Did you know that there is a theory of the yawn that draws its origins back to the tribal need to remain together? Yep, apparently, in order to survive, a group had to keep everyone on the same schedule (i.e. sleeping and waking at the same time) in order to survive. If someone got off track, was sleeping while the rest were moving on in their hunting and gathering, they'd be SOL, alone and eventually eaten by a bear or something. We all know that yawns are contagious, in fact, you're probably yawning once or twice as you read this little post, but perhaps they're so contagious because they serve that purpose of keeping everybdy together. SO...when your friend yawns, she's not really telling you that she's tired, but instead, that YOU should be getting tired, and sleeping, or you'll wind up alone and dead. Never thought a lazy yawn could be so threatening.