Lecture 25- Evolution and brains Flashcards

1
Q

Do big or small animals have proportionally larger brain?

A

-small animals have proportionately larger brain -more of their bodyweight is devoted to the brain

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2
Q

What is the best way to measure brain size?

A
  • a) total body weight
    b) percentage body weight
    c) encephalisation factor
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3
Q

What is the encephalisation factor?

A
  • encephalization factor= if put all the vertebrates on a log scale= the factor is how far you deviate from that line
  • we deviate by 0.69
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4
Q

How have brain changed in size in evolution?

A
  • birds, mammals and cartilaginous fish have increased relative brain size
  • separate only the mammals
  • what pattern is it?
  • birds fall into a similar pattern as cartilaginous fishes (sharks and rays) -mammals and birds seem to have the same relationship
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5
Q

How do brains differ in regional sizes in different animals?

A
  • cerebral cortex increases in humans
  • neocortical scaling mammals have more cerebral hemisphere
  • regionally the difference is the amount of cerebral hemisphere
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6
Q

Do human and rat brain differ in the regions they have?

A
  • no, still the same regions just different sizes
  • all the bits we have other mammals have
  • midbrain is remarkably similar
  • same functions in the brainstem
  • difference: in cerebral hemisphere(bigger in humans) and olfactory bulb (bigger in rats)
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7
Q

Are small brains simpler than large brains?

A
  • similar structure in simple nervous systems as in complex
  • just a miniature of the big brain
  • complex incredibly small brain
  • when in goldfish
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8
Q

Are bigger brains more sophisticated brains?

A
  • the human= layers
  • in whales= don’t seem to have as much stratification (the goldfish has the layers)
  • big brain is more folded
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9
Q

What is the pattern of gyrification in primate brains?

A
  • larger brains more folded
  • bigger brain= more gyrification
  • starts to fold on itself (like the insula cortex)
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10
Q

Has the cortical thickness change in brains?

A
  • the cortical thickness does not change in brains
  • not much
  • relatively
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11
Q

Why hasn’t the cortical thickness changed?

A
  • folding the cortical sheet allows more cortex in a smaller volume, also thinner cortex allows tighter folding
  • as you increase the number of layers= have to have the connecting fibres
  • as more cells= decrease density as have to accommodate more of the connecting fibres
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12
Q

What are the three things that are different in primate brains?

A
  1. bigger brains (in relation to body size) 2. more neocortex 3. more distinct architectures in the neocortex
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13
Q

What is the pattern with primate brains in terms of gyrification?

A

-larger brains= more gyrification

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14
Q

What are the three ancestors of Homo sapiens we look at the most? (hominids)

A

1.Australopithecine-Africa only, 2 million years 2. Homo habilis- 2-1.5 MYA- lineage to erectus? (only in Africa) 3. Homo erectus- 1.5 MYA found on three continents (Africa, Europe, Asia), but how recent was that migration?

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15
Q

What was the story about the newly discovered skull?

A

-the skull recently discovered= rewrote the history, has features only seen in separate species -small brain in homo habilis -large teeth- homo rudolfensis -long face= homo erectus -1.8 million years ol = suggests more interaction among our ancestors

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16
Q

Has relative brain size increased in the hominids?

A

-yes

17
Q

Was bipedalism the trigger for brain growth?

A

-The evolution of grassland - the plain - has been considered a driver of evolutionary change towards intelligence [ie freeing the forelimbs to allow hands to make tools etc.] -But, brain size has increased well after bipedalism: bipeds existed for two million, many several million, years before brains got bigger than chimp size. Freed hands wasn’t a trigger for cerebral expansion

18
Q

Has the recent development of high culture been associated with any evolutionary change in the brain?

A
  • hands develop before the big brain
  • teeth= duration of childhood maybe the change in habilis and erectus
  • all the stuff we think of as the result of big brain quite recent
19
Q

What drove the growth of the brain in the hominids? (Variability Selection Hypothesis)

A

-Some say that rapid climate changes forced adaptation. Pulsing climate change; great lakes appearing and disappearing over 1000 years in the rift valley. The period of high climate variability (in Africa) lasted from about 2 Mya to 0.5 Mya. -The “Variability Selection Hypothesis” proposes that relatively rapid environmental change replaced habitat-specific adaptations and favored adaptations that increased the ability to respond and accommodate this change (such as increased intelligence and greater social complexity). Problem solvers survive.

20
Q

When did our brain get bigger?

A

0.5 MY

21
Q

What can you look for in the skull of an australophitecus?

A

-But australopithecine apes may have had longer childhoods. A theory says the lunate sulcus in chimps divides visual from other neocortex, and that “late afarensis” [australopithicus] endocasts show lunate sulcus positions suggestive of bigger proportion of non-visual cortex.

22
Q

What is the role of the birth canal size in the brain size?

A
  • birth canal size limits brain size
  • there used to be more space, like chimps have more generous fit
  • more of the brain growth occurs in humans after birth than in chimps
23
Q

Does lot of brain growth in humans occur after birth?

A

-yes, especially in comparison with chimps

24
Q

What is the significance of tooth development?

A

-tooth development is slow in modern humans, used to be faster in homo erectus -slower still in austrolophicitens -slow teeth= means must be nurtured for longer

25
Q

What was the homo sapiens migration like?

A

-

26
Q

What is the deal with Homo floriensis?

A

-flor.= look like erectus -really recent -13 000 years old -discovered in indonesia -tiny brain, short -maybe coexisted with Homo sapiens -possibly more interaction among the ancestors than we thought

27
Q

What are the features of a bigger brain in our lineage and near relatives?

A

-

28
Q

What is the difference/lack of in parcellation in humans and other animals?

A

-no difference in the regions, just the size

29
Q

How does gene expression come into evolution of the brain?

A
  • rather than genomic homology, patterns in gene expression might be more indicative of evolutionary changes in the brain v other organs
  • gene expression pattern differ in the brain
  • so maybe that is why
  • the way the genome has been used to make the brain different, not big changes we could see
30
Q

What is the pressure on brains to become bigger? (2)

A

1.benefits of social organisation 2.survival enhanced by being smarter (tools, clothes, hunting/gathering)

31
Q

What are the high costs of the big brain? (4)

A
  1. Big brains need long gestation and long parental care= huge burden 2. Big head= difficult birth 3. Complexity: more genes, more mutations 4. Large energy expenditure/heat production
32
Q

How do brains get bigger (2)?

A
  1. Faster growth? 2. Longer growth?