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April 18, 2008
Running Head: FIDELITY
TITLE
Fidelity: Why Are People Faithful to Their Mates? Perspectives from Evolutionary
Psychology, Sociology, and Social Psychology
AUTHORS
David A. Frederick
Yael R. Filossof
Kelly Gildersleeve
Natalya C. Maisel
Melissa E. Phuphanich
Joshua C. Poore
Mariana A. Preciado
Darby E. Saxbe
Proud Usahacharoenporn
1. Department of Psychology, University of California, Los Angeles
2. FPR-UCLA Center for Culture, Brain, and Development
3. UCLA Center for Behavior, Evolution, and Culture
4. UCLA Interdisciplinary Relationship Science Program
Correspondence to: David A. Frederick, 1285 Franz Hall, Department of Psychology, 3rd
Floor Mailroom, University of California, Los Angeles, CA 90095-1563. Email:
enderflies1@aol.com.
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Why Are People Faithful to Their Mates? Perspectives from Evolutionary
Psychology, Sociology, and Social Psychology
Cinderella captured the heart of a prince who was interested in marrying her and
only her. Sleeping Beauty married her one true love after he wakened her with a kiss.
Throughout our lives we are taught to find a soul mate and take a vow to be with just one
person “til death do us part.” This belief that we should be emotionally and sexually
faithful to our romantic partners is called “Fidelity.” But are people actually faithful to
their mates? Large national studies in the United States have found that the vast majority
of men (70%-80%) and women (80%-90%) report being faithful to their current partners
(see Figure 1). Why do humans seek monogamous relationships and stay faithful to their
partners? Evolutionary psychologists, social psychologists, and sociologists provide a
variety of different answers to this question.
Evolutionary Psychology
Why Did Fidelity Evolve?
How did the challenges faced by our ancestors influence the way that we think
and behave today? Evolutionary psychologists believe that there are mechanisms in the
human mind that evolved over millions of years. These mechanisms helped us survive
and reproduce more successfully. Evolutionary psychology can help us understand why
humans evolved the tendency to stay faithful to our partners in long-term relationships.
Evolution of Long-term Relationships. The practice of marriage exists in almost
all cultures across the world. Sometimes these marriages are polygynous, which is when
one man marries several women. The vast majority of marriages among humans are
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monogamous, which is when one man marries one woman. Why do most humans form
long-term relationships and why are they typically monogamous?
Comparing the mating systems of humans to non-human animals can give us
some clues to why humans are monogamous. Interestingly, only 4% of mammals form
stable monogamous relationships. Monogamous relationships, however, are very
common among birds. One striking similarity between monogamous mammals and birds
is that they have very fragile babies who need a tremendous amount of care and attention.
Unlike the offspring of most other mammals, human children are very weak for a
relatively long time and must depend on their parents for food, protection, and guidance
for many years. Most mothers have more than one developing child to raise at a time and
this can make parenting very difficult.
The fact that our offspring are so fragile means that males in our ancestral past
who stuck around to help raise their children probably had more children who survived
and reproduced than males who abandoned their children to seek other mates. We can’t
travel back in time to actually observe whether offspring who lived with both parents
survived and reproduced more successfully. Instead, we can look at “hunter-gatherer
societies” where people still live in conditions that are somewhat similar to those of our
ancestors. In these societies, men and women typically form couples and care for the
offspring. Children without fathers are less likely to survive than children with fathers in
many hunter-gatherer societies. Over evolutionary time, men who developed mental
mechanisms that led them to form bonds with a partner and invest in offspring would
have out-reproduced other men.
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Evolution of fidelity. This does not mean that evolutionary psychologists think
that men and women will always be faithful to each other. People in relationships might
cheat on their spouses if they are able to produce more or healthier offspring by having an
affair with someone they are not in a long-term relationship with. Overall, however,
there are many benefits to forming long-term committed relationships in terms of
producing offspring that survive. These benefits would have led to the evolution of a
preference for fidelity in many individuals.
What Evolved Mechanisms Keep People Faithful?
If we believe that the impulse to be faithful is partly the result of evolution, what
are the actual biological and mental mechanisms that keep us faithful? [See also textbox
1]?
Our emotions are good examples of evolved mechanisms. Each emotion has a
clear evolutionary function. Fear makes us run from danger, and anger makes us
confront individuals who have threatened or wronged us. Three emotions are very
important for keeping people faithful to each other: Romantic Jealousy, Guilt, and Love.
Romantic Jealousy can be a powerful emotion that we experience when we are
afraid of losing our partner to someone else. Imagine that your partner was interested in
having sex or dating someone else. How would you feel? Jealousy can make us more
controlling of our partners and we can become consumed with negative thoughts and
worries. But jealousy can also lead us to be more attentive and loving to our partners
when we are afraid we might lose them.
Love may be another powerful force that keeps people faithful to each other.
Evolutionary psychologists think of love as a "commitment device". This commitment
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device keeps us glued to our partner for the long-term and stops us from pursuing
alternative partners who might only be exciting or interesting in the short-term. Love
keeps us focused a single partner rather than spending costly time and energy searching
for a new partner.
Guilt is an emotion that we experience when we feel that we have wronged or
hurt someone else. When we do think about cheating on our partners, we feel guilt. The
thought of feeling guilty can prevent us from cheating - something that might damage or
end a long-term relationship.
Evolutionary psychologists believe that individuals who evolved the capacity for
jealousy, love, and guilt would have reproduced more successfully than individuals who
did not evolve these emotions.
Sociology and Social Psychology
Other researchers, including the vast majority of sociologists and many social
psychologists, use different theories to explain why humans are faithful. Sociologists
examine how our behavior is influenced by large societal institutions (e.g., the
government, religions). Social psychologists study our thoughts and feelings and how
they influence our interactions with other people.
Sociology. Sociologists believe that people are faithful to their partners because
we receive many messages from friends, family, and media that tell us it is wrong to be
unfaithful. They believe that “social norms”, or beliefs about how people do and should
behave, have a strong influence on people’s behavior. One study found that 90% of
Americans believe that marital infidelity is “always” or “almost always” wrong. A
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second study of over 60,000 men and women found that men and women who think that
most people are faithful are more likely to be faithful to their own partner (see Figure 3).
These social norms in promoting fidelity can be very strong in religious communities.
Studies have found that individuals who are involved in religious communities are more
likely to stay faithful. This may be because some people believe it is a sin to cheat and
because they are afraid of being viewed negatively by other members of the religious
community. These studies by sociologists suggest that people who believe that it is a
“social norm” to be faithful are more likely to stay faithful to their partners.
Social Psychology. Social psychologists are interested in how these and other
beliefs people have about their relationships impact whether they are faithful. The
“Investment Model” has been used by social psychologists to understand who stays
faithful and who does not.
In the Investment Model, there are three factors that strongly predict whether
people feel committed to their current relationship:
1)
Relationship Satisfaction: People who are more satisfied with their
relationships are more likely to feel committed to their partner.
2)
Personal Investments: People who have invested more time, money,
energy, and emotional effort into their relationship are more likely to
feel committed to their relationship.
3)
Quality of Alternatives: People who have fewer alternative dating
options, hobbies, or job opportunities are more likely to feel committed
to their partners.
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Research has shown that these people who feel committed to their relationship are less
likely to cheat on their partners.
Conclusion
Researchers from different fields have offered many different answers to the
question “Why are people faithful to their mates?” Some researchers, however, are
trying to form one comprehensive explanation for fidelity using findings and theories
from sociology, social psychology, and evolutionary psychology. Future scientists and
researchers who are familiar with research in these three fields are needed to form a more
complete explanation for why people are faithful to their mates.
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TEXTBOX 1
Hormones and Fidelity
Researchers believe that some hormones make people more faithful to their
partners. Hormones are chemicals that are released by the brain and other parts of the
body and they can influence how a person thinks and behaves. The hormone “oxytocin”
is released when people hug, touch, massage each other, and have sex and is sometimes
called the “feel-good hormone.”
Much of what we know about oxytocin comes from research on prairie voles, a
species that mates for life (see Figure 2). During sex, prairie voles release oxytocin,
which then activates receptors in the brain associated with feeling good after receiving a
reward. In contrast to prairie voles, montane voles do not have these receptors in the
brain and do not mate for life. It appears that prairie voles have evolved a system that
causes them to form long-term partnerships.
Oxytocin has a similar effect in humans. People become more generous and
trusting in experiments when they are given doses of oxyctocin. People who are falling
in love have more oxytocin in their blood. Women who have less contact with their
partners or friends have lower oxytocin levels. These low oxytocin levels might motivate
people to seek out and form stronger bonds with others, which then leads to a rise in
oxytocin. These findings suggest that oxytocin might play an important role in keeping
people faithful.
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Further Reading
Why We Love by Helen Fisher
The Dangerous Passion by David Buss
Sex in America by Edward Laumann, Robert Michael, and Gina Kolata.
Author Website: http://dfred.bol.ucla.edu
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FIGURE 1: How Common is Fidelity in the U.S.?
Caption: In two large studies, most people report that they have been sexually faithful to
their partner. Over 96% report that they are currently faithful to their partner.
How Common is Fidelity in the U.S.?
Men
Women
100
90
Percent Faithful
80
70
60
50
40
30
20
10
0
National Sample:
Always Faithful
Internet Sample:
Always Faithful
Source of Data
Internet Sample:
Faithful Now?
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FIGURE 2: The Prairie Vole
Caption: Prairie voles typically mate with one partner for life and the hormone oxytocin
plays an important role in keeping them bonded to one partner.
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FIGURE 3. The Association of Perceived Social Norms and Fidelity
Caption: Men who believe that the vast majority of other men are faithful to their spouse
are most likely to report being faithful to their own partner. The same is true for women.
The Association of Perceived Social Norms and Fidelity
Men
Women
100
90
Percent Faithful
80
70
60
50
40
30
20
10
0
Vast Majority
More than Half
Less Than Half
How many married men and women are faithful to their
spouse?