Origins of Fair Play

Ken Binmore

k.binmore@ucl.ac.uk

Origins ofFair Play

John Mackie’s

Inventing Right and Wrong

Metaphysical moral philosophy

is unsound. Look instead at:

Anthropology

Game theory

Social Contracts

No bosses

Fair division

The social contracts of pure hunter-gatherer societies have two universal properties:

Pure hunter-gatherers

Toy games

dove

hawk

Prisoners’Dilemma

dove

hawk

Stag Hunt

Adam’s strategies

Toy games

Prisoners’Dilemma Stag Hunt

dove hawk dove hawk

Eve’s strategies

Toy games

dove

hawk

Prisoners’Dilemma

dove

hawk

Stag Hunt

dove hawk dove hawk

Adam’s payoffs

2 0

3 1

4 0

3 2

Toy games

dove

hawk

Prisoners’Dilemma

dove

hawk

Stag Hunt

dove hawk dove hawk

Eve’s payoffs

2 3

0 1

4 3

0 2

Toy games

dove

hawk

Prisoners’Dilemma

dove

hawk

Stag Hunt

dove hawk dove hawk

2 3

0 1

4 3

0 2

2 0

3 1

4 0

3 2

Nash Equilibria

dove

hawk

Prisoners’Dilemma

dove

hawk

Stag Hunt

dove hawk dove hawk

3

3

11

44

22

22

0

0

30

03

Coordination Games

left

right

Driving Game

box

ball

Battle of the Sexes

left right box ball

11

11

12

21

0

0

00

00

0

0

Reciprocal Altruism

indefinitely repeated Prisoners’ Dilemma

2 3

0 12 0

3 1

2 3

0 12 0

3 1

2 3

0 1

2 0

3 1

2 3

0 1

2 0

3 1

2 3

0 1

2 0

3 1

Reciprocal Altruism

d h

d

Grim strategy

h

2 3

0 12 0

3 1

2 3

0 12 0

3 1

2 3

0 1

2 0

3 1

2 3

0 1

2 0

3 1

2 3

0 1

2 0

3 1

Reputation and Trust

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are needed to see this picture.Sure I trust him. You know the onesto trust in this business. The ones

who betray you, bye-bye.

Vampire bats share blood on a reciprocal basis to insure each other against hunger.

Folk Theorem

efficientequilibria

currentstatus quo

Eve’spayoff

Adam’spayoff

0

Equilibrium selection

Fairness is evolution’s solution tothe equilibrium selection problem.

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Equilibrium selection

Fairness is evolution’s solution tothe equilibrium selection problem.

Fairness therefore evolved as a means of balancing power---not as a substitute for power.

Deep structure of fairness norms

As with language, fairness has adeep structure that is universal in the human species. This deep structure is embodied in Rawls’

original position

John Rawls’ original position

Veil of ignorance

Comparison of welfare

Enforcement

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I might be Adam and Oskar might be Eve. Or Oskar might be Adam and I might be Eve

Original Position

Adam Eve

Oskar

John

implicit insurancecontracts

deep structure of fairness?

implicit insurancecontracts

implicit insurancecontracts

original position

deep structure of fairness?

original position

implicit insurancecontracts

original position

utilitarianism egalitarianism

external enforcement

self-policing

Who is right?

Harsanyi Rawls

Modern Equity Theory

What is fair … is what is proportional. AristotleEve

Adam0

status quo

slope is ratio of the players’ context-dependent social indices

implicit insurancecontracts

original position

utilitarianism egalitarianism

external enforcement

self-policing

standard of

interpersonal comparison

cultural evolution

.

..

0Adam’spayoff

Eve’spayoff

Utilitarianism and Egalitarianism

The slopes are determined by the standard of interpersonal comparison.

utilitarian outcome

egalitarian outcome

state of nature

.

..

0Adam’spayoff

Eve’spayoff

Utilitarianism and Egalitarianism

The slopes are determined by the standard of interpersonal comparison.

utilitarian outcome

egalitarian outcome

.

.

0Adam’spayoff

Eve’spayoff

Utilitarianism and Egalitarianism

The slopes are determined by the standard of interpersonal comparison.

utilitarian outcome

egalitarian outcome

.

.

0

Utilitarianism and Egalitarianism

The slopes are determined by the standard of interpersonal comparison.

Nash bargaining solution

€

(x1 − ξ1)(x2 − ξ 2) = c

€

x1

€

x2

€

ξ

.

.

0

Cultural Evolution: Egalitarian Case

medium-run past

Nash bargaining solution

€

x1

€

x2

€

ξ

.

short-run present

egalitarian solution

Analogy with language

Chomsky discovered that all languages have a deep structure which is universal in the human species, but the particular language spoken in a society is determined by its cultural history.

Fairness norms similarly have a common deepstructure, but the standard of interpersonal comparison that is necessary as an input to theoriginal position is culturally determined.

Moral relativism

• Need• Ability• Effort• Status

Social indices always respond to these parameters in the same way, but the degree of response varies with a society’s cultural history.

Reform?

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