What constrains or enables the capacity of human beings to work in groups is not so much the technology, but rather the capacity of the human brain to have and monitor social interactions.

We cannot understand our humanity just by studying individuals.

It used to be thought that our genes were historically immutable and that it was not possible to imagine a conversation between culture and genetics.

It is the spread of the good things that vindicates the whole reason we live our lives in networks. If I was always violent to you or gave you germs, you would cut the ties to me and the network would disintegrate. In a deep and fundamental way, networks are connected to goodness, and goodness is required for networks to emerge and spread.

My entire youth was spent with an incredibly ill parent... I don't think you can grow up that way and not be marked by that experience.

If your friends are obese, your risk of obesity is 45 percent higher. ... If your friend's friends are obese, your risk of obesity is 25 percent higher. ... If your friend's friend's friend, someone you probably don't even know, is obese, your risk of obesity is 10 percent higher. It's only when you get to your friend's friend's friend's friends that there's no longer a relationship between that person's body size and your own body size.

People have just assumed that... if we call our Facebook acquaintances our friends, we must be influenced by them, too. But we're not.