For most of human history, men have worn beards. It's not hard to understand why - cave men had no choice, lacking any kind of blade to remove facial hair.
Once metallurgy has been refined in any civilization, though, the technology of knives and scissors quickly follows. These tools become more and more refined, and the refinements lead to the development of the razor - the sharpest knife there is. With a very sharp knife, shaving becomes possible
Even with these developments, however, men preferred beards.
For one thing, many religions prohibited shaving. (Some orthodox religions still practice this today.) For another, shaving with a straight razor could be a dangerous activity better left to professionals - professionals who lived largely in cities and charged a lot for their services. And so, as late as the early 20th century, beards were fashionable and most men wore them.
That changed in the United States after World War I, for two reasons:
- Gillette had introduced the "safety razor" in 1901. The safety razor made it possible and inexpensive for men to shave daily, and - thanks to a massive ad campaign - it was gaining popularity.
- Soldiers in the U.S. Army were required to shave, so the gas masks that protected them from chemical agents deployed as a weapon would fit properly. The Army bought millions of Gillette razors and blades to make shaving possible.
- When "Johnny came marching home," the American soldier was a hero with a clean-shaven face. Doughboys appeared in their home towns, and they were seen in movie newsreels. Aided by ad campaigns from companies like Gillette, the clean-shaven face became the rage. In the Roaring '20s, the Great Depression, the World War II era and the booming '50s, beards were decidedly unfashionable. That taboo has eased since the 1960s, but it's still far more common for men to shave than not. And it's strictly a fashion statement, largely the result of advertising by such companies as Schick, Norelco and Gillette.
To put it another way: If you have a beard, no one makes any money.