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My latest Mind and Matter column in the Wall
Street Journal is on yawning:
Even as scientists get better at finding explanations for animal
behavior-at the genetic, physiological, evolutionary and neural
level-certain habits remain implacably mysterious. And this is true
even when we're the species in question and can see the behavior
from the inside. Yawning, for instance: You might think that we
would know why we yawn, but it has no obvious need, function or
A recent study confirmed that babies who open their mouths in
the womb are indeed yawning, not just gaping. This was long
suspected and may help to nail shut the coffin of a theory that has
refused to die: that yawning is about filling the lungs with oxygen
or emptying them of carbon dioxide.
It's now 25 years since Dr. Robert Provine, now at the
University of Maryland, did the obvious experiment. He enriched the
oxygen or the carbon dioxide in the air breathed by experimental
subjects and found not a hint of suppression or exacerbation of
yawning compared with control subjects breathing normal air.
So what is known about yawning? Dr. Provine-who is a champion of
what he calls "sidewalk neuroscience," experiments anybody can do
at home without special equipment-has spent years teasing out the
details of yawning, as recounted in his recent book "Curious Behavior: Yawning,
Laughing, Hiccupping and Beyond." By asking people to pinch their
noses or grit their teeth while yawning he found that "the motor
program…will not run to completion" unless you can inhale through
your mouth and gape your jaw wide.
Experiments by Andrew Gallup at Princeton University, his father
Gordon Gallup and a colleague found that yawning is suppressed by a cool
pack strapped to the forehead or by summer temperatures that are
higher then body temperature, and that therefore the purpose of
yawning may be to cool the brain by inhaling air. But then why do
fetuses yawn and why does the need to yawn not get satiated? Having
yawned, you often yawn again; it comes in bouts.
Folklore is correct that yawning is triggered by boredom,
drowsiness, stretching or other people yawning. Yawning is so
contagious and suggestible that even reading an article about it
can trigger the reflex, though the contagion is unconscious: It
isn't easy to yawn to order. Nor is such contagion confined to
human beings; it has been found in baboons, perhaps, and
chimpanzees, for sure.
If yawning is empathetic, Matthew Campbell and Frans de Waal of
Emory University in Atlanta predicted that chimpanzees would catch yawning
from their "in-group" friends but not from "out-group" strangers.
Sure enough, 23 chimps yawned more while watching videos of their
in-group yawning than when watching videos of strange apes yawning
(or familiar apes not yawning).
Yawning can be triggered by the hormone oxytocin-which is
released in the brain during empathetic actions like touching,
kissing or cooperating, and which triggers a release of dopamine, a
feel-good neurochemical. Fabrizio Sanna and colleagues at the
University of Cagliari in Italy injected oxytocin into particular
parts of the brains of rats and induced yawning, or blocked the
effect by injecting an oxytocin-blocking chemical first.
But this is where introspection lets us down. Contagious yawning
doesn't feel much like collaborative social bonding; it just feels
like involuntary emulation with little emotional baggage. Nor does
empathy suggest a physiological "reason" for yawning (after all, we
yawn when alone), though Dr. Provine thinks that it may be "a
response to and facilitator of change in behavioral or
physiological state," maybe synchronizing a group of people about
to embark on a behavioral transition. There's a persistent anecdote
that parachutists yawn just before jumping out of airplanes.
Perhaps the main purpose of yawning is to remind us how
mysterious human beings still are, even to themselves.