Sexual desire

Sexual desire. The phrase alone holds such loaded, voluptuous power that the mere expression of it sounds like a come-on — a little pungent, a little smutty, a little comical and possibly indictable.

Everybody with a pair of currently or formerly active gonads knows about sexual desire. It is a near-universal experience, the invisible clause on one’s birth certificate stipulating that one will, upon reaching maturity, feel the urge to engage in activities often associated with the issuance of more birth certificates.

Yet universal does not mean uniform, and the definitions of sexual desire can be as quirky and personalized as the very chromosomal combinations that sexual reproduction will yield. Ask an assortment of men and women, “What is sexual desire, and how do you know you’re feeling it?” and after some initial embarrassed mutterings and demands for anonymity, they answer as follows:

“There’s a little bit of adrenaline, a puffing of the chest, a bit of anticipatory tongue motion,” said a divorced lawyer in his late 40s.

“I feel relaxed, warm and comfortable,” said a designer in her 30s.

“A yearning to kiss or grab someone who might respond,” said a male filmmaker, 50. “Or if I’m alone, to call up exes.”

“Listening to Noam Chomsky,” said a psychologist in her 50s, “always turns me on.”

For researchers in the field of human sexuality, the wide variance in how people characterize sexual desire and describe its most salient features is a source of challenge and opportunity, pleasure and pain. “We throw around the term ‘sexual desire’ as though we’re all sure we’re talking about the same thing,” said Lisa M. Diamond, an associate professor of psychology at the University of Utah. “But it’s clear from the research that people have very different operational definitions about what desire is.”

At the same time, the researchers said, it is precisely the complexity of sexual desire, the depth, richness and tangled spangle of its weave, that call out to be understood.

An understanding could hardly come too soon. In an era when the rates of sexually transmitted diseases continue to climb; when schools and parent groups spar bitterly over curriculums for sex education classes; when the Food and Drug Administration angers both religious conservatives and women’s groups by approving the sale of the morning-after pill over the counter but then limiting those sales to women 18 years or older; and when deviations from the putative norm of monogamous heterosexuality are presented as threats to the social fabric — at such a time, scientists argue that the clear-eyed study of sexual desire and its consequences is vital to public health, public sanity, public comity.

“Sexual desire may be complicated, but that doesn’t mean it’s chaotic,” said Julia R. Heiman, director of the Kinsey Institute for Research in Sex, Gender and Reproduction in Bloomington, Ind. “We can make an honest attempt to understand what sexual desire is and what it is not, and that it is important to do so.”

Meredith L. Chivers, a researcher at the Center for Addiction and Mental Health in Toronto, concurs. “Sexuality is such a huge part of who we are. How could we not want to understand it?”

Unabashed about acting on their academic appetites, sexologists have gained a wealth of new and often surprising insights into the nature and architecture of sexual desire. They are tracing how men and women diverge in their experience, and where they converge. They are learning how and why people pursue the erotic partners they do, and the circumstances under which those tastes are either fixed or fluid.

Some researchers are delving into the neural, anatomical and emotional mechanisms that modulate and micromanage sexual desire and sexual arousal; others are exploring the role that culture plays in plucking or muffling the strings of desire. The pragmatists in sexology’s ranks are seeking better bedside medicines — new ways to help people who feel they suffer from an excess or deficit of sexual desire.

One recent standout discovery upends the canonical model of how the typical sex act unfolds, particularly for women but very likely for men as well.

According to the sequence put forward in the mid-20th century by the pioneering sex researchers William H. Masters, Virginia E. Johnson and Helen Singer Kaplan, a sexual encounter begins with desire, a craving for sex that arises of its own accord and prods a person to seek a partner. That encounter then leads to sexual arousal, followed by sexual excitement, a desperate fumbling with buttons and related clothing fasteners, a lot of funny noises, climax and resolution (I will never drink Southern Comfort at the company barbecue again).

A plethora of new findings, however, suggest that the experience of desire may be less a forerunner to sex than an afterthought, the cognitive overlay that the brain gives to the sensation of already having been aroused by some sort of physical or subliminal stimulus — a brush on the back of the neck, say, or the sight of a ripe apple, or wearing a hard hat on a construction site and being surrounded by other men in similar haberdashery.

In a series of studies at the University of Amsterdam, Ellen Laan, Stephanie Both and Mark Spiering demonstrated that the body’s entire motor system is activated almost instantly by exposure to sexual images, and that the more intensely sexual the visuals, the stronger the electric signals emitted by the participants’ so-called spinal tendious reflexes. By the looks of it, Dr. Laan said, the body is primed for sex before the mind has had a moment to leer.

“We think that sexual desire emerges from sexual stimulation, the activation of one’s sexual system,” she said in a telephone interview.