We're all connected. You can send an e-mail message to a friend, and your friend can pass it on to one of his or her friends, and that friend can do the same, continuing the chain. Eventually, your message could reach just about anyone in the world, and it might take only five to seven e-mails for the message to get there.

Scientists recently tested that idea in a study involving 24,000 people. Participants had to try to get a message forwarded to one of 18 randomly chosen people. Each participant started by sending one e-mail to someone they knew. Recipients could then forward the e-mail once to someone they knew, and so on.

Targets, who were randomly assigned by researchers from Columbia University in New York, lived in 13 countries. They included an Australian police officer, a Norwegian veterinarian, and a college professor.

Out of 24,000 chains, only 384 reached their goal. The rest petered out, usually because one of the recipients was either too busy to forward the message or thought it was junk mail.