all the articles written by Bob Provine and more then 1600 other webpages : history, neurophysiology, neuropharmacology, pathology, explanation about its contagiosiness and more

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“The idea that we yawn to get rid of carbon dioxide and take in more oxygen has been disproved by research, but persists as the “common wisdom” answer. According to this theory, people breathe more slowly when they’re bored or tired and less oxygen gets to the lungs. As CO2 builds up in the blood, the brain reflexively prompts a deep, oxygen-rich breath.

The problem with this theory is a 1987 study by Dr. Robert Provine, who is regarded as the world’s foremost yawn expert. Provine set up an experiment in which volunteers breathed one of four gases that contained varying ratios of CO2 to O2 for 30 minutes. Normal air contains 20.95% oxygen and 0.03% carbon dioxide, but neither of the gases in the experiment with higher concentrations of CO2 (3% and 5%) caused the research subjects to yawn more.”

The explanation that yawning cools down the brain has more support (read on in the Mental_Floss blog), but sadly, there is no definitive answer to why we yawn.

Hold on, all this talk about yawning is…. making me…. yawn.