There was a time when people happily used chickens, pigs, or a nice pile of lumber as payment for a cow, some clothes, or anything else of value. And then some smart people got behind a breakthrough—they introduced currency.

Swatches of buckskin, stamped pieces of gold, and later, paper notes—these were a mighty intellectual and technological leap ahead from that clucking bird. It may not seem like it in today's world, where cash has a whiff of the downright prehistoric, but paper currency was mind-blowing in its heyday—the first U.S. government-issued currency debuted during the Civil War—because of its advanced features: It was lightweight, portable, reliable (hyper-inflationary events notwithstanding), efficient, and powerful. These are descriptors we might apply to the latest smartphone today.