A set of ten studies suggests that intuition promotes cooperation, but rational thought turns us selfish.

Are humans instinctively cooperative or are we naturally selfish? This question has been a topic of inquiry for thousands of years, argued over by philosophers, psychologists, and theologians. Most recently, a group of researchers from Harvard University weighed in on the question in this week’s issue of Nature.

The scientists conducted ten studies on cooperation to examine its cognitive basis in humans. The goal of this set of experiments was to determine whether we are predisposed to selfishness but become more generous once we are given time to think about it, or whether people are naturally cooperative, with selfishness only creeping in when we reflect more on our options. Taken together, the set of studies suggest that we are instinctively generous, but rational thought may make us greedier.

For several of their studies, the researchers recruited subjects from around the world using Amazon Mechanical Turk, or AMT. AMT is an online labor market that connects people to employers willing to pay small sums of money for a quick “job.” In this set of studies, the jobs consisted of short games or tasks designed to measure the correlation between generosity and response time. Participants recruited in this way are much more diverse than the undergraduates that are often the subjects in these types of experiments.

In the first study, 212 participants were given 40 cents and asked to contribute whatever portion they liked to a communal pool; at the end, whatever had been donated was doubled by the experimenters and divvied up evenly among the participants. The researchers measured the time it took each participant to make a decision about how much to give, and compared it to the amount of money they contributed. The longer people took to decide, the less generous they were.

Then, the researchers conducted a variation of this study, but manipulated the amount of time people had in which to decide how much to donate. One group of subjects had to make their decisions within ten seconds; other subjects had to wait ten seconds before they were allowed to contribute anything, and third group of participants had no time constraints at all. The researchers found that subjects under time pressure gave significantly more money than either those that had to wait or those that were unconstrained. Participants in the ‘time-delay’ condition were the least generous, donating significantly less money than those in the other two groups. In other words, those that were forced to respond instinctively cooperated much more than those that had more time to consider their options.

It appears from these studies that humans are predisposed to cooperation and generosity, and only become selfish when they take time to think about the situation. The effect was robust, occurring both in subjects recruited from AMT and in college students. Furthermore, a meta-analysis of previously published work showed that this effect was observed not only in the donation scenario described above, but also in other social “games” (such as the prisoners’ dilemma) that are either played just once or repeated multiple times.

The researchers were even able to manipulate participants into being either selfless or greedy, based on whether they were primed to think about intuition or careful reasoning. Some participants were primed to believe in their intuition by asking them to either write an essay about a time in their life when their intuition was right, or when careful reasoning was wrong. A second group, which had to write about when their intuition led them astray or when careful reasoning proved helpful, was primed to promote rationality. When asked to contribute money, donations were much higher in the first, intuitively-primed group than in the second group, which had been primed for rationality and reflection.

So where do these cooperative instincts come from? The researchers rightly warn that these results don’t necessarily mean that generosity is hardwired into our DNA; nurture may play an important role here. Humans are reared in a generally cooperative society where we engage in repeated interactions with people we know, and where our reputations are important. Under these conditions, we likely learn that cooperation is the best way to proceed, and subsequently act this way instinctively.

Only when people are put into a situation where cooperation is not advantageous (such as these experiments) and given time to think about the situation do they become more self-serving. Indeed, the researchers found that the effect disappears after repeated trials; people become less cooperative as they gain greater familiarity with these laboratory tasks.

The particularly intriguing—and somewhat counterintuitive—implications of this body of research are that the traditional ways we try to foster cooperation and generosity may actually be doing the opposite. It is possible when we ask people to consider donating to a cause or to reflect on the benefits of working together, we may actually be promoting greater levels of self-interest.

Nature, 2012. DOI: 10.1038/nature11467 (About DOIs).