Did cavemen have money, Tom? Or did they just go and get their food/water/air?
Yes, very early humans had money. The exchange of debt is a natural part animal nature. Monkeys, wolves, cats, and all other higher order creatures exchange debt. For example, apes will often use favors as debts - I scratch your back, you scratch mine. They exchanged favors through grooming, sharing of food, sex, protection, etc. If one ape is doing lots of favors for you, it's expected that you return the favors lest they stop. An ape will remember that Ape1 has done lots of favors for him, that Ape2 has done a few favors for him, and Ape3 has done no favors for him at all.
As primates evolved into man this form of thought currency simply transitioned into a physical representation of debt owed for better accuracy. We know that Ancient Native Americans used sticks with marks in them to keep track of debts. If you were exchanging favors with someone, you would each keep sticks with both your names on it and make identical ticks in the wood when favors were exchanged to help keep track of who owed what. This form of debt currency was later represented by feathers, sea shells, shiny stones, and finally coins and paper money -- all representing debts owed.
Animals exchanged money long before man came along. But since they didn't have tools to create physical representations of debt, they had to keep track of their debts in their own heads, enforced by implicit social contract.