Hi. I’m interested to know what causes people yawn? Is there an explanation for this?
Cecil’s take on the matter: http://www.straightdope.com/classics/a2_309.html
I have heard more about the suggesting that its a social signal - a bareing of teeth, so to speak, that humans just continue to do, just like animals. Google will likely find a lot of information for you, but the short answer is, no one really knows.
cool, thanks mnemosyne!