This research brings to mind the obsrvation of Blaise Pascal, "The heart has its reasons that the mind knows not." It appears that negative behaviors like overeating and smoking are in some hidden way transmitted through our social networks, even when we are not in contact with those others who are influencing us. Likewise, it turns out that happiness is spread in a similarly diffuse and oblique fashion.

Really fascinating - you should read the whole piece. Been thinking about and working on networks a lot lately.