The Biology of Benevolence

Humans may be hardwired to cooperate. The choice to cooperate stimulates pleasure centers in the brain.

By Dan Schulman, published on November 01, 2002 - last reviewed on May 02, 2006

Is virtue really its own reward? When it comes to altruism, the brain seems to pat itself on the back. The choice to cooperate stimulates pleasure centers in the brain and can even overcome the urge to strive for increased financial gains. This reward circuitry may provide a biological basis for altruism, selfless behavior that is unique to humans.

Researchers at Emory University scanned the brains of 36 women as they played Prisoner's Dilemma, a game that pits two subjects against each other and has been used in the study of social behavior for at least half a century. Subjects were rewarded money based on their choice to defect or to cooperate: A defection resulted in greater financial gain, while cooperation activated areas of the brain linked to the processing of pleasures such as drugs and food. Researchers also paired subjects with a computerized partner, but cooperation in this instance stimulated only one region of the brain, as opposed to the three distinct areas involved in positive human interactions.

Subjects reported feelings of trust and camaraderie toward their partners—emotions key to sustaining cooperation. And after cooperating in one round, participants were less likely to defect. "This reward circuit is strong enough to override the temptation to opt for selfish short-term gains," explains James Rilling, Ph.D., the lead investigator and a postdoctoral research fellow at Princeton University. The study used only female subjects to avoid the confounding factor of gender roles. Rilling speculates that the outcome would be the same with male subjects.

Rilling notes that there is one instance in which subjects shunned cooperation: when reacting to a partner who had previously defected on them. "If you can't trust the other person, sometimes the safest thing to do is defect."