Without thinking, people act with more generosity than if they take some time to weigh the logic of their behavior.
Contrary to popular and pessimistic thought, the discovery suggests that, by default, our gut instincts lead us to be more helpful than selfish. That may explain why door-knocking and phone solicitations, which demand immediate responses, tend to bring in bigger donations than statistics-laden e-mail messages or direct mail, which puts people in a rational frame of mind and allows them to think for a while before deciding whether to give.
Likewise, people who commit heroic acts -- like the man who jumped onto New York City subway tracks in front of an oncoming train to save a young man having a seizure five years ago -- often make split-second decisions to do the altruistic thing.
"If you look at testimony of a lot of people like that describing their decisions, you can see they are heavily weighted towards intuitive thinking," said David Rand, a behavior scientist at Yale who conducted the new study while at Harvard. "People say, 'I didn't think about it. I just did it.'"
In a 2011 best-selling book called "Thinking, Fast and Slow," Nobel-Prize winning economist Daniel Kahneman argued that a lot of decision-making comes out of a tension between two types of brain processes. On the one hand, we have quick and intuitive thoughts, which are often emotional. The other mode is slower, allowing for more controlled and calculated thinking.
Until now, Rand said, researchers had yet to combine the two kinds of thought processes in a way that explained how people actually behaved.
"You could imagine either that people are intuitively selfish, that our default is to be nasty and that the way to get ourselves to do the right thing is through willpower and restraining selfish impulses," Rand said. "On the other hand, our automatic response might be to be predisposed toward cooperation, then to stop and think and realize that it's in my selfish interest to be a jerk."
To find out which scenario best explains how our minds work, Rand and colleagues conducted a series of 10 experiments that compared how people behaved when they made decisions either instantly or after a pause.
In the first experiment, people were put into groups of four and given 40 cents. Participants could choose how much of it they wanted to contribute to a common pot, which would be doubled and divided evenly among all four people. No one learned how much the others gave until the donations were completed.
In this scenario, the most lucrative strategy is to be as selfish as possible. But if everyone is generous, the group as a whole can do better.
People who made the quickest decisions about how much to give, the team reports today in the journal Nature, contributed the most cash to the common good. Those who acted in less than 10 seconds gave nearly 70 percent of their money, while those who took longer put in just over half of their original sum.
In follow-up experiments, people who were asked to recall memories that put them in an intuitive frame of mind contributed more than people who were primed to think reflectively.
And people who were randomly assigned to make their decisions more quickly gave more than people who were told to wait 10 seconds before putting in their money.
For decades, many experts have assumed that people are naturally and automatically selfish, said Simon Gächter, an experimental economist at the University of Nottingham in the United Kingdom. The new findings may offer a kinder view of humanity.
"Many decisions we have to make every day are intuitive and many people don't think through everything," Gächter said. "Apparently our gut instinct is to support cooperative behavior rather than selfishness. That's important information."
Despite the temptation to make conclusions about human nature, the new findings don't necessarily mean that people are naturally good and cooperative, Rand pointed out. He compared the automatic instinct to be generous with an impulse to eat a box of donuts.
"If you think about yourself in situations where you have a first impulse and then stop to think about it, it's not at all clear that the first impulse is the real you," he said. "You want to eat the doughnut and then you're like, 'Well no, the doughnut is not good for me.' It's not like the real you is the doughnut-eater."
Instead, we may simply learn and internalize cooperative habits that help society run more smoothly.
Either way, his study reinforces what fund-raisers already know -- that showing people a picture of a starving orphan is more likely to pull at their intuitive and emotional heartstrings. Lists of facts more often push potential donors away.
For people who strive to be better versions of themselves, the take-home message might be that sometimes, it's best to resist rationalizing and instead let your gut feelings lead the way.