The earliest reference to the ‘six steps’ theory is linked to Italian telecoms radio engineer Marconi, during his Nobel Prize acceptance speech in 1909. Although Marconi was referring to the number of ‘hops’ required between transmitters to connect everyone on Earth, the seed of the theory was born. 

 

Ultimately though, it was American sociologist, Stanley Milgram, who made the theory famous.

In 1967, he conducted small-scale experiment in which a random selection of just 96 people around the US had to get a message to a designated addressee unknown to them. The messages sent by US Mail took an average of six people to reach their destinations.

More recently, the Internet has allowed researchers to add significant weight to the theory.

 

In June 2007 Eric Horvitz of Microsoft Research and Jure Leskovec of Carnegie Mellon University analysed 30 billion conversations among 240 million people using MSN Messenger. It turned out that the average path length (or degree of separation) among all the users was 6.6.