Nicholas Christakis: How Do Our Social Networks Affect Our Health? Physician and social scientist Nicholas Christakis explains how face-to-face social networks and their structures influence behaviors and phenomena in human society and the natural living world.

How Do Our Social Networks Affect Our Health?

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NICHOLAS CHRISTAKIS: So we use the word spread and we think that we understand what we're saying, but actually germs spread differently than emotions, which spread differently than money, which spread differently than behavior. So different things spread in different ways.

CHRISTAKIS: So we use the word spread and we think we understand what we're saying, but actually, germs spread differently than emotions, which spread differently than money, which spread differently than behavior. So different things spread in different ways.


This is Nicholas Christakis.

CHRISTAKIS: I'm a physician and social scientist at Yale University where I direct the Human Nature Lab, and I'm also the co-director of the Yale Institute for Network Science.

RAZ: And to understand Nicholas's interest - or his obsession, really - with the question of how things spread - well, first, we need to go back about 300 years.

CHRISTAKIS: This was in 1744, or something like that.

RAZ: And around that time, some French mathematicians decided to examine death among monks and nuns. And the conventional wisdom at the time was that living in holy purity - no sex, no marriage - it should have meant that monks and nuns live longer.

CHRISTAKIS: And they began to find that, actually, the monks and the nuns did not live longer. It was very perplexing to them 'cause it wasn't in keeping with their sort of religious ideas about what should be going on.

RAZ: So - theory quashed. But then about 100 years later...

CHRISTAKIS: About 1858, I think it was...

RAZ: A British statistician, named William Farr...

CHRISTAKIS: Well, I think you could think of him as the father of demography, actually.

RAZ: He had been wondering about that study from a hundred years before so he did one of his own. But instead of studying monks and nuns, who lived in relative isolation, he studied married couples - people who had each other.

CHRISTAKIS: And he found that, actually, married people lived longer.

RAZ: But there was another surprise in the study too.

CHRISTAKIS: He also found that people who were widowed lost life. They lived less long.

RAZ: This phenomenon became known as the widowhood effect.

CHRISTAKIS: And beginning in the 1960s, some physicians and some demographers and other social scientists continued to study this topic in a famous paper was published, called, "Dying Of A Broken Heart."

RAZ: And it basically says if you're a man and your wife dies, your risk of death in the following year doubles.

CHRISTAKIS: And when a woman's husband dies, her risk of death goes up by approximately 20 percent and then it sort of gradually rises and then gradually returns to baseline.

RAZ: Wait - wait, just stop for a moment. I mean...


RAZ: ...This is crazy, right? Like, a spouse dies - like, a wife or a husband dies - and then the possibility of death spreads to the surviving spouse?

CHRISTAKIS: Yes, that's right. That's exactly what happens, and the reason is that because people are connected, their health is connected. There's something very deep and fundamental about human connection. I mean, we fare better and worse because we're connected to others.

RAZ: So years ago, Nicholas was studying this effect - the widowhood effect.

CHRISTAKIS: And I just suddenly had this very simple realization that, in fact, we could see the widowhood effect as a simple case of a much broader phenomenon, as a simple case of social network effects more generally.

RAZ: For Nicholas, this was the moment when his career became less about death about husbands and wives and more about the profound, but hidden ways we are all connected, and how those connections fuel the spread of, well, everything. Here's Nicholas on the TED stage.


CHRISTAKIS: And I started to see the world in a whole new way. And then I realized that, in fact, these connections were vast and that we were all embedded in this broad set of connections with each other. This thing - this network - has a memory. It moves, things flow within it. It has a kind of consistency - people can die, but it doesn't. It doesn't die - and it has a kind of resilience that allows it to persist across time. And I became obsessed with this. I became obsessed with how it might be that we're embedded in these social networks and how they affect our lives. So social networks are these intricate things of beauty and they're so elaborate and so complex and so ubiquitous in fact, that one has to ask what purpose they serve. I think understanding social networks and how they form and operate can help us understand not just health and emotions but all kinds of other phenomena like crime and warfare and economic phenomena like bank runs and market crashes and the adoption of innovation.

RAZ: When we come back, Nicholas Christakis dives into his research on social networks and explains how everything spreads among everyone. I'm Guy Raz, and you're listening to the TED Radio Hour from NPR. It's the TED Radio Hour from NPR.

It's the TED Radio Hour from NPR. I'm Guy Raz, and on the show today, ideas about how things spread. And, before the break, we were hearing from social scientist Nicholas Christakis. And early in his career, he wanted to understand how behavior and even the choices we make spread through social networks.

CHRISTAKIS: And eventually we became interested in the structure of human social networks, like, why do we have this structure at all? Why do humans make networks with these ornate, reproducible patterns?

RAZ: So how does it work? Like, give me an example.

CHRISTAKIS: So if you can imagine, you could think about this in terms of how you arrange workplaces. For example, you might employ a thousand engineers, and you might find that if we organize the engineers in certain ways they're inventive and cooperative. Or we take the same engineers and organize them in a different way - you know, who's talking to whom for example - and we find that those engineers are on uninventive and uncooperative. Same human beings, different typology - different architecture of ties - completely changes the kind of group properties that these individuals evince, and many experiments that we've done have shown this. You take a group of people, and you arrange them one way and they're healthy and innovative and cooperative and kind, or you take the same people and you arrange them a different way and they're unhealthy and uncooperative and unkind. And it's that insight about how the whole comes to be greater than the sum of its parts that is, is in my judgment, one of the most crucial insights arising from the study of human social networks.


CHRISTAKIS: Now, how does this help us figure out some of the problems that are affecting us these days? Well, the argument I'd like to make is that networks have value. They are a kind of social capital. Our experience of the world depends on the actual structure of the networks in which we are residing and on all the kinds of things that ripple and flow through the network. The reason I think that this is the case is that human beings assemble themselves and form a kind of super organism. Super organisms have properties that cannot be understood just by studying the individuals. And so I came to see these signs of social networks as living things that we could put under a kind of microscope and study and analyze and understand. And we used a variety of techniques to do this, and we started exploring all kinds of other phenomena. So we looked at smoking and drinking behavior and voting behavior and divorce - which can spread - and altruism.

RAZ: So we could get to a place where, you know, we could be so good at mapping social networks and behaviors that we could actually predict how, you know, how they're going to react - how things spread even before it happens?

CHRISTAKIS: Oh, yeah. Not only can we do that, but even more, we can put information into the network. My colleague, James Fowler, published a paper where he - working with Facebook - where he randomly assigned 61 million people - he and his colleagues - to a voter intervention, showing that we could increase civic engagement in our country by exploiting the fact that people are more likely to vote when their friends vote. And in a study that we just published a couple of months ago, working in Honduras, my laboratory showed that actually we could strategically target clean water and vitamin interventions, and create artificial tipping points in villages in Honduras by taking advantage of and understanding of network structure so that we picked structurally-influential people in these villages, persuaded them to change their behavior, and as a result, the behavior change spread rapidly through the population.

RAZ: I mean, there's so many things that you could spread just by identifying the right people and the right entry points.

CHRISTAKIS: Yes, that's exactly right. Now, I should say this technology, like any technology, is a dual-use technology. You can use this thing not only to spread desirable properties but undesirable properties. So you can foster the spread of germs in bio-terror attacks, or you can foster the spread of fascism, or you can make groups not more cooperative but less cooperative.

RAZ: So am I, like, the only one who thinks this is kind of scary? Like, you - people like you - have a lot of power - like you are kind of an evil genius, Nicholas.

CHRISTAKIS: Yes, yes, yes. It - that - it's a concern. But like, it's like guns or nuclear weapons or drugs which are poisons, you know, it's a very scary thing to contemplate.

RAZ: Yeah.

CHRISTAKIS: So I was giving a talk about this work, about how our ideas, you know, could be used to make the world better. And I was doing this in a foreign - in an unnamed, foreign country. And afterwards, all these official-looking people came up to talk to me, and I became aware at some point that they were very interested in what I was doing, but, you know, for the wrong reasons. Yes, so all of this is a dual-use technology, but I would beg to suggest that this is not specific to, you know, network science. So this is a problem in all sciences. But as a network scientist, we need to be mindful of this as well.


CHRISTAKIS: I think we form social networks because the benefits of a connected life outweigh the costs. If I was always violent towards you or gave you misinformation or made you sad or infected you with deadly germs you would cut the ties to me and the network would disintegrate. So the spread of good and valuable things is required to sustain and nourish social networks. Similarly, social networks are required for the spread of good and valuable things like love and kindness and happiness and altruism and ideas. I think, in fact, that if we realized how valuable social networks are, we'd spend a lot more time nourishing them and sustaining them because I think social networks are fundamentally related to goodness.

RAZ: The more you understand about how things spread, are you optimistic about all of this stuff?

CHRISTAKIS: God, yes. I mean, I wouldn't be engaged in this work and have devoted so much time to it if I wasn't moved, frankly, by the prospect of using this technology to make the world better. Many of the problems that beset human beings, at their root, have behavioral origins. And so I think inventing technologies that allow us to change behavior at scale, in populations for the better is crucial. And I really believe that these types of technologies and ideas offer tremendous hope for improving the human condition.

RAZ: Nicholas Christakis teaches at Yale University. You can see both of his talks at

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