When barter has appeared, it wasn’t as part of a purely barter economy, and money didn’t emerge from it—rather, it emerged from money. After Rome fell, for instance, Europeans used barter as a substitute for the Roman currency people had gotten used to. “In most of the cases we know about, [barter] takes place between people who are familiar with the use of money, but for one reason or another, don’t have a lot of it around,” explains David Graeber, an anthropology professor at the London School of Economics.

The man who arguably founded modern economic theory, the 18th-century Scottish philosopher Adam Smith, popularized the idea that barter was a precursor to money. In The Wealth of Nations, he describes an imaginary scenario in which a baker living before the invention of money wanted a butcher’s meat but had nothing the butcher wanted.“No exchange can, in this case, be made between them,” Smith wrote.
It was the fifth lasagna that did it. Three months into the project, Simmons had signed up over 80 Barter Babes, and every time she bartered her financial services, she seemed to get a lasagna in return. She was trying to shove yet another five-pound pasta dish into her freezer when the tears started to flow. “I don’t need another lasagna!” she yelled at her boyfriend. “I need a haircut! I need a bicycle!” She was overwhelmed with doubts about her bartering experiment: I’m so ridiculous. What the hell was I thinking? This whole thing is never going to work. Trades weren’t happening at the frequency she had anticipated, and Simmons was feeling depressed. She couldn’t afford a dye job at a salon, and she had started gaining weight. She’d gone from ballin’ to having $200 in her joint account.