encephalisation - gradual increase in brain size

Question 1

what is the encephalization quotient?

Answer 1

-measure of the brain size obtained from the ratio of actual brain size to the expected for an animal of particular body size

Question 2

What species has the largest encephalization quotient?

Answer 2

H sapiens

Question 3

what is the primary way in which brain size is compared?

Answer 3

The encephalization quotient

Question 4

EQ tells us the difference between …

Answer 4

actual and predicted brain size

Question 5

increase in EQ beyond predicted values?

Answer 5

any increase beyond predicted values should reflect excess capacity - not devoted to regulating basic metabolic functions

Question 6

where is EQ most useful?

Answer 6

at the general taxonomic level

-doesnt take into account different reasons for encephalization - e.g. humans and dolphins

Question 7

what do most formulae based on body size suggest modern human brainsize should be?

Answer 7

600cc

modern human brains 1251 cc

Question 8

what kind of trend can we see with hominin brain size increase?

Answer 8

exponentially, its doesnt just grow. It spikes

Question 9

what is the radiator hypothesis?

Answer 9

a hypothesis that explains the limitations on increasing brain size

Question 10

explain the radiator hypothesis

Answer 10

• hot environs - brain temo may be the biggest limit on survival
• human brains generate lots of energy and thus heat
• A afarensis began to develop (emissary foramina) through which blood could flow out to cool the brain
• ‘radiator’ (emissary foramina – holes in the skull that aid cooling? – weren’t present in earlier hominins) released this constraint.
• arteries also bring colder blood to the brain
• older hominins brains couldn’t cool brains quickly enough - brains couldn’t grow too large

Question 11

what is the expensive tissue hypothesis?

Answer 11

explanation of why brain size is limited

Question 12

what is the expensive tissue hypothesis

Answer 12

• large brain is energy hungry - 25% of our energy

- need for energy rich food to run the brain

Question 13

what is the cost of a bigger brain?

Answer 13

brain takes precedence in body thus takes energy awat from other energy hungry organs
   - larger brain, much smaller 
     gut and liver - digestive 
     tract is therefore less 
     effiecient

Question 14

would humans on an ape diet be able to sustain a human sized brain?

Answer 14

• relatively short gut - humans wouldnt be able to eat enough food on a chimp diet to feed an energy demanding brain
• also, H ergaster brain size while teeth grew smaller - would need more than 5 kilos a day in raw plant material to keep our brain going - 6hrs per day would be spent chewing
• cooking plant foods would be necessary to unleash maximum nutrition
• there was then a need to consume an even more energy rich source of food to maintain a demanding brain

Question 15

what is the ‘man the hunter’ hypothesis?

Answer 15

did meat consumption drive human evolution by fueling hungry brain?

• homo habilis used stone tools to cut meat from bone and break bones open to access marrow at 2.1 mya
• modern foragers get >50% calories from meat
• man had to seek rich foods - moved to other parts of the world following sources of these foods

Question 16

what is a key brain nutrient and what is a source of it?

Answer 16

iodine

aquatic animals

Question 17

what is iodine deficiency evidence for?

Answer 17

shoreline foraging provided high protein animals and the shore rather than the savannah became a crucial and niche place to find nutrient rich foods that were able to fuel a larger brain

Question 18

what is an endocast and what does it do?

Answer 18

• liquid latex cast of a reconstructed cranium

- reflects external brain features impressed on the cranial bone

Question 19

which features are well and not so well preserved in cranial bones?

Answer 19

• well preserved - grpss features: overal shape/size, lateral fissure and other major lobes
• not well preserved = features that arent very prnounced - gyri and sulci

Question 20

what are the two main types of evidence that we can get from endocasts?

Answer 20

• the overall shape of the brain

- locations of specific surface features of brain anatomy

Question 21

explain the evidence of overall brain shape that can be seen from endocasts

Answer 21

• height, length, breadth, arcs and chords
• reflects the animal’s way of life
• comparing at higher taxonomic levels

Question 22

explain the evidence of locations of specific surface features of brain anatomy that can be seen from endocasts

Answer 22

• gyri and sulci location
• can help trace evolutionary expansion
• comparing at the lower taxonomic levels

Question 23

what are some differences between modern human brains and older hominin brains that can be seen using endocasts?

Answer 23

- Asymmetries in overall shape
     Enlarged left occipital lobe 
     - language
     Expanded right frontal 
     lobe - cognition
-Locations of specific surface features
   Lunate sulcus
      Marks boundary between
            Parietal lobes
            Occipital lobes
      Expanded parietal lobes

Question 24

what are the brain areas that grew during evolution?

Answer 24

frontal lobe
volume of white matter
cerebellum

Question 25

what is the role of the frontal lobe?

Answer 25

associated with synthesizing information from other areas and inhibiting action

Question 26

what is the role of the white matter?

Answer 26

brain interconnections - grows faster than neocortex, eventually constituting 34% of human brain.

Question 27

what is the role of the cerebellum?

Answer 27

Coordinates muscular activity

Question 28

what initially kicked off brain enlargement?

Answer 28

• the primate lifestyle
• eating behavior of primates is more complex than other animals - finding fruit is more difficult
• need for good sensory, spatial and memory skills
  fruit eaters have larger brains

Question 29

what is the social brain hypothesis?

Answer 29

• the average size of a group has a correlation with the ratio of neocortex with the rest of the brain
• living in a group is something complex and needed alot of brain power and intelligence

Question 30

what is the neocortex?

Answer 30

a part of the cerebral cortex that is concerned with sight and hearing in mammals

Question 31

is intelligence all in the brain?

Answer 31

• if we dont teach the brain - wont reach full potential
• human company influences intellect
• human is especially immature at birth - brain less developed = open wider learning window

Question 32

what doe language, culture, symbolic systems and other devices create in humans?

Answer 32

• external supports for cognitive abilities
• generate developmental environments that shape the biological unfolding of humans
• human brains are shot through with culture

Question 33

what are two recent changes in the brain?

Answer 33

In last 35,000 years, brain size has shrunk 11%.

In last 10,000 years, brain size has shrunk 8%.

Question 34

why are brains smaller today than 20 000 years ago?

Answer 34

• getting dumber
• its wiring became more efficient, transforming us into quicker, more agile thinkers *
• tamed ourselves - like animals
• Scaling? Increased temperatures resulted in reductions in body proportions including brain size?
• Consumption of less nutritious foods?