Here’s a theory: most men’s facial hair trends stem from a simple dynamic. The vast majority of men don’t think facial hair looks good in itself or makes them more attractive. Yet, there is something “fun” about having facial hair. That sounds like an immature reason to have facial hair (especially since that’s not really something that you can explain. How exactly is having a mustache fun? It sounds preposterous, but it’s true). To reconcile this desire for facial hair with the understanding that having it is actually stupid, men have devised ingenious methods to “trick” themselves into having facial hair. Once a man sees that someone else has developed a method for having facial hair without having to defend it or claim that it looks good, that man is very eager to glom on to this idea. Thus, the rapid growth of “movember”, playoff beards, ironic hipster mustaches, and Seattle.
I’ve met some women who like beards (I’ve yet to meet a woman who liked mustaches). And judging by the “bear” stereotype, there are gay dudes who like beards, too. I am also at press time unsure whether the invention of religiously motivated beards can be motivated by this dynamic. A grand unified theory of facial hair is still, clearly, an elusive goal. But I think this is a good start.