Why Is Yawning Contagious?

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What is yawning? And why do we do so much of it? Neuroscientist and yawn expert Robert Provine says it's "ancient and autonomic." It stems from early evolution and is common to many creatures—even fish do it. It's autonomic in the sense that it roots in the brainstem, way down in the basement level of the brain, where certain responses are so built-in they don't even qualify as reflexes.

Yawning has many triggers, including boredom, sleepiness, and temperature. A 2014 study suggested that there's a "thermal window" (at around 68°F) for human yawning; as ambient temperature approaches body temperature or goes down near freezing, we yawn less. According to the paper, we may yawn to regulate the temperature of our brains. This isn't the same as saying we yawn to take in extra oxygen, as evidence to date says we don't. It means that yawning might act to draw brain-soothing ambient air in through the nose and mouth.

COPYCAT YAWNING?

Over the years, scientists have observed "contagious yawning" in chimpanzees, humans, baboons, bonobos, wolves, and, to a certain extent, dogs. Yawning feels good, so why not join in when someone else yawns? Well, you're not really "joining in," because you aren't copying the yawn on any conscious level. It happens because you just can't help it. If you become self-conscious about a yawn, it stops.

While many past studies have documented the phenomenon, a more recent study, published in the journal Adaptive Human Behavior and Physiology, contends that yawns may not be contagious after all—or at least that we have not yet proven it. Experimental psychologist Rohan Kapitány of the University of Oxford conducted a review of the scientific literature on contagious yawns and found very little conclusive evidence to back up our long-held assumption that yawns are contagious.

"The belief that yawns are contagious seems self-evident," Kapitány told PsyPost, "but there are some very basic reasons for why we might be mistaken in this. If we fail to dissect that which we think we know, we might end up with conclusions that do not reflect reality. In this instance, the literature hasn't questioned the basic features of contagious yawning, and ended up with a wide range of unstandardized methodologies and conclusions."

Still, because Kapitány's study was small and extremely limited, he and his fellow authors urge other scientists to challenge their findings with experiments of their own.

"I may be wrong!" Kapitány said. "Maybe yawns are contagious!" Kapitány says he'd like to see "more robust" attempts to falsify the claim that yawns are contagious rather than "simply demonstrating it over and over [in] slightly different contexts with richer and richer explanations."

WHO DOESN'T CATCH YAWNS?

Some people with autism or schizophrenia don't exhibit a yawn-contagion response. The same is true of children under the age of four years. This has led to a variety of theories about yawning's relationship to empathy and the brain's mirror-neuron system (MNS). The idea here is that MNS deficits might lead to missing hidden empathetic cues that trigger contagious yawning. The MNS seems to be involved in the process to some extent. fMRI scans on a range of people have shown that other parts of the brain also "light up" in response to images of yawning, perhaps more so than the areas normally associated with empathy.

YAWN AND RUN

Parts of the amygdala—a brain area associated with fear and heightened attention—light up in response to images of yawning. We sometimes yawn when we're nervous, such as before a sporting performance.

So, perhaps we yawn at those times to prepare our brains for "fight or flight." Maybe contagious yawning is a smart evolutionary shortcut for readying the brains of an entire group of hominins for swift action in response to a threat. (If that's the case, then some older members would have been left behind, because older people are a little less susceptible to yawn contagion.) We are social mammals; this kind of evolutionary refinement of an existing trait (general purpose yawning becoming contagious yawning) might have helped groups to survive.

Or maybe it's a lot less deep than that. Laughing also feels good, and it too can be contagious. Like laughter, contagious yawning might help groups to bond—by signaling unselfconscious, relaxed sleepiness. Perhaps it has more to do with feeling safe than with feeling threatened.

STRAGGLERS AND FAKES

Contagious yawning is still a bit of a scientific mystery. We love to speculate about it and try to home in on the reason for it. But why should an evolutionary trait have one specific reason behind it? Often, traits survive because they cover a number of bases. Other times, they're simply evolutionary stragglers whose original purpose has faded out, but because they don't work against a creature's survival, there's no pressure to get rid of them.

One modern adaptation of yawning is not so contagious—fake yawning. You might do this as a less-than-subtle means of signaling that a conversation has dragged on too long. Why not engage in a scientific experiment next time you're in a meeting with your boss? Lean back in your chair and yawn, then note down whether he or she yawns right back at you. Maybe there's a scientific discovery in there … but probably no pay raise.

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

Why Do People Get Ice Cream Headaches?

CharlieAJA, istock/getty images plus
CharlieAJA, istock/getty images plus

Reader Susann writes in to ask, "What exactly is the cause of brain freeze?"

You may know an ice cream headache by one of its other names: brain freeze, a cold-stimulus headache, or sphenopalatine ganglioneuralgia ("nerve pain of the sphenopalatine ganglion"). But no matter what you call it, it hurts like hell.

Brain freeze is brought on by the speedy consumption of cold beverages or food. According to Dr. Joseph Hulihan—a principal at Paradigm Neuroscience and former associate professor in the Department of Neurology at the Temple University Health Sciences Center, ice cream is a very common cause of head pain, with about one third of a randomly selected population succumbing to ice cream headaches.

What Causes That Pain?

As far back as the late 1960s, researchers pinned the blame on the same vascular mechanisms—rapid constriction and dilation of blood vessels—that were responsible for the aura and pulsatile pain phases of migraine headaches. When something cold like ice cream touches the roof of your mouth, there is a rapid cooling of the blood vessels there, causing them to constrict. When the blood vessels warm up again, they experience rebound dilation. The dilation is sensed by pain receptors and pain signals are sent to the brain via the trigeminal nerve. This nerve (also called the fifth cranial nerve, the fifth nerve, or just V) is responsible for sensation in the face, so when the pain signals are received, the brain often interprets them as coming from the forehead and we perceive a headache.

With brain freeze, we're perceiving pain in an area of the body that's at a distance from the site of the actual injury or reception of painful stimulus. This is a quirk of the body known as referred pain, and it's the reason people often feel pain in their neck, shoulders, and/or back instead of their chest during a heart attack.

To prevent brain freeze, try the following:

• Slow down. Eating or drinking cold food slowly allows one's mouth to get used to the temperature.

• Hold cold food or drink in the front part of your mouth and allow it to warm up before swallowing.

• Head north. Brain freeze requires a warm ambient temperature to occur, so it's almost impossible for it to happen if you're already cold.

This story has been updated for 2019.

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

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

This article has been updated for 2019.

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