We yawn because we care

How contagious is yawning? Enough that I'm yawning right now just from writing about it. Admittedly, I'd never given it much thought, but I always kind of assumed that contagious yawning—that tendency to pick up a yawn from the people around you and pass it on like the evil videotape in The Ring—was something all humans were susceptible to.
We yawn because we care