Biologists who study mate choice across species have suggested that attention-getting male features—such as the peacock’s tail, or the deer’s antlers—are attractive to females because they’re largely useless and impractical. They’re often a disadvantage in areas of life besides attracting a mate, but they signal to females that a male is healthy enough to divert some energy away from surviving and put it towards looking good.
“The very fact that you’re able to stay alive with this handicap means that the female choosing you is getting a high-quality mate,” says Anthony Little, Ph.D., a research fellow at the University of Stirling, in the UK, who did not participate in the new research but has studied how human faces communicate information.
Rugged features aren’t exactly seen as a handicap in humans, but a similar dynamic nevertheless may be at work, Little says. “Humans don’t have colorful feathers, but we pay lots of attention to things like facial appearance and body appearance.”
The handicap hypothesis has been around since 1975, but the new study is the first to provide concrete evidence for a link between high testosterone levels, good immune system function, and attractiveness in humans.
In the study, researchers asked a large group of female college students in Latvia to look at photographs of 74 male students and rate their facial attractiveness. Meanwhile, the researchers tested the men’s testosterone and cortisol levels and gauged their immune-system function by measuring their antibody response to the hepatitis B vaccine.
The men with the strongest immune systems—those with the most antibodies—generally got the highest marks on looks. “Women seem to be able to detect the men who’ve got the strongest immune response, and they seem to find them the most attractive,” says study coauthor Fhionna R. Moore, Ph.D., a psychology lecturer of Abertay University in Dundee, Scotland.
A stronger immune system was also linked to higher testosterone levels, but all of these links were weaker in men who also had high cortisol levels. It’s as though cortisol, which tends to suppress the immune system, interferes in the conversation between testosterone, immune response, and attractiveness.
Cortisol isn’t a perfect marker for stress, Little notes. It’s not clear from one test, for instance, whether high cortisol levels are due to a momentary spike in stress or to chronic stress that keeps cortisol persistently elevated.
Still, he says, the fact that cortisol appears to come between testosterone and facial attractiveness suggests there’s something about stress that women find unattractive.
Once again, Hollywood seems to have beaten science to the punch: It’s no secret that there’s something attractive about a man who seems relaxed and cool under pressure.