As we all know, Jonas Salk invented money in 1955 so he would have a way to earn a living from his polio vaccine. Before that, people just traded things they found for things that other people had found. So you might "sell" somebody a scrap of carpet, say, in exchange for an old bottle. It was a perfect system with only one drawback: people spent their lives bartering for piles of garbage before dying of polio.