Money is nothing more than a way for people to exchange labor.
Paper money can be thought of as a ticket entitling the holder to a certain amount of someone else's hard work. While man lived a savage existence in history, he was not able to perform all functions necessary to break out of the routine of kill, eat, grow, harvest, without the skills gained from the labor of another. Barter is the simplest form of trading labor, but it is inherently inefficient. If you cannot easily locate someone with the exact item you want, you are out of luck. You can compress more value into a relatively small package with gold and silver.