The Biblical parable of the Good Samaritan, a traveler who stops on the road to help a badly wounded robbery victim that others had passed by, is a story that we see repeated again and again in the news.
In Fort Lauderdale, Fla., after a woman lost control of her car on an Interstate freeway and flipped into a water-filled ditch, a man jumped in to rescue her from drowning. In Arizona, after a community college student lost a wallet containing her cash, credit cards, student ID and immigrant work permit, an unidentified person found it and dropped it off at her school's office. In Oklahoma, after a teenage skateboarder tumbled from his board and suffered a concussion, a man he didn't know found him by the side of the road and took him to get help.
What motivates people to stop and help others that they didn't previously know, with no apparent benefit to themselves?
Traditionally, we've viewed people who engage in prosocial behavior -- that is, voluntary acts performed to benefit others or society as a whole -- as being motivated by moral character or spiritual beliefs. But in recent years, increasing evidence has emerged to suggest that the tendency to be a do-gooder may be influenced by genes.
In a newly-published study in the journal Social Neuroscience, for example, researchers found that a single variation in a genotype seems to affect whether or not a person engages in prosocial acts. Individuals who have one variation of the genotype have a tendency toward social anxiety -- that is, unease around other people, and are less inclined to help others in ways that involve personal interaction.
Those who have another variation, in contrast, not only were less anxious, but also were more likely to be helpful. The genetic region involved is 5-HTTLPR, which regulates transport of serotonin, a neurotransmitter chemical in the brain. The researchers studied the genomes of 398 college students, and asked the subjects to fill out a questionnaire to provide information about their behavior and anxiety levels.
University of Missouri social psychologist Gustavo Carlo, one of the study's co-authors, said that the the genotype variation is just one "indirect pathway" that could lead a person to being a Good Samaritan. Another potential influence, he said, is the brain's ability to use dopamine, another brain chemical. Other genetic variations in brain chemistry may play a role as well.
"This is a really exciting area for research," Carlo said. "There are a lot of studies being done right now that focus on the micro-level biological processes associated with altruistic behavior."
Co-author Scott F. Stoltenberg, a researcher at the University of Nebraska-Lincoln's Behavior Genetics Laboratory, says the findings build on previous studies that suggest a link between relative levels of anxiety and prosocial behavior.
"It makes sense that people who have less social anxiety are more likely to help out," Stoltenberg explained. "When they're confronted with a situation where another person needs help, they don't have a problem going over to them and engaging." A person with social anxiety, in contrast, might experience so much discomfort that he or she would avoid the encounter.
Both serotonin and dopamine are neurotransmitters related to the sensations of pleasure and satisfaction, which may explain why people who perform selfless acts of generosity report that they feel good as a result.
Carlo cautioned that the study's findings don't necessarily mean that people with a genetic predisposition toward anxiety also lack empathy, the ability to care about others. While it may be more difficult for them to engage in public acts of prosocial behavior, they may instead make anonymous contributions to a person in need, or help in some other way that doesn't require personal interaction.
Why humans developed the capacity to be Good Samaritans is another widely-debated question. In the 1970s, evolutionary biologist Richard Dawkins, a believer in the notion that "genes are selfish," argued that prosocial behavior existed to ensure genetic continuity. His view was influenced by studies suggesting that organisms were most likely to help their own kin.
But as Ohio State University psychologists Baldwin M. Way and Kyle G. Ratner wrote in an essay that appeared in the same journal as Carlo's and Stoltenberg's study, Dawkins' view fails to account for the many instances in which humans have helped others to whom they were not closely related, and have done so with no apparent genetic benefit to themselves.
Previous studies have indicated that the tendency toward prosocial behavior may be at least in part heritable -- that is, passed on from generation to generation genetically -- rather than totally the result of the moral influence of parents or teachers. A 2007 study of Korean twins, for example, found that about 55 percent of the variance in prosocial behavior seemed to be due to genetics, and that the genetic link seemed to increase as the children got older.