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Abstract

Moral evolution theories have emphasized kinship, reciprocity, group selection, and equilibrium selection. Yet, moral virtues are also sexually attractive. Darwin suggested that sexual attractiveness may explain many aspects of human morality. This paper updates his argument by integrating recent research on mate choice, person perception, individual differences, costly signaling, and virtue ethics. Many human virtues may have evolved in both sexes through mutual mate choice to advertise good genetic quality, parenting abilities, and/or partner traits. Such virtues may include kindness, fidelity, magnanimity, and heroism, as well as quasi-moral traits like conscientiousness, agreeableness, mental health, and intelligence. This theory leads to many testable predictions about the phenotypic features, genetic bases, and social-cognitive responses to human moral virtues.
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Volume 82, No. 2 June 2007THE QUARTERLY REVIEW OF BIOLOGY
97
The Quarterly Review of Biology, June 2007, Vol. 82, No. 2
Copyright 2007 by The University of Chicago. All rights reserved.
0033-5770/2007/8202-0002$15.00
SEXUAL SELECTION FOR MORAL VIRTUES
Geoffrey F. Miller
Psychology Department, University of New Mexico
Albuquerque, New Mexico 87131 USA
e-mail: gfmiller@unm.edu
keywords
agreeableness, alternative mating strategies, altruism, assortative mating,
behavior genetics, commitment, conscientiousness, costly signaling theory,
equilibrium selection, emotion, empathy, ethics, evolutionary psychology,
fitness indicators, genetic correlations, good genes, good parents, good
partners, human courtship, kin selection, kindness, individual differences,
intelligence, mate choice, mental health, moral virtues, mutation load, mutual
choice, person perception, personality, reciprocal altruism, sexual fidelity,
sexual selection, social cognition, virtue ethics
“Human good turns out to be the activity of the soul exhibiting excellence.”
Aristotle (350 BC)
abstract
Moral evolution theories have emphasized kinship, reciprocity, group selection, and equilibrium
selection. Yet, moral virtues are also sexually attractive. Darwin suggested that sexual attractiveness
may explain many aspects of human morality. This paper updates his argument by integrating recent
research on mate choice, person perception, individual differences, costly signaling, and virtue ethics.
Many human virtues may have evolved in both sexes through mutual mate choice to advertise good
genetic quality, parenting abilities, and/or partner traits. Such virtues may include kindness, fidelity,
magnanimity, and heroism, as well as quasi-moral traits like conscientiousness, agreeableness, mental
health, and intelligence. This theory leads to many testable predictions about the phenotypic features,
genetic bases, and social-cognitive responses to human moral virtues.
Introduction
A
MONG HUMANS, attractive bodies may
elicit short-term desire, but attractive
moral traits can inspire long-term love. Is this
a coincidence, or are there some functional
similarities between sexual ornaments and
moral virtues? Many sexually attractive physi-
cal traits evolved to reveal phenotypic condi-
tion and genetic quality, including health, fer-
tility, and longevity (Langlois et al. 2000; Fink
and Penton-Voak 2002). This paper explores
the possibility that some human moral traits
evolved through sexual selection to serve an
analogous display function. The most roman-
tically attractive mental traits (i.e., kindness,
bravery, honesty, integrity, and fidelity) often
have a moral dimension.
Recent empirical research suggests that
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98 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
many moral traits are sexually attractive, and
may serve as mental fitness indicators: they
are judged as reliably revealing good mental
health, brain efficiency, genetic quality, and
capacity for sustaining cooperative sexual re-
lationships as well as investing in children
(e.g., Gurven et al. 2000; Hawkes and Bliege
Bird 2002; Alvard and Gillespie 2004). Thus,
the moral virtues that we consider sexually at-
tractive are not culturally or evolutionarily ar-
bitrary. Rather, they evolved to advertise indi-
vidual fitness (including genetic quality as well
as parenting and relationship-coordination
abilities) in hard-to-fake ways that can be un-
derstood through a combination of sexual se-
lection theory (Kokko et al. 2002; Andersson
and Simmons 2006) and costly signaling the-
ory (Gintis et al. 2001; McAndrew 2002).
(“Fitness” here means adaptive design for re-
productive success, or the statistical propen-
sity to survive and reproduce successfully; it
may not equal achieved reproductive success
under evolutionarily novel conditions, espe-
cially given contraception.)
The hypothesis is that sexual selection
shaped some of our distinctively human
moral virtues as reliable fitness indicators.
Precursors of many human virtues, such as
empathy, fairness, and peacemaking, have
been discovered in other great apes (Preston
and de Waal 2002; Brosnan and de Waal
2003). My claim is not that sexual selection
created our moral virtues from scratch in our
species alone; rather, sexual selection ampli-
fied our standard social-primate virtues into
uniquely elaborated human forms.
This mate choice model is intended to
complement, not replace, other models of
human moral evolution. Besides sexual selec-
tion, various forms of social selection proba-
bly shaped human morality, including:
kin selection (Hamilton 1964);
reciprocal altruism (Trivers 1971; Ridley
1996; Sugiyama et al. 2002);
discriminative parental solicitude (Triv-
ers 1974; Mock and Parker 1997);
commitment mechanisms (Frank 1988;
Nesse 2001);
risk-sharing mechanisms (Boone 1998;
Sugiyama and Sugiyama 2003);
social norm and punishment mechanisms
(Henrich and Boyd 2001; Fehr and Fisch-
bacher 2004);
group selection (Sober and Wilson 1998);
and
equilibrium selection among alternative
evolutionary strategies (Boyd and Rich-
erson 1990; Alvard and Nolin 2002).
Each of these moral evolution models has
led to valuable insights and progressive re-
search traditions. Some are better at explain-
ing moral virtues such as love of children, sib-
lings, and parents, and righteous anger at
cheaters and promise-breakers. This morality-
through-mate-choice model also has distinc-
tive strengths and weaknesses that can ex-
plain some moral virtues—especially those
that show high sexual attractiveness, assorta-
tive mating, phenotypic and genetic variance,
heritability, condition-dependent costs, con-
spicuous display in courtship settings, and
young adult age peaks in display.Yet, for each
of the traditional mechanisms above, sexual
selection should anticipate, sharpen, and am-
plify the social selection pressures to produce
a more extreme, costly, prosocial version of
the moral virtue than social selection could
achieve alone. The reason is that nonsexual
forms of social selection can shape morality
only insofar as they confer fairly concrete sur-
vival benefits (e.g., shared food, protection
from predators) on the morally virtuous.
Mate choice can shape morality much more
powerfully and broadly because it demands
only that moral behaviors carry some signal-
ing value about a potential mate’s good genes
and/or parent/partner abilities. In general,
sexual selection can “supercharge” other evo-
lutionary processes by adding positive feed-
back dynamics that tend to trigger evolution-
ary innovation and speciation (Miller and
Todd 1995; Crespi 2004). If a moral virtue be-
comes useful in kinship, reciprocity, or group
prosperity, our ancestors probably did not ig-
nore it when choosing mates.
Some moral virtues may be attractive as sig-
nals (e.g., heroism as a signal of compe-
tence), whereas others may seem attractive as
traits in their own right (e.g., fairness as an
intrinsically valuable trait in a long-term sex-
ual relationship). This distinction requires
caution, however, because there is almost al-
ways scope for misrepresenting one’s traits
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June 2007 99SEXUAL SELECTION FOR MORAL VIRTUES
during courtship. A potential mate may act
agreeable and easygoing during courtship,
then become irritable and cantankerous af-
ter a couple years. In this case, courtship-
agreeableness was valued as a signal of likely
future relationship-agreeableness, but it proved
unreliable. Sexual commitment often brings
moral disappointment. The costly signaling
perspective is helpful in identifying such
pitfalls—not only situations where one trait is
unreliably correlated with another, but also
situations where the present value of a trait is
unreliably correlated with its future value.
From this viewpoint, all moral virtues dis-
played during sexual courtship are poten-
tially fallible signals of other traits or future
traits, so their reliability and stability must be
analyzed in a costly signaling framework.
To propose that human moral virtues
evolved through mate choice is not to suggest
that human morality is sexually motivated at
the level of individual behavior. Evolutionary
functions do not equal proximate motivations
(Radcliffe Richards 2000; Pinker 2002). Even
if the evolutionary payoffs for moral behavior
were mainly reproductive, moral behavior
can arise at the proximate level from genu-
inely moral personalities and motives (Frank
1988; de Waal 1997), not just copulatory mo-
tives. Indeed, sexual patience is a key virtue
in courtship: if a potential male mate shows
sexual self-restraint for a long time, this pro-
tects female mate choice, signaling that the
male is not just looking for a short-term affair
or extra-pair copulation.
This paper argues that there is substantial
overlap between sexually attractive personal-
ity traits and human moral virtues, but does
not pretend that all sexually attractive traits
are virtues, or that all virtues are sexually at-
tractive under all conditions. Some individ-
uals may feel most aroused by potential mates
who show Machiavellian cunning (Whiten
and Byrne 1997), aggressive ferocity (Chag-
non 1988), or rampant promiscuity (Oliver
and Sedikides 1992). To argue that some
moral virtues evolved through mate choice is
not to argue that vice is never attractive.
Moral Virtues and Virtue Ethics
This paper tries to integrate relevant in-
sights from individual differences research,
behavior genetics, and moral philosophy. It
goes beyond my book, The Mating Mind
(Miller 2000a), by emphasizing relevant em-
pirical and theoretical work since 2000. For
example, it connects recent person percep-
tion research with person-level approaches to
moral philosophy, especially virtue ethics
(Flanagan 1991; Stohr and Wellman 2002)
and naturalistic approaches to understanding
moral intuitions (e.g., Nesse 2001; Dennett
2003).
I do not assume that the “virtues” histori-
cally identified by philosophers will equal the
moral adaptations that can be identified in
humans using standard adaptationist criteria
of special design (e.g., Andrews et al. 2002).
Nor do I assume that the idealistic reasons for
advocating certain virtues in normative ethics
will have anything to do with the selection
pressures that may have actually shaped those
virtues phylogenetically. So why mention vir-
tue ethics at all? First, virtue ethics provides a
useful counterbalance to the traditional con-
sequentialist (utilitarian, payoff-based) ethics
that have influenced previous evolutionary
theories of altruism (e.g., kin selection and
reciprocal altruism). Also, as I will argue in a
later section, virtue ethics shifts the level of
analysis usefully from isolated altruistic acts to
stable personality traits. Third, many virtue
ethicists write carefully and insightfully about
our emotional and cognitive responses to
other people’s virtues and vices (e.g., Flana-
gan 1991), and their work can be construed
as a useful first draft of the qualitative, de-
scriptive moral psychology that may prove
useful in understanding the “receiver psy-
chology” of moral signaling. Finally, virtue
ethics offers a new route whereby evolution-
ary theory can influence the contemporary
humanities and social sciences. Thus, my al-
lusions to virtue ethics are intended in the
spirit of maximizing the interdisciplinary
relevance of adaptationist research.
Costly Signaling Theory, Fitness
Indicators, and Moral Virtues
Costly signaling theory has its intellectual
roots in many traditions and academic fields,
some of which construed human moral vir-
tues as costly signals. In Friedrich Nietzsche’s
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100 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
(1887) On the Genealogy of Morals, pagan vir-
tues were considered attractive signals of
health and power. In Thorstein Veblen’s
(1899) The Theory of the Leisure Class: An
Economic Study in the Evolution of Institutions,
conspicuous consumption and conspicuous
charity were seen as hard-to-fake signals of
wealth and social status. In 1970s biology,
Amotz Zahavi (1975) viewed many animal
signals and prosocial behaviors as hard-to-
fake indicators of animal fitness (Zahavi and
Zahavi 1997).
Since about 1990, costly signaling theory
has revolutionized the study of both sexual
selection and human altruism (Gintis et al.
2001; McAndrew 2002). Most animal com-
munication is relentlessly narcissistic, adver-
tising the signaler’s own individual species,
sex, age, health, fertility, social status, phe-
notypic condition, and/or genetic quality
(Bradbury and Vehrencamp 1998). How-
ever, animals often have incentives to lie
about their own qualities to attract more
mates, solicit more parental investment, or
deter more predators and rivals. Costly sig-
naling theory offers a solution to this prob-
lem of lying: if a signal is so costly that only
high health, high status, high condition ani-
mals can afford to produce it, the signal can
remain evolutionarily reliable (Zahavi and
Zahavi 1997).
Almost any fitness-related cost will work:
matter, energy, time, or risk. For example,
a peacock’s tail is burdensome in all four
senses: its growth and maintenance requires
several hundred grams of mass, many calo-
ries, a long time to grow, and much risk; its
costs undermine immunocompetence and
parasite resistance (Møller and Petrie 2002;
Loyau et al. 2005). Often, the most complex,
elaborate, and puzzling signals observed in
nature are the result of sexual selection
through mate choice (Darwin 1871). These
sexual ornaments almost always impose
high costs on the bearer, guaranteeing their
reliability as indicators of condition and fit-
ness.
This paper argues that many human virtues
evolved through sexual selection as costly sig-
nals. This hypothesis has been advanced by a
few previous researchers (e.g., Darwin 1871;
Hawkes 1991; Tessman 1995; Zahavi and Za-
havi 1997; Roberts 1998), and its empirical
testing has been one of the most active areas
of evolutionary psychology and evolutionary
anthropology in the last few years. Indeed,
many prosocial behaviors that were assumed
to arise through kinship or reciprocity are
now thought to have emerged as costly signals
of individual fitness favored by social and sex-
ual selection.
For example, it was often assumed that
risky big-game hunting evolved so the best
hunters could better feed their own offspring
(Stanford 1999). However, most hunted meat
from big game is distributed too widely in
hunter-gatherer clans for this paternal provi-
sioning theory to work (Hawkes et al. 2001;
Alvard and Nolin 2002). Recent research sug-
gests that the most successful hunters, who
provide the prosocial public good of hunted
meat, also tend to attract more high quality
female mates (Gurven et al. 2000; Sosis 2000;
Hawkes and Bliege Bird 2002; Alvard and Gil-
lespie 2004). Meat-provisioning may not be a
conscious sexual strategy, or even the causal
mediator of good hunters’ increased repro-
ductive success; good hunting and high at-
tractiveness may both be caused by an under-
lying trait such as high genetic quality.
Nevertheless, such research raises the possi-
bility that altruistic meat-provisioning was fa-
vored, at least in part, by sexual selection.
Likewise, our mate preferences for other
moral virtues may be explained by costly sig-
naling theory. If a young woman places a
single’s ad stating, “SHF, 26, seeks kind, gen-
erous, romantic, honest man,”we might trans-
late this in evolutionary terms as “single His-
panic female, 26, seeks a healthy male of
breeding age with a minimal number of per-
sonality disorders that would impair efficient
coordination and parenting in a sustained
sexual relationship, and a minimal number
of deleterious mutations on the thousands of
genes that influence the development of
brain systems for costly, conspicuous, altruis-
tic displays of moral virtue.” Of course, this
hypothetical ad itself is not good psychologi-
cal evidence or a costly signal in its own
right—it is cheap and easy to fake. Rather, the
ad identifies some desired moral virtues that
would be difficult to fake consistently during
a lengthy courtship.
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June 2007 101SEXUAL SELECTION FOR MORAL VIRTUES
good genes, good parents,
and good partners
Sexually-selected costly signals typically ad-
vertise two classes of traits: good genes or
good parenting abilities (Kokko et al. 2002).
Different moral virtues might advertise one
or the other, or both. They might also adver-
tise the capacity to be a good partner in a
long-term sexual relationship—someone re-
liable, trustworthy, adaptable, agreeable, and
efficient at coordinating joint activities.
Good genes indicators advertise general
“genetic quality,” which probably reflects hav-
ing a low “mutation load” (i.e., fewer than av-
erage errors in DNA replication) (Ridley
2001). By favoring mates with a below average
number of harmful mutations, sexually re-
producing organisms can increase the ex-
pected survival and reproductive prospects of
their offspring, even if their mate contributes
nothing as a parent after fertilization (Houle
and Kondrashov 2002).
Moral virtues may function as good genes
indicators by being difficult to display im-
pressively if one has a high mutation load
that impairs the precision of body and brain
development. For example, displaying a so-
phisticated, empathetic social intelligence
requires the development of a complex
Theory of Mind, which might be easily dis-
rupted by a variety of mutations associated
with autism, schizophrenia, mental retarda-
tion, social anxiety, and language impair-
ments (Baron-Cohen 2002; Shaner et al.
2004; Keller and Miller 2006). Thus, a con-
spicuously expert level of empathy may func-
tion as a sort of neurogenetic warranty. For
moral virtues to function as good genes in-
dicators, they must show at least moderate de-
grees of genetic variance, heritability, and
positive genetic correlations with other fit-
ness-related traits (Shaner et al. 2004; Pro-
kosch et al. 2005; Miller and Penke 2006).
By contrast, good parent indicators adver-
tise phenotypic traits that help care for off-
spring, such as feeding them, grooming them
to remove parasites, protecting them from
predators, resolving sibling rivalries, and
teaching life skills through play and practice
(Kokko 1998). A genuinely empathic per-
sonality may also function as a good parent
warranty, guaranteeing the likely patience,
kindness, protectiveness, playfulness, and
conscientiousness that helps children thrive.
For moral virtues to function as good parent
indicators, they need not show genetic vari-
ance, heritability, or genetic correlations
with other fitness-related traits; they need
only show reliable phenotypic correlations
with parenting-relevant abilities.
Finally, good partner indicators advertise
phenotypic traits that promote efficient co-
ordination and high mutual benefits in long-
term sexual relationships. In game theory
terms, such relationships (e.g., marriages)
are iterated, mixed-motive games with very
complex conflicts and confluences of inter-
est, many possible equilibria, and incomplete
information about the other player’s possible
tactics and preferences. Some of a potential
mate’s moral virtues could function as signals
that maximize one’s payoffs and minimize
one’s risks in such relationship games. For ex-
ample, moral capacities for conscientiousness
and patience may signal a partner’s likeli-
hood of playing mutually beneficial strategies
given the repeated interaction nature of long-
term relationships. Moral capacities for em-
pathy and sympathy may signal that a partner
attaches positive utility to one’s own happi-
ness in addition to their own, which makes it
much more likely that a Pareto-optimal (mu-
tually beneficial) equilibrium will be main-
tained in the relationship. A moral prefer-
ence for romantic commitment over violent
aggression may signal that a partner will seek
to sustain a cooperative relationship through
promises rather than threats. In each case,
the moral trait as a good partner indicator
may seem intuitively attractive for its own
sake, since conscientious, empathetic, com-
mitted partners make life easier. As noted ear-
lier, however, whenever there are incentives
to act like a better partner during courtship
than after reproduction, the problem of trait
stability arises.
Mate preferences for human moral virtues,
whether as good genes, good parent, or good
partner indicators, may have originated in
other social preferences concerning kin se-
lection (Hamilton 1964), reciprocal altruism
(Trivers 1971), social commitment (Nesse
2001), progeny choice (Mock and Parker
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102 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
1997), or other domains. For example, psy-
chological adaptations for detecting, remem-
bering, and avoiding cheaters in the domain
of social reciprocity (Sugiyama et al. 2002)
could have been extended (“exapted”) to the
domain of mate choice as a preference for
the moral virtues of honesty and reliability.
Indeed, mate preferences for moral virtues
may have originated as nonfunctional by-
products of these other social preferences,
and would have been more appropriately an-
alyzed using “receiver bias” models (e.g.,
Ryan 1998) rather than costly signaling mod-
els of sexual selection. Given the central adap-
tive importance of mate choice, however, it
seems likely that such nonfunctional prefer-
ences would have been rapidly eliminated (if
they had net fitness costs), or modified and
specialized for adaptive mate choice (if they
had net fitness benefits) (Kokko et al. 2002).
sexually selected signals and sex
differences
From a costly signaling perspective, sexual
selection is not restricted to explaining sex dif-
ferences; it can also explain sexual similarities
(nondimorphism) in extravagant traits when
mutual mate choice is at work (Kokko and
Johnstone 2002). Humans are unusual among
mammals in showing intensive offspring care
by both mothers and fathers (Geary 2000),
which favors roughly equal levels of male and
female mate choice for long-term socially mo-
nogamous relationships (Kenrick et al. 1990).
This has resulted in low-dimorphism physical
ornamentation in humans (e.g., long head
hair, relatively hairless bodies, and everted
lips) and low-dimorphism psychological orna-
mentation (e.g., cognitive abilities for lan-
guage, art, music, humor, and ideology)
(Miller 2000a). Thus, a sexual selection ac-
count of moral virtues does not imply that
males evolve all the conspicuous virtues
and females play the passive role of virtue-
assessment (cf. Darwin 1871). Given mutual
choice, both human sexes should show con-
spicuous, sexually attractive moral virtues
during mate attraction and retention.
Human males face higher variance in re-
productive success, however, so they are pre-
dicted to allocate somewhat more energy,
time, and risk to mating effort, including
costly, dangerous, public displays of moral vir-
tue. For example, this model naturally ex-
plains why males are overrepresented among
prosocial heroes who risk their lives to save
unrelated strangers (Farthing 2005). It may
also explain why males remain overrepre-
sented in high risk, underpaid, altruistic, ro-
mantically attractive professions such as the
police, fire, and military services, whereas
women remain overrepresented in low risk,
underpaid, altruistic, romantically attractive
professions such as nursing and school teach-
ing. The biased sex ratios in these high risk
versus low risk professions are undoubtedly
influenced by social norms regarding gender,
danger, and sex roles (Byrnes et al. 1999).
Nonetheless, human gender norms seem un-
likely to be the whole explanation, given the
cross-species ubiquity of sex differences in
risk-taking (Campbell 1999) and the evidence
that human sex differences in risk-taking are
largely mediated by sex differences in person-
ality traits such as sensation-seeking, aggres-
siveness, and extraversion, rather than gen-
der roles concerning risk (Zuckerman and
Kuhlman 2000).
More generally, sexual selection is probably
relevant whenever there are cross-culturally
stable sex differences in the display or judg-
ment of human moral virtues. By contrast,
most traditional theories of human moral
evolution through kinship, reciprocity, group
selection, and equilibrium selection are sex-
blind. Therefore, they have trouble account-
ing for any observed sex differences in the
means, variances, heritabilities, genetic cor-
relations, and life-history profiles of specific
quantifiable moral virtues and any associated
social, political, or religious attitudes (e.g.,
Barriga et al. 2001; Skoe et al. 2002).
evaluating moral persons versus
moral acts
Costly signaling theory portrays human
moral actions in a new light, as reliable cues
of personal moral traits. This may seem a pe-
culiar idea to most moral philosophers, who
have traditionally focused on judging the mo-
rality of isolated acts rather than the moral
virtues of a person as a whole. Recently, as act
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June 2007 103SEXUAL SELECTION FOR MORAL VIRTUES
ethics has been supplanted by virtue ethics
(Stohr and Wellman 2002), attention has re-
turned to the moral-person level of descrip-
tion—just the right level of description to
consider in costly-signaling models of moral
evolution. It is the level that unifies the study
of quantitative traits in evolutionary genetics,
mate choice in evolutionary psychology, per-
son perception in social psychology, person-
ality traits in behavior genetics, parole deci-
sions in criminal justice, and voter choice in
democratic elections.
It seems unlikely that our prehistoric an-
cestors made moral judgments about isolated
behavioral acts. Rather, as in other domains
of person perception (Funder 2004), they
probably interpreted the behavioral acts as
cues of stable individual traits (virtues or
vices). In small-scale hunter-gatherer bands,
morality came in person-sized units, not act-
sized units. Ancestral hominids had to choose
their lovers, friends, and allies as integrated
moral packages—good or bad, hero or vil-
lain, lover or stalker, reciprocator or cheat.
Moreover, it would not make adaptive
sense to judge isolated moral acts in tightly-
knit prehistoric social groups. Individual ac-
tions must be assessed in the context of indi-
vidual qualities, such as age, sex, status,
physical and mental health, personality, intel-
ligence, and genetic relatedness. We tolerate
theft by our own toddlers more than theft by
unrelated adults. We forgive unkind words
spoken by the sick during high fevers. We do
not expect a keenly empathic Theory of Mind
in the severely brain-damaged or autistic. Also,
individual actions must be assessed in the con-
text of ongoing relationships, as different so-
cial interaction domains call for different
moral judgment criteria, focused on different
virtues. We may favor kindness and fidelity
more in mate choice, honesty and conscien-
tiousness more in reciprocity, and genetic sim-
ilarity, residual reproductive value, and grati-
tude more in kin-directed altruism. This is why
mothers can love their psychopathic sons.
Only in social reciprocity with unrelated ac-
quaintances do we see the tit-for-tat moral
accounting that corresponds to traditional act
ethics (see Sugiyama et al. 2002).
The moral person and moral act levels of
description show some other key differences
relevant to this mate choice model. First, “mo-
rality” means something different at the per-
son level compared to the act level. A moral
act may be one that obeys some rationally de-
fensible, universal, deontic, or consequential-
ist principle. However, from the point of view
of a standard prehistoric hunter-gatherer, a
moral person is someone who embodies pro-
social virtues that make them a good mate,
friend, relative, or trading partner. In evolu-
tionary terms, a moral person is simply one
who pursues their ultimate genetic self-interest
through psychological adaptations that em-
body a genuine, proximate concern for others
(de Waal 1997; Nesse 2001).
Second, the moral person level emphasizes
that perceived moral virtue is an emergent
property of interaction between the moral
judgment maker and the morally judged—
just as beauty arises from the sexual orna-
ments of the displayer interacting with the
perceptual adaptations of the beholder (Sy-
mons 1995). Beauty is neither subjective nor
objective, but what one could call “objectively
relational:” it is a real emergent property of a
costly signaling system including both orna-
ments and preferences. Likewise, for moral
virtues in this mate choice model, the moral-
ity emerges from the interaction of traits and
preferences. By contrast, the moral act level
of description tends to downplay the role of
the observer in making moral judgments,
pretending that there can be direct contact
between a moral act to be judged and a uni-
versal normative principle, such as Kant’s cat-
egorical imperative or Mill’s utilitarian prin-
ciple.
Finally, we generally accept that “ought im-
plies can” when we judge moral acts (Sinnott-
Armstrong 1984). We do not expect the poor
to donate to charity, or quadriplegics to jump
in front of trolleys to save children. They can-
not do the moral thing, so we do not expect
it. However, when judging the morality of
whole persons in real relationships, we are
rarely so forgiving. If a potential mate has
Tourette’s syndrome and cannot refrain from
screaming “psycho prick!” repeatedly during
a public first date, a second date is unlikely,
no matter how much we understand about
verbal disinhibition in neurological disor-
ders. If a potential hunting partner suffered
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104 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
a severe head injury that renders him too
clumsy to hunt effectively, we may pity him,
but will still exclude him from the hunt.
When the fitness stakes are high, we hold peo-
ple morally accountable, even for faults that
are not their own. Moral culpability is a slip-
pery idea, since everyone must be a joint
product of their genes, environment, and
random developmental events (Pinker 2002;
Dennett 2003). If our ancestors could not os-
tracize helplessly evil people, they could not
have protected themselves from serial rapists,
psychopaths, or hot-tempered murderers.
Romantic Virtues and Moral Virtues
This sexual selection model may appear bi-
zarre at first to moral philosophers and moral
psychologists. From Saint Augustine through
Sigmund Freud, sexuality has been viewed as
morality’s nemesis. When Western thought
was gripped by the traditional dichotomies of
body versus spirit, lust versus virtue, and sin-
ners versus saints, it was hard to imagine that
moral virtues might arise through mate
choice. Even within evolutionary theories of
morality, moral capacities are usually seen as
efficient tactics to increase individual or
group survival prospects rather than as costly,
conspicuous signals to increase individual re-
productive prospects.
To overcome these intellectual biases, it
may help to take a step back and consider the
role of moral virtues in real human mate
choice. Apart from physical appearance and
social status, which traits most excite our ro-
mantic impulses? People often fall in love
based on positive assessments of each other’s
generosity, kindness, honesty, courage, social
sensitivity, political idealism, intellectual in-
tegrity, empathy to children, respectfulness to
parents, or loyalty to friends. The most ro-
mantic personal traits are often those that
have been considered praiseworthy moral vir-
tues by the world’s most influential philo-
sophical and religious traditions from ancient
Greece, Israel, Arabia, India, China, and Ja-
pan. These attractive virtues include not only
the traditional prosocial virtues of European
Christendom (e.g., faith, hope, charity, love,
kindness, fairness, equality, humility, and con-
science), but also Nietzsche’s (1887) pagan
virtues (e.g., leadership, bravery, strength,
skill, health, fertility, beauty, tolerance, joy,
humor, and grace).
courtship as a moral obstacle course
Moral virtues are, among other things, per-
sonal traits that we are proud to display dur-
ing courtship. Indeed, courtship in most cul-
tures can be viewed as a moral obstacle
course—a ritualized test of diverse moral vir-
tues, such as kindness in gift-giving, consci-
entiousness in keeping promises, empathy in
listening, and sexual self-control. For court-
ship to be reliable, valid, and discriminating
as a moral test, it must lead to a perceivable
range of moral failures (e.g., broken prom-
ises, revealed prejudices, irritabilities, infi-
delities, impatient sexual pressures) that re-
flect an underlying population distribution
of moral traits.
In archetypal romance stories across cul-
tures, both characters fall in love, enjoy bliss,
grow lazy, commit some moral errors, have a
moral crisis, recognize their moral failures,
resolve to improve their moral character,
magnanimously forgive each other, and live
happily ever after. It is not romantic for char-
acters to make and forgive purely perceptual
failures (e.g., failures of depth perception or
color constancy) or purely cognitive failures
(e.g., base-rate neglect or hindsight bias). If
neither individual in a sexual relationship
cares about projecting moral virtues (as in re-
lations between prostitutes and clients or mas-
ters and slaves), then the relationship is con-
sidered superficial and unloving.
Subjectively, romantic emotions seem to
amplify the perceived variance in moral char-
acter across potential lovers. When we fall in
love, new lovers seem morally exemplary;
when they make moral errors, they seem mor-
ally treacherous; when they make amends,
they seem morally redeemed; when they di-
vorce us, they seem morally repulsive. Bor-
derline personality disorder (the tendency to
view intimate partners in unstable, dichoto-
mized ways, as alternately extremely good or
extremely evil) (Koenigsberg et al. 2002) is
just an exaggerated form of the normal hu-
man tendency to alternately overvalue and
undervalue our lovers’ virtues. Of course,
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June 2007 105SEXUAL SELECTION FOR MORAL VIRTUES
such emotions may not increase the objective
accuracy of moral information (in the sense
of more accurate perceptual discrimination
of moral traits across individuals), but they
may increase the salience of such informa-
tion—its accessibility to other brain systems
for attention, memory, decision making, lan-
guage, and motor behavior.
Conversely, moral vices are character flaws
that we would be embarrassed to reveal to
potential mates. These sexually embarrass-
ing vices include not just obviously antisocial
behaviors (killing, raping, lying, cheating),
but also victimless addictions (sloth, glut-
tony, greed, envy, pride, drinking, smoking,
drug-taking, gambling, masturbating), fail-
ures of prosocial magnanimity (undertip-
ping waiters, ignoring starving children,
fleeing combat), and acts of symbolic mean-
ness (kicking toys, burning books, spitting
on tombs). Although this may sound like an
odd assortment of crimes, sins, foibles, and
insanities from most traditional viewpoints
(evolutionary altruism theories, law, reli-
gion, psychiatry), from a virtue ethics view-
point (and from the sexual signaling view-
point of this article), these moral vices have
an important common denominator: they
lead potential mates to hold our moral char-
acter in lower esteem, making them less
likely to breed with us. Also, the leading
causes of divorce across cultures (infidelity,
abuse, addiction, unemployment (Betzig
1989)) are almost all seen as serious moral
failures. To moral philosophers, the sexual
costs of moral vice may seem tangential to
human moral evolution. Yet, to evolutionary
biologists, a direct connection between
moral vice and impaired reproductive suc-
cess should be highly suggestive.
example: courtship generosity
The moral virtues most readily explained
by sexual selection are those most conspicu-
ously manifest in sexual courtship and rela-
tionships, and consistently valued in mate
choice across cultures. Courtship generosity
is the most obvious example, with clear par-
allels to courtship feeding by animals, in
which nuptial gifts are given by males to fe-
males as good-genes indicators and good-
parent investments (Vahed 1998). Human
courtship generosity would include altruism,
kindness, and sympathy to the sexual partner,
to his or her children from previous relation-
ships (step-children), and to his or her family
members (in-laws). Since this sort of court-
ship generosity is directed at nonrelatives and
is not expected to be reciprocated, it is hard
to explain through kin selection or reciprocal
altruism, and it qualifies as evolutionary altru-
ism by traditional definitions.
Courtship generosity may even include
much of the paternal effort that is usually as-
sumed to arise through kin selection (where
“kin” include “offspring”), since most di-
vorced fathers reduce their paternal invest-
ment as soon as they are denied sexual access
to mothers (Hofferth and Anderson 2003).
Thus, what looks like simple paternal invest-
ment in one’s offspring may turn out to be
better described as ongoing courtship gen-
erosity by males to maintain sexual access to
the mothers of those offspring. Under ances-
tral small-group conditions, it may have been
perfectly clear which males cut off aid to their
children after ending relationships with their
mothers. Such males may have been consid-
ered immoral and selfish, and may have suf-
fered reputational and reproductive costs as
a result. Depending on the exact social con-
text and social norms, however, those moral
costs may have been lower than the net fitness
costs of continued paternal investment with-
out sexual access to the mother. As with all
complex psychological adaptations, recogni-
tion of such situational contingencies is not
handwaving; it can lead to precise testable
predictions about the social, cultural, and
economic conditions under which males will
continue paternal investment following rela-
tionship termination.
Moral and Quasi-Moral Traits in
Individual Differences Psychology
Some of the best-studied individual differ-
ences dimensions in psychology have moral
or quasi-moral status when they are assessed
in social and sexual interaction. These in-
clude personality traits, mental health traits,
and intelligence. These heritable dimensions
of individual variation are morally valenced,
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106 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
and their morally praiseworthy extremes in-
crease sexual attractiveness. These traits are
interrelated not because they share some ab-
stract set of necessary and sufficient condi-
tions, but because, in the real world, they
tend to be disrupted by the same kinds of
pleiotropic genetic mutations, developmen-
tal errors, and neuropsychological abnormal-
ities.
personality traits
Current research on personality traits is
dominated by the “Big Five” model, which
identifies five key personality traits that can
be reliably measured, that validly predict di-
verse behaviors, that are stable across the
lifespan, and that replicate across cultures
(Costa and McCrae 1992; Matthews et al.
2003; Funder 2004). These traits can be re-
membered with the acronym OCEAN: open-
ness to experience, conscientiousness, extra-
version, agreeableness, and neuroticism. Of
these, conscientiousness and agreeableness
are most strongly sought in long-term mates
(Botwin et al. 1997; Berry and Miller 2001;
Donnellan et al. 2004; Ozer and Benet-
Martinez 2006), and best predict good part-
ner traits (Noftle and Shaver 2006; Ozer and
Benet-Martinez 2006) and good parent traits
(Spinath and O’Connor 2003; Kochanska et
al. 2004), so are most likely to have been
shaped as moral virtues by sexual selection.
Conscientiousness implies fulfilling prom-
ises, respecting commitments, and resisting
bad habits. It subsumes individual differences
in industriousness, self-control, responsibility,
and several other virtues (Roberts et al.
2005). It predicts emotional maturity (Mc-
Crae et al. 1999) and romantic loveability in
relationships (Engel et al. 2002). It also pre-
dicts prosocial civic and organizational en-
gagement (Organ and Ryan 1995), as well as
honesty, integrity, dependability, trustworthi-
ness, and reliability at work (Sackett and Wa-
nek 1996). Further, conscientiousness posi-
tively predicts virtually every health-related
behavior that increases longevity, including
eating a healthy diet, exercising, and avoiding
tobacco, excessive alcohol, addictive drugs,
risky sexual behavior, risky driving, and sui-
cide (Bogg and Roberts 2004). Conscien-
tiousness is also closely related to the capacity
for willpower, self-control, and delay of grati-
fication, which are key virtues across many so-
ciosexual domains (Metcalfe and Mischel
1999). Prefrontal brain damage, as in the fa-
mous case of Phineas Gage (Damasio et al.
1994), tends to reduce conscientiousness and
disinhibits impulsive antisocial behavior, so it
reduces both moral virtue and long-term sex-
ual attractiveness.
Agreeableness implies warmth, kindness,
sympathy, and nonaggressiveness; it predicts
benevolence and respect for moral traditions
(Roccas et al. 2002), the quality and peace-
fulness of social relationships (Asendorpf and
Wilpers 1998), and success in jobs requiring
teamwork and social interaction (Mount et al.
1998). Gentle, agreeable behavior fits the
“tend-and-befriend” response to stress that is
favored by female social primates (Taylor et
al. 2000). Individuals who score low on agree-
ableness tend have more personality disor-
ders (Saulsman and Page 2004). They also
tend to be aggressive, arrogant, conceited,
domineering, narcissistic, and lacking in em-
pathy—usually considered moral vices. Since
agreeableness increases satisfaction and sta-
bility in sexual relationships (Watson et al.
2000), as in other social relationships (Gra-
ziano et al. 1996; Asendorpf and Wilpers
1998), it is probably valued especially as a
good parent and good partner indicator.
The other three of the Big Five traits (open-
ness, extraversion, and neuroticism) are
more morally ambiguous, and tend to result
in assortative mating through preferences for
self-similarity. For example, high openness
(interest in novel experiences, aesthetics, and
culture) predicts the moral virtues of emo-
tional sensitivity (Schutte et al. 1998), social
tolerance (Dollinger et al. 1996), political lib-
eralism (McCrae 1996; Butler 2000), and sup-
port for universal values—the sort that would
be supported by Kant’s categorical imperative
(Roccas et al. 2002). On the other hand, low
openness predicts the moral virtues of tem-
perance, chastity, stoicism, community soli-
darity, pride in one’s people and traditions,
and clarity of gender role (manliness or fem-
ininity) (see Kendler et al. 1997; Lacey et al.
2004)—which academics tend to label vices
(“right-wing authoritarianism,” racism, sex-
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June 2007 107SEXUAL SELECTION FOR MORAL VIRTUES
ism) ( Jost et al. 2003; Van Hiel et al. 2004).
The strong assortative mating for political
and religious attitudes reflecting each point
along the openness dimension (Botwin et al.
1997; Watson et al. 2004) suggests that sexual
selection may have amplified variance in
openness, but is unlikely to have pushed it
consistently in either direction.
Are personality traits such as conscientious-
ness and agreeableness really relevant to the
evolution of morality? Moral philosophers
have lately rediscovered the old social psy-
chology critiques of personality psychology, as
in the “person versus situation” debate (Mis-
chel 1968), and work on the “fundamental
attribution error” (Sabini et al. 2001). Social
psychology’s concern was that apparently sta-
ble personality traits may not really exist, but
may only be projections of a biased social-
attribution system. Citing this literature, Doris
(1998) and Harman (1999) argued that virtue
ethics cannot succeed because social psychol-
ogy shows there are no stable personality traits
that could correspond to virtues. Unfortu-
nately, virtue ethicists (e.g., Merritt 2000) have
not usually responded to these critiques on
empirical grounds, by citing the well-estab-
lished reliability, validity, stability, and herita-
bility of personality traits (Matthews et al. 2003;
Funder 2004), which have been established
across cultures and even across species (Gos-
ling 2001; King et al. 2005).
mental health traits
All major mental illnesses tend to increase
perceived selfishness and to decrease per-
ceived moral virtue, sexual attractiveness, and
social status (McGuire et al. 1994). This seems
especially true for the most common and se-
vere psychopathologies, such as depression,
schizophrenia, and psychopathy (Wilson et
al. 1996; Nesse 2000; Shaner et al. 2004).
Many personality disorders, such as paranoid,
narcissistic, and borderline personality disor-
ders, also predict antisocial behavior (Coid
2003). Signs of mental illness typically lead to
social and sexual rejection by others, that is,
to stigmatization through negative social at-
tributions (Crisp et al. 2000). Serious mental
illness almost always reduces reproductive
success by reducing sexual attractiveness
(e.g., Haukka et al. 2003). Indeed, many men-
tal disorders can be viewed as catastrophic
failures of “mating intelligence”—of the cog-
nitive and motivational systems that allow nor-
mal individuals to display moral virtues, ver-
bal creativity, and social savvy in courtship
(Shaner et al. 2004).
Severe mental disorders disrupt moral vir-
tues, but they disrupt almost everything else
too (e.g., education, employment, relation-
ships, hygiene). Do less severe, more com-
mon mental disorders, such as personality
disorders, have especially harmful effects on
sexually-preferred moral virtues? Many of
them seem to, and have highly sex-skewed
prevalence rates that suggest some involve-
ment of sexual selection in their evolutionary
etiology. Asperger syndrome (a milder, com-
mon version of autism) is a highly male-biased
condition characterized by serious deficits in
social empathy and communication that result
in pervasive, consistent problems in attracting,
retaining, and understanding sexual partners
(Baron-Cohen 2002). Narcissistic personality
disorder (extreme arrogance, grandiosity, and
self-promotion) reflects obsessive overinvest-
ment in conspicuous, public fitness-displays to
attract multiple short-term mates (Buss and
Shackelford 1997; Robins and Beer 2001).
Antisocial personality disorder and psychopa-
thy (pervasive, highly male-biased patterns of
callous, exploitative, impulsive, violent, and
promiscuous behavior) can be construed as
overreliance on deceptive, coercive, and short-
term mating tactics (Krueger et al. 2002;
Dunsieth et al. 2004). Borderline personality
disorder (a highly female-biased pattern of
promiscuity, relationship instability, drug and
alcohol abuse, risky driving, and impulsive be-
havior (Skodol et al. 2002a)) is associated with
many vices. All of these personality disorders
seriously reduce long-term mating success,
relationship satisfaction, and marital stability
(Skodol et al. 2002b), and they have fairly high
prevalence rates in the general population
(Grant et al. 2004). Thus, the study of mental
disorders and their effects on intimate rela-
tionships is highly relevant to understanding
moral virtues and vices, and their possible or-
igins through mate choice.
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108 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
intelligence
Intelligence (in the sense of general cog-
nitive ability, the g factor, or IQ) is a morally
valenced concept, which is why it has been so
controversial throughout a century of psycho-
metrics (since Spearman 1904). It is well-
established that intelligence predicts objec-
tive performance and learning ability across
all important life domains that show reliable
individual differences ( Jensen 1998; Deary
2000). Based on thousands of psychometric
studies, almost all reputable intelligence re-
searchers agree that the best single measure
of intelligence is the g factor (a dimension of
general cognitive ability), which can be statis-
tically extracted from any reasonably diverse
battery of reliable cognitive tests given to any
reasonably large sample (Carroll 1993; Neis-
ser et al. 1996).
Less appreciated is that higher intelligence
predicts many behaviors that we consider
morally virtuous, such as being emotionally
sensitive to the needs of others (Schulte et al.
2004), working conscientiously (Kuncel et al.
2004), staying healthy through exercise and
diet (Gottfredson 2004), and staying happily
married (Gottfredson 1997). Intelligence
also predicts many forms of social, economic,
and aesthetic success that are sexually attrac-
tive and morally valenced, including creativity
(Miller 1999, 2000c; Kanazawa 2000), artistic
virtuosity (Miller 2001), and achieving social
status and wealth through individual merit
(Ellis 2001). These moral correlates of intel-
ligence may be one reason why intelligence is
so attractive when both men and women con-
sider potential long-term partners (Buss
1989; Kenrick et al. 1990; Li et al. 2002). Con-
versely, lower intelligence predicts many be-
haviors considered morally wrong, such as
murder, rape, assault, alcoholism, drug addic-
tion, absenteeism, child abuse and neglect,
passing along sexually-transmissible infec-
tions, and causing fatal traffic accidents (Gor-
don 1997; Lubinski and Humphreys 1997).
Many lines of research, from longitudinal
studies to multivariate genetic studies, suggest
that intelligence is not just correlated with
these diverse traits and behaviors, but that in
each case, intelligence is either causally pri-
mary, or intelligence and the other trait are
driven by an underlying dimension of genetic
quality (e.g., Jensen 1998; Plomin and Spi-
nath 2002; Zammitt et al. 2004; Prokosch et
al. 2005; Kovas and Plomin 2006).
One might object that intelligence is not
really a moral virtue; it just happens to predict
a wide range of specific moral behaviors. Yet,
what is a moral virtue if not an individual-
differences dimension that predicts a wide
range of specific moral behaviors? Moral vir-
tues are socially attributed traits that carry
predictive information about morally rele-
vant behaviors. If kindness is a moral virtue
because it predicts specific prosocial behav-
iors, and is valued as such, then intelligence
must also be a moral virtue, along with being
an academic, economic, and epistemological
virtue. Another reason for accepting the
quasi-moral status of intelligence is the recent
convergence between virtue ethics and “vir-
tue epistemology,” the study of cognitive and
intellectual virtues (Axtell 2000; Brady and
Pritchard 2003; DePaul and Zagzebski 2003).
Traditional epistemology tried to evaluate the
truth of particular conceptual systems
through consistency and coherence criteria.
By contrast, for the virtue epistemologist, true
beliefs arise from acts of intellectual virtue,
those typical of intelligent, rational, cogni-
tively complex agents (Zagzebski 1996) who
show impartiality, epistemic responsibility,
and intellectual courage (Code 1987; Kvanvig
1992; Montmarquet 1993). For example, Ar-
istotle named intuition, wisdom, prudence,
and science as intellectual virtues. In virtue
epistemology as in virtue ethics, the favored
level of description is the whole individual as
a cognitive/moral agent, not the isolated be-
lief or moral act. This naturally leads to an
emphasis on individual differences in episte-
mological virtue, differences that intelligence
researchers have already succeeded in mea-
suring with unparalleled reliability and valid-
ity for over a century ( Jensen 1998). Thus,
intelligence is a sexually attractive, quasi-
moral trait at the intersection of virtue epis-
temology and virtue ethics.
Are These Traits Really Judged
as Moral Virtues?
In what sense do these personality, mental
health, and cognitive traits have a quasi-moral
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June 2007 109SEXUAL SELECTION FOR MORAL VIRTUES
status? There are at least four reasons to think
they do—three from social psychology and
one from popular culture. First, most people
show a “just world belief” (Lerner 1980) that
creativity, beauty, status, and wealth are mer-
ited by those who enjoy them, as both causes
and consequences of moral virtue. People
judge these traits as morally valenced and
morally correlated. Second, research using
the Implicit Association Test shows that many
dimensions judged in person perception are
highly evaluative, and load on a common
good/bad dimension that confounds moral
goodness, likeability, pleasantness, status,
racial similarity, and physical attractiveness
(Greenwald et al. 2002). Third, there is a
powerful “halo effect” around such traits, so
they are judged as boosting the likely moral
virtues of judged individuals (Eagly et al.
1991). For example, defendants in criminal
cases who are physically attractive and high in
social status are more likely to be acquitted or
given lighter sentences by juries of their (of-
ten lower status) peers (McKelvie and Coley
1993). Conversely, information that a person
is morally virtuous (e.g., honest) boosts rat-
ings of their health and physical attractiveness
(Paunonen 2006). Some halo effects may re-
flect accurate inferences about genuinely cor-
related traits (true halo), rather than per-
ceiver bias (halo error) (Solomonson and
Lance 1997; Jussim 2005). In each case, peo-
ple conflate moral virtues with personality
traits, mental health, intelligence, and physi-
cal attractiveness.
Finally, the popular culture reason: people
often attribute these quasi-moral traits in ex-
aggerated form to mythical beings who have
strong moral valences, such as gods, patri-
archs, political leaders, movie characters, and
comic book superheroes. In religion, believ-
ers typically credit benevolent deities with su-
pernatural levels of the quasi-moral person-
ality traits (intelligence, conscientiousness,
agreeableness, and emotional stability), as
well as the standard sexually-selected fitness
indicators (size, strength, status, beauty, lon-
gevity) (Boyer 2001; Roes and Raymond
2003). In monotheistic religions, these traits
are bundled together; in polytheistic reli-
gions, different super-normal traits are at-
tributed to different deities. Contemporary
fantasy films and comic books show the stan-
dard polytheistic pattern, with different super-
normal quasi-moral traits attributed to differ-
ent superheroes.
Ever since Socrates, philosophy has tried to
develop precise distinctions between theo-
retical constructs that are often empirically
correlated. Most philosophers think in terms
of necessary and sufficient conditions, not in
terms of factor analysis. Thus, moral philos-
ophers may balk at such flagrantly irrational
conflations of moral goodness, social reputa-
tion, economic power, and sexual attractive-
ness. Indeed, they may be tempted to quote
a cautionary verse from Ogden Nash: “It’s al-
ways tempting to impute / Unlikely virtues to
the cute.” But moral philosophers did not
drive the genetic evolution of human virtues;
ordinary people did. If we are seeking a de-
scriptive explanation for human morality, we
should attend to the person-perception judg-
ments that may have causally driven moral
evolution in our species. Ultimately, it is an
empirical question whether ordinary people
judge these traits to have a moral or quasi-
moral status when making social and sexual
judgments about others.
Are the Moral Virtues Really
Sexually Attractive?
Research shows that many particular moral
virtues are sexually attractive and relation-
ship-stabilizing; these include:
kindness: emotional responsiveness to the
needs of others (e.g., Jensen-Campbell et
al. 1995; Li et al. 2002);
empathy: lovingness, affection, fondness,
commitment, forgivingness, trust, and
perspective-taking (e.g., Kilpatrick et al.
2002; Fincham et al. 2004);
niceness: agreeableness and nonviolence
(e.g., Botwin et al. 1997; Gottman et al.
1998; Urbaniak and Kilman 2003);
honesty (e.g., Boon and McLeod 2001;
Haselton et al. 2005); and
heroism (e.g., Johnson 1996; Kelly and
Dunbar 2001; Farthing 2005).
Most of these moral virtue preferences are
stronger when seeking a serious long-term
partner than a short-term lover (Urbaniak
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110 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
and Kilman 2003). Others, such as the pref-
erence for risky, prosocial heroism, may be
stronger when females are seeking a short-
term male partner (Farthing 2005).
The problem is that these studies have not
been able to distinguish whether the moral
virtues are preferred because they signal
good genes, good parents, and/or good part-
ners. As with most mate choice research, the
first step is to demonstrate a preference that
could drive selection for a signaling trait; the
second step is to clarify why the preference
exists, which often demands more nuanced,
experimental research methods (e.g., Møller
and Alatalo 1999). For example, if a certain
moral virtue signals mainly genetic quality
rather than parent or partner quality, it
should be most preferred by women just be-
fore ovulation, within each monthly cycle,
when it could be passed along to offspring
(Gangestad et al. 2004; Haselton and Miller
2006). Likewise, good genes moral virtues
should be more preferred in short-term sex-
ual liaisons and extra-pair copulations than
in long-term relationships. Conversely, good
parent and good partner virtues should be
more preferred by women at less fertile cycle
phases, and in longer-term relationships.
Much more research is needed along these
lines.
What about Cross-Cultural Differences
in Moral Norms and Mate Preferences
for Virtues?
The cross-cultural studies of mate prefer-
ences cited above raise the question: if some
moral virtues are species-typical, sexually se-
lected indicators, why do we see large cross-
cultural differences in some moral norms
and behaviors? Here again, the virtue ethics
framework helps clarify different levels of
analysis. I suspect that individuals from every
culture tend to value intelligence, mental
health, and emotional stability as moral vir-
tues in potential mates, but that radically dif-
ferent behaviors can be used to demonstrate
these traits in different social, cultural, eco-
nomic, and ecological contexts.
The two largest cross-cultural studies of
mate preferences have been coordinated
by David Buss (1989) and David Schmitt
(2004a,b). Buss (1989) and his collaborators
asked 10,047 people from 37 cultures to rate
and rank the desirability of several traits in a
sexual partner. Among the top ten traits
most desired by both men and women across
almost all cultures were: kindness, intelli-
gence, exciting personality, adaptability, cre-
ativity, chastity, and beauty. Each of these has
at least quasi-moral status in many cultures.
Schmitt (2004a,b) and collaborators gath-
ered data on 17,804 people from 62 cultures
and found similarly close links between
morality and mate choice. Across most cul-
tures, sexual promiscuity, infidelity, and
“mate poaching” were predicted by low agree-
ableness and low conscientiousness (Schmitt
2004a,b). Also, many studies show that sin-
gles’ ads across cultures often advertise and
seek moral traits, especially kindness, gener-
osity, honesty, fidelity, and capacity for com-
mitment (e.g., Oda 2001; Burmann et al.
2002; Koziel and Pawlowski 2003). Ideally, fur-
ther research would examine cross-cultural
preferences for moral virtues using more sub-
tle, indirect, ecologically valid measures, such
as revealed preferences in “fast dating” par-
ties for real singles, rather than stated pref-
erences on questionnaires and in singles’ ads,
which may be biased by strategic self-presen-
tation and adaptive self-deception.
sexual selection and equilibrium
selection
An especially interesting, powerful, and ne-
glected interaction may occur between sexual
selection and group-level equilibrium selec-
tion (Boyd and Richerson 1990; Miller
2000a). Many evolutionary games have mul-
tiple equilibria (states where each player is
maximizing their individual payoffs given the
strategies already played by others). Some
equilibria are better for everybody, bringing
net positive payoffs to everyone (“Pareto-
dominant”); some equilibria are worse for
everybody (“Pareto-inferior”), but cannot be
escaped easily because individuals who de-
viate from the equilibrium do even worse.
Normally, natural selection alone is not very
good at escaping from such Pareto-inferior
equilibria to reach Pareto-dominant equilib-
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June 2007 111SEXUAL SELECTION FOR MORAL VIRTUES
ria (Boyd and Richerson 1990). Sexual selec-
tion may help, by conferring reproductive
benefits on individuals who deviate from self-
ish, antisocial equilibria (Miller 2000a). This
sexual payoff for virtue is functionally similar
to the social-reputation payoffs for virtue
modeled by other researchers (e.g., Nowak
and Sigmund 1998; Milinski et al. 2002; Bar-
clay 2004).
However, standard social-reputation mod-
els create a second-order “free rider” prob-
lem (Gintis 2000): who will altruistically take
the trouble to punish the wicked and reward
the virtuous? As research from behavioral
game theory (e.g., the Ultimatum Game)
shows, most humans are emotionally com-
pelled to impose this sort of “altruistic pun-
ishment” of others who act selfishly (Fehr and
Ga¨chter 2002); the question is why? Most ex-
planations for altruistic punishment appeal
to the dynamics of cultural evolution or social
norms (e.g., Boyd et al. 2003), without iden-
tifying any plausible individual fitness payoffs
for punishing the wicked. By contrast, this
mate choice model identifies selfish mate-
choice incentives (e.g., good gene and good
parent payoffs) for “rewarding” the virtuously
punitive with sexual relationships. That is, the
effective imposition of punishment on anti-
social others (at substantial risks and costs to
oneself) should be seen as virtuous, socially
status-enhancing, and hence sexually attrac-
tive—and recent research suggests that it is
(e.g., Henrich et al. 2001; Boyd et al. 2003;
Nakamura and Iwasa 2005; Rucas et al. 2006;
Seinen and Schram 2006). Thus, individual
sociosexual payoffs for virtuous behavior can
help solve the collective-action problems that
pervade human social life. (Of course, pro-
social punishers are likely to gain other costly-
signaling benefits, being viewed as more
dominant, capable, and confident, and thus
attracting more friends, allies, and support
from kin.)
Most contemporary theories of moral evo-
lution accept the importance of multilevel se-
lection across genetic, individual, and group
levels, either explicitly or implicitly (Sober
and Wilson 1998). Generally, group-level se-
lection for prosocial behavior is what breaks
the symmetry between alternative equilibria
in evolutionary games to allow the evolution
of genuine empathy and altruism (Lahti and
Weinstein 2005). This model of sexual selec-
tion interacting with group-level equilibrium
selection is a potent way that prosocial virtues
can establish a genetic beachhead in an oth-
erwise selfish population, long before group-
level equilibrium selection can favor morally
unified groups.
sexual choosiness as a moral virtue
In traditional sexual selection theory there
is a crisp distinction between mate preference
and preferred trait (Darwin 1871; Kokko et
al. 2002). However, if mate choice started to
favor human sexual fidelity, chastity, and
choosiness as moral virtues, the stage would
be set for a new positive feedback process. Just
as poor taste in friends and associates can re-
flect moral inadequacy, poor taste in previous
mates can as well. Thus, in our highly social
species, given capacities for observing, re-
membering, and gossiping about other peo-
ple’s sexual relationships, a conspicuously ex-
cellent capacity for mate choice could come
under sexual selection as a preferred trait,
perhaps even becoming a costly moral signal
in its own right. The resulting evolutionary
dynamics of such metaselection (sexual selec-
tion for sexual choosiness) have not, to my
knowledge, been explored.
Predictions of the Sexual Selection
Model for Moral Virtues
Given the theoretical plausibility of so many
moral evolution models, how can they be
tested empirically? This sexual selection model
makes many discriminating predictions. These
often take an unusual form, since costly sig-
naling adaptations have very different pheno-
typic and genetic features compared to other
types of adaptations. In particular, many of
these predictions concern individual differ-
ences in virtues, whereas evolutionary psy-
chology and moral philosophy have tended to
focus on species-typical moral judgments and
behaviors.
To test most of these predictions, one would
need to develop measurement scales that can
identify stable individual differences in partic-
ular kinds of moral virtues, and that fulfill stan-
dard psychometric criteria for reliability and
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112 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
validity. To discriminate between rival theories
concerning the evolutionary origins and adap-
tive functions of specific human virtues, we
need to assess the adaptive design features of
each putative virtue in reliably quantitative
ways. This will require much more psychomet-
rically sophisticated approaches to virtue
ethics, not just asking people to give answers
to a few multiple-choice “trolley problems”
from moral philosophy.
Generally, sexually selected virtues (as
quantified in this way) should show most of
the following 12 features. No one feature
alone is strong evidence for the mate choice
model, but these features are highly discrim-
inating when used in combination, as they
would not be expected from most other mod-
els of moral evolution through other selec-
tion pressures (e.g., kin selection, reciprocity,
group selection), especially those that implic-
itly depend on stabilizing rather than direc-
tional selection. This list is intended mainly
to help discriminate between different ma-
cromodels of moral evolution (e.g., sexual se-
lection versus kin selection, reciprocity, and
group selection), although certain criteria are
also helpful in discriminating different micro-
models within the sexual selection framework
(e.g., virtues evolved as good genes indicators,
good parent indicators, or good partner indi-
cators).
genetic features of moral virtues
Positive heritability: If virtues are good
genes indicators, they should prove geneti-
cally heritable in twin and adoption studies,
with substantial additive genetic variance
maintained by polygenic mutation-selection
balance (Rowe and Houle 1996; Tomkins et
al. 2004; Keller and Miller 2006). Many stud-
ies report substantial heritability for various
forms of antisocial behavior and its person-
ality correlates, such as psychopathy, sensation-
seeking, and disagreeableness (see Krueger et
al. 2001; Rhee and Waldman 2002). Moderate
heritability for altruism, empathy, nurtur-
ance, and/or responsibility has been found in
a few twin studies (e.g., Zahn-Waxler et al.
1992; Davis et al. 1994; Rushton 2004). Also,
if virtues are costly and evolved under sexual
selection, the genes underlying virtues should
also show a distinctive life history of herita-
bility, and become more expressed only after
sexual maturity, perhaps in response to sex
hormones. This should lead to higher virtue
heritability in adults than in children, as has
been found with intelligence (Plomin et al.
2001). On the other hand, if virtues are
mainly good parent and good partner indi-
cators, they may show low heritability, though
they should still show a distinctive life history
that reflects the shifting costs and benefits of
producing good parent/partner indicators,
depending on whether one is sexually im-
mature, mature but unmated, or mated se-
curely.
Genetic inbreeding and paternal age ef-
fects: If virtues are good genes indicators,
heritable variation in virtues should reflect
variation in overall mutation load: the off-
spring of sibling or cousin marriages should
show reduced virtue levels as a result of in-
creased expression of harmful homozygous
mutations (inbreeding depression). Also,
since mutation load in sperm increases dra-
matically as men age (Crow 2000), all else be-
ing equal, younger fathers should sire more
virtuous children. Such paternal age effects
have been shown for various virtue-reducing
mental illnesses, such as schizophrenia (Mal-
aspina et al. 2002; Byrne et al. 2003) and au-
tism (Reichenberg et al. 2006). Future re-
search could use similar methods to investigate
other virtues more directly.
Elusive molecular-genetic basis: Specific
virtue-reducing alleles should be maintained
mostly by mutation-selection balance. Thus,
virtue-reducing alleles should be mostly of
fairly recent evolutionary origin—recent,
harmful mutations that have not yet been
eliminated by sexual selection in particular
breeding populations. Thus, despite the her-
itability of specific virtues, as found in twin
and adoption studies, it should be extremely
difficult to find specific “virtue genes” that
replicate across human groups using stan-
dard linkage and association studies (Keller
and Miller 2006). Rather than finding virtue
genes, molecular geneticists should find
mostly “vice genes,” lineage-specific, evolu-
tionarily transient, rare, recent mutations that
decrease virtue, rather than common haplo-
types that increase virtue.
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June 2007 113SEXUAL SELECTION FOR MORAL VIRTUES
phenotypic features of moral virtues
Conspicuous courtship display: During
courtship, individuals should conspicuously
(if unconsciously) display virtues to the op-
posite sex. This could be measured across dif-
ferent time scales, comparing courtship to
noncourtship situations across different ovu-
lation cycle stages, relationship stages, and so-
cial contexts. For example, priming people to
think about potential romantic situations may
increase their displays of conspicuous benev-
olence and heroism, as it does for displays of
conspicuous creativity (Griskevicius et al.
2006) and conspicuous consumption (Wilson
and Daly 2004). Good genes virtues should be
selectively displayed more in short-term, op-
portunistic, or extra-pair mating (e.g., John-
son 1996; Kelly and Dunbar 2001; Gangestad
et al. 2004; Farthing 2005); good parent/part-
ner virtues should be displayed more in long-
term mating (e.g., Goldberg 1995; Brase
2006).
Condition-dependent costs and positive
correlations with other fitness indicators: Vir-
tues should incur a significant cost to produce,
in energy, time, risk, or nutritional resources
(technically, they should incur a significant
relative marginal cost) (Getty 2006). Without
the condition-dependence requirement, this
feature sounds tautological, insofar as altru-
istic virtues always imply evolutionary costs.
However, with the condition-dependence re-
quirement, we can make more specific falsi-
fiable predictions. For example, individuals
with higher genetic fitness or better pheno-
typic condition should be better able to bear
the costs of conspicuous moral virtues as good
genes indicators, so should more often dis-
play those virtues. Thus, good genes virtues
should correlate positively with other well-
established fitness indicators, such as physical
and mental health, longevity, fertility, body
size and symmetry, as well as intelligence
(e.g., Gangestad and Simpson 2000; Gottfred-
son 2004; Prokosch et al. 2005). In particular,
genuine phenotypic correlations should exist
between good genes virtues, physical attrac-
tiveness, social status, and charisma, not just
stereotyped “halo effects” in which more
physically attractive people are seen as virtu-
ous (cf. Eagly et al. 1991). By contrast, moral
virtues as good parent/partner indicators
may derive their temporal reliability (from
early courtship to long-term relationship) not
so much from condition-dependence, as
from the endogenous stability and increasing
heritability of personality traits across the life-
span (McCrae et al. 2000; Roberts and Del-
Vecchio 2000), the social-reputational costs of
moral back-sliding (Brandt and Sigmund
2005), and the ever-looming threat of divorce
for moral degeneracy (see Betzig 1989; Brad-
bury et al. 2000).
Comorbidity among vices, developmental
instabilities, and brain abnormalities: If dif-
ferent virtue deficits reflect harmful pleiotro-
pic mutations with partly overlapping effects,
then vices should show positive genetic cor-
relations (genetic comorbidity) with each
other, especially as they become more serious
and extreme. Also, if vices reflect harmful
mutations that impair normal neurodevel-
opment, then they should be associated with
various standard brain abnormalities widely
observed for other fitness-reducing behav-
ioral traits such as mental illness and mental
retardation: smaller cortical volume, larger
ventricles, abnormal cortical lateralization,
and atypical localization of processing as ob-
served in fMRI studies (Yeo et al. 1999).
Higher trait variance in males: In species
that evolved with some degree of polygyny
and some frequency of extra-pair copulation,
the higher male variance and skew in repro-
ductive success should favor a risk-seeking
pattern of trait expression, such that male vir-
tue levels show higher variance than female
trait values (see Archer and Mehdikhani
2003). That is, there should be more conspic-
uously super virtuous males (e.g., Gandhi and
Martin Luther King, Jr), but also more virtue-
deficient males (e.g., Vlad the Impaler and
Joseph Stalin). (The proclivity of conspicu-
ously super virtuous males to have covert sex-
ual affairs with many females is evidence for
this mate choice model, not evidence that
they were unvirtuous.)
Young adult peak in trait expression: For
sexually selected behavioral traits, conspicu-
ous virtue displays should peak in young
adulthood, at the apex of mating effort. They
should be low before puberty, increase rap-
idly thereafter, and then decline gradually as
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114 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
individuals shift their time and energy from
courtship to parenting.
Alternative mating strategies: Individuals
lacking the sexually attractive virtues should
more often pursue alternative mating strate-
gies that try to circumvent mate choice by the
opposite sex and mate-guarding by same-sex
rivals, just as animals with lower quality
ornaments tend to do (Norman et al. 1999;
Matsubara 2003). This may include in-
creased use of short-term opportunistic mat-
ing, deceptive affairs, sexual harassment,
sexual stalking, and/or sexual coercion
(Thornhill and Palmer 2000; Baumeister et
al. 2002; Dreznick 2003). If so, we might
predict vicious cycle effects in which initially
virtue-deficient individuals fail in the mating
market and adopt increasingly desperate
and exploitative alternative mating strate-
gies, which further undermine their virtues.
This is not a surprising prediction for behav-
ioral ecologists, but it offers a view of sexual
aggression quite different from the domi-
nant feminist model in the social sciences
(rape as a crime of patriarchal aggression,
not sex, see Thornhill and Palmer 2000),
and it may lead to more effective antirape
interventions.
mate choice for moral virtues:
Mate preferences: All else being equal, vir-
tues should be favored in mate choice. They
should be highly valued aspects of potential
mates that individuals are motivated not just
to judge passively by observation, but to
probe actively, by arranging various socios-
exual situations that test the specific virtues
of potential mates. (Such virtue tests are a
central plot device in sitcoms and romantic
comedies.) For example, a potential mate’s
honesty and fidelity may be tested by arrang-
ing for a same-sex friend to flirt with them
and report the outcome. Further, virtues as
good genes indicators should be favored
more often in short-term relationships and
extra-pair copulations, and by women at peak
fertility near ovulation (see Gangestad et al.
2004; Haselton and Miller 2006). Virtues as
good parent/partner indicators should be fa-
vored more often by individuals seeking long-
term relationships, by those who already have
children from previous relationships, and by
women at lower fertility phases of the ovula-
tory cycle.
Positive assortative mating: In species with
social monogamy such as ours, individuals
should assortatively mate with respect to vir-
tues because the competitive mating market
should ensure that high virtue individuals
prefer each other, leaving lower virtue indi-
viduals no choice but to settle for each other
(Todd and Miller 1999).
Sexual derogation and gossip about trait
values: If virtues are valued in courtship,
same-sex rivals should selectively derogate
each other with respect to virtue deficits such
as lying and cheating (Schmitt and Buss
1996). Also, in social species such as ours with
collective mate-choice that takes into account
the views of family and friends, gossip about
potential mates should focus considerable at-
tention on virtues as fitness indicators. Virtue
should be praised and vices condemned, es-
pecially when people discuss potential mates
for their kin and friends. This may sound tau-
tological (what are virtues but socially praised
traits?), but the mate choice model can lead
to more specific predictions about sex differ-
ences and relationship context effects on the
sexual derogation of virtues. For example,
men seeking a short-term copulation value fe-
male promiscuity as a virtue (probably under
a morally palatable euphemism such as fun,
liberal, or adventurous), whereas men seek-
ing a long-term relationship value female
chastity as a virtue (Oliver and Sedikides
1992; Schmitt et al. 2001). Thus, a clever fe-
male will derogate or gossip about a short-
term sexual rival as a “frigid conservative,” or
a long-term marriage rival as an “insatiable
nympho.” Thus, the sexual attractiveness and
moral valence of specific rival traits should re-
verse under predictable conditions.
Example: Sexual Fidelity as a Moral Virtue
Suppose a researcher hypothesizes that
sexual fidelity evolved by sexual selection
through mutual mate choice rather than
through kin selection, reciprocal altruism, or
group selection. Fidelity might minimize the
spread of sexually-transmissible pathogens,
the risk of cuckoldry (a male investing in off-
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June 2007 115SEXUAL SELECTION FOR MORAL VIRTUES
spring that were sired by another male), and
the costs of polygyny (a female losing invest-
ment in her own children if a male sires chil-
dren by another female). How could this
hypothesis be tested? It might be easiest to
go in reverse order of the 12 criteria listed
above: start with mate choice for the virtue,
then phenotypic features of the virtue, then
genetic bases of the virtue.
A first step would be to investigate mate
choice for fidelity. Do surveys, interviews, and
experiments show that people prefer sexually
faithful mates, all else being equal? Yes, al-
though males are attracted to promiscuous fe-
males as potential short-term mates (Oliver
and Sedikides 1992; Schmitt et al. 2001), nei-
ther sex respects high levels of promiscuity in
potential long-term mates (Marks and Fraley
2005). Also, jealousy research shows that men
and women across cultures react very nega-
tively to sexual infidelity, yet are highly moti-
vated to discover it (Buss 2000). Do people
verbally derogate their sexual rivals for being
unfaithful? Yes, moral derogation of sexual ri-
vals (using morally charged terms such as
skank, slut, or sleazeball) is a common mating
tactic (Schmitt and Buss 1996; Bleske and
Shackelford 2001). Do courting people often
display their likely future fidelity to potential
mates? Yes, lovers typically make impassioned,
adaptively self-deceptive declarations of infi-
nite, eternal, exclusive love.
If the moral trait shows most of these adap-
tive mating-related features, then the re-
searcher might progress to phenotypic studies
of sexual fidelity as an individual-differences
dimension. Are there stable individual differ-
ences in the likelihood of fidelity versus infi-
delity, or is infidelity driven entirely by chance
and opportunity? Research on the opposite of
fidelity, the personality construct of “sociosex-
uality” (interest in promiscuous, short-term, or
extra-pair mating), confirms there are stable
individual differences in this trait dimension
(Gangestad and Simpson 2000). Is fidelity pos-
itively correlated with other desirable moral
virtues and fitness-related traits, such as kind-
ness, conscientiousness, agreeableness, mental
health, longevity, and intelligence? This ques-
tion becomes complicated, since individuals of
higher mate value will be sought more often
for short-term, extra-pair copulations, and
thus will be tempted by more opportunities for
infidelity (Gangestad and Simpson 2000).
Mate value and infidelity opportunities would
have to be carefully statistically controlled in
studies of fidelity’s correlations with other
moral virtues.
The genetic studies of infidelity would be
the most difficult to perform, but often the
most informative. Would twin and adoption
studies show that the propensity to infidelity
versus relationship stability is heritable? (Ac-
tually, they do already: Cherkas et al. 2004;
Lyons et al. 2004). After controlling for over-
all mate value, would higher genetic in-
breeding and paternal age reduce fidelity,
suggesting a role for partially recessive harm-
ful mutations in driving infidelity? Would
one find positive genetic correlations be-
tween the tendency to fidelity and the mate
preference for fidelity, as might be expected
if there has been sexual selection for the trait?
Clearly, the sexual selection hypothesis for
moral virtues is eminently testable. However,
it requires new ways of thinking about costly
signaling and sexually selected adaptations
that are now commonly understood by evo-
lutionary biologists, but that have been slow
to permeate evolutionary psychology. In par-
ticular, evolutionary psychology still empha-
sizes criteria such as low cost, high efficiency,
high modularity, low phenotypic variance,
low heritability, and reliable development
to identify psychological adaptations (e.g.,
Tooby and Cosmides 1990a,b; Andrews et al.
2002). These criteria are often appropriate
for survival adaptations, but not for sexually
attractive signals (Miller 2000b,c; McAndrew
2002). For naturalistic moral philosophy to
benefit most from recent evolutionary in-
sights, it must not only increase its apprecia-
tion of sexual selection’s power, but also ex-
pand its understanding of how to analyze
costly signaling adaptations by using, refin-
ing, and expanding the 12 expected features
of moral virtues listed above.
Implications for Normative Ethics
Normative ethics is supposed to help us dis-
tinguish right from wrong and good from
evil. It tries to achieve a “reflective equilib-
rium” between (1) possible universal moral
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116 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
principles, (2) derived moral implications
that would apply in particular situations, and
(3) human moral intuitions that react to
those principles, implications, and situations
(Daniels 1996). The hope is that normative
ethicists can articulate a set of universal, co-
herent, consistent moral principles that yield
intuitively acceptable moral implications
across all possible situations, thereby embody-
ing a rational distillation of human moral sen-
sibility. Almost all moral philosophers accept
that this is the legitimate goal of normative
ethics, though debates still rage between con-
sequentialists and deontologists, act ethicists
and virtue ethicists. However, if moral virtues
rose through sexual selection, this reflective-
equilibrium approach to normative ethics will
probably continue to fail, as it has for 2,500
years, for at least three reasons.
First, suppose human moral intuitions
evolved as part of our person-perception sys-
tem for inferring stable, morally valenced,
mating-relevant personality traits from ob-
servable behaviors. If so, moral philosophers
are trying to do ethical alchemy: trying to re-
fine unconscious, domain-specific, person-
perception adaptations (the base metal) into
verbally articulated, domain-general, univer-
sal moral principles (the gold). This is likely
to be an uphill battle. One problem is that we
seem to have a dual-process system of moral
judgment, as in so much of person percep-
tion and social attribution— our “hot” moral
intuitions usually precede “cool” moral rea-
soning (Haidt 2001). These hot moral judg-
ments are often driven by morally judgmental
emotions that figure prominently in sexual
relationships, such as anger (Ellis and Mala-
muth 2000), disgust (Rozin et al. 1999), jeal-
ousy (Buss 2000), embarrassment (Keltner
and Buswell 1997), shame (Tangney 1999),
and gratitude (McCullough et al. 2001). Our
moral judgments may also arise from im-
plicit social attitudes that may be difficult to
consciously articulate into normative-ethical
principles (see Greenwald et al. 2002).
Second, if our person-perception system re-
lies on social-inference heuristics that are fast,
frugal, and pragmatic, then our moral judg-
ments will often violate procedural norms of
rationality derived from logic, statistics, and
rational choice theory, such as consistency,
transitivity, and completeness (Gigerenzer
and Todd 1999). There are deep decision-
theoretic reasons why it may be impossible to
derive a set of consistent, coherent moral
preferences from the operation of such
social-inference heuristics. To know whether
this is a fatal objection to the reflective equi-
librium approach, we need to learn a lot
more about moral judgment heuristics in the
context of person-perception research (e.g.,
Funder 2004; Haselton and Nettle 2006).
Third, human moral intuitions evolved to
assess people’s stable moral virtues in ances-
trally typical, fitness-relevant situations, and
to guide ancestrally feasible forms of social
response such as forming friendships or
mateships, gossiping about liars, punishing
cheaters, or ostracizing psychopaths. There is
no reason to expect our moral intuitions to
show consistent, logically defensible reactions
to evolutionarily novel moral dilemmas that
involve isolated, hypothetical, behavioral acts
by unknown strangers who cannot be re-
warded or punished through any normal so-
cial primate channels.
For example, we often seem cognitively
paralyzed by many current debates in repro-
ductive bioethics (Petrinovich 1995). How
should we feel about abortion, sperm and egg
donation, surrogate pregnancy, human clon-
ing, genetic testing, or genetic enhancement?
Different framings of these issues will activate
different domain-specific moral intuitions
(Haidt 2001). This is precisely why rhetorical
metaphors are effective in such moral de-
bates. For example, genetic enhancement
may seem perniciously fascist if we view it as
a limited resource that will be appropriated
by the powerful for their nefarious ends, or it
may seem democratically liberating if we view
it as a natural extension of good genes mate
choice for those whose own suboptimal mate
value precludes getting good genes from a
willing partner (Miller 2000a). Is there any
neutral, rational position from which we can
judge such issues without assimilating them
to one or another of our domain-specific
moral intuitions? Probably not. Rational de-
cision making depends upon subjective utility
functions that must be supplied either by the
genetic imitation of ancestral utilities (gut in-
stinct), or the social imitation of peer utilities
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June 2007 117SEXUAL SELECTION FOR MORAL VIRTUES
(learning, social norms). Gut moral instincts
will be mute or misleading guides to moral
dilemmas raised by new technology, and
moral conformity to peer opinion will be bi-
ased by vested political, corporate, and media
interests that define the current ethical issues
in their own interests.
Basically, there is no compelling reason to
think that our moral intuitions have any true
normative credibility as guides to genuinely
moral behavior. Of course, there may be evo-
lutionary reasons to expect that species-typi-
cal human moral intuitions would tend to
maximize inclusive fitness under ancestral
conditions. However, that is quite different
from claiming that they are normatively jus-
tifiable in any broader sense. For example,
Singer (1995) has made some compelling but
counterintuitive arguments concerning ani-
mal rights, euthanasia, and infanticide; in
such cases, it seems impossible to reach a re-
flective equilibrium between our gut moral
instincts and our scientifically informed nor-
mative judgments.
This is not to say that rationally adjudicated
principles of normative ethics are impossible
to achieve—only that most humans are likely
to find such principles emotionally uncom-
pelling and cognitively incomprehensible.
The analogy to higher mathematics may be
instructive. Humans did not evolve cognitive
capacities for manipulating abstract symbol
systems to prove difficult mathematical theo-
rems. Only a tiny minority of humans with
extraordinarily high intelligence can do so,
given years of rigorous training. When Ter-
ence Tao was awarded the 2006 Fields Medal
in mathematics for his contributions to par-
tial differential equations, combinatorics,
harmonic analysis, and additive number the-
ory, the popular science press could not hope
to convey the substance of his contributions
to these areas. They could only hint at the
magnitude of his genius, by mentioning that
Tao was promoted to full professor at UCLA
at age 24. Of course, there are a few thousand
mathematicians in the world who can under-
stand Tao’s work and reach a consensus about
its creativity, but to ordinary people, good
harmonic analysis work is indistinguishable
from bad harmonic analysis work. Normative
ethics seems likely, at best, to become a dis-
cipline like higher mathematics—a small
world of like-minded geniuses pursuing con-
sensual moral truths that remain forever be-
yond the moral imaginations of most hu-
mans.
In light of these problems, consider two dif-
ferent forms of a typical normative-ethics
question. Abstract form: Is it morally right to
assassinate a genocidal war criminal? (Per-
haps, many have praised the attempted assas-
sination of Adolf Hitler by Colonel Claus von
Stauffenberg on July 20, 1944). Personal
form: Suppose there is a 21st century head of
state, who ordered his country into a fraud-
ulent and illegal war that resulted in thou-
sands of needless civilian casualties, but who
is almost certain to avoid accountability to the
International Criminal Court in The Hague.
Is it morally right for a woman to feel sexually
attracted to a man who succeeded in killing
the wicked head of state with a single head
shot from a Barrett M82A1 .50-caliber sniper
rifle at 800 meters on a windy day? The per-
sonal form is much more specific about the
identities of the moral judgment-maker, the
morally-judged individual, the civilian vic-
tims, the nature of the assassination, and the
fitness relevant, sociosexual implications of
the moral judgment. These details should
and do matter in making adaptive mate-
choice judgments about the moral virtues of
snipers. A woman who knows her ordnance
might admire the sniper’s good genes indi-
cators, such as his resourcefulness (the
M82A1 costs $7,775 retail), his physical con-
dition (the 13 kilogram, 145 cm-long rifle is
hard to carry), and his marksmanship (the
800 meter head shot was near the rifle’s max-
imum effective antipersonnel range of 1000
meters). Yet, she may equally worry about his
good parent indicators: his vigilante action
may reveal psychopathy, paranoid schizo-
phrenia, bipolar disorder, impulsiveness,
fame-seeking narcissism, or high-risk sensa-
tion seeking (Meloy et al. 2004). She can
only tell by gathering further information
about his virtues, both moral and nonmoral,
which is a central function of prolonged hu-
man courtship.
acknowledgments
For helpful feedback on these ideas, thanks to Paul
Andrews, Rosalind Arden, Joseph Bilbulia, James
Name /jlb_qrb822_3060012/820202/Mp_118 03/07/2007 04:48PM Plate # 0 pg 118 # 22
118 Volume 82THE QUARTERLY REVIEW OF BIOLOGY
Boone, Oliver Curry, Dylan Evans, Steve Gangestad,
Walter Sinnott-Armstrong, Peter Todd, and an anon-
ymous reviewer. Special thanks to Lars Penke for ex-
cellent suggestions on shortening this paper.
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... We can distinguish between two types of selective processes on the individual level: (a) adaptation to the successful interaction between the individual and its natural environment and (b) social forms of selection involving adaptation to the successful interaction between the individual and its conspecifics (cf. (Miller, 2007)). ...
... Box 2: Why some females are choosy producing differences between groups due to four properties (Miller, 2000): (1) sexual selection is to some extent independent from the natural environment, (2) sexual selection can be a stronger and more precise force than adaptation processes due to the interaction with the natural environment, (3) anything perceptible can be a target of sexual selection, and-most importantly-(4) sexual selection can begin by chance and then escalate in a runaway process (Fisher, 1930) (Jones & Henshaw, 2019), thereby influencing the reproductive strategy of both sexes (Miller, 2007) and the fitness of the group (Cally, et al., 2017). ...
... On the contrary, I argue that if there are variations in predominant female choice criteria between groups and this variation in female choice produces differences in group fitness, then the female choice criteria will be selected on the group level for producing groups that displace others (cf. (Miller, 2007)). ...
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Humans distinguish themselves from other primates by their cognitive abilities and social structure. This paper aims to show that the distinctive structure of human societies is the foundation of the evolution of human cognition and not merely a result of already human-like existing individuals coming together. It is suggested that, triggered by a geological event, the social structure of our ancestors fundamentally changed to an evolutionary configuration where-driven by a novel reputation economy and its non-cognitive functional precursor-culture and the brain coevolved in a runaway process. It is argued that many distinctive human traits-such as language, human cooperation, theory of mind, epistemic vigilance, overimitation, the desire for recognition, sensitivity to values, social emotions, and the notion of moral agency-can be explained by an adaptation to the novel evolutionary configuration, as individuals needed to communicate and understand past actions and how they were valued in a given society. A gradual scenario is presented which explains how the system developed from a configuration in which absent actions were instinctively and unconsciously displayed using natural signs to a social system in which knowledge of past actions was transmitted by stories and translated into reputation and social status-making both cooperative behavior and linguistic communication reproductively beneficial. This major transition in evolution changed the relation between social status and the exploitation of the environment in a way that can eventually unite the hunting hypothesis and the social intelligence hypothesis of human evolution.
... itness indicator that showcases good genes, good health, and good psychological functioning (G. F. Miller, 2000;Prokosch et al., 2009). It should, therefore, be both desirable and detectable in potential mates. Similar arguments have been made for creativity (G. F. Miller, 2000;Prokosch et al., 2009) and emotional competence (Gignac & Callis, 2020;G. F. Miller, 2007). The high relevance of interpersonal perception for a species as social as humans likely led us to be good judges of others (Vazire & Carlson, 2011). And indeed, ability estimates by others can be similarly or sometimes even slightly more accurate than self-estimates (e.g., Borkenau & Liebler, 1993;Denissen et al., 2011) and show releva ...
... In line with this, another speed-dating study reported an accuracy of intelligence estimates of only around 0.1 (Driebe et al., 2021). This might be unexpected at the first moment, given that person perception tends to be particularly accurate in pragmatically relevant domains (Gill & Swann, 2004) and that evolution-based theories (e.g., G. F. Miller, 2000Miller, , 2007 and crosscultural studies (e.g., Buss et al., 1990;Walter et al., 2020) suggest that intelligence, creativity, and emotional competence are important in mating contexts. However, current findings-based on data reported here and another speed-dating study (Driebe et al., 2021)-suggest that these abilities might play a lesser role for initial attraction. ...