People want to have something as "a formal token of delayed reciprocal altruism (Richard Dawkins)" and these tokens have probably existed as long as language (~100k years) first starting as shells of a specific size and species. The first DDG hit of this phrase[1] brings up an essay that looks interesting, although I have not had time to read it yet. Gold and silver (and credit based on them) have been that token for most societies since around 600BC. Fiat currencies have been used but flame out spectacularly. I don't think one has lasted more than 100 years. Private gold was made illegal in the US in 1933 and the dollar debased. State exchanges of gold and currency at a fixed rate ended in 1971 with the dollar going full fiat. People are looking for the new token.

[1] http://nakamotoinstitute.org/reciprocal-altruism-in-the-theo...