Your Brain On Us

The neuroscience of social interactions

The altruism instinct

An antidote to the tragedy of the commons

There's a reason that all social groups should fall apart, which can be illustrated by the following scenario. You are a cattle farmer, sharing open pasture with 100 other farmers, and are trying to decide whether to add another animal to your herd. Like any rational person, you weigh the costs and benefits of this decision. You stand to gain all the resources an extra animal can provide, and the cost (overgrazing of the pasture) is spread across the entire group, such that each person will hardly notice the change. So you decide to get another animal (or 2, or more). Problematically, the 100 other farmers have used the same calculations and made the same choice, leading the group unstoppably towards sharing a barren patch of land.

This problem was widely publicized 40 years ago by Garrett Hardin, an ecologist who realized exactly how dramatic it could be. Titling the phenomenon "the tragedy of the commons," Hardin concluded, "Ruin is the destination toward which all men rush, each pursuing his own best interest." The tragedy of the commons is not hypothetical, and we can find examples from the trifling to the troubling in everyday life. On New York City subways at rush hour, commuters hold train doors open while trying to crowd on, so often that a new campaign against door holding has begun. Door holding is a micro tragedy of the commons. Imagine that it saves the holder 5 minutes of waiting for the next train, and only takes 10 seconds. While this seems like a time-bargain, at rush hour there can be up to 2,500 people on a train, meaning that overall, the holder can cost the group almost 7 hours. Much more profound examples of this effect include the reluctance of countries and individuals to lower their carbon emissions in the face of climate change, potentially the largest tragedy of the largest commons we share.

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This picture of human nature is bleak enough to fit into the trailer for 2012, but luckily it fails to account for a major part of human behavior. Altruism--helping others at no benefit, and sometimes at a cost, to the helper--cannot be explained by Hardin's rational self-interest. And altruism is everywhere. In the United States alone, almost 90 million people volunteer regularly, generating a value of over 200 billion dollars a year. What accounts for this selfless behavior? This question is of interest to anyone trying to run a charity, increase public service, or get their children to share toys with each other.

This question has also interested evolutionary theorists for centuries. Robert Trivers first formalized this thinking by demonstrating that altruism might not be so selfless: organisms from fish to humans tend to pay back helpful behavior, resulting in increased evolutionary fitness for helpers as compared to free riders. The fact that people can gain from helping others is often used as evidence that altruism is "impure," based on cold calculations not so different from self-interest.

In my opinion (and that of others), this argument misses the point by confusing the results and sources of actions. Take the example of sex. Sex evolved because it results in reproduction, but animals that are unaware of the relationship between sex and offspring have sex anyways, and whole industries are devoted to helping humans have sex without reproducing. In this case, the result of the action (reproduction) and its source (pleasure) are quite different. Similarly, altruism might be beneficial down the road, but those benefits alone might not be enough to drive helping. In fact, there's evidence that directly rewarding adults or children for helping decreases their altruistic behavior.

Instead, it is likely that two other factors drive helping. The first is positive reputation. Most of us would not survive a week alone in the woods. We count on the cooperation of others, who we assume will provide us with everything from protection to food, so long as we pitch in. Behaving altruistically is a sure-fire sign that we have pitched in, and shows others that we are the type of person they should trust and help. In such a system, a good reputation is the most important currency we have, and there is evidence that people value that currency, acting altruistically more often in public than in private. Charities build on this value, publicizing donations and even providing reputation-boosting tokens like NPR bumper stickers and Livestrong bracelets.

If desiring a good reputation was the only psychological source of altruism, we may be tempted to agree that helping is impure. However, there is probably a more basic source powering altruism, one so ingrained that we could call it an "altruism instinct." Evidence for this comes from infants who act altruistically even though they likely don't understand the ins and outs of reputation building. Children as young as 18 months help others without being prompted, and there is evidence that preferences for altruism develop much earlier than that. In a recent study 3-month olds were shown a puppet trying to climb up a hill. Two other puppets arrived: one helping the first one up the hill and the second hindering it (see videos here). When given the option to choose between these two puppets, even babies in their first months of life preferred the helpful puppets, suggesting that innately, humans simply like altruism more than selfishness.

An instinct for altruism is an antidote to the tragedy of the commons, and is probably among the reasons why groups don't fall into ruin as quickly or completely as Hardin predicted. But what drives this instinct? In my next posts, I will describe emotional responses we have to other people's experiences, which may be at the heart of our altruistic impulses.

Jamil Zaki is a neuroscientist studying empathy and social interactions at Columbia University.

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