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Years from now, everyone will remember where they were the day they first caught wind of what has been dubbed the "Beard War." Prince Harry of Wales has grew a beard, and his grandmother, Queen Elizabeth II, insisted that he shave it off.

Whether his beard, grown during a trip to Antarctica, will be a casualty of war or manages a reign as long as that of the queen herself, Prince Harry is part of a long and proud tradition of individuals who have grown what first-century theologian Clement of Alexandria long ago dubbed "the mark of a man."

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Facial hair is a secondary sex characteristic that may have been present in our evolutionary lineage for millions of years. Given that facial hair isn't necessary for survival, Charles Darwin, himself a beard enthusiast, surmised that this trait functioned in sexual selection, making our heavily bearded ancestors appear more attractive to mates and intimidating to rivals.

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Throughout the ancient world, beards were common, a sign of masculinity, virility, age and wisdom. Beards weren't simply grown; they were cultured. Ancient Assyrian men, for example, were known to curl their beards and sprinkle gold dust in them, according to "Encyclopedia of Hair: A Cultural History" by Victoria Sherrow. Ancient Persian kings laced their beards with gold thread.

For a man to have his beard shaved off would be a punishment or form of humiliation.

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A painting by Charles Le Brun, 17th century, depicting Alexander the Great.Heritage-Images

During the 4th century B.C., the clean-shaven look started to catch on with the rise of Alexander the Great. In 345 B.C., he decreed that his soldiers would shave their beards, so that their enemies couldn't grab hold of them for an advantage in battle. As Alexander's influence and empire grew, so did the practice beyond the Macedonians.

The Macedonians didn't invent the look, however. There are depictions of clean-shaven men in cave paintings dating back to 10,000 B.C.

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Before the first century B.C., ancient Roman men grew long beards and viewed clean-shaven faces as effeminate. Following the footsteps of another conqueror, Julius Caesar preferred the hairless look, inspiring Roman men to follow suit.

Emperor Hadrian two centuries later would reverse that trend, however, when he made beards once again fashionable by sporting one himself.

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While beards have gone in and out of fashion in different societies over the years, there are religious denominations, including Sikhs, Muslims, the Amish and sects of Judaism, that encourage or require men to have facial hair. The reason for the requirement is fairly simple, according to Slate's Brian Palmer: to promote masculinity.

In some religious traditions, facial hair fashions were also used to distinguish members of one faith or culture from another. The ancient Israelites, for example, are often depicted as bearded, while the Philistines were clean-shaven. Similarly, early Muslims were directed to trim their mustaches and beards a certain way to distinguish themselves from Christians.

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In Christian history, facial hair has a bit of a tangled history. The question of whether to shave or not to shave divided the early church, reflecting one of many tensions that would lead to the Great Schism, or the separation of the Roman Catholic Church and the Eastern Orthodox Church. When a French cardinal attempted to excommunicate the Patriarch of Constantinople, facial hair was one of the "heresies" listed as grounds for the expulsion.

In 1170, Pope Alexander III prohibited beards among members of the clergy.

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Throughout the Middle Ages, popular interest in facial hair waxed and waned within a matter of a few generations. Certain styles also fell in and out of fashion. During the 17th century, for example, Van Dyke beards, a style of facial hair involving a pointed mustache and goatee, named after Flemish painter Anthony van Dyck, were considered stylish amongst European men.

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In order to modernize Russia, Peter the Great instituted a tax on long beards in 1705, emulating the Western European fashion of clean shaven faces. In addition to paying the tax, anyone sporting a beard would have to carry around the copper coin shown here indicating that they had paid up. Inscribed on the coin is the phrase: "The beard is a superfluous burden."

This tax stood in stark contrast to Ivan the Terrible, who one and a half centuries before Peter the Great, declared: "To shave the beard is a sin that the blood of all the martyrs cannot cleanse."

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Although beards were common when the first explorers arrived on the shores of the Americas, facial hair fell out of favor among early American colonialists. As Sherrow notes, all of the men who signed the Declaration of Independence were beardless, as were the first 15 presidents of the United States.

Our 16th president, Abraham Lincoln, reversed that trend, becoming the first U.S. president with facial hair.

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Beards in the 21st century still hold the same fascination that they have throughout human history, with their fair share of fans and critics alike. Modern beards aren't just about style; they're also about sport and the spirit of competition.

First hosted in 1990, the World Beard and Moustache Championships are held annually and attract competitors from all over the world. Once dominated by European clubs in its early days, Beard Team USA has found success in the competition in recent years.