Five Principles for the Unification of the
Behavioral Sciences
Herbert Gintis
Santa Fe Institute
Central European University
University of Siena
University Press
University Press
Evolutionary Game
University Press
Disarray of the Behavioral Sciences
The behavioral sciences (economics, sociology,
anthropology, psychology, political science, biology)
are in profound disarray, with incompatible models of
human behavior.
We now have the analytical and empirical basis for
beginning to construct an integrated behavioral
Four Incompatible Models of Human
Choice and Strategic Interaction
Economics: Homo economicus, the self-regarding
maximizer with unlimited and costless information
processing capacity, who acts prosocially when the
incentives align with selfish motives.
Sociology: Homo sociologicus, the compliant actor
socialized to fill social roles.
Biology: The fitness maximizer whose prosociality is
based on inclusive fitness (kin altruism) and selfinterested reciprocity (reciprocal altruism).
Cognitive/Social Psychology: The irrational and
illogical decision-maker.
Four Incompatible Models of Human
Choice and Strategic Interaction
The evidence for the existence and content of these four
models comes from
--what is taught in introductory graduate textbooks
in the discipline.
--what can be assumed in a disciplinary journal
article without comment or defense.
--what professionals in the discipline share in
common, specialized fields being more nuanced.
Four Incompatible Models of Human
Choice and Strategic Interaction
At least three of these four models must be wrong.
In fact they are all wrong,
although all include fundamental insights that must be
incorporated into a unified basic model of human
choice and strategic interaction.
Five Principles for the Unification of the
Behavioral Sciences
1. Gene-culture Coevolution (biology)
2. Socio-psychological Theory of Norms
(sociology, cognitive psychology, social psychology)
3. Game Theory (economics, biology)
Classical, Epistemic, Behavioral, and Evolutionary
4. The rational actor model, a.k.a. the
Beliefs, Preferences, and Constraints (BPC) Model
(economics, decision theory, biology).
5. Complexity Theory
Gene-culture Coevolution
Individual fitness in humans depends on the structure of
social life.
Because culture is limited and facilitated by human
genetic propensities,
human cognitive, affective, and moral capacities are the
product of an evolutionary dynamic involving the
interaction of genes and culture (Cavalli-sforza and
Feldman 1982; Boyd and Richerson 1985, 2004).
This coevolutionary process has endowed us with
preferences that go beyond the self-regarding concerns
emphasized in traditional economic and biological
Gene-culture Coevolution
Gene-culture coevolution explains why we have a social
epistemology facilitating the sharing of intentionality
across minds,
as well as why we have such non-self-regarding values as
a taste for cooperation, fairness, and retribution,
the capacity to empathize, and
the ability to value character virtues (e.g., honesty)
Gene-culture Coevolution
g : genetic structure
c : cultural structure
e : environmental structure
Note that it is plausible to add a link from c to e, so
H(e)  H(e,c), or even from g to c, as in niche
construction theory, so H(e)  H(g,c,e).
Evolutionary Game Theory
Evolutionary game theory provides the analytical
apparatus for building a dynamic model of changing
gene frequencies and the distribution of cultural forms.
Genes and culture obey similar dynamic laws, often
captured by the replicator dynamic of evolutionary
game theory.
The analogy is not perfect, however, so cultural dynamics
must be supplemented by several structural principles
in addition to the “imitation” mechanism at the heart
of the replicator dynamics.
Evolutionary Game Theory
Important additions are the notion of vertical, horizontal,
and biased transmission (Cavalli-sforza and Feldman,
Boyd and Richerson) and the cognitive approach to
norm-following (Castelfranchi and Conte).
The Socio-psychological Theory of
All social species have a division of labor, individuals
being prepared for particular roles by nutritional and
genetic differences.
Human society has a division of labor characterized by
dozens of specialized roles,
appropriate behavior within which is given by social
and individuals are prepared to fill these roles
through a process of socialization.
The Socio-psychological Theory of
Socialization transmits moral values by leading
individuals to internalize norms,
through which they are induced to conform to the
duties and obligations of the role-positions they
will occupy.
There are important limits to socialization, so
additional causal processes are involved in cultural
dynamics (Gintis, Journal of Theoretical Biology
The Socio-psychological Theory of
This concepts of socialization and the internalization of
norms goes back to Durkheim (1902), but was later
developed by Parsons, Goffman, and many others.
The socio-psychological theory of norms supplies
mechanisms missing from game theory that promote
coordinated behavior.
The Rational Actor Model
Evolutionary principles suggest that individual decision
making can be modeled as optimizing a preference
function subject to subjective beliefs and objective
Natural selection leads the content of preferences to
reflect biological fitness
although the isomorphism between fitness and utility
disappears outside the environment in which the
preferences evolved.
This is why humans do not maximize fitness in the postPleistocene era.
The Rational Actor Model
The principle of expected utility extends this optimization
to stochastic outcomes.
The resulting model is called the rational actor model
or the beliefs, preferences, and constraints (BPC) model.
The Rational Actor Model
Four caveats are in order.
First, individuals do not consciously maximize something
called utility, or anything else.
Second, individual choices, even if they are selfregarding (e.g., personal consumption) are not
necessarily welfare-enhancing.
Third, preferences must be stable across time to be
theoretically useful,
but preferences are ineluctably a function of an
individual's current state.
The Rational Actor Model
Fourth, beliefs are the Achilles’ heel of the BPC model,
because the model treats beliefs as subjective, whereas
individual beliefs are in fact constituted through a social
network of interdependent beliefs.
Game Theory
In the BPC model, choices give rise to probability
distributions over outcomes, the expected values
of which are the payoffs to the choice from which
they arose.
Game theory extends this analysis to cases where
there are multiple decision makers.
In the language of game theory, players are endowed
with strategies, and have certain information, and
for each array of choices by the players, the game
specifies a distribution of payoffs to the players.
Game theory predicts the behavior of the players by
assuming each maximizes a preference function
subject to available information, personal beliefs,
and exogenous constraints.
Game Theory
Game theory is a logical extension of evolutionary
Game theory is population biology with frequency
dependent payoffs.
Game theory has become the basic framework for
modeling animal behavior (Maynard Smith 1982;
Alcock 1993; Krebs and Davies 1997).
Evolutionary and behavioral game theory do not
require the formidable information processing
capacities of classical game theory,
so disciplines that recognize that cognition is scarce
and costly can make use of contemporary gametheoretic models.
Game Theory
In particular, agents may use by rule-of-thumb
heuristics rather than maximization techniques
(Gigerenzer and Selten 2001)
and of course we need not assume individuals are
Society as
Complex Adaptive System
The behavioral sciences advance not only by
developing analytical and quantitative models,
but by accumulating historical, descriptive and
ethnographic evidence that pays heed to the
detailed complexities of life.
Historical contingency is a primary focus for many
students of sociology, anthropology, ecology,
biology, politics, and even economics.
By contrast, the natural sciences have found little use
for narrative along side analytical modeling.
Society as
Complex Adaptive System
The reason for this contrast between the natural and
the behavioral sciences is that
living systems are generally complex, dynamic
adaptive systems
with emergent properties that cannot be fully captured
in analytical models that attend only to the local
The deductive methods of game theory, the BPC
model, and even gene-culture coevolutionary
theory must therefore be complemented by the
work of behavioral scientists who adhere to a more
historical and interpretive traditions.
Complex Systems
A complex system consists of a large population of
similar entities
in our case, human individuals
who interact through regularized channels (e.g.,
networks, markets, social institutions)
with significant stochastic elements,
without a system of centralized organization and
A complex system is adaptive if undergoes an
evolutionary (genetic or cultural) process of
reproduction, mutation, and selection.
Complex Systems
To characterize a system as complex adaptive does
not explain its operation, and does not solve any
However, it suggests that certain modeling tools are
likely to be effective that have little use in a noncomplex system.
In particular, the traditional mathematical methods of
physics and chemistry must be supplemented by
other modeling tools, such as agent-based
simulation, network theory, and narrative thick
Five Principles for the Unification of the
Behavioral Sciences Redux
1. Gene-culture Coevolution (biology)
2. Socio-psychological Theory of Norms (sociology,
cognitive psychology, social psychology)
3. Classical, Epistemic, Behavioral, and Evolutionary
Game Theory (economics, biology)
4. The rational actor model, a.k.a. the
Beliefs, Preferences, and Constraints (BPC) Model
(economics, decision theory, biology).
5. Complexity Theory

Evolutionary Game Theory