Term
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Definition
Robin Dunbar (2003) - 'The cognitive demands of living in complexly bonded social groups selected for increases in executive brain (principally neocortex - responsible for sight and hearing)
"we are very clever because we use our intelligence to manipulate social situations" |
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Term
| SBH - where does the demand for high cognition come from? |
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Definition
| complex social groups, not rocket science |
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Term
| primary evidence for social brain hypothesis |
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Definition
clear correlation: the larger the group size in an anthropoid species, the larger the neocortex, brain, and ratio of neocortex to the rest of the brain
"to live in a group of the same size, chimps require more brainpower than a baboon would" |
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Term
| SBH - secondary correlations with neocortex ratio |
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Definition
grooming clique size
frequency of tactical deception
frequency of social play |
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Term
| SBH - ecological indices do not correlate with neocortex ratio |
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Definition
proportion of fruit in diet
home range size
day journey range |
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Term
| SBH - social solutions to ecological problems |
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Definition
social interactions determine individual foraging patterns by defusing conflicts, either egalitarianly or hierarchically:
- locating resources
- gathering
- eating order |
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Term
| SBH - main problem facing primates? |
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Definition
Predation:
- running away
- loud calling (at cost to self)
- interspecies grouping
low predation rates doesn't necessarily mean it's not a significant threat |
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Term
| SBH - why is behavioural flexibility required? |
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Definition
for social cohesion in large groups so that individuals can take advantage of social cooperation:
- social learning |
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Term
| SBH - what is theory of mind? |
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Definition
the knowledge that other individuals are 'agents' rather than 'things'
- they are known and how they might act is known
- cognitively demanding, hence higher brain power |
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Term
| SBH - what is inner group? |
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Definition
a number of key social partners or allies
- often the number of regular grooming partners
- limit seems to correspond to the limit on the number of individuals who are willing to act as allies during conflict |
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Term
| SBH beyond anthropoids - strepsirrhines |
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Definition
no correlation between 'relative brain size' and group size
is a correlation between brain size and diet |
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Term
| SBH beyond anthropoids - frugivores vs folivores |
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Definition
| frugivores have larger brains than folivores, suggesting that ecological factors may explain brain size in strepsirrhines |
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Term
| SBH beyond anthropoids - birds, carnivores, artiodactyls, bats |
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Definition
| correlation between brain size and group size is negative |
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Term
| SBH - Monogamous vs polygamous |
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Definition
in birds, carnivores, artiodactyls and bats, monogamous species have relatively larger brain sizes than polygamous (parental care doesn't explain this as it is absent in antelopes)
this is reversed in primates |
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Term
| SBH - primates - brain size larger in polygamous species |
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Definition
develop a strong bond to individuals who are not their mating partner
"used the kinds of cognitive skills used for pair bonded relationships to create relationships with non-reproductive partners"
can make long-lasting alliance that extend cooperation between kin
not necessarily unique to primates but lack of data makes it hard to test |
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Term
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Definition
| extrapolating the ratio between neocortex ratio and group from arthropoids to humans predicts that the 'inner group' size of our species should be around ~150 people |
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Term
| SBH - grooming to language |
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Definition
grooming time increases with primates; up to a max of ~20% of total time
humans would spend around 40% grooming in order to maintain 'inner group' --> hence language evolved:
maintenance of social alliances and friendships at a lower cost |
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Term
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Definition
why did only primates evolve correlation?
within primates, why have only haplorhines extended 'bonding' from breeding pairs to social groups |
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Term
| Visual Specialisation Hypothesis |
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Definition
ecological model
visual adaptation to a new foraging niche
"the relatively large brains of frugivorous species are products of selection on the ability to perceive and select fruits using specific visual cues such as colour" (Barton 1998) |
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Term
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Definition
a transition from insect eating to fruit eating (evolution) would explain:
- early transition from a nocturnal to a mostly diurnal niche of haplorhines
- why strepsirrhines are not encephalized (since most remained insect eaters)
- reversal to full colour vision (three vs two colour receptors) in haplorhines (old world monkey and some new world monkeys)
- not all primates have three colour receptor |
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Term
| VSH - haplorhines are highly visual |
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Definition
primates lineage has been characterised by the loss of olfactory and receptor genes
we have 15 olfactory receptor pseudogenes
mice have over a thousand groups of olfactory receptor genes |
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Term
| VSH - visual pathways in the primate brain |
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Definition
| information sent through optic nerve and optic tract to lateral geniculate nucleus (LGN) in the thalamus |
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Term
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Definition
parvocellular layers analyse fine detail and colour
magnocellular layers process detection and movement
visual input is relayed from LGN to V4 in primary visual cortex in the occipital lobe |
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Term
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Definition
primates with larger brains have larger LGN areas
primates with larger brains have larger colour areas in LGN (parvocellular layers); organisms that eat insects need bigger magnocellular layers
frugivorous species have larger LGN areas and visual cortex (V1) |
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Term
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Definition
primates solve social problems visually, explaining the correlation between brain size and social group
"spatial cognition in primates depends extensively on visual processing of complex and rapid social interactions...including facial expressions, gaze direction, posture, and subject-object interaction"
however, are our social interactions and cognition visual? is language visual? |
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Term
| VSH - problems with brain size |
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Definition
visual areas are too small to explain encephalisation - evidence is poor
increase in primate brain size caused by neocortex expansion, the site of high cognition - LGN isn't in the neocortex
neocortex expansion occurred in non-V1 areas - a visual mind without a visual brain
if vision has anything to do with our high cognition, it is how we process it, which is not vision directly itself |
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Term
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Definition
| VSH cannot "explain why primates need brains that are so much larger than, say, squirrels, to cope with what are essentially the same foraging decisions" |
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Term
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Definition
both models for the evolution of specialised cognitive domains: while there are species with highly developed specific modules (echolocation in bats, spatial navigation in bees etc), large-brained primates are not just highly social or visual: we are intelligent in general!
neither theory sees culture as a factor in the evolution of human cognition
"culture, and particularly those aspects of high culture that seem to be so crucial to the human condition, depends on advanced social cognition" (Dunbar 2003) |
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Term
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Definition
| The g factor: a variable that summarises positive correlations among different cognitive tasks, reflecting the fact that an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks |
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