We've heard it whispered at the grocery store, in the park, at the PTA meeting: first one, then another then ANOTHER friend is getting divorced. What is happening? It seems that divorce can be "contagious" in close social groups.

It is not just divorce that appears contagious among circles or networks of friends: getting married can be "contagious" too. So can having babies. Financial markets suffer from such contagion as well: consider the various 'bubbles' in which herds of investors drove up prices for stocks past all rational levels. We all recall our mothers telling us as teenagers to resist peer pressure and think for ourselves: "If everyone jumps off a cliff are you going to jump too?" But now it seems there actually is social science research that may now document—and start to explain—the phenomenon.

As social scientists (people who study patterns of human behavior) have adopted the scientific methods of the physical or biological sciences, social science researchers are getting closer to understanding how attitudes, beliefs and behaviors can spread through populations as if they were somehow "infectious." But, unlike studying a virus, studying the rational, and irrational, human in his or her culture is a particularly challenging task. It seems we understand and predict the effect of mysterious dark matter better than we can predict group human behavior! Social science is still trying to understand the particular mechanism of group behavior that underlies "social contagion."

A first step toward better understanding the "social contagion" phenomenon was published in 2012, using data from decades-long studies of residents of Framingham, Massachusetts that had been researching the causes of heart disease. In reviewing three decades of data on marriage, divorce and remarriage of more than 12,000 Framingham residents in that heart study, Rose McDermott of Brown University found that, statistically, participants were 75% more likely to become divorced if a friend was divorced and 33% more likely to end their marriage if a friend of a friend is divorced.

Various explanations for this have been proposed. If divorce had been an unwanted option in a social group, and one person in the group takes the divorce option and talks about it, or even advocates for that option in order to buttress their divorce decision, this conduct will have a significant affect on those individuals close to the divorcing party. It gives the people around them information about what divorce is like. If a respected member of a social group (including a family) takes the divorce option, the status of that person may lend authority and legitimacy to that option for others in the group—even giving some the courage to take the step toward divorce. Sometimes, close friends who talk and support their divorcing friend become enmeshed in the struggle, taking on their friend's emotions and internalizing hurt and conflict that may spill over into their own marriage. Of course, once the divorce ball starts rolling through a social group, it seems that it picks up momentum and one, then another, then another pursue the divorce option.

Another explanation for the statistics garnered from the Framingham residents may have less to do with simple "contagion." People usually construct their social groups based on common social values and outlook, e.g. faith communities, political parties etc. Even social groups based on family ties will have a close spectrum of social values and outlook. In other words, is it possible that social groups which experience high rates of "divorce contagion" are also groups where divorce may be an acceptable option for a troubled marriage? The researchers of the Framingham data did not have this depth of information available to them in order to answer these, and similar, questions.

Nevertheless, researchers assert that common group values cannot, alone, explain the phenomenon observed over the years of documented mass hysteria, contagious rule-breaking behavior or even financial contagion phenomenon. These researchers assert that we simply have evolved a predisposition to copy the behavior of those around us. This tendency, they say, is the foundation of all human culture.

In the end, are we humans merely higher orders of "fish schools?" The new research helps us to understand ourselves, a little. We may instinctively want to copy our social group, but as humans we also can recognize the "social contagion" effect and, hopefully, look with our eyes wide open before we take that leap off the cliff.