An extensive new study has found evidence that links physical attractiveness to the functioning of the immune system.
While there are still numerous questions left to answer, the researchers suggest their findings show "a relationship between facial attractiveness and immune function is likely to exist."
Just how reliable that relationship is remains to be seen, however.
The truth behind beauty is something scientists have been puzzling over since the discovery of evolution. Are social standards of attractiveness in any way affected by the gentle prodding of sexual selection, or is beauty well and truly in the eye of the beholder?
The answer is not as simple as choosing one side or the other. Even Charles Darwin, a renowned proponent of natural selection, didn't think beauty was a signal of better health or good genes.
Universal constants of what we all might find to be beautiful have been a constant source of debate, with little consensus on what they might be (let alone if they even exist). Yet throughout history, all sorts of human cultures have deemed certain physical characteristics as attractive, while disregarding others.
While the notion of there being an objective standard of beauty remains contentious, some researchers propose that facial features considered to be attractive could actually be markers of good health, implying that our attraction to them might potentially benefit the survival of our offspring.
It's an intriguing idea in theory, but it lacks quality evidence. Against this backdrop, the authors of the current study say their research is the most rigorous on the topic to date.
Their study included 159 young adults, whose pictures were rated for attractiveness by 492 people in online surveys. After the participants' headshots were taken, each individual also had a series of tests done to assess the state of their immune system, the level of inflammation in their body, and their self-reported health.
When analyzing the findings, the authors found that people whose faces were seen as attractive had relatively healthier immune function, especially in regards to bacterial immunity.
Interestingly, there was no link between higher inflammation and attractiveness among participants. This could suggest facial attractiveness is a better proxy for a high-functioning immune system than signs of acute sickness.
In short, the primary function of facial attractiveness might have less to do with avoiding a sick mate than avoiding a mate who can impact the health of your future offspring – hypothetically speaking, at least.
The study also happened to reveal some interesting sex differences. Men, for instance, were more likely to be deemed attractive if their natural killer cells were high-functioning. These cells are crucial in clearing the body of viral infections.
Women, on the other hand, were considered more attractive when they showed slower growth of a bacterium in their plasma, which is linked to blood levels of minerals, glucose, and antibodies.
The results suggest facial attractiveness may be linked to immune factors that can be passed on in genes, but that doesn't mean there aren't cultural factors impacting individual perceptions of beauty, too. How each one weighs up is unclear.
"It is also possible that links between attractiveness and health may be obscured in modern humans, given that human mate preferences were forged before the advent of modern medicine," the authors suggest.
"That is, although attractiveness may have cued both health and immune function in ancestral populations, the links with health may no longer occur as modern medicine allows those with low immunocompetence to stay in relatively good health."
Ultimately, one study isn't enough to determine why human aesthetics exist, and what evolutionary purpose, if any, facial beauty might serve. Further research will be needed to replicate these results, if they can be, and explore what is driving the association between physical attractiveness and immune function.
Until then, beauty will remain an enigma.
The study was published in the Proceedings of the Royal Society B: Biological Sciences.