Is Generosity An Evolutionary Trait?

Despite the assumptions of some economists and biologists, new experiments prove that natural selection favors treating others as if the relationship will continue–even when it’s rational to believe it will not.



According to evolutionary psychologists at the University of California at Santa Barbara, generosity–acting to help others in the absence of foreseeable gain–emerges naturally from the evolution of cooperation. This means that human generosity is likely to rest on more than social pressure; it is built in to human nature. Their findings appear in the July 25, 2011 online issue of the Proceedings of the National Academy of Sciences.

Imagine dining at a restaurant in a city you’re visiting for the first time–and, most likely, the last. Chances are slim to none that you’ll ever see your server again, so if you wanted to shave a few dollars off the tab by not leaving a good tip, you could do so. And yet, if you’re like most people, you will leave a nice tip anyway.

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.

As Max Krasnow, UCSB Center for Evolutionary Psychology and one of the paper’s lead authors, says: “When past researchers carefully measured people’s choices, they found that people all over the world were more generous than the reigning theories of economics and biology predicted they should be. Even when people believe the interaction to be one-time only, they are often generous to the person they are interacting with.”

The UC Santa Barbara team used computer simulations to test whether it was really true that evolution would select against generosity in situations where there is no future payoff. Andrew Delton, the paper’s other lead author, says:

“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. 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.”

Leda Cosmides, co-director of the Center for Evolutionary Psychology, adds:


“There are two errors a cooperating animal can make, and one is more costly than the other. Believing that you will never meet this individual again, you might choose to benefit yourself at his expense–only to find out later that the relationship could have been open-ended. If you make this error, you lose out on all the benefits you might have had from a long-term, perhaps life-long, cooperative relationship. This is an extraordinarily costly error to make.”

The other error is to mistakenly assume that you will have additional interactions with the other individual and therefore cooperate with him, only to find out later that it wasn’t necessary. Although you were ‘unnecessarily’ nice in that one interaction, the cost of this error is relatively small. Without knowing why, the mind is skewed to be generous to make sure we find and cement all those valuable, long-term relationships.”

The simulations, which are mathematical tools for studying how natural selection would have shaped our ancestors’ decision making, show that–over a wide range of conditions–natural selection favors treating others as if the relationship will continue–even when it is rational to believe the interaction is one-time only.

According to John Tooby, co-director of the Center for Evolutionary Psychology, economic and evolutionary models both predict that humans should be selfish in one time only situations. Yet, experimental work–and everyday experience–shows that humans are often surprisingly generous: “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.”

Read more at EurekAlert

[Image: Flickr user Giorgio Montesino]


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