From:
http://www.nytimes.com/2009/09/13/magaz ... anted=2&em
....Good behaviors — like quitting smoking or staying slender or being happy — pass from friend to friend almost as if they were contagious viruses. The Framingham participants, the data suggested, influenced one another’s health just by socializing. And the same was true of bad behaviors — clusters of friends appeared to “infect†each other with obesity, unhappiness and smoking. Staying healthy isn’t just a matter of your genes and your diet, it seems. Good health is also a product, in part, of your sheer proximity to other healthy people.
Yet there is also, the two scientists argue, something empowering about the idea that we are so entwined. “Even as we are being influenced by others, we can influence others,†Christakis told me when we first met. “And therefore the importance of taking actions that are beneficial to others is heightened. So this network thing can cut both ways, subverting our ability to have free will, but increasing, if you will, the importance of us having free will.â€
As Fowler pointed out, if you want to improve the world with your good behavior, math is on your side. For most of us, within three degrees we are connected to more than 1,000 people — all of whom we can theoretically help make healthier, fitter and happier just by our contagious example. “If someone tells you that you can influence 1,000 people,†Fowler said, “it changes your way of seing the world.â€