Kohler isn’t sure why this happened, but he has some ideas. “Think about it,” he says. “You know that animals like cows, oxen, horses, sheep, goats, pigs, all are Old World domesticates.” Through an accident of geography and evolution, they simply didn’t exist in the Americas before Columbus arrived.

So it was only in the Old World that ancient farmers could use oxen to plow more fields, expand production, and get richer, compared to poorer farmers who could not afford those animals.

They were accumulating wealth, what economists call capital — a term that Kohler says is no accident. “Our word ‘capital’ comes from the same proto- Indo-European root as our word for ‘cattle’ does,” he says.