• 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.