Passage Summary: The author argues that because modern people start bartering when they run out of cash, bartering must have been the original way humans traded before money was ever invented.

Conclusion: The earliest human economies were based on bartering, with currency appearing only later in history.

Reasoning: In modern times, when isolated economies lose their currency, they revert to bartering before returning to money once it becomes available again.

Analysis: The argument assumes that because a system 'reverts' to a certain state today, that state must have been its original historical starting point. This is a bit like saying that because a modern smartphone becomes a paperweight when the battery dies, the very first communication devices must have been paperweights. It ignores the possibility that bartering in a post-currency world is a fallback behavior rather than a mirror of prehistoric origins. We should look for an answer that identifies this flawed assumption about historical progression.