How superstitions spread

Summary: A new game theory model demonstrates how superstitious beliefs become established in a society’s social norms. The model shows how distinct belief systems can evolve as a coordinated set of behaviors which are enforced by a consistent set of social norms.

Source: University of Pennsylvania

Ancient Roman leaders once made decisions about important events, such as when to hold elections or where to build new cities, based on the presence or flight patterns of birds. Builders often omit the thirteenth floor from their floor plans, and many pedestrians go well out of their way to avoid walking under a ladder.

While it’s widely recognized that superstitions like these are not rational, many persist, guiding the behavior of large groups of people even today.

In a new analysis driven by game theory, two theoretical biologists devised a model that shows how superstitious beliefs can become established in a society’s social norms. Their work, which appears in Proceedings of the National Academy of Sciences, demonstrates how groups of individuals, each starting with distinct belief systems, can evolve a coordinated set of behaviors that are enforced by a set of consistent social norms.

“What’s interesting here is that we show that, beginning in a system where no one has any particular belief system, a set of beliefs can emerge, and from those, a set of coordinated behaviors,” says Erol Akçay, an assistant professor of biology at Penn.

“Slowly, these actors accumulate superstitions,” adds Bryce Morsky, a postdoctoral researcher. “They may say, ‘Ok, well I believe that when I observe this event I should behave this way because another person will behave that way,’ and over time, if they have success in using that kind of a strategy, the superstitions catch on and can become evolutionarily stable.”

Morsky and Akçay’s work is an application of game theory, which attempts to predict how people will interact and make decisions in a social setting. They specifically considered what are known as correlated equilibria, scenarios in which all actors are given correlated signals that dictate their response to any given situation.

“A classic example is a traffic light,” says Akçay. “If two people are approaching an intersection, one will get a ‘stop’ signal and one will get a ‘go’ signal and everybody knows that. It’s rational for both parties to obey the light.”

The signal, in this case, the traffic light, is known as a correlating device, or more evocatively, a “choreographer.” But the Penn team wanted to know what would happen if there was no choreographer. If people could pay attention to a variety of other signals that could direct their actions, and their beliefs were transmitted according to the success of their actions, would coordinated behaviors arise? In other words, can evolution act as a “blind choreographer?”

“What if a cyclist is riding toward an intersection, and instead of a traffic light they see a cat,” Akçay says. “The cat is irrelevant to the intersection, but maybe the person decides that if they see a black cat, that means they should stop, or that maybe that means the approaching cyclist is going to stop.”

Despite the color of a cat having no bearing on the likelihood of an approaching cyclist stopping or going, sometimes this kind of conditional strategy might result in a higher payoff to the cyclist–if it is correlated with superstitions of other cyclists.

“Sometimes it may be rational to hold these irrational beliefs,” Morsky notes.

In their model, Morsky and Akçay assume that individuals are rational, in that they do not follow a norm blindly, but only do so when their beliefs make it seem beneficial. They change their beliefs by imitating successful people’s beliefs. This creates an evolutionary dynamic where the norms “compete” against one another, rising and falling in prevalence through the group. This evolutionary process eventually leads to the formation of new social norms.

Morsky and Akçay showed that the evolutionarily stable norms, those that cannot be replaced by others, have to be consistent, meaning that they successfully coordinate individual behavior even in the absence of an external “choreographer. ”

They found that these evolutionarily stable norms, in both prescribing how an actor should behave and also describing that actor’s expectations of how others should behave, create a consistent belief system that helps coordinate the overall behavior of many actors, even if that coordination is not being directed by any outside choreographer.

This shows a girl with a swirly orb
While it’s widely recognized that superstitions like these are not rational, many persist, guiding the behavior of large groups of people even today. The image is in the public domain.

To further explore their findings, the researchers hope to engage in social experiments to see whether individuals might start devising their own superstitions or beliefs when none are provided.

“What I like about this work,” says Morsky, “is that these beliefs are made-up superstitions, but they become real because everybody actually follows them, so you create this social reality. I’m really interesting in testing that further.”

Funding: Support for the research came from the Defense Advanced Research Projects Agency (Grant D17AC00005) and Army Research Office (Grant W911NF-12-R-0012-03)

Erol Akçay is an assistant professor in the School of Arts and Sciences’ Department of Biology at the University of Pennsylvania.

Bryce Morsky is a postdoctoral researcher in the School of Arts and Sciences’ Department of Biology who works with Akçay.

About this neuroscience research article

University of Pennsylvania
Media Contacts:
Katherine Unger Baillie – University of Pennsylvania
Image Source:
The image is in the public domain.

Original Research: Closed access.
“Evolution of social norms and correlated equilibria”
Bryce Morsky and Erol Akçay. PNAS doi:10.1073/pnas.1817095116


Evolution of social norms and correlated equilibria

Social norms regulate and coordinate most aspects of human social life, yet they emerge and change as a result of individual behaviors, beliefs, and expectations. A satisfactory account for the evolutionary dynamics of social norms, therefore, has to link individual beliefs and expectations to population-level dynamics, where individual norms change according to their consequences for individuals. Here, we present a model of evolutionary dynamics of social norms that encompasses this objective and addresses the emergence of social norms. In this model, a norm is a set of behavioral prescriptions and a set of environmental descriptions that describe the expected behaviors of those with whom the norm holder will interact. These prescriptions and descriptions are functions of exogenous environmental events. These events have no intrinsic meaning or effect on the payoffs to individuals, yet beliefs/superstitions regarding them can effectuate coordination. Although a norm’s prescriptions and descriptions are dependent on one another, we show how they emerge from random accumulations of beliefs. We categorize the space of social norms into several natural classes and study the evolutionary competition between these classes of norms. We apply our model to the Game of Chicken and the Nash Bargaining Game. Furthermore, we show how the space of norms and evolutionary stability are dependent on the correlation structure of the environment and under which such correlation structures social dilemmas can be ameliorated or exacerbated.

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