The Evolution of Prestige-Biased Transmission

Karthik PanchanathanDepartment of Anthropology, UCLACenter for Behavior, Evolution, and Culture

karthikpanchanathan@gmail.comhttp://buddha.bol.ucla.edu/

PrestigeDominance

Henrich and Gil-White 2001Two Routes to Status

A prestige-bias may improve social learning

Henrich and Gil-White 2001

Social learning

Culture

Henrich and Gil-White’s Argument

1. Rank models and imitate the prestigious (“selective” imitation)

Learn from a distance

Learn in close proximity

2. Trade deference for proximity

(“deferential” imitation)

Wright’s ‘island model’

Each sub-population has a uniquely adaptive behavior

emigrantsimmigrants

residents

Life History

1. Juveniles socially learn (random, selective, or deferential imitation)

2. Juveniles attempt to innovate (if necessary)

3. Some individuals migrate to a new social group

4. Reproduction proportionate to fitness

Social Learning Rules

1. Random Imitators- Choose a model at random- Imitate from a distance

2. Selective Imitators- Choose a prestigious model- Imitate from a distance

3. Deferential Imitators- Choose a prestigious model- Trade deference for intimate learning

Costs and Benefits

1. Adults who possess the adaptive behavior and don’t migrate receive a fitness benefit b

2. Fixed cost for selective imitation

3. Fixed cost for deferential imitation

4. Market-based deference cost

Hypothesis 1:Does a prestige-bias increase adaptability?

Cultural Adaptation

Adaptation through individual learning and social learning

i

si s

s ss s i

sss i sss

Social learning biasesincrease adaptation

s s

i

s si

s s ss s si

s s sss s ssi

time

Random Imitation

0.001 0.004 0.016 0.064 0.2560.00

0.25

0.50

0.75

1.00

Freq

uenc

y of

Ada

ptive

Beh

avio

r (q)

e = 0.001

I = 0.1

I = 0.01

I = 0.001

0.001 0.004 0.016 0.064 0.256

Migration Rate (m)

e = 0.01

0.001 0.004 0.016 0.064 0.2560.00

0.25

0.50

0.75

1.00e = 0.1

Freq

uenc

y of

A

dapt

ive

Beha

vior

(q)

0

1

.001 .256.016

Migration Rate (m)

.001 .01 .1

Social Learning Errors (e)

.1

.01

.001

Innovation Rates

Constraints: - innovation- migration- social learning error

q̂ ≈ i

i + m + e

Selective imitation

0.001 0.004 0.016 0.064 0.2560.00

0.25

0.50

0.75

1.00

Freq

uenc

y of

Ada

ptive

Beh

avio

r (q)

Selective Imitators (s=1, d=0)

e = 0.01e = 0.1

e = 0.2

0.001 0.004 0.016 0.064 0.256

Migration Rate (m)

Deferential Imitators (s=0, d=1)

I = 0.001

I = 0.01

I = 0.1

0.001 0.004 0.016 0.064 0.2560.00

0.25

0.50

0.75

1.00Selective Deferential Imitators (s=1, d=1)

Freq

uenc

y of

A

dapt

ive

Beha

vior

(q)

0

1

.001 .256.016

Migration Rate (m)

Social Learning Error Rates

.01

.1

.2

Constraints: - migration- social learning error

q̂ ≈ 1−m− e

Deferential imitation

0.001 0.004 0.016 0.064 0.2560.00

0.25

0.50

0.75

1.00

Freq

uenc

y of

Ada

ptive

Beh

avio

r (q)

Selective Imitators (s=1, d=0)

e = 0.01e = 0.1

e = 0.2

0.001 0.004 0.016 0.064 0.256

Migration Rate (m)

Deferential Imitators (s=0, d=1)

I = 0.001

I = 0.01

I = 0.1

0.001 0.004 0.016 0.064 0.2560.00

0.25

0.50

0.75

1.00Selective Deferential Imitators (s=1, d=1)

Freq

uenc

y of

A

dapt

ive

Beha

vior

(q)

0

1

.001 .256.016

Migration Rate (m)

q̂ ≈ 1−mConstraints: - migration

Conclusion 1: Selective and deferential imitation

increase population-wide adaptation

Hypothesis 2: Does natural selection favor a prestige-bias?

Hypothesis 2a: When is selective imitation

favored over random imitation?

Selective imitators are always present at equilibrium, though rarely going to fixation

5

benefit / selective imitation cost ratio

0.001 0.004 0.016 0.064 0.2560.00

0.25

0.50

0.75

1.00

Deg

ree

of s

elec

tive

imita

tion

(s)

e = 0.001

0.001 0.004 0.016 0.064 0.256

Migration Rate (m)

e = 0.01

b cs= 5

10

20

0.001 0.004 0.016 0.064 0.2560.00

0.25

0.50

0.75

1.00e = 0.1

.001 .256.016

Migration Rate (m)

.001 .01 .1

Social Learning Errors (e)

Equi

libri

um F

requ

ency

of

Sel

ectiv

e Im

itato

rs

0

1

10 20

Hypothesis 2b: When is deferential imitation

favored over selective imitation?

0.001 0.004 0.016 0.064 0.256

Migration Rate (m)

0

5

10

15

20

25

30

Bene

fit−C

ost R

atio(b

c d)

e = 0.2

e = 0.1

e = 0.05

Selection favors either all or no deferential imitators

.05social learning

error rate

.001 .256.016

Migration Rate (m)

.1

.2

Bene

fit–F

ixed

D

efer

ence

Cos

t R

atio

0

30

15

b

cd≈ 1

e

Conclusion 2:Selection likely favors

selective and deferential imitation

But you left out all the interesting complexities of the real world?

Acknowledgments

Rob Boyd Sarah Mathew

The Evolution of Prestige-Biased Transmission

Karthik PanchanathanDepartment of Anthropology, UCLACenter for Behavior, Evolution, and Culture

karthikpanchanathan@gmail.comhttp://buddha.bol.ucla.edu/