We are highly social creatures. Our lives center around our interpersonal relationships and our social groups. We pay attention to who has status, who is kind, and who should be avoided.
Even more fascinating, we mimic the people we like. We mimic their posture, rate of breathing, mannerisms, speech patterns, you name it. So, it should come as no surprise that many of our behaviors from smoking, to drinking, to gaining weight are simply a function of who we know. It is called "social contagion."
The New York Times has an interesting article on the subject:
By analyzing the Framingham data, Christakis and Fowler say, they have for the first time found some solid basis for a potentially powerful theory in epidemiology: that 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.
I have always had the suspicion that people who cheat on their spouses are friends with other cheaters. I don't have any data to back this up, but given what we know about social contagion and our desire to conform to the norm, it would not surprise me at all.
