Researchers said yawning is a mechanism that keeps the brain vigilant in times of stress.

They've posited the contagious nature of yawns evolved from a number of species to protect family and friends by keeping everyone vigilant. Changes in brain chemistry trigger yawns, which normally occur for about six seconds and in clusters.

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Gregory Collins, a researcher at the University of Texas Health Science Center in San Antonio, stated these cues indicate how complicated a system yawning is. He's worked on understanding the chemical processes at work in the brain.

Many misconceptions surround yawning. It was believed yawning when in the presence of another yawner was an expression of empathy. It was also thought that yawning was the body's way of correcting a lack of oxygen.

Scientist have begun to build clues that lead them to understand yawning's real nature.

They observed that yawning occurs more during summer time. Also, infants and schizophrenics aren't affected by the contagious nature of yawning.

Most significant is that people yawn at odd times, like parachutists before jumping out of a plane or Olympic athletes before their event.

Dozens of experiments with animals were performed to understand why this is. All animals with backbones seem to have yawning as a unifying factor.

The leading hypothesis is that yawning keeps the brain cool and at its optimal working temperature.

The brain is very sensitive to overheating, said Andrew Gallup, an assistant professor of psychology. Reaction times slow and memory wanes when the brain's temperature varies from the standard 98.6 degrees Fahrenheit.

Stress and anxiety serve to make brains hotter, which is why yawning helps cool and maintain the prime and maximum efficiency of the brain, said Gallup.

While studies show that people yawn more when tired, it still isn't clear why.

Provine said yawning may usher a change of states, such as from sleeping to waking, though the psychological side of it all is still obscure.

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