Human society is rife with examples of individuals helping each other, but they can be a confusing and contentious subject for evolutionary biologists. We often help others at our own expense, whether it’s a matter of holding a door for someone or rescuing them from an oncoming train. Where does this behavior come from, and why do we do it? A special issue of PNAS, dedicated to evolution and social behavior, reviews the latest research on cooperation and suggests that humans may differ from other animals in how and why we help others.

Humans choose to help, but look for fairness too

Scientists have developed a battery of tests to study helping behavior (“prosocial sentiment,” in scientific jargon) in a range of species. For humans, the most common tests involve giving a participant money and asking him or her to distribute the cash. In one simple variation, called the Dictator Game, the participant must decide whether to give any of this money—and, if so, how much—to an anonymous partner. When faced with this question, people tend to give between 20 and 30 percent of the cash away.

In another variation, called the Ultimatum Game, a second step is added: the recipient then gets to decide whether he wants to take what is offered, or turn the proposal down. If the recipient rejects the offer, neither he nor the first player gets any money at all. This tests how people respond to inequality; recipients generally turn down offers of less than 20 percent, no matter how much cash that represents.

Another variation allows a third participant to decide whether or not to punish the proposer. In this game, the third party can punish the proposer by reducing his payoff, but he must spend his own money to do so. Even under these conditions, many people choose to inflict punishment if they see the deal as unfair to the recipient. In these studies, people in all roles tend to seek somewhat fair outcomes, even if that comes at a cost to themselves.

Mixed Motivations

But what makes us behave this way? At best, maybe we’re concerned about the welfare of those around us. Alternatively, maybe we want to be seen by others as helpful and caring, or perhaps we’re afraid of retribution. It’s also possible that helping others just makes us feel better by getting rid of an unpleasant situation.

Perhaps not surprisingly, research attempting to answer these questions has turned up mixed results. Some studies do find that we empathize with the plights of others, and just want to help out. Participants in one study saw a worker getting a series of electrical shocks. When told that they could reduce the number of shocks the worker got by volunteering to get shocked themselves, most volunteered for the jolt. The response was the same whether the participant would continue to see the worker after their decision or not, indicating that they weren’t just trying to make the unpleasant situation disappear. Instead, the researchers suggest that the participants wanted the best for the worker.

However, studies show that the prospect of someone else watching—even if it’s just a drawing of a pair of eyes—makes us more cooperative. Similarly, when participants in the Ultimatum Game are told that their offers will be made public, they tend to offer a greater proportion of their cash. Clearly, our motives aren’t all selfless.

How prosocial are other primates?

It’s obviously much harder to figure out the intentions and motivations of animals, but scientists have created clever tests to study prosocial behavior in primates. Most of these tests have to do with whether or not individuals will share food with others.

In one study, chimpanzees could pick between two options: getting food and also letting a companion get food (called the 1/1 option), or getting food and not letting the companion get any (the 1/0 option). Here, it costs the chimpanzee nothing to help, but the results show that they choose the 1/0 option as often as the 1/1 option. Several variations of this experiment produced similar results, indicating that the chimps were "indifferent to the welfare of other individuals." There is some evidence that other primate species, such as marmosets and capuchin monkeys, will give food to conspecifics during similar experiments, but only under certain conditions.

However, other studies have shown that chimpanzees are willing to help humans and other chimps complete tasks, even when there is little or no reward for doing so. And, unlike humans, they never reject offers given to them by another individual, no matter how small.

A question of validity

Critics of these studies claim that the situations used to study prosocial behavior in both humans and animals are poorly designed. For humans, the major criticism is that the tests are unrealistic; how often must you decide whether or not to donate money to someone you don’t know anything about and will never interact with again? Critics suggest that other primates simply don't understand what is being asked of them in these experiments, leading to the mixed results in non-human studies.

These criticisms are certainly valid, and scientists acknowledge that there is much we haven't been able to study or measure effectively. Experiments to study prosocial behavior are notoriously difficult to design and implement, and scientists are generally careful not to overstate their findings. The PNAS paper’s authors suggest that, in the future, researchers must standardize their methods, as well as replicate studies in multiple populations and across species in order to better understand helping behavior.

The take-home message

Despite the potential problems with experimental studies of prosocial behavior, there is overwhelming agreement in the scientific community that the motives underlying helping behavior in humans are much more complex and varied than those in other primates. We’re concerned about the welfare of others, we are the only species that seems to be offended by inequalities that we aren't affected by, and as far as we know, we're unique in our liberal use of punishment. There is also little evidence that other species cooperate in complex pursuits such as trade and territorial defense.

However, our helping behavior doesn’t come totally out of left field. Like other animals, humans do tend to favor their relatives over non-relatives, help group members at a higher rate than they help outsiders, and cultivate lasting relationships with cooperative partners. It's likely that these traits come from our shared ancestry, but, thanks to culture, technological innovation, and evolutionary change, we’ve continued to develop our own style of helping behavior.

PNAS, 2011. DOI: 10.1073/pnas.1100305108 (About DOIs).

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