MySpace and other Web sites have unleashed a potent new phenomenon of social networking in cyberspace,     1    at the same time, a growing body of evidence is suggesting that traditional social     2    play a surprisingly powerful and under-recognized role in influencing how people behave.
    The latest research comes from Dr. Nicholas A. Christakis, at the Harvard Medical School, and Dr. James H. Fowler, at the University of California at San Diego. The     3    reported last summer that obesity appeared to     4    from one person to another     5    social networks, almost like a virus or a fad. In a follow-up to that provocative research, the team has produced     6    findings about another major health     7    : smoking. In a study published last week in the New England Journal of Medicine, the team found that a person's decision to     8    the habit is strongly affected by     9    other people in their social network quit—even people they do not know. And, surprisingly, entire networks of smokers appear to quit virtually     10    .
    For     11    of their studies, they     12    of detailed records kept between 1971 and 2003 about 5,124 people who participated in the landmark Framingham Heart Study. Because many of the subjects had ties to the Boston suburb of Framingham, Mass., many of the participants were     13    somehow-through spouses, neighbors, friends, co-workers—enabling the researchers to study a network that     14    12,067 people.
    Taken together, these studies are     15    a growing recognition that many behaviors are     16    by social networks in     17    that have not been fully understood. And     18    may be possible, the researchers say, to harness the power of these networks for many     19    , such as encouraging safe sex, getting more people to exercise or even     20    crime.