What's in a Yawn

Everyone knows that yawns are contagious, but what is the reason behind the respiratory phenomenon. Yawning has been seen in many other vertebrates besides humans, and even the contagious characteristic of yawns is seen in other animals, such as monkeys. Many people believed that an increase in CO2 levels or a decrease in oxygen levels within the body would trigger a yawn, however in the article below, the author cites research claiming this is not the case. However, it is true that we yawn when we are tired, hungry, or just waking up. So why do we do this? Well, no one knows for sure, but some scientists speculate that this is an important part in changing emotional or physiological states. For example, when you wake up in the morning, and yawn and stretch, this is probably an important part in rearranging internal organs, and changing self perception, playing an important role in the change from tired and lethargic to aware and awake. Also, support for this hypothesis is found when professional athletes yawn before a big event. I know I always yawn when I workout, excessively. This could possibly be a mechanism for the body to change to a more aware state, or trigger attentiveness. Hope you enjoyed a good yawn while reading this article; maybe now you'll be slightly more attentive and aware while studying.
http://www.seedmagazine.com/news/2006/05/the_incredible_communicable_ya.php