The Power of Your Friend’s Friend’s Friend

Social networks "magnify whatever they’re seeded with”—from germs to altruism to a diet of muffins and beer.
  • Transcript


Question: Are there key differences in the way different phenomena spread through networks?

Nicholas Christakis: I think it’s important to emphasize that not everything spreads in networks and not everything that spreads, spreads by the same mechanism. So germs spread differently than money, which spread differently than behaviors, which spread differently than ideas, which spread differently than emotions, and so on. So just because something spreads doesn’t mean it spreads the same way.  And what is interesting is that we’re used to or we’re…most people would accept that claim or would be used to thinking of it in any case if we spoke about germs for example. So we know that sexually transmitted diseases spread differently than the flu. Not all germs spread the same way. Similarly we shouldn’t expect all other phenomena to spread the same way, so mechanistically there are a variety of social, psychological and biological processes, which can undergird these spreading phenomenon, how things might spread within the network and, for example, in the case of obesity there are at least two possible explanations for why your friend’s friend’s friend’s weight gain might ripple through the network and cause your weight gain. Or why well just to stick with the obesity example for a moment, so there are at least a couple of possible… So there are at least a couple of possible explanations for why your friend’s friend’s weight gain might spread through the network and affect you. One is, is that there is a spread of a behavior through the network, so your friend for example says let’s go have muffins and beer. That’s a terrible combination, but you pick up this bad habit from your friend and in so doing you come to adopt the weight status of your friend. Another possibility is that your friend starts gaining weight and it changes your ideas about what an acceptable body size is, so now it’s spreading from your friend to you as not a behavior, but rather a norm: a specific idea about acceptable body size. And both these behaviors and these norms could in principle…not in principle, actually do spread not just from one person to another person, but from person to person to person and person to person to person to person. So, for example, your friend’s friend’s friend can gain weight and that can ripple through the network and affect you either because of the spread of behaviors or because of the spread of norms or both and we find suggestive evidence for both.

Question: How can social networks multiply positive health effects?

Nicholas Christakis: Well we’ve looked at a variety of phenomena. I mean we’ve also looked at, for example, the spread of smoking cessation, the spread of sleep behaviors, a variety of other health related phenomenon... the spread of adherence to medications, proper self management if you have various chronic diseases. And we find similar influence processes for these other phenomena.

So what's crucial to understand about networks…So what is crucial to understand about networks is that they are kind of agnostic. Networks magnify whatever they are seeded with, good or bad. They will magnify fascism. They will magnify germs. They will magnify sadness, but so too will they magnify love and altruism and smoking cessation and ideas. In fact, we just did some work that was just published a couple of weeks ago on…doing some experiments where we studied a kind of "pay it forward" phenomenon where we took random individuals and they played something called the Public Goods Game. And we found that if one person was kind to another person that person then went on to be kind to a total stranger and then that stranger in turn went on to be kind to yet another stranger, so we could see the signature of my kindness. If A is kind to B and B goes on to be kind to C and C goes on to be kind to D we can see in the interactions between C and D a signature of the interactions between individuals A and B, even though A never interacted with C or D, never saw C or D. So you have a kind of rippling through the network of this kind of pro-social positive kind of kind or behavior we found in these experiments that we did. 

So and actually interestingly that also spread to three degrees of separation like some of the observational we’ve done with other phenomena. But here is the point: networks magnify whatever they are seeded with, good or bad, but on balance the reason human beings form social networks is that the benefits of a connected life outweigh the costs, and the magnification of good things outstrips the magnification of bad things. So even though our connection to others puts us at risk for instance of getting germs, it also puts us a risk for getting ideas. And the benefits of getting information from other people in this simple example more than outweighs the cost that we pay from our connection to others. Look, if you wanted to avoid ever getting the flu or sexually transmitted disease or any other kind of interpersonal pathogen, be a hermit. Don’t talk to anybody, but if you did that you would lose all the benefits of social interaction and so it’s because of those benefits that we assemble ourselves into social networks.

Recorded March 31, 2010

Interviewed by Austin Allen