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The Evolution of Chalkboard Torture

On the universal terribleness of fingernails scratching a chalkboard.

Having grown up in New York City in the mid-nineties, I was spareth’d the rod of classroom corporal punishment.  Wrist slapping, spankings, canings – these were methods of discipline I saw in movies and read about in books, often inflicted on slight, well-meaning cockney schoolboys.  But when my old French teacher, Madame G, launched her fingernails-on-the-chalkboard assault, French class became third-period waterboarding.  Far worse than the occasional verbal scolding, “time out,” or shameful walk to the principal’s office, there was something to be said for the gripping discomfort caused by the hellish timbre of keratin on slate.

Loud, high-pitched noises are good at cutting through the low rumble of background noise – that’s why our alarms aren’t baselines, violins play lead, and it’s impossible to ignore the aspirant opera singer among the 2 a.m. karaoke dregs.  But the sound of fingernails on the chalkboard isn’t your run-of-the-mill bothersome high-pitched noise. It’s unique in its cross-culture universality, an annoyance that only the most masochistic of us enjoy hearing, and only the most malicious enjoy producing.  Why is it that so?  One theory says it has something to do with the distress calls of chimpanzees.

Not all sounds are created equal – our brains have evolved to attribute special significance to certain ones.  For instance, we all experience a particularly strong emotional response to the sound of a crying baby. The sound arouses our instinct to care for the young, telling us that a helpless little whelp needs something, and we can’t help but empathize (unless you’re on a bus and it’s not yours).  The evolutionary roots of this response are clear: If humans innately treated a baby’s cry as they did, say, a bird’s chirp, our species, having left its babies unattended and undernourished, surely wouldn’t have survived long enough to be the successful, world-raping genius race it has become.

In addition to crying, screaming and yelling have a special place too.  They communicate distress – someone needs help, someone is angry, or danger is close by.  Cries, screams, and yells aren’t elements of language, they’re more basic, they’re unlearned;  you are born crying and screaming, and you never forget how to.  Such unlearned shouts primarily exist to communicate a simple though important message (i.e. “danger!”) and trigger an appropriate emotional response in the listener (i.e. “fear”).  They’re nature’s expletives.

Most vertebrates have their own expletives, like when your neighbor’s pit bull barks “f*** you intruder!” at you while you innocently trot by his fenced yard, or when your surly cat meows “feed me you lazy failure!” while you watch the Weather Channel in your underpants.  Intriguingly, we are able to sense the emotions of other animals when they exclaim – our innate response to human cries of pain and threatening screams also generalizes to other species.  We obviously didn’t adapt to understand when gerbils are frightened, but we know it when we hear it.

So, with all that in mind, could the enigmatically universal response to the sound of fingernails on the chalkboard have something to do with our innate response to distressed yells?  Maybe.  Randolph Blake, a neuroscientist at Vanderbilt University has showed that the nail-on-chalkboard sound is remarkably similar acoustically to the distress calls of our cousins, the chimpanzees.  According to Blake, we cringe at chalkboard torture because ancient parts of our brains think a chimpanzee is screaming.

But why would we fear a chimpanzee’s scream?  Well, 6.5 million years ago we diverged from the chimps, and during the vast majority of that time we evolved alongside them in the East African savannah.  Though chimps mainly stuck to the trees while human ancestors moved to the ground, they shared predators (lions, cheetahs, big birds of prey, etc). Chimps, along with other apes and several species of monkey, have notoriously loud distress calls.  When a chimp sees danger – say, a skulking lion – she lets out a piercing high-pitched screech, like a knife through the jungle.  These screeches would surely have been heard by our ancestors, and, because we don’t speak chimp, it would take generations of natural selection for humans to develop an innate fear-response to the sound and, ultimately, for that response to generalize to similar sounds, like the ones that come out of French teachers’ nails scraping chalkboards.  Et Voilà – the chalkboard scratch is uniquely abhorrent because it mimics the once-familiar distress call of a threatened chimp neighbor, an auditory relic of our perilous evolutionary past.

A fair objection to the tidy little story above is that humans could merely learn, through experience, that when chimps scream, trouble is about.  What evidence do we have that it is an innate response rather than a learned one?  Well, not much.  But here’s a brief experiment -  take a listen to this chimp distress call. Goosebumps? Cringing?  Wet your pants?  I would venture a guess that you’ve never heard a chimp distress call until now, and I would also guess you reacted to it with fear and surprise.  No, there isn’t a lion near you (though you should check), but something in your viscera is telling you this sound bodes badly.

It’s generally impossible to prove that a modern human eccentricity is the result of an ancient adaptation because we can’t go back in time, but if a theory makes sense it should be entertained.  It’s funny to think that my French teacher may have been unknowingly mimicking a chimpanzee when she tortured us with the chalkboard maneuver.  I should be thankful she didn’t take the imitation a step further and throw her feces at me.

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