Why Do We Yawn?

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The Old Wives told tales of yawning as a response to a need for increased amounts of oxygen all at once. If the old wives had consulted the physiologists before they spoke, they might not come off sounding like Bobby Boucher's "Mama".. or maybe she was one of the old wives herself. Our bodies do need oxygen to stay upright, but our respiratory system isn't regulated by O2 levels, but CO2 levels (which might make us the embodiment of Global Warming, since that is apparently all CO2 is good for. ;~D). So, that would make us consider yawning a response to the need to get CO2 out of our systems. This would make sense, and could even be true... but, well... it just isn't. There are "experts" for everything, and one of he reigning gurus of yawn is Dr. Robert Provine of The University of Maryland's Psychology Department. He did several studies and tests on human volunteers. Among the tests he did was putting tape over the mouths of volunteers for hours on end. He noted that the subjects yawned while they mouths were tape, but never felt that satisfying buzz that comes after a good one. They never really felt satisfied, but they also didn't continue to yawn. Also neither their O2 or CO2 levels changed significantly before or after the yawns. He also stuck the suckers in to air sealed rooms. While they were cooling their heals in these rooms, he manipulated the O2 and CO2 available for them to breath. In this case, the human guinea pigs' O2 and CO2 levels changed perportionately to the manipulated room gasses... but their yawning didn't. Which of his tests did have a significant effect on yawning? He had the subjects watch music videos for awhile, then he had them stare and black and white images test patterns. Sure enough, the test patterns seemed to elicit more yawns per minute than the videos. (apparently they weren't watching Yanni or Interpol videos.. which are almost as excited as test patterns... almost). So, what causes us to exercise our platysma muscles to just short of sure strain? I got my answer one time watching an MGM movie. Ok, I wasn't actually watching the movie yet, and the sound was all the way down. What I saw was the famed MGM lion roaring... but without sound, I only saw him to his trademark schtick. It looked a lot like a yawn. That got me thinking. If we did roar, when would we do it? My military training answered this question. In the military I had a pretty impressive "bellow" (otherwise known as "sounding off"). I could be heard a couple of blocks away and (although no one seems to believe me on this one) I even knocked down a hanging plant. Anyway, I went to the mirror and did a little Provinian study of my own. I admit that my bellow didn't rattle the windows like it used to, but sure enough, looking in the mirror my facial contortions were similar to what happens to my face when I yawn. In the military we "sound off" for a few reasons. We do it to motivate ourselves (few things take us from being ready to give up to full of vim and vinegar than a hightly motivated "AIRBORNE!", "ARTILLERY!" or "ADMINISTRATIVE SPECIALIST! (ok the last one probably doesn't even motivate the most proud 71L in the history of the U.S. Military... but I wouldn't want to leave the REMFs out completely here). The shot of adrenalin that comes with a high decible yell has helped me over that wall more than once. We do it to motivate others. When one troop yells from the bottom of their diaphragm, others join in. Everything I brought up in the last paragragh works logorithmically to the number of troops who join in. The other reason we do it is to intimidate others. This is done by Drill Sergeants to keep the recruits on edge and off kilter. Some people see Drill Sergeants in movies and TV and wonder why someone yelling all the time is intimidating. They just don't understand. Even the best "surround sound" set up can't do justice to the well trained and oft practiced bellow of a Drill Sergeant. When one person's voice echoes over the woodline and you hear the rafters creek in deference... well, it is an experience beyond a speaker's abilities to reproduce. So, let's get back to yawning. When do we yawn? We yawn when we are tired, bored... or when someone else yawns. In other words, we yawn at times when we could use a little motivating rebel yell, or when someone else seems to be trying to intimidate us. I wonder if there was a time in our genetic history when humans roared... but through time and for reasons of "decorum" we turned down the sound and are left with the remnants... and the opposite effect.