Beards. You either love ’em or you hate ’em. Science tells us that beards make a man look more masculine, older and more powerful. Apparently women think they’ll make better fathers. But new research published earlier this year suggests that the attractiveness of beards might merely come down to their novelty – beards are under negative frequency-dependent sexual selection, and we may soon pass peak beard.

As movember draws to a close, I for one shall breath a sigh of relief – don’t get me wrong, I’m all for it as a charitable campaign and I’m sure it does a great deal of good, but as one of many single women who doesn’t appreciate facial hair, November has recently become the most dangerous month for dating. You can argue about it until you’re blue in the face (and I have done – well, almost!) but ultimately the facial hair debate is a matter of opinion.

Whether women like it or not, the beard appears to be in, at least for the time being. Beards seem to come in and out of favour – they follow cyclical fashions. In the 1890s, more than 90% of men photographed for London Illustrated News had some facial hair, compared to just 20% in 1970. The mid-19th century was taken over by sideburns, and this latest trend of beardiness began somewhere around 2005.

The beard is a striking example of sexual dimorphism – differences between the sexes, which are often caused by sexual selection. Sexual selection is a special type of natural selection that favours males that are sexy to females because those males tend to have more offspring. Darwin suggested that beards may have evolved through sexual selection, as an attractive signal to females. Other scientists have since suggested it may instead be a signal used in male-male competition over females, another driver of sexual selection. It’s true, beards make a man look more masculine, and several studies have indicated that beards are an important influence on the judgements men make about other men. Bearded men are also viewed as more aggressive, suggesting beards may play a role in aggressive facial communication between men.

Female Preferences

Women perceive bearded men to be more healthy; they see them as more masculine and better parents. Bearded men are also seen as being older and of higher status, a connotation that persists across cultures. Beards are often ranked as being more attractive than the clean-shaven look, although there is a lot of variation between women.

Several studies have suggested that stubble, rather than a full beard, is the most attractive, with one study going so far as to claim that the 10-day beard represents the peak of physical attractiveness. These affects may be greater for women who are at a fertile stage of their menstrual cycle – a time at which health, strength and parenting skills would be of great significance when choosing a mate.

Interestingly, several studies have shown that men consistently rank other men as more attractive than women do – men overestimate the quality of their competition. So, it’s not as bad as it’s seems, guys!

Honest Signalling

One hypothesis that is often used to explain the root of sexually selected characteristics is that they are an honest signal of high genetic quality. In this case, females who mate with bearded men will have more successful offspring who are also more likely to be beareded, and so on. As an explanation for sexual selection, the ‘good genes’ hypothesis is a compelling one, and has ample support from studies in animals. One study attempted to test this for human beards, however, and found an unexpected result. Contrary to their hypothesis, facial masculinity and attractiveness were negatively correlated with semen quality – that is, more attractive men produced lower-quality sperm. This suggests there may instead be a trade-off between the need for testosterone to fuel sexual signalling, and the damaging effects it can have on sperm quality.

Frequency Dependent Selection

Recently, another explanation for the patterns of facial hair in humans has been proposed and gained some empirical support and excessive media coverage. ‘Peak beard’ as it is being called, refers to the idea that the attractiveness of beards depends on their rarity. At some point, beards become too common and loose their wow factor. Research conducted at the University of New South Wales showed that beards were ranked most attractive when seen in a stream of clean-shaven photos. The reverse was also true; beardless men were rated more attractive when their pictures were shown along with many bearded men. It seems, we’re just suckers for novelty.

This concept is known as frequency dependent selection, and it is a central theorem in evolutionary biology that explains how variation can be maintained within a population. Of nearly 1500 women in Australia who viewed 36 images selected from over 200 men, most women rated facial hair as more attractive after a sequence of beardless men, and vice versa. Likewise, in guppies, males with an unusual pattern of coloured spots are less noticeable to predators and more attractive to females. They do very well with the ladies and produce lots of offspring; in a few generations their new pattern is very common, predators begin to learn it and the benefits disappear. If it is true that human beards are subject to negative frequency dependent selection at the behavioural level, then as beards become increasingly common they will lose their magic, we will pass peak beard and the fashion will turn.

Want to Know More?

• The Guardian (2014) Fashion-conscious men warned we may have reached ‘peak beard’
• Janif, Brooks & Dixson (2014) Negative frequency-dependent preferences and variation in male facial hair Biology Letters
• BBC (2014) Beard trend is ‘guided by evolution’
• Soler et al (2014) Male facial attractiveness and masculinity may provide sex- and culture-independent cues to semen qualityJournal of Evolutionary Biology
• Dixson & Brooks(2013) The role of facial hair in women’s perceptions of men’s attractiveness, health, masculinity and parenting abilities Evolution and Human Behaviour
• Dixson & Vasey (2011) Beards augment perceptions of men’s age, social status, and aggressiveness, but not attractivenessBehavioral Ecology