Men are sprouting beards everywhere. Did the economic crisis have something to do with it? Are razor blades and shaving foam too expensive? Is this just another hot indie rocker hipster trend?

Scientists are saying that it may not be just fashion but rather some evolutionary forces that are playing a role in the rise and fall of beards and other facial hair patterns on men.

According to a new study, Negative frequency-dependent preferences and variation in male facial hair, by Zinnia J. Janif, Robert C. Brooks and Barnaby J. Dixson, published in the Royal Society journal Biology Letters, on April 16, 2014, we may soon be able to see men’s faces again.

In an evolutionary sense, it appears that beards are more attractive when they are rare, but as they become more common they will be considered less attractive.

“In a world full of bearded men, beards are less sexy than they are in a world full of clean-shaven men,” says evolutionary biologist, Professor Rob Brooks of the University of New South Wales.

Robert C. Brooks and colleagues set up an online experiment in which men and women rated different kinds of facial hair. Specifically they looked at evolutionary process called ‘negative frequency dependence’ which is a form of selection pressure on genes according to how rare it is.

“When a gene or trait is rare it experiences an advantage,” says Brooks. “But if it is too common there is a disadvantage.”

An example of “negative frequency-dependent selection is an orchid that evolves to look like a female insect in order to attract a male insect to get pollinated. This strategy works for a while until the male insects learns the trick and stop pollinating the orchid.

Brooks says the same thing happens when too many people follow a fashion trend.

In the online study male and female participants rated 24 faces to a “set” scene with the faces having either, 5-day growth, 10-day growth, full beard or clean shaven. Then they were shown a standard set of 12 faces with an even spread of the four facial hair types.

Brooks and colleagues found that both women and men thought heavy stubble and full beards more attractive when these facial patterns were rare during the scene-setting period.

Similarly, clean-shaven faces were judged more attractive when they were rare and less attractive when they were common.

Facial hair patterns were judged as having intermediate attractiveness when they were presented with intermediate frequencies during the scene setting.

“The idea that something like this is either ‘evolutionary or cultural’ is a hackneyed old way of thinking that should have died in the 20th Century,” he says. “What is cultural is deeply evolutionary and a lot of evolutionary changes happen through cultural mechanisms.”

We are closing in on almost a decade of not seeing a man’s clean-shaven face. In 2006, a New York Times article, The Beard: Hip, but Hot, stated: “This trend reached a tipping point in the spring, at which time Urbandictionary.com defined a “Riker” (named for a character on “Star Trek”) as “a Williamsburg or Lower East Side hipster with a beard.

Though Professor Brooks doesn’t tell us how long it will take us to catch on to this “trick of evolution”, hopefully soon we will be able to see what’s hiding under all that hair.