Have you ever heard something from a friend of a friend? Or thought you knew somebody who knew somebody who knew the president? Stanley Milgram believed that such chains were the world's basic social communication system.
      Milgram was a Harvard University social psychologist and father of the "small world phenomenon": the theory that everybody is connected to everybody else by short chains of social acquaintances.
      In 1967, Milgram sent 300 letters to randomly selected addresses in Omaha, Nebraska and Wichita, Kansas. Each letter contained a small packet and instructions to get the packet to a person in the Boston area that was known as the target. The letter provided the target's name, location, and occupation.
     The Nebraskans and Kansans could only send the packet to the target through a chain of personal contacts--people they knew on a first-name basis. Those people were also supposed to send it along using the same criteria--through people they knew such as friends of friends, relatives, or business connections, getting closer and closer to the target each time.
     Sixty packets, through sixty different chains of people, eventually reached the target. Of those, Milgram found that the average number of people in the chain was about six, a discovery that was called the "six degrees of separation." Milgram theorized that we are only a short chain away from anyone else and that the implications of such a small world could be enormous in business and communications.Now researchers at Columbia University are testing Milgram's hypothesis for the entire world. Using e-mail, they are trying to determine whether everyone is indeed only six social acquaintances away from everyone else.They may find that, because of rapid communication, the world is even smaller than it used to be, or that we've grown farther apart and have fewer acquaintances to build chains with.
26. This article is mainly about _
(A) the importance of social networks.
(B) why you can always send a letter anywhere.
(C) Stanley Milgram and his theory.
(D) how our privacy may be invaded.