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The Nature of Human Altruism

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The Nature of Human Altruism Powered By Docstoc
					 Altruistic Punishment and
    Human Cooperation
                      Urs Fischbacher
                     University of Zurich

                     NWO, Utrecht 2004

Fischbacher, Gächter and Fehr, Are People Conditionally Cooperative?
Evidence from a Public Goods Experiment, Economics Letters 2001.
Fehr and Gächter, Altruistic Punishment in Humans, Nature 2002.
Fehr and Fischbacher, Third Party Punishment and Social Norms,
Evolution and Human Behavior 2004.
Fehr and Fischbacher, The Nature of Human Altruism, Nature 2003.
De Quervain, Fischbacher, Treyer, Schellhammer, Schnyder, Buck,
and Fehr, The Neural Basis of Altruistic Punishment, Science 2004.
                 Overview

Human cooperation and strong reciprocity
Experimental evidence for strong reciprocity
Proximate models of strong reciprocity
Altruistic punishment activates reward related areas in
the brain
Ultimate models of strong reciprocity
     Humans’ Large-Scale
        Cooperation
Humans societies are a huge anomaly in the animal
world. They are based on a detailed division of labor
and cooperation of genetically unrelated individuals in
large groups.
In most animal species there is little division of labor
and cooperation is limited to small groups.
Why do Humans cooperate?
Strategic cooperation (cooperation to induce cooperation by
the other players) in the form of
    Reciprocal altruism, i.e. self-interested exchanges in
    repeated interactions, at a scale and in domains of
    behavior that is unprecedented in the animal world.
    Reputation-based cooperation is also a powerful force
    among humans and differs in scale and in kind from
    what has so far been observed in animals.
However, human altruism even goes beyond reciprocal
altruism and reputation-based cooperation, taking the form
of strong reciprocity.
        Strong Reciprocity

Is a combination of altruistic rewarding (strong positive
reciprocity) and altruistic punishment (strong negative
reciprocity).
Altruistic rewarding: A readiness to incur costs to
reward others for cooperative, norm-abiding behaviors
in the absence of any individual economic benefit for
the rewarding individual.
Altruistic punishment: A readiness to incur costs to
punish others for norm violations in the absence of any
individual economic benefits for the punishing
individual.
  Public-Goods Experiment
N players get an endowment.
Decide simultaneously how many point of they contribute to
the public goods.
The contributions are summed up, multiplied with a factor F
(e.g. 2) and distributed equally between all players.

If F>1, it is efficient to contribute (cooperate).
If F/N<1, it is a dominant strategy not to contribute (defect).
Structure mimics the logic of many important real world
examples. Whenever individual actions have positive or
negative effects on other individuals a similar situation arises:
Pollution problems, over-fishing the seas, cooperative
production and food-sharing in small-scale societies,
cooperative hunting and warfare, etc.
      Altruistic Rewarding

(Fischbacher et al. 2001, see also FKR 93 or BDM 95)
Standard public goods situation (endowment =20, N =
4, F=1.6); played only once
Subjects can make a conditional contribution to the
project, i.e. they fill out a contribution table in which
they can condition their contribution on every possible
contribution of the others
                 Predictions

Selfish subjects (e.g. subjects who cooperate for
strategic reasons only) always put in zero into the
schedule.

Strongly reciprocal subjects’ contribution increases in
the average contribution of the other group members.
   The other subjects’ contribution is a cooperative act which
   deserves altruistic rewarding.
                                Average schedules
                                    Fischbacher, Gächter, Fehr 2001


                   20
                   18
Own contribution




                   16                                                    Strong
                   14                                                    reciprocators
                   12                                                    50%
                   10
                                                                         Mean
                    8                                                    (N=44)
                    6
                    4
                                        Hump-shaped 14%
                   2
                   0                                                     Selfish 30%
                        0   2   4   6    8   10   12 14   16   18   20
                        Average contribution level of other group members
      Altruistic Punishment
(Fehr & Gächter, American Economic Review 2000,
                  Nature 2002)

 Public goods game as above.
 Six periods to allow for learning and to study the
 stability of cooperation. At the end of each period group
 members are informed about individual contributions of
 other group members without revealing their identities.
 No repeated interaction with the same subjects. In each
 period each subject faces new group members.
 Nobody knows the previous actions of the other group
 members.
     Altruistic Punishment:
           Treatments
Control treatment: exactly as described above.
Punishment treatment: adds the opportunity to punish
other group members after being informed about their
investments. Two Stages in each period
  The first stage is identical to the control treatment.
  At the second stage each group member can allocate
  punishment points to the other members.
  The first stage payoff of the punished individuals is reduced.
  Punishing is costly for the punisher. Each € "invested" into
  punishment reduces the payoff of the sanctioned player by
  3€.
     Predictions with selfish
           individuals
  Since punishment is costly for the punisher and yields
  not material benefits no selfish subject will ever punish.
  If nobody punishes in the punishment condition then
  the cooperation behavior in the punishment condition is
  predicted to be identical to the behavior in the control
  condition.


In both treatments cooperation should be zero.
                         Cooperation without and
                            with punishment
                              Source: Fehr&Gächter Nature 2002
                    20        without punishment
                    18

                    16

                    14
Mean contribution




                    12

                    10

                     8

                     6

                     4

                     2

                     0
                          1      2    3    4       5   6        7   8   9   10   11   12
                                                       Period
                         Cooperation without and
                            with punishment
                              Source: Fehr&Gächter Nature 2002
                    20        without punishment                    with punishment
                    18

                    16

                    14
Mean contribution




                    12

                    10

                     8

                     6

                     4

                     2

                     0
                          1      2    3    4       5   6        7   8   9    10   11   12
                                                       Period
                         Cooperation with and
                         without punishment
                             Source: Fehr&Gächter Nature 2002

                    20
                             with punishment                without punishment
                    18
                    16
Mean contribution




                    14
                    12
                    10
                     8
                     6
                     4
                     2
                     0
                         1     2   3   4       5   6    1   2   3    4   5       6
                                                   Period
                                                             Punishment
                                  10       3.4
Mean expenditure by punishing group




                                      9


                                      8


                                      7                   6.7
                                      6
             members




                                      5


                                      4
                                                                       19.7
                                      3


                                      2
                                                                                    31.1
                                      1
                                                                                                 32.4            6.7

                                      0
                                          [-20,-14)       [-14,-8)     [-8,-2)       [-2,2]       (2,8]          (8,14]


                                               Deviation from the average cooperation level of the other group
                                                                         members
Is Punishment an altruistic
          act?
The presence of punishers establishes a credible threat that
deters non-cooperation - all group members benefit from this
threat.
Punished subjects contribute more in the next periods - future
interaction partners of the punished subjects benefit from the
punishment.
Punishing subjects bear costs.
Strong reciprocity is documented
       in dozen of studies
It has been documented in a wide variety of situations:
   It applies among strangers. Virtually all experiments
   implement anonymous interactions among subjects.
   Confirmed under experimenter-subject anonymity (Berg et
   al. 1995, Bolton and Zwick 1995, Abbink et al. 1997, etc.)
   Confirmed under rather high stake levels (Cameron 1999,
   Fehr, Tougareva & Fischbacher 2002, three months' income)
   Confirmed under one-shot repetitions (Roth et al. 1991,
   Fehr et. al 1998, Charness 1996, etc.)
   Strong variation across different small-scale societies
   (Henrich, Boyd, Bowles, Camerer, Gintis, Fehr & McElreath
   2001)
Proximate Motives behind
   Strong Reciprocity
Inequity aversion
      Fehr & Schmidt 1999, Bolton & Ockenfels 2000.
    Ui = pi – ai | pi – pj |

Intention based reciprocity
      Rabin 1993, Levine 1998, Dufwenberg & Kirchsteiger 2004,
      Falk & Fischbacher forthcoming.
    Ui = pi + ri kindnessj->i pj


All theories assume a fairness motive in addition to
self interest.
  Neural Basis of Altruistic
        punishment
De Quervain, Fischbacher, ....., and Fehr, Science 2004

There is well documented evidence for reward related
areas in the brain (Nucleus Accumbens, Nucleus
Caudate). These areas are activated when subjects get
reward in the form of
   Money
   Beautiful faces
   Cocain
Fairness theories assume that people derive utility from
altruistic rewarding and from altruistic punishment.
Are reward related areas in the brain also activated
when subjects have the opportunity to punish?
            The basic game
Two traders, A and B, are matched anonymously. The
good possessed by A is four times more worth for trader
B. Thus, if A gives the good to B and B pays A a fair
share of the gains from trade both traders can benefit.
However, trade takes place sequentially, i.e., A first has
to give the good to B, then B pays A. Thus, A has to trust
B and B can abuse A's trust by not paying.
Both are endowed with 10 MUs. A can send his 10 MUs to
B. The experimenter quadruples this amount so that B
has, in total, 50 MUs. Then B can send back 25 MUs to A.
After B has made his payment decision A has the
opportunity to punish B. By spending 1 MU on
punishment he can reduce B's income by 2 MUs. A can
spend up to 20 MUs on punishment.
       Behavioral Results

The vast majority of A sends the 10 MUs.
Roughly 50-60% of the B's send back nothing.
Roughly 80% of the A's punish those B's who abuse
their trust.
Average payoff reduction for the B's is 23 MUs.
     Treatment conditions

Punishment is costly for both A and B (Costly, IC). A is
hypothesized to experience a desire to punish cheating and
he can in fact punish.
Punishment is only symbolic, i.e., A and B have no costs of
punishing (Symbolic; IS). A is also hypothesized to
experience a desire to punish cheating but he cannot
punish.
Punishment is free for A but costly for B (Free, IF). A is
hypothesized to experience a desire to punish cheating and
he can in fact punish - even without a cost.
We scanned the brain of player A (with PET) in the
sequential trading game when A's trust was abused and A
decided whether (and how much) to punish B.
                Hypothesis

The possibility for punishing unfair behavior activates
reward-related neural circuits. (Nucleus Accumbens,
Nucleus Caudate).

IF - IS is hypothesized to activate reward related brain
regions.
IC - IS is also hypothesized to activate reward related
brain regions
IF-IS and IC-IS do activate
    the caudate nucleus
      Individuals with higher caudate
         activation punish more I0.08


                                 0.06
Response at [10, 26, -2] in IC




                                 0.04


                                 0.02


                                    0


                                 -0.02                                                           Is the activation
                                                                                                 caused by the
                                 -0.04                                                           punishment act?

                                 -0.06
                                         0   2   4    6     8    10   12    14    16   18   20

                                                 Amount invested for punishing in IC
                           Individuals with higher caudate
                              activation punish more II
                                0.06
                                                                                                Those with high
                                0.04                                                            caudate activation in IF
                                                                                                treatment punished
Response at [10, 26, 0] in IF




                                0.02                                                            more in the IC
                                                                                                treatment.
                                   0                                                            Caudate activation has
                                                                                                to do with expected
                                -0.02                                                           satisfaction of
                                                                                                punishment.
                                -0.04



                                -0.06
                                        0   2   4    6    8    10    12    14   16    18   20

                                                Amount invested for punishing in IC
                     Overview

   Human cooperation and strong reciprocity
   Experimental evidence for strong reciprocity
   Proximate models of strong reciprocity
   Altruistic punishment activates reward related areas in
    the brain
    Ultimate models of strong reciprocity
   Prevailing Evolutionary
Theories of Human Cooperation
  Kin Selection (Hamilton 1964) - Individuals are
  genetically related
  Reciprocal Altruism (Trivers 1971, Axelrod and Hamilton
  1981) - Individuals are engaged in repeated interactions.
  Helping today yields benefits from the other individual in
  the future.
  Indirect Reciprocity (Alexander 1987, Nowak and
  Sigmund 1998) - Helping creates a good reputation in the
  group. Individuals with a good reputation are more likely
  to receive help from others in the future.
  Signaling (Zahavi and Zahavi 1997) - Cooperative acts
  signal personal qualities that are not directly observable
  like, e.g., good genes. The signals generate some benefits
  in the future.
Problem of the Theories in Explaining
      Large-Scale Cooperation
   Kin selection: Cooperation limited to close kin. Subjects
   in experiments are unrelated strangers.
   Reciprocal altruism, indirect reciprocity: Cooperation
   limited to situation in which reputation can be formed,
   cooperation in experiments also in one-shot situations.
   Signaling theory: In the absence of selection between
   groups it is hard to understand why the signal is pro-
   social.
   Moreover, all these theories apply, in principal, equally
   well to many animal species. They do not answer the
   question, why humans are such an outlier.
                Maladaption
Theories above can rationalize strong reciprocity only as a
maladaptive trait.
   i.e., the proximate mechanisms driving human behavior are
   not yet fine-tuned to interactions among unrelated people in
   non-repeated interactions where reputational gains are small
   or absent.
Problem of the maladaption hypothesis:
   Humans are capable to distinguish between situations in
   which reputation can be gained and situation in which this is
   impossible.
          Ultimatum game
                (Güth et al. 1982)

A proposer and a responder are matched anonymously.
The proposer receives 10 money units and must make
one proposal how to allocate the money between the
two players.
If the responder accepts, the proposal is implemented.
If he rejects, both get nothing.
     Ultimatum game with
          reputation
Treatment condition without reputation:
   Normal ultimatum game. Repeated with different players.


Treatment condition with reputation:
   Proposers get to know which offers were rejected in the
   past by the responder they are matched with. Repeated
   with different players.


Maladaption prediction: Subject cannot distinguish
between situations in which they can build up reputation
and situation in which they cannot. Therefore: Whether
responders can build up reputation for being tough or
not, they have the same threshold for accepting.
Average Rejection Threshold in Ultimatum Game
    with and without Reputation Formation
                                   (Source: Fehr and Fischbacher, NATURE 2003)
                   5
                                        Filled markers indicate a situation with reputation


                   4
Average hreshold




                   3


                                         Empty markers indicate a situation without reputation
                   2


                                              Average over 5 sessions starting without
                   1                          reputation
                                              Average over 5 sessions starting with
                                              reputation




                   0
                       1   2   3    4     5      6      7      8     9     10     1      2   3   4   5   6   7   8   9   10
                                                                          Period
                            Rejection Threshold in Ultimatum Game
                            with and without Reputation Formation
                                        (Source: Fehr and Fischbacher, NATURE 2003)



                                5

                              4.5

                                4
Threshold with reputation




                              3.5

                                3

                              2.5

                                2

                              1.5

                                1

                              0.5

                                0
                                    0   0.5   1   1.5       2        2.5        3      3.5   4   4.5   5
                                                        Threshold without reputation
                            Rejection Threshold in Ultimatum Game
                            with and without Reputation Formation
                                        (Source: Fehr and Fischbacher, NATURE 2003)



                                5

                              4.5

                                4
Threshold with reputation




                              3.5

                                3

                              2.5

                                2

                              1.5

                                1

                              0.5

                                0
                                    0   0.5   1   1.5       2        2.5        3      3.5   4   4.5   5
                                                        Threshold without reputation
The Evolution of Altruistic
      Punishment
Boyd, Bowles, Gintis and Richersen, PNAS 2003
Types of behavior
   Contributors: incur cost c to produce total benefit b, which
   is shared equally among n group members.
   Defectors: incur no costs and produce no benefits.
   Altruistic Punishers: contribute and punish all those who
   defect at cost k for themselves and cost p for each
   defector.
If there are no punishers, individual selection favors
defectors over contributors.
If punishers are frequent, defectors do worse than
altruistic punishers and contributors.
However, contributors do always better than altruistic
punishers.
The Evolution of Altruistic
     Punishment II
Boyd, Bowles, Gintis and Richersen, PNAS 2003
Evolutionary dynamics
  Individual selection: Individuals imitate more successful
  individuals within the group.
  Migration between groups.
  Group selection mechanism: With some probability
  unsuccessful groups are extinct and replaced by successful
  groups.
                                         Simulation Results
                           Fehr/Fischbacher, Nature 2003; based on Boyd et al. PNAS 2003

                             1

                           0.9

                           0.8
Average cooperation rate




                           0.7

                           0.6

                           0.5

                           0.4

                           0.3
                                                                            no punishment possible
                           0.2

                           0.1

                             0
                                 2   4    8    16    32    64   128   256
                                              Group size
                                         Simulation Results
                           Fehr/Fischbacher, Nature 2003; based on Boyd et al. PNAS 2003

                             1

                           0.9

                           0.8
Average cooperation rate




                           0.7

                           0.6

                           0.5

                           0.4
                                                                            punishment of defectors
                           0.3                                              possible
                                                                            no punishment possible
                           0.2

                           0.1

                             0
                                 2   4    8    16    32    64   128   256
                                              Group size
  Why Does Selection not
Remove Altruistic Punishers?
 If punishers are frequent and defectors are rare,
 punishers rarely incur the cost of punishment. Thus, in
 the absence of mutant defectors punishers would do
 equally well as pure contributors.
 In the presence of mutant defectors punishers have a
 small disadvantage relative to pure contributors.
 Selection among groups can outweigh this disadvantage
 of altruistic punishers.

 Remark: Group selection without punishment does not
 work: Without punishment cooperators have a fitness
 disadvantage independent of their frequency.
                                         Simulation Results
                           Fehr/Fischbacher, Nature 2003; based on Boyd et al. PNAS 2003

                            1

                           0.9

                           0.8
Average cooperation rate




                           0.7

                           0.6

                           0.5
                                                                            punishment of defectors
                           0.4                                              and non-punishers possible
                                                                            punishment of defectors
                           0.3                                              possible
                                                                            no punishment possible
                           0.2

                           0.1

                            0
                                 2   4    8    16   32     64   128   256
                                              Group size
  Why does Migration not
Undermine Group Selection?
Because it is based on a cultural process of payoff-
biased imitation. Those who have a high payoff are
imitated.
Traditionally, in genetic models of group selection
migration and within-group selection remove between-
group differences in the share of defectors. Thus, group
selection cannot become operative.
Payoff-biased imitation maintains group differences. In
groups with a low share of altruistic punishers defectors
do best and they are imitated. In groups with a high
share of punishers, contributors do best and they are
imitated and defectors do worst.
                       Summary
1. Human cooperation represents a spectacular outlier in the animal
   world. This is probably due to human forms of altruism that are
   unique in kind and in scope.
2. Reciprocal altruism and reputation-seeking are powerful forces of
   cooperation in dyadic interactions.
3. However, humans exhibit even strong reciprocity, a combination of
   altruistic rewarding and altruistic punishment that is associated with
   net costs for the altruist.
4. Altruistic punishment is key for understanding cooperation in multi-
   lateral interactions. Without altruistic punishment cooperation
   unravels; if opportunities for altruistic punishment exist cooperation
   flourishes.
5. Humans seem to experience altruistic punishment as psychologically
   rewarding. Caudate nucleus is a key component in the neural
   circuits involved in altruistic punishment.
6. Reciprocal altruism and reputation-seeking are powerful forces of
   cooperation in dyadic interactions but they have difficulties in
   explaining the evolution of cooperation in N-person public goods
   situations.
The end
   Conditional cooperation
           design
(Fischbacher et al. 2001, see also FKR 93 or BDM 95)
Standard public goods situation (endowment =20, N =
4, F=1.6); played only once
Subjects have to make two decisions:
An unconditional contribution to the project
A conditional contribution to the project (conditional on
every possible contribution of the others – called
„contribution table“)
For 3 subjects, their unconditional contribution is
relevant. For a randomly selected group member
his/her contribution schedule is relevant for the
decision.
 Testing Evolutionary Models
     Environment                    Types of behavior
        Game(s)
Is the environment               Are the types complete?
representative?
                                    Are there no type who can
    Does the game                   invade the population?
    correspond the the
    interaction how it            Does the type distribution
    actually took place in the   correspond the distribution
    relevant time period?        which is actually observed?
                                    This question can be
                                    addressed with
                                    experiments.


           Evolutionary
             Dynamics
                                 Simulation Results
                       Fehr/Fischbacher, Nature 2003; based on Boyd et al. PNAS 2003
                  1

                 0.9

                 0.8

                 0.7

                 0.6
Share of types




                                                                             2nd level Punishers
                                                                             Punishers
                 0.5
                                                                             Cooperators
                                                                             Defectors
                 0.4

                 0.3

                 0.2

                 0.1

                  0
                       0                                              2000
                                              Time
   Typical experimental outcome
                  Isaac, Walker, Thomas (1984)




                                         There is
                                         cooperation.
                                         Cooperation
                                         declines over
                                         time.

10H:N=10, F=7.5    4H: N=4, F=3
10L: N=10, F=3     4L: N=4, F=1.2;

				
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