Evolution and the Capacity for Commitment

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Chapter 1
Natural Selection and the
Capacity for Subjective
Commitment
RANDOLPH M. NESSE
O
nce you recognize them, commitments are everywhere. The
commitment we all know is marriage. By giving up the op-
tion to leave for someone else, spouses gain security and an
opportunity for a much deeper (and more efficient!) relationship than
would otherwise be possible.Yet many commitments are not at all
nice. When John F. Kennedy committed the United States to eliminat-
ing missiles from Cuba, millions of human lives were put at risk.
When a thuggish-looking man offers unrequested fire insurance to a
small retail shop, the implied threat of arson may well influence the
owner’s behavior. In a more banal vein, nearly everyone has waited
for a repairman who never arrives. From the personal to the political
to the mundane, commitments are everywhere. Threats and promises
change people’s beliefs and, therefore, their actions.
In a world without commitments social exchanges arise mainly
from helping relatives and trading favors. In such a world individuals
can reliably be expected to act straightforwardly in their own inter-
ests. The advent of commitment changes everything. As soon as one
individual finds a way to convince another that he or she will act
other than in simple self-interest, social life is transformed. Now, indi-
viduals must consider the possibility that others may fulfill promises
and threats. Sometimes the situation itself makes fulfillment worth-
while, but apparently irrational commitments also may influence
others profoundly. A whole new category of social influence emerges.
From: "Evolution and the Capacity for Commitment," 
edited by Randolph M. Nesse, Russell Sage Press, NY, 2001

2 Evolution and the Capacity for Commitment
Reputations become important predictors of behavior, and people be-
gin spending vast amounts of effort to convince others that they will
fulfill their promises and threats.
One way to convince others of one’s credibility in a commitment is
to give up options in order to change the incentives in a situation.
Others observe that compliance is now in the person’s interests, and
change their expectations and behavior accordingly. By signing a
lease, for instance, a person gives up the option to leave on short
notice, and induces the landlord to give up the option of raising the
rent in the middle of winter. Not all commitments, however, are
backed by such tangible incentives. As Frank and Hirshleifer argue
(Hirshleifer 1987; Frank 1988), people also can convince others that
they will keep their promises by emotional displays that testify to
their irrationality. Such commitments give rise to profound para-
doxes. In order to influence others an individual must convince peo-
ple that he or she will act in ways that are not in his or her interests.
Sometimes it is possible to reap the benefits of this influence without
having to fulfill the commitment. Kennedy did not want a fight, he
simply wanted the missiles out of Cuba; because the Russians be-
lieved he would follow through on his threat, he didn’t have to. More
often, however, convincing others requires fulfilling the commitment
to some degree. If your fianc´ee gets sick on the day you have tickets
for the big game, too bad, you have to stay home. Also, once commit-
ment strategies are widespread, reputation becomes so valuable that
maintaining it requires fulfilling some commitments irrespective of
the effects. The gang leader who rules by ruthlessness cannot show
mercy for fear of losing his power. Before you know it, commitments
lead people to do all kinds of things they would rather not do,
whether this means carrying out spiteful threats or helping others
who will never be able to reciprocate. Social life becomes rich and
complex. Foresight and empathy become essential tools for social sur-
vival. In a world where commitments influence behavior a workable
theory of mind becomes more useful than a sharp stone axe.
The capacity for using commitment strategies effectively is so im-
portant that natural selection may have shaped specialized capacities
to make this possible. These capacities may help to explain the human
tendency to emotionally extreme behaviors that often seem senseless.
Such explanations may help to bridge the gap between the social sci-
ences and evolutionary approaches to behavior. Even more important,
they may help us find ways to cope with the great moral and intellec-
tual crisis precipitated by the discovery that natural selection works
mainly at the level of the gene, and its corollary, that natural selection
cannot shape a capacity for altruism that gives a selective advantage
to genes different from one’s own This is turning out to be a major

Natural Selection and the Capacity for Subjective Commitment 3
psychic trauma to humankind, one that may be even more disturbing
than the previous two: while the Copernican revolution shook reli-
gious cosmology off its foundations, it did little to challenge people’s
belief that human life has special meaning as the culmination of a
divine plan; the second trauma—the discovery of natural selection
and our evolutionary origins—was more personal (Richards 1987;
Cronin 1991). Finding out we are only one species among many, all
shaped by the mindless force of natural selection, fundamentally
threatens our sense of the significance of human life (Ruse 1989; Den-
nett 1995). Resistance to this fact remains passionate, and creates an
emotional fissure that still ruptures the political and social landscape.
Even as we struggle to accept the facts about our evolutionary ori-
gins, however, we confront a third trauma, this one a more direct
threat to our individual moral identities. For decades biologists com-
placently had thought that selection shapes traits that benefit groups
and species (Wynne-Edwards 1962). This assumption made it easy to
view self-sacrifice for the sake of the group as entirely natural and
expected. With simple but ruthless logic, Williams showed in 1966
that selection at the group level is feeble compared to selection at the
individual level (Williams 1966). Natural selection, it turns out, acts
mainly to benefit genes and individuals, not groups or species (May-
nard Smith 1964). Many implications follow from this, but the most
profound is the transformation of altruism from a natural tendency
into an evolutionary mystery (Dawkins 1976; Badcock 1986; Barash
1977; Krebs 1970). E. O. Wilson called altruism “the central theoretical
problem of sociobiology” (Wilson 1975, 3). Previously, animals were
thought to help each other because natural selection shaped behav-
ioral tendencies to sacrifice for the good of the group. It is now clear,
however, that genes that lead to sacrifice for the group tend to be-
come less and less frequent, except in very special circumstances. Any
natural tendency to help others now must be explained in terms of
how it benefits the actor’s genes. If no such explanation can be found,
the tendency becomes an anomaly in need of special explanation. No-
tice that the object of explanation here is a tendency, not a behavior.
Individuals may decide to behave in ways that are not in their repro-
ductive interests, and social structures may foster many such behav-
iors. Yet all tendencies shaped by natural selection must provide an
inclusive fitness benefit in the long run, otherwise they will be elimi-
nated.
Most people think of altruism as a costly effort that helps others.
Many people also identify with their genes. Learning that organisms
are shaped to act in ways that benefit their genes can make people
feel that helping their relatives is somehow helping themselves and,
therefore, not generous in the same way that helping a nonrelative

4 Evolution and the Capacity for Commitment
would be. From this viewpoint, genuine altruism can appear impossi-
ble, or at least contrary to nature (Richards 1993). Furthermore, many
people, on grasping that all organisms are necessarily designed to act
in the interests of their selfish genes, instantly (and incorrectly) con-
clude that individuals must be selfish by nature. Some take this a step
further, concluding that our moral passions are mere pretensions or,
worse, self-deceptive strategies for manipulating others (Ghiselin
1969).
Of course, individuals do help each other. To explain this, Wil-
liams’s insight was quickly complemented by the recognition of two
specific ways in which helping others can benefit the helper’s genes.
The first is kin selection. As Hamilton pointed out, because related
individuals share a proportion of genes that are identical by descent,
natural selection can shape tendencies to act in ways harmful to the
self if there is enough benefit to kin (Hamilton 1964). Thus, natural
selection can increase the frequency of a genetic tendency that makes
a mother blue jay risk her life to defend her eggs because of the bene-
fits to identical copies of the same genes that exist in other individ-
uals (who are not yet hatched). The second way in which altruistic
acts can offer benefits is by reciprocal exchange. As Trivers made
clear, trading favors can yield a net reproductive benefit to both par-
ties (Trivers 1971). In the long run mutual helping gives a net payoff,
so long as one avoids being exploited. On these two pillars, a new
theory of sociality is being constructed (Trivers 1985). Every social
tendency has been attributed to benefits from some combination of
kin selection and reciprocity. Those that cannot be explained in these
terms have become anomalies that require interpretation as abnormal
behavior, or products of manipulation or socialization in our novel
modern environment.
The scientific impact of these developments has been enormous.
They have transformed social ethology from a descriptive science to a
predictive one based firmly on evolutionary theory (Trivers 1985; Al-
cock 1997). Hundreds of studies now investigate the role of kin selec-
tion in behaviors ranging from mating strategies to food sharing and
defense (Alcock 1997). Tom turkeys court females in cooperative
groups; it turns out that the groups are almost always composed of
brothers. The sentinel prairie dog that warns the group about ap-
proaching coyotes is especially likely to have many relatives in the
group. Human infants are eighty times more likely to die from child
abuse if they are in a family with a stepparent (Daly and Wilson
1987). Kin selection is one of the great discoveries in our time.
The principle of reciprocity is an equally powerful advance for ex-
plaining social behaviors among unrelated individuals (Trivers 1985;
Cronin 1991). Examples range from mating alliances between male

Natural Selection and the Capacity for Subjective Commitment 5
chimpanzees to blood sharing in vampire bats (Dugatkin 1997). Indi-
viduals who trade favors judiciously do better than those who go it
alone. Often, of course, individuals trade favors with relatives, thus
getting benefits via both mechanisms. Together, kin selection and reci-
procity are widely thought to fully explain social behavior. They are
certainly hugely important, but are they sufficient? Or, as many have
suggested (Boehm 1999; Hirshleifer 1999; Humphrey 1999), might
there be other routes to social behavior that have been neglected?
Certainly there are. The tendency to use reciprocity to stand for all
cooperative relationships is itself a vast oversimplification. Among
other possibilities, cooperation also can arise from mutualism, coer-
cion, and social organizations that control incentives. Mutualism, in
particular, has been neglected. A great proportion of social coopera-
tion is mutualistic; individuals get benefits only if they contribute, so
cheating is not possible. (For more on this discussion see Adams in
chapter 5.) Much additional cooperation is coerced; an individual
with control over resources can impose punishments that make cheat-
ing of no value. These are among several routes to cooperation that
are often neglected. Here we are concerned in particular with one
additional means of social influence—commitment. Our goal is to ex-
amine how commitment strategies work, how they are used in prac-
tice, and the core question of whether the ability to make and assess
commitments gives selective advantages that have shaped our minds.
The importance of this core question, and its place in the explanation
of social behavior, will be clear only after outlining the full magnitude
of the current crisis and the responses it has provoked.
The sketch described here uses intentionally bold brushstrokes to
illustrate the crisis at the intersection of science and morality created
by the demise of group selection and its replacement by kin selection
and reciprocity. Subtleties and caveats abound, but here they are set
aside intentionally to highlight the dark simplicity of the problem,
summarized best in Dawkins’s phrase “the selfish gene.” He knows
perfectly well that genes have no motives, but his metaphor of genes
as self-serving agents has enabled thousands of readers to view life
from this dramatically new perspective (Dawkins 1989). We are jerked
to attention by picturing ourselves as lumbering robots acting at the
behest of our genes. Given how natural selection works, we know
that the genes that influence behavior in any species are those that
have given rise to actions that tend to increase the numbers of copies
of those genes in future generations. All evolved tendencies, includ-
ing those motivating generosity and morality, somehow must have
increased the frequency of the genes that give rise to them. The ex-
trapolation that individuals must therefore be selfish, however, is in-
correct. Indeed the very existence of sympathy and moral passions

6 Evolution and the Capacity for Commitment
suggests that they likely give a selective advantage; yet how do such
traits advance the interests of an individual’s genes? One possibility is
by improving the individual’s capacity to benefit from commitment.
Is this issue really so dramatic? Is all this talk about psychic
traumas and moral crises just the latest attempt by academics to in-
flate the importance of their arcane arguments about human nature? I
think not. What we believe about ourselves and human nature is im-
portant because it influences how we act (Beck 1976). Those actions
shape our societies that in turn shape our beliefs, thus setting long-
running cultural cycles in motion (Fukuyama 1995). Evidence that
much is at stake can be seen in the intensity of reactions to these ideas
(Caplan 1978; Ruse 1982; Rose and Rose 2000). Many people find it
repugnant to think that humans are inherently selfish, and despicable
to think of altruism as just another way to serve one’s interests. They
assume that people who advocate such ideas must themselves be self-
ish and lacking in respect for society’s rules. Attacking such appar-
ently immoral nonconformists is sanctioned and even required by
many social groups. Thus, criticisms of evolutionary approaches to
human behavior often segue, without notice, qualms, or apologies,
into ad hominem attacks against individuals and moral condemna-
tions of whole groups. If the tone of recent letters in the New York
Review of Books provides insufficient evidence, consider the subtitle of
a new book: Arguments Against Evolutionary Psychology. (Rose and
Rose 2000). The acrimony in this debate has created a dust storm of
rhetoric and anger that obscures many legitimate issues. The battle
has engaged the general public, whose insights often are consider-
able, thanks to the availability of accessible yet meaningful treatments
of the main issues (Wright 1994; Ridley 1997; Wilson 1993). For pro-
fessional audiences, the number of books and articles exceeds any-
one’s ability to keep up (Campbell 1975; Schwartz 1986; Ruse 1986;
Alexander 1987; Oyama 1989; Maxwell 1990; Frank 1992; Nitecki and
Nitecki 1993; Wilson 1993; Bradie 1994; Midgley 1994; Petrinovich
1995; Hurd 1996; Katz 2000).
Reactions to the Trauma
Responses to this psychic trauma take a variety of forms. A brief
treatment cannot catalog all of them, nor can it adequately explain
and justify any of them in full detail; it can, however, map the land-
scape of these controversies. Moreover, the intensity and diversity of
reactions are testimony to the central role of the problem of altruism.
A review of twelve kinds of reactions to this crisis will set the stage
for further consideration of the role of commitment as a possible, al-
beit partial, solution.

Natural Selection and the Capacity for Subjective Commitment 7
•
Many people take one look at this controversy and dismiss the idea
that all motivational systems must benefit the actor’s genes. The
theory seems to be contradicted by too many examples. Soldiers
dive on grenades to save their buddies. Enraged spouses murder
their partners, knowing that this will mean decades spent in prison.
Suicide bombers destroy themselves to advance their causes. Heroes
dive into icy rivers. Ascetics meditate for years. Some people decide
not to have children. Some even decide not to have sex. Others quit
jobs to care for their disabled children or demented spouses. Anony-
mous benefactors give money to charity. Saints sacrifice their lives for
their beliefs. Do such examples suffice to demonstrate that an evolu-
tionary view is simply wrong? It is possible that we may attend to
such examples precisely because they are so anomalous, but they still
offer a challenge. They suggest that models based only on kin selec-
tion and reciprocity are inadequate; some other principle is needed.
•
The crudest form of opposition is also the most prevalent—to deny
the very phenomenon of evolution, or at least its application to hu-
mans. Fundamentalist Christian theology fosters pride in such de-
nial. According to a 1999 Gallup poll, 47 percent of Americans be-
lieve “God created human beings pretty much in their present form
at one time within the last 10,000 years or so” (Moore 1999). Scien-
tific evidence has little impact on such beliefs, except to spawn
more subtle and apparently scientific versions of creationism (Behe
1996; Dembski 1998) that are so insidiously confusing that they be-
fuddle not only school boards but even some otherwise clear-thinking
scientists. Conversations with creationists often reveal high motives,
however; many sincerely believe that natural selection is incompat-
ible with the possibility of human goodness and meaning in life.
•
Others challenge the fundamental genetic perspective of evolution-
ary thinking. Oyama, in particular, views organisms as systems that
sustain themselves by passing along various characteristics by di-
verse means, genetic material being only one source of information
among many (Oyama 2000). Her developmental systems theory in-
terprets individuals as products of overlapping cycles of gene-
environment interaction far more complex than those usually con-
sidered. She wants to challenge what she calls the “central dogma”
that phenotypes are genetically programmed, and to replace the
nature-nurture dichotomy with “a radical reformulation of both.”
Interestingly, these views become the basis for an attack on the no-
tion that individuals are naturally selfish (Caporael et al. 1989;
Oyama 1989, 48). Whether these ideas simply lend themselves to
such arguments or helped to motivate their development is hard to
determine.

8 Evolution and the Capacity for Commitment
•
Scientists do not have the option of denying the fact of natural se-
lection, and most seek to understand nature through descriptions
that increase simplicity, not complexity. Those who object can, how-
ever, try to blunt the impact of this new knowledge in other ways.
One is to emphasize the limits of natural selection—its stochastic
nature, its inability to create perfection, and the difficulties of study-
ing adaptations (Gould and Lewontin 1979; Kitcher 1985). Such crit-
icisms are certainly justified when applied to silly just-so stories and
the uncritical and na¨ıve view of adaptation that gives rise to them.
Some critiques, however, tend to damn the whole enterprise of
using evolutionary theory to understand adaptations in general, be-
havior in particular, and human behavior especially. As Wright
points out, they also may give fuel to creationists (Wright 2000,
chapters 18 and 19). Daunting challenges remain, however, includ-
ing finding better criteria for determining what is an adaptation and
what is not, and better understanding how natural selection shapes
maladaptations as well as adaptations. These tasks are difficult, but
by no means impossible (Williams 1992; Rose and Lauder 1996).
Criticism of specific proposals is valuable, but even more valuable
are well worked-out tests of adaptationist hypotheses.
•
This brings us to objections based on admittedly political aims that
sometimes come with the trappings of science (Caplan 1978; Seger-
str˚ale 2000). For instance, in critiques of so-called genetic reduction-
ism, otherwise careful scientists create confusion by confounding
questions about evolution and adaptation with quite different ques-
tions about genes and mechanisms (Gould and Lewontin 1979;
Lewontin, Rose, and Kamin 1984). Closely related is the tendency to
fail to distinguish evolutionary studies about the functions of be-
havior from fundamentally different behavioral genetic studies that
seek to explain individual differences as a result of genetic differ-
ences. Such conflation fosters overtly political attempts to associate
modern evolutionary approaches to understand human behavior
with eugenics and the horrors of the Third Reich (Lewontin, Rose,
and Kamin 1984). As the political motivations of these gambits are
better recognized, they are having less and less effect, at least in the
natural sciences (Segerstr˚ale 2000). Furthermore, any association of
evolutionary biology with conservative causes is dissolving because
most in the field today lean toward the political left. Some even
argue that evolutionary principles give direct support to such lib-
eral goals as combating inequality, sexism, and racism (Konner
1999; Singer 2000). The general debate over the utility of evolution-
ary approaches to behavior is coming to a close. Sociobiology has
demonstrated its utility and has developed into a strong new

Natural Selection and the Capacity for Subjective Commitment 9
branch of science (Alcock 2001), even if sometimes called by other
names, even if proponents sometimes advocate unsupportable theo-
ries, and despite the difficulty of finding the best ways to formulate
and test some specific hypotheses.
•
Another way to attempt to escape the controversy is to try to go
back, to resurrect the principle of group selection. One tireless, out-
going scientist, David Sloan Wilson, has made this his mission. In a
series of articles, books, interviews, and lectures he has succeeded
in making it appear that a mistake was made, that group selection
is important after all (D. Wilson 1975; Wilson and Sober 1994). In
fact, his model of trait group selection is considerably different from
the original na¨ıve models of group selection. Trait group selection
for genes is certainly theoretically possible, and Wilson describes a
few examples from nature, although others contest their signifi-
cance (Wilson and Sober 1994). What is clear, however, are his mo-
tives. He and his colleagues want to find a mechanism by which
natural selection can shape motivations for moral behavior (Sober
and Wilson 1998; Smuts 1999). I share that motive and agree that
some behaviors and emotions cannot be explained by kin selection
and reciprocity alone; however, group selection is not the only pos-
sible alternative. I also agree that emergent properties of social
groups are powerful forces of selection that are likely to explain
important aspects of human nature, including our moral capacities.
Along with most other scientists (Dawkins 1982; Williams 1992;
Smuts 1999; Maynard Smith 1998), however, I remain unconvinced
that differential success of human social groups is a viable potential
explanation for the genetic tendencies that shape brain mechanisms
that give us moral capacities. Furthermore, if group selection indeed
were powerful, it would account equally well not only for coopera-
tion within the group, but also for competition between groups—
including tendencies to dehumanize, exploit, and kill members of
out-groups, hardly typical examples of moral behavior. While atten-
tion to different levels at which selection acts is essential (Maynard
Smith and Szathm´ary 1995; Williams 1992), trying to resurrect the
phrase group selection creates unnecessary confusion that distracts
attention from trying to understand exactly how the emergent prop-
erties of social groups may have shaped the moral passions.
•
A related explanation is better supported. In two decades of work
Richerson and Boyd have developed models that show how cul-
tural group selection can account for many complex traits, includ-
ing cooperation (Boyd and Richerson 1985; Richerson and Boyd
1999; see also chapter 9). In their model these traits, not genes, give
benefits to groups and therefore spread. The benefits these traits

10 Evolution and the Capacity for Commitment
bestow on the group can themselves influence the course of natural
selection. Boyd and Richerson do not challenge the predominance
of selection’s power at the level of the individual; they instead show
how cultural selection of socially transmitted traits can help to ex-
plain the rise and fall of groups and the nature of culture, and how
emergent properties of social groups can become forces of genetic
selection for at least two instincts, ethnocentrism and moralistic ag-
gression (Richerson and Boyd 1999).
•
Others present culture as if it were an alternative to evolutionary
explanations. When pressed, they usually describe examples of peo-
ple fulfilling the expectations of cultural roles, even when that
seems to do little for their reproductive success. Or, they describe
the vast variety of human behaviors in different cultures in order to
show that human nature is profoundly malleable, that our behavior
is not susceptible to explanation as a product of a few drives and
fixed action patterns (Lewontin 1982). There is no disputing that
humans live in grandly diverse ways, and that our capacity for
learning allows us to adapt to vastly different environments. It re-
mains an elementary mistake, however, to posit culture as an alter-
native to evolutionary explanations (Tooby and Cosmides 1989; Bar-
kow 1989a). In fact, our capacity for culture has almost certainly
been shaped by natural selection, and it seems likely that emergent
properties of cultures are powerful forces of natural selection (Dur-
ham 1982; Tooby and Cosmides 1989; Cosmides and Tooby 1989;
Tooby and Cosmides 1992; Flinn and Alexander 1982). Understand-
ing culture is important, even essential, if we are to understand
how cooperation is possible, as is well known by those who have
developed models of gene-culture coevolution (Cavalli-Sforza and
Feldman 1981; Lumsden and Wilson 1981; Durham 1991; Wilson
1998).
•
Then there is human will. People can decide to do things that harm
their reproductive success. They can decide to inhibit deep im-
pulses. They can decide not to eat, not to sleep, to sacrifice their
firstborn, or to be generous even when they are being exploited.
This profoundly human capacity—a property of mental mecha-
nisms shaped by natural selection—is an observable reality. It is
admirable when it motivates helping, terrifying when it motivates
enduring attempts to harm an enemy at all costs. Whether such a
capacity offers the best explanation for altruistic behavior is far less
certain. After providing extensive reviews of the distressing discov-
eries described here, several books on evolution and human behav-
ior conclude with the hope that we can use this sad and frightening
new knowledge about ourselves to make willful decisions to hold

Natural Selection and the Capacity for Subjective Commitment 11
back our primal tendencies in ways that can improve our societies
and ourselves (Wilson 1978; Dawkins 1989; Wright 1994; Ridley
1997). This may be correct, yet there is a canyon of ignorance be-
tween this hope and realizing the dream of a more peaceful world.
•
The distress aroused by these discoveries does not always result in
opposition. Some, especially those whom William James would
characterize as “hardheaded,” look at the facts with an unwavering
gaze and proclaim that genuine morality cannot emerge from na-
ture, and we should get used to it. Barash, in particular, seems to
have been deeply affected by the recognition that what had seemed
selfless turns out to help one’s genes (Barash 1979; Barash 1982).
Williams, who was perhaps the first to confront these issues (Wil-
liams and Williams 1957), has even gone so far as to call Mother
Nature a “wicked old witch,” because all organisms are inherently
selfish in the sense that natural selection has shaped them inexora-
bly to do whatever maximally benefits their genes (Williams 1993).
His position follows that of Julian Huxley (Huxley and Huxley 1989
[1893]), which in turn follows Thomas Henry Huxley’s in his 1894
Romanes lecture (Huxley 1897). From this point of view, moral ac-
tion is inherently in opposition to natural tendencies. While such
views seem bleak, they often arise, it seems to me, from the same
deep dismay that arouses others to oppose an evolutionary view.
•
Others react by embracing and extolling the brutality of nature. The
initial political offspring of Darwinian theory was, after all, Social
Darwinism, with its grand leap from the facts of nature to advocacy
of ethical principles that now are widely recognized as promoting
vast social harm. The distinction between what is and what should
be was trampled. Social Darwinism remains a signal example of
powerful people using their resources to spread an ideology that
benefits their interests. More recently, some with a cynical bent
seem almost gleeful in their attempts to explain every apparently
altruistic act as somehow deviously selfish. As Ghiselin puts it,
“Scratch an altruist and watch a hypocrite bleed” (Ghiselin 1969,
247). Kohn cites Santayana as going even further: “Generous im-
pulses are self-deceptive hypocrisies. Dig a little beneath the surface
and you will find a ferocious, persistent, profoundly selfish man”
(Kohn 1990, 205). Such statements make it clear that these issues are
deep and emotionally charged. It should be no surprise that peo-
ple’s reactions are intense and markedly varied.
•
Finally, one can respond to the difficulties by carrying out a careful
analysis of exactly what we mean by altruism and whether it in-
deed follows that selfish genes necessarily make selfish individuals.
Radcliffe-Richards has done just this, examining the flawed reason-

12 Evolution and the Capacity for Commitment
ing that concludes that a behavior is in the individual’s self-interest
just because it is in the interests of that person’s gene (Radcliffe-
Richards 2000). She goes further, still in a strictly gene-selectionist
paradigm, to consider the philosophical problem of whether the al-
truism that is shaped by natural selection can be “real altruism.” She
notes that while natural selection cannot shape a completely altruis-
tic organism, “genuine and limited concern are not opposed. . . .
Coming to show how altruism comes to exist no more shows that it
is not real altruism than explaining how a cake was made shows it
is not a real cake” (170, 175). This analysis focuses attention where
it belongs, on the question of whether natural selection could have
shaped capacities that induce people to fulfill their commitments
even when they would rather not. Even if such actions advance a
person’s genetic interests in the long run, they are examples of gen-
uine altruism.
This concludes our summary of twelve responses to the debate con-
cerning altruism precipitated by recognition that selection acts at the
level of the gene. Their extraordinary range and intensity are as im-
portant as their content. These reactions demonstrate the remarkable
impact and continuing controversy arising from the discovery that
innate tendencies to altruism can exist only if they have somehow
increased the frequency of genes that shape them. While there is no
hole in this logic, it leaves many observations unexplained. People
often follow rules, do their duty, remain loyal, keep their promises
and fulfill their threats, even when such actions are clearly not in their
interests. How can this be possible? Wouldn’t it be better to decide
what is in one’s best interests at each stage of the game? Why keep
a promise if it requires a big sacrifice with no payoff? Why follow a
rule if violating it will bring no punishment? Something seems to be
missing.
Commitment
Signing an apartment lease, threatening nuclear retaliation, taking re-
ligious vows, burning bridges behind you, changing lanes without
looking, caring for a spouse with Alzheimer’s, threatening arson to
enforce an extortion scheme, and waiting for a tardy deliveryman—
these all have something in common. All are social strategies carried
out not because they bring benefits via kin selection or reciprocity, but
because they influence others via commitment. A credible commit-
ment changes other people’s expectations, and thus their behavior.
For the dictator of a small country, launching nuclear missiles would
be suicidal. Nonetheless, if he can convince others that he will really

Natural Selection and the Capacity for Subjective Commitment 13
do it, they will be extraordinarily cautious about violating his borders.
A renter who signs a lease gives up the option to move out on a
whim, but gains a secure place to live at a stable rent. An army that
has burned its bridges motivates itself and intimidates its foe. Taking
religious vows of celibacy certainly is usually not in one’s reproduc-
tive or personal interests, but priests do it, and we therefore treat
them differently. The taxi driver who changes lanes without looking
will certainly cause an accident if others do not yield. So they do. It is
one thing to promise to care for each other in sickness and in health,
but when one spouse succumbs to Alzheimer’s, what can be the
sense of keeping a commitment to someone who does not even recog-
nize you? Yet some do. As for the mob, it has to convince business
owners that their businesses will burn if they do not pay protection
money. To make the threat believable, the mob must, on occasion,
commit arson.
Note that the initial focus has shifted. The discussion began with
the challenge of explaining altruism but moves now to commitment,
which covers not only altruistic promises to help, but also terrible
threats of harm. That threats and promises influence by different
means is an argument for treating them separately, yet commitment
binds them together as two ways of influencing people by changing
their expectations.
In a series of books and articles starting in the 1960s Thomas
Schelling laid out the framework for understanding commitments
(Schelling 1960, 1978a, 1978b, forthcoming). He was preoccupied with
cold war strategy, but he extended his analysis to personal relation-
ships and problems of social life in general. This work has influenced
many, not only economists but also philosophers who see that it can
help to solve some long-standing puzzles involving morality (Parfit
1984; McClennen 1990).
Commitment is fundamentally different from kin selection and
reciprocity. Kin selection changes behavior toward relatives owing
to the benefits of helping those who share genes identical by de-
scent. More a phenomenon than a social strategy, kin selection ex-
plains why organisms help kin even when an action is costly and
gives no direct payoff. Reciprocity is based on the expectation of a
net benefit from the actions of exchange partners who also act in
their own calculated best interests. Commitment, however, is differ-
ent—it changes behavior by giving up options and thereby chang-
ing people’s beliefs.
A commitment is an act or signal that gives up options in order to
influence someone’s behavior by changing incentives or expectations.
Some commitments change the objective situation so that fulfilling
them becomes in a person’s interests. Other commitments are pledges

14 Evolution and the Capacity for Commitment
to act in ways that will be contrary to obvious self-interest; they are
not enforced by external incentives, but by some combination of repu-
tation and emotion.
Examples are everywhere. If you believe your spouse will care for
you in sickness, you will be much more likely to make and keep the
same promise. If you believe your spouse will kill you if you try to
divorce, you will be much more reluctant to leave. If either unfortu-
nate circumstance arises, it will be disadvantageous to make good on
these commitments. Caring for a sick spouse can sap life’s energies;
murder is likely to result in a long prison term (to say nothing of
guilt). Yet people do make such commitments, and others believe
them and are influenced because people often fulfill commitments
even when doing so is costly. In the long run, however, a capacity for
making commitments brings net benefits. These benefits may explain
how natural selection shaped tendencies to follow rules and fulfill
promises and threats even when that is not in a person’s interests. In
short, commitment may offer some of what has been missing from an
evolutionary understanding of social behavior—a potential means by
which natural selection could shape mental faculties for genuinely
moral (and immoral) action.
This use of the word commitment follows its technical meaning in
economics and game theory; other uses need to be distinguished.
Sometimes people say they are committed to having dinner tonight or
to going to a movie. These are only announcements of plans, not com-
mitments in the sense used here. As Hirshleifer puts it, “A promise or
a threat must be to do something that the individual would not other-
wise be motivated to do. That is what distinguishes these pledges
from mere forecasts” (Hirshleifer 1987, 309). Similarly, people some-
times say they have a commitment at two o’clock. Such obligations
that a person cannot easily abrogate are related to the technical sense
of commitment in that options are foreclosed, and many such com-
mitments are intended to influence the behavior of others. If you make
a commitment to meet others for lunch, they will likely be there.
In psychology commitment often refers to the strength of a per-
son’s determination to pursue a goal (Brickman and Coates 1987;
Klinger 2000). The goal may be a specific task or a desire to change
relationships, religion, or employment. This concept of psychological
commitment is also similar to the meaning considered here; both indi-
cate that a person will follow through to reach a difficult goal. The
game theory sense of strategic commitment, however, emphasizes the
influence on others, while commitment as studied in psychology
more often refers to personal commitments individuals make to con-
trol their own future behavior—a commitment to lose weight, for in-

Natural Selection and the Capacity for Subjective Commitment 15
stance, or to write for three hours each morning. One strategy for
controlling one’s behavior is to change the incentive structure by giv-
ing up options so that short-term pleasures are set aside to achieve
long-term gains. Some people keep their cigarettes in their car, where
they cannot easily reach them; others mail their own computer cables
to themselves to enjoy a weekend free from Internet addiction (Burn-
ham and Phelan 2000). Gibbard sees such examples as evidence for a
system “peculiar to human beings” of normative motivation that can
conflict with what he calls the “animal control system” (Gibbard 1990,
57). Such internal mental conflicts, usually between short- versus
long-term benefits, have long been recognized by psychoanalysts, al-
though they tend to emphasize the mental conflict and neglect the
real strategic dilemmas that give rise to them (Nesse 1990b). Brickman
and colleagues have conducted a provocative early exploration of the
interfaces between these several aspects of commitment (Brickman
and Coates 1987), with particular attention to the utility of irra-
tionality: “Behavior that is not rational, behavior that is chosen on
logically inadequate grounds or carried out with utter disregard for
costs, can still be functional and effective for the actor. . . . The appar-
ent blindness that follows commitment may be irrational and still a
precondition for effective action” (35).
Within the game theory concept of commitment addressed here,
several distinctions can help to separate different subtypes. Some
commitments are promises to help, others are threats to harm; the
difference is whether others perceive a new potential benefit or a new
danger. Threats and promises are treated here as two faces of commit-
ment, although an argument could be made that they should be con-
sidered as independent phenomena. Commitments can be conditional
or unconditional. Threats are usually conditional attempts to prevent
another person’s potential action; promises are more likely to be un-
conditional, though often they are conditional on the other fulfilling a
matching promise. Commitment can be intentional or unintentional;
some commitments are entered into specifically to influence people,
others are not. Schelling’s chapter describes these varieties in vivid
detail.
Perhaps the most profound distinction between different kinds of
commitments arises from how they are enforced—that is, why others
believe the commitment will be fulfilled. Sometimes the commitment
itself makes some options impossible (for example, burning bridges
or being bound to the mast). In other situations the options remain
available but are no longer advantageous after a third party is given
control over tangible incentives (a lease, for instance). A pledge of
reputation, such as a public oath, is another way to convince people

16 Evolution and the Capacity for Commitment
that a commitment is valid. Finally, commitments can be enforced by
emotions such as pride and guilt. Observing such emotions may in-
crease confidence in a commitment.
The first two kinds of commitments—those enforced by the situa-
tion itself or by third parties—can be thought of as “secured” because
once such a commitment is made, its fulfillment becomes in the ac-
tor’s interests. Many commitments are, however, unsecured by such
tangible enforcers—their fulfillment depends on emotions and con-
cerns about reputation; we will call these subjective commitments.
While reputational commitments put real social resources at risk, they
also are strongly enforced by emotions such as pride and guilt, so it
seems appropriate to include them under subjective commitments.
The fulfillment of externally enforced commitments also involves
emotions, yet the emotions involved are not these special moral pas-
sions but rather the usual emotions that regulate goal pursuit (Nesse
1999). Many actual situations incorporate several of these mecha-
nisms simultaneously. Marriage, for instance, is enforced by a mix
that includes legal contracts, reputational pledges, and emotional
bonds. Thomas Schelling has distinguished the subtleties of various
kinds of commitments. He points out, for example, that belief in a
deity who will reward goodness and punish evil transforms many
situations from subjective to secured, at least in the believer’s mind
(Schelling, personal communication, 2000).
Subjective commitments are of special interest because they influ-
ence others only by convincing them that an individual will, in some
specified future situation, act in ways not in his or her interests. The
possibility that natural selection has shaped emotions to help to guar-
antee subjective commitments was brought to wide attention by Rob-
ert Frank’s book Passions Within Reason (Frank 1988) and by Jack
Hirshleifer’s chapter “Emotions as Guarantors of Threats and Prom-
ises” (Hirshleifer 1987). Each recognized that the utility of commit-
ment strategies could have provided a selection force that shaped
emotions such as anger, trust, pride, and guilt, and that the very exis-
tence of these emotions might be evidence for this hypothesis. Hirsh-
leifer and Frank summarize their positions in very similar terms:
It is possible to analyze, in terms of effects upon rationally calculated
self-interest, the consequences of non-self-interested motivations and of
limitations upon the ability to calculate. The economist must go beyond
the assumption of “economic man” precisely because of the economic
advantage of not behaving like economic man—an advantage that pre-
sumably explains why the world is not populated solely by economic
men. (Hirshleifer 1987, 322)

Natural Selection and the Capacity for Subjective Commitment 17
The commitment model is a tentative first step in the construction of a
theory of unopportunistic behavior. It challenges the self-interest
model’s portrayal of human nature in its own terms by accepting the
fundamental premise that material incentives ultimately govern behav-
ior. Its point of departure is the observation that persons directly moti-
vated to pursue self-interest are often for that reason doomed to fail.
They fail because they cannot solve commitment problems. These prob-
lems can often be solved by persons known to have abandoned the
quest for maximum material advantage. The emotions that lead people
to behave in seemingly irrational ways can thus indirectly lead to
greater material well-being (Frank 1988, 258).
This insight is profound. It means that the rational pursuit of self-
interest is sometimes an inferior strategy. People influence others by
convincing them that they will do things that would not otherwise be
in their interests. This is the essence of intimate social life. The social
fabric has a warp of promises and a weft of threats. We spend our
lives making and assessing commitments. We are constantly preoc-
cupied with assessing other people’s reputations and protecting our
own. We are enraged when others do not fulfill deep commitments.
Most of us are a bundle of anxieties when tempted to renege on a
pledge. Elster (who remains unconvinced) points out that Frank and
Hirshliefer have turned the usual idea of emotions on its head (Elster
2000). Instead of interfering with rational strategy they claim that
emotional behaviors can be strategically superior to those based on
rational calculation. If it turns out to be correct that natural selection
has shaped emotional mechanisms for mediating strategic commit-
ments, this will be of enormous importance. This book is devoted to
further developing this idea and trying to determine where it does
and does not apply.
To summarize, there are four main reasons to believe that a com-
mitment will be fulfilled:
1. a commitment can be self-enforcing if it is secured by incentives
intrinsic to the situation;
2. a commitment can be secured by external incentives controlled by
third parties;
3. a commitment can be backed by a pledge of reputation; and
4. a commitment can be enforced by internal emotional motives.
In a sense these are four different kinds of commitments: self-enforcing,
contractual, reputational, and emotional. As already noted, all four fac-
tors may influence a single commitment, so it is probably better to

18 Evolution and the Capacity for Commitment
think of them as factors rather than distinct kinds. Note that the first
two types of commitment are secured, in much the same way that a
loan is secured by collateral. Making the commitment changes the
situation so that fulfillment becomes in the individual’s interests.
Such commitments give up options in ways that change the objective
nature of the situation. The latter two types of commitment are quite
different: they do not change the objective contingencies, only what a
person says he or she will do; they are subjective commitments in that
they involve a continuing option for reneging. This may be why there
is a special need for emotions to maintain motivation to fulfill such
commitments, and to try to convince others that the commitment will
be fulfilled.
The Significance of Commitment
The importance of commitment is no doubt becoming clear, but a few
points deserve emphasis. Benefits that come from an ability to make
and assess commitments could shape mental mechanisms that induce
individuals to follow rules, even when that is not in their interests.
This requires the peculiarly human ability to inhibit short-term self-
interested action, offers a potential explanation for the origins of mo-
tives for moral behavior, and suggests that the apparently irrational
excesses of both love and hatred may emerge from the same source.
Commitment offers a framework that engages much of the richness
and complexity of human relationships, and it gives genuine moral
capacities a place in human nature. This gives it the potential for de-
creasing the stigma associated with pursuing evolutionary studies of
human behavior,thus allowing those studies to proceed with new un-
derstanding and support.
Commitment even offers a potential link with much recent social
science based on postmodern theories. Criticism of the excesses of
such thinking has obscured the value of recognizing how we create
our own social environments. Our commitments change other peo-
ple’s expectations about what we will do. Although there is usually
nothing coldly calculating about them, our commitments can be seen
as strategies for creating beliefs in others. Taken together, these beliefs
are the fabric of culture. If our capacity for inducing and assessing
such subjective beliefs has been shaped to some degree by natural
selection, this may offer a much-needed bridge between fields that
otherwise seem determined to ignore or misunderstand each other.
While much progress has been made in understanding culture in an
evolutionary context (Barkow 1989a, 1989b; Boyd and Richerson 1985;
Atran 1990; Sperber 1996; Diamond 1997), much remains to be done
to find the mechanisms that make culture possible (Flinn and Alex-

Natural Selection and the Capacity for Subjective Commitment 19
ander 1982; Dunbar, Knight, and Power 1999) and the extent to which
these mechanisms have been shaped by natural selection.
Similarly, commitment can offer insights into the origins and func-
tions of religious beliefs. One main function of religious groups is to
systematically cultivate and reinforce beliefs that make commitment
more accessible and less risky. Many religions insist vehemently that
their beliefs are not intended to bring gain, but to foster goodness, at
least toward members of the church. Such explicitly subjective ideo-
logies that disavow any motive for individual gain may provide
stronger foundations for deep commitments than any appeal to ratio-
nality or self-interest (Irons 1996). When a religious group is difficult
to enter, and involves most of a person’s relationship partners, all of
whom monitor one another’s behavior, the cost of defecting can be-
come so high that what began as subjective commitments become
strongly secured. Religious communities, even more than other
groups, provide members with protections that allow commitments to
flourish (Dennett 1995; Wilson and Sober 1994). This may help to ex-
plain why so many religious groups oppose an evolutionary ap-
proach to human behavior, and perhaps why some Islamic cultures
take such desperate measures to inhibit the importation of Western
influences.
The major Western religions, according to Rue, offer commitment
on a grand scale (Rue 1989). Worshipers enter into a covenant with
God, agreeing to submit and obey unconditionally in return for a bet-
ter life and, often, eternal life. The deepest blessings of such systems
are, Rue says, in the mental changes that come from living in a world
imbued with meaning and order, and the social benefits of living
among other people who follow the rules. He contrasts this sharply
with the alienated and meaningless worlds inhabited by so many
nonreligious people in modern industrial economies (Klinger 1998;
Emmons 1999). As noted earlier, if entering a religious group has high
opportunity costs and requires major continuing investments of time,
effort, and money, then the cost of leaving the group will be so sub-
stantial that the threat of expulsion is a potent enforcer of group
norms. This is a classic example of commitment—giving up options
in order to influence others in a way that changes their behavior and
yields net benefits. Almost any emotional or mystical justification for
the rules will do, but as soon as calculated self-interest comes to the
fore, subjective commitment is fatally undermined.
Finally, as becomes especially clear from practicing psychiatry, our
individual social worlds are much of our own making. Individuals
who believe that everyone is out for himself or herself are incapable
of making subjective commitments; their social worlds are populated
only by exchange partners whose motives are always suspect. By con-

20 Evolution and the Capacity for Commitment
trast, individuals who can believe in other’s subjective commitments
reap the benefits of relationships that go beyond mere reciprocity.
They also run the risk of major betrayal. Frank has conducted a series
of studies to show that learning economic theory decreases contribu-
tions to public goods, although how widely the findings can be repli-
cated and generalized remains unclear (Frank, Gilovich, and Regan
1993). One presumes that the same would be true for teaching about
social evolution, but the study has not been done insofar as I know.
The novelist A. S. Byatt recently looked at the conflict between social
science and evolutionary science and concluded that it arouses such
intense passions because we care so much about our fundamental
human nature (Byatt 2000). We intuitively know that what we believe
about human nature profoundly shapes how we conduct our lives
and the structure of our societies. The belief that all behavior is fun-
damentally selfish itself changes behavior. As Oyama puts it, “Assum-
ing cooperation to be, at best, a competitive strategy can make it con-
ceptually unstable” (Oyama 2000, 207). It seems possible that the
spread of simplistic notions about the evolutionary origins of social
relationships could make individual relationships more conflicted and
society even more brutal. One antidote may be an evolutionary ap-
proach to behavior that incorporates a capacity for commitment.
Background
The concept of commitment, as developed by Frank and Hirshleifer
following the lead of Schelling, emerges from a long line of related
thinking. Actually the precursors are better described as several lines,
since many of them seem to be unaware of each other. This section
outlines some of these ideas, starting with those from economics and
game theory, and moving to those from philosophy and ethics.
The initial application of game theory to animal behavior by John
Maynard Smith (1982) developed in parallel with the application of
game theory in economics (Von Neumann and Morgenstern 1944).
The possibilities for synergy seem substantial, especially since econo-
mists have long restricted their studies to a species well-suited to
such explanations, Homo economicus. As Kohn puts it, “Egoism is not
an assumption but the assumption underlying neoclassical eco-
nomics” (Kohn 1990, 185). Such individual utility maximizers are little
different from the animals studied by evolutionary ethologists. There
is no room for genuine altruism, spiteful threats, or other such irra-
tionality here. People are expected to do whatever best advances their
own interests. This grand assumption generally works very well in-
deed. Economists claim to be able to predict not only what specimens
of Homo economicus will buy, but also which ones will join a labor

Natural Selection and the Capacity for Subjective Commitment 21
Table 1.1 Social Emotions and the Prisoner’s Dilemma
Other Cooperates Other Defects
You cooperate Trust or friendship Suspicion or anger
You defect Anxiety or guilt Rejection
Source: Nesse 1990a.
union, when they will choose to retire, and even whom they will
marry (Becker 1991).
Studies of reciprocity relationships have prospered in this frame-
work. The usual model is the prisoner’s dilemma, a game in which
two players each choose, on every move of the game, to either cooper-
ate or defect. Mutual cooperation brings the greatest net benefit (say,
three points each, for a total of six), but an individual who chooses
defection gets a greater reward (say, five points) if the other chooses
cooperation (and gets zero). This creates a continuing tension between
a wish to get steady maximal mutual rewards, the temptation to de-
fect, and the suspicion that the other might defect. Hundreds of ex-
periments have confirmed that this is quite a good model for much
cooperation. The strategy of doing whatever the other person did on
the past move (tit for tat) has proved a robust strategy (Axelrod and
Hamilton 1981; Axelrod 1984) that allows individuals to avoid exploi-
tation while taking advantage of cooperation when that is available.
Much work now compares tit for tat to other strategies, some of
which are superior in some circumstances. Playing this game well is
essential for members of a species where fitness depends on recipro-
cal exchange. As seen in table 1.1, the four situations defined by the
four boxes in the prisoner’s dilemma have arisen so often in the
course of evolution that they seem to have shaped emotions specific
to each situation (Trivers 1971, 1981; Gibbard 1990; Nesse 1990, 1999).
People do not, however, always do what is predicted by rational
choice theory (Gintis 2000a, ch. 11). They do not always pursue straight
self-interest, and their decisions are not always Bayesian rational. In the
prisoner’s dilemma, for instance, the game theory optimum for any
limited sequence of plays against a game theory–rational opponent is
to defect right from the start. This is because defection is the optimal
last move of any finite game, and cooperation unravels backward
from this endpoint. Yet that is not what people do. Most cooperate
early on in the game, and stop cooperating only if the other defects or
a specific endpoint is near (Axelrod 1984). Likewise, in public goods
games, people cooperate vastly more than expected. According to
game theory, an individual’s best strategy is to accept the advantages
while letting others contribute money to public radio, blood to the

22 Evolution and the Capacity for Commitment
blood bank, and land to preservation trusts. Actual human behavior
is different. Gintis provides a comprehensive review, emphasizing,
“In neither the everyday nor the narrower economic sense of the term does
rationality imply self-interest” (Gintis 2000a, 243). Even in the labora-
tory people don’t act according to the dictates of rational choice the-
ory. When each subject contributes anonymously to a pot that is then
sweetened by a percentage and then divided equally among all players
in the game, the average contribution is about half of an individual’s
reserves in the early moves of the game. The individual variation is
huge, however, from large contributions to none. When it becomes
obvious that some individuals are not cooperating, contributions ta-
per off and usually end. When individuals can find out who is not
contributing, some will spend their resources to punish such individ-
uals, even though they get no individual benefit from such actions
(Fehr and G¨achter 2000). The suggestion has even been made that
complex human organizations became possible only when the ability
to throw projectiles precipitously reduced the “cost of punishment”
for coalitions trying to enforce their rules (Bingham 1999).
In the ultimatum game one person proposes how to divide a re-
source (say, ten dollars), and a second person decides either to accept
that split or turn all the money back to the experimenter. The Sub-
game-Perfect Equilibrium is for the proposer to offer the smallest pos-
sible amount and for the responder to accept anything offered. A
penny is better than nothing, after all. The corresponding game theo-
ry–rational strategy for the individual who proposes the split is to
offer one penny to the other player. Yet this is not what most univer-
sity student subjects do. Instead they tend to offer something close to
an even split. And the recipients of a low offer often choose to forgo
all benefits, thus getting spiteful revenge (Roth et al. 1991; Fehr and
Falk 1999). Interestingly, there are wide cultural variations in patterns
of response, with most individuals in some groups accepting low of-
fers (Henrich 2000). Recent work has shown that men with low tes-
tosterone are more willing to accept an unfair split, while those with
high testosterone are likely to turn down anything but a nearly fair
division (Burnham, forthcoming.). Such tendencies seem closely re-
lated to the norms in honor-based societies, where even the slightest
insult may lead to threats of violence (Nisbett and Cohen 1996; see
also Cohen and Vandello, chapter 8 herein). Such threats signal an
intention to defend resources from others who try to take them, even
if that means accepting a huge cost. The alternative—fighting only
when it is rational to do so—yields ridicule and impoverishment.
Males who are not “demonic” may do poorly (Wrangham and Peter-
son 1996).
Most attempts to explain the anomalies in behavioral economics

Natural Selection and the Capacity for Subjective Commitment 23
are basically within the framework of rational choice theory (RCT)
and its two assumptions: that people ultimately pursue self-interest
exclusively, and that self-interest is maximized by acting on the basis
of rational calculation. Binmore, for instance, emphasizes how diffi-
cult it is to escape the implications of RCT. He observes that people
only rarely base their behavior on predictions that others will act in
ways that are not in their self-interest (Binmore 1994), and he will
have none of Gauthier’s concept of constrained maximization (Bin-
more 1993). Likewise, Skyrms at first seems to have little sympathy
for attempts to transcend RCT, saying, “A strategy that is not modular
rational in these terms is just one that in certain circumstances would
require such a rational agent to choose what she would not choose. . . .
If expected utility theory is kept in mind, the idea of modifying the
normative theory by somehow building in commitment appears quix-
otic” (Skyrms 1996, 41). He avoids contradiction by incorporating
emotional outcomes as a part of utility, citing Frank and Hirshleifer.
He proceeds to demonstrate how “Fairman” strategies can persist in
equilibrium with other strategies, even when they might not survive
otherwise, and concludes, “Evolution may—if the conditions are
right—favor commitment over modular rationality strategy. Mixed
populations that include individuals using strategies that are not
modular rational in Darwinian fitness can evolve according to the
replicator dynamics” (42).
Such models assume rational self-interested agents and pose the
problem in terms of finding situations in which tendencies to cooper-
ate can survive. Much depends on the details of the model. Axelrod
has shown how the initial proportion of cooperators and defectors are
powerful determinants of whether a group goes to increasing cooper-
ation or devolves into constant defection (Axelrod 1986, 1997). Yet
even here there is a stochastic element to the outcome, which is stable
once it tips in one direction or the other. In actual human groups, as
managers know all too well, organizational cultures have enduring
power far beyond that of any individual.
Another line of work has emphasized the role of reputation. Alex-
ander was one of the first to elaborate this in an evolutionary frame-
work (Alexander 1982, 1985, 1987). He noted how hard it is to explain
generalized cooperation and concluded that it may arise mostly from
indirect reciprocity. This works because people observe whether or
not others are cooperators and seek to create relationships with those
who appear generous. In his framework, the optimal strategy is to
appear very generous while actually contributing as little as possible.
This leads to substantial emphasis on deception and self-deception,
including the idea that our experiences of ourselves as moral agents is
a self-deception that allows us to better deceive others (Alexander

24 Evolution and the Capacity for Commitment
1974; Trivers 1976; Alexander 1987; de Waal 1984; Mitchell and
Thompson 1986; Lockard and Paulhus 1988; Nesse and Lloyd 1992).
Akerlof challenges the “core assumption of economic behavior . . .
that all persons are totally selfish. . . . [T]his assumption is made for
reasons of convenience, not because economists empirically assume
that all persons act only out of selfishness” (Akerlof 1983, 54). He
presents a model showing “that honest and cooperative behavior
pays off; the honest person is not just a systematic ‘sucker’” (55). As
an example he cites the rewards of being a “bonded” courier. While
the need for such bonding demonstrates the need for external en-
forcers to motivate honesty, Akerlof claims the system can lead to
genuine honesty because “the appearance of honesty and class loyalty
are beneficial; the easiest way to achieve these appearances is to be
honest and loyal, even though honesty and loyalty themselves in-
volve sacrifices” (61). Thus his model is parallel to Alexander’s but
emphasizes the benefits of integrity despite its costs, instead of the
benefits of deception despite its risks. Note the central role that repu-
tation plays in this argument.
Kitcher takes a very similar position, arguing that morality can per-
sist in the face of cheaters because individuals can choose those with
whom they play prisoner’s dilemma games. “Discriminating altru-
ists” eschew contact with defectors, to the substantial cost of those
known to be defectors. His mathematical model demonstrates the via-
bility of this strategy, and thus, presumably, how it could have been
favored by natural selection (Kitcher 1993). These selective associa-
tions are the same engine that allows moral tendencies to prosper in
Wilson’s trait groups.
More recently, Nowak and Sigmund have developed a computer
simulation that demonstrates how tendencies to provide benefits via
indirect reciprocity can evolve even when the players meet each other
only once (Nowak and Sigmund 2000). This is possible when infor-
mation about an individual’s cooperative “image” is public and when
a reputation as a cooperator brings increased benefits via indirect rec-
iprocity. They note, parenthetically and profoundly, “The evolution of
human language as a means of such information transfer has cer-
tainly helped in the emergence of cooperation based on indirect reci-
procity” (576). This work has been replicated and extended with
experiments on humans (Wedekind and Milinski 2000; Nowak and
Sigmund 2000). Reputation proves crucial to making indirect reciproc-
ity viable. A capacity for commitment allows individuals to act in
ways that reap the benefits of image scoring, and to avoid the costs of
being recognized as an exploiter. In this and similar models individ-
ual agents generally are assumed to pursue one strategy. The strategy

Natural Selection and the Capacity for Subjective Commitment 25
may take account of the reputations of other individuals, but it has
trouble coping with social groups in which individuals act differently
toward each other based on a long history of prior interactions.
Clearly, reputation is a major mediator for the benefits of indirect
reciprocity. So long as each player’s reputation is revealed sufficiently,
cooperation can grow. The optimal cost to spend on monitoring
others depends on the ratio of cooperators to defectors in the popula-
tion. In intermediate proportions monitoring allows cooperators to
exclude defectors and to benefit from exchanges with one another. If
either type is too rare, the costs will not be worth it. On a grand scale
this has been used as the foundation for a theory of sociopathy as a
frequency-dependent strategy that succeeds when it is rare in com-
parison to the proportion of cooperators who, when prevalent, let
down their guard (Mealey 1995).
Elster emphasizes that rationality often requires taking steps to
make precommitments in anticipation of temptations that will yield a
short-term gain and a long-term cost (Elster 1979). By “depositing
one’s will” one gains global maximization. While he emphasizes the
limitations of the human ability to resist temptation, and the work-
around of making temptations inaccessible or ultimately more painful
than the reward, he also describes strategies of building up one’s
character that make this much more feasible and yield moral behavior
(Elster 2000). He sees perfect rationality as supporting something like
Gauthier’s constrained maximization, but he doubts that many hu-
mans have sufficient willpower to use such strategies.
Gintis defines strong reciprocity as a tendency to follow norms that
promote cooperation with cooperators, and punishment of cheaters
even when those acts are costly. He contrasts this with weak reciproc-
ity, which is reciprocal altruism (Gintis 2000b). Strong reciprocity pro-
duces fewer replicas in the next generation, but the strategy can still
invade and persist because those who violate the norms are recog-
nized and excluded from the benefits of being in groups with strong
reciprocators. This is not exactly group selection, because it does not
depend on the relative success of different groups. It is, however, so-
cial selection, because emergent properties of groups become forces of
natural selection that change the prevalence of genotypes, and thus
individual behavior. He summarizes many laboratory experiments
demonstrating otherwise unaccountable cooperation and presents a
formal model demonstrating the viability of strong reciprocity. The
key is that “defectors are excluded from participation in the commu-
nity for a number of periods just sufficient to make defecting a subop-
timal strategy, at zero cost to the community” (Gintis 2000a, 273).
Many examples in the ethnographic literature also support the thesis

26 Evolution and the Capacity for Commitment
that tendencies to strong reciprocity evolved via this route. His posi-
tion is summarized by his preference for viewing humans as Homo
reciprocans rather than Homo economicus.
Strong reciprocity is very nearly the same as subjective commit-
ment. The main difference is that strong reciprocity models place less
emphasis on individual communications of threats and promises and
the associated complexities of relationships and signaling, and instead
focus on groups that monitor deviations from norms and exclude
nonconformists. Strong reciprocity may be possible because individ-
uals have capacities for subjective commitments to enforce group
norms, even when that is costly. One could equally well explain the
evolution of the capacity for commitment as a result of the costs of
being excluded from a group of cooperators, especially if you con-
sider groups with only two members. As Gintis notes, his position is
presaged by Campbell, who said in 1983, “mutual monitoring forc[es]
altruism on group members who cannot survive without cooperative
group membership” (Campbell 1983, 37). On the macro scale, the pro-
portion of strong reciprocators may vary from society to society, per-
haps with major economic consequences, such as lack of economic
growth (Knack and Keever 1997). For instance, in low-trust environ-
ments levels of investment are low, possibly explaining the poverty
trap in which some groups and countries find themselves mired (Zak
and Knack 2001).
Ideas closely related to commitment are found throughout the de-
velopment of evolutionary and game theory perspectives on relation-
ships. Even in The Origin of Species Darwin was aware of a “special
difficulty” with respect to sterile castes of insects, “which at first ap-
peared to me insuperable, and actually fatal to the whole theory”
(Darwin 1859). Hamilton, after answering Darwin’s quandary, ex-
plored the psychological mechanisms that mediate cooperation (Ham-
ilton 1975). Even earlier, Alexander had worked out the dynamics of
evolved sociality and some implications for morality (Alexander 1974).
Trivers, in the original paper on the evolution of reciprocity, said,
“People who are altruistically motivated will make more reliable part-
ners than those motivated by self-interest” (Trivers 1971, 157). He also
recognized that “The tendency to like others, not necessarily closely
related, to form friendships and to act altruistically towards friends
and towards those one likes will be selected for. . . . In other words,
selection will favor liking those who are themselves altruistic”
(Trivers 1971, 48). He saw the possibilities for gross and subtle cheat-
ing in friendships and said that this would shape moralistic aggres-
sion, although it has turned out to be difficult to see exactly how
benefits come to those who bear the costs of moralistic aggression. He
further went on to show how emotions such as gratitude and guilt

Natural Selection and the Capacity for Subjective Commitment 27
could be shaped by natural selection, and crucial roles of trust and
suspicion in regulating relationships (Trivers 1981).
McClennen (1990) notes that in the publication that established
game theory, Von Neumann and Morgenstern anticipate commitment
strategies in their distinction between “dead” variables and those that
“reflect another person’s will or intention.” He goes on to say,
What Von Neumann and Morgenstern proceed to do, however, and
what others have done since, is build a theory denying, in the end, that
the behavior of each other player could be parameterized. . . . In effect
what they do is reduce the problem for each participant to that of a
standard maximization problem. . . . The assumption that rational
players are bound by the principle of maximization of expected utility
proves to be quite paradoxical . . . it ensures that rational players . . .
will have to settle for outcomes that are mutually disadvantageous . . .
why, if the possibility of gain drives them to enforcement devices, does
it not also drive them beyond, to an even more efficient form of coor-
dination? (McClennen 1990, 258–60)
The usual solution—to create precommitments and constraints—is
suboptimal and fails to explain the existence of moral constraints that
cannot be set aside when they become disadvantageous. Justifications
for following such rules have been divided, he says, between those,
such as Hobbes and Hume, who emphasize the tangible benefits of
acting according to moral principles, as compared to others “like Kant
[who] postulate that they must be grounded in some radically differ-
ent fashion” (264). Neither, he says, is satisfactory because both are
stuck in a limited view of rationality. Building on Gauthier (Gauthier
1986), his solution, resolute choice, “might, one would hope, provide a
way to bridge the gap between moral choice and rational interested
choice” (McClennen 1990, 260). As important, resolute choice also
postulates a force of selection that could shape the moral passions
that make commitment possible. “Whereas the sophisticated self acts
under a constraint on choice imposed by the logic of belief, the reso-
lute self acts under a constraint of a different sort altogether, a con-
straint of commitment” (160).
Gauthier provides a rationalist foundation for Rawls’s contrac-
tarian ethics (Rawls 1971; Gauthier 1986). Gauthier’s notion of ratio-
nality transcends the usual standard of modular rationality, which ex-
pects only “straightforward maximization” and instead says there are
advantages to having a disposition to practice “constrained maximi-
zation,” by which he means fulfilling promises even when that will
not be advantageous (Gauthier 1986). These advantages are the key to
his thesis that it can be rational to follow rules even when that means
sometimes acting in ways that are not in a person’s self-interest (Sug-

28 Evolution and the Capacity for Commitment
den 1993). Gibbard takes this further in his suggestion that natural
selection has shaped emotional dispositions supporting a “normative
control system” to facilitate constrained maximization and thereby
give a selective advantage (Gibbard 1990). In Frank’s terms, the emo-
tions are “self-control devices” (Frank 1988, 81) that allow people to
protect themselves and their reputations from their impulses to act in
their short-term interests.
All of this harks back to Hume and Adam Smith with their em-
phasis on the importance of sympathy. Hume made it the foundation
of his moral theory. We cannot, he said, derive oughts from our obser-
vations of the world or from any theory. They come instead from our
intuitions, from our emotions. Mill, for all his utilitarianism, also em-
phasized the emotional origins of social cooperation, especially “the
fear of exposure” (Mill 1848, 135). This theme continues to the present
with work by psychologists showing that our moral choices emerge
more from emotion than reason (Kagen 1984) and philosophical treat-
ments of morality based on the natural origins of “apt feelings” for
making normative judgments (Gibbard 1990).
Adam Smith, subtle psychologist that he was, emphasized the role
of natural emotions in human affairs, especially empathy.
However selfish soever man may be supposed, there are evidently
some principles in his nature, which interest him in the fortunes of
others, and render their happiness necessary to him, though he derives
nothing from it except the pleasures of seeing it. Of this kind is pity or
compassion, the emotion which we feel for the misery of others. . . .
That we often derive sorrow from the sorrows of others, is a matter of
fact too obvious to require any instances to prove it. . . . Nature, when
she formed man for society, endowed him with an original desire to
please, and an original aversion to offend his brethren. She taught him
to feel pleasure in their favourable and pain in their unfavourable re-
gard. (Smith 1984 [1759], 91, 116)
His outrage at a cynical view of commitments makes it clear that at
least one aspect of the so-called sociobiology controversy has been
going on for centuries:
There is, however, another system which seems to take away altogether
the distinction between vice and virtue, and of which the tendency is,
upon that account, wholly pernicious: I mean the system of Dr. Mande-
ville . . . Dr. Mandeville considers whatever is done from a sense of
propriety, from a regard to what is commendable and praiseworthy, as
being done from a love of praise and commendation, or as he calls it
from vanity . . . I shall endeavour to show that the desire of doing what
is honourable and noble, of rendering ourselves the proper objects of

Natural Selection and the Capacity for Subjective Commitment 29
esteem and approbation, cannot with any propriety be called vanity.
(Smith 1984 [1759], 308–9)
Hobbes, in 1651, said it best of all in his Third Law of Nature: “That
men performe their Covenants made. . . . In this law of Nature, consisteth
the Fountain and Originall of J
USTICE
. . . the definition of I
NJUSTICE
is
no other than the not Performance of Covenant.” He notes that “there
must be some co¨ercive Power to compel men equally to the perfor-
mance of their Covenants, by their terror of some punishment greater
than the benefit they expect by the breach of their Covenant” (Hobbes,
1996 [1651] no. 2693, 100). But then he goes on, in the parable of the
Foole, to ask why people should keep their promises if the violation
will not be punished.
The Foole hath sayd in his heart, there is no such thing as Justice; and
sometimes also with his tongue; seriously alleaging that every mans
conservation and contenement, being committed to his own care, there
could be no reason why every man might not do what he thought con-
duced thereunto: and therefore also make or not make, keep or not
keep Covenants, was not against reason, when it conduced to ones ben-
efit. . . . From such reasoning as this, Successful wickedenesse hath ob-
tained the name of Vertue. . . . Where there is no Civill Power erected
over the parties promising . . . there is the question whether it be
against reason, that is against the benefit of the other, to performe, or
not. And I say it is not against reason. . . . He therefore that breaketh his
Covenant, and consequently declareth that he thinks he may with rea-
son do so, cannot be received into any Society that unite themselves for
Peace and Defense, but by the errour of them that receive him . . . if he
be left, or cast out of Society, he perisheth.” (Hobbes, 1996 [1651], 100–
102)
This Foole will be recognized, of course, as Homo economicus. Cen-
turies ago Hobbes understood why commitment persists. Those who
announce that they do not need to keep their promises are cast out
from society, where they perish. What could be a more fitting descrip-
tion of how natural selection shapes motives for keeping commit-
ments? Moreover, what explanation could better explain why people
are so hostile toward economists and evolutionists who seem to por-
tray human behavior as self-interested and cynically deceptive?
Natural Selection
The core question remains: What does natural selection have to do
with the capacity for commitment? In one sense, it may not matter
that much. There are wide cultural variations in patterns of commit-

30 Evolution and the Capacity for Commitment
ment, and much of this variation seems to arise from different beliefs
about human nature. It should be possible to understand how com-
mitment functions in relationships and societies without knowing
whether natural selection shaped tendencies specifically to make
commitments possible. Yet, as noted by Byatt, we care deeply about
our biological nature. Perhaps this should not influence us, but it
does. Perhaps we should realize that what is natural is no guide to
what is good, but when we discover (or start to believe in the absence
of any evidence) that a tendency is a part of our nature, in fact we
behave differently. As Hume pointed out, it is logically incorrect to try
to get oughts from what is in nature; emotionally, though, the leap
from is to ought seems easy and natural. This tendency fuels the fire
about debates on human nature (Ruse 1982; Rose and Rose 2000;
Segerstr˚ale 2000).
This enormous range of cultural variation indicates that tendencies
to use commitment strategies are by no means as hardwired as the
preference for sweets. This variation does not, however, mean that
natural selection is unimportant, any more than the wide variation in
the foods people eat means that food preferences are not shaped by
natural selection. Is it possible that the capacity for commitment in
fact has not been shaped by natural selection? Yes, but this seems
unlikely. If selection has not shaped special faculties for making and
assessing commitments, some other explanation must be found for
our moral passions, our preoccupations with reputation and honor,
and our irrational wishes to fulfill commitments to help loved ones
and harm enemies. Furthermore, despite wide variation in specific
patterns, the emotional capacity for commitment seems to be a hu-
man universal, one that is complex, costly, and peculiar, and therefore
difficult to explain unless it somehow increases reproductive success.
Psychological studies of mechanisms that could mediate commit-
ment are just beginning; increasingly these studies have used an evo-
lutionary context. Cosmides and Tooby have pursued an extensive
program of research designed to show that our minds have a built-in
system for conducting social relationships, especially a “cheater de-
tection module” (Cosmides and Tooby 1992). They find support in
their extensive data showing that people make fewer mistakes on the
Wason selection task when the content is related to social obligations
as compared to nonsocial information (Tooby and Cosmides 1989).
This cheater detection module presumably has evolved not just to
calculate the odds that another player will cooperate on the next
move, but whether the partner is pretending to be a friend when he is
actually just a “banker” who is willing to invest only when a payoff
can be guaranteed (Tooby and Cosmides 1984, 1996). This model is
closely related to the notion of commitment developed here.

Natural Selection and the Capacity for Subjective Commitment 31
Theories of social relationships on a large scale likewise nearly al-
ways identify some relationships as intimate or based on “communal
sharing” in which the boundaries of the individuals merge (Fiske
1991). People take great pains to differentiate these relationships from
those based on mere exchange. Psychological studies have found that
friendship satisfaction is highly predicted by self-disclosure and trust,
and is decreased by an exchange orientation (Jones 1991). Most people
experience friendships as communal relationships (Mills and Clark
1982) as distinct from exchange relationships, with a “deep structure”
that is distinct from the “superficial structure” of exchange (Hartup
and Stevens 1999).
Perhaps the strongest evidence that friendships are based on com-
mitment and not reciprocity is the revulsion people feel on discover-
ing that an apparent friend is calculating the benefits of acting in one
way or another. People intuitively recognize that such calculators are
not friends at all, but exchangers of favors at best, and devious ex-
ploiters at worst. Abundant evidence confirms this observation. Mills
has shown that when friends engage in prompt reciprocation, this
does not strengthen but rather weakens the relationship (Mills and
Clark 1982). Similarly, favors between friends do not create obliga-
tions for reciprocation because friends are expected to help each other
for emotional, not instrumental reasons (Mills and Clark 1994). Other
researchers have found that people comply more with a request from
a friend than from a stranger, but doing a favor prior to the request
increases cooperation more in a stranger than a friend (Boster et al.
1995). Owing to the important differences between friendship and ac-
quaintanceship, people seem to take care with new potential friends
to communicate whether they do or do not intend for the relationship
to become a friendship. Communications that blur this distinction
make people distinctly uncomfortable (Lydon, Jamieson, and Holmes
1997).
The importance of commitment is also a likely explanation for why
people care so much about not only what others do, but why they do
it. The meaning of an act differs dramatically depending on whether
it is motivated by desire to influence or by emotional concern for a
person’s well-being. This is consistent with the emphasis philoso-
phers have long placed on motives in determining the moral status of
an act (Darwall, Gibbard, and Railton 1997). The significance of the
difference between calculated versus real altruism has been long rec-
ognized (Krebs 1970). The capacity for making and keeping commit-
ments allows people to engage in relationships that are impossible for
those who just exchange favors. The more negative side of this same
capacity is seen in studies of honor cultures (Nisbett and Cohen
1996). Individuals who give a calculated response to aggression can

32 Evolution and the Capacity for Commitment
be exploited easily. Those who are taken over by rage are far more
formidable opponents. This is expanded at length in the chapter by
Cohen and Vandello herein.
Finally, contemporary studies of moral psychology are compatible
with evolutionary perspectives on commitment. As Krebs notes:
From an evolutionary perspective Kohlberg’s stages represent cognitive
structures that were selected in ancestral environments because they
upheld adaptive systems of social interaction. For example, Stage 1
structures upheld social systems based on obedience to authority; Stage
2 judgments upheld cooperative systems based on instrumental, indi-
vidual exchanges (e.g., tit-for-tat reciprocity) and Stage 3 judgments up-
held cooperative systems based on harmonious in-group relations. The
cognitive structures that uphold Stage 4 judgments may have evolved
relatively recently to uphold the maintenance of social structures, such
as legal systems, within more complex societies. . . . Put another way,
the original function of moral judgment was to constrain others from
advancing their interests at the expense of those with whom they
formed cooperative relations. (Krebs, Denton, and Wark 1997, 131)
Demonstrating how such psychological traits give a fitness advan-
tage is only one half of an evolutionary explanation; the other is dis-
covering their precursors and how they were shaped to their present
forms. This brings us to the precursors of capacities for commitment.
While commitment itself is a strategy, not a trait, it offers benefits that
may well have shaped various psychological mechanisms. Certainly
capacities for commitment may have precursors in tendencies shaped
by kin selection and reciprocity. As many have pointed out, we
evolved in small kin groups where helping others often helps the
actor’s genes (Alexander 1985; Irons 1998; Richerson and Boyd 1999).
In such a circumstance it may be more efficient to just help rather
than to calculate. Likewise, while the reciprocity literature emphasizes
sequential favor trading, many social relationships seem to be based
on metacommitments that people make to keep cooperating despite
occasional difficulties. Our relationships, even those based on com-
mitment, depend on some balance between what is offered and what
is received. Yet success in social life depends on the ability to main-
tain relationships during dry periods without being exploited. Like-
wise, conflicts are inevitable, and it appears that humans, like pri-
mates, have a built-in motivation to reconcile differences (de Waal
1989). Such motivations may be crucial precursors to capacities for
commitment.
A closely related second possibility is that the capacity for commit-
ment may have emerged from the benefits of political alliances.
Chimpanzees spend their lives making alliances. Subdominant males

Natural Selection and the Capacity for Subjective Commitment 33
routinely make coalitions to compete against the alpha male who, in
turn, must maintain alliances with others to keep his position (de
Waal 1982, Goodall 1986; Runciman, Maynard Smith, and Dunbar
1996). Human hierarchies are different from those of other primates,
with strong tendencies toward egalitarianism (Boehm 1999) and are
based as much on prestige as they are on dominance (Henrich and
Gil-White 2000). Nonetheless, political alliances are central to human
competition, and modeling them as reciprocal exchanges misses much
of how they work (Masters 1983; Trivers 1981). Instead of monitoring
each move to anticipate patterns of cooperation and defection, politi-
cal partners support each other in general, over multiple situations
during long periods of time. This is exactly the kind of situation in
which selection might well shape tendencies for emotional loyalty
and commitment. Such relationships are, of course, continually threat-
ened by third parties. Social life is composed of triangles (Kerr and
Bowen 1988). An individual cannot always fulfill the wishes of both
other parties, especially when each seeks an ally in a conflict with a
fourth party. Furthermore, humans routinely use the strategy of split-
ting—flattering one member of a partnership while denigrating the
other in order to disrupt the alliance and get a new ally. Ending all
relationships at the first such difficulty is not an option; that would
end participation in social life. Finding ways to overlook these devia-
tions in order to continue can be of great value. Tact—the ability to
suppress just the right information while talking with someone—may
be deception of a sort, but it is the glue that makes social life possible
(Nesse 1990b).
One further consideration may turn out to be enormously impor-
tant. When potential mates are assessing each other, one of their top
priorities is to find someone who is kind and honest. (This is the
central but neglected finding of the cross-cultural study of mate
choice by Buss [1989].) Otherwise, when bad times come, all the good
genes and resources in the world will not be of much use. Miller
(2000) has suggested, in the course of his work on selection for traits
that display quality, that sexual selection may have augmented the
capacity for altruism in a runaway escalation. If men and women
each have a genetic tendency to seek mates who are kind and honest,
this will select strongly for acting kind and honest, and the best way
to accomplish this is to actually be kind and honest. In short, in addi-
tion to all the other selective advantages of a capacity for commit-
ment, it may have been subject to sexual selection.
Social selection may be crucial to the capacity for commitment. If
groups routinely give rise to emergent forces of natural selection, this
can shape otherwise unaccountable individual behavior tendencies.
For instance, if individuals simply avoid those who have betrayed

34 Evolution and the Capacity for Commitment
them, the net effect on an individual prone to defection is, as Hobbes
said, exclusion from the group and probable death. It is as if the
group had decided to shape its future membership, but no foresight is
needed. The effect emerges from the uncoordinated actions of many
individual agents. Groups, of course, often do make decisions about
who is welcome and who is not, and they sometimes act in unison to
punish a deviant. Once commitments are established, such actions are
especially easy to explain. Such sequences readily give rise to coevo-
lution, in which social structures shape individual traits that in turn
create slightly different social structures (Cavalli-Sforza and Feldman
1981; Lumsden and Wilson 1981; Boyd and Richerson 1985; Durham
1991; Dunbar, Knight, and Power 1999). Many psychological traits
seem to exist to make culture possible, such as the tendency to confor-
mity and identification with the group leader, and the susceptibility
of children to indoctrination (Boyd and Richerson 1985; Barkow
1989a). Simon has suggested that the benefits of conforming to cul-
tural expectations have shaped a tendency to “docility,” a tendency to
learn and follow social norms that can result in genuine altruism (Si-
mon 1990). His argument depends on bounded rationality and the
assumption that individuals cannot accurately distinguish what is
good for them from what is good for their group, but it has the virtue
of explaining prosocial traits as a result of social selection (West-
Eberhard 1987; Simon 1990; Jason, Brodie, and Moore 1999).
The benefits of using commitment strategies effectively are them-
selves likely to be potent selection forces that emerge from the struc-
ture of a complex social environment. Furthermore, the functions of
the newest part of our brain, the frontal lobes, closely match the abili-
ties needed to use commitment strategies. The frontal lobes seem cru-
cial in calculating the tradeoffs between the short-term costs of giving
up options and long-term benefits that may or may not be obtained.
Many of these calculations involve social capital, with resulting inor-
dinate complexity (Alexander 1975; Humphrey 1976). The frontal
lobes also are essential to inhibiting the pursuit of short-term goals in
order to fulfill commitments in pursuit of long-term goals. They are
deeply involved in the social calculations needed to decide whether
another person will fulfill a commitment. This decision is made best
by an empathic identification with the other in order to anticipate
what he or she is likely to do. To use commitment successfully re-
quires not only higher cognition, but also a theory of mind (Baron-
Cohen 1995), intuitive empathy, and a capacity for “mind reading”
(Krebs and Dawkins 1984).
Our ability to read fiction, indeed perhaps our tendency to crave
and enjoy stories, may well arise because of the huge advantages of
getting into the mind of another in order to anticipate whether he or

Natural Selection and the Capacity for Subjective Commitment 35
she is likely to follow through on commitments (Carroll 1995; Turner
1996). We watch Sophocles’ play with understanding and horror as
Antigone reveals her determination to bury the body of Polynices,
despite the king’s edict. As she keeps her commitment, and the king
keeps his, tragedy unfolds. As we watch, we consider the importance
and the risks of keeping our commitments. Likewise, Odysseus over-
comes giant obstacles and forgoes the pleasures of various isles to
make his way home to his wife. Penelope, the very model of faithful-
ness, has been using her wiles to stave off the rapacious suitors.
When Odysseus finally arrives home, we understand his state of
mind perfectly as he takes his bloody revenge. One wonders if the
rise of commitment was a key to the growth and power of Greek
civilization.
To be explicit about this line of speculation, it seems possible that
capacities for commitment have given such substantial fitness advan-
tages that they could have shaped high intelligence, language ability,
empathy, a theory of mind, an ability to inhibit impulses, and our
fascination with fiction. Furthermore, once commitments become es-
tablished in a group, they create emergent forces of selection that fur-
ther speed development of these capacities in a runaway race for so-
cial intelligence. Expulsion of those who do not keep commitments
will quickly shape tendencies to honesty and loyalty, even if that re-
sults in tendencies to act in ways that are genuinely altruistic, or self-
destructively spiteful.
Such a scenario could address many long-standing problems. Most
important, it offers a possible explanation for how natural selection
could shape a moral capacity for acting according to rules instead of
calculated self-interest. The parallel benefits of threats and promises
offer a deep link between the origins of good and evil. Commitment
also offers a possible explanation for why we humans are such ex-
traordinarily emotional and apparently irrational creatures. Many
commitments work only if they are based on emotion or beliefs that
are outside the range of reason. This offers a way to understand our
human fascination with mythology, religion, and ideology, why we
spend so much effort constructing social realities, and how those so-
cial realities cycle back into tangible costs and benefits that further
shape human minds by means of natural selection.
While plausible and consistent with much evidence, these specula-
tions are nowhere near being facts. Taken together they make an in-
triguing story, but we do not yet even know how important the ca-
pacity for commitment really is, nor do we know how people use
commitment strategies differently within and among cultures. That
capacities for commitment have been shaped by natural selection
seems likely, but this needs much more exploration. This book re-

36 Evolution and the Capacity for Commitment
views prior work and summarizes the state of the field from diverse
perspectives in order to call attention to the importance of commit-
ment and pose clear questions that will advance our understanding.
This chapter was greatly improved by comments and suggestions from
Stephanie Brown, Terry Burnham, Dov Cohen, Lee Dugatkin, Alexander
Field, Alan Gibbard, Lillian Gleiberman, Martin Gold, Jack Hirshleifer,
Matt Keller, Philip Kulkulski, Peter Railton, Thomas Schelling, Natalie
Smith, two anonymous reviewers, and members of the University of
Michigan Evolution and Human Adaptation Program Weekly Seminar.
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