美国国家公共电台 NPR Yawning May Promote Social Bonding Even Between Dogs And Humans（在线收听）

RACHEL MARTIN, HOST:

So obviously, teens aren't the only ones yawning. It's something everyone does - humans but also bears, bats, guinea pigs, giraffes. Yawning is common animal behavior. Here's reporter Michelle Trudeau. And no matter how interesting Michelle's story is, I dare you not to yawn during this story.

MICHELLE TRUDEAU, BYLINE: Let me introduce the father of yawn research.

ROBERT PROVINE: I'm Robert Provine, professor of psychology and neuroscience at the University of Maryland, Baltimore County.

TRUDEAU: Provine has studied what he calls yawn science since the early 1980s, publishing dozens of research articles on it. Turns out, the simple yawn - not so simple.

PROVINE: There are many causes for yawning, such as boredom, sleepiness.

TRUDEAU: Hunger, anxiety, stress - they all cause changes in brain chemistry which triggers a yawn. But, says Provine, there's still no consensus on the purpose of a yawn. One strong contender is that a yawn perks you up by increasing heart rate, blood pressure and respiratory function. It's a behavior...

PROVINE: It stirs up our physiology, and it plays an important role in shifting from one state to another. For example, with violinists getting ready to go onto a stage play to play a concerto...

TRUDEAU: They often yawn, as do some Olympians right after competition.

PROVINE: Paratroopers getting ready to do their first jump - they are also yawning.

TRUDEAU: But to Provine, the most intriguing aspect of yawning is that it's highly contagious.

PROVINE: In fact, yawning is so contagious that anything having to do with it will trigger a contagious response - looking at yawns, hearing yawns, thinking about yawns or talking about yawns, as we're doing right now.

TRUDEAU: Contagious yawning may have evolved in early humans to boost social bonding, says Provine. A good group yawn perks everyone up to be more vigilant about danger.

PROVINE: When one person yawns and others yawn, this involves a neurologically programmed bonding of individuals.

TRUDEAU: The social bonding theory has some evidence. For example, you're more likely to yawn if the yawner is someone from your family versus a stranger. And newborns - they yawn spontaneously, but they don't start to show contagious yawning until age 4 or so, around the same time they're becoming more socially connected. And one more finding - individuals with autism, a disorder that has impaired social bonding - they have relatively little contagious yawning.

Now what about other animals? We know that all vertebrates - that's critters with backbones - they all yawn spontaneously, but very few yawn contagiously.

PROVINE: Till the last few years now, the feeling was that contagious yawning was unique to humans.

TRUDEAU: But recently, two more species have been added to the list of contagious yawners.

PROVINE: Our cousins the chimpanzees as well as highly social mammals, such as dogs.

TRUDEAU: Provine suggests you do a little at-home experiment. Watch your dog when he yawns. Do you catch the yawn yourself? If so, that's a brilliant demonstration of contagious yawning between different species. For NPR News, I'm Michelle Trudeau.

(SOUNDBITE OF IMAGINED HERBAL FLOWS' "CLOUDS")