A new UC Davis study about the origin of cooperation may shed light on why nations punish other countries for human rights violations or why people sanction those who do not vote.

Political scientist James Fowler has created a mathematical model of human behavior that suggests that "moralists" who voluntarily pay a cost to punish "misbehavers" can come to dominate a population and ensure cooperation among its members.

"This may help explain mass political behaviors like voting," Fowler said. "When individuals say, 'It doesn't really matter if I vote,' others -- programmed genetically or by social norms -- may seek to punish them, even though it means a self-sacrifice."

He believes that humans may have physically or developmentally evolved to altruistic punishment. Previous studies found that "acting the moralist" stimulates the reward center in the brain.

Some researchers have suggested that cooperation may make sense in a society with altruistic punishers -- essentially, moralists who are willing to pay a personal cost to punish free-riders.

Fowler said his theory can also be used to explain some behaviors in international politics. For instance, the U.S. advocacy for human rights in China has continued for years, despite financial incentives to ignore them. "Our security risks from China's human rights abuses are tenuous at best, but we seem to be engaging in altruistic punishment anyway," Fowler said.

The United States government is willing to have both political and economic losses from its stance because of the stable international system that has evolved so that it is dominated by the "moralists," Fowler says.

Fowler's mathematical model simulates interacting behaviors in a society over time. He found altruistic punishers can enter a population of cooperators and non-cooperators and change the dynamics of the group.

Under certain conditions, altruistic punishment is so beneficial to the population that it will come to dominate the behavior of the group and keep non-cooperators at bay.

Fowler's article, "Altruistic punishment and the origin of cooperation," was published this week in the Proceedings of the National Academy of Science.