Is altruism a genetic trait?
—Daniel Hall, Oceanside, Calif.
Nicholas R. Eaton, a doctoral student in psychology at Washington University in St. Louis, responds, writing in collaboration with professor of clinical psychology Robert F. Krueger and doctoral students Jaime Derringer and Abigail Powers:
People often go out of their way to help perfect strangers for no apparent personal gain. Many of us assume that altruism is something that parents teach—be nice, don’t talk with your mouth full, do unto others.... But science says that altruistic impulses are largely instinctive.
Compelling evidence that altruism is a genetic trait comes from studying our close relative, the chimpanzee. Chimps don’t teach their young to be nice the way humans do, but in 2007 scientists at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, found that chimps do behave selflessly, helping their human caretakers reach a stick or unfamiliar chimps open a cage full of food, without expecting a reward.
Soon after, another team from the same Max Planck Institute found evidence that altruistic behavior is innate in humans as well. In 2009 the researchers reported that infants younger than 18 months engaged in altruistic acts, such as helping adults reach objects or open cabinet doors. The infants’ attention to the needs of others most likely preceded their full understanding of the social pressures associated with being selfless.
Genes, however, do not tell the full story of what prompts people to be generous. By examining altruism in identical twins, who share nearly 100 percent of their genes, and fraternal twins, who share 50 percent of their genes, researchers can estimate the extent to which genes and the environment contribute to selfless inclinations and behaviors. Overall, these twin studies suggest that genes explain between 30 and 60 percent of altruistic tendencies, with the remaining variation coming from cultural or social effects.
Interestingly, some studies indicate that the influence of genes may vary over time. For example, scientists in the U.K. showed that altruistic behaviors in younger children arose mostly from their environment, such as the family’s belief system. In the teenage years, however, when youths typically become more independent, genes have a much stronger influence on altruism.