A report in Science speculates that altruism evolved among human ancestors who cooperated by sharing scarce resources to survive in harsh conditions and warfare.
Those sharing, caring practices likely had a personal cost -- you've got less food for yourself if you share it with someone else -- but they would have helped a group survive and grow closer.
As a result, cooperation may have forged stronger groups that had a survival edge over greedier groups, according to the paper by Samuel Bowles, PhD.
Bowles is a research professor and director of the behavioral sciences program at the Santa Fe Institute in New Mexico and an economics professor at Italy's University of Siena.
Bowles hasn't found an "altruism" gene.
But he supports his theory with a complex series of calculations, based on genetics, climate, and populations from as long as thousands of years ago.
Lots of question marks remain. No one knows exactly what went on among people that long ago, or whether their actions echo through our genes today.
Bowles' theory may explain "the stability" of altruism among people, "but whether it is sufficient to explain its origin is not yet clear," notes editorialist Robert Boyd, PhD.
Boyd works in the anthropology department of the University of California, Los Angeles. His books include Not By Genes Alone: How Culture Transformed Human Evolution.
"Bowles' hypothesis is consistent with suggestions that people have innate, pro-social motivations, and that these feelings are elicited by cues of common group membership," Boyd writes.
"These are old questions, but important ones," Boyd writes. "The kind of quantitative empirical work that Bowles has done will help answer them."
SOURCES: Bowles, S. Science, Dec. 8, 2006; vol 3144: pp 1569-1572. Boyd, R. Science, Dec. 8, 2006; vol 314: pp 1555-1556. News release, Science.
By Miranda Hitti
Reviewed by Louise Chang