It's a decentralized record of accounts (except the accounts are forgotten).
A natural step from barter is a record of who owes what (so you don't have to bring some grain just to buy 1 beer from someone you have a good trust relationship with). A natural step from there is a token representing value, and there are lots of reasons to make them portable and interchangeable.
A natural step from barter is a record of who owes what (so you don't have to bring some grain just to buy 1 beer from someone you have a good trust relationship with). A natural step from there is a token representing value, and there are lots of reasons to make them portable and interchangeable.