Everything Is Obvious_ _Once You Know the Answer - Duncan J. Watts [41]
Nevertheless, Milgram still found that not all message handlers are created equal. In fact, of the sixty-four messages that got through, nearly half of them were delivered to the target by one of three people, and half of those—sixteen chains—were delivered by a single person, “Mr. Jacobs,” a clothing merchant who was a neighbor of the target. Struck by this concentration of messages into the hands of a few individuals, Milgram speculated that what he called sociometric stars might be important to understanding how the small-world phenomenon worked.6 Milgram himself didn’t conclude much more than that, but three decades later, in an essay called “Six Degrees of Lois Weisberg,” New Yorker writer Malcolm Gladwell used Milgram’s finding about Mr. Jacobs to make the argument that “a very small number of people [like Mrs. Weisberg] are linked to everyone else in a few steps, and the rest of us are linked to the world through those few.”7 In other words, even though Mr. Jacobs and Ms. Weisberg are not “important” in the same way that Mrs. Roosevelt or Mr. Ford were important, from a network perspective they end up serving the same kind of function—like hubs in an airline network that we necessarily pass through in order to get from one part of the world to another.
Like Jacobs’s hierarchy, the airline network metaphor is an appealing one, but it says more about how we would organize the world if given the opportunity to do so than it says about how the world is actually organized. If you think about it for minute, in fact, the metaphor is actually quite implausible. Some people clearly have more friends than others. But people are not like airports—they can’t just tack on an extra wing when they need to handle more traffic. As a result, the number of friends that people have doesn’t vary by nearly as much as the traffic in airports. An average person, for example, has a few hundred friends, while the most gregarious top out around a couple of thousand—roughly ten times as many. That is a big difference, but not remotely comparable to a true hub like O’Hare, which handles thousands of times as many passengers as a small airport. So how is it that connectors in social networks can nevertheless act like hubs in airline networks?8
In fact, they do not, as my collaborators Roby Muhamad and Peter Dodds and I found several years ago when we replicated Milgram’s original experiment—only this time we used e-mail in place of physical packets, allowing us to work on a much larger scale. Whereas Milgram had three hundred initial senders in two cities attempting to reach a single target in Boston, we had more than twenty thousand chains in search of one of eighteen targets in thirteen different countries around the world. By the time the experiment had ended, the chains had passed through over 60,000 people in 166 countries. Using some more up-to-date statistical analysis than Milgram had available to him, we were also able to estimate not only the length of the chains that made it to their targets, but also how long the chains that failed would have been had they continued. Our main finding was remarkably close to Milgram’s—roughly half of all chains should be expected to reach their targets in seven steps or fewer. Given the differences between the two experiments, which were conducted on very different scales using different technologies and nearly forty years apart, it is actually sort of amazing that the results accorded so closely, and provides strong support for the claim that many people—although certainly not all people—can connect to one another through short chains.9
Unlike Milgram’s findings, however, we discovered no “hubs” in the delivery process. Rather, messages reached their targets through almost as many recipients as there were chains. We also asked people why they chose the next person in the chain, and here, too, we discovered little evidence of hubs or stars. Subjects