The Spread of Goodness

In recent years, it's become clear that much of our individual behavior depends on the dynamics of our social network. It doesn't matter if we're talking about obesity or happiness: they all flow through other people, like a virus or a meme. Last year, I profiled James Fowler and Nicholas Christakis in Wired, who have conducted several fascinating studies that demonstrate the power of social networks:

There's something strange about watching life unfold as a social network. It's easy to forget that every link is a human relationship and every circle a waistline. The messy melodrama of life--all the failed diets and fading friendships--becomes a sterile cartoon.

But that's exactly the point. All that drama obscures a profound truth about human society. By studying Framingham as an interconnected network rather than a mass of individuals, Christakis and Fowler made a remarkable discovery: Obesity spread like a virus. Weight gain had a stunning infection rate. If one person became obese, the likelihood that his friend would follow suit increased by 171 percent. (This means that the network is far more predictive of obesity than the presence of genes associated with the condition.) By the time the animation is finished, the screen is full of swollen yellow beads, like blobs of fat on the surface of chicken soup.

The data exposed not only the contagious nature of obesity but the power of social networks to influence individual behavior. This effect extends over great distances--a fact revealed by tracking original subjects who moved away from Framingham. "Your friends who live far away have just as big an impact on your behavior as friends who live next door," Fowler says. "Think about it this way: Even if you see a friend only once a year, that friend will still change your sense of what's appropriate. And that new norm will influence what you do." An obese sibling hundreds of miles away can cause us to eat more. The individual is a romantic myth; indeed, no man is an island.

In their latest paper, published this week in PNAS, Christakis and Fowler re-analyzed an earlier set of experiments led by Ernst Fehr and Simon Gachter, which investigated "altruistic punishment," or why we're willing to punish others even at a cost to ourselves.

Christakis and Fowler demonstrate that, when one of the students gave money to help someone else - they were cooperating - the recipients of that cash then became more likely to give their own money away in the next round. (Every unit of money shared in round 1 led to an extra 0.19 units being shared in round 2, and 0.05 units in round 3.) This leads, of course, to a cascade of generosity, in which the itch to cooperate spreads first to three people and then to the nine people that those three people interact with, and then to the remaining individuals in subsequent waves of the experiment.


The paper itself is filled with optimistic sentences, but it's worth pointing out that 1) selfishness is also contagious and 2) there's a big difference between lab experiments played with strangers and the messy social networks of real life. That said, altruistic cascades like this make me happy:

We report a chain of 10 kidney transplantations, initiated in July 2007 by a single altruistic donor (i.e., a donor without a designated recipient) and coordinated over a period of 8 months by two large paired-donation registries. These transplantations involved six transplantation centers in five states. In the case of five of the transplantations, the donors and their coregistered recipients underwent surgery simultaneously. In the other five cases, "bridge donors" continued the chain as many as 5 months after the coregistered recipients in their own pairs had received transplants. This report of a chain of paired kidney donations, in which the transplantations were not necessarily performed simultaneously, illustrates the potential of this strategy.

Update: I've gotten a few emails wondering what this means for free will. After all, if our decisions are so determined by the decisions of others, then where is there space for human autonomy? My first reaction is that the new science of social networks still leaves plenty of elbow room for individual decisions. We're talking about risk factors and tendencies and statistical correlations. Just because we're influenced by others doesn't mean we can't reject those influences. I asked James Fowler a related question last year and this was his eloquent response:

Everyone always tells me that this research is so depressing and that it means we don't have free will. But I think they're forgetting to look at the flipside. Because of social networks, your actions aren't just having an impact on what you do, or on what your friends do, but on thousands of other people too. So if I go home and I make an effort to be in a good mood, I'm not just making my wife happy, or my children happy. I'm also making the friends of my children happy. My choices have a ripple effect.


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Quine theorized the basis for freewill within a web of relationships long ago. According to Quine, we are free so long as our mental state is a link in a chain of causation that leads to the act.

See Quine's Two Dogmas of Empiricism ("The totality of our so-called knowledge or beliefs, from the most casual matters of geography and history to the profoundest laws of atomic physics or even of pure mathematics and logic, is a man-made fabric which impinges on experience only along the edges.â) and some additional commentary here.

Birds of a feather flock if friends give the appearance that happiness can be found in food....of course, you will be more inclined to eat. We all want happiness, and sometimes forget that it can't be found outside of ourselves. It is the nature of suffering. Fowler speaks of the effects of living a mindful life, aware that we are not an island, and how we can positively affect others with gentle waves of goodness.

The power of memes is uncanny.

We're in a constant state of flux, and memes may be the primary driver--depending upon how much adventurous spirit you have.

Rather than autonomy, "moral luck" is a more applicable problem. Cf.
In this territory, Thomas Nagel is more helpful than Kant. Everyone is still making independent choices, since there are multiple inputs to choose from, but the set of choices is heavily influenced by environment.

By Andrew Wells-Qu (not verified) on 10 Mar 2010 #permalink

Can national differences be partially explained by the experiment of Christakis and Fowle? Each nation is a sort of relatevely close social network due to language, geographic borders and so on.

I am European and grew up in a country where people are selfish and not community-oriented at all but after a few years in the United States, surrounded by Americans, I am slowly becoming more altruistic. And fat. :)

"every action of ours is passed on to others according to its value, of good or evil, it passes from father to son, from one generation to the next, in a perpetual movement."
- Antonio Gramsci

Determinism only applies to inlaws you inherit, perhaps quite unwillingly.



couldn't these network results be regarded as a particular instance of framing effects in action?

I would be interested in how introversion, up to being a loner (and millions of people are living alone now) factor in to a social network.
What social, familial, marital involvement Iâve had over the years has been more bad for me than good. My health is much improved since I have stopped trying to be like âthem.â

There are other examples of social influence in research that shows people both start and stop smoking in groups. The influence appears to exist whether the behavior is good or bad, healthy or unhealthy. What I wonder is what factors determine who influences who within a social group? If one member becomes obese while another loses weight, then what happens to their social networks?

Diffusion process have been taken into account for a long time in Social Science; ideas like these can be traced back to Durkheim and even more recently in Symbolic Interactionism. The recent theories of social networks, which began around the 70`s but have become much more important since the appearance of Internet, have a very interesting point of view in the sense that they combine Network techniques used by engineers, with the knowledge of Social Science.