Humans live in an interconnected, interdependent world. This is true for all social species. These facts have led researchers to study the effects of social isolation for many different types of animals. What they have found is that, for instance, isolation decreases the lifespan of the fruit fly, and leads to type II diabetes and obesity in mice. They have also found that, in rhesus monkeys, isolation negatively effects their psychological and sexual development. The effects of isolation can be even more profound in humans perhaps because our kids have the longest period of dependency of any species. Researchers have also discovered that it is not the objective number of social contacts that predicts loneliness, but rather our perceived feelings of social isolation.
Recently, researchers have been looking at how loneliness spreads within communities. In a 2009 edition of the Journal of Personality and Social Psychology researchers John Cacioppo, Nicholas Christakis and James Fowler looked at this question more closely. The researchers looked at data from a famous medical study that tracked people from a small town over a close to 40-year period. Cacioppo and his colleagues were looking for patterns of connection, loneliness and isolation.
The researchers were able to rule out two different hypotheses. First, that lonely people attract other lonely people. Second, that the environment that lonely people were in was creating their sense of loneliness. For instance, that going away to college or getting divorced led to persistent or increased loneliness. Instead, what they found was that loneliness acts rather like a contagion, and that it spreads through face-to-face discussions and disclosures. In effect, they found that lonely people tend to make non-lonely people, lonely. Furthermore, they found that this phenomenon is evident to three degrees. That is, that lonely people make friends of friends, of friends, lonelier.