evolving the collective brain · brains tracking even larger brains shelter clothing. ancestral ape...
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Evolving the Collective Brain
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Joseph HenrichDepartment of Human Evolutionary Biology
Harvard University
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https://en.wikipedia.org/wiki/Early_human_migrations#cite_note-9 2
A puzzle
Big brains, problem solving?
40,000
60,000
50,000
20,000
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Aboriginal Processing• Grind, leach, heat
and use mussel shell spoon
• Grind, leach, bake in ash Poisoned and
starved on a full stomach
Escaped
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Morton Bay Chestnut
Why could any local adolescent survive easily, but Burke and Will could not?
What are those big brains for?
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Success of humans
not explained by
“intelligence”
relative to other
apes
We humans get much smarter from 2.5 to 25. Apes do not. Why?
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Culture makes us ‘smarter’
Oksapmin count to 27
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• It’s not our intelligence.
• Culture: we depend on cumulative
bodies of cultural information—
cultural adaptations.
• Collective Brains: larger, more
interconnected populations
generate more complex repertoires
and larger toolkits
• Culture-driven genetic evolution
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Who to learn fromWhat to pay attention toWhen to rely on different sources of info
Genetic EvolutionNatural Selection
Culture andCultural Evolution
Vs.
Genetic EvolutionNatural Selection
Culture andCultural Evolution
Psychological capacities for cultural learning
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Cultural Adaptations
Genetic EvolutionNatural Selection
Psychological capacities for cultural learning
Cultural Adaptations
Spices
• Non-conscious• No causal
understanding• Causal understanding
negative
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• Collective Brains: larger, more interconnected populations
generate more complex repertoires and larger toolkits
• High fidelity cultural transmission
• Sociality
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Population Size and Tool Complexity
10 societies, Oceania
Does population predict the size and complexity of toolkits?
Marine foragingtool complexity
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Kline and Boyd 2010
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Log Scale
Technological variety and complexity
Larger islands had larger populations, more tools, and greater tool complexity. This all occurred in a few thousand years. Stands up to many control variables (ecological variables).
ß = 0.706
p = 0.022 ß = 0.805
p = 0.005
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Bigger cities—>more innovationsSuper-linear: each person is more likely to innovate when they live in a bigger cities
Inve
nti
on
s
Cities in the U.S.A.
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Can sociality influence skill?
• Replicate target image
• Time limit
• Paid for own and student’s performance.
• Access 1 or 5 models
• After task: can write up to 2 pages for “student”
• Next generation gets the (1) model’s product, (2) write-up and (3) target
Target Image
Target Image14
Muthukrishna et. al. 2013
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2 times better with more social interconnections
Generation (round)
Mea
n Im
age
Rat
ing
(ski
ll)
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The raw data
In Generation 10
Everyone in 5-Model treatment is more skilled than the best guys in the 1-Model treatment.
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Generation 1
Generation 10
Generation 5
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Just copying the best?
• For 5 model treatment:
• Broke image down in binary elements
• Use t-1 generation ‘teachers’ elements to predict presence of elements in learners.
• Learners copied according to skill level, which meant that all ‘teachers’ had some influence except the worse.
Recombination from multiple models → innovation without invention
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Not “intelligence”Not incentivesJust sociality
Difference in equilibrium skills
More sociality slows decay rate and raises equilibrium skill level
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Tools and rules for communication
• Languages are products of cultural evolution, sets of tools and rules.
• Ergo, the same predictions apply
– Larger speaker communities have
✓More words—gain & loss
✓More phonemes
✓Informationally more efficient
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Speaker Population Size
Ph
on
em
ic D
iver
sity
Phonemes vary from 11 to 140 across languages
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Larger collective brains makes us individually smarter
Cultural practices harness innate mental capacities to yield specialized cultural-cognitive abilities.
• Spatial reference & technology
– Left vs. Right.
– Mental abacus—extraordinary computation abilities
• Rise in IQ in many societies over the last century.
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1900 2010
Increase in IQ
Evolved culturally to fit our brains
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Evolving the Collective Brain
Innovation is driven by:
• The recombination of ideas, fueled the interaction of diverseminds
• Broader social interconnectedness and relational flexibility
• More trust in strangers, and willingness to share ideas
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Genetic Evolution
Stone toolsFood processing
LargerBrains
Tracking
Even larger brains
ShelterClothing
Ancestral Ape
Intertwined Dual Inheritancesystem
CulturalEvolution
Firecooking
TubersWater containers
Adhesives (resins)SpearsMedicinal plants
Springy arches
Long legs
Greater dexterity
Artifact and intuitive biological cognition
Projectiles
Thin bones and weak muscles
Shortcolons
More cultural info
Brains for acquiring, organizing, storing and re-transmitting cultural information
Faith or ‘overimitation’
Products of a long-running and ongoing culture-gene interaction
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Thanks for listening
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Field Evidence
• Tasmania
• Polar Inuit
• Banks Islanders
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Tasmania watercraft (no paddles)
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Quentin Atkinson50 language families
Hay and Bauer 2007
Sound (phonemes) InventoriesPhonemes vary from 11 to 140 across languages
More phonemes → shorter words
WEIRDist Language: English(most words, high IE, morpho-simple)
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• Goal: replicate a complex series of rock climbing knots
• Time limit• Paid for own and student’s
performance.• Access 1 or 5 models• After task: make video
demonstration• Next generation gets model score
and video• Skill = similarity to target
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Experiment 2: Experts in Generation 1
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Effect of Log (N) on mean techno-units holds up to many controls