The newest theory put forward about human yawning from the State University of New York at Albany claims it's because yawning cools the brain.
In the May issue of Evolutionary Psychology, a psychology professor and colleagues wrote that experiments showed volunteers yawned more often in situations in which their brains were likely to be warmer.
Volunteers were shown videos of people laughing, being neutral and yawning, and researchers counted how many times the volunteer responded with their own "contagious yawns," the New York Times reported Wednesday.
The volunteers were in three groups: some were instructed to breathe only through their noses, which is thought to cool the brain; a second group applied cold packs to their foreheads, also a cooler, and the third group applied hot packs to their foreheads.
"The two conditions thought to promote brain cooling practically eliminated contagious yawning," the researchers wrote.
Copyright 2007 by United Press International
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