Change

Preface

The science of networks is the study of how things spread. How do the connections we share with the people around us affect the way that diseases, ideas, trends, and behaviors move through communities and societies and around the world?

In the spring of 2020, as I was finishing work on this book, the world was suddenly transformed by two powerful new examples of things that spread very far, very fast. The first, of course, was the novel coronavirus, which emerged in a market in Wuhan, China, and, in a matter of weeks, spread throughout China, then to the Middle East and Europe, and from there to every corner of the world.

What made the virus so deadly and disruptive was how easily it could be transmitted. It was small, it was hard to kill, and it was airborne. You could catch it from someone standing a few feet away from you, and it lingered in the air for hours. What made the virus even more insidious was the fact that if you caught it, you could then spread it to others before you felt any symptoms, before you even knew you’d been infected. Every person was a potential source of contagion. Every contact was a mode of transmission. A hug. A handshake. Receiving a package in the mail. Accepting a piece of paper from your colleague. And so the disease spread rapidly, at choir practices and funerals and family reunions, through hospitals and nursing homes and meatpacking plants, between husbands and wives and between complete strangers. By June, more than six million people had been infected worldwide, a third of them in the United States. Once the virus took hold, it expanded exponentially.

But something else was spreading that spring. It wasn’t a disease. It was a behavior.

Governments around the world reacted differently to the coronavirus pandemic—some responded much more quickly than others—but within a few months, public health advice worldwide had coalesced around four basic preventive measures: Wash your hands. Stay at home. Wear a mask. And stay at least six feet away from other people. As these directives took shape, a new question emerged: Would people follow them? Could the entire world change its behavior in such dramatic ways?

People looked first to their friends and neighbors. Were they wearing masks? Were they social distancing? Mostly, remarkably, they were. In many communities—small towns and large cities—the sidewalks were nearly empty. People stayed home. If they did go out, they usually wore face masks. And they afforded one another exaggeratedly wide berths as they passed on the street. In country after country, people changed the way they worked, socialized, went to school, raised children, and went on dates. New behavioral norms had sprung up, seemingly overnight, and they had propagated across the globe.

Gradually, these behaviors changed the course of the disease. After weeks of headlines full of death and despair, there was good news for the first time in months: the spread of the disease was slowing. New cases were going down. Hospital intensive-care units were emptying out.

And then the weather warmed. People began to weary of the daily reminders to maintain their white-knuckled vigilance. Summer was arriving. And the new norms began to unravel.

Some people stopped wearing masks, others became less cautious about social distancing. Their friends and neighbors tried to figure out what to do. Which behaviors were acceptable? Which were overly cautious? Which were selfish or reckless? Different communities responded differently. Some groups wore face masks; others didn’t. Some gathered together; still others kept their distance.

The disease, meanwhile, kept spreading the same way as before. Every person, every surface, every contact remained a potential source of infection. And the caseload continued to rise.

For nearly a century, scientists have believed that behaviors spread just like viruses do. But as the world saw in 2020, the spread of human behavior in fact follows very different rules than the spread of diseases.

Today, epidemiologists and public health experts can forecast the path of a virus, and they can use that science to develop policies to help slow it down. But how can we forecast the spread of new behaviors? How can we identify policies that will improve the uptake of positive behaviors? How can we recognize policies that will unintentionally cause those behaviors to unravel? Why do the rules of social influence seem to vary with culture and identity, and how can we ever hope to understand these complexities?

This book is an attempt to answer those questions. In the pages ahead, I’ll show you what the brand-new science of networks tells us about how and why and when human behavior changes. I’ll show you the factors that determine the spread of social change, explain why we’ve misunderstood them for so long, and reveal how they really work.

Behavior change, we now understand, is not like a virus, spreading through casual contact. It does follow rules, but learning these rules takes us beyond the spread of diseases to reveal a process that is deeper, more mysterious—and much more interesting.

Introduction

In 1929, Werner Forssman was a twenty-five-year-old heart surgeon with a big idea. He had invented a radical new lifesaving procedure that he thought would change the world. But the medical community met his idea with contempt: he was ridiculed by his colleagues, fired from his job, and driven from the field of cardiology. Thirty years later, Forssman was working as a urologist in a small town in the remote hills of Germany. One night at the local pub, he received a phone call with some startling news: his long-ago discovery had won the 1957 Nobel Prize in Medicine and Physiology. Today, cardiac catheterization is used in every major hospital around the world. How did Forssman’s unpopular innovation become one of the most widely accepted procedures in medical science?

In 1986, American citizens could be incarcerated for up to five years for possessing marijuana—a jail sentence that would forever alter a person’s prospects for financial success, marriage, and even political participation. Today, storefronts in shopping malls sell marijuana openly and pay federal taxes on the proceeds. How did a behavior that was both illegal and regarded as socially deviant become so acceptable that previously stigmatized “drug dealers” became part of the mainstream American business community?

In 2011, internet powerhouse Google launched its new social-media tool, Google+. Although Google had over a billion users worldwide, the company struggled to transfer its dominance in the search-engine market to the social-media market. By 2019, Google+ was forced to shut its doors. During the same period, the start-up Instagram entered the arena. It reached one million users within two months. Within eighteen months the company was purchased by Facebook for $1 billion, and by 2019 Instagram had become a staple among social-media users. What did Google do wrong? And how did Instagram, with fewer resources and less time, outcompete the search-engine juggernaut?

In April 2012, the hashtag #BlackLivesMatter was first posted on social media in response to a jury’s acquittal of the man who shot and killed seventeen-year-old Trayvon Martin. In the two years that followed, several police-related deaths of African American men and women were reported in the news and on social media, but by June of 2014 #BlackLivesMatter had been used only 600 times. Two months later, however, the death of eighteen-year-old Michael Brown in Ferguson, Missouri, triggered a revolution: within months, #BlackLivesMatter had been used more than a million times, and a national movement to protest police violence was underway. Six years after that, in response to the killing of George Floyd in May 2020, #BlackLivesMatter transformed again, this time into a global phenomenon, with solidarity protests in more than 200 cities worldwide and new federal legislation to reduce police violence. What happened to transform decades of overlooked police violence into a powerful, self-organized popular movement?

This book is about change. How it works, and why it so often fails. It’s about the spread of unlikely innovations, the success of fringe movements, the acceptance of unpopular ideas, and the triumph of contentious new beliefs. And it’s about the strategies that help them succeed. Those success stories all have one thing in common: the radical new ideas at their core all expanded and spread through social networks.

I have a unique perspective on these questions because I am a sociologist who studies the science of social networks. In fact, over the last couple of decades, my ideas have helped shape this new field. In the fall of 2002, I made a series of discoveries that altered our scientific understanding of social networks, and launched a new way of studying how change spreads. The resulting insights have helped to explain why social change can be hard to predict, and why it so often confounds our most trusted ideas about which strategies will work and which others will fail.

For decades, our standard ideas about social change have been based on a popular metaphor—that change spreads like a virus. Recently, we have all been reminded how a virus works: one person gets infected, they pass it on to one or two or three (or a hundred) others, and the contagion spreads through the population. The idea that “influencers” are the key to spreading innovations is based on the notion that well-connected individuals can play an outsize role in the spread of a disease—for instance in a viral pandemic. Similarly, the idea that stickiness is essential for a successful social-marketing campaign is based on the idea that certain viruses are particularly infectious.

These viral metaphors are useful when we’re talking about the dispersal of simple ideas or information (headline news of a volcanic eruption, for example, or the marriage of royal celebrities). And those bits of information really are contagious: easy to catch, easy to transmit. But there’s a big problem with the viral metaphor: to create real change, you need to do more than spread information; you must change people’s beliefs and behaviors. And those are much harder to influence. Viral metaphors are able to describe a world where information spreads quickly yet beliefs and behaviors stay the same. It is a world of simple contagions—catchy ideas and memes that spread quickly to everyone but lack any lasting impact on what we think or how we live.

But social change is far more complicated. Innovative ideas and behaviors do not spread virally; simple exposure is not enough to “infect” you. When you are exposed to a new behavior or idea, you don’t automatically adopt it. Instead, you have to make a decision about whether to accept or reject it. And that decision can often be complex and emotional.

My research, and that of many others in this field, has shown that as we consider whether to adopt a new belief or behavior, we are guided, much more than we realize, by our social networks. Through the hidden power of social influence, the network around us shapes how we respond to an innovation, causing us either to ignore it or to adopt it. This much-deeper process of social spreading is called complex contagion, and it has given rise to a new science for understanding how change happens—and how we can help make it happen.

When we discuss “social networks,” it is important to remember that these networks are not necessarily digital. They have existed for as long as humans have been around. They include everyone we talk to, collaborate with, live near, and seek out. Our personal network makes up our social world. The science of social networks studies the web that binds these social worlds together—from neighbors living on the same street to strangers on different continents—and how social contagions can spread among them.

This book crystallizes over a decade of new research by myself and hundreds of other sociologists, computer scientists, political scientists, economists, and management scholars working to discover the most effective strategies for spreading complex contagions. But the idea at its heart is a simple one: successful social change is not about information; it’s about norms. Social networks are not merely the pipes through which ideas and behaviors flow from person to person. They are also the prisms that determine how we see those behaviors and interpret those ideas. Depending on how a new idea comes to us, we may either dismiss it or jump on board.

Unlike perceptual bias, in which our eyes distort visual information, or cognitive bias, which distorts our reasoning about economic information, network bias is the way our social networks invisibly shape the beliefs we hold and the norms we follow.

The social network that links the members of a community together can inadvertently reinforce people’s existing biases, preventing innovative ideas and movements from catching on. Yet with slight changes, the same network can instead trigger collective enthusiasm for an innovation, accelerating its adoption throughout the community.

My goal in this book is to help you unravel some of the mysteries of societal transformation by showing you how these social networks function. From protests in the streets to new management strategies in an organization—from the spread of healthy diets to the adoption of solar power—social networks are the force that drives the potential for social change.

In the pages ahead, I will take you to Silicon Valley, where you will see innovations unintentionally crushed by the very “influencers” who are supposed to help promote them.

We will visit Denmark and discover how a clever group of computer scientists deployed a network of autonomous Twitter bots to spawn human social networks that spread social activism to thousands of people.

You will venture behind the scenes at Harvard University, where network scientists pioneered and patented networking strategies to accelerate the adoption of innovative technologies.

Finally, I will show you how President Barack Obama used novel networking strategies to improve the quality of his presidential decisions.

When I began exploring these topics, I worked mostly in the realm of theory, studying the civil rights movement and the worldwide growth of social-media technologies. But a decade or so ago, I realized that if I really wanted to understand why social change succeeds or fails, I would need to find a way to test my theory of networks in the real world. In Parts II, III, and IV of this book, I will detail for you a series of large-scale social experiments I conducted, in which I directly manipulated the behavior of entire populations. Some of these populations were young professionals attending exercise classes at a local gym; others were Democrats and Republicans debating climate change; and still others were physicians engaged in clinical diagnosis. As you will see, these experiments revealed profound new truths about the nature of social change.

By the end of this book, you will understand how the science of networks can empower you to gain control of your own social network and the influence it has on you and others. And you will see how the social networks around you guide people’s behaviors, their receptivity to innovations, and their ability to maintain healthy and productive cultural habits.

In the next chapter, I will begin by identifying popular myths and mistakes in our understanding of social change. But throughout the book, my focus will be on solutions. My ultimate goal in presenting this new perspective on social change is to allow readers from all walks of life to acquire the resources they need to create the change they want to see.