The Dangerous Passion: Why Jealousy Is as Necessary as Love and Sex (13 page)

Reality or illusion? To understand this puzzle, we must return
to the problem of signal detection and probe the psychology of managing errors
of inference.

Humans live in an uncertain world. We rely on our senses to pick
up information from that world, and then use our information processing
capacities to make inferences about the true state of the world. Real threats
to our survival and relationships are not always readily apparent, given the
ambiguity and uncertainty of the information.

Consider a relatively simple problem of walking through the
woods and fleetingly sensing a slithering object scurry underneath some leaves
in the path directly in front of you. There are two possible states of reality:
either there is a dangerous snake in your path or there is not a dangerous
snake in your path. Given the incomplete and uncertain information that you
have perceived, there are also two inferences you could make. There is indeed a
dangerous snake, and you act to avoid it. Or you could conclude that there is
no snake and continue walking down the path. Two states of possible reality,
two possible inferences.

There are also two different ways you could be wrong. You could
believe that there is a snake when in fact no snake exists. Or you could
believe that no snake exists when in fact a venomous rattler is lurking right
in your path. The costs of these two types of errors, however, are vastly different.
In the first case, your belief causes you to incur the trivial metabolic cost
of taking an unnecessary evasive action. By giving a wide berth to the area
that you believe harbors a snake, you have merely gone out of your way a
little, incurring a minor delay in your walk. In the second case, however,
failing to detect a snake that is in fact lurking in your path can cost you
your life. The two ways of being wrong carry substantially different costs.

Now imagine that this scenario not only repeats itself thousands
and thousands of times in your lifetime, but billions and billions of times
over human evolutionary history. Those who made the first kind of mistake
tended to survive, whereas those who made the second kind of mistake tended to
die. As a result, modern humans have descended from a line of ancestors whose
inferences about the uncertain world erred in the direction of believing that
snakes existed more than they do. These can be called “adaptive errors.”

Martie Haselton of the University of Texas at Austin, Todd DeKay
of Franklin and Marshall College, and I have proposed a new theory of error
management (EMT) to explain errors of this sort. According to EMT, evolution by
selection will favor the inference that leads to the less costly error in order
to avoid the more costly error.

Consider uncertainty about whether your romantic partner is
having an affair or is likely to have an affair. Affairs, of course, are almost
always veiled and clandestine. Your partner’s intentions are also hidden from your
inquiring eyes. Who can tell what really lurks in another’s mind? In many ways,
the shroud of uncertainty about a partner’s infidelity is even larger than the
uncertainty about whether danger lurks beneath some rustling leaves. When
signals coming from the world are degraded, muffled, or impoverished, accurate
inferences about reality become horrendously difficult.

To explore just how uncertain people really are about a
partner’s infidelity, Luci Paul and her colleagues at Temple University
surveyed a large sample of young men and women who were involved in long-term
romantic relationships. They asked each person privately whether they were
certain or uncertain that their partner had always been faithful to them. Of
the women polled, 45 percent reported that they were certain their partner had
been totally faithful; 41 percent reported that they were certain their partner
had been unfaithful; and 14 percent reported that they were uncertain about
their partner’s fidelity. Now consider the men’s responses: 36 percent reported
that they were certain their partner had been faithful; 28 percent reported
that they were certain their partner had been unfaithful; and a sizable 36
percent reported uncertainty about whether or not their partner had remained
faithful.

We don’t know precisely why more men than women report
uncertainty. Perhaps women are better than men at detecting a partner’s
infidelity. Perhaps men are less skilled at concealing their own infidelities,
leading to easier detection by women. Perhaps women intentionally keep their
partners in a greater state of uncertainty. Still another possibility is that
women are too confident when they shouldn’t be. All these explanations may
account for a portion of the sex difference. Regardless of the origin of this
sex difference, the key point is this: a substantial fraction of both sexes
report living in a state of uncertainty about their partner’s fidelity.

Now consider the two possible types of errors. You can infer an
infidelity by your partner when none has occurred. Or you can err in believing
that a partner is eternally devoted to you, when in fact your partner
passionately embraces someone else whenever your back is turned. Which error is
more costly? The answer seems clear in light of human evolution. A man who
mistakenly accused his wife of infidelity might trigger a fight with her, which
can be costly, but it might also cause her to increase her displays of loyalty.
A flare-up of jealousy can deter a partner who might otherwise stray. The costs
of making this type of error are relatively low and the benefits are
potentially great.

What about failing to detect an infidelity that has occurred or
might occur? A man who erred by failing to detect a real infidelity may
jeopardize his entire reproductive career. He would incur the many costs of
infidelity, possibly directing his parenting toward another man’s children and
losing all of his wife’s resources. If these events occurred repeatedly over
evolutionary time, according to Error Management Theory, natural selection
would create adaptations designed to err in one direction. The adaptive
solution would be to set a low threshold for inferring a partner’s infidelity,
like a hair trigger on an alarm. In this way, one avoids costs of failing to
detect actual infidelities, even if it means sometimes falsely accusing a
partner of betrayal.

The same logic applies to women. An ancestral woman who erred in
thinking that her husband violated their marriage vows when he did not would
have incurred minor costs. Her neighbor who erred in failing to detect the fact
that her best friend was fornicating with her husband on the side would have
risked the diversion of her husband’s resources and commitments to her
“friend.” The conclusion is clear. According to EMT, selection will favor women
who err on the cautious side, setting a low threshold for inferring a husband’s
infidelity, even at the risk of being wrong some of the time.

Error Management Theory provides a powerful explanation for some
important aspects of the Othello syndrome. It explains why men and women
sometimes have “delusions” that a partner is unfaithful when he or she has
remained loyal. It accounts for why men and women are highly sensitive to
signals of betrayal. It explains why men and women train their eyes laserlike
on rivals who flirt with their partners at parties. But EMT, by itself, does
not explain the particular circumstances in relationships that might cause a
sudden increase in sensitivity to a partner’s possible betrayal. To explain
these psychological shifts, we must turn to the conditions that actually
predict when a partner might stray, starting with sexual problems in the
relationship.

In the animal world, monogamy—mating with a single partner—is
statistically rare. It occurs in only 3 percent of the roughly 4,000 species of
mammals. Biologists long believed that birds differed, and they assumed that
most avian species practice monogamy. DNA fingerprinting technology, however,
has revealed that many bird species previously believed to be monogamous in
fact engage in considerable infidelity. In some species of birds, as many as 40
percent of the chicks turn out to have been sired not by the male at the nest
but by a neighbor a few territories away with whom the female has copulated
clandestinely.

Among the avian species, however, some are more monogamous than
others. Ring doves tend to be one of the most loyal, with quite low cuckoldry
rates. Even so, ring doves experience a “divorce rate” of roughly 25 percent
per season. Why? The major cause of breaking a bonded dove pair is infertility,
the failure to produce offspring. Pairs that produce chicks in one breeding
season remain coupled for the next one; those that fail to reproduce in one
season say good-bye to their partner and seek out a replacement mate.
Difficulty in producing offspring has many causes among both birds and humans,
including occasional sterility of one member or genetic incompatibility of the
couple. But one cause among humans is failure in sexual relations, an event
that can shatter an otherwise harmonious relationship.

When the drug Viagra was introduced, it quickly became the
best-selling prescription drug on the market. Millions of men flooded doctors’
offices demanding it. This outpouring pointed to a problem that plagues
millions of men—the problem of impotence, or erectile dysfunction as it is now
called in the clinical literature. Although large-scale studies are scarce,
available evidence suggests that impotence is not a rare problem. In one study
of British men, for example, 120 out of 284 men, or 42 percent, reported that
they sometimes, often, or always suffered from impotence.

The causes of impotence, of course, are many, ranging from
organic problems such as diabetes and the ravages of age to psychological
sources such as insecurity or performance anxiety. The evolutionary
anthropologist Pierre Van den Berghe of the University of Washington provides a
poignant illustration of the prevalence of men’s anxiety about impotence in the
context of intrasexual competition:

“A boy, a man, on a date, is in competition against an unknown
number of invisible competitors, and in an unpredictable number of different
arenas. He can be deflated and cut down when he makes the date (“I really don’t
anticipate a free evening for several weeks . . .”); when he comes to fetch her
(“I thought you had a convertible . . .”); at the restaurant (“Oh dear, my
dress is too formal for this place; if you had told me . . .”); during dinner
(“You
really
don’t know how to eat an artichoke?”); in conversation
(“Everybody today reads Kierkegaard, of course . . .); when paying (“My father
always tips at least 15 percent . . .”); after dinner (“Is there nothing more
exciting you can suggest? I hate those stuffy little movie houses . . .”); on
the way home (“You surely don’t expect me to get that familiar on a first
date?”); etc. Whatever he does, and which way he does it, he risks the
possibility that his penis may be just a little smaller, just a little less
adept, than someone else’s.”

There is no reason to believe that impotence is a new problem or
merely one that plagues only modern societies. Although rarely studied in a
systematic fashion, many anthropologists who have lived with traditional
peoples from around the globe report cases of impotence. In a survey of the
so-called Standard Sample, a data bank containing information about a wide
variety of cultures, fear of impotence is explicitly reported in 80 percent of
the 40 cultures for which the relevant information is available. The Mehinaku,
an Amazonian tribe of Indians in central Brazil, provides a perfect
illustration. Among the Mehinaku, a man’s sexual failures become matters of
common knowledge, since gossip travels quickly throughout this closed
community. Stories of impotence are reflected in Mehinaku folklore, as
illustrated by the following tale, called “The Armadillo and the Footprint”:

Armadillo left his house to wander about through the woods,
leaving his penis in a basket suspended from the rafters. As he walked along
the path, he saw a beautiful woman: “Hey! Come here, woman. Let’s have sex.”

“Are you good to have sex with, Armadillo?” she asked.

“I make it really delicious,” he replied. Armadillo sat down on
the ground in preparation for sex, looked down between his legs, and discovered
that his penis wasn’t there. “Oh, I forgot my penis,” he said. “I’ll get it.”

Returning to the house, Armadillo was greeted by his wife:
“What’s up?” she inquired.

“Oh, nothing. I was just getting my bow to shoot a bird.”

Retrieving his penis, Armadillo left the house and returned to
look for his girlfriend. “Hey, here I am!” he called. “I brought my penis with
me this time. Wow, now I have an erection! Won’t we have sex, woman?”

Armadillo looked all over for the woman, but she had left. All
he could find was her footprint, and he had sex with that. His penis “ate” the
earth.”

We are amused at the image of the Armadillo leaving his penis
behind, a clear reference to impotence. But impotence is no laughing matter to
the Mehinaku men. Impotent Mehinaku men sometimes lose their mates, who go off
in search of more potent partners. One indication of the seriousness of
impotence among the Mehinaku is the number of names they have for the problem.
These include
maiyala euti,
which means “the penis is tired”;
iaipiripyai
euti,
which means “the penis is ashamed”; and
akama euti,
which
means “the penis dies.”

Another indication of its significance is the extraordinary
effort the men go to in order to find cures for it. These are described with
the term
japujate euti,
which describes procedures designed to “make
the penis angry.” Among the seven cures for impotence are rubbing an entire
needle fish against the penis; rubbing the head and neck of a turtle against
the penis; rubbing bamboo on the penis while chanting
“Yanapi
[penis],
yanapi,
go into the vagina,
yanapi
”; rubbing sap from a
latex-producing plant onto the penis; scarring the penis with the teeth from a
dogfish; and
ejekeki,
which means “breath magic,” consisting of an
individual who blows onto the penis while chanting magical incantations.