This means two things. First, our thoughts,
feelings, and behavior are produced not only by our individual
experiences and environment in our own lifetime but also
by what happened to our ancestors millions of years ago.
Second, our thoughts, feelings, and behavior are shared,
to a large extent, by all men or women, despite seemingly
large cultural differences.
Human behavior is a product both of our innate
human nature and of our individual experience and environment.
In this article, however, we emphasize biological influences
on human behavior, because most social scientists explain
human behavior as if evolution stops at the neck and as
if our behavior is a product almost entirely of environment
and socialization. In contrast, evolutionary psychologists
see human nature as a collection of psychological adaptations
that often operate beneath conscious thinking to solve problems
of survival and reproduction by predisposing us to think
or feel in certain ways. Our preference for sweets and fats
is an evolved psychological mechanism. We do not consciously
choose to like sweets and fats; they just taste good to
The implications of some of the ideas in this
article may seem immoral, contrary to our ideals, or offensive.
We state them because they are true, supported by documented
scientific evidence. Like it or not, human nature is simply
not politically correct.
Men like blond bombshells (and women want to look like
Long before TV—in 15th- and 16th-
century Italy, and possibly two millennia ago—women
were dying their hair blond. A recent study shows that
in Iran, where exposure to Western media and culture
is limited, women are actually more concerned with their
body image, and want to lose more weight, than their
American counterparts. It is difficult to ascribe the
preferences and desires of women in 15th-century Italy
and 21st-century Iran to socialization by media.
Women's desire to look like Barbie—young
with small waist, large breasts, long blond hair, and
blue eyes—is a direct, realistic, and sensible
response to the desire of men to mate with women who
look like her. There is evolutionary logic behind each
of these features.
Men prefer young women in part because
they tend to be healthier than older women. One accurate
indicator of health is physical attractiveness; another
is hair. Healthy women have lustrous, shiny hair, whereas
the hair of sickly people loses its luster. Because
hair grows slowly, shoulder-length hair reveals several
years of a woman's health status.
Men also have a universal preference for
women with a low waist-to-hip ratio. They are healthier
and more fertile than other women; they have an easier
time conceiving a child and do so at earlier ages because
they have larger amounts of essential reproductive hormones.
Thus men are unconsciously seeking healthier and more
fertile women when they seek women with small waists.
Until very recently, it was a mystery
to evolutionary psychology why men prefer women with
large breasts, since the size of a woman's breasts has
no relationship to her ability to lactate. But Harvard
anthropologist Frank Marlowe contends that larger, and
hence heavier, breasts sag more conspicuously with age
than do smaller breasts. Thus they make it easier for
men to judge a woman's age (and her reproductive value)
by sight—suggesting why men find women with large
breasts more attractive.
Alternatively, men may prefer women with
large breasts for the same reason they prefer women
with small waists. A new study of Polish women shows
that women with large breasts and tight waists have
the greatest fecundity, indicated by their levels of
two reproductive hormones (estradiol and progesterone).
Blond hair is unique in that it changes
dramatically with age. Typically, young girls with light
blond hair become women with brown hair. Thus, men who
prefer to mate with blond women are unconsciously attempting
to mate with younger (and hence, on average, healthier
and more fecund) women. It is no coincidence that blond
hair evolved in Scandinavia and northern Europe, probably
as an alternative means for women to advertise their
youth, as their bodies were concealed under heavy clothing.
Women with blue eyes should not be any
different from those with green or brown eyes. Yet preference
for blue eyes seems both universal and undeniable—in
males as well as females. One explanation is that the
human pupil dilates when an individual is exposed to
something that she likes. For instance, the pupils of
women and infants (but not men) spontaneously dilate
when they see babies. Pupil dilation is an honest indicator
of interest and attraction. And the size of the pupil
is easiest to determine in blue eyes. Blue-eyed people
are considered attractive as potential mates because
it is easiest to determine whether they are interested
in us or not.
The irony is that none of the above is
true any longer. Through face-lifts, wigs, liposuction,
surgical breast augmentation, hair dye, and color contact
lenses, any woman, regardless of age, can have many
of the key features that define ideal female beauty.
And men fall for them. Men can cognitively understand
that many blond women with firm, large breasts are not
actually 15 years old, but they still find them attractive
because their evolved psychological mechanisms are fooled
by modern inventions that did not exist in the ancestral
Humans are naturally polygamous
The history of western civilization aside,
humans are naturally polygamous. Polyandry (a marriage
of one woman to many men) is very rare, but polygyny
(the marriage of one man to many women) is widely practiced
in human societies, even though Judeo-Christian traditions
hold that monogamy is the only natural form of marriage.
We know that humans have been polygynous throughout
most of history because men are taller than women.
Among primate and nonprimate species,
the degree of polygyny highly correlates with the degree
to which males of a species are larger than females.
The more polygynous the species, the greater the size
disparity between the sexes. Typically, human males
are 10 percent taller and 20 percent heavier than females.
This suggests that, throughout history, humans have
been mildly polygynous.
Relative to monogamy, polygyny creates
greater fitness variance (the distance between the "winners"
and the "losers" in the reproductive game) among males
than among females because it allows a few males to
monopolize all the females in the group. The greater
fitness variance among males creates greater pressure
for men to compete with each other for mates. Only big
and tall males can win mating opportunities. Among pair-bonding
species like humans, in which males and females stay
together to raise their children, females also prefer
to mate with big and tall males because they can provide
better physical protection against predators and other
In societies where rich men are much richer
than poor men, women (and their children) are better
off sharing the few wealthy men; one-half, one-quarter,
or even one-tenth of a wealthy man is still better than
an entire poor man. As George Bernard Shaw puts it,
"The maternal instinct leads a woman to prefer a tenth
share in a first-rate man to the exclusive possession
of a third-rate one." Despite the fact that humans are
naturally polygynous, most industrial societies are
monogamous because men tend to be more or less equal
in their resources compared with their ancestors in
medieval times. (Inequality tends to increase as society
advances in complexity from hunter-gatherer to advanced
agrarian societies. Industrialization tends to decrease
the level of inequality.)
Most women benefit from polygyny, while most men benefit
When there is resource inequality among
men—the case in every human society—most
women benefit from polygyny: women can share a wealthy
man. Under monogamy, they are stuck with marrying a
The only exceptions are extremely desirable
women. Under monogamy, they can monopolize the wealthiest
men; under polygyny, they must share the men with other,
less desirable women. However, the situation is exactly
opposite for men. Monogamy guarantees that every man
can find a wife. True, less desirable men can marry
only less desirable women, but that's much better than
not marrying anyone at all.
Men in monogamous societies imagine they
would be better off under polygyny. What they don't
realize is that, for most men who are not extremely
desirable, polygyny means no wife at all, or, if they
are lucky, a wife who is much less desirable than one
they could get under monogamy.
Most suicide bombers are Muslim
According to the Oxford University sociologist
Diego Gambetta, editor of Making Sense of Suicide
Missions, a comprehensive history of this troubling
yet topical phenomenon, while suicide missions are not
always religiously motivated, when religion is involved,
it is always Muslim. Why is this? Why is Islam
the only religion that motivates its followers to commit
The surprising answer from the evolutionary
psychological perspective is that Muslim suicide bombing
may have nothing to do with Islam or the Koran (except
for two lines in it). It may have nothing to do with
the religion, politics, the culture, the race, the ethnicity,
the language, or the region. As with everything else
from this perspective, it may have a lot to do with
sex, or, in this case, the absence of sex.
What distinguishes Islam from other major
religions is that it tolerates polygyny. By allowing
some men to monopolize all women and altogether excluding
many men from reproductive opportunities, polygyny creates
shortages of available women. If 50 percent of men have
two wives each, then the other 50 percent don't get
any wives at all.
So polygyny increases competitive pressure
on men, especially young men of low status. It therefore
increases the likelihood that young men resort to violent
means to gain access to mates. By doing so, they have
little to lose and much to gain compared with men who
already have wives. Across all societies, polygyny makes
men violent, increasing crimes such as murder and rape,
even after controlling for such obvious factors as economic
development, economic inequality, population density,
the level of democracy, and political factors in the
However, polygyny itself is not a sufficient
cause of suicide bombing. Societies in sub-Saharan Africa
and the Caribbean are much more polygynous than the
Muslim nations in the Middle East and North Africa.
And they do have very high levels of violence. Sub-Saharan
Africa suffers from a long history of continuous civil
wars—but not suicide bombings.
The other key ingredient is the promise
of 72 virgins waiting in heaven for any martyr in Islam.
The prospect of exclusive access to virgins may not
be so appealing to anyone who has even one mate on earth,
which strict monogamy virtually guarantees. However,
the prospect is quite appealing to anyone who faces
the bleak reality on earth of being a complete reproductive
It is the combination of polygyny and
the promise of a large harem of virgins in heaven that
motivates many young Muslim men to commit suicide bombings.
Consistent with this explanation, all studies of suicide
bombers indicate that they are significantly younger
than not only the Muslim population in general but other
(nonsuicidal) members of their own extreme political
organizations like Hamas and Hezbollah. And nearly all
suicide bombers are single.
Having sons reduces the likelihood of divorce
Sociologists and demographers have discovered
that couples who have at least one son face significantly
less risk of divorce than couples who have only daughters.
Why is this?
Since a man's mate value is largely determined
by his wealth, status, and power—whereas a woman's
is largely determined by her youth and physical attractiveness—the
father has to make sure that his son will inherit his
wealth, status, and power, regardless of how much or
how little of these resources he has. In contrast, there
is relatively little that a father (or mother) can do
to keep a daughter youthful or make her more physically
The continued presence of (and investment
by) the father is therefore important for the son, but
not as crucial for the daughter. The presence of sons
thus deters divorce and departure of the father from
the family more than the presence of daughters, and
this effect tends to be stronger among wealthy families.
Beautiful people have more daughters
It is commonly believed that whether parents
conceive a boy or a girl is up to random chance. Close,
but not quite; it is largely up to chance. The normal
sex ratio at birth is 105 boys for every 100 girls.
But the sex ratio varies slightly in different circumstances
and for different families. There are factors that subtly
influence the sex of an offspring.
One of the most celebrated principles
in evolutionary biology, the Trivers-Willard hypothesis,
states that wealthy parents of high status have more
sons, while poor parents of low status have more daughters.
This is because children generally inherit the wealth
and social status of their parents. Throughout history,
sons from wealthy families who would themselves become
wealthy could expect to have a large number of wives,
mistresses and concubines, and produce dozens or hundreds
of children, whereas their equally wealthy sisters can
have only so many children. So natural selection designs
parents to have biased sex ratio at birth depending
upon their economic circumstances—more boys if
they are wealthy, more girls if they are poor. (The
biological mechanism by which this occurs is not yet
This hypothesis has been documented around
the globe. American presidents, vice presidents, and
cabinet secretaries have more sons than daughters. Poor
Mukogodo herders in East Africa have more daughters
than sons. Church parish records from the 17th and 18th
centuries show that wealthy landowners in Leezen, Germany,
had more sons than daughters, while farm laborers and
tradesmen without property had more daughters than sons.
In a survey of respondents from 46 nations, wealthy
individuals are more likely to indicate a preference
for sons if they could only have one child, whereas
less wealthy individuals are more likely to indicate
a preference for daughters.
The generalized Trivers-Willard hypothesis
goes beyond a family's wealth and status: If parents
have any traits that they can pass on to their children
and that are better for sons than for daughters, then
they will have more boys. Conversely, if parents have
any traits that they can pass on to their children and
that are better for daughters, they will have more girls.
Physical attractiveness, while a universally
positive quality, contributes even more to women's reproductive
success than to men's. The generalized hypothesis would
therefore predict that physically attractive parents
should have more daughters than sons. Once again, this
is the case. Americans who are rated "very attractive"
have a 56 percent chance of having a daughter for their
first child, compared with 48 percent for everyone else.
What Bill Gates and Paul McCartney have in common with
For nearly a quarter of a century, criminologists
have known about the "age-crime curve." In every society
at all historical times, the tendency to commit crimes
and other risk-taking behavior rapidly increases in
early adolescence, peaks in late adolescence and early
adulthood, rapidly decreases throughout the 20s and
30s, and levels off in middle age.
This curve is not limited to crime. The
same age profile characterizes every quantifiable human
behavior that is public (i.e., perceived by many potential
mates) and costly (i.e., not affordable by all sexual
competitors). The relationship between age and productivity
among male jazz musicians, male painters, male writers,
and male scientists—which might be called the
"age-genius curve"—is essentially the same as
the age-crime curve. Their productivity—the expressions
of their genius—quickly peaks in early adulthood,
and then equally quickly declines throughout adulthood.
The age-genius curve among their female counterparts
is much less pronounced; it does not peak or vary as
much as a function of age.
Paul McCartney has not written a hit song
in years, and now spends much of his time painting.
Bill Gates is now a respectable businessman and philanthropist,
and is no longer a computer whiz kid. J.D. Salinger
now lives as a total recluse and has not published anything
in more than three decades. Orson Welles was a mere
26 when he wrote, produced, directed, and starred in
A single theory can explain the productivity
of both creative geniuses and criminals over the life
course: Both crime and genius are expressions of young
men's competitive desires, whose ultimate function in
the ancestral environment would have been to increase
In the physical competition for mates,
those who are competitive may act violently toward their
male rivals. Men who are less inclined toward crime
and violence may express their competitiveness through
their creative activities.
The cost of competition, however, rises
dramatically when a man has children, when his energies
and resources are put to better use protecting and investing
in them. The birth of the first child usually occurs
several years after puberty because men need some time
to accumulate sufficient resources and attain sufficient
status to attract their first mate. There is therefore
a gap of several years between the rapid rise in the
benefits of competition and similarly rapid rise in
its costs. Productivity rapidly declines in late adulthood
as the costs of competition rise and cancel its benefits.
These calculations have been performed
by natural and sexual selection, so to speak, which
then equips male brains with a psychological mechanism
to incline them to be increasingly competitive immediately
after puberty and make them less competitive right after
the birth of their first child. Men simply do not feel
like acting violently, stealing, or conducting additional
scientific experiments, or they just want to settle
down after the birth of their child but they do not
know exactly why.
The similarity between Bill Gates, Paul
McCartney, and criminals—in fact, among all men
throughout evolutionary history—points to an important
concept in evolutionary biology: female choice.
Women often say no to men. Men have had
to conquer foreign lands, win battles and wars, compose
symphonies, author books, write sonnets, paint cathedral
ceilings, make scientific discoveries, play in rock
bands, and write new computer software in order to impress
women so that they will agree to have sex with them.
Men have built (and destroyed) civilization in order
to impress women, so that they might say yes.
The midlife crisis is a myth—sort of
Many believe that men go through a midlife
crisis when they are in middle age. Not quite. Many
middle-aged men do go through midlife crises, but it's
not because they are middle-aged. It's because their
wives are. From the evolutionary psychological perspective,
a man's midlife crisis is precipitated by his wife's
imminent menopause and end of her reproductive career,
and thus his renewed need to attract younger women.
Accordingly, a 50-year-old man married to a 25-year-old
woman would not go through a midlife crisis, while a
25-year-old man married to a 50-year-old woman would,
just like a more typical 50-year-old man married to
a 50-year-old woman. It's not his midlife that matters;
it's hers. When he buys a shiny-red sports car, he's
not trying to regain his youth; he's trying to attract
young women to replace his menopausal wife by trumpeting
his flash and cash.
It's natural for politicians to risk everything for
an affair (but only if they're male)
On the morning of January 21, 1998, as
Americans woke up to the stunning allegation that President
Bill Clinton had had an affair with a 24-year-old White
House intern, Darwinian historian Laura L. Betzig thought,
"I told you so." Betzig points out that while powerful
men throughout Western history have married monogamously
(only one legal wife at a time), they have always mated
polygynously (they had lovers, concubines, and female
slaves). With their wives, they produced legitimate
heirs; with the others, they produced bastards. Genes
make no distinction between the two categories of children.
As a result, powerful men of high status
throughout human history attained very high reproductive
success, leaving a large number of offspring (legitimate
and otherwise), while countless poor men died mateless
and childless. Moulay Ismail the Bloodthirsty, the last
Sharifian emperor of Morocco, stands out quantitatively,
having left more offspring—1,042—than anyone
else on record, but he was by no means qualitatively
different from other powerful men, like Bill Clinton.
The question many asked in 1998—"Why
on earth would the most powerful man in the world jeopardize
his job for an affair with a young woman?"—is,
from a Darwinian perspective, a silly one. Betzig's
answer would be: "Why not?" Men strive to attain political
power, consciously or unconsciously, in order to have
reproductive access to a larger number of women. Reproductive
access to women is the goal, political office but one
means. To ask why the President of the United States
would have a sexual encounter with a young woman is
like asking why someone who worked very hard to earn
a large sum of money would then spend it.
What distinguishes Bill Clinton is not
that he had extramarital affairs while in office—others
have, more will; it would be a Darwinian puzzle if they
did not—what distinguishes him is the fact that
he got caught.
Men sexually harass women because they are not sexist
An unfortunate consequence of the ever-growing
number of women joining the labor force and working
side by side with men is the increasing number of sexual
harassment cases. Why must sexual harassment be a necessary
consequence of the sexual integration of the workplace?
Psychologist Kingsley R. Browne identifies
two types of sexual harassment cases: the quid pro quo
("You must sleep with me if you want to keep your job
or be promoted") and the "hostile environment" (the
workplace is deemed too sexualized for workers to feel
safe and comfortable). While feminists and social scientists
tend to explain sexual harassment in terms of "patriarchy"
and other ideologies, Browne locates the ultimate cause
of both types of sexual harassment in sex differences
in mating strategies.
Studies demonstrate unequivocally that
men are far more interested in short-term casual sex
than women. In one now-classic study, 75 percent of
undergraduate men approached by an attractive female
stranger agreed to have sex with her; none of the women
approached by an attractive male stranger did. Many
men who would not date the stranger nonetheless agreed
to have sex with her.
The quid pro quo types of harassment are
manifestations of men's greater desire for short-term
casual sex and their willingness to use any available
means to achieve that goal. Feminists often claim that
sexual harassment is "not about sex but about power;"
Browne contends it is both—men using power to
get sex. "To say that it is only about power makes no
more sense than saying that bank robbery is only about
guns, not about money."
Sexual harassment cases of the hostile-environment
variety result from sex differences in what men and
women perceive as "overly sexual" or "hostile" behavior.
Many women legitimately complain that they have been
subjected to abusive, intimidating, and degrading treatment
by their male coworkers. Browne points out that long
before women entered the labor force, men subjected
each other to such abusive, intimidating, and degrading
Abuse, intimidation, and degradation are
all part of men's repertoire of tactics employed in
competitive situations. In other words, men are not
treating women differently from men—the definition
of discrimination, under which sexual harassment legally
falls—but the opposite: Men harass women precisely
because they are not discriminating between men and