Did Reason Evolve to Persuade?

June 24, 2011

The psychology world is abuzz over a recent paper by Hugo Mercier and Dan Sperber suggesting that reason evolved not to know what’s true, but to help us win arguments. “Reasoning doesn’t have this function of helping us to get better beliefs and make better decisions,” says Mercier. “It was a purely social phenomenon. It evolved to help us convince others and to be careful when others try to convince us.”

I think this idea, which they’re calling the argumentative theory of reasoning, is partially correct – but only partially. The rationales for our actions are the causal rules coded into our mental models of the world. The accuracy of those models was honed, through natural selection, by the feedback loop that links causes with effects. For most of our evolution, this process was driven almost entirely by the laws of physics. We noticed that we got sick after eating a certain kind of berry, so we stopped eating it. Argumentative skill would not have contributed to adaptiveness in a world in which most of the effects having implications for human survival did not have social causes.

But we’ve been social animals for a long time, too. Long enough for evolution to have made us better at leveraging the natural biases and capacity limitations of human cognition to get other people to create physical effects for us (wealth, status) that contribute to our survival. The development of argumentative skills could be seen as a refinement of our ability to manipulate one particular kind of tool (other people) whose influence in determining our fate was elevated by civilization.

It’s all about the cause-and-effect feedback loop. Effects – be their agents the wind, germs, or other people – promote behaviors that maximize salutary outcomes and minimize disadvantageous ones.


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