Women have used sex as currency for as long as we have had written history

Its not just a human thing. In 2005 an economist and psych taught capuchin monkeys about money, exchanging tokens for food.

It took several months of training for the capuchins to learn that they could exchange such a token for fruit.[...] Researchers observed that the monkeys could even budget. Researchers then changed the market and put Jell-O at a lower price, to see if monkeys would buy fewer grapes and more Jell-O. They acted exactly like the current laws of economics dictate for humans as well.

But then they decided to limit the number of tokens to create scarcity

One of the researchers, during the chaotic episode mentioned earlier, observed how one of the monkeys (a female) exchanged money with another (a male) for sex. After the act was over, the monkey which was paid immediately used it to buy a grape.

Link to study (on Sci-Hub because fuck JSTOR): https://sci-hub.ru/10.1086/503550