No one really knows why yawning is contagious or why we yawn at all. Some scientists are wondering if yawning is from our deep past -- part of our evolutionary history.

In early humans, yawn contagiousness might have helped people communicate their alertness levels to each other, and thus coordinate their sleep schedules. Dr. Provine suggests that perhaps yawning is like stretching. Yawning and stretching increase blood pressure and heart rate and also flex muscles and joints. Apparently, the urge to copy an observed yawn is clearly an automatic response triggered by our brains, but it is also an unconscious behavior.

Researchers have found that wherever yawning might affect the brain, it bypasses the part of the brain that consciously analyzes and mimickes other peoples actions,called the mirror-neuron system (MNS), a part of the brain also linked to learning and understanding. The MNS contains a special type of neurons that become active when doing something consciously. The researchers found that yawning actually deactivates a different part of the brain, called the left periamygdalar region. This means that there is neuro-physiological evidence showing that yawning is contagious. One thing seems clear from the study is that contagious yawning does not rely on brain mechanisms of action understanding and it is automatically released and generally unconscious action.