Saturday, August 6, 2005

Apple #95: Yawns

So the other day I was waiting in an office with a good friend of mine. This was fairly early in the morning and we were both tired. It happened three or four times that he yawned, and then I yawned. Or I yawned, and then he yawned. Contagious yawning, right? But I wondered, why are yawns contagious?

(I bet by the time you've finished reading this, you'll have yawned at least twice.)

  • Actually, some scientists say that not everybody is susceptible to the contagious yawn. They estimate that only 40% to 60% of the population will catch a yawn from another person.
  • They think it has to do with a person's ability to empathize with someone else. Actually, they say a person has to be able to do two things: be aware of his or her own mental state, and also be able to see things from another person's point of view.
  • Babies, for example, don't catch yawns from adults. This fits with the theory: babies have no idea who they are, and they sure can't put themselves in an adult's brain.
  • Scientists also say it's rare that people will catch a yawn from a dog or other animal, because you can't really empathize with a dog. But I'm going to beg to differ on both points -- I think I can empathize with a sleepy dog, and I think I have caught a yawn at least once or twice from our dog.
  • Some people have suggested that yawning is contagious because it's a leftover evolutionary trait, designed to signal to other members of the pack that it's time everybody did something -- sleep, presumably. Nobody's proven that chimps catch yawns from each other, or that orangutans can catch yawns from people, or anything like that, so this is still just a major guess.
  • In other words, while researchers have been able to establish that people who are more empathetic tend to yawn more in response to yawning stimuli, they don't really know why yawns are contagious.
  • Okay, so if we don't know why we catch yawns from other people, do we know why we yawn at all? You may have heard, once upon a time, the theory that people yawn to get rid of extra carbon dioxide (CO2) and pull in more necessary oxygen (O2).
  • Well, now, researchers are saying this idea is a bunch of crap. They've done studies where they changed the balance of CO2 and O2 in the room, to see if people yawned more or less, and it didn't have any effect on the yawning rate. So that idea is out.
  • And that's as far as the scientists have gotten, really. They've rejected the dominating theory as implausible, but they haven't found another reason for why we yawn. There's some speculation that maybe it has something to do with slowing the blood flow, and stretching, since we often stretch while yawning (but not always, and not really), but it's not really a strong theory and nobody's running around saying, "Yes! THIS is why we yawn!"
  • To make up for the fact that I don't have the answer, here are a couple more facts about yawns:
    • It's estimated that the first time you ever yawned was before you were born, 11 weeks after you were conceived.
    • Yawns become contagious between year 1 and year 2 of life. (Hmm, this makes me question the empathy part of the equation)
    • The average yawn lasts about 6 seconds.
    • Pandiculation is the term for yawning and stretching.

Have you yawned yet? How about now?

This is Formula One racing champion Michael Schumacher, yawning

And now?

Brooke Shields, yawning
(Photo from an entire blog of celebrities yawning)

Or will you yawn if you listen to the Yawning Song? (2.4 MB download)

Even if it hasn't made you yawn, has this apple made your Top Ten?

Eric H. Chudler, Ph.D., University of Washington, Neurscience for Kids, Contagious Yawning
The Straight Dope, Why are yawns contagious?
Yawningjelle, Yawning: Why do we yawn and why are yawns contagious?
Howstuffworks, What makes us yawn?

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