How superstitions spread

Ancient Roman rulers have already made decisions about important events, such as the timing of elections or the location of new cities, depending on the presence or pattern of bird flight. Builders often omit the thirteenth floor of their floor plans and many pedestrians strive not to go under a ladder.

It is widely recognized that such superstitions are not rational, but many persist, guiding the behavior of large groups even nowadays.

In a new theory-of-games analysis, two theoretical biologists have devised a model that shows how superstitious beliefs can be established in the social norms of a society. Their work, which appears in Proceedings of the National Academy of Sciences, shows how groups of individuals, each starting with distinct belief systems, can develop a coordinated set of behaviors that are reinforced by a set of coherent social norms.

"What's interesting here is that we show that in a system where no one has a particular belief system, a set of beliefs can emerge, and of these, a set of behaviors coordinated, "says Erol Akçay, assistant professor of biology. at Penn.

"Slowly, these actors are accumulating superstitions," adds Bryce Morsky, postdoctoral researcher. "They can say:" Ok, well, I believe that when I observe this event, I should behave in this way, because another person will behave this way ", and with the time, if they succeed in using this type of strategy, on and can become stable evolutionary ".

The work of Morsky and Akçay is an application of game theory that attempts to predict how people will interact and make decisions in a social context. They have specifically examined what are called correlated equilibria, scenarios in which all actors receive correlated signals that dictate their response to a given situation.

"A classic example is a traffic light," says Akçay. "If two people approach an intersection, one of them will receive a stop signal and the other will be reported and everyone knows it. is rational that both parties obey the light. "

The signal, in this case the traffic light, is known as a correlation device, or more evocative, a "choreographer". But the Penn team wanted to know what would happen if there was no choreographer. If people could pay attention to various other signals that could guide their actions and if their beliefs were conveyed according to the success of their actions, could coordinated behaviors appear? In other words, can evolution act as a "blind choreographer?"

"And if a cyclist was heading to an intersection and saw a cat in the place of a traffic light," says Akçay. "The cat does not matter for the intersection, but maybe the person decides that if she sees a black cat, it means that she should stop, or maybe to be that means that the approaching cyclist is going to stop. "

Despite the color of a cat having no bearing on the likelihood that an approaching cyclist will stop or go, this type of conditional strategy can sometimes be more cost-effective for the cyclist, provided that this is correlated with the superstitions of other cyclists.

"Sometimes it can be rational to keep those irrational beliefs," notes Morsky.

In their model, Morsky and Akçay assume that individuals are rational, in that they do not follow a standard blindly, but only do so when their beliefs make it beneficial. They change their beliefs by imitating the beliefs of successful people. This creates an evolutionary dynamic where standards "compete" with each other, their prevalence increasing and decreasing across the group. This evolutionary process ultimately leads to the formation of new social norms.

Morsky and Akçay have shown that stable evolutionary norms, ones that can not be replaced by others, must be consistent, which means that they can coordinate behavior. individual even in the absence of an external "choreographer".

They found that these evolutionarily stable norms, both in prescribing the behavior of an actor and in describing the actor's expectations of the behavior of others, create a coherent belief system. to coordinate the general behavior of many actors, even if this coordination is not implemented. directed by an outside choreographer.

To further explore their discoveries, researchers hope to conduct social experiments to see if individuals could begin to conceive of their own superstitions or beliefs without being provided.

"What I like in this work," says Morsky, "is that these beliefs are invented superstitions, but they become real because everyone follows them, so you create that social reality." I'm really interested in testing this more. "