One study says there are 4 types of people. 2 of them might screw you over. Which are you?

How much do you really trust people?

That's what scientists in Spain wanted to find out. So they staked out a festival in Barcelona and recruited about 500 volunteers to play a little carnival game for fun, prizes, and, you know, advancing our knowledge of human psychology.

Step right up! Step right up and learn whether you can trust your friends! Photo from iStock.


The games were all variations of the prisoner's dilemma.

What's the prisoner's dilemma? I'll explain. (You can read this section in a gangster-y detective voice if you want).

Image from iStock.

It's a famous thought experiment that helps us figure out how people manage trust, risk, and temptation while making decisions, see? If you're being traditional, what you do is get two wise guys, separate the lugs, and tell 'em that they're both under arrest. But you're a nice guy, and you've really got their best interests at heart, so you'll cut 'em a deal: If they rat on their buddy, they go free.

But here's the twist, if they both rat, both go to the slammer. Of course, they could both clam up, in which case you can't do much. Maybe give 'em a little time in the clink, but that's about it.

Imagine that you were the prisoner: Do you trust your friend and clam up so you're both safe from prison?

Or do you think you can play 'em by turning them in and getting yourself a better deal? (You can stop the gangster voice now. Or don't. It's a free country.)

This kind of game also happens on reality TV all the time when partners have to decide whether they want to split the money or take it all. And you can tweak the game by changing how big the rewards and punishments are, too.

In the case of the Spanish study, the scientists made the volunteers play a few different games with different setups.

Instead of trying to place people's reactions in pre-existing categories, the scientists in this study gathered everyone's results, then let a computer group the people together as best it could.

This is what it found:

First, there were the optimists. These people will work together whenever the everyone-works-together option is most rewarding. They seem to believe that when the payoff's obvious, everyone will work for it.

Then, there were the pessimists. These people always expect to get screwed over and will only try to cooperate when they'll benefit anyway.

Thirdly, there were the trusting people. They'll always cooperate, whether it makes sense or not. Bless their (naive) little hearts.

Finally, we get the envious people. Envious players don't really seem to care what the outcome is, as long as they're getting more.

There were roughly the same number of optimists, pessimists, and trusting people — about 20% of the group each. Envious was a bit more, at about 30%. There was also a mysterious fifth category, which the computer couldn't classify.

Living in a world of envious people might seem like a downer, but we can actually do a little scientific jujitsu on this and turn it into something awesome.

That's because this experiment is part of game theory, a branch of mathematics that studies how people make decisions, which carries important consequences in designing things like laws, political systems, or jobs.

While we like to assume people will always act rationally, this study suggests that people think with their gut as much as their brains. And knowing more about people's motivations means we can add new little incentives to big projects that affect lots of people. Maybe that new anti-poverty law needs a little bonus for the rich to appease envious players, for example — or maybe it needs a fail-safe to keep the pessimists happy.

By understanding what motivates people, we can motivate people to do good in the world.

As for what the mysterious fifth category is, maybe it's this guy:

Family
Facebook / Mikhail Galin

Putting your pet in cargo during a flight isn't always safe. In 2016, the Department of Transportation reported a total of 26 pet deaths and 22 injuries on flights. Because conditions in cargo can be uncomfortable for animals, the Humane Society recommends taking your pet aboard when you fly, or just leaving it at home.

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