Actor Keanu Reeves and supermodel Devon Aoki have more in common than fame, fortune and good looks—both are also part Asian. Known in popular culture by the Hawaiian term hapa (meaning "half"), people with mixed Asian and European origins have become synonymous with exotic glamour. In Hong Kong and Singapore, half-Asian models now crowd runways once dominated by leggy blondes. In the elite world of Asian fashion, half-Asian is the new white.

The trend may seem little more than an effect of 21st century globalization. As more individuals of mixed descent achieve fame (think Norah Jones and Tiger Woods), it seems natural that society would embrace the mixed look. Media exposure, however, doesn't fully explain the perception of hapa beauty.

Eurasians may possess genetic advantages that lead to greater health and, as a result, enhanced . That's according to a study, the first to find that hapa faces are rated as more beautiful than European or Japanese faces. Researchers say the finding may extend to other racial mixes as well.

The experiment by Gillian Rhodes, a psychologist at the University of Western Australia, found that when Caucasian and Japanese volunteers looked at photos of Caucasian, Japanese and Eurasian faces, both groups rated the Eurasian faces as most attractive. These visages were created by first digitally blending a series of faces from each race into "composites" to create average, middle-of-the-road features typical of each race. Past studies show that "average" features are consistently rated as more attractive than exaggerated features—such as an unusually wide forehead or a small chin.

The finding that Japanese and white subjects preferred mixed-race faces was surprising because, earlier in the same study, most volunteers rated their own race as more beautiful than others. That is, white people typically prefer whites when choosing an ideal image of beauty; blacks prefer blacks; etc.

So why might hapas be considered particularly beautiful? Evolutionary psychologists say it's because Eurasians and other mixed race individuals appear healthier. Humans, like other animals, look for markers of good genetic health in their quest for a reproductive partner. Take facial symmetry, for example: Studies show that, whether they know it or not, people prefer individuals with evenly spaced eyes and other signs of congruence. In evolutionary terms, these markers are associated with healthy conditions in the womb. Infants exposed prenatally to toxins or pathogens may develop facial irregularities and asymmetry. The human brain may be wired to avoid these overt cues of lackluster health, says R. Elisabeth Cornwell, a psychologist at the University of Colorado. "The signs of beauty are the signs of health," she says. Rhodes' findings seem to fit this paradigm: Participants in her study said the Eurasian faces appeared healthier, too.

Similarly, evidence suggests that half-Asians' diverse genetic ancestry would enhance health. According to evolutionary psychologist Randy Thornhill, at the University of New Mexico, "If you hybridize two genetically diverse populations—another way of saying you cross races—then you create more genetic diversity in the offspring."

Genetic diversity, or heterozygosity, is associated with a lower incidence of some diseases. Genetic diseases, such as hemophilia and Tay-Sachs, occur when a person inherits two copies of a defective gene. This is more likely to happen in isolated populations with little genetic diversity.

In 2004, Craig Roberts, professor of biology at the University of Newcastle in the U.K., found the first direct link between diverse and facial attractiveness. He examined genes of the major histocompatability complex (MHC)—a set of genes crucial to a well-functioning immune system. Photos of people with the greatest MHC diversity were rated more attractive than individuals with less MHC diversity. Here, actual health—the ability to resist infection—was linked to perceptions of attractiveness. Roberts believes this preference helps humans pick healthy mates.

Which features radiate both health and beauty? One may be the appearance of the skin. In a second experiment, Roberts found that women rated close-up photos of heterozygous males' skin as healthier than close-ups of homozygous males' skin, and these judgments correlated with ratings of overall attractiveness.

Ostensibly, evidence that Caucasians and Asians prefer mixed race faces counters a major tenet of theory: that we are drawn to partners who resemble ourselves, such as those with similar hair and eye color.

So does this new research explain the popularity of Brazilians, who frequently have blended racial heritage, as fashion models? That remains to be seen. Says Rhodes: "If a preference for mixed-race faces occurs for many different mixes, we could be more confident that it is tapping into something fundamental about human perceptions of attractiveness."