These commonplace acts of generosity –– where no future return is likely –– have long posed a scientific puzzle to evolutionary biologists and economists. In acting generously, the donor incurs a cost to benefit someone else. But choosing to incur a cost with no prospect of a compensating benefit is seen as maladaptive by biologists and irrational by economists.
If traditional theories in these fields are true, such behaviors should have been weeded out long ago by evolution or by self-interest. According to these theories, human nature is fundamentally self-serving, with any "excess" generosity the result of social pressure or cultural conformity.
"Our simulations explain that the reason people are more generous than economic and biological theory would predict is due to the inherent uncertainty of social life," added Andrew Delton, also a postdoctoral scholar at the Center for Evolutionary Psychology and the paper's other lead author. "Specifically, you can never know for certain whether an interaction you are having right now will be one-time only –– like interacting with a server in a distant city –– or continue on indefinitely –– like interacting with a server at your favorite hometown diner."
Krasnow and Delton co-authored the paper with Leda Cosmides, professor of psychology and co-director of the Center for Evolutionary Psychology; and John Tooby, professor of anthropology and also co-director of the Center for Evolutionary Psychology.
Delton continued: "Nonetheless, even though their beliefs were as accurate as possible, our simulated people evolved to the point where they essentially ignored their beliefs and cooperated with others regardless. This happens even when almost 90 percent of the interactions in their social world are actually one-time rather than indefinitely continued."
According to Tooby, economic models of rationality and evolutionary models of fitness maximization both predict that humans should be designed to be selfish in one-time only situations. Yet, experimental work –– and everyday experience –– shows that humans are often surprisingly generous.
"So one of the outstanding problems in the behavioral sciences was why natural selection had not weeded out this pleasing but apparently self-handicapping behavioral tendency," Tooby said. "The paper shows how this feature of human behavior emerges logically out of the dynamics of cooperation, once an overlooked aspect of the problem –– the inherent uncertainty of social life –– is taken into account. People who help only when they can see a gain do worse than those who are motivated to be generous without always looking ahead to see what they might get in return."
Andrea Estrada | EurekAlert!
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