What are different stages in the evolution of money?

Commercial exchanges existed long before the invention of
money. A farmer might trade olive oil with a potter in exchange for jars, or a herder
might trade wool or beast hides with a cobbler in exchange for shoes. While this system
of barter still exists in many agricultural societies, and is becoming increasingly
popular again with the internet making it easier to find particular exchanges, in
complex societies it doesn't work out very well. If a cattle ranger needs barbed wire,
he won't necessarily be able to find a barbed-wire manufacturer in need of beef;
instead, he might find an accountant who needs beef, who works for a doctor who attends
to the medical needs of the barbed wire company owner. These sorts of long chains
quickly become unwieldy. 

The next stage in the evolution
of money is using some sort of generally agreed upon valuable substance as a standard
currency. The earliest known such standard was cattle, which are still treated as units
of value in some African tribes. Later, more portable good such as cowrie shells, gold,
and silver became standard, with states or cities beginning to mint
coinage. 

In the modern period, financial instruments have
proliferated, now including not just physical money, but virtual currencies such as the
bitcoin or currencies in massive online video games. Perhaps the most dramatic moment in
the evolution of modern currency was 1933 when the US went off the gold standard. Before
that, currency in most countries stood for physical reserves of gold, but after that
date, currencies became increasingly a matter of fiat, valued by trust and
contract.