This week’s question was asked by friends.
QUESTION: Why do people yawn?
ANSWER: No one knows for sure. Babies yawn, teens yawn, middle-age people yawn and older people yarn. All humans yawn. So do most vertebrate animals. Yawning certainly must serve some useful function. But the act of yawning has puzzled scientists throughout the ages.
The common explanation is that we yawn to gulp in extra oxygen. But recent studies suggest that people given pure oxygen yawn just as much as people breathing ordinary air. These same studies show that yawning may be a way of preventing oxygen-carrying blood from leaving the brain.
Another theory suggests that we are bored or tried and that we are not breathing as deeply as we should. By yawning, we gulp in more air and get rid of more carbon dioxide. When we yawn, the head tilts back, and our eyes squint. The jaw drops and stretches, increasing blood flow in the neck, face, and head. That deep intake of breath forces a downward flow of spinal fluid and blood from the brain. The cool air breathed into the mouth cools these fluids.
Another speculation says that yawning and stretching are ways to flex the lungs, muscles and joints and increase the heart rate and make us feel more awake.
Yet another theory poses that yawning is a way to redistribute surfactant, the oil-like substance that keeps the lungs lubricated inside and keeps the lungs from collapsing.
Is yawning contagious? “Yawning is a physiologic mechanism coming from being bored, sleepy, and waking up slowly. It is considered to be a slow breath.” according to Dr. Wayne Lawson, Department of Respiratory Care at University of Texas Hospital at Houston. “Yawning is psychological because you can tell yourself not to do it and you won’t. This is the reason why it is not contagious.”
“If yawning was contagious, you would not be able to do anything about it. Your subconscious is responsible for making you yawn,” says Dr. Jerry Yee, also at the University of Texas Hospital.
A series of recent experiments suggests a surprising reason for yawning. It cools the brain, says Andrew C. Gallup, PhD, a postdoctoral research associate at Princeton University.
“Together these processes may act like a radiator, removing overly hot blood from the brain while introducing cooler blood from the lungs and extremities, thereby cooling the brain surfaces,” Gallup says.
Gallup’s theory predicts that colder outside air should cool the brain better than hot air. The body should therefore yawn more when the air is cool, and yawn less when the air is hot. Where better to test this than in Tucson, Arizona. Gallup’s team went there twice: Once in the winter, when it was a cool 71.6 degrees Fahrenheit outside, and once in early summer, when it was 98.6 degrees Fahrenheit.
Sure enough, in the cooler weather 44 percent of people yawned. But in hotter weather, only 24 percent of people yawned. Moreover, people yawned more if they’d been outside longer in the cool weather and yawned less if they’d been outside longer in the hot weather.
There are a lot of good theories out there. Some or all may account for our yawning.
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