Why Do We Yawn?

iStock/BraunS
iStock/BraunS

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.

2.

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.

While 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.

In What Field Was Dr. Martin Luther King Jr. a Doctor?

Express Newspapers/Getty Images
Express Newspapers/Getty Images

Martin Luther King Jr. earned a doctorate in systematic theology from Boston University in 1955. He’d previously earned a Bachelor of Arts from Morehouse College and a Bachelor of Divinity from Crozer Theological Seminary. His dissertation, “A Comparison of the Conception of God in the Thinking of Paul Tillich and Henry Nelson Wieman,” examined the two religious philosophers’ views of God in comparison to each other, and to King’s own concept of a "knowable and personal" God.

In 1989, some three decades after King had earned his doctorate, archivists working with The Martin Luther King Papers Project discovered that King’s dissertation suffered from what they called a “problematic use of sources.” King, they learned, had taken a large amount of material verbatim from other scholars and sources and used it in his work without full or proper attribution, and sometimes no attribution at all.

In 1991, a Boston University investigatory committee concluded that King had indeed plagiarized parts of his dissertation, but found that it was “impractical to reach, on the available evidence, any conclusions about Dr. King's reasons for failing to attribute some, but not all, of his sources.” That is, it could have been anything from malicious intent to simple forgetfulness—no one can determine for sure today. They did not recommend a posthumous revocation of his degree, but instead suggested that a letter be attached to the dissertation in the university library noting the passages lacked quotations and citations.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

Who Is 'The Real McCoy'?

Inventor Elijah McCoy is may or may not be "The Real McCoy."
Inventor Elijah McCoy is may or may not be "The Real McCoy."
Ypsilanti Historical Society, CC BY-SA 4.0 via Wikimedia Commons

After taking a cool, carbonated sip of champagne from the Champagne region of France, you might say, “Ah, now that’s the real McCoy.” Sparkling wine from anywhere else is technically just sparkling wine.

The phrase “the real McCoy,” which can be used to describe any genuine version of something, has several possible origin stories. And while none of them mention champagne, a few do involve other types of alcohol.

According to HowStuffWorks, the earliest known recorded instance of the saying was an 1856 reference to whisky in the Scottish National Dictionary—"A drappie [drop] o' the real MacKay”—and by 1870, a pair of whisky distillers by the name of McKay had adopted the slogan “the real McKay” for their products. As the theory goes, the phrase made its long journey across the pond, where it eventually evolved into the Americanized “McCoy.”

Another theory suggests “the real McCoy” originated in the United States during Prohibition. In 1920, Florida-based rum runner Bill McCoy was the first enterprising individual to stock a ship with alcohol in the Caribbean, sail to New York, and idle at least three miles offshore, where he could sell his wares legally in what was then considered international waters. Since McCoy didn’t water down his alcohol with substances like prune juice, wood alcohol, and even turpentine, people believe his customers started calling his top-notch product “the real McCoy.” There’s no definitive proof that this origin story is true, but The Real McCoy rum distillery was founded on the notion.

There are also a couple other leading theories that have nothing to do with alcohol. In 1872, inventor Elijah McCoy patented a self-regulating machine that lubricated parts of a steam engine without the need for manual maintenance, allowing trains to run continuously for much longer distances. According to Snopes, the invention’s success spawned a plethora of poor-quality imitations, which led railroad personnel to refer to McCoy’s machines as “the real McCoy.”

Elijah McCoy’s invention modernized the transportation industry, but he wasn’t the only 19th-century McCoy who packed a punch. The other was welterweight champion Norman Selby, better known as Kid McCoy. In one story, McCoy decked a drunken bar patron to prove that he really was the famous boxer, prompting others to christen him “the real McCoy.” In another, his alleged penchant for throwing fights caused the press to start calling him “the real McCoy” to acknowledge when he was actually trying to win. And yet another simply suggests that the boxer’s popularity birthed so many McCoy-wannabes that Selby started to specify that he was, in fact, the real McCoy.

So which “the real McCoy” origin story is the real McCoy? The 1856 Scottish mention of “the real MacKay” came before Elijah McCoy’s railroad invention, Kid McCoy’s boxing career, and Bill McCoy’s rum-running escapades, but it’s possible that the phrase just gained popularity in different spheres at different times.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

SECTIONS

arrow
LIVE SMARTER