It’s written all over your face

Eye candy might more appropriately be called brain candy. Seeing a pretty face is like eating a piece of oh-so-sweet chocolate — for the brain, if not for the stomach. In fact, attractive faces activate the same reward circuitry in the brain as food, drugs and money. For humans, there is something captivating and unforgettable about the arrangement of two balls, a point and a horizontal slit on the front of the head.

The power of faces isn’t lost on psychologists. “Faces are interesting because they impart so much information — expression, attention — and these interact with facial beauty,” says Anthony Little of the University of Stirling in Scotland.

So it’s no surprise that making faces attractive is big business. Each year, Americans spend more than $13 billion on cosmetic surgery and tens of billions on cosmetics and beauty aids.

But while facial improvements leave those who subscribe to them with a healthy glow and the illusion of youth — subtracting a few years can bump you up a few notches on the hot-or-not barometer — studies of attractiveness have tended to leave the scientists who undertake them with puzzled looks, gray hairs and wrinkles.

Recently, though, researchers seeking to unmask the essence of facial attractiveness have been using computer technology to isolate the characteristics long rumored to underlie beauty. New methods reveal that averageness, or a lack of distinctness, makes someone more appealing, while facial symmetry doesn’t automatically make a knockout, as most people believe. Features that make a man look manly or a woman feminine can trump both averageness and symmetry, but only sometimes. And studies of faces in motion support the idea that femininity and masculinity are important to attractiveness.

Researchers have also started focusing on why faces are attractive, not just what makes them so. Attractiveness may signal good genes and a good mate. A new study links averageness to diversity in the major histocompatibility complex — a cluster of genes that plays a major role in the immune system. And brain-imaging studies are poised to capture how the brain responds to potential cues to genetic fitness.

Seeking (to define) beauty

Believing beauty to be in the eye of the beholder isn’t exactly wrong, but research suggests that there are some universal standards to attractiveness that everyone seems to apply.

“When you look at what people find attractive, it is consistent across cultures,” says evolutionary psychologist Hanne Lie of the University of Western Australia in Perth. “We have some innate or hardwired beauty detector.”

Most attractiveness research has focused on three aspects of a pretty visage — averageness, symmetry and sexual dimorphism.

Early research into these three characteristics relied on photographs and a ruler, so it was difficult to separate the characteristics from each other. Nowadays computer technology has revealed a deeper understanding of beauty.

“The huge benefit of computer graphics,” Little says, “is in manipulating one thing and one thing only.” For example, he says, it is possible to take any face shape and make it perfectly symmetrical. It is possible to mark points to determine average positions, such as the height of the ears, length of the nose and distances between the eyes. It’s even possible to morph faces to accentuate masculine or feminine features. Isolating such characteristics has revealed new complexities to how averageness, symmetry and sexual dimorphism help define beauty.

Averageness, one researcher quipped, could account for as much as 85 percent of good looks. Here, average does not mean dull or boring, but rather nondescript, lacking distinct or dramatic features. In the late 1870s, Sir Francis Galton combined photos of men convicted of serious crimes to develop an image of the prototypical criminal’s face. He found the composite image — with its smoothed out features and absence of irregularities — surprisingly attractive. More than a century later, in the early 1990s, psychologist Judith Langlois, now at the University of Texas at Austin, and her colleagues confirmed that blended faces are more attractive than the originals. (Averaged faces are also preferred by infants; babies stare at composites longer.)

Symmetry as a feature of attractiveness dates back to Plato’s day. He believed the “golden proportion” was the key to a good-looking face. The width of the ideal face would be two-thirds its length and the nose no longer than the distance between the eyes. Modern research suggests that symmetry judgments depend on how well one half of the face reflects the other, Little says. Asymmetry makes a face look a bit off; the two sides don’t quite match. “Essentially, it’s wonkiness,” he says.

And anyone who has gawked at a supermodel with big eyes and high cheekbones or the prominent jaw of a soap opera hunk knows that these beauties bring something else to the mirror. Sexually dimorphic characteristics — meaning those that make someone very masculine or very feminine — can take a face from beautiful to, well, sexy.

Fully understanding facial beauty requires studying how these three facial characteristics relate and interact. Averageness is attractive, says Lisa DeBruine, an experimental psychologist at the University of Aberdeen in Scotland. But, she says, when it comes to some key features, such as big eyes and small chins in women, being distinctly nonaverage (being very feminine) can be better. Distinctness is, by default, thought of as bad because, she says, “there are more ways to be nonaverage and ugly than there are ways to be nonaverage and beautiful.”

In a series of studies, researchers including Little and Steven Gangestad of the University of New Mexico in Albuquerque also found that symmetrical faces have attractive features independent of their symmetry. Symmetry was attractive in male faces, for instance, but women shown only half of an attractive male face still found the face attractive, Little and colleagues reported in 2001 in the Proceedings of the Royal Society.

A further study, published by Little on May 7 in PLoS ONE, suggests that symmetry goes up and down with sexually dimorphic features in Europeans, African hunter-gatherers and in nonhuman primates. Symmetrical males had more masculine features and symmetrical females had more feminine features. Gangestad has shown that symmetry and masculinity vary together in men — as one increases, the other does too, suggesting the two characteristics point to some unknown underlying quality. So, perhaps, symmetry is important not on its own, but as a proxy for other characteristics — identified or not yet identified, researchers suggest.

Other missing elements in evaluating beauty have begun to emerge with the use of new technology. Video techniques have allowed for dynamic rather than static interpretations of beauty.

“Real faces move,” says Edward Morrison of the University of Bristol in England. “If you show someone a moving face, they can recognize it quicker. There is more information.”

And it turns out that how faces move may contribute to how good they look. In a 2007 paper in Evolution and Human Behavior, Morrison reported that more of the movements known to be indicators of femininity — blinking, nodding and head tilting — made women’s faces more attractive to male and female volunteers.

“Movement can convey important meanings,” Morrison says. “If that person likes you or doesn’t. If that person is being aggressive. If the person is being flirtatious. The face can start to convey these kinds of things.”

The findings echo results from studies of static faces, supporting the conclusion that sexual dimorphism is important in evaluating women’s faces, and less important in evaluating men’s faces, which tend to move less.

Little says that while scientists are slowly finding all the pieces, fitting them together remains a challenge. “As far as the actual relative weight of these things,” he says, “I don’t know whether we have a good handle on what is most important.”

Designed to impress

If the first goal is to find out what is attractive, the next is to understand why. More than triggering mere identity, facial features can reveal the sex, age and race of their owners. Movement can indicate mood and interest. And clues to personality may also be present, or at least people may think they are. (Studies have shown that voters believe baby faces suggest incompetence while jutting chins and angular noses are clues to capability in candidates. Another study suggests that people think baby faces make more honest CEOs.)

But faces are far subtler vessels still. If a male peacock can show a female his fitness by growing colorful feathers, maybe humans can, more subtly, reveal their fitness with the features on their faces. And people may subconsciously pick up on the cues that identify a good mate.

Under this assumption, masculine features may signal a strong and protective partner, while feminine features communicate youth and fertility. Asymmetries would signal underlying developmental instability. An individual’s genetic profile would also contribute to averageness.

Lie and her colleagues Gill Rhodes and Leigh Simmons, both also of the University of Western Australia, connected averageness, genetic profile and attractiveness in a recent study. In male faces, attractiveness signaled diversity within the major histocompatibility complex, the team reports in the October 2008 Evolution.

This cluster of 128 genes and surrounding genetic material plays an important role in the immune system. The genes encode molecules on the cell surface that recognize self from nonself and detect pathogens and parasites. In rhesus macaques, diversity in the MHC has been linked to reproductive success. And female fat-tailed dwarf lemurs have been shown to prefer males with greater MHC diversity.

Lie looked at genetic diversity in 80 men and 80 women whose faces were rated on a 10-point attractiveness scale by volunteers. The researchers found that those rated most attractive showed greater diversity in the MHC. Taking the study a step further, Lie and her colleagues linked averageness to diversity in the MHC for the first time. More diversity means a better mate, the thinking goes. Presumably, more variation in the MHC will help a person fight off diseases and infection, and a potential mate would pass on this fitness advantage to future offspring.

A number of other studies have attempted to link the features that make a face attractive to perceived, and in a few cases, actual health. A 2000 study by Rhodes and Leslie Zebrowitz of BrandeisUniversity in Waltham, Mass., showed that volunteers rated people with more symmetrical and more average faces as appearing healthier. Faces of 17-year-olds that were rated as distinct were associated with poor past health records. And a study in 2004 linked apparent health of facial skin to attractiveness. Some studies have hinted that attractiveness is related to longevity, body mass index and even semen quality.

Most intriguing to Little and others are studies revealing that when women are at the most fertile time in their monthly cycle — when male quality might be most important to them reproductively — they are more interested in men with masculine and symmetrical faces.

“Women prefer all sorts of things when they are ovulating,” Gangestad says. “More masculine faces, more masculine voices, more muscular bodies. Taller men. More dominant men. Certain scents.”

At other times, researchers suspect, women might be interested in other traits — like a man’s nurturing ability or willingness to hang around and raise children.

“There are trade-offs,” Gangestad says. For example, “more masculine men may be less reliable partners.”

Presumably women are more tuned in to indicators of quality when they are able to conceive, so researchers say studying those women might provide the best clues to what makes a man attractive and why. Studying the women at other times may explain the factors beyond attractiveness that contribute to choosing a life partner — why, for example, women don’t always just go for the more manly man.

“Facial features don’t tell us everything,” Gangestad says, “but we know they tell us something.”

DeBruine says studies reveal that individuals’ preferences for faces are not arbitrary, but vary in specific, systematic ways. New research shows that men’s preferences also change depending on their hormone levels. Working with DeBruine, Little and other colleagues, Lisa Welling of Aberdeen found that when men have higher levels of salivary testosterone, they prefer more feminine faces. If high testosterone is a signal of better quality, men with such levels may know that they can better compete in the good-female-getting game. Men with lower levels may look for lower quality (less feminine) women. “Maybe I think Brad Pitt is the most attractive mate possible, but I am not going to win him,” DeBruine says. “It is not a good strategy for me to set my sights on him.” The study, which appeared online last August in Hormones and Behavior, and others suggest that attractiveness preferences may depend on a person’s own perceived attractiveness.

So your personal preferences aren’t entirely personal. Studies out of Aberdeen suggest that, in addition to your hormonal profile and how attractive you think you are, how much someone looks like you and how much attention they pay you can influence just how attracted you are, in quite predictable ways.

Beauty in binary

But here’s the catch. Caring about specific features is one thing, articulating those preferences is another. Even people who consistently rate symmetrical faces as attractive, for example, have trouble identifying symmetrical faces. People just know an attractive face when they see it.

So does at least one computer. Eytan Ruppin of TelAvivUniversity in Israel and colleagues have trained a computer to recognize what humans would rate as an attractive female face. The machine, described in January 2008 in Vision Research, automatically extracted measurements of facial features from raw images rated by study participants for attractiveness. It considered thousands of features and then condensed them. Then it went to work on a fresh set of faces. The computer predicted attractiveness in these new faces in line with human preferences.

Even more intriguing, the computer replicated at least one human bias. Symmetry studies often involve taking the right side of a face and mirror imaging it to create a full face or taking the left side and doing the same. Humans show a surprising bias; in two-thirds of cases, they prefer left-left images (from the point of view of the onlooker). Somehow, this bias must have been embedded in the original rankings the computer received because it also preferred these faces. But no one is sure why or how.

Though replicating human ratings is a fun exercise in artificial intelligence, Ruppin says a computer can’t help scientists understand what people find attractive. “It says what is in the mind of the computer, not the mind of a human.”

Some researchers are, in fact, turning to the human mind to explore attractiveness. The brain has special machinery for recognizing faces. One front-on glance and a human shape among masses of others becomes a long-lost friend, a beloved family member or an irritating coworker.

Face recognition may be “the most fine-tuned system we have,” says Alice O’Toole of the University of Texas at Dallas. “However we code them neurally, we are able to keep track of what makes individual faces unique. When I look at you, I would code what makes you different from every other face I have ever seen.”

Some work suggests that attractiveness is processed as a variation from the mean (which could hint at why averageness matters). In a 2007 study published in Neuropsychologia, participants underwent fMRI while viewing faces of varying degrees of attractiveness. The study suggested that people’s brains have strong responses in the right amygdala — part of the brain that has been linked to both positive and negative emotions — to pretty faces and ugly faces, and less response to middle-of-the-road faces. (So ugly faces are also intense like chocolate, not because they create longing, perhaps, but fear.)

Joel Winston of University College London, an author of the study, says early brain-scanning research took a linear approach to attractiveness, finding that some brain regions responded more to attractive faces and others to unattractive faces. But the recent study included faces that fell between the extremes and found that some brain responses are elicited by unattractive and attractive faces but not less distinct faces.

In this respect, Gangestad says, you could think of characteristics like averageness in terms of preference and avoidance. “It may well be that in our ancestral past certain kinds of mutations caused malformations of all sorts of bodily features, including the face, and that is part of what you are picking up on,” he says.

Winston says the imaging studies don’t look at nitty-gritty brain activity, but still hold promise. “There is some evidence in basic visual science research that with an fMRI scanner we can actually decode what the subject is looking at better than the subject can,” he says. “Certainly the brain knows more about the world than you do in the sense of your conscious self.”

Steve Platek of the University of Liverpool in England agrees that indicators of potential fitness ought to activate sensors in the brain. “The average person you pass on the street is probably not ‘hot or not,’” he says. “But if they are hot or not, they should activate some kind of socially behavioral response [the reward circuitry] that says go after that person at all costs or avoid them at all costs because mating could be really horrific for your [offspring’s] genes.”

Such a drive might underlie the utility of attractiveness. And elucidating how the brain responds to large, obvious differences in attractiveness could help researchers understand how the brain responds to differences that are subconscious and difficult to articulate. Platek says he does have results, as yet unpublished, that look at the brain’s response to good-gene indicators.

While computers have enabled the isolation of facial features for study, Lie says the next step will be in reassembling attractiveness — joining studies on facial features with predicted fitness and brain scans. “I have a feeling when we perceive attractiveness in the real world, it is a holistic process,” she says. “It becomes more than the sum of its parts.”

The next time a face catches your eye, you may not be able to articulate what turns your head or makes your heart jump, but you will certainly know what you feel. Call it instinct, call it evolution, call it what you want. It may take researchers many more years to understand why you find a super-fine face to be so sweet. But that shouldn’t stop you from looking.