An evolutionary game
approach to culture:
Illustration by an adaptive norm
development
Tatsuya Kameda (Hokkaido University)
tkameda@let.hokudai.ac.jp
http://lynx.let.hokudai.ac.jp/members/kameda
CEFOM/21, 2nd Workshop
Culture, Norm, and Evolution
Hokkaido University, Aug. 6-8, 2003
1
Overview
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Resurgence of collective constructs (e.g.,
norms, conventions, values) in social sciences
How can we study these collective constructs
fruitfully? – Adaptive perspective
Evolutionary game theory as a useful
research tool
An illustration with communal-sharing norm
in primordial societies
2
Social norm

Cialdini & Trost (1998)
“Social norms are rules and standards that are
understood by members of a group, and that guide
and/or constrain social behavior without the force of laws.
These norms emerge out of interaction with others; they
may or may not be stated explicitly, and any sanctions
for deviating from them come from social networks, not
the legal system” (p.152).

Socially-shared rules that emerge and are
sustained through people's autonomous
interaction, not necessarily with formal
regulating authorities or forces such as laws
3
Theory of norm development?
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Emergence and sustainability of social norms as
core issues for any theory of social norms.
But, do we have a reasonable theory of norm
development in this sense?
Classic studies on norm development (e.g., Sherif,
1936; Jacobs & Campbell, 1961): adaptively
irrelevant “norms”
Social/cultural learning as a general engine for
norm development, but…
4
Theory of norm development?

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A more fundamental question: Why some
beliefs are acquired socially and are
maintained as a shared rule, while other
beliefs are not.
Adaptive/evolutionary perspective

Beliefs that help us acquire a fit behavior in a
given social/physical environment are more likely
to be transmitted culturally and maintained as a
social norm.
5
Illustration: Norms about foodsharing in primordial societies
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Kaplan & Hill (1985): Fieldwork on the Ache
foragers in Paraguay
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Collected resources (vegetables, fruits)
 Kin-sharing
Hunted game (peccary, monkey, deer)
 Communal-sharing including non-family
members widely
Existence of two different sharing
rules/norms in the same society: Why?
6
Why communal-sharing of hunted
games?

Risk-reduction hypothesis
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Acquisition of a meat is a highly variable,
uncertain prospect, compared to the provision
of collected resources.
Communal-sharing system functions as a
collective-risk reduction device.
By including more individuals in the riskpooling group, the variance in food supply
decreases exponentially.
7
Intuitively appealing, but truly
adaptive explanation?
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Problem of egoism in social sharing
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Hunted meat is often regarded as a common
property or public goods in hunter-gather societies.
What if egoists emerge in the group who just
share others’ acquisitions but are never willing to
share his own acquisition?
Emphasizing adaptive function of the whole
system, but silent about how those egoists are
precluded in the group.
Need a theory based on individual-level
adaptation rather than group-level adaptation.
8
A theory about development of
the communal sharing norm


Proposing a theory based on individual-level
adaptation
Using an evolutionary game analysis

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Maynard Smith (1982): Evolutionary biology
Axelrod (1984): Introduction to social sciences
9
Evolutionary game

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Represents various behavioral/cognitive
properties of individuals as strategies in a game.
Examines how each strategy performs in the
game against other strategies in terms of net
profit.
More fit strategies proliferate in the population
gradually (via social/cultural learning).
Different from classical game theory, it does not
assume players with super-intelligent
information processing ability.
10
Applying the evolutionary game analysis
to adaptive norm development
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EGA: “Does the interaction among given
individual behavioral/cognitive strategies lead to
a stable collective state (“evolutionary
equilibrium”) where the population is dominated
by a single strategy (or a set of strategies)?”
Social norm: a stable set of socially-shared
behavioral/cognitive properties (Cialdini & Trost,
1998)
EGA is particularly suited for examining adaptive
norm developments in societies.
11
Our model: 4 behavioral strategies
about sharing under uncertainty
When in the non-acquirer role
When in
the
acquirer
role
Demanding
communal-sharing
Granting
another
acquirer’s
ownership
Provisioning as a
common property
Communal
sharer
Saint
Claiming private
ownership
Egoist
Bourgeois
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Key Question: Can communal sharers
outperform other types of members in
the population?
Basic Model
Acquirer with
a resource of
value V (e.g.,
hunted meat)
Depending on behavioral strategies, some individuals
may demand communal sharing of the resource.
Refusal of the acquirer to share the resource leads to
fights that may incur cost C to each loser.
13
Evolutionary computer
simulations
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Implement the four behavioral strategies in a
same population and let them interact.
A strategy that achieves higher profit than the
other strategies increase its proportion in the
population gradually.
Emergence of a stable equilibrium over time?
14
Results of a simulation starting with
nearly 100% egoists in the population
Stable
Proportions in the group
1
0.9
0.8
0.7
0.6
Bourgeios
Saint
Egoist
Communal Sharer
0.5
0.4
0.3
0.2
0.1
Generation
48 00
45 00
42 00
39 00
36 00
33 00
30 00
27 00
24 00
21 00
18 00
15 00
12 00
90 0
60 0
Evolvable from
nearly zero
30 0
0
0
15
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2nd-(and higher-) order free-riding? How can
this issue be solved?
16
Communal sharers
“Lukewarm” normenforcers
(1st -order free riders)
>
Committed Enforcers
Tolerant toward the lukewarm
members (2nd-order free
riders)
>
Intolerant
17
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However, the infinite regress is blocked.
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The lukewarm members (1st-order free rider) quickly
acquire behavioral propensity to be less reactive (less likely
to engage in fighting when refused access to the resource)
against intolerant members (p2), than against non-sharers
(p1). p1 > p2
Lukewarm members’ p1 is already small. Thus, p2 is
negligible. That is, lukewarm members back off, when
refused to access the resource by the intolerant members.
So, no fitness differences accrue between the tolerant and
the intolerant members. Tolerant members can survive,
while effectively eliminating the lukewarm members.
See Kameda, Takezawa & Hastie (2003) for details.
18
“Communal-sharing mind” under
uncertainty?
16
Certain
Uncertain
14
Frequencies of donators
12
10
8
6
4
2
0
0
～100 ～200 ～300 ～400 ～500 ～600 ～700 ～750
The amount of money donated (in yen)
Conceptually parallel patterns were also obtained with
American samples (see Kameda, Takezawa, Tindale, & Smith, 2002)
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Conclusion
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Communal-sharing ideology can develop to a
stable equilibrium (-- socially-shared rule) under
uncertainty, as a result of individual-level fitness
maximization.
Although living in modern societies (US and
Japan), “communal-sharing minds” are triggered
easily for uncertain resources.
Such an operation of mind is adaptive under
uncertainty.
Evolutionary game analysis is a powerful
research tool to understand various micro-macro
dynamics in our societies.
20
Some thought experiment: Two
imaginary commentators
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Promising conclusion, but any limitations in
the current communal-sharing model?
Two imaginary commentators
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A behavioral ecologist
A comparative institutional economist
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Behavioral ecologist
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“An interesting talk. Methodologically sound and
theoretically coherent with work in behavioral ecology.”

One critical question – “Given your model, why don’t
chimps (or other social animals) engage in communal
sharing? They may have the same adaptive problem of
uncertainty-reduction in food supply, but no primates
other than humans have a broad food-sharing system.
What elements in your model limit its scope just to
humans? Some sophisticated cognitive mechanisms are
assumed in your model?”
22
A comparative institutional
economist
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“I like your talk, but share the concern with
the behavioral ecologist.”
“…Technological and ecological factors…
may not be the sole determinants in the
selection of a (social) equilibrium; historical
and social factors may also matter.
Otherwise, norms are nothing but a
mechanical transformation of technological
and ecological characteristics…” (Aoki, 2001,
p.50)
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What do these (imaginary)
criticisms imply?
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My model: Communal-sharing norm as evoked by
the local ecological conditions
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High variance (uncertainty) in meat supply
Group-living: no “privacy”
Behavioral ecologist: Chimps and other social
animals may have the same local ecological
condition. Then, why don’t they have the
communal-sharing norm? Do they lack
sophisticated cognitive mechanisms? What exactly
are these mechanisms?
Comparative institutional economist: Just a
mechanical transformation of ecological
characteristics into a “norm”? Specific historical and
social factors leading to the norm? Any role of
beliefs?
24
“Evoked culture” vs.
“Epidemiological culture”

Tooby & Cosmides (1992)
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Evoked culture: “Culture triggered by local
circumstances; Shared local conditions lead to
within-group behavioral similarities and betweengroup behavioral differences.”
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Local ecological conditions evoke culture.
Epidemiological culture: “Culture maintained by
constructing shared representations.”
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Traditional conceptualization of culture (“transmitted
culture”) in social sciences (e.g., Sperber, 1996)
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(cont’d)
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Evolutionary psychologists tend to emphasize
the role of evoked culture in human societies.
However, in the evoked culture, cultural
beliefs, in principle, do not play a unique,
independent role from behavior. Beliefs are
just psychological counterparts (reflections)
of the adaptive behavior in the local
environment, and might even be argued as a
redundant concept.
However, cultural beliefs matter!
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Chimps vs. humans (re. cultural capacities)
Social/historical changes
26
Challenges!
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So, real challenge is to go beyond the evoked
culture and theoretically incorporate the
epidemiological (transmitted) culture into the
adaptive perspective.
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Cross-fertilization among different disciplines is
essential.
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Psychology
Evolutionary anthropology
Economics (comparative institutional analysis)
Game-theoretic framework (including evolutionary
and repeated game approaches) provides a
common platform.
27
References
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