Nicholas A. Christakis

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.

I'm not suggesting that social scientists stop teaching and investigating classic topics like monopoly power, racial profiling and health inequality. But everyone knows that monopoly power is bad for markets, that people are racially biased and that illness is unequally distributed by social class.

Everyday interactions we have with other people are definitely contagious, in terms of happiness.