I’d meant to reply to a post over at Yglesias’ a little while back that examined one theory about D.C.’s notoriously stoic rock audiences: It’s suggested to be a legacy of Fugazi front-man Ian MacKaye’s disdain for fratboy moshers, which metastasized into a general loathing of motion.

This actually got me thinking about an interesting phenomenon in evolution called “sexual selection,” which can push new phenotypes to sometimes surprising extremes far faster than ordinary natural selection. (Sometimes these dramatic changes are called “runaway selection,” and seem, in one sense, maladaptive in ordinary natural-selection terms.)

My favorite example is peacock feathers. Those huge, beautiful bright tails are both a beacon to predators and an impediment to mobility; they seem like the sort of thing that evolution should have weeded out quickly. Mate selection explains how this apparently maladaptive trait might have survived. Imagine you’ve got a peacock (or proto-peacock?) population millions of years ago, and one subgroup has tails somewhat larger and brighter than the average. As you might expect, many of them are quickly snatched up by predators; only the fittest of the bright-tails survive. But this now means that the bright-tails (having been winnowed down) are actually fitter than the rest of the peacock population: They’re the ones for whom the disadvantage of the tail was outweighed by their speed, fighting ability, whatever. And, crucially, they’re carrying around a big, bright indirect signal of that fitness. Which, since it’s not easy for Ms. Peahen to directly inspect the quality of a prospective beau’s DNA, is a very handy way for her to decide whose genes she ought to be letting into her scarce eggs.

The crucial turn comes when the peahens evolve an attraction to tails that are larger and brighter than average. This is initially adaptive in the ordinary sense, because since the bright-tailed males really are unusually fit, the females with that preference will tend to have children who are themselves better suited to survive and reproduce. The problem, of course, is that this becomes an arms race: Tails keep getting bigger and brighter as the birds with the most impressive tails in each generation have the most reproductive success, raising the bar for what will count as “bigger and brighter than average” in the next generation. Pretty soon, the tails have become a much bigger disadvantage. But at that point, the bright-tail preference is locked in. A bird with a smaller duller tail may be far better off in terms of getting around and escaping predators, but he’s not going to be able to find a mate.

Anyway, you can probably see where I’m going with this: It’s pretty easy to apply the same kind of logic, mutatis mutandis, to social behaviors (or memes, if you prefer) and peer selection. You have some inital (indeed, understandable) move to bring social pressure to bear against the most aggressive dancers—the ones who’re actually making it annoying for others at the show. They either tone it down or decide they’re not welcome at those shows. But now the next most energetic dancers are the new standouts. In short, you get an inverted Lake Wobegon effect, where everyone wants to be below average. Pretty soon, the median groove-level is pushed down to that familiar arms-crossed, maybe swaying slightly if you really want to rock out.

This slight modification of the Fugazi theory has the advantage of not requiring that some 20-year-old who’s attending a show today know or care what Ian McKaye said at a concert in 1992. Because once you’ve got the initial momentum going, all that’s necessary is for newcomers to feel a little out of place or awkward being the one with limbs akimbo—which is probably going to be the case even without any overt social pressure, and still more so if people soon internalize the sense (even not knowing how it got started) that our sort of people don’t dance at concerts. As with the peacocks, maybe almost everyone would actually be happier with a norm that encouraged some dancing. But as long as they have an even stronger preference not to be the weird kid among the weird kids, the “standing still” stays locked in. On the other hand, it suggests (well, that and some other social psychology findings) that if you could get a critical mass of people dancing, to the point where others felt comfortable acting on their true preference to dance some, you might be able to change the norm pretty quickly. So here’s a proposal for my showgoing comrades: Next time we’ve got a sufficiently large posse at a concert (15? 20?), let’s conduct an informal experiment in group dynamics. Even if it doesn’t work, we’ll probably be having more fun than the kids with their arms crossed.