contagious yawning

There's long been a line of thought that the explanation for the altogether odd phenomenon of contagious yawning -- feeling the overwhelming urge to yawn after observing another person yawn -- is found in the empathy of the individual observing the yawn. The idea goes that the more empathetic among us are the most susceptible to contagious yawning and research shows this hypothesis tends to hold up among humans and higher apes.

Yawning is contagious, but why? Check out the leading theories on contagious yawning and empathy in this HowStuffWorks podcast.