Aping each other's yawns.
People yawn when they're tired, bored, or nervous, but sometimes they yawn just because they've seen someone else do it. Now, for the first time, "contagious yawning" has been documented in another species: chimpanzees. James Anderson of the University of Stirling in Scotland and colleagues in Japan found that a third of adult chimps exposed to videos of yawning chimps yawned themselves. No one knows exactly why people yawn contagiously, but recent research suggests that the roughly 50 percent of adult humans who do it are more empathetic than those who don't. Anderson says there's evidence that chimps show empathy too. And after hours of watching chimps yawn, he has a notion that yawning can be contagious across species. "When I was analyzing the videotapes," he says, "it was enough to set me off."