__Six degrees of separation__ is the idea that all people are six, or fewer, social connections away from each other. Also known as the 6 Handshakes rule. As a result, a chain of "friend of a friend" statements can be made to connect any two people in a maximum of six steps.
It was originally set out by Frigyes Karinthy in 1929 and popularized in an eponymous Six Degrees of Separation (play) written by John Guare. It is sometimes generalized to the average Path length being logarithmic in the size of the population - wikipedia
Several studies, such as Small world experiment, have been conducted to measure this connectedness empirically. The phrase "six degrees of separation" is often used as a synonym for the idea of the "small world" phenomenon - wikipedia
However, detractors argue that Milgram's experiment did not demonstrate such a link, and the "six degrees" claim has been decried as an "academic urban myth". Also, the existence of isolated groups of humans, for example the Korubo people and other native Brazilian populations, would tend to invalidate the strictest interpretation of the hypothesis.
# See also