Black Death Predated ‘Small World’ Effect, Say Network Theorists, who characterizes the small-world effect is a modern phenomenon

The “small-world effect” is the observation that one can find a short chain of acquaintances, often of no more than a handful of individuals, connecting almost any two people on the planet.

It is often expressed in the language of networks, where it is equivalent to the statement that most pairs of individuals are connected by a short path through the acquaintance network. Although the small-world effect is well-established empirically for contemporary social networks, we argue here that it is a relatively recent phenomenon, arising only in the last few hundred years: for most of mankind’s tenure on Earth the social world was large, with most pairs of individuals connected by relatively long chains of acquaintances, if at all.

The conclusions of a group of net-work scientists divulge quite another kind of society. The conclusions are based on observations about the spread of diseases, which travel over contact networks between individuals and whose dynamics can give us clues to the structure of those networks even when direct network measurements are not available. As an example the scientists have considered the spread of the Black Death in 14th-century Europe, which is known to have traveled across the continent in well-defined waves of infection over the course of several years. Using established epidemiological models, the scientists show that such wave-like behavior can occur only if contacts between individuals living far apart are exponentially rare. They further show that if long-distance contacts are exponentially rare, then the shortest chain of contacts between distant individuals is on average a long one. The observation of the wave-like spread of a disease like the Black Death thus implies a network without the small-world effect.

This is a very interesting article. One reason is that it has hitherto been believed that the exact opposite was the case. In a world where the only form of transport was by horse, oxcart or  foot, wandering was believed to be much more common in an age before extensive barge navigation and railroad traffic took off; after the introduction of these modern inventions (and especially freight trains and steamers) people simply did not have to walk to the market in order to sell their surplus, which was the case before the 19th century (as witnessed by peasant diaries from the 16th century and onwards). After the introduction of modern transport technologies people organized it differently – and became much more stuck in their local community; which by the way started the fashion for the regional and local history as identity formation projects, which became widespread in the 19th century.

Now it seems medieval people did not interact to the extent it has hitherto been believed. Or rather, medieval people must really have felt stranded in a very small world (which is something quite different from the “small world” we live in!)

A fascinating conclusion worth a European-wide research programme. The question is: how can we get a sense of what it felt like to live in a depopulated countryside in a disconnected hamlet at the periphery of a moor in 1350? And yet live in very close quarters, huddling under the same carpet. And then experience the death of your bed-fellow?

SOURCE:

The small-world effect is a modern phenomenon
By Seth A. Marvel, Travis Martin, Charles R. Doering, David Lusseau, M. E. J. Newman
(Submitted on 9 Oct 2013)
arXiv:1310.2636 [physics.soc-ph]or arXiv:1310.2636v1 [physics.soc-ph]