However, the evolution of society towards increased specialisation and exchange is not unidirectional. History is littered with examples of people who moved back towards self-sufficiency as they grew less prosperous. Unable to find trading partners to do mutual service with, they had to serve themselves and that made them poorer.

Two examples, both from The Rational Optimist:

The economist Vernon Smith, in his memoirs, recalls how in the Depression his family moved in the 1930s from Wichita, Kansas, to a farm when his father was laid off as a machinist, because ‘we could at least grow most of our own food and participate in a subsistence economy.’

And the end of the Roman empire.

As Roman rule disintegrated, at least in the west, money lending at interest stopped and coins ceased to circulate so freely. In the Dark Ages that followed, because free trade became impossible, cities shrank, markets atrophied, merchants disappeared, literacy declined and – crudely speaking – once Goth, Hun and Vandal plundering had run its course, everybody had to go back to being self-sufficient again. Europe de-urbanised. Even Rome and Constantinople fell to a fraction of their former populations. Trade with Egypt and India largely dried up, especially once the Arabs took control of Alexandria, so that not only did oriental imports such as papyrus, spices and silk cease to appear, but those export-oriented plantations in Campania became the plots of subsistence farmers instead. In that sense, the decline of the Roman empire turned consumer traders back into subsistence peasants. The Dark Ages were a massive experiment in the back-to-the-land hippy lifestyle (without the trust fund): you ground your own corn, sheared your own sheep, cured your own leather and cut your own wood. Any pathetic surplus you generated was confiscated to support a monk, or maybe you could occasionally sell something to buy a metal tool off a part-time blacksmith. Otherwise, subsistence replaced specialisation.