|Evolution of Direct Reciprocity Proposed to Explain Human Generosity|
|Living - The Dialogue|
|TS-Si News Service|
|Saturday, 06 August 2011 02:00|
Santa Barbara, CA, USA. Scientists show that generosity –– helping others in the absence of foreseeable gains –– emerges naturally from the evolution of cooperation, so it is built in to human nature more than social pressure.
Computer simulations tested whether evolution would select against generosity in situations where there is no future payoff. The findings appear in the Proceedings of the National Academy of Sciences (PNAS).
"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," said Max M. Krasnow, a postdoctoral scholar at UCSB's Center for Evolutionary Psychology, and one of the paper's lead authors. "Even when people believe the interaction to be one-time only, they are often generous to the person they are interacting with."
Imagine you're dining at a restaurant in a city you're visiting for the first –– and, most likely the last –– time
Chances are slim to none that you'll ever see your server again, so if you wanted to shave a few dollars off your tab by not leaving a tip, you could do so.
And yet, if you're like most people, you will leave the tip anyway, and not give it another thought.
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." [cf. Sidebar]
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.
"There are two errors a cooperating animal can make, and one is more costly than the other," noted Cosmides.
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. "Although it's impossible to know the true state of the world with complete certainty, our simulated people were designed to use the 'gold-standard' for rational reasoning –– a process called Bayesian updating –– to make the best possible guesses about whether their interactions will continue or not," Krasnow noted.
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."
SimulationThe simulation program was written in Java by Max M. Krasnowa and checked for errors by Andrew W. Deltona. Source code is available on request to Max M. Krasnowa.
CitationEvolution of direct reciprocity under uncertainty can explain human generosity in one-shot encounters. Andrew W. Deltona, Max M. Krasnowa, Leda Cosmidesa, John Tooby. Proceedings of the National Academy of Sciences 2011; doi:10.1073/pnas.1102131108
Are humans too generous? The discovery that subjects choose to incur costs to allocate benefits to others in anonymous, one-shot economic games has posed an unsolved challenge to models of economic and evolutionary rationality. Using agent-based simulations, we show that such generosity is the necessary byproduct of selection on decision systems for regulating dyadic reciprocity under conditions of uncertainty. In deciding whether to engage in dyadic reciprocity, these systems must balance (i) the costs of mistaking a one-shot interaction for a repeated interaction (hence, risking a single chance of being exploited) with (ii) the far greater costs of mistaking a repeated interaction for a one-shot interaction (thereby precluding benefits from multiple future cooperative interactions). This asymmetry builds organisms naturally selected to cooperate even when exposed to cues that they are in one-shot interactions.
Author Note: Of course, for an interaction to qualify as repeated in a way that enables cooperation to evolve, the actor must be able to identify the interactant as being the same individual across repeated interactions. In empirical work, experimental anonymity plays two conceptually distinct roles. It precludes third parties from responding to player behavior, and it prevents partners from recognizing each other across interactions. The models that we present here preclude any third-party responses but presume that interactants can identify each other across repeated interactions.
Keywords: altruism, cooperation, ecological rationality, social evolution, evolutionary psychology.
|Last Updated on Friday, 05 August 2011 22:06|