I have entertained a slightly different theory most of my life. If we look at the times of occurance and facts:
- seems to be contagious
- when waking up
- when tired
- when not tired
- when interacting with other people
- when alone
We can just about throw out the "when" since they are all countered, and we are left with the contagious bit.
My theory:
Yawning was, and still is largly a sub-concious method of communication.
Back when humans had less developed language and brain functions, we would still need some method to communicate. As humans have a highly developed sub-concious system (heart movements, breathing, walking maybe), it seems reasonable that early humans would require a communicitive method that didn't require higher order brain functions. I'll cut out most of the other support theories and jet right over to a slight defense of why wouldn't we know it?
Well? It seems I tell me where to walk, or can control where to breathe. Why don't I understand when I yawn? I think that the higher order systems don't communicate well with the lower order systems. You can override many functions--you tell yourself when to walk and where to walk, and can hold your breath, but you don't know when your heart is going to beat until it does. Have you ever thought about how you walk? How do you do it? Who knows? Yes, I realize neurons relay to the muscles causing them to expand or more specifically when to contract, but *how* do you know what signaling in the brain to use? This all leads (to me) to the premise that higher functions can't easily communicate with lower functions, vis-versa. Ergo we don't understand why we yawn.
The whole bit about about contagious is helpful. When you speak to others, do they not usually respond? Logic dictates that if a yawn is communication, a responce is usually in order.
I guess I'll leave it at that. Thoughts? Do me a favor and pm me when you reply to my idea. I don't like email notifications...