From time to time Sam Blackman, a paediatric oncologist in Philadelphia, checks up on people other than patients. Namely, other Sam Blackmans. No stethoscope is needed to take the pulse of his namesakes, though — just a Google search. And while he has never met the men he refers to as Sam 2.0 and Sam 3.0, when one of those other Sam Blackmans posted a photograph of his wife on the Internet, Blackman, 39, couldn't help but feel a twinge of pleasure.

"I'm like 'Oh! Sam Blackman got married,'" he said. "I felt like I should send a card or check his registry on Amazon."

Now that the telephone book has been all but replaced by the minutia-rich Web, searching out, even stalking, the people who share one's name has become a common pastime. Bloggers muse about their multiple digital selves, known as Google twins or Googlegangers. In "Finding Angela Shelton," a book published this month, a writer named Angela Shelton describes her meetings with 40 other Angela Sheltons. Anita Smith, an illustrator, has posted drawings of six of her Googlegangers on her blog. There are name-tally Web sites like SameNameAsMe, and Facebook coalitions including nearly 200 people named Ritz (their insignia is a cracker box logo) and a group aiming to break a world record by gathering together more than 1,224 Mohammed Hassans. But while many people are familiar with Googlegangers, a fundamental question has gone unanswered: Why do so many feel a connection — be it kinship or competition — with utter strangers just because they share a name? Social science, it turns out, has an answer. It is because human beings are unconsciously drawn to people and things that remind us of ourselves.

A photo editor named Tim Connor, who saw a photograph of another man with his name, wrote on his blog that the image "made him intensely real to me. I felt in some way I already knew him." Connor's Googleganger also provoked comparison and self-reflection. "I don't feel the usual mixture of rage and shame knowing that my father would have understood and been comfortable with my Googleganger's career," Connor wrote on Timconnor.blogspot.com, "and he never was with mine."

There are more prosaic reasons that people may feel connected to their Googlegangers, though. They may share a name because they belong to the same ethnic group, or their families may have had similar aspirations for them. Of the 40 Angela Sheltons that Shelton, the writer, met with in researching her book, many of them were nurses!  There is also plenty of rivalry. People are increasingly aware of how to manage their identity online. As Jon Lee, a student and a Web developer who wants to be the first Jon Lee to turn up in a Google search, explained on his blog, "I have to top a recruitment firm, a washed-up pop star, a dead drummer and an IBM guy."