London: Men`s beard fashions may be guided by Darwinian selection, according to a new study.
Australian scientists found the more beards there are, the less attractive they become - giving clean-shaven men a competitive advantage.
When "peak beard" frequency is reached, the pendulum swings back toward lesser-bristled chins - a trend we may be witnessing now, researchers said.
In an experiment, women and men were asked to rate different faces with "four standard levels of beardedness". Both beards and clean-shaven faces became more appealing when they were rare, accoding to the study published in the Royal Society journal Biology Letters.
The pattern mirrors an evolutionary phenomenon - "negative frequency-dependent sexual selection", or "an advantage to rare traits".
Scientists at the University of New South Wales decided to test this hypothesis for men`s facial hair - recruiting volunteers on their Facebook site.
"Big thick beards are back with an absolute vengeance and so we thought underlying this fashion, one of the dynamics that might be important is this idea of negative frequency dependence," said Professor Rob Brooks, one of the study`s authors.
"The idea is that perhaps people start copying the George Clooneys and the Joaquin Phoenixs and start wearing those beards, but then when more and more people get onto the bandwagon the value of being on the bandwagon diminishes, so that might be why we`ve hit `peak beard`," Brooks said.
In the study, 1,453 women and 213 men were asked to rate the attractiveness of different samples of men`s faces.
Some were shown mostly "full" beards. Others were shown mostly clean-shaven faces. A third group was shown an even mixture of all four varieties - clean-shaven, light stubble, heavy stubble and full beard.
Both women and men judged heavy stubble and full beards more attractive when they were rare than when they were common. The same was true for clean-shaven faces.
Brooks` team is now testing how people like faces with varying levels of beardedness.
"Heavy stubble seemed to be the best in our last study. Maybe a 5-10 day growth. But those describe average tendencies," he said.