The fantastic ability of humans to cooperate with each other is everywhere we look. Just marvel at how far human beings have come from their evolutionary beginnings to the construction of complex civilizations. In your own experience, your food, shelter, clothing, and physical safety, not to mention roads, electric power, waste management, intricate electronics, mass transit systems, institutions of higher education, and social welfare programs are all available to you thanks to the cooperation of many people. What’s more, the big challenges facing humanity today boil down to problems of group cooperation: How do conflicting groups come to trust each other? How can groups with competing interests make compromises and reach agreements?

Because cooperation is critical for groups to develop trade and build economic relationships, the psychological study of cooperation and trust is often carried out by researchers interested in behavioral economics and decision making. The method used in this research is to have participants make a decision so that researchers can measure how they weigh their own self-interest against a larger goal. These types of decisions are called social dilemmas because they occur in situations in which what is good for the individual (and in the short term) might not be good for the group or within a larger social context.

The Prisoner’s Dilemma

The best known social dilemma is the Prisoner’s Dilemma, modeled after a scene you’ve probably seen played out on countless television law dramas. FIGURE 9.2 depicts a typical setup. You and your partner have been apprehended after committing a burglary and hiding your loot. The detectives are interrogating the two of you in separate rooms. They know you did the crime, but they need to build their case. You are offered a lighter charge if you confess to the heist and rat on your friend. The dilemma is that you know that your partner is being offered the same deal. If you both remain silent (i.e., cooperate with one another), the prosecution’s case will be flimsy, and you’ll both get light sentences. But the best-case scenario for you personally would be to confess and squeal on your partner, assuming he’s faithfully keeping quiet. By adopting this more competitive strategy (sometimes called defection), you walk away with a fine, whereas he does a long stretch at Sing Sing. Then again, if he’s thinking the same thing, you might both end up confessing and both be locked up for five years. So maybe you should just keep your mouth shut and hope he does the same. Such a decision requires trust, and if your partner violates that trust and confesses, you’ll be the one spending 20 years in the joint. What would you do?

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When people are paired with partners to play this game over a series of trials, they often end up adopting a tit-for-tat strategy, reciprocating whatever their partners did on the last trial. A cooperative move on one trial cues the partner to make a cooperative move on the next trial. Of course, competition will also be reciprocated with competition. And generally once one player begins playing competitively, the other person responds in kind to avoid getting burned in future trials. A better strategy than tit for tat is win-stay, lose-shift: Stick with a strategy if it was successful on the previous trial but switch if the previous strategy resulted in failure (Nowak & Sigmund, 1993).

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At the heart of the prisoner’s dilemma is a very basic decision. Can I trust you or can’t I? If I can’t, I’d better protect myself by defecting. Once distrust is there, both sides compete with each other. This is how nations racing to have the largest armed force and weapons stockpiles end up finding it difficult to strike a new, more cooperative pact for disarmament.

Resource Dilemmas

The Prisoner’s Dilemma is a scenario in which the outcome of a decision is interdependent with the choices that others make. Other social dilemmas involve competition for scarce resources. One resource dilemma is called the commons dilemma. The term commons comes from medieval times, when people would bring their herds to the town commons to graze (Hardin, 1968). Although it was in everyone’s self-interest to keep the commons healthy, overgrazing by each individual farmer could easily spell the destruction of the resource, creating the “tragedy of the commons.” The same dilemma arises in people’s modern lives. Nearly all issues of environmental conservation are examples of the commons dilemma. It is easy for each individual to think, “Oh, if I use just a little more water than I should, not much harm will be done,” or for a corporation to say, “If we cut down just a bit more rain forest than we need, no one will notice.” The problem is that when many people or groups think this way, the common resources start to dry up. Solving a commons dilemma requires cooperation of self-restraint to avoid depleting a limited resource.

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Another type of resource dilemma is called the public goods dilemma. A valued resource can continue to exist only if everyone contributes something to it. Local blood banks, libraries, and public radio and television are all examples of public goods that endure only because enough people chip in to keep them going. Solving a public goods dilemma requires cooperation of contributions so that the resource can be maintained. Indeed, taxes are society’s solution to this dilemma: Although you might not like to see those taxes come out of your weekly paycheck, they do help pay for the roads you drive on, the schooling you have received, and the parks where you vacation.

In both kinds of resource dilemmas, beware of free riders. These are individuals who take more than their fair share from the common pool or refuse to contribute to the public good, even while enjoying the same benefits. Free riders serve their own self-interest instead of cooperating for the larger social goal.

Distribution Games

Researchers also study cooperation by looking at how people behave when faced with distribution games. These are called games because they involve somewhat artificial situations, yet they are not frivolous: They reveal the fundamental psychological processes by which people make cooperative decisions in their everyday lives. Distribution games are set up so that one person or group has the power to decide how resources get distributed. In the ultimatum game, one person (the decider) is given a real sum of money and told that she can decide how much to keep and how much to give to another person. The other person (the recipient) then chooses to either accept or reject this offer; but if the recipient rejects the offer, no one gets money. Researchers can look at whether people are more or less likely to distribute outcomes equally. The dictator game is similar, except that the recipient doesn’t have the option of “punishing” the decision maker by rejecting his or her sum. This allows researchers to look at people’s reactions to unfair distribution of resources.

In both games, people often distribute money equally, even though it clearly would be in their self-interest to take the whole pot and give nothing to the recipient (Camerer, 2003). People value fairness. In fact, when deciders playing the dictator game are primed with the concept of fairness and thus motivated to do the right thing, they sometimes give away more money than they keep for themselves (Jonas et al., 2013). Recipients also will punish an unfair decider by rejecting his or her offer in the ultimatum game, even when such punishment comes at a cost to themselves. If your partner offers you only $2.00 and chooses to keep $8.00 for himself, you might reject the offer and forfeit your two bucks in order to send a clear message to your partner that his unfairness is unacceptable.

These dilemmas and games allow researchers to study cooperation in its essence: How do people decide between what’s good for other people (cooperation) and what’s good for themselves (competition)? A number of factors nudge people toward either cooperation or competition. One factor is the norm that is salient in the person’s immediate context. When a prisoner’s dilemma was labeled the “Community Game,” participants chose to cooperate on twice the number of trials than when the same dilemma was called the “Wall Street Game” (Liberman et al., 2004).

In fact, very subtle contextual cues can make a difference, although these cues often interact with people’s personalities. In one study, subliminal primes of competition cued more competitive behavior in the Prisoner’s Dilemma, but only among participants who generally were high in competitiveness (Neuberg, 1988). There are also interesting interactions between people’s own dispositions and how their partner plays the game (Kuhlman & Marshello, 1975). Highly competitive people consistently defect regardless of the strategy their partners adopt, but highly cooperative people conform to their partner’s strategy by cooperating when he cooperates, but defecting if he defects. This means that when a consistently competitive person plays with a cooperative person, competitive strategies rule the day.

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Culture also plays a role in cooperative tendencies. On the surface, it might seem that individuals from collectivist cultures would generally be more cooperative. After all, what better way to achieve social harmony than through cooperation? The full picture is more complex. People from collectivist cultures do cooperate more than those from individualist cultures, but only when they are interacting with friends (Leung, 1988); when interacting with strangers, collectivists can actually be more competitive. We see this in studies that prime different cultural identities. When Chinese Americans are primed to think about their Chinese identity (rather than their American identity), they become more cooperative when playing with friends but not with strangers (Wong & Hong, 2005). To sum up, cooperative tendencies might be more or less accessible for some individuals than others, but these dispositions are also cued by who you are with and what’s going on around you.

After considering factors that influence when people cooperate, we might wonder why people cooperate. Some researchers have addressed this issue by studying the neurocognitive and physiological processes that are triggered when people make decisions about social dilemmas. One line of research looks at the biological basis of trust, a prerequisite for cooperation. The hormone oxytocin is a biological marker of a range of prosocial behaviors including caregiving, social attachment, love, and trust (Porges, 1998). When other people place their trust in you, your levels of oxytocin rise and increase your willingness to act in a trustworthy way (Zak et al., 2005). Perceiving more trust also increases oxytocin levels, greasing the wheels of further trust and cooperation.

You can see oxytocin at work in a study by Kosfeld and colleagues (Kosfeld et al., 2005). Participants were randomly assigned to receive an injection of either oxytocin or a placebo. They then played the trust game, in which they decided how much money they wanted to invest with another player (called the trustee). The experimenter tripled whatever was invested, but much as in the dictator game, the trustee got to decide how much of that money she would pay back to the investor. Those who had received the boost in oxytocin were twice as likely to make the maximum investment as the placebo group.

People are not, however, blindly controlled by biochemical secretions. If the social basis for trusting others is absent, as when an interaction partner appears unreliable, an induced oxytocin boost does not increase trust (Mikolajczak et al., 2010). Oxytocin seems to signal that others are trustworthy, but it does not simply make people more gullible.

If trust influences people’s tendency to be fair, what about their reactions to being treated unfairly? Take away a child’s toy on the playground, and you will get a clear taste of an immediate, negative, and not to mention loud reaction to unfairness. We get a quieter indication of this negative reaction in neuroimaging studies. When people receive low offers in the ultimatum game, scans reveal activation in the anterior insula region of the brain, which is associated with an automatic emotional response. But people in these situations also exhibit increased activation of the dorsolateral prefrontal cortex, which suggests an additional cognitive deliberative response (Sanfey et al., 2003). By revealing the role of emotions, these findings contradict traditional views that decision making is a purely rational process. But they also show that when people reject an unfair offer, they override an initial impulse to take anything profitable that comes their way. In fact, if people’s right dorsolateral prefrontal context is temporarily deactivated, they become more likely to accept unfair offers, even while acknowledging that they are getting the short end of the stick (Knoch et al., 2006).

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The consistent evidence of cooperation in decision-making studies points to what might be a universally evolved mechanism for fairness and prosocial behavior (Fehr & Gächter, 1998; Hoffman et al., 1998). How did these norms for fairness evolve? Treating others fairly is beneficial to each of us because people tend to reciprocate how they are treated. If I am fair with you, you likely will be fair with me. Those who are fair are treated better by others in return, thereby improving the chances that the genes associated with a propensity for fairness will be represented in future generations.

Cooperation and fairness also have a strong cultural component. As we mentioned earlier, people sometimes reject offers in the ultimatum game even at a cost to themselves. By punishing these unfair offers, people enforce broader cultural norms of fairness. If this reaction were part of a biological adaptation, we might expect to see it across cultures and in our closest genetic nonhuman relatives. In fact, when chimpanzees play a version of the ultimatum game and one partner makes an unfair offer, the recipient will hiss and spit at the other chimp even while grudgingly accepting it (Proctor et al., 2013). Just like a child who is told by a parent that all the Halloween candy is gone, these close primate relatives express their outrage at having been shortchanged.

However, other research reveals that human norms of fairness vary across cultures. In large-scale industrialized societies, people playing the ultimatum game typically offer a 50-50 split of the resources. If they are in the role of recipient, they usually reject any offer below 20 or 30% (Henrich & Henrich, 2007). But when members of small-scale societies consider the same decision, they show much more variability in their responses. In some communities where almost all interaction takes place face to face, people make very low offers to others and are willing to accept even the most unbalanced proposal (Henrich et al., 2010).

At first glance, you might think that small-scale, face-to-face agrarian cultures would be more communal and more cooperative with each other than those of us living in the world of telecommuting and Facebook. But what Henrich and his colleagues (2010) argue is that once society grows beyond the reach of family and personal histories of reciprocating with others, norms of fairness and cooperation develop to help govern the needs of an expanding network of trade relationships. How could you comfortably eat that tuna-salad sandwich if you didn’t implicitly trust that the farmer isn’t poisoning you with contaminated lettuce and that the cannery didn’t process spoiled fish? Large-scale societies such as ours can come into being and endure only if people have strong norms of fairness that dictate their own behavior and their treatment of those who violate these norms.

At the other end of the spectrum, historical factors that erode the development of trust can also curtail economic development. Nathan Nunn (2008), an economist at Harvard, has observed that those African countries that were most affected by the slave trade have seen the least amount of economic development and also exhibit the lowest levels of trust (Nunn & Wantchekon, 2011). His theory is that because people in former African slave-trading countries worried about being tricked or sold into slavery, sometimes even by acquaintances and friends, a culture of mistrust developed that impeded later political and economic cooperation even after the slave trade ended. There is, of course, an important lesson to be learned from this theory. If individuals and groups don’t develop a basis for trusting each other, it will be that much more difficult to solve the challenges that they face.

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