A study at the Yale Institute of Network Science has found that social networks are critical to humans’ motivations for participation in group violence.
The researchers mapped social connections among 91 men of the Nyangatom tribe, which is known for participating in group raids of neighboring tribes, in Ethiopia over three years. The study found that men were more likely to participate in a raid if they were recruited by a friend rather than recruited by the leader of the raid. These results are relevant to other violent phenomena, such as mobs, revolutionary movements and gang warfare, because they show that people are more likely to participate in risky behaviors if their friends are participating as well.
“What we found is that people go to war with their friends,” said Nicholas Christakis ’84, the co-director of the Yale Institute of Network Science and a senior author of the study.
To determine friendship networks, the researchers mapped a gift-exchange network within the community, Christakis said. The researchers asked each man in the Nyangatom tribe to whom he would like to give a small gift, and these gift networks were then mapped to show the social networks of the individuals within the tribe.
The results found that a Nyangatom man was 19.2 percent more likely to participate in a given raid for every nonleader friend going on the raid, while he was only 6.8 percent more likely to participate if the friend was a leader of the raid.
Additionally, the study found that there was no significant increase or decrease in a man’s likelihood to participate in a raid when a sibling was participating in the raid, nor was likelihood to participate affected by physical characteristics such as height or weight.
“What this suggests is whether you purchase an iPad or whether you read the [Yale Daily News] may have less to do with your gender or your major or which dorm you live in and more to do with what are your friends doing,” Christakis explained. “These phenomena are not fully explainable or even well explainable based on assumptions about your attributes. Instead they may have to do with the structure of the group and what is happening around you.”
These social networks are known to be very similar across human societies, said Alexander Isakov, a co-first author of the study who focused on data analysis. Therefore, the results found in this study could actually mirror what occurs in certain violent groups in western society, such as gang violence or terrorism, he explained.
According to Isakov, the violence caused by these groups and the Nyangatom tribe raids are both similar in that it is not formal military conflicts. He added that these raids also do not have traditional leaders, which forces them to rely on pre-existing ties within the community.
“The social ties that exist in this community, the friendship ties, actually amplify this collective violence,” Isakov said.
Christakis pointed out that this study addressed the “collective action problem,” which deals with how to recruit others to participate in potentially dangerous behaviors, especially when the risks are individual but the benefits are shared by the group.
Christakis added that these social networks obey very particular biological, psychological, sociological and mathematical rules, and the goal of the Yale Institute of Network Science is to understand these rules and how to use them to make changes.
“We are studying how to facilitate global health behavior change,” Christakis said. “How do you create artificial tipping points in developing world villages so if one person starts vaccinating their children the whole village starts vaccinating their children?”
The study also developed a mathematical model for determining the leaders in the raid.
Sol Goldman Family professor of social and natural science Nicholas Christakis ’84 joined Yale’s teaching faculty just last year and now heads the ambitiously and eye-catchingly titled Human Nature Lab, where he and his students study phenomena at the intersection of the social and the natural sciences. Last fall he co-taught the wildly popular residential college seminar “Great Big Ideas” with Adam Glick, and now offers an iteration of a course he used to teach at Harvard, Sociology 126, “Health of the Public.”
Besides his high-powered teaching career, Christakis has a natural flair for storytelling and is an eminently accessible conversationalist. He carved out some time to kick his feet up, drink a Diet Coke and tell stories about his adventures inside and outside of the ivory Tower.
Q. What’s your connection to Yale?
A. I’m one of those guys that has a picture of me as a one-year-old baby with a T-shirt that says “Yale, Class of ???” because my parents were graduate students at Yale — my dad in physics and my mother in chemistry. Apparently I was on Science Hill even in utero. My mother was very happy when she went into labor with me, because it meant she got out of a very, very difficult chemistry final exam. My parents left New Haven when they got degrees and I came back here as an undergraduate many years later and was in Ezra Stiles College and studied biology. While I was a student here I took a year off, which I think is a very good thing to do.
Q. Why do you say that?
A. At the time, I couldn’t decide whether to major in biology or French. And I was a good French speaker. So I wanted to go and work in a laboratory in France if I could. It was not easy to find such a position, but through sheer serendipity my mother ran into a neighbor of ours in Washington, D.C. who had a laboratory at the National Institutes of Health. He was hosting a French scientist and suggested that I write to him. This was between my sophomore and junior years in college. So I wrote to the French scientist and he said, “We’d love to have you, because you could help us translate from French to English to publish in English journals.” That was about the only skill I had that could be useful at that stage in my life — I could speak English.
So the summer after my sophomore year, when I was working in a biology lab at Woods Hole, Mass., and when I was still waiting to see if everything was going to work out, I get a letter confirming that I was going to work in a laboratory with a French virologist. I was ecstatic. The postdoc with whom I was working that summer said that we should go and look him up and see what kind of work he did. And of course I hadn’t cared until that point. So we went to the library and we pulled dusty thick volumes and pulled out hard copies of his papers and saw he was very interested in viruses that stay in pets and cause diarrhea. And it said in the “materials and methods sections” of the manuscripts that research assistants “were dispatched to the streets of Paris to retrieve dog feces” to bring back to the laboratory.
The postdoc with whom I was working started laughing and he said, “This is going to be your job when you go to Paris — not to translate papers from French into English.” And he was right. (Laughs.) So when I got to Paris one of my jobs was to take a stainless steel Pooper Scooper and go out into the streets of Paris — and if you’ve ever been to Paris, in those days especially there was dog poop everywhere — collect specimens and bring them back to the laboratory, where we would extract the corona virus. That was my job during my year in Paris, collecting dog poop and translating things into English. It was a good time.
Q. You’re a professor of sociology, evolutionary biology, and medicine, and while at the University of Chicago you did work in hospice. What got you interested in that side of things?
A. When I was growing up, my mother was seriously ill and she died when I was 25, so all through college and medical school she was quite sick. I think partly as a result of that, I always wanted to be a doctor ever since I was a little boy; and also partly as a result of my clinical training, when I became aware of the low quality of care that we give to the dying in our society, I became interested in how to do a better job of caring for the dying. If you think about it, it’s very fashionable to speak about vulnerable populations in our society, but it’s hard to imagine a more vulnerable population than those among us who are terminally ill, and we neglect them. And that’s how I became interested in networks, because part of my interest in care for the dying led to my interest in the “widowhood effect,” which is the fact that you’re more likely to die when your partner dies.
Q. Tell us about your work now.
A. I direct the Human Nature Lab, which is a group of people who are focused on an interrelated set of topics at the intersection of the natural and the social sciences. We’re interested in how the social becomes biological and how the biological becomes social. I’m interested in the part of human nature that relates to our sociality — how we interact with others, why we interact with others. What does it mean for our lives that we create networks and live in networks?
Q. How does that research play out?
A. We look at the evolutionary biology and the genetics and the sociology of social interaction, and we do experiments to see how we can intervene in the world to make it better. How can you form groups or target people with information to change people’s behavior? For example we’re doing a big project in Honduras, where we’re trying to identify who the influential people are in villages, and to get them to adopt clean water interventions or maternal health interventions. We’re trying to change the whole village’s mindset by taking advantage of our understanding of how people interact and how they influence each other.
Q. You sound like an optimist.
A. I’m an inveterate optimist. I just think that it’s possible to do things. I mean, who would want to be pessimistic and nihilistic? To me it’s not a very appealing way to go through one’s life.
Q. Do you still do field work?
A. My graduate students tease me that I don’t do field work anymore. In fact, they laugh at the thought. They say that I wouldn’t survive without hot showers. I don’t think that’s true but I let them mock me. [He pauses.] I’m going to revise that statement. I know that’s not true, but they can tease me anyway.
Q. What do you like about working with students?
A. I love the energy of young people. I like the enthusiasm and optimism of young people. I have hundreds of students who are Facebook friends of mine because I was a House Master at Harvard before I came here. I was in intimate contact with the slang, with the music, with events that were happening. I know weeks before my peers what’s going to be cool because I hear it first from 20-year-olds. Six weeks from now a friend of mine will say, “Did you see this?” and I’ll say, “Yes, I saw it six weeks ago,” because of my connection with students. (Pauses.) I have a rule though, which is I never friend anybody because it would be creepy if I did; but I accept all friendings.
Q. You were at Harvard when Facebook started. How was that?
A. Well, I wish I had bought stock. (Laughs.) Jokes aside, at the time we were very interested in network structure. One day this student came to me, and she said, “You know there’s this new thing online called Facebook, where you can map the whole graph of the network of Harvard. You should look at it.” And to look at it I had to get an account. So I got one and I looked at the graph of Harvard students. I thought it was incredible – I mean, scientifically incredible. I wish I had realized how commercially incredible it was too, but scientifically it was obvious.
Q. What is your goal as an educator?
A. I think the best thing I can do for my students is take them by the shoulders, move them to the scientific frontier and tell them, “Stand here and look out: that’s where the new stuff is.”
