Cooperation between two different species may be driven by individual interests rather than fear of punishment, according to Harvard researchers.

The findings, to be published next week in the U.S. journal Proceedings of the National Academy of Sciences, discount the idea that mutually beneficial relationships result from the promise of rewards or the threat of retaliation.

E. Glen Weyl, a Harvard post-doctoral economics fellow who led the study, examined the relationship between plants and ants in Peru to test the Host Sanction Theory that the host species—or plant, in this case—had evolved to punish, or reward the ants.

But when Weyl teamed up with two biologists from Harvard and the University of Toronto to analyze real-world data, the results were inconsistent with the model’s predictions.

“Plants didn’t evolve to give an incentive, but the ants naturally had an incentive to protect the plant—that is, if the plant died, they wouldn’t have anywhere to live,” Weyl said.

Most symbiotic relationships form between species such as plants and smaller insects or bacteria.

The study’s findings, researchers said, resulted from the application of economic theory to inter-special social interaction—two fields that Harvard biology professor Naomi E. Pierce said traditionally work independently of each other.

“While economists have very sophisticated models of human thinking, biologists look at fitness,” Pierce said. “Both have similar models...but both look at different perspectives.”

Weyl and Megan Frederickson, an ecology and evolutionary biology assistant professor at the University of Toronto, traveled to Peru last year to collect data for the study.

The team also used existing data documenting mutualism behavior between a legume and a soil bacterium, and between a yucca and a moth, Weyl said.

A theoretical economist, Weyl said his research in Peru contrasted sharply with his time writing math across white boards.

“I not only literally got his hands dirty by the data, but also got bitten by the data,” he said.

—Staff writer Gautam S. Kumar can be reached at gkumar@college.harvard.edu.