Social networks exhibit strikingly systematic patterns across a wide range of human contexts.  Here I detail some of our recent efforts to understand the impact networks have on a variety of health and social outcomes, including obesity, smoking, drinking, cooperation, political participation, happiness, loneliness, and depression, and then I discuss a "Three Degrees of Influence Rule" that I conjecture applies to a wide variety of phenomena.  I then explore the biological basis of social networks.  After a brief review of behavior genetics methodology, I show that several social network attributes are heritable.  These results suggest that natural selection may have played a role in the evolution of social networks and may help to explain specific gene associations with a wide variety of traits.