Im Allgemeinen wird Stanley Milgram für die Entdeckung der “Six Steps of Separation” verantwortlich gemacht. Milgram befand sich mit seinem berühmten Briefexperiment jedoch in einer von Forschern, die das Phänomen kleiner Welten, wie es Duncan Watts genannt hat, untersucht haben. Bei Watts findet sich dann auch die Herleitung des Konzepts aus ganz anderen Quellen:
“Research specific to the small-world phenomenon did not commence until the 1960s with the formulation and initial mathematical investigation of the problem by Manfred Kochen and Ithiel de Sola Pool (Pool and Kochen 1978). These authors made substantive progress on the problem, estimating both the average number of acquaintances that people possess and the probability of two randomly selected members of a society being connected by a chain of acquaintances consisting of one or two intermediaries. They developed these approximation under a variety of assumptions about the level of social structure and stratification present in the population and concluded (speculatively) that even quite structured populations would have acquaintance chains whose characteristic path lengths are not much longer than those of completely unstructured populations (where the probability of A knowing C, given that A knows B, is independent of whether or not B knows C). For a population about that of the United States and an estimated average number of acquaintances per person of about a thousand, Pool and Kochen estimated that any member of the population could be connected to any other with a chain of associates consisting of at most two intermediaries (hence three degrees of separation).
The study of distances in social networks, however, had begun over twenty-five years before the publication of Pool and Kochen’s work, with Anatol Rapoport and his colleagues at the University of Chicago. In a series of papers in the 1950s and 1960s, published in the Bulletin of Mathematical Biophysics, Rapoport and colleagues established the theory of random-based nets, which describes the statistics of Disease spreading through populations with varying degrees of structure. (Duncan Watts, Small Worlds, S.12).