James H. Fowler, a professor of medical genetics and political science at the University of California, San Diego, explored the effects of social networks on human interaction in a lecture on Wednesday, arguing that an individual’s behavior has an impact far beyond their immediate social circle.

“The ultimate question is this,” said Fowler in his talk at the Harvard Kennedy School. “When one person changes does that cause another person to change? And then another person? And another, like falling dominoes?”

A study authored by Fowler and sociology professor Nicholas A. Christakis entitled ‘The Spread of Obesity in a Large Social Network Over 32 Years,’ concluded that people are more likely to be obese if their friends are obese. Further research revealed that this tendency was true for friends of friends and even friends of friends of friends.

Both men’s work led to the ultimate conclusion that obesity was not so much an “epidemic,” as it is so often labeled, but rather that it occurred in clusters – in networks. They determined that this principle applies just as equally to smoking, happiness, loneliness, and depression.

However, after much outcry by statisticians that the sample used for their conclusions was not sufficiently randomized or controlled, they turned to a much larger population – the 61 million Facebook users in the United States who logged on to the website on election day 2010.

They created an experiment in which 60 million users were shown an ‘I Voted’ button that they could click, accompanied by the faces of friends who had already clicked the button. 600,000 users were shown the same button, but without their friends’ faces and 600,000 users were not shown the button at all.

Through this study, they determined that by clicking the “I Voted” button, a user created a probability increase of .9% that their friends would express that they too voted and an increase of 1.8% in the probability that their friends actually voted, translating to about 280,000 more votes cast.

Fowler said that this study and its focus on human interactions hold significant weight for analyses of human behavior.

“Networks are a fundamental part of our biology as a species. We are human because we network,” said Fowler.

Fowler said that the next step in his study is focusing on the driving forces behind these results.

“Why is it that these social networks have such a large impact and how can we learn from it to help us do better in the real world?” said Fowler. “I hope that people will come to understand the effect they have on the lives, not only of the people they can see, but the people they can’t see. It makes you live life a little differently.”