It was a small round object sent around the planet, and it changed the course of human history. Call it "Spudnik." It was a potato. On Columbus Day, the U.S. commemorates the grand global changes - discoveries and destruction alike - that unfolded after Christopher Columbus linked the New World and the Old. But some scholars take a more granular view of what Columbus wrought. They look at the very seeds, seedlings and tubers that began crisscrossing the oceans in what they call the "Columbian Exchange."

The potatoes, tomatoes, corn, peppers, cassava and other plants native to the Americas did more than enliven the cook pots of Europe, Africa and Asia. They transformed cultures, reshuffled politics and spawned new economic systems that then, in a globalizing feedback loop, took root back in the New World as well.