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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.

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How Does Catnip Work?
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If you have a cat, you probably keep a supply of catnip at home. Many cats are irresistibly drawn to the herb, and respond excitedly to its scent, rubbing against it, rolling around on the floor, and otherwise going nuts. There are few things that can get felines quite as riled up as a whiff of catnip—not even the most delicious treats. But why does catnip, as opposed to any other plant, have such a profound effect on our feline friends?

Catnip, or Nepeta cataria, is a member of the mint family. It contains a compound called nepetalactone, which is what causes the characteristic catnip reaction. Contrary to what you might expect, the reaction isn’t pheromone related—even though pheromones are the smelly chemicals we usually associate with a change in behavior. While pheromones bind to a set of specialized receptors in what’s known as a vomeronasal organ, located in the roof of a cat's mouth (which is why they sometimes open their mouths to detect pheromones), nepetalactone binds to olfactory receptors at the olfactory epithelium, or the tissue that lines the mucus membranes inside a cat’s nose and is linked to smell.

Scientists know the basics of the chemical structure of nepetalactone, but how it causes excitement in cats is less clear. “We don’t know the full mechanisms of how the binding of these compounds to the receptors in the nose ultimately changes their behavior,” as Bruce Kornreich, associate director of the Cornell Feline Health Center, tells Mental Floss. Sadly, sticking a bunch of cats in an MRI machine with catnip and analyzing their brain activity isn’t really feasible, either from a practical or a financial standpoint, so it’s hard to determine which parts of a cat’s brain are reacting to the chemical as they frolic and play.

Though it may look like they’re getting high, catnip doesn’t appear to be harmful or addictive to cats. The euphoric period only lasts for a short time before cats become temporarily immune to its charms, meaning that it’s hard for them to overdo it.

“Cats do seem to limit themselves," Michael Topper, president of the American Veterinary Medical Association, tells Mental Floss. "Their stimulation lasts for about 10 minutes, then it sort of goes away.” While you may not want to turn your house into a greenhouse for catnip and let your feline friend run loose, it’s a useful way to keep indoor cats—whose environment isn’t always the most thrilling—stimulated and happy. (If you need proof of just how much cats love this herb, we suggest checking out Cats on Catnip, a new book of photography from professional cat photographer Andrew Martilla featuring dozens of images of cats playing around with catnip.)

That said, not all cats respond to catnip. According to Topper, an estimated 70 percent of cats react to catnip, and it appears to have a genetic basis. Topper compares it to the genetic variation that causes some individuals to smell asparagus pee while others don’t. Even if a cat will eventually love the smell of catnip, it doesn’t come out of the womb yearning for a sniff. Young kittens don’t show any behavioral response to it, and may not develop one until several months after birth [PDF].

But some researchers contend that more cats may respond to catnip than we actually realize. In one 2017 study, a group of researchers in Mexico examined how cats might subtly respond to catnip in ways that aren’t always as obvious as rolling around on the floor with their tongue hanging out. It found that 80 percent of cats responded to catnip in a passive way, showing decreased motor activity and sitting in the “sphinx” position, an indicator of a relaxed state.

There are also other plants that have similar effects on cats, some of which may appeal to a wider variety of felines than regular old catnip. In a 2017 study in the journal BMC Veterinary Research, researchers tested feline responses to not just catnip, but several other plants containing compounds similar in structure to nepetalactone, like valerian root, Tatarian honeysuckle, and silver vine. They found that 94 percent of cats responded to at least one of the plants, if not more than one. The majority of the cats that didn’t respond to catnip itself did respond to silver vine, suggesting that plant might be a potential alternative for cats that seem immune to catnip’s charms.

Despite the name, domestic cats aren’t the only species that love catnip. Many other feline species enjoy it, too, including lions and jaguars, though tigers are largely indifferent to it. The scent of the plant also attracts butterflies. (However, no matter what you’ve heard, humans can’t get high off it. When made into a tea, though, it reportedly has mild sedative effects.)

The reason Nepeta cataria releases nepetalactone doesn’t necessarily have to do with giving your cat a buzz. The fact that it gives cats that little charge of euphoria may be purely coincidental. The chemical is an insect repellant that the plant emits as a defense mechanism against pests like aphids. According to the American Chemical Society, nepetalactone attracts wasps and other insect predators that eat aphids, calling in protective reinforcements when the plant is in aphid-related distress. That it brings all the cats to the yard is just a side effect.

Because of this, catnip may have even more uses in the future beyond sending cats into a delighted frenzy. Rutgers University has spent more than a decade breeding a more potent version of catnip, called CR9, which produces more nepetalactone. It’s not just a matter of selling better cat toys; since catnip releases the compound to ward off insects, it’s also a great mosquito repellant, one that scientists hope can one day be adapted for human use. In that case, you might be as excited about catnip as your cat is.

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

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Why Are Mugshots Made Public Before a Suspect is Convicted by the Court?
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Jennifer Ellis:

Several reasons.

1. Mugshots can help find people when they have absconded, or warn people when someone is out and dangerous. So there is a good reason to share some mugshots.

2. Our legal system requires openness as per the federal constitution, and I imagine most if not all state constitutions. As such, this sort of information is not considered private and can be shared. Any effort to keep mugshots private would result in lawsuits by the press and lay people. This would be under the First and Sixth Amendments as well as the various Freedom of Information Acts. However, in 2016 a federal court ruled [PDF] that federal mugshots are no longer routinely available under the federal FOIA.

This is partially in recognition of the damage that mugshots can do online. In its opinion, the court noted that “[a] disclosed booking photo casts a long, damaging shadow over the depicted individual.” The court specifically mentions websites that put mugshots online, in its analysis. “In fact, mugshot websites collect and display booking photos from decades-old arrests: BustedMugshots and JustMugshots, to name a couple.” Some states have passed or are looking to pass laws to prevent release of mugshots prior to conviction. New Jersey is one example.

a) As the federal court recognizes, and as we all know, the reality is that if your picture in a mugshot is out there, regardless of whether you were convicted, it can have an unfortunate impact on your life. In the old days, this wasn’t too much of a problem because it really wasn’t easy to find mugshots. Now, with companies allegedly seeking to extort people into paying to get their images off the web, it has become a serious problem. Those companies may get in trouble if it can be proved that they are working in concert, getting paid to take the picture off one site and then putting it on another. But that is rare. In most cases, the picture is just public data to which there is no right of privacy under the law.

b) The underlying purpose of publicity is to avoid the government charging people and abusing the authority to do so. It was believed that the publicity would help protect people. And it does when you have a country that likes to hide what it is up to. But, it also can cause harm in a modern society like ours, where such things end up on the web and can cause permanent damage. Unfortunately, it is a bit of a catch-22. We have the right to know issues and free speech rights smack up against privacy rights and serious damage of reputation for people who have not been convicted of a crime. The law will no doubt continue to shake out over the next few years as it struggles to catch up with the technology.

This post originally appeared on Quora. Click here to view.

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