Generosity Psychology

New research explains why it makes evolutionary (and mathematical) sense for us to be kind to strangers.

"It makes evolutionary sense for me to never let go of you...ever!"

The study, published in the Proceedings of the National Academy of Sciences, shows that people are, on average, more generous to strangers than most mathematical models predict – and that there’s a logical reason for cooperation to evolve this way: it often doesn’t cost much to be generous, but a single act of stinginess could cost you a long-term friend. In other words, petty greed just isn’t worth the risk.

This conclusion might seem face-slappingly obvious, but what’s intriguing here is the fact that it has a solid mathematical basis. A team led by psychologists Andrew Delton and Max Krasnow of the University of California, Santa Barbara constructed computer simulations of natural selection systems.

The “agents” (i.e., simulated individuals) used a Bayesian reasoning process to predict whether they would interact with the same partner in the future, and factored this information into their decisions about whether or not to be generous in a Prisoner’s Dilemma-type game. As it turned out, though, cooperation was a more evolutionarily stable strategy whether or not an agent reasoned that it would encounter the same partner again:

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.

This is in stark contrast to loads of previous mathematical models, which predicted that the best strategy is to be generous with one’s regular reciprocal partners, but selfish in one-time-only interactions. Instead, this research shows that the cost/benefit ratio for both these kinds of generosity is about the same:

The conditions that promote the evolution of reciprocity — numerous repeat interactions and high-benefit exchanges — tend to promote one-shot generosity as well. Consequently, one-shot generosity should commonly coevolve with reciprocity.

It’s also interesting to note that this model predicts the same sort of generosity regardless of the size of the group – what’s important isn’t how likely you are to meet the same person again, but simply that there is a chance, however slight, that they might help you in the future.

This research caught my eye because of something that happened to me the other night: my friend and I were eating at a restaurant, when we noticed the people at the next table over loudly lecturing the waitress – scolding her, even – over the allegedly poor quality of the food. They refused to pay, and finally stormed out of the place. When my friend and I asked the waitress what had happened, she rehashed the customers’ complaints for us, then mentioned that almost every other table in the restaurant had called her over to offer stern judgments of the rude customers, and supportive words for her (both of which we also did).

As this research demonstrates, it was more than just empathy or an ancestral tribe mentality that influenced our actions that night – though those factors did have their roles, and might be reflections of a more underlying mathematical truth (as so many patterns in nature are). But odds are, neither we nor the rude customers will ever see that waitress again – and being kind to her only gained us a few moments of positive feelings. Nevertheless, being nice to that harmless stranger “felt right” to us – and as it happens, there’s an evolutionary reason for that.

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