“She was,” he proclaimed, “so extraordinarily beautiful that I nearly laughed out loud. She … [was] famine, fire, destruction and plague … the only true begetter. Her breasts were apocalyptic, they would topple empires before they withered … her body was a miracle of construction. … She was unquestionably gorgeous. She was lavish. She was a dark, unyielding largesse. She was, in short, too bloody much. … Those huge violet blue eyes … had an odd glint. … Aeons passed, civilizations came and went while these cosmic headlights examined my flawed personality. Every pockmark on my face became a crater of the moon.”

So Richard Burton described his first sight of a 19-year-old Elizabeth Taylor. He didn’t record what happened next, but a growing cadre of scientists would bet their lab coats and research budgets that sometime after that breath-catching, gut-gripping moment of instant mutual awareness, Liz tossed her hair, swayed her hips, arched her feet, giggled, gazed wide-eyed, flicked her tongue over her lips and extended that apocalyptic chest. And that Dick, for his part, arched his back, stretched his pecs, imperceptibly swayed his pelvis in a tame Elvis performance, laughed loudly, tugged his tie and clasped the back of his neck, which had the thoroughly engaging effect of stiffening his stance and puffing his chest.

What eventually got these two strangers from across the fabled crowded room to each other’s side was what does it for all of us — in a word, flirtation, the capacity to automatically turn our actions into sexual semaphores signaling interest in the opposite sex as predictable and instinctively as peacocks fan their backs, codfish thrust their pelvic fins or mice twitch noses and tilt their backs to draw in the object of their attention.

Flirtation is gaining new respectability, thanks to a spate of provocative studies of animal and human behavior in many parts of the world. The capacity of men and women to flirt and to be receptive to flirting turns out to be a remarkable set of behaviors embedded deep in our psyches. Every come-hither look sent and every side-long glance received are mutually understood signals of such transcendent history and beguiling sophistication that only now are they beginning to yield clues to the psychological and biological wisdom they encode.

We’re negotiating

This much is clear so far: Flirting is nature’s solution to the problem every creature faces in a world full of potential mates — how to choose the right one. We all need a partner who is not merely fertile, but genetically different, as well as healthy enough to promise viable offspring and help in the hard job of parenting, and offer some social compatibility.

“Flirting is a negotiation process that takes place after there has been some initial attraction,” says Steven W. Gangestad, Ph.D., an evolutionary psychologist at the University of New Mexico in Albuquerque, who is studying how people choose their mates. “Two people have to share with each other the information that they are attracted, and then test each other” on an array of attributes. From nature’s standpoint, the goal of life is the survival of our DNA. Sex is the way most animals gain the flexibility to healthfully set and mix their genes. Getting sex, in turn, is wholly dependent on attracting attention and being attracted. And flirting is the way a person focuses the attention of a specific member of the opposite sex.

A silent language of elaborate gestures, flirting is “spoken” by intellect-driven people, as well as instinct-driven animals. The very universality of flirting, preserved through evolutionary history from insects to man, suggests that a flirting plan is wired into us, and that it has been embedded in our genes and on our brain’s operating system. And it has evolved just like pheasant spurs and lion manes: to advertise ourselves to the opposite sex.

Flirtation emerged as a subject of serious scrutiny a scant 30 years ago. Irenaus Eibl-Eibesfeldt, now honorary director of the Ludwig-Boltzmann Institute for Urban Ethology in Vienna, was already familiar with the widespread dances and prances of mate-seeking animals. Then he discovered that people in dozens of cultures, from the South Sea islands to the Far East, Western Europe, Africa and South America, engage in a fairly fixed repertoire of gestures to test sexual availability and interest.

Having devised a special camera that allowed him to point the lens in one direction while photographing in another, he “caught” couples on film during their flirtations and discovered, for one thing, that women, from primitives with no written language to those who read Cosmopolitan, use nonverbal signals that are startlingly alike: a female smiling at a male, then arching her brows to make her eyes wide, quickly lowering her lids and, tucking her chin slightly down and coyly to the side, averting her gaze, followed within seconds, almost on cue, by putting her hands on or near her mouth and giggling.

Couples who continued flirting placed a palm up on the table or knees, reassuring the prospective partner of harmlessness. They shrugged their shoulders, signifying helplessness. Women exaggeratedly extended their neck, a sign of vulnerability and submissiveness.

For Eibl-Eibesfeldt, these gestures represented primal behaviors driven by the old parts of our brain’s evolutionary memory.

The lounge acts

Since then, researchers have turned up the intensity, looking, for example, at compressed bouts of flirting and courtship in hotel bars and cocktail lounges. From observations at a Hyatt hotel cocktail lounge, researchers documented a set of signals that whisks a just-met man and woman from bar-room to bedroom. Her giggles and soft laughs were followed by hair twirling and head-tossing; he countered with body arching, leaning back in the chair and placing his arms behind head, not unlike a pigeon puffing his chest.

If all went well, a couple would invariably progress from touching themselves to touching each other. The first tentative contacts could be termed “lint-picking.” She would lift an imaginary mote from his lapel; he would brush a real or imaginary crumb from her lips. Their heads moved closer, their hands pressed out in front of them on the table, their fingers inches from each other’s, playing with salt shakers or utensils. Whoops! An “accidental” finger touch, more touching and leaning in cheek to cheek.

Social psychologist Timothy Perper, Ph.D., an independent scholar and writer based in Philadelphia, and anthropologist David Givens, Ph.D., spent months in dim lounges documenting these flirtation rituals.

Flirting is a largely nonexplicit drama, but that doesn’t mean that important information isn’t being delivered. By swaying her hips, or emphasizing them in a form-fitting dress, a flirtatious woman is riveting attention on her pelvis, suggesting its ample capacity for bearing a child. By arching her brows and exaggerating her gaze, her eyes appear large in her face, the way a child’s eyes do, advertising, along with giggles, her youth and “submissiveness.” By drawing her tongue along her lips, she compels attention to what many biologists believe are facial echoes of vaginal lips, transmitting sexual maturity and her interest in sex. By coyly averting her gaze and playing “hard to get,” she communicates her unwillingness to give sex to just anyone.

For his part, by extending a strong chin and jaw, expanding and showing off pectoral muscles and a hairy chest, flashing money, laughing resonantly, smiling and doing all these things without accosting a woman, a man signals his ability to protect offspring, his resources and the testosterone-driven vitality of his sperm, as well as the tamer side of him that is willing to stick around, after the sex, for fatherhood. It’s the behavioral equivalent of “I’ll respect you in the morning.”

“I can’t tell you why I was attracted to her the instant she walked into my office,” recalls a 32-year-old screenwriter. “It was chemistry. We both flirted and we both knew it would lead nowhere. I’m happily married.” The statement is almost stupefyingly commonplace, but also instructive. Each of us “turns on” not to mankind or womankind, but to a particular member of the opposite sex. Certain stances, personal styles, gestures, intimation of emotional compatibility, perhaps even odors, automatically arouse our interest because they not only instantly advertise genetic fitness, but they match the template of Desired Mate we all carry in our mind’s eye.

As with Dick and Liz, the rational, thinking part of their brains got them to the place where girl met boy; they had the event on their calendars, planned what to wear, arranged for transportation. But in that first meeting, their capacity to react with their instinct, not their heads, overrode their cognitive brains.

The rational brain is always on the lookout for dangers, for complexities, for reasons to act or not act. If every time man and woman met they considered all the possible risks and vulnerabilities they might face if they mated or had children, they’d run screaming from the room.

It’s no secret that the brain’s emotionally loaded limbic system sometimes operates independently of the more rational neocortex, such as in the face of danger, when the fight-or-flight response is activated. Similarly, when the matter is sex — another situation on which survival depends — we also react without even a neural nod to the neocortex. Instead, the flirtational operating system appears to kick in without conscious consent.

The moment of attraction, in fact, mimics a kind of brain damage. At the University of Iowa, where he is professor and head of neurology, Antonio Damasio, M.D., has found that people with damage to the connection between their limbic structures and the higher brain are smart and rational — but unable to make decisions. In attraction, we don’t stop and think; we react, operating on a “gut” feeling, with butterflies, giddiness, sweaty palms and flushed faces brought on by the reactivity of the emotional brain. We suspend intellect at least long enough to propel us to the next step in the mating game — flirtation.

Somewhere beyond flirtation, as a relationship progresses, courtship gets under way, and with it, intellectual progresses resume. Two adults can then evaluate potential mates more rationally and decide whether to love, honor and cherish. But at the moment of attraction and flirtation, bodies, minds and sense are temporarily hostage to the more ancient parts of the brain, the impulsive parts that humans share with animals.

If flirting is a form of self-promotion, nature demands a certain amount of truth in advertising. “For a signaling system to convey something meaningful about a desirable attribute, there has to be some honesty,” explains Gangestad, “so that if you don’t have the attribute, you can’t fake it.” Just as the extravagant colors of birds that figure so prominently in their flirting rituals proclaim the health of animals so plumed, humans have some signals that can’t be faked.

Waist-hip ratio is likely one of them. Science has now calculated just how curvy a woman has to be to garner appreciation: The waist must measure no more than 60 percent to 70 percent of her hip circumference. It is a visual signal that not only figures powerfully in attraction but is a moving force in flirtation.

In simplest terms, says Gangestad, waist-hip ratio is an honest indicator of health. Studies have shown that hourglass-shaped women are less likely than other women to get diabetes and cardiac disease. They are also most likely to bear children, as hips take their shape at puberty from the feminizing hormone estrogen.

Scientists know that the testosterone that gives men jutting jaws, prominent noses and big brows, and, to a lesser extent, the estrogen that gives women soft features and curving hips, also suppresses the ability to fight disease. But looks have their own logic, and bodies and faces that are exemplars of their gender signal that their bearer has biological power to spare.

A nice balance

Whatever specific physical features men and women are primed to respond to, they all have a quality in common — symmetry. Attributes deemed attractive have an outward appearance of evenness and right-left-balance.

Albery Thornhill, a biologist at the University of New Mexico and a pioneer in the study of symmetry in attraction and flirtation, has conducted studies with Gangestad that demonstrate not only do women prefer symmetrical men, but they prefer them at a very specific time — when they are most fertile. “We found that female preferences change across the menstrual cycle,” Gangestad says. “Because the preference for symmetry is specific to the time of ovulation, when women are most likely to conceive, we think women are choosing a mate who is going to provide better genes for healthy babies. It’s an indirect benefit, rather than a direct or material benefit to the female herself.”

And men, for their part, rate symmetrical women as more fertile, more attractive, healthier, and better marriage material.

Flirtation, it turns out, is most successful among the most symmetrical. Men’s bodily symmetry matches up with the number of lifetime sex partners they report having. Symmetrical men also engage in more infidelity in their romantic relationships. And they get to sex more quickly after meeting a romantic partner, compared to asymmetrical men. They lose their virginity earlier, too.

When women flirt with symmetrical men, what their instincts are reading might once have been banned in Boston. Male symmetry is also shorthand for female sexual satisfaction. Gangestad and Thornhill surveyed 86 couples in 1995 and found that women with symmetrical partners were more than twice as likely to climax during intercourse. Thrills are only a short-term payoff, however; female orgasm is really a shill for fertilization, pulling sperm from the vagina into the cervix.

Successful as symmetrical men are at flirtation, it’s only their presumably better genes that women really want. Women do not prefer symmetrical men for long-term relationships. Men who possess symmetry are too busy spreading it around.

A guy who will stick around and help out with parenting is on most women’s wish list of qualities in a mate, Gangestad concedes. “I wouldn’t exclude the possibility that men have been doing some direct parental care for some time, and so a preference for that might also have evolutionary basis.” But also on a woman’s wish list from an evolutionary standpoint would be someone who is going to provide good genes for healthy babies. Unfortunately, says the researcher, “what can and does happen in a mating market is that those things don’t all come in the same package.”