[nhaehnle]

This is a pretty good summary, except that there is quite a lot of doubt by anthropologists that the historical succession ever happened like this. Apparently, various forms of money came into being out of debt, without the detour via precious metals.

The reasoning is roughly this: When you trade, it is extremely rare for a "double coincidence of wants" to actually happen with real goods at a fixed point in space and time. So people extend credit and remember who owes what to whom. Money then grows out of the increasing formalization of this process. Coins are then created by a state that wants to make lots of uniform payments (i.e. payment to soldiers, hence the name soldi for certain Roman coins).