Bears do it; bats do it. So do guinea pigs, dogs and humans. They all yawn. It’s a common animal behavior, but one that is something of a mystery.

There’s still no consensus on the purpose of a yawn, says Robert Provine, professor of psychology and neuroscience at the University of Maryland, Baltimore County. Provine has studied what he calls “yawn science” since the early 1980s, and he’s published dozens of research articles on it. He says the simple yawn is not so simple.

“Yawning may have the dubious distinction of being the least understood common human behavior,” Provine says.

There are many causes for yawning. Boredom, sleepiness, hunger, anxiety and stress — all cause changes in brain chemistry, which can trigger a spontaneous yawn. But it’s not clear what the yawn accomplishes. One possibility is the yawn perks you up by increasing heart rate, blood pressure and respiratory function.

“[Yawning] stirs up our physiology and it plays an important role in shifting from one state to another,” Provine says.

When violinists get ready to go on stage to play a concerto, they often yawn, says Provine. So do Olympians right before a competition, or paratroopers getting ready to do their first jump. One study found that yawning has a similar impact on the brain as a dose of caffeine. To read more from MICHELLE TRUDEAU and JANE GREENHALGH, click here.

How do early-life traumas get under our skin? A researcher details his quest for the stress-causing mechanism.

By the late 1990s, our group at the Canadian Institute for Advanced Research had identified robust connections between early adversity and lifelong anxiety and stress, leading to problems in social relationships and mental and physical health—and even to shorter lives. What we needed was an explanation for why this was happening: How does early-life stress “get under the skin”?

Enter Michael Meaney, a professor at McGill University who specialized in neurology, stress, maternal care, and gene expression. He had been studying rodents displaying stress dysregulation (SDR), who were over-reactive to stressors and stayed in a stressed-out state longer. He had discovered physiological differences and behavioral problems in rats who’d been deprived of maternal nurturing, which aligned with previous studies, but he also arrived with a brand-new and as yet unpublished finding. He had actually found a biological mechanism—a process that seemed to explain why those who experienced stress early in life had so much trouble thereafter. As he explained what he had learned, we suddenly realized that this was the missing piece of our puzzle. To read more from Daniel P. Keating, click here.

Airline passengers have to deal with a lot these days; getting bumped from flights and losing luggage on top of the general anxiety that nervous flyers always feel.

At the Cincinnati Northern Kentucky International Airport, miniature horses deliver a calming force two times a month. Denver and Ruby, two of 34 therapy horses at Seven Oaks Farm in southwest Ohio, trot out of their trailer and into the ticketing area.

That’s where Shoma Anjola spots them. He’s traveling from Toronto and saw a therapy dog at another airport. “It’s quite amazing that I saw one on my way and then one [on the way] back to Canada. I’ve never seen any in my entire time traveling around different airports.”

During Kentucky Derby season, therapy horses dress the part as they greet passengers at the Cincinnati Northern Kentucky International Airport. More than 30 airports across the country now have therapy dogs. San Francisco has a therapy pig. San Jose, Calif., began a dog program after the Sept. 11 attacks and now has 21 therapy dogs and a therapy cat. To read more from ANN THOMPSON, click here.

At long last, introverts are having their day. Over the last few years, being quiet and inner-directed has become not only acceptable, but downright trendy. But introversion often gets mistaken for its more restrictive, self-conscious, but treatable cousin, social anxiety

For the quiet types among us, “introversion” and “social anxiety” frequently get used interchangeably. Or, just as often, social anxiety is mistakenly thought of as an extreme form of introversion. But while you can definitely be a socially anxious introvert, you can also be socially anxious extrovert—for example, you may really want to go to the bar with your co-workers but worry they actually don’t want you there. Or you may crave company but obsess about the possibility you’ll say something stupid.

But the two terms are actually quite different. Far from being a psychological tomato-tomahto, the two are more like apple and orange—here are five big differences. To read more from Ellen Hendriksen click here.

When you’ve been hurt by someone, it’s not always easy to let it go. But holding on to a grudge will only make you feel worse—and not just emotionally. Resentment can cause your blood pressure to spike and trigger the release of stress chemicals that can make you physically sick. And the truth is: It doesn’t really do any good anyway. As the saying goes: “Not forgiving is like drinking poison and expecting the other person to die.”

The paradox is, when you’ve been wronged, forgiveness is the only thing that provides relief from the pain. Sound like a bitter pill to swallow? Read on to learn how forgiving others (and yourself) can help you release the heavy burden of resentment and experience more freedom.

1. Understand forgiveness

Before you attempt to force forgiveness on your most tender hurts, consider what it is you’re asking of yourself: Forgiving doesn’t mean that you condone what happened or that the perpetrator is blameless. It is making the conscious choice to release yourself from the burden, pain, and stress of holding on to resentment. To read more from Stefanie Goldstein and Elisha Goldstein, click here.

An impressive amount of research has linked frequency of sex with greater happiness. One study even put a monetary estimate on it. They said that the happiness spurt from having sex once a week compared with monthly is similar to the boost you’d get from earning an extra $50,000 a year (though for anything more frequent than weekly sex, the benefits seemed to tail off).

Asking if and why more sex makes us happier may sound like asking the blindingly obvious, but of course a lot of pleasurable activities don’t have long-term emotional benefits; it’s also tricky to rule out the simple alternative possibility that we’re more likely to have sex if we’re happy.

In a series of studies in Personality and Social Psychology Bulletin, psychologists in Switzerland and Canada have looked beyond the immediate bliss that sex can bring, and they say that the main reason that more sex seems to contribute to greater long-term happiness is because of all the cuddling (and other expressions of affection) that’s involved, both at the time, and for hours afterwards. To read more from Christian Jarrett, click here.

On a family trip to Rome a few years ago, I had the brilliant idea to take my sleep-deprived young daughters to the Vatican. It didn’t go well. “This is boooring!”

Finally we made it to the Sistine Chapel. One of my girls glanced at the image of Adam and God and said, “Why is there only a man?” Then her sister pointed out, “Is that Eve under God’s arm?”

That’s when it hit me. Since antiquity, one story has stood at the center of every conversation about men, women and sexuality in the West. That couple is Adam and Eve. Yet instead of celebrating them, history has blamed them for bringing sin, lust, even death into the world. Adam and Eve — but mostly Eve — are victims of the greatest character assassination ever.

I’ve spent the last few years traveling in the footsteps of history’s maiden couple, from the Garden of Eden in Iraq to John Milton’s London to Mae West’s Hollywood, trying to figure out whether our culture’s first relationship can teach us something about relationships today. To read more from BRUCE FEILER, click here.

March 20 is the International Day of Happiness, the result of a UN resolution adopted in 2012 that identifies the pursuit of happiness as “a fundamental human goal” and promotes a more holistic approach to public policy and economic growth — one that recognizes happiness and wellbeing as important pieces of sustainable and equitable development.

The official page for the International Day of Happiness, HappinessDay.org, goes one step further in declaring happiness a “universal human right.”

But is happiness really a human right? And is happiness a goal we should actively pursue? I think the answers are “no” and “it depends.” To read more from TANIA LOMBROZO, click here.

Lonely People Report More Severe Cold Symptoms, Study Finds.

A study published Thursday in Health Psychology found that among people who fell ill after being exposed to a cold virus, those who were lonely were more likely to report severe runny nose, sneezing, sore throat and other symptoms. That adds to the evidence linking loneliness to more serious health problems including heart disease and early death.

There’s been much less research on whether loneliness is correlated with common, acute, short-term illnesses like colds, says Angie LeRoy, an author of the study and a Ph.D. candidate in psychology at the University of Houston who is also affiliated with Rice University. To read more from KATHERINE HOBSON, click here.

Telehealth takes a lot of forms these days. Virtual visits with a health care provider can take place by video, phone or text, or via the Web or a mobile app. The one commonality: You get to consult a doctor from your home, the office, Starbucks or anywhere with a wifi or mobile connection.

These appointments can be quick, and save you from having to schlep across town and sit in a waiting room, leafing through year-old Time magazine articles, as prelude to every visit with a doc.

There’s no debating that telehealth appointments can be convenient — and potentially even life-saving for people who live in remote areas. But are they also cheaper than in-person visits, as the telehealth companies claim? Not necessarily, according to a study published this month by the RAND Corporation, in the journal Health Affairs. To read more from Jon Brooks, click here.