The prehistoric people were autonomous, they knew each other in the group and their economy was based on favours: I give you this, you do that, we make the other. When the qroup grew to about 100 people it had to be divided as they couldn't maintain close relationships. At the beginning of rural society people exchanged products that did't want with products or services they needed; the problem soon emerged, what value each service and product had? how fair exchange would be if the price was subjective and constantly negotiable. It was necessary to find a unit of measurement that represents the value of things, a replacement, so money was created, in fact many different types of money.
The first kind of money was a barley of wheat, appeared before -3000 in Sumeria; it was standard barns filled with barley. People could now have a unit of measurement, that many barleys cost an outfit, so much a goat, so much the repair of the wall. People have been able to turn one thing into something else of their value and to store their measurable wealth. It was difficult, however, to carry this wealth; how a wealthy merchant to move to another city if all of its bio were in thousands of barrels of potatoes? The need pushed them to replace the barley silt with a more concentrated unit, the silver shekel. The shekel was not a coin, it was 8.33 grams of silver, if someone paid 10 shekels to buy something meant he had to weigh and give 83.3 grams of silver. Great progress, but again there were difficulties, they had to weigh each piece of silver and determine the exact weight.
They spent almost two millennia, and after using dozens of different kinds of money until the man is led into the currency revolution. The first were made in -640, in Lydia of Asia Minor; they contained a certain weight of silver or gold and had a printed identification mark. The sign certified the quantity of precious metal and declared the authority that issued it which guaranteed its contents. Counterfeiting currency was one of the biggest crimes because it was a subversive act against power.
In addition to barley and coins, many other types of money have existed at different times and different places, such as shells (a certaain kind of shell was used in Asia and Africa for nearly 4000 years), gemstone pieces, skins, animals, salt, beads, fabrics , cigarettes (in prisons). Anything useful to man could be used as money. Money bridges any cultural gap and makes no distinction, either in tribes or in religions or in ages. Thanks to money, people from different parts of the world can work together even if they do not trust each other.
When money has no inherent value, such as animals, barley, salt, cloth, then its value has to do with trust in the authority that supports it. Today's money is more of an intangible loyalty to governments and banks, as 90% of the money being traded exists only on computers.