One reason it's hard to study emotions is that it's tricky to recreate them in a lab. Ever since university ethics committees started getting sniffy about inflicting psychological damage on members of the public, it's been bad form to induce, say, sadness by tricking people into believing a relative has died; researchers play gloomy music instead. (To induce happiness, they lamely hand out free coffee mugs, or £5 notes.) But embarrassment is an exception: it's easy to embarrass people, within ethics guidelines, by asking them to suck a dummy, or sing along to cheesy music, or by wiring a pyramid of toilet rolls in a supermarket so it collapses when someone passes, which experimenters have actually done.
Yet none of their work has dispelled the fundamental weirdness of embarrassment. It's an emotion concerned with mere social niceties, yet it's often overpowering. Memories of mortification persist for decades; studies find we'll go to dangerous lengths to avoid it, skipping medical checkups, having unsafe sex rather than buying condoms, even hesitating to save people from drowning for fear of misjudging the situation. People "underestimate how much they will allow the threat of embarrassment to govern their own future choices," writes the psychologist Christine Harris. "We tend to make choices that maintain a veneer of smooth social interaction," even when they're hugely risky.
Embarrassment, it was originally assumed, was a response to breaking social rules. (Condom-buying and medical checkups don't break rules, but feel like they do.) Then a pathbreaking 60s analysis of 3,000 reports of embarrassing incidents showed that rule-breaking wasn't required. Just being the centre of attention, or being praised, was enough; people even got embarrassed by things happening to others. The discovery of "empathic embarrassment" caused a stir, but to us acute sufferers, it's old news: we leap to change channels when Borat makes people look stupid, even when they're racists who deserve it; at weddings, we cringe pre-emptively during speeches, even if they're good. (This makes reading embarrassment research difficult. I felt for the thief, representing himself, who asked a witness: "Did you get a good look at my face when I took your purse?")
Why might an emotion largely associated with etiquette breaches be so overwhelming? In a new book, Born To Be Good, the scholar Dacher Keltner makes a powerful case that embarrassment is evolution's answer to the "commitment problem": it's in everyone's interests to collaborate for long-term gain, but how do you weed out the conmen who want to take advantage? Perhaps because they're unembarrassable. Embarrassment - signalled by facial microexpressions that can't be faked and that are remarkably consistent across cultures - "reveals how much the individual cares about the rules that bind us together". In the moment you realise you've come to the restaurant without your wallet, your eyes shoot down, your head tilts, a smile flickers. These are "the most potent nonverbal clues we have to an individual's commitment to the moral order". It's little solace, but your blushes keep society functioning.