Desire is, at its most literal, “the feeling that accompanies an unsatisfied state.” Desire can lead to new and better things; it can also get us in trouble. Since Aristotle, philosophers and theorists have considered desire the impetus for just about everything; desire is possibility.

Typically, we tend to think of desire as an emotion — that is, arising from our mental status, akin to affection or anger or grief or surprise or ecstasy. But this is probably not the case. Many scientists and psychologists now believe that desire is, in fact, a bodily urge, more analogous to hunger or the blood’s need for oxygen. For anyone who has been maddeningly in love, driven to the edge of despair by an unquenchable desire for another, this probably doesn’t seem so far-fetched. According to clinical psychologist Dr. Rob Dobrenski (denizen of, “in many ways we can’t control what we desire because it is a hard-wired emotional and physiological response.”

Dr. Dobrenski is talking specifically about sexual desire. No surprise: desire and sexuality are practically inextricable. The word “desire” probably brings to mind tawny romance novels, adult-only activities, and a longing for sexual connection. Sexual desire may in fact be the only type of desire; psychoanalytic theory holds that all other forms of desire and creative energy are the result of rerouted sexual energy — often called “the libido” — towards other endeavors. The bodily urge of desire is only sexual in nature; everything else is an emotional state developed out of this primary desire.

Whether or not you buy that, it is clear that sexual desire is one of the — if not the — strongest of human needs. Typically, it takes up a huge portion of our time, emotional energy, and lives. Why? What drives the often unstoppable freight train of sexual desire?

According to sexologists Miss Jaiya and Ellen Heed, “desire is the coming together of visual, biochemical, emotional, and biomechanical cues that trigger a hormonal cascade that may culminate in the successful fertilization of an egg by a sperm.” A pretty clinical explanation, but one held widely throughout the profession and related fields of study. David Buss’s keystone work The Evolution of Desire: Strategies of Human Matingis perhaps the textbook on the subject. Buss argues that, in essence, instincts rule our desire; the preferences we have in our sexual lives are, more or less, simply an expression of our search for evolutionary advantage.

In the book, Buss affirms a number of tenets of popular wisdom regarding sexual preference through an evolutionary appeal:

  • Good looks are more important to men than they are to women because good looks signal good health and thus an enhanced ability to reproduce.
  • Women find social standing essential in a mate because that signals a capability to care and protect their future children.
  • Women prefer older men because they are more likely to have the resources to provide for them and their children.

Buss claims that these and a few other basic instincts drive desire and are the same across all cultures and societies. When it comes down to it, for Buss and many others, it’s all about the need to reproduce.

Obviously, Buss’s explanation greatly simplifies the complexity of human sexuality. Some might argue that he simplifies it to the point of offense. Where, for example, do men who prefer men as sexual partners fit into this explanation? Or women who prefer women? And why do people who are physically unable to reproduce still feel sexual desire? Nevertheless, the argument is compelling.

Dr. Dobrenski agrees: “Desire is indeed based on an evolutionary need,” he said. “We have a very strong, sometimes unconscious desire to perpetuate our species.” Dobrenski points out an important distinction: Perpetuating mankind is unconscious. The expression of sexual desire — our conscious feelings and our performances of sexuality — is far more complex than just trying to have babies.

The expression of sexual desire is most likely rooted in childhood. As stress-management expert Debbie Mandel points out, “children observe their parents and absorb lessons about parental sexuality and desire.” Although at first we do not have the ability or the occasion to express them, these initial impressions of desire are not lost on us. When we enter puberty, we start to feel the evolutionary desire towards reproduction. Immediately, this desire begins to express itself as the learned sexuality we have been soaking up since childhood. As we grow older, it changes as it is shaped by social cues from our peers and by mass media portrayals. It may take one of any number of forms; though desire may be simple, sexuality is multifarious and varied. Sexuality is the expression of desire, and the aspect of desire we can access, manipulate, and enjoy.

Sexual desire itself is a drive lodged deep in the gut, working without our knowledge and beyond our control. Jaiya and Heed believe that we are attracted to one another on a subconscious level, as the result of biomechanical cues, including posture and the pheromones they give off — their sexual “scent” — that cause us to choose the mates we do. Perfume manufacturers and ad-men have latched onto this theory of pheromones, marketing scents that supposedly will “help you attract sexual attention instantly from the opposite sex!” But what are they actually selling?

Pheromones are chemical signals sent out by one member of a species in order to trigger a natural response in another member of that same species. It’s been well observed that pheromones are used by animals, especially insects, to communicate with each other on sublingual levels. In 1971, Dr. Martha McClintlock published a now well-known study showing that the menstrual cycles of women who live together in close quarters tend to become synchronized over time. McClintlock and others believe this effect is caused by human female pheromone communication and that this is only one example of a type of sexual communication that is constantly occurring between humans on the sublingual level.

Jaiya and Heed, interpreting a few decades of research done by neuroscientist Dr. R. Douglas Fields, believe that pheromones “talk to the sex centers of the brain and can trigger a release of specific sex hormones,” testosterone and estrogen. The effects of pheromones are clearest in cases where, for example “couples who for every reason should be disinterested in each other suddenly can’t stay out of each other’s presence after an ‘up-close-and-personal encounter'” — coworkers on a business trip, for example.

In recent years, scientists have begun to suspect that a little-known cranial nerve may be the key to the mysterious workings of pheromones. First discovered in humans in 1913, the “cranial nerve zero” or “terminal nerve” runs from the nasal cavity to the brain, ending in what Dr. Fields calls “the hot-button sex regions of the brain.” For years, scientists believed that nerve zero was part of the olfactory nerve, helping our brain interpret smells. But in 2007, Dr. Fields discovered that while the brain of a pilot whale had no olfactory nerve whatsoever, it did have nerve zero. What difference does a whale brain make? Whales long ago evolved to lose the ability to smell, their noses becoming blowholes. And yet, though whales no longer have neural hardware for smell, they still have nerve zero, connecting the whale’s blowhole to its brain. Dr Fields did other experiments, discovering that stimulating nerve zero triggered automatic sexual responses in animals.

Dr. Fields, along with many others, now believe that cranial nerve zero may be responsible for translating the signals of sex pheromones and initiating reproductive behavior. In other words, cranial nerve zero may be the bio-machinery for desire.

A Potent Cocktail

Pheromones may act as a kind of stoplight for sexual desire. They let us know that we’re good to go, but they certainly don’t work alone. Regardless what turned it on, something’s still got to be driving the car. It turns out to be an intoxicating mix of hormones and neurochemicals firing in the brain.

That “hot-button sex region” mentioned by Dr. Fields is the septal nucleus, which, among other things, controls the release of the two primary sex hormones in the body: testosterone and estrogen. Both hormones are essential in the process of desire. Scientists know this, because as men grow older, they tend to lose testosterone and, as a result, develop erection and libido problems. Women also lose testosterone as they age. However, due to poor results from tests involving testosterone administration in women with a loss of sexual desire, scientists now believe that a combination of testosterone and estrogen is the ultimate “love hormone.”

Estrogen and testosterone, in turn, stimulate neurochemicals in the brain — specifically, dopamine, serotonin, norapenephine and oxytocin. Dr. Craig Malkin, a clinical psychologist who is currently writing a book about how we control desire, noted that the power of this neurochemical cocktail can be potent. “The combination of neurochemicals triggers dizzying feelings of excitement, euphoria, and passion,” he said. “Some brain imaging studies show a similarity between neural activity in subjects with obsessive-compulsive disorder and those who are falling in love.” Love — or at least desire — literally drives you crazy. How? What are these chemicals actually doing?

  • Dopamine – Dopamine has mostly been studied in the context of drug addiction. Essentially, it’s the neurotransmitter that makes external stimuli arousing. Dopamine trains you to associate the feeling of being satiated and pleasured with certain things. In the case of sexual desire, dopamine is released in the brain whenever you encounter something to which or someone to whom you’re attracted.
  • Serotonin – Serotonin is similar to dopamine; it is a neurotransmitter that teaches your body a cycle of desire and satisfaction.
  • Norapenephrine – Usually, this neurotransmitter is stimulated when we need extra energy to escape a dangerous or scary situation. But it also tends to increase during masturbation and sex, peaking at orgasm and then declining.
  • Oxytocin Oxytocin has been called the “cuddle hormone.” It is believed to play an essential role in parent-child bonding and in partner formation. A 1992 study by the National Institute of Mental Health of the prairie vole — an animal known for being firmly monogamous — showed that when forming a bond with a mate, the vole’s brain releases a rush of oxytocin. Even more telling, when oxytocin is blocked, the vole can’t make a connection at all. Oxytocin doesn’t cause arousal, but it may be part of the overall drive that is desire. According to Dr. Malkin, it “relaxes our guard and deepens trust.”

Various studies through the years have shown that all of these neurochemicals and more (including epinephrine, alpha melanocyte polypeptide, phenethylamine, and gonadotropins), are in one way or another involved in sexual desire. But when it comes down to it, it’s pretty much impossible to isolate any one mechanism. It’s helpful to take a small step back to see why.

Mysteries of Desire

When the technology to look at brain activity during sexual stimulation became available, scientists expected it to show a fairly straight path from visual recognition to emotional/sexual interest. And yet the brain-imaging studies done by Stephanie Ortigue and Francesco Bianchi-Demicheli in 2007 showed that sexual desire creates an incredibly intricate and non-linear network of brain activity, including lighting up regions in the brain typically devoted to “higher” functions, such as self-awareness and understanding others, prior to lighting up the more straightforward physical-response sections. It all happens incredibly fast and often below the radar of consciousness. In many cases, people do not even seem to know what turns them on.

Attempting a scientific explanation of desire is a murky business: Ortigue and Bianci-Demicheli’s study revealed more complexity. The interaction of neurochemicals involved in desire is dense and convoluted. And the mechanics of what may turn out to be the most essential element of desire – phermones and cranial nerve zero – still remains unclear. All of this confusion does help to explain why treatment methods for loss of libido seem at best haphazard and often ineffective. In many cases, placebos tend to work just as well as the real thing. [If you’re interested, yes, Viagra works, but it doesn’t actually affect desire; it affects arousal, an entirely different bodily mechanism (and a whole other discussion)].

Maybe the confusion isn’t so bad. What’s nice about the inability of science to fully unravel this mystery is that it keeps some of the magic of love and desire alive. After all, if desire was a thing known, perhaps it would no longer be a thing to keep us going. Perhaps without the uncertainty, we wouldn’t have had Adam and Eve, or the Sorrows of Young Werther, or Titanic. So perhaps it’s best not to know after all.