encephalisation - gradual increase in brain size Flashcards
what is the encephalization quotient?
-measure of the brain size obtained from the ratio of actual brain size to the expected for an animal of particular body size
What species has the largest encephalization quotient?
H sapiens
what is the primary way in which brain size is compared?
The encephalization quotient
EQ tells us the difference between …
actual and predicted brain size
increase in EQ beyond predicted values?
any increase beyond predicted values should reflect excess capacity - not devoted to regulating basic metabolic functions
where is EQ most useful?
at the general taxonomic level
-doesnt take into account different reasons for encephalization - e.g. humans and dolphins
what do most formulae based on body size suggest modern human brainsize should be?
600cc
modern human brains 1251 cc
what kind of trend can we see with hominin brain size increase?
exponentially, its doesnt just grow. It spikes
what is the radiator hypothesis?
a hypothesis that explains the limitations on increasing brain size
explain the radiator hypothesis
- 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
what is the expensive tissue hypothesis?
explanation of why brain size is limited
what is the expensive tissue hypothesis
- large brain is energy hungry - 25% of our energy
- need for energy rich food to run the brain
what is the cost of a bigger brain?
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
effiecientwould humans on an ape diet be able to sustain a human sized brain?
- 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
what is the ‘man the hunter’ hypothesis?
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
what is a key brain nutrient and what is a source of it?
iodine
aquatic animals
what is iodine deficiency evidence for?
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
what is an endocast and what does it do?
- liquid latex cast of a reconstructed cranium
- reflects external brain features impressed on the cranial bone
which features are well and not so well preserved in cranial bones?
- well preserved - grpss features: overal shape/size, lateral fissure and other major lobes
- not well preserved = features that arent very prnounced - gyri and sulci
what are the two main types of evidence that we can get from endocasts?
- the overall shape of the brain
- locations of specific surface features of brain anatomy
explain the evidence of overall brain shape that can be seen from endocasts
- height, length, breadth, arcs and chords
- reflects the animal’s way of life
- comparing at higher taxonomic levels
explain the evidence of locations of specific surface features of brain anatomy that can be seen from endocasts
- gyri and sulci location
- can help trace evolutionary expansion
- comparing at the lower taxonomic levels
what are some differences between modern human brains and older hominin brains that can be seen using endocasts?
- 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 lobeswhat are the brain areas that grew during evolution?
frontal lobe
volume of white matter
cerebellum
what is the role of the frontal lobe?
associated with synthesizing information from other areas and inhibiting action
what is the role of the white matter?
brain interconnections - grows faster than neocortex, eventually constituting 34% of human brain.
what is the role of the cerebellum?
Coordinates muscular activity
what initially kicked off brain enlargement?
- 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
what is the social brain hypothesis?
- 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
what is the neocortex?
a part of the cerebral cortex that is concerned with sight and hearing in mammals
is intelligence all in the brain?
- 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
what doe language, culture, symbolic systems and other devices create in humans?
- external supports for cognitive abilities
- generate developmental environments that shape the biological unfolding of humans
- human brains are shot through with culture
what are two recent changes in the brain?
In last 35,000 years, brain size has shrunk 11%.
In last 10,000 years, brain size has shrunk 8%.
why are brains smaller today than 20 000 years ago?
- 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?
