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We think about sex. We about sex. We spend an inordinate amount of time and money in the pursuit of sex. We have sex. When you consider AIDS, childbirth, or "honor" killings, our survival and death are often intertwined with sex. Thus, it is worthwhile to spend some time on what scientists have learned about .

In 1990, the editor of the Journal of Sex Research wrote:

"[F]uture generations will find it incomprehensible—and perhaps unconscionably negligent—that so little effort was marshaled to obtain data on and establish a science of human sexual behavior."

But scientists, like many in society, are prudish. This is why nearly every psychological model of well-being ignores even a mention of human sexuality, and why nearly every recent book on and well-being ignores sexuality.

Human beings are infinitely complex. Just as there is no universal reason for eating hot dogs (whether trying to win a contest or scarfing them in front of the television out of habit), there is no single reason across time, culture, and history that people engage in sex. But I want to share some insights from well-replicated findings on the motives behind having sex.

Why is this important?

Prior to 2007, a glimpse of the scientific literature led to a mere two reasons why people had sex—procreation (think Mormonism) and pleasure (think Hedo Rick). Then in 2007, Cindy Meston and David Buss plugged the gap. In the first of many studies, they asked hundreds of people aged 17 to 52 to assist them in creating a comprehensive list of the reasons why people engage in sexual intercourse. Everyone was given one question:

"Please list all the reasons you can think of why you, or someone you have known, has engaged in sexual intercourse in the past.’’

Since that first investigation, several replications have led to a final tally of 4 major factors and 13 subfactors for why we do it:

Physical reasons.

Under this broad umbrella, we find: (1) tension relief (search on YouTube for the Peaches song '%$# the pain away'); (2) pleasure (sometimes it is pure hedonism despite the prudish scientists who downplay the benefits); (3) physical desirability (simply, we find our partner to be hot); and (4) experience-seeking (improving and practicing your sexual skills).

Goal attainment.

Under this broad umbrella, we find: (5) resources (trying to obtain the objects of our desires); (6) social status (concerns about what other people think and our reputation—see our study on what people high in social anxiety gain from mind-blowing sexual escapades); (7) (the desire to hurt somebody—which has an evolutionary basis); and (8) utilitarian (using sex to gain an advantage in a relationship or life domain).

Emotional reasons.

Under this broad umbrella, we find: (9) love and commitment (a way to maintain a secure, deep ); and (10) expression (one of the ultimate ways of communicating, at least with one's romantic partner).

Insecurity.

Under this broad umbrella, we find: (11) boost (a strategy to gain a modicum of strength and power); (12) duty/pressure (anything from obligation or coercion by another person); and (13) mate guarding (doing the deed to ward off poachers).

You might be curious about differences in the reasons behind sexual activity. Let me quote directly from the authors about their interesting discoveries, because the differences were substantial:

Men, significantly more than women, endorsed reasons centering on the physical appearance and physical desirability of a partner, such as ‘‘The person had a desirable body,’’ ‘‘The person’s physical appearance turned me on,’’ and ‘‘The person had an attractive face.’’ These findings support the evolution-based hypothesis that men tend to be more sexually aroused by visual sexual cues than are women, since physical appearance provides a wealth of cues to a woman’s fertility and reproductive capacity (Buss, 1989b, 2003; Symons, 1979).

Men, significantly more than women, also endorsed reasons indicating experience seeking and mere opportunity. Examples include ‘‘The person was 'available,'’’ ‘‘The opportunity presented itself,’’ and ‘‘I wanted to increase the number of partners I had experienced.’’ Women exceeded men in endorsing certain of the emotional motivations for sex, such as ‘‘I wanted to express my love for the person’’ and ‘‘I realized that I was in love.’’ These findings support the evolution-based theory that women, more than men, prefer sex within the context of an ongoing committed relationship, and feelings or expressions of love provide signals of that commitment (Buss, 2003; Townsend, 1998). Also supporting this theory were findings that suggest sex without emotional involvement was a more powerful motivator for men than for women. Men exceeded women, for example, in endorsing items related to pure physical pleasure, such as wanting to achieve an , because it felt good, or simply because they were ‘‘horny.’’ It is important to note, however, that most of the emotional motivations for engaging in sex were not endorsed more frequently by women (e. ., ‘‘I wanted to feel connected to the person’’; ‘‘I wanted to intensify my relationship,’’ ‘‘I desired emotional closeness’’). In fact, the Love and Commitment and Expression subfactors were the only two of 13 subfactors that were not endorsed with significantly more frequency among men than women. This finding supports a growing body of clinical evidence suggesting that both men and women at times desire and emotional connectedness from sexual activity. ...[M]en more than women endorsed reasons for having sex that involved a variety of utilitarian functions, such as ‘‘to change the topic of conversation,’’ ‘‘to get a favor from someone,’’ or ‘‘to improve my sexual skills.’’ These findings contradict the stereotype that women, more than men, use sex to obtain special favors or treatment. Another cluster of gender differences not specifically predicted involved enhancement of social status/boosting reputation, establishing bragging rights, and desiring to tell friends that they had sex with someone famous. Nonetheless, these findings were consistent with the empirical data that suggest that men who are actually or effectively polygynous are granted higher social status.

These findings point to an important fact: When comparing men and women, the largest differences are found in sexual motives and behaviors. It is worth remembering that most differences between men and women are non-existent or small except when the subject turns to sexuality.

So what can you do with this knowledge?

My suggestion is that you engage in a bit of self-exploration to know thyself. Spend a month journaling about the motives behind your sexual proclivities, and carefully observe and talk to your partners about their own. You might learn something obvious about yourself that you never noticed, and you might initiate some important conversations with your romantic partners about how you converge and diverge.

Sex is the most underappreciated element of well-being in the psychology (except among evolutionary psychologists). Perhaps it is time for scientists and practitioners interested in well-being to spend less time reading articles and more time talking to feral humans to discover what makes them tick.

For more, visit toddkashdan.com