July 24, 2006

Selfish genes make humans selfless, new theory suggests

ANN ARBOR, Mich.—Humans are altruistic by nature, according to a new theory published in the current issue of Psychological Inquiry.

The theory focuses on explaining the kind of altruistic behavior that involves costly long-term investment in others, such as parenting, caring for the sick or injured, and protecting family and comrades in times of conflict or war. This behavior typically entails considerable sacrifice—of time, effort, health and even life itself.

"Considering the self-centered motives that are evolutionarily ancient and that continue to drive human behavior today, it's worth considering why people make these kinds of sacrifices," said University of Michigan psychologist Stephanie L. Brown, who developed the new theory in collaboration with her father, Michael Brown, a psychology professor at Pacific Lutheran University.

Brown and Brown argue that the social bond--the glue of close interpersonal relationships--evolved to discount the risks of engaging in high-cost altruism. They propose that social bonds override self-interest and motivate costly investment in others. The formation of social bonds must have occurred mainly between individuals who were dependent upon one another for reproductive success, or whose evolutionary fates were linked. "This linkage would have provided givers with a genetic safety net, making them resistant to exploitation," Stephanie Brown said. 

Effectively, the new theory--"selective investment theory"--presents a striking alternative to traditional self-interest theories of close relationships that tend to emphasize what individuals get from others, not what they give.

"Viewed through the lens of selective investment theory," Stephanie Brown said, "the fabric of close relationships appears different.  Sacrifice becomes a characteristic feature of healthy, enduring relationships rather than aberrant, inexplicable, or diagnostic of pathology".

What makes selective investment theory distinctive is not only its focus on high-cost altruism, but also its premise that "selfish genes" are ultimately responsible for selfless, other-directed behavior.

 "Selfish genes can produce selfless humans," said Stephanie Brown, explaining that high-cost altruism helped to insure the survival, growth and reproduction of increasingly interdependent members of ancestral hunter-gatherer groups. "Viewed in this way, the spread of altruism in humans is no surprise. Even altruism directed to genetically unrelated individuals is not as mysterious as some have supposed."

In support of their theory, Brown and Brown cite evidence from a wide range of fields, including neuroendocrinology, ethology and behavioral ecology, and relationship science. "The same hormones that underlie social bonds and affiliation, such as oxytocin, also stimulate giving behavior under conditions of interdependence," said Stephanie Brown.

According to the Browns, their theory has important implications for relationship science. "We do not deny that close relationships involve selfish motivation," said Stephanie Brown, "but the picture may be more complex. If social bonds evolved to support altruism then we may need to re-think the way we view human sociality. Models of psychological hedonism and rational self-interest may need to be expanded in order to describe our behaviors in families, at work, and even on the national stage."

In the same issue of Psychological Inquiry, experts in relationship science and evolutionary psychology offer a series of commentaries on the new theory.

Stephanie Brown is an assistant professor of general medicine at the U-M Medical School and a faculty associate at the U-M Institute for Social Research (ISR), affiliated with the ISR Evolution and Human Adaptation Program. 

Contact:  Diane Swanbrow
Phone: (734) 647-9069