More people will be flying this summer than ever, and they’re going to be squeezed into tighter and tighter spots. In this file photo, United Airlines planes sit on the tarmac at Newark Liberty International Airport. (Julio Cortez/Associated Press)

More people will be flying this summer than ever, and they’re going to be squeezed into tighter and tighter spots.

Does that mean that videos and other reports of dysfunctional and occasionally violent behavior will keep social media busy?

You bet, fight fans.

Airlines for America, the industry’s lobby, expects a record 234.1 million people will be flying this summer, up an estimated 4 percent compared to last year. Meanwhile, the airlines continue cramming more seats onto their aircraft. It seems intuitive that the more passengers airlines cram into an aircraft, the more aggressive those passengers become. But there’s also some science that suggests that’s the case.

More than 50 years ago, John B. Calhoun, a researcher at the National Institute of Mental Health conducted experiments with rats and mice that demonstrated the ill effects of crowding. When crammed into one place with nowhere to go, the animals suffered a dramatic breakdown in normal behavior. They became hyperaggressive and even violent, or morbidly withdrawn as their ability to cope vanished. The more density, the more aggression and deviant behavior these rodents showed one another. People can act the same way, he argued.

Daniel Stokols, a professor of psychology and social behavior at University of California at Irvine who has conducted research on the effects of crowding, witnessed those stresses firsthand during a recent coast-to-coast flight. If anything, airlines may be contributing to the psychological conditions that aggravate people’s stress.

“People are like cattle being squished together, to get as many people on that plane,” Stokols said. “And so tempers can flare. It’s a situation where people feel vulnerable.”

Stokols and other scientists caution against drawing close parallels between animals and humans, and it should be noted that Calhoun’s pioneering experiments were focused on entire populations, not the sort of temporary crowding people endure on trains or planes. But there are still valid conclusions to be drawn from those animal studies that explain why passengers and flight crews act out on an overcrowded plane, especially when considering nuances.

For one thing, density itself is not a bad thing for us. Think of a rock concert or a party, Stokols said in an interview Tuesday.

“You want a party to have high density,” Stokols said. “The more people who show up, the rowdier and exciting the party, that makes it a desirable event. The same thing with an athletic event.”

So although animals can become undone by simple density of a crowd, the physical proximity they share to each other, for people, the number of bodies doesn’t necessarily translate into what Stokols calls “crowding stress.” People can not only tolerate intense crowding, they might like it in certain circumstances. Other factors need to be part of the mix for people to wig out, and those happen to be in good supply aboard a commercial airline flight.

On flights, people do not find themselves surrounded by friends or fellow Bruce Springsteen fans. They’re surrounded by strangers who want to recline their seats or put the tray table down. They’re cramped. They can feel vulnerable to contracting diseases or infections from the sniffling and coughing passengers around them. They’re forced to form a line near a tiny lavatory that’s teeming with microbes. The people sitting in the aisle seats near that line feel hemmed in even more.

“It’s a much more fraught situation,” Stokols said. “[W]hen you feel like the airlines are against you and you feel they’re trying to exploit your comfort for their profit, and others on the plane are in your way and you don’t know them, the situation is more ripe for conflict.”

Research has also shown that certain variables can amp up stress further, such as competition. Think of that next time you’re in a race to find an empty overhead bin.

What to do?

“One approach would be to relax the Almighty profit-margin ideal and trade some of that off to really go out of their way to provide good service,” Stokols said.

Best pack boxing gloves next time you fly.

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