Those who stay together yawn together

You're more likely to respond to a yawn with another yawn when it comes from family member or a friend than from a stranger, says a study published Dec. 7 in the online journal PLoS ONE.

The phenomenon of "yawn contagion" is widely known but little understood, and this new study, led by Ivan Norscia and Elisabetta Palagi of the University of Pisa in Italy, suggests that it occurs at least in part as a form of social empathy. The researchers found that yawn contagion was highest in response to kin, then friends, then acquaintances, and finally strangers - the same pattern as is seen for other measures of empathy as well.

Based on these results, the authors conclude that "for the first time, yawn contagion is affected by the empathic bond that links two people, by considering humans in their natural settings."