I was studying the history of beards, because I'm a man who often lacks things to do, and because I was curious about whether or not the current tendency for beards to fade in and out of fashion every couple of years carried on back through history.
What I found was that beards, at first, seemed to be either fashionable or unfashionable based on the local culture's traditions. For example, Greeks thinking it unmanly to have a shaven face, with men growing beards for centuries to continue this custom until Alexander changed it for his troops. Romans being all clean-shaven as a sign of not being Greek is another example, and it continued for centuries.
Other examples of all men of a culture following the same grooming rules for centuries exist as well. One especially standout example is the Langobard people of Lombardy, who were named (by themselves I believed) for the length of their beards: Langobard = Long Beard.
As times grew closer to the present day, facial hair began to fade in and out more rapidly. During the renaissance there was a century of beardedess followed by decades of clean-shaven fashion, with beards coming back again for further decades and so on. In the 20th century there were several beard decades, such as the 60s and 70s, and then by the late 90s and early 00s whether or not a beard was "acceptable" seemed to have become something that changes every couple of years. Now it seems like fashion-conscious people must wake up in the morning and check www.beardsyeaornay.com before heading to the washroom.
Clothing seems to be similar in many ways. I'm sure we're all familiar with examples of historical dress attributed to specific cultures. For example, we imagine all Greeks and Romans as wearing togas and sandals. Surely there were slight variations over time, and more frequent fashion changes in the upper classes, but overall people seemed to wear their "cultural garb" more often than not.
Nowadays there exist dozens if not hundreds of named and studied individual fashion styles, with yearly changes planned and orchestrated by the fashion industry (mostly the top designers that own the big labels).
Depending on subculture, one's concern for fashion trends and, perhaps, just plain old personal taste, we can now go somewhere and find twenty people who are all dressed differently, but in ways according to the recent changes particular to them. We can tell that guy is a hipster, or that woman is into hip hop culture, based on their clothes - and the effects are very different appearances. That said, whatever it is a hipster or a hip hop enthusiast wears is carefully chosen and changed from year to year.
It seems to me like society, culture and subcultures all have some form of ADHD now. Constant change, often with bizarre or unusual results, just for the sake of activity (since in this case activity results in the perceived pinnacle of all human goals, monetary gain, being achieved).
I wonder what the Greeks or Romans or Langobards would think of people who wear one thing and have beards one year, and then wear another thing and shave their faces the next. I wonder what they'd think about seeing older people who look vastly different from their children, as if they have abducted an entire culture from some far-off land and taken over their care. They'd probably think we're all insane.