That’s why you need a warning, Garrity says, and TRPA1 is found pretty much everywhere that our bodies meet the outside world: our gut, our nose, our eyes, our skin. When it signals the alarm, the body snaps into operation purge. “One of its main jobs is to help flush stuff out.” TRPA1 in our lungs prompts a coughing spell when we inhale pollutants such as cigarette smoke. It makes us cry when we cut onions. Garrity says, “My guess is that it’s why you vomit when you eat stuff that’s bad for you, and it could be why you get the runs when you have something in your GI tract that isn’t necessarily good for you.”
This irritant alarm is ancient. Unlike smell and taste, which appear to have evolved multiple times over the course of history, the signal for irritation has been conserved since the Cambrian period. Our ancestors—in fact, the ancestors of all vertebrates and invertebrates—had this protein five hundred million years ago, meaning that these chemicals could have been annoying life on Earth for half a billion years.
Irritation through this receptor may be so constant over the eons because it’s difficult to evolve around it. The receptor is turned on by the same mechanism that mucks up the proteins and the lipids in the cells. “You’ve basically built yourself a sensor that is tremendously good because it recognizes the property that is damaging,” says Garrity. The damaging part is the electron sharing. If, in an attempt to go undetected by TRPA1, an electrophile gave up its need for electrons, it would no longer be damaging either.
That the irritant sensor is ubiquitous also makes this class of irritants a good defense mechanism for plants. If everything from insects to humans is annoyed by the same type of compound, it’s a pretty foolproof way of warding off a wide range of predators. Plants have taken advantage of this. “Did you ever eat a raw mustard green? At first you chew it, and it tastes like a green. Then after fifteen, twenty seconds, your mouth starts to burn,” explains Garrity. That’s because mustard greens store two components that, when mixed, form an electrophile. “One compartment has the precursor and the other compartment has an enzyme that breaks down that precursor to create wasabi. When you chew it, you mix together the two ingredients, and you create the reactive electrophiles.” This separate packaging is intentional—that way, the electrophiles don’t do damage to the plant cells either. The electrophile appears only when the green is attacked—when something is chewing on it.
David Julius demonstrated that electrophiles don’t come only from plants. A paper that he and his colleagues published in the Proceedings of the National Academy of Sciences showed that electrophiles can also be generated when our tissues are injured—in arthritis, for example.{62} In addition, inflammation can produce electrophiles that activate TRPA1, says Julius.
“That’s why you can’t necessarily tell whether you just got a reactive electrophile on yourself or whether you maybe did something to yourself,” says Garrity. “What you’ve done is you’ve basically built something that sees a wide spectrum of the world around you that’s damaging, and I’m guessing that’s why it’s been so conserved.” Because tissue damage and wasabi activate the same sensor, these pains feel the same.
The curious thing about physical irritants is that they produce reactions that are nearly indistinguishable from psychological irritants. Get onion juice in your eye, and you start to cry. Your nose runs, and you sniffle. The reaction isn’t so different from how most people would respond to an annoying bully hurling insults. “I often wonder why we have the kinds of responses that we have,” says Garrity. “The similarities in our responses to chemical irritants and our responses to some kinds of emotional upset are striking—whether they share some mechanistic similarities is unknown at this point, but I wouldn’t be surprised if they did. My sense is that what we end up doing is kludging stuff together.”
Natural selection is famous for reusing existing systems for new purposes. The jaw bones of reptiles, for example, ultimately became the tiny bones in the middle ear, writes Neil Shubin in his book Your Inner Fish.{63}
What if our machinery for responding to chemical irritants is also partly used to respond to cognitive irritants? “That’s a bit too speculative for me, I’m afraid,” says Julius. “Who knows? I’m not trying to be a reductionist nerd here, but I’m not ready to crawl out on that limb just yet.”
Conclusion
According to the International Programs Center of the U.S. Census Bureau, the total population of the world, projected at September 24, 2010, at 19:32 Greenwich Mean Time was 6,870,906,129. That number is significant. It means that on September 24, 2010, there were more than 6.8 billion opinions about what is the most annoying thing in the world.
It’s difficult to imagine consensus on this question. Everything is annoying to someone. On the other hand, some things do come close to being universal irritations. Hearing half of a cell phone conversation seems to be one of these super-annoyances.
The main problem with listening to someone else’s cell phone call seems to be that it’s distracting. Whether we’re interested or not, our brains can’t help but tune in to the conversation, no matter how banal. If it were merely random noise or an unfamiliar language, we might be able to ignore it—like New Yorkers with an ambulance siren. Tuning out understandable speech is next to impossible, however, because our brains are built to predict what is coming next—especially with speech. With only half of a conversation to work with—a halfalogue, as it is known—there’s not enough context. We are constantly frustrated in our effort to anticipate. On top of the cell phone call distracting us from what we’d rather be thinking about, we likely won’t even get the satisfaction of making an accurate prediction about the conversation. This may explain why trying to understand why someone on a call would say “He’s arriving tomorrow” ten or twelve times in a row is enough to make your head explode. In other words, it’s unpleasant—another key component of an annoyance.
Also, even though we know the call will end, the uncertainty of when adds to the annoyance. She must be finished. “He’s arriving tomorrow.” That’s got to be the last one. “He’s arriving tomorrow.” Please tell me this is the end. “He’s arriving tomorrow.” Aaargh.
If you’re particularly unlucky, you’ll be listening to someone whose voice captures some of the same sound qualities as fingernails on a chalkboard. That sound is supremely annoying, perhaps because it has similar qualities to a human scream.
On top of everything else, maybe you’re working with a cognitive overlay or two. Your ex, let’s say, logged many hours halfalogueing in your presence, and you always fought about it, but now you miss her, and you wonder whether she misses you, and so forth, and so on.
The inevitable question is, does the knowledge of what makes a super-annoyance annoying provide any hints on how to overcome it? Maybe.
We know that socially unacceptable things are annoying. Trimming your nails in public seems to fall into that category for a lot of people. So does talking on a cell phone in a crowded public space. You could try to convince yourself that because cell phones are so ubiquitous and so essential to modern life, it’s unfair to think of them as no longer socially acceptable. You could try that.
We know that things that keep us from accomplishing a task are annoying. If the call distracts you from giving your full attention to your workout or completing that difficult crossword puzzle, you could try to convince yourself that the task at hand isn’t all that important, and a temporary distraction won’t matter that much. You could try that.