Shelling Out: The Origins of Money

Nick Szabo puts forward a theory of collectibles. The early versions of what could fulfill the role of money today in enabling cooperation between humans. If you seek better understanding of exchange and cooperation and the role money or money-like objects play in it, this could prove an enlightening read. The original purpose of Bitcoin was to enable just that - voluntary exchange between agents acting in their rational self-interest (peer-to-peer, free market, anyone?)