• Culture and human adaptation
• Culture and design
• Culture and ultimate causation
Why Baboons Don’t Have History
• Culture and design
• Culture and ultimate causation
Modal Social Science: Human behavior is highly flexible, not innate
• Innate, genetically transmitted behaviors are rigid inflexible
• Human behavior is flexible, determined by environments not genes
Evolutionary Psychology™: Flexibility requires more instincts, not fewer
• Phenotypic flexibility requires innate information Environmental cues predict best behavior Mapping depends on innate information
• More information allows more accurate adaptation, or… adaptation to a wider range of environments
• Limited information storage tradeoff between accuracy and generality Mechanisms which allow highly accurate learned adaptation work in
limited environments, e.g. indigo bunting navigation Crude mechanisms based on statistical association or trial and error work
in wider range of environments
Thought experiment:
• Suppose we transplanted groups of baboons between habitats.
• Allow no contact with other baboons new area.
• Prediction: Rapid convergence to local behavior and social organization.
• Chacma baboons live in a variety of habitats.
Kuiseb
Okavangodelta
Drakensberg
Matopos
A second thought experiment:
• Suppose we transplanted groups of humans between habitats.
• Allow no contact with other humans new area.
• Prediction: Some convergence to local behavior and social organization, but many persistent differences.
Mbuti
!Kung San
• Humans live in a variety of habitats.
Hadza
Culturally evolved adaptations allowed foragers to occupy a wider ecological range than any other species
Deserts Tropical rain forest
The Arctic
not great intelligence /
Social learning allows unspecialized learning mechanisms to give rise to complex adaptations in many small steps
• Imitation finesses the accuracy-generality trade-off
• Key design information stored in brains not genes
• Unspecialized mechanisms allow small improvements to existing solutions
• Repeated application over generations creates and maintains accurate adaptations
• Culture and human adaptation
• Culture and design
• Culture and ultimate causation
Why Baboons Don’t Have History
Culture is part of the design problem for human psychology
• Adaptationist reasoning requires specification of design problem
• Evolutionary Psychology™ ignores culture when specifying design problem for human psychology Cognition evolved to solve problems for a small group living foraging
species Culture is the result, not cause of psychology Humans were just smarter chimpanzees
E.g. Imitation not important
But why would selection ever produce a psychological mechanism
That specifies a rule such as: detect the features of female bodies that
those around you perceive as attractive and perceive those as attractive
yourself?...If there were such a mechanism, standards of sexual
sexual attractiveness would be as arbitrary as the relationship between the
word “apple” and the fruit. There would be no consistent relationship
between standards of attractiveness and female “mate value.”
An evolutionary psychologist
Wrong because social learning creates feedback between psychology and environment
psychology
behavior
selection
psychology
behavior
A model in which imitation reduces learning costs
• Large population of organisms
• Environment has two states 1 & 2
• Switches states with constant probability each time period
• Two behaviors Behavior 1 favored in environment 1 Behavior 2 favored in environment 2
• Two genotypes Learners observe environmental cue and “choose” behavior Imitators copy a random individual
Learning leads to errors when cues are imperfect predictors of environment
Environmental Cue
Trait 1 FavoredTrait 2 Favored
Choose Trait 1 Choose Trait 2
Learning Rule
Probability in Environment 1
Error
Correct Choice
Imitation evolves…
Frequency of Imitators0 1
Fitness of Imitators
Fitness of Learners
Cost of Learning
but doesn’t change average fitness
Equilibrium Mix of Types
Average Fitness at Equilibriumexpected payoff – learning cost
Random Behavior
Can add complications without changing result
• Multiple traits, multiple environments
• Spatial variation
• Imitators can identify learners
Reason:
• Learners allow population to track environment
• Spread of imitators reduces quality of information available to imitators.
• Spread continues until both types have the same fitness
Imitation increases average fitness when it makes individual learning more efficient
Frequency of Imitators0 1
Fitness of Imitators
Fitness of Learners
Average Fitness at Equilibrium
Average Fitness at Equilibrium
Two ways imitation can make individual learning more efficient:
• Social learning allows cumulative cultural adaptation Small improvements less costly per unit than big ones Copy + learn less costly than learning alone
• Social learning allows selective learning Cost or accuracy of learning situations vary Learn when learning is cheap or accurate otherwise copy is less
costly than learning alone
Imitation allows selective learning
Environmental Cue
Trait 1 FavoredTrait 2 Favored
Choose Trait 1 Choose Trait 2
Learning RuleChoose Trait 2 Imitation
Choose Trait 1
Probability in Environment 1
Imitation allows selective learning increase average fitness
Frequency of Imitators
Average Fitness
Learners
Imitators
If learning is error prone and environments change slowly, the ESS amount of imitation can be substantial
1.0
0.0
0.0 2.0
Equilibrium Probability of Imitation
Standard Deviation of Environmental Cue
= 0.02
= 0.05
= .25
Slower Environmental Change
More Error Prone Learning
What is the best way to use social information?
• So far how to balance social and non-social information Environment provides cues Behavior of others provides cues When should individuals depend on one or the other?
• But, the distribution of behavior among models also provides cues: Commoness: Is everybody doing it? Or, just a few? Prestige: Are cool people doing it? Or, everybody? Similarity: Are people like you doing it? Or, other kinds of people?
• Can use population methods to investigate how selection should shape the psychology responds to social cues
• Imitate the successful provides good short-cut for hard to evaluate traits Some traits lead to success Don’t know which ones Imitate all traits plausibly connected to
success
• People will “pay” to get close to successful Deference Resources
• Amount of deference a good index of success
• May explain prestige psychology in humans
Selection favors imitation of the prestigious
Joe Henrich
Francisco Gil-White
Model makes many testable predictions
• People will copy prestigious individuals, even outside their range of expertise
• Skilled individuals have higher prestige
• Older individuals will have higher prestige
• Skilled or knowledgeable individuals will get goodies
• Prestigious people are memorable
• Prestige is associated with a different ethology than dominance
• Culture and human adaptation
• Culture and design
• Culture and ultimate causation
Why Baboons Don’t Have History
Culture allows the spread of maladaptive behavior
• Benefit: evolve fancy, habitat specific adaptations using unspecialized psychological mechanism
• Cost: have to be credulous…
• Result: Maladaptive ideas can spread
• Many examples: Dangerous hobbies Drug use Academic careers
• But, why should they spread?
Natural selection leads to the spread of maladaptive cultural variants
• People in influential social roles play may be important in cultural transmission Teachers, Bosses, Rock-stars in contemporary society Warriors, political leaders, religious specialists in smaller scale
societies
• People vary in their success in attaining influential social roles
• This variation is affected by beliefs and values
• Cultural variants that lead to success in attaining influential social roles will tend to spread
• Such variants may often be maladaptive Famous climbers take horrendous risk Successful academics give up family success
Both birth and death rates have fallen as countries industrialized
• Growth in wealth associated with modernization leads to a demographic transition
• Before industrialization European population growth was low High birth rate, but… Also high death rate
• As industrialization begins death rates fall
• Followed by a fall in birth rates
• Leading to low population growth
Economic development leads to new patterns of cultural transmission
• Pre-modern agrarian societies Most people live in isolated villages with little exposure to elites Elite prestige is inherited not earned Local prestige associated with large families (especially true for
women)
• Modernizing societies Literacy and urbanization lead to extensive social contact Modernizing economy provides much wider opportunities for
increased wealth/prestige But, positions require education, delayed marriage Competition for status leads to spread of preferences for goods
that signal status
Anabaptist groups have not undergone transition despite great prosperity
• Hutterites
• Amish
Live mainly in Saskatchewan Large, modern mechanized farms
Mainly in Pennsylvania Family farms with little mechanization
• Both groups Very successful economically Minimize public schooling Minimize contact with non-Anabaptist Very high birth rates
Rapid cumulative adaptation novel evolutionary processes
• Adaptation stronger compared to diffusion in cultural evolution than genetic evolution
• Many equilibria are likely for many reasons Ordinary adaptive problems have many solutions Network externalities Conventions Repeated social interactions Conformist social learning
• Strong adaptation + multiple equilibria = between group variation
• Stable variation between groups novel evolutionary processes
Ethiopia
U ganda
KenyaZaire
C entra l A frican R epublic
E th iopia
U ganda
KenyaZaire
C entra l A frican R epublic
E th iopia
U ganda
KenyaZaire
C entra l A frican R epublic
The 19th century expansion of the Nuer is an example of cultural group selection.
180018401880
Nuer
Dinka
Drawn from data in Kelly 1985
Nuer expansion resulted from cultural differences between Nuer and Dinka.
• Nuer and Dinka exploited same habitat using same technology.
• Each group consisted of a 10 to 30 independent polities.
• Striking cultural differences between two groups
Nuer Dinka
Sovereign political unitsWar parties Political organization
10,000 people1500 fighters
Segmentary lineages
3,000 people600 fighters
Territorial groups
SubsistenceCows per capitaPolitical organization
More grains and milk2.6
50% male
More meat1.1
10% male
Bride wealth Ideal Minimum Credit
32–40 cows22 cows
no
18–20 cowsNoneyes
Data from Kelly 1985
Natural selection acting on culture is an ultimate cause
• Why do birds fly south in the winter? Proximate: day length cues lead to hormonal changes, etc. Ultimate: Birds who did this in the past had more offspring
• Why do people in modernizing societies have so few children? Proximate: because they have acquire ideas/values that cause them to
allocate resources to other activities Ultimate: Because people with such ideas were more influential in
cultural transmission
• Depends on genes…so what?
• Same traits may be influenced by other ultimate causes.
This jasper scarab with an engraved baboon was recovered from the Late Bronze Age ship wreck site of Uluburun near the southern coast of Turkey.