A

Associated with reasoning, planning, parts of speech, movement, emotions, and problem solving.

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34
Q

Whats the function of the parietal lobe?

A

Associated with movement, orientation, recognition, perception of stimuli.

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35
Q

Whats the function of the temporal lobe?

A

Associated with perception and recognition of auditory stimuli, memory, and speech

36
Q

Whats the function of the occipital lobe?

A

Associated with visual processing.

37
Q

What is the function of the cerebellum?

A

Associated with fine motor control.

38
Q

What exactly about the brain changed over evolution?

A

The evolution of the human brain was not just about the brain getting larger, but involved changes at all levels of organization

39
Q

Who has the largest motor area out of humans, chimps, and orang-utang?

A

Orang-utang. (13.57cm^2)(121%)

40
Q

Who has the smallest motor area out of humans, chimps, and orang-utang?

A

humans (7.34cm^2)(65%)

41
Q

Who has the largest prefrontal cortex out of humans, chimps, and orang-utang?

A

Humans (181.4cm^2) (220%)

42
Q

Who has the smallest prefrontal cortex out of humans, chimps, and orang-utang?

A

Chimps (52.84cm^2)(87%)

43
Q

Who has the largest other cortexes out of humans, chimps, and orang-utang?

A

Humans (499.6 cm^2)(149%)

44
Q

Who has the smallest other cortexes out of humans, chimps, and orang-utang?

A

Chimps (280.96 cm^2)(84%)

45
Q

What can brain function be inferred from?

A

Brain function can also be inferred from the relative size and form of the different brain areas, especially the frontal cortex.
This can be seen using endocasts

46
Q

Define endocast.

A

impressions left by the cortex convolutions on the internal surfaces of the cranium

47
Q

Compare ape-like brains to human-like brains.

A

Ape-like brains have smaller parietal and temporal lobes; in human-like brains the parietal and temporal lobes predominate.

48
Q

What suggestion is there for when reorganization of the brain occurred?

A

Ape-like brains have smaller parietal and temporal lobes; in human-like brains the parietal and temporal lobes predominate

49
Q

What is the Taung specimen?

A

a specimen of an A. africanus child.

50
Q

Why is the Taung specimen important?

A

The Taung specimen of an A. africanus child is significant because it left a natural endocast of the fossilized cranium

51
Q

What part of the Taung specimen is being focused on the most?

A

attention has focused on the lunate sulcus, a crescent-shaped groove that divides the occipital lobe (where visual information is processed) from the rest of the brain

52
Q

How is the Taung specimens lunate sulcus different to that of other apes?

A

the lunate sulcus is displaced rearwards which is a human feature because in apes it is more forward

53
Q

What was the size reduction of the occipital lobe of the lunate sulcus accompanied by?

A

accompanied by an enlargement of parts of the brain associated with higher cognitive functions.

Some disagree with this saying the Taung childs brain are like those of apes and not humans.

54
Q

What do endocasts of H. habilis skulls indicate?

A

Endocasts of H. habilis skulls, however, indicate that the prefrontal region or cortex (associated with conceptual thinking) and Broca’s and Wernicke’s regions (associated with speech) were more developed in this species than in Australopithecines (still contentious).

55
Q

What is H. habilis associated with?

A

H. habilis is also the species generally associated with the first stone tools

56
Q

What other changes occurred in homo?

A

Reduction in male/female size dimorphism
Appearance of stone tool technology
Redistribution of blood vessels (radiator hypothesis) needed to cool the brain

57
Q

What changes occurred in A. afarensis 3.5 - 3.0 mya?

A

Reduction of primary visual striate cortex, area 17, and relative increase in posterior parietal cortex

58
Q

What changes occurred in the H. rudolfensis, H. habilis, and H. erectus?

A

Reorganization of frontal lobe (Third inferior frontal convolution, Broca’s area, widening prefrontal)

Cerebral asymmetries, left occipital, right-frontal petalias

59
Q

What changes occurred in H. erectus to present?

A

Refinements in cortical organization to a modern Homo pattern

60
Q

What were the australopithecines?

A

The Australopithecines were a diverse set of species that thrived for several million years with little or no change in brain volume

61
Q

The development and use of what drove brain expansion?

A

Stone tools, and their increasing complexity.

62
Q

What was the most dramatic increase in brain size?

A

H. habilis - H. erectus.

63
Q

What did the increasing complexity of stone tools require?

A

A large brain with the ability to think in the abstract - to ‘conceptualise’ the finished tool in the raw stone?

64
Q

Was cogntitive skills or manual dexterity more important in stone tool advances?

A

greater cognitive skills were more important in stone tool advances than manual dexterity

65
Q

What parts of the brain are responsible for action planning for tool making and language use?

A

action planning for tool-making and language use the same brain structures (pre-motor and Broca’s area) and suggest that the two co-evolved

66
Q

When might have aspects of language first emerged?

A

This means that aspects of language (e.g. gestures) might have emerged as early as 1.75 Mya with the start of Acheulean tool technology

67
Q

Did sociality drive brain expansion?

A

May have done.

68
Q

What did social complexity require in early hominins?

A

Greater cognitive processes and therefore larger brains.

69
Q

Give some examples of complex interactions between group members?

A

the formation of coalitions and tactical deceptions (these required larger brains)

70
Q

What do primates with more complex social structures have?

A

a larger neocortex.

71
Q

What does more complex social interactions result in?

A

More complex social interactions means that individuals are better able to pool resources to solve problems like finding food, and so they survive better – greater fitness

72
Q

Chimpanzees exhibit different…

A

…cultures.

ie: washing sweet potato, tool use.

73
Q

Which came first – a larger brain or a change in diet?

A

the transition from a predominantly vegetarian diet to hunting and meat-eating (driven by climate change?) allowed for brain expansion.

Others argue that increases in brain size in early humans drove changes in diet because of the need to increase protein (energy) intake to fuel the brain

74
Q

What food may have led to the evolution of larger brains?

A

cooked tubers provided an improved energy intake that could have driven the evolution of larger brains.

75
Q

Why is the theory of cooked tubers causing the evolution of larger brains contested?

A

this would have required early humans to have mastered fire about 1.8 million years ago, when the first clear evidence for hearths is 250,000 years ago.

76
Q

What is the consequence of increased brain size?

A

The evolution of larger brains resulted in a larger head needing to pass through the pelvic bones surrounding the birth canal.

77
Q

What is the solution to the difficult birth of babies through the birth canal/pelvis due to increased brain size?

A

The solution is for human babies to be born very prematurely compared to those of apes

78
Q

What does premature birth require?

A
  1. An increase in maternal care while the offspring is incapable of caring for itself
  2. An extended period of dependency for infants to learn new skills
79
Q

How has larger brain size impacting the mating system?

A

linked with the evolution of a mating system favouring pair-bonding over promiscuity

This is different from chimpanzees with their promiscuous mating system and mothers having sole responsibility for infants

80
Q

Describe the metabolism of the brain.

A

high metabolism

81
Q

What does a large brain with a high metabolism require?

A

A large, working brain with its high metabolism requires efficient temperature control to function properly. This required remodelling of the vascular system of the brain (Falk’s radiator hypothesis)

82
Q

Describe the change in size of the foramina from Australopithecus africanus to homo sapiens?

A

increase in size of the foramina as brain size increased from Australopithecus africanus to Homo sapiens

83
Q

What veins occur more frequently in humans compared to apes?

A

Parietal and mastoid emissary veins occur in relatively high frequencies in humans compared to apes

84
Q

What did the evolution of the cranial radiator cause the release of?

A

Evolution of the cranial radiator released a thermal constraint that previously kept brain size small.

85
Q

Why did the environment impact selection pressure and cause the evolution of larger brains?

A

the complex, uncertain and dangerous environment of early hominins represented a selective pressure for the evolution of larger brains

86
Q

What happened as a result of the evolution of Homo?

A

With the evolution of Homo, brain power and tools began to replace brute strength and the food (energy) demands shifted (from vegetarian to meat)

87
Q

What individuals were more likely to survive and pass on their genes?

A

Those individuals that were able to survive by using tools, remembering where and when trees fruited, and were able to hunt game were more likely to survive and pass on their genes to the next generation.

Introduction to Evolution and Genetics (18 decks)

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