Hipsters take note: Beards may be all the rage — and they might be making you more attractive for now — but this is a fashion trend that could ultimately be the cause of its own undoing.
A recent experiment by Zinnia Janif, Rob Brooks, and Barnaby Dixson from the University of New South Wales shows that, as beards become more common, they subsequently become less attractive. It's not that beards make men ugly — it's just a consequence of a Darwinian effect known as negative frequency-dependent sexual selection.
Previous work by the same research team shows that women perceive men with facial hair as being more attractive and better father-material than clean shaven ones. Women also assess bearded men as more masculine, healthy, and more likely to make good parents.
But the new study, which now appears in the Royal Society's Biology Letters, suggests this could be a fleeting perception.
In the battle to attain reproductive fitness, animals tend to converge around advantageous traits. Over time, however, popular, or common, characteristics can become disadvantageous. John Bohannon from Science AAAS explains:
A classic example is the coloration of guppies, in which rare color variants are less likely to be noticed by predators. This gives the nonconformist fish a slight fitness advantage because predators focus on the most common hues, allowing the unorthodox coloration to be passed on and spread in the population. But once the odd coloration gets too common, the advantage disappears—predators start to chow down on the formerly cryptic fish and the cycle begins anew.
This is how negative frequency-dependent sexual selection works. It's a mechanism that explains how and why diversity is maintained in a population.
It's important to note, however, that sexual traits can only diverge so much before they're perceived as being unattractive, or even grotesque.
But does this apply to human beards? They are, after all, a secondary sexual trait that's subject to considerable cultural variation. To find out, the researchers conducted an interesting test.
For the experiment, 1,453 women (self-identified as being either heterosexual or bisexual) and 213 men (self-identified as hetereosexual) were asked to rate the attractiveness of different samples of men's faces. Specifically, they looked at pictures of 36 different men who were recruited to grow beards and have their pictures taken at different intervals: clean-shaven, light stubble (5 days), heavy stubble (10 days), and full beard (4 weeks).
One group of participants was primarily shown pics of men with fully grown beards, while a second group was shown mostly clean-shaven faces. Other groups were shown an evenly distributed mix of all four varieties.
Results showed that both women and men perceived heavy stubble and and full beards as more attractive — by as much as 20% — when they were rare as compared to when they were common. Importantly, and in confirmation of the negative frequency-dependent sexual selection effect, clean-shaven faces were deemed more attractive when they were rare. Interestingly, the effect was equal for men and women.
So if this conclusion is correct, when a certain level of beardedness appears in the population, the facial-hair-pendulum will start to swing in the opposite direction. Then, when the clean-shaven look reaches a certain popularity threshold, the pendulum will swing once again towards facial hair.
Read the entire study at Royal Society: Biology Letters: "Negative frequency-dependent preferences and variation in male facial hair." Supplementary sources: BBC and Science AAAS.