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 — that unfolded after Christopher Columbus linked the New World and the Old. But some scholars take a more granular view — looking 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.

It was a grand shuffling of organisms with results both great and disastrous: Malaria-fighting quinine from the South American cinchona tree aided European colonization in the tropics; the ballast dumped in Virginia by ships picking up tobacco introduced earthworms to the mid-Atlantic. Diseases common in the Old World devastated the indigenous populations in the New.

“What happened after Columbus,” journalist Charles Mann wrote in his book “1493,” “was nothing less than the forming of a single new world from the collision of two old worlds — three, if one counts Africa as separate from Eurasia.”

The potato alone gets credit for population booms in parts of northern Europe that paved the way for urbanization and, in turn, fueled the Industrial Revolution. Some American foods became staples abroad, from the tomato in Italy and the cassava in Africa to the peppers that became the paprika of Hungary and the curries of India. “There really was no spicy food in the world before the Columbian Exchange,” said Nancy Qian, an economics professor at Northwestern University.

By far the most consequential transfer of organisms, Qian said, was the introduction of unknown pathogens into the Americas. In the first century-and-a-half after Columbus, smallpox, measles, whooping cough, typhus and other infectious diseases killed up to 80 percent of native people, said demographer Noble David Cook. And when Europeans introduced sugar, cotton and other plantations to the Americas, they enslaved more than 12 million Africans.

On the other side of the Atlantic, Qian said, “It’s hard to imagine a food having a greater impact than the potato.” In many northern European climes, crops were largely limited to turnips, wheat, buckwheat and barely. Even so, when potatoes began arriving from America, it took awhile for locals to realize that the strange lumps were, comparatively speaking, nutritional grenades.

Eventually, starting with monks on Spain’s Canary Islands in the 1600s, Europeans figured out how to cultivate potatoes, which form a nutritionally complete — albeit monotonous — diet when combined with milk to provide vitamins A and D. The effects boosted populations in Ireland, Scandinavia, Ukraine and other cold-weather regions by up to 30 percent, Qian’s research said. The need to hunt declined — and, as more land became productive, so did conflicts over land.

Frederick the Great ordered Prussian farmers to grow them, and the potato moved to the center of European cultures from Gibraltar to Kiev. “Let the sky rain potatoes,” Shakespeare wrote. Their portability made them ideal to transport into the growing cities, feeding the swelling population that would be needed for a factory labor force.

Cassava, which remains the foundation of many African diets, had a similar nutritional impact as it spread from the Americas. Sweet potatoes, too, proved hardy in flood-prone fields.

Some of the most notable additions to global cuisine are nutritionally neutral: chocolate (made from cacao beans); vanilla (which was first processed to improve the flavor of chocolate); and the tomato, a native of the Andes that had been transported to Mexico. There, Mann said, “native plant breeders radically transformed the fruits, making them bigger, redder, and, most important, more edible.” The result would transform the cuisine of Italy and bestow upon the world pizza, ketchup and the Bloody Mary. “We don’t need them to survive,” Qian said. “But I don’t want to imagine a world without tomatoes and chocolate.”