The Dangerous Passion: Why Jealousy Is as Necessary as Love and Sex (26 page)

A long-term study of 2,033 married couples supports this
interpretation. Early in the study, each person was asked about their perceived
marital alternatives. “These days, there are many uncertainties, and marriages
break up unexpectedly. While it may be an unlikely event, I would like to ask you
a few questions about how you would get along on your own if your marriage
ended in divorce or separation. How difficult do you think it would be for you
to find another (husband/wife)? Would it be very difficult, somewhat difficult,
not too difficult, or not difficult at all?” The researchers also gathered
information about each participant’s income. The results dovetailed with those
of our study. Women who perceived that they would have difficulty replacing
their current partner were more likely to remain married if their husband
cheated, whereas women who perceived their mating alternatives as more
promising were more likely to get divorced. Furthermore, women who had higher
levels of income were more likely to get divorced than women with less personal
income.

Divorce is not an inevitable consequence of sexual infidelity.
The odds depend heavily on the relative desirability of the partners. Those who
are more desirable relative to their current mate have better options
elsewhere, and hence are more likely to dump a cheating partner. With this
background of the secrets and lies of married life, we now turn to a more
targeted question: why women stray.

Why Women Have Affairs

You never seem to want to do anything with me anymore . . .
When I try to talk to you you never listen, you just put it down to my
hormones, or it’s a woman’s thing. I felt alone, insecure, unattractive, and
stupid, lately, that’s how you make me feel. Robert makes me feel alive, and
sexy, and interesting.

—Kitzinger and Powell,
Engendering Infidelity, 1995

W
OMEN BEAR THE PLEASURES AND
burdens of childbearing. Nine months
of internal gestation is metabolically costly, restricts a woman’s mobility,
and makes her more vulnerable. Women don’t have a choice. No woman can scale
back her investment to, say, four, six, or eight months of pregnancy. Nor can
the man directly share the load. One woman I interviewed declared that she
wished men could carry half of the pregnancy, “preferably the second half!” In
exchange for nine months of a woman’s obligatory investment, the man need put
in as little effort as it takes to complete a single act of sexual
intercourse—an evening, an hour, a few minutes, or even a few seconds. There
are individual differences among men, of course, but the inescapable fact is
that the biology of reproduction is more costly for women.

These fundamental physiological sex differences led to the
evolution of several psychological sex differences; men view sex one way, women
another. Men evolved a more powerful desire for sexual variety, which increased
their chances of impregnating women. Men express a desire for more than four
times as many sex partners in their lifetimes, have more than twice as many
sexual fantasies, more often engage in partner switching during the course of a
single fantasy episode, lower their standards to abysmal levels in casual sex,
let less time elapse before seeking sexual intercourse with a new partner,
spend more time trying to initiate sex, and are more willing to consent to sex
with a total stranger.

So powerful, direct, and obvious are the reproductive benefits
to men who succeed in a quest for sexual variety that scientists have largely
overlooked a fundamental fact about short-term mating: the average number of
sexual partners for men and women who engage in short-term mating, of which
infidelity is a primary variety, must be identical. Every time a man has sex
with a particular woman for the first time, the woman is simultaneously having
sex with that man for the first time. In fact, men could not possibly have
evolved a desire for sexual variety without women who were willing. As noted by
the feminist evolutionist Sarah Hrdy, of the University of California at Davis:
“females . . . potentially determine the direction in which the species will
evolve. For it is the female who is the ultimate arbiter of when she mates and
how often and with whom.”

If men’s desires require willing women, willing women require
benefits. Our ancestral mothers must have reaped advantages sufficiently weighty
to more than exceed all of the treacherous costs of infidelity. Natural
selection could not have forged a female psychology of infidelity if it failed
to carry substantial advantages.

The idea that women are not by nature monogamous makes many men
nervous. Women’s sexual strategies, however, have evolved not for men’s
benefit, not for the good of the group, not even for the good of the species.
Women’s sexual psychology, including their desire to stray, exists today solely
because that’s what benefited ancestral women.

Co-evolution guarantees that women’s sexual desires for men
other than their husbands sometimes will be held in check. Men’s jealousy
drives them to control, sequester, constrain, coerce, restrict, stifle,
isolate, lock up, box out, bind, enslave, encircle, truss, and shackle women. A
man’s jealousy tethers a woman’s sexual strategies, preventing her from
pursuing what is best, evolutionarily speaking, for her.

The principle of co-evolution also dictates that women will not
accept jealous control passively. Over human history, women fought back,
evolving an array of strategies specifically designed to escape men’s control.
Women have evolved concealed or cryptic ovulation most likely to disguise their
time of ovulation, making it more difficult for men to target their
mate-guarding to specific times of the month. But the fact of concealed
ovulation, even if it evolved to escape a husband’s control, does not explain
why women stray. We now have some answers to this enigma.

The logic of the mating market dictates that women will
generally be able to get a more attractive partner for a casual sexual
encounter than for a permanent husband. Attractive men are often willing to
have sex with less desirable women, as long as they do not become encumbered by
entangling commitments. Rock stars and sports stars perfectly illustrate this
logic. They often have groupies for casual sex with no hint of commitment. This
mating market logic leads to a disturbing consequence. Women married to men
matched to their level of desirability will sometimes be tempted to have
affairs with men whom they find sexier than their husbands.

Why risk discovery, ruin a good reputation, and chance
abandonment by having an affair with a man higher than her partner on the mate
value scale? Steve Gangestad and Randy Thornhill proposed one answer: Women can
acquire better genes from higher value extrapair matings than from their
regular mates. Good genes may bring better resistance to disease, increasing
the health and hence survival of their children. Women, of course, don’t think
about these things consciously. Their passions for other partners are blind to
the evolutionary functions that have shaped them. Women just need to find other
men sexy; knowing why is unnecessary.

One indicator of good genes has emerged over the past decade:
symmetry. Humans, like many organisms, show a physical arrangement
characterized by bilateral symmetry. If you draw a line straight down the
middle of your body, starting with your face, the two halves are more or less
mirror images of each other. The “more or less” qualifier is the key, since no
one is perfectly symmetrical. Each of us carries a host of small deviations
from perfect symmetry, ranging from Cindy Crawford’s small mole to Lyle
Lovett’s lopsided grin.

Deviations from symmetry have many causes, but they have been
most strongly linked with two determinants. First, symmetry signals
“developmental stability,” a genetic resistance to pathogens and mutations. A
person who is genetically susceptible to pathogens and mutations will develop a
more lopsided face and body than those who are genetically resistant to
pathogens and mutations. Second, symmetry is a sign of a genetic resistance to
a host of other “environmental insults,” such as extreme temperatures, poor
nutrition in childhood, and exposure to toxins. It is, in short, a genetic
marker of health.

Symmetry can be measured in practically any organism. With
humans, researchers typically take a variety of measurements, such as feet,
ankles, hands, wrists, elbows, and ears. By taking multiple measurements,
researchers achieve a higher level of reliability in their index of actual
symmetry. To study the effects of symmetry on human mating, Gangestad and
Thornhill studied 203 heterosexual couples who had been involved in a romantic
relationship for at least one month. After assuring participants of
confidentiality and anonymity, they questioned each person about whether they
had ever had sex with someone else while in their current relationship. They
also queried participants about whether they had sex with someone else whom
they knew was already married to, or seriously involved with, someone else.
They then applied steel calipers to assess participants’ degree of symmetry,
taking seven measurements from each side of the body.

Gangestad and Thornhill discovered a groundbreaking result.
Women preferentially chose symmetrical men as affair partners. Assuming that
symmetry is a marker for genes for health, women who have affairs appear to
select men who, for genetic reasons, are unusually healthy and whose genes then
make children more healthy and resistant to diseases. Men who are rather
asymmetrical are especially prone to being cuckolded by their more symmetrical
rivals.

How do women “detect” such symmetrical men? The most obvious
answer is simply to look. In extreme cases of asymmetry like Lyle Lovett or
symmetry like Denzel Washington, women merely need to gaze through their own
eyes. But there is a more subtle means by which women can detect
symmetry—through their sense of smell. In an innovative study, Gangestad and
Thornhill asked men who varied in symmetry to wear the same T-shirts for two
days straight without showering or using deodorants. They instructed these men
not to eat any spicy food—no peppers, garlic, onions, and so on. After two
days, they collected the T-shirts, and then brought women into the laboratory
to smell them. The women rated each shirt on how good or bad it smelled. They
were of course not aware of the purpose of the study in advance, nor did they
know the men who had worn the T-shirts. The fascinating finding was that women
judged the T-shirts that had been worn by symmetrical men as more pleasant
smelling, but only if they happened to be in the ovulation phase of their
menstrual cycle. So one clue to the mystery of how women detect men with good
genes lies with the “scent of symmetry.”

Some women pursue a “mixed” mating strategy—ensuring devotion
and investment from one man while acquiring good genes from another. Women
detect the scent of symmetry, prefer that scent when ovulating, and choose more
symmetrical men as affair partners. This may not be good news for lopsided men.
After all, the genes a man is born with are beyond his control, and it may seem
a gross injustice that women are more likely to cheat on these men. But women’s
sexual psychology is designed neither for fairness for nor justice. It is
designed to help women reproduce more effectively, regardless of the pain
inflicted on their partners.

There are two potential criticisms of this reasoning, but they
turn out to crumble under close examination. The first is that modern women
often don’t want to have babies with their lovers, and so one might argue that
the quality of their lover’s genes is irrelevant. Women’s sexual psychology,
however, was forged in an evolutionary furnace lacking birth control. Sex led
to babies regardless of a woman’s conscious desire to reproduce or not.
Ancestral women who had affairs with healthier, more symmetrical men tended to
bear healthier, more symmetrical babies. Modern women have inherited from their
successful ancestors an attraction to these men. The fact that roughly 10
percent of children today have genetic fathers other than their putative
fathers suggests that these internal whisperings continue to operate today in
the modern world.

A second possible objection is: Why wouldn’t women want
symmetrical mates as husbands as well as affair partners? The answer, of
course, is that they should and do. But the economics of the mating market
means that most women are able to attract a more symmetrical man as an affair
partner than as a husband. Some women, in short, are able to get the best of
both worlds—attracting investment from one man while obtaining superior genes
from another.

Men’s obsession with a woman’s physical appearance and sexual
availability results in what many women experience as objectification, or being
treated as “sex objects.” But men don’t hold the monopoly on sexual
objectification. The modern phenomenon of female rock groupies provides a
perfect example. Groupies typically get neither investment nor attention nor
much time from the rock stars whom they seek for sex. As Pamela des Barres
observed in her book
I’m with the Band: Confessions of a Groupie,
a
half-hour “quickie” can make a groupie’s day. Most of these women do not delude
themselves that the male rock star will fall in love with them, have a
relationship with them, or even remember their names in the morning. And they
risk a lot by such brief flings—the loss of their regular boyfriends and the
possibility of contracting sexually transmitted diseases. Why do they do it?

My studies with Heidi Greiling support an intriguing idea known
as the theory of “sexy sons.” Women who mate with sexy men tend to bear sexy
sons. When these “sexy sons” grow up, they attract an above-average number of
women, thereby gaining a genetic edge on the competition. Their mothers gain in
ultimate reproductive success through the increased reproduction of their sexy
sons.