‘The existence and use of money remained an embarrassing puzzle for monetary analysis. We observe over man's history that social groups without generally accepted media of exchange exhibit poor survival characteristics. Most social groups do not use assets (or commodities) at random in the execution of exchanges. One observes that a small subset of assets is dominantly used in transactions. These transaction-dominating assets are usually referred to as money. The literature contains many suggestive attempts to explain the emergence and role of money. The classic writers made passing references in somewhat pictorial language to the extension markets and increasing labor productivity induced by the use of a general medium of exchange. This idea has never been systematically developed however.’ — Karl Brunner (1971)