Wired Magazine profiles an extremely interesting book on the power of social networks, and how the actions of one individual can spread throughout it:
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.