the Tipping Point, How little things can make a big difference- Malcolm Gladwell
In the late 1960s, the psychologist Stanley Milgram conducted an experiment to find an answer to what is known as the small-world problem. The problem is this: how are human beings connected? Do we all belong to separate worlds, operating simultaneously but autonomously, so that the links between any two people, anywhere in the world, are few and distant? Or are we all bound up together in a grand, interlocking web? In a way, Milgram was asking the very same kind of question that began this chapter, namely, how docs and idea or a trend or a piece of news — the British are coming! — travel through a population?
Milgram’s idea was to test this question with a chain letter. He got the names of 160 people who lived in Omaha, Nebraska, and mailed each of them a packet. In the packet was the name and address of a stockbroker who worked in Boston and lived in Sharon, Massachusetts. Each person was instructed to write his or her name on the packet and send it on to a friend or acquaintance who he or she thought would get the packet closer to the stockbroker. If you lived in Omaha and had a cousin outside of Boston, for example, you might send it to him, on the grounds that — even if your cousin did not himself know the stockbroker — he would be a lot more likely to be able to get to the stockbroker in two or three or four steps. The idea was that when the packet finally arrived at the stockbroker’s house, Milgram could look at the list of all those whose hands it went through to get there and establish how closely connected someone chosen at random from one part of the country was to another person in another part of the country. Milgram found that most of the letters reached the stockbroker in five or six steps. This experiment is where we get the concept of six degrees of separation.
That phrase is now so familiar that it is easy to lose sight of how surprising Milgram’s findings were. Most of us don’t have particularly broad and diverse groups of friends. In one well-known study, a group of psychologists asked people living in the Dyckman public housing project in northern Manhattan to name their closest friend in the project; 88 percent of the friends lived in the same building, and half lived on the same floor. In general, people chose friends of similar age and race. But if the friend lived down the hall, then age and race became a lot less important. Proximity overpowered similarity. Another study, done on students at the University of Utah, found that if you ask someone why he is friendly with someone else, he’ll say it is because he and his friend share similar attitudes. But if you actually quiz the two of them on their attitudes, you’ll find out that what they actually share is similar activities. We’re friends with the people we do things with, as much as we are with the people we resemble. We don’t seek out friends, in other words. We associate with the people who occupy the same small, physical spaces that we do. People in Omaha are not, as a rule, friends with people who live halfway across the country in Sharon, Massachusetts. “When I asked an intelligent friend of mine how many steps he thought it would take, he estimated that it would require 100 intermediate persons or more to move from Nebraska to Sharon,” Milgram wrote, at the time. “Many people make somewhat similar estimates, and are surprised to learn that only five intermediaries will — on average — suffice. Somehow it does not accord with intuition.” How did the packet get to Sharon in just five steps?
The answer is that in the six degrees of separation, not all degrees are equal. When Milgram analyzed his experiment, for example, he found that many of the chains from Omaha to Sharon followed the same asymmetrical pattern. Twenty-four letters reached the stockbroker at his home in Sharon, and of those, sixteen were given to him by the same person, a clothing merchant Milgram calls Mr. Jacobs. The balance of letters came to the stockbroker at his office, and of those the majority came through two other men, whom Milgram calls Mr. Brown and Mr. Jones. In all, half of the responses that came back to the stockbroker were delivered to him by these same three people. Think of it. Dozens of people, chosen at random from a large Midwestern city, send out letters independently. Some go through college acquaintances. Some send their letters to relatives. Some send them to old workmates. Everyone has a different strategy. Yet in the end, when all of those separate and idiosyncratic chains were completed, half of those letters ended up in the hands of Jacobs, Jones, and Brown. Six degrees of separation doesn’t mean that everyone is linked to everyone else in just six steps. It means that a very small number of people are linked to everyone else in a few steps, and the rest of us are linked to the world through those special few.(Gladwell- The Tipping Point 34-37)