Lecture 25- Evolution and brains

Question 1

Do big or small animals have proportionally larger brain?

Answer 1

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

Question 2

What is the best way to measure brain size?

Answer 2

• a) total body weight
  b) percentage body weight
  c) encephalisation factor

Question 3

What is the encephalisation factor?

Answer 3

• 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

Question 4

How have brain changed in size in evolution?

Answer 4

• 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

Question 5

How do brains differ in regional sizes in different animals?

Answer 5

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

Question 6

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

Answer 6

• 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)

Question 7

Are small brains simpler than large brains?

Answer 7

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

Question 8

Are bigger brains more sophisticated brains?

Answer 8

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

Question 9

What is the pattern of gyrification in primate brains?

Answer 9

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

Question 10

Has the cortical thickness change in brains?

Answer 10

• the cortical thickness does not change in brains
• not much
• relatively

Question 11

Why hasn’t the cortical thickness changed?

Answer 11

• 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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

-larger brains= more gyrification

Question 14

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

Answer 14

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?

Question 15

What was the story about the newly discovered skull?

Answer 15

-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

Question 16

Has relative brain size increased in the hominids?

Answer 16

-yes

Question 17

Was bipedalism the trigger for brain growth?

Answer 17

-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

Question 18

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

Answer 18

• 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

Question 19

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

Answer 19

-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.

Question 20

When did our brain get bigger?

Answer 20

0.5 MY

Question 21

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

Answer 21

-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.

Question 22

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

Answer 22

• 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

Question 23

Does lot of brain growth in humans occur after birth?

Answer 23

-yes, especially in comparison with chimps

Question 24

What is the significance of tooth development?

Answer 24

-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

Question 25

What was the homo sapiens migration like?

Answer 25

-

Question 26

What is the deal with Homo floriensis?

Answer 26

-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

Question 27

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

Answer 27

-

Question 28

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

Answer 28

-no difference in the regions, just the size

Question 29

How does gene expression come into evolution of the brain?

Answer 29

• 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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

How do brains get bigger (2)?

Answer 32

1. Faster growth? 2. Longer growth?