This article suggests that acne is simply an unfortunate byproduct of going hairless. While that’s a good explanation for why it originally developed, it’s not a good reason why we still have it.

It’s maladaptive, in that people with visible acne are seen as less desirable mates. But fifteen percent of people rarely if ever get it. That’s lots more than evolution would need to eliminate it entirely — if it hadn’t provided some kind of survival advantage to our ancestors.

When you think about it that way, it’s not hard to come up with a couple plausible answers. Why would being ugly, especially in their early teens, help humans to survive?

• Being uglier might drive the afflicted person to become more intelligent than (s)he otherwise would. Loneliness and rejection are powerful incentives to social animals like us, and being even slightly more intelligent than others in your tribe can offset many minor physical imperfections, if you can turn that intelligence to useful tasks or politics.

• Acne won’t drive off tigers or disease, but it might discourage the most dangerous predator of humans: other humans. At least long enough for women to finish maturing. It’s more dangerous for a woman to bear children in her early teens than later in life, so that might help more women to bear more children by delaying her childbearing to a somewhat safer time.

It’s just a hypothesis, of course, and one that would be devilishly tricky if not impossible to prove with today’s tools. It’s also one that, so far as I know, no scientist has suggested (though I’d be very surprised if it hadn’t been considered already). Of course, it wasn’t long ago that medical science thought that the tonsils and appendix were evolutionary leftovers, serving no useful purpose in modern man. Now scientists know better, both are still quite useful, but in my parents’ day kids routinely had their tonsils removed before their teenage years, even if they were perfectly healthy, which is insane by modern medical standards. Maybe a scientist will eventually address the evolutionary reasons why acne is still around, or already has and neither I nor the author of that article have heard about it yet. We’ll see.

This is the kind of system that I find endlessly fascinating.