It looks like one mechanism for the already observed spread of obesity through social networks may be extremely simple: people tend to eat more when dining with people who are fatter. Thanks to an ingeniously simple experimental design, this paper shows that it's not due to any difference in the fatter people's behaviour. It's solely due to their size. Interesting.

The study deliberately used eating companions for the study, making this a clear network effect in which people are influenced by those with whom they share a reciprocal connection. I'd be intrigued to discover whether it would make any difference if the fatter people (wearing body prostheses) were simply strangers sitting in the same restaurant, not eating together. I'd hypothesise that the effect would still show up, probably more weakly, but that it might be proportional to the number of people who appeared to be obese. In fact, I am guessing it would probably be more complex than that: for instance, that we might be more influenced by those that we thought were more like us or that we took more of a shine to. If so, this would be more of a set than a network effect. It would be not unlike flocking behaviour in birds: until quite recently it was thought that birds flocked due to a simple network effect that spread from neighbour to neighbour but, as it turns out, they are simply counting the birds nearby that are behaving in a particular way, and going with the majority. Memes may work the same way.

This is about as far from intentional communication as it can get - it's not even a behaviour that is being copied here but some imagined and possibly inaccurate belief about someone's past behaviour - and yet the effects may be quite profound and, spread through a society, might have massive large scale effects that spread over into many different aspects of many people's lives, affecting everything from population health to the economy. It's one of the reasons that schools and universities are a good idea, quite apart from, and independently of, any intentional teaching that might or might not be having an effect. When you see people around you behaving in a particular way, you are more likely to behave similarly. If it seems normal to be actively learning, there's a much greater chance that you will do so too. Behaviours (even imagined ones) are highly infectious.