According to the Six Degrees of Separation Theory, any human being is at a maximum distance of six levels from any other human being in the planet, i. e., between any two people randomly selected, there can be established a bond that can be of first degree, in case they know each other personally/have a direct relationship, until a maximum of six degrees, and in this case the two individuals are separated by six relational bonds, which means they are separated by five other individuals.
This hypothesis was first placed in 1929 by Hungarian writer Frigyes Karinthy in one of his short stories, titled “Chains”, even though the idea was presented in a philosophical and entertaining way, and not as a scientific proposal; in his story, Karinthy mentions the evolution of modern societies and the great technological developments, and defends that besides the fact that human population continuously grows and that there are huge physical distances between individuals, the human connections and creation of networks of contact make the social distance between people smaller day by day. The tale, which is one of the first literary approaches to social networks, or networking, Karinthy concludes that any person on Earth is separated by any other person until a maximum of five connection levels.
In the 50’s, Ithiel de Sola Pool and Manfred Kochen studied this theory from a scientific point of view for the first time, and tried to prove it mathematically, but they were only able to problematize it mathematically, and never fully solved the problem they created.
It was only in 1967 that the Six Degrees of Separation was established as a valid scientific theory, and it was tested in the field of Social Sciences, by Stanley Milgram. The sociologist approached the problem in a completely different way, and choose a random sample of people, in the United States of America, who should send a package to a stranger, that was arbitrarily attributed to them. Each of the persons included in the study new the name, professional occupation and location of the people they should send the package to, and their task was to send the package to someone they already knew and that they thought was more likely to know the person in question; each person who received the package should follow the same procedure, which is, either deliver it to its final recipient, or send it to someone they though that might knew the recipient, and the packages should be passed on until they reached the final destination. In the end of the test, Milgram concluded that each package was passed on, in average, by five to seven people, and then published an essay in the magazine Psychology Today. However, the name “Six Degrees of Separation” only became popular in 1990, following the premiere of the theatre play with the same name, written by John Guare.
This theory, though already established, wasn’t still globally accepted, being the main criticism against it the fact that Milgram’s sample in his study was too small. In the years after the popularization of the concept due to John Guare’s play, the theory began being investigated again, and there where made several studies and tests. In 2001, college professor Duncan Watts recreated Milgram’s experiment, this time in the Internet, i. e., the original package became an e-mail, and approximately 48,000 people from 157 countries took part in the test, and once again the average of separation levels was six, which reinforced the plausibility of the theory. A few years later, in 2008, Microsoft also tried to validate this theory, using the Microsoft Messenger database, with millions of users registered, and the average of relation connection levels between individuals was 6,6. More recently, in 2016, Facebook developed a study related to the same problematic, and came to the conclusion that over the last few decades, the average of connections between individuals decreased, at least among the users of this social network, being the average of levels of separation between users 3,5.
Technological developments, the globalization of the labor market and the continuous growth of social networks and increasing number of users make it expectable that the levels of connections between each individual in the world with any other continues to decrease, so the average of degrees of separation between any two persons in the world will become continuously smaller.
WATTS, Duncan J., Six Degrees: The Science of a Connected Age, W. W. Norton & Company, 2004
BHAGAT, Smitri; BURKE, Moira; DIUK, Carlos; EDUNOV, Sergey; FILIZ, Ismail Onur, Three and a half degrees of separation, Facebook Research, 2016