(FORTUNE Magazine) – American men wouldn't dream of shelling out billions annually to update home appliances without checking Consumer Reports. Yet they spend riotously on personal renovation, from preening aids to plastic surgery, with only the foggiest notions about what comprises quality looks. Is big hair a best buy? Are higher dividends paid by deflating the spare tire or inflating the cheeks? Will chin dimples be demode in a decade?

These are urgent questions--$9.5-billion-a-year big at last glance--and the cryptofop hunched in his secret lavatory knows all too well how blind experiments can blow up on one's face. Fortunately, science can help. It is probing the deep past to give cosmetologists exciting glimpses of the origin of Mr. Universe: Increasingly, it appears the ideal male is just a slightly warped version of the perfectly average Stone Age Joe.

Researchers at Britain's University of Saint Andrews even teased apart sexiness by using a computer to "morph" faces in ways that enhanced their allure to panels of raters. Borrowing from that work, FORTUNE morphed the faces of some very familiar executives to resemble the study's "optimized" male--judge for yourself which benefits the most from this virtual plastic surgery.

But how dare scientists tear the wings off the sublime enigma of cuteness? Besides, we're schooled from infancy by the contemporary rules on pulchritude--juxtaposing today's female models with Twiggy argues that beauty is the plastic plaything of cultural whim. Still, some of its ingredients transcend time and place: Youth and health have exerted head torque everywhere for millennia. And even the most politically correct among us harbor looksist leanings--consider how exquisitely attuned we are to facial indicators of age.

Such evidence suggests our brains contain hard-wired attractiveness criteria. They aren't dictatorial passions--we clearly can override them, just as we can refuse to eat meat or learn to like having boa constrictors draped around our necks. But they may well influence us more than we care to admit when playing the mating game. One thing we know for sure about our direct ancestors is that they all were winners in that game--in a way, we're their prize, for the goal isn't sex but hurling genes forward in time. Whatever helped make them top seeds, including built-in preferences for the fittest of teammates, was naturally handed down.

The legacies differ for men and women. Females' fertility depends on age much more than it does for males, so men tend to value youth more than women do when selecting mates: Men often marry younger women, but the converse is relatively rare. (Indeed, some executives reportedly have gotten face-lifts to avoid being mistaken for their trophy wives' fathers.) Still, biology gives men no reason to let up on primping. Says David Perrett, a psychologist at the University of Saint Andrews: "If anything, females ought to be choosier than men about their mates--if you're going to spend nine months making a child, and a lot longer looking after him, you want to get the genes right. There's little comparative cost for males."

This is Economics 101 in the animal kingdom, and it explains why the females of many species play the role of coy pickers, while males competitively strut in hopes of being chosen. So what's a guy to strut?

Height, for one thing. It signals physical strength, which was crucial for ascending the social ladder before the invention of the Peter Principle. Even today big guys get ahead: A 1990 study at the University of Pittsburgh found that businessmen's average yearly salary rose with height at a rate of $1,300 an inch--6-footers' average earnings, for example, were $6,500 higher than those who were 5 foot 7. In one study showing the subliminal respect we still accord those who could beat us up, researchers asked subjects to walk up to people of different heights and found they stopped farther away from tall men. Perhaps because tall males have long garnered more goodies, females worldwide tend to look up at them with yes in their eyes. Some 80% of U.S. women who mention height in personal ads seek men at least six feet tall, according to one study. So pass the growth hormone. But wait--if you're reading this instead of playing Nintendo, it's probably too late.

Short men needn't despair--they can still loom large, for women's inner radar screens seem highly attuned to V-shaped torsos. The latest iron-pumping fad may be a genuflection to this presumably evolved preference. But Nancy Etcoff, a psychologist at Boston's Massachusetts General Hospital who is writing a book about beauty, thinks there's another attraction: "Men use big muscles to show they have the leisure, time, and money to cultivate their bodies." Thus, bulging pecs, once a mark of blue-collar work, may now advertise that well-known aphrodisiac, high social rank.

Head shaving is another trick men use to beef up their looks: "It makes the neck and body look bigger," says Etcoff. But isn't hair a sign of youth, and don't women count that as a major plus, if not as much as men do? All too true. "But if a man is going bald, shaving his head can be a preemptive strike because then no one knows how much hair he might have." Moreover, male baldness is tied to testosterone, which helps endow men with their gender's larger size, as well as sexual potency. "Eunuchs never go bald," notes Etcoff.

Still, head shaving smacks of resignation on the youth issue. That's hardly important to Michael Jordan, but biology's message for most aging males is harder: Youth rates, and you're only as young as you look. Plastic surgeons bank on this, of course. They would do well to ponder other Darwinian insights. Example: the importance of being regular.

In the 1870s, Francis Galton, the father of eugenics, discovered that when multiple faces are combined by a photographic process melding their features, the resulting "average" face is more attractive than any of the constituent ones. The finding aborted his plan to render the prototypical criminal face, but it was pregnant with implications.

Some scientists now argue that attractiveness is largely a matter of being close to the average. That makes sense, for abnormal genes are usually harmful. It also meshes with symmetry research: After noticing a few years ago that females of various animal species prefer males with the most symmetrical bodies, scientists found a similar bias in humans--their data suggest we tend to rate symmetrical faces as more attractive than slightly skewed ones. This too makes sense, for diseases often cause subtle deviations from the body's bilateral balance. Says Boston's Etcoff: "A lot of the problems that occur in plastic surgery are due to things like not getting the eyelids exactly symmetrical." It also may explain Galton's discovery, since the composite, average faces are highly symmetrical.

But what about Mel Gibson, whose face is symmetrical but also seems way above average? Exploring this paradox, researchers led by Britain's Perrett showed that melding female faces rated as attractive yields a composite deemed prettier than one created by averaging many faces picked at random. With computer morphing, they then amplified the differences between the two composites to create a third artificial face that was rated by people of both sexes as fairest of all. Conclusion: The average face is more attractive than most, but truly riveting faces have certain exaggerated features. It isn't clear why deviants are cuter, but one theory posits that their strange attractors are linked to sex hormones, and thus are crude indicators of fertility or prowess.

Anyway, for males the deviations include extra-prominent eyebrow ridges and relatively big jaws. For females, the exaggerations are captured by a line from an old tune: "You've got the cutest little baby face." Indeed, the idealized female's salient features--a short, round face with big eyes--are just what researchers have shown comprise "baby facedness" in adults, including men like Babe Ruth and Billy Crystal.

Babyish features are "almost the opposite" of those associated with social "dominance," says Brandeis University psychologist Leslie Zebrowitz. Her studies indicate we expect less of baby-faced people--they carry the same cross as short ones. Yet baby facedness may not be all bad for men: She has found that as teenagers they tend to be extra motivated and aggressive, as if rebelling against the stereotype. Bill Clinton is more than a little baby faced--note the nose and face shape.

If you're out to cultivate the dominant look, Allan Mazur at Syracuse University warns that it "is more of a gestalt than a set of identifiable features." Still, he points to a study of 1950 West Point graduates. The faces of cadets who went on to become generals "tend to be muscular-looking, not skinny or round. They have strong brows and chins. Glasses tend to make men look less dominant. So does smiling or ears that stick out."

Let's see, say we morph Alan Greenspan, subtract the glasses, power up the hair and chisel the cheekbones--why it's...it's Maggie Thatcher!

REPORTER ASSOCIATE Alicia Hills Moore