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See Inside December 2011

Tortoises Don't Catch Yawns

Sleepiness and boredom aren't always contagious



Paul A. Souders/Corbis

The following post is from a series about the annual Ig Nobel Prizes in science, which honor “achievements that first make people laugh and then make them think.” They were awarded in September in Cambridge, Mass.

Now we come to the Ig Nobel Physiology Prize. Yawns are notoriously contagious in humans and in other social animals, especially primates. In humans, yawning has been thought to do various things, including cooling the brain, increasing arousal when you’re sleepy and, possibly, helping to synchronize group behavior.

Could yawning be a form of unconscious empathy? This would mean that in order to have a contagious yawn, the animals involved would have to be capable of empathy, of fellow feeling. We know that dogs and primates, and humans, probably are, but that means we can’t really test for whether it’s empathy or not. We need a species that is social but probably can’t feel for its compatriots.

That’s where tortoises come in. To test whether yawning requires empathy and thus get at the real purpose that yawning might serve, Anna Wilkinson of the University of Lincoln in England and her colleagues took a group of red-footed tortoises that lived together and trained one of them to yawn when exposed to a red square. Then they had tortoises watch the trained tortoise in action and checked them for yawns. The researchers also checked for yawns when no other tortoise was present and when the trained tortoise had no red square and so wasn’t yawning.

What they got was a big, fat negative. The test tortoises showed no notice of the other animals’ huge yawns. This may mean that contagious yawning is not just the result of a fixed-action pattern triggered when you see someone else yawn. If that were the case, the tortoises would have yawned right along with their compatriots. Contagious social yawning may require something more, a social sense or a sense of empathy resulting from complex social interactions. Of course, it could also mean that tortoises are just a really bad choice for contagious yawning. But the social explanation seems a little more supported.

—From the Scicurious Brain at http://blogs.scientificamerican.com/scicurious-brain

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