Why Do We Yawn?

The short answer is that no one really knows.

The long answer is that no one really knows, but there are plenty of interesting theories:

1. 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.


Last year, a team of researchers at the University of Albany proposed that the purpose of yawning is to cool the brain. They conducted an experiment similar to Provine's and again found that raising or lowering oxygen and carbon dioxide levels in the blood did not change the amount or length of yawns.

Subsequent experiments focused on two well-established brain cooling mechanisms: nasal breathing and forehead cooling. When you breathe through your nose, it cools the blood vessels in the nasal cavity and sends that cooler blood to the brain. Likewise, when you cool your forehead, the veins there, some of which are directly connected to the brain, deliver cooler blood. The researchers found that their test subjects with warm or room temperature towels pressed against their heads yawned more than those with cold towels. Subjects who breathed through their noses during the experiment did not yawn at all.

The researchers said their evidence suggests that taking in a big gulp of air with a yawn cools the brain and maintains mental efficiency.

3. Another theory says that yawning has more to do with sociology than physiology and also tackles the question of contagious yawning.

Almost all vertebrates yawn spontaneously, but only humans, chimps and macaques yawn as a result of watching another individual do it. Given that these are social creatures that live in groups, the contagious yawn may have evolved as a way to coordinate behavior and maintain group vigilance. When one individual yawned, the group took that as evidence that their brain temperature was up and their mental efficiency was down. If all members of the group then yawned, the overall level of vigilance in the group was enhanced. In humans, who have color-coded charts to signal how vigilant they should be, yawns may still be contagious as a vestigial response.

charlotte.jpgWhile yawns are still largely a mystery, here are some things we know for certain:

"¢ The average yawn lasts about six seconds.

"¢ In humans, the earliest occurrence of a yawn happens about 11 weeks after conception "“ while we're still in the womb.

"¢ Your heart rate can rise as much as 30% during a yawn.

"¢ 55% of people will yawn within five minutes of seeing someone else yawn.

"¢ Blind people yawn more after hearing an audio tape of people yawning.

"¢ Reading or even thinking about yawning can cause you to yawn.

"¢ While researching and writing this story, I yawned 37 times.

Quick True/False: World Capitals
Bain News Service - Library of Congress, Public Domain, Wikimedia Commons
10 Pats Born on St. Patrick's Day
A photo from the 1919 wedding of Princess Patricia of Connaught to the Hon. Alexander Ramsay.
A photo from the 1919 wedding of Princess Patricia of Connaught to the Hon. Alexander Ramsay.
Bain News Service - Library of Congress, Public Domain, Wikimedia Commons

Need some St. Patrick's Day conversation fodder that doesn't involve leprechauns or four-leaf clovers? Ask your friends to name a "Pat" born on St. Patrick's Day. If they can't, they owe you a drink—then you can wow them with this list of 10.


Princess Patricia was the granddaughter of Queen Victoria, who gave up all of her royal titles when she married a commoner. She was born at Buckingham Palace on March 17, 1886.


The Dallas star was born on March 17, 1949. And here's a totally random fact about Duffy: His nephew is Barry Zito, former MLB pitcher for the Oakland Athletics and the San Francisco Giants.


Pattie Boyd
Larry Ellis, Express/Getty Images

Pattie Boyd is well-known to lovers of classic rock: She has been married three times, including once to George Harrison and once to Eric Clapton, who both wrote a couple of the most romantic songs in rock history in her honor (including The Beatles's "Something" and Clapton's "Wonderful Tonight"). Boyd was a model when she met Harrison on the set of A Hard Day's Night in 1964; the pair were married two years later. They divorced in 1977 and she married Clapton, Harrison's close friend, in 1979. She also had an affair with Ronnie Wood of the Rolling Stones toward the end of her marriage to The Quiet Beatle.


Belfast-born Pat Rice is a former footballer and coach who spent the bulk of his career with Arsenal F.C. (that's "football club," a.k.a. soccer to us Americans). He joined the Gunners in 1964 as a mere apprentice, turning pro a couple of years later. He became captain in 1977 and left the club for a few years in the early 1980s to go to Watford, but returned after he retired from playing in 1984. In 2012, after nearly 30 years with the organization, he announced his retirement.


Patty Maloney is an actress with dwarfism who stands just three feet, 11 inches tall. She has appeared in many movies and T.V. shows over the years, including operating the Crypt Keeper puppet in Tales from the Crypt. She also played Chewbacca's son Lumpy in The Star Wars Holiday Special.


Michael C. Hall and Mathew St. Patrick in 'Six Feet Under'

Ok, so Mathew St. Patrick is the stage name of the actor, but he was born Patrick Matthews in Philadelphia on March 17, 1968. You probably know him best as David's boyfriend Keith on Six Feet Under.


He may not be a household name, but the recording artists Patrick Adams writes for and helps produce certainly are. Adams has been involved in the careers of Salt-N-Pepa, Sister Sledge, Gladys Knight, Rick James, and Coolio, among others.


It's possible you look at Patrick McDonnell's work every day, depending on which comics your newspaper carries. McDonnell draws a strip called Mutts featuring a dog and a cat named Earl and Mooch, respectively. Charles Schulz called it one of the best comic strips of all time.


 Singer/Guitarist Billy Corgan of Smashing Pumpkins performs onstage during Live Earth New York at Giants Stadium on July 7, 2007 in East Rutherford, New Jersey
Evan Agostini, Getty Images

Yes, you know him better as just plain old Billy Corgan: he's the face of the Smashing Pumpkins, engages in public feuds with Courtney Love, and maybe once dated Jessica Simpson. He made his debut on March 17, 1967.


Patricia Ford is a retired model probably best known for her Playboy photoshoots in the 1990s.


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