There is likely no public secular holiday more controversial than Columbus Day. Since the observance first began to be celebrated in the nineteenth century it has been opposed by a diverse rage of groups, from the Ku Klux Klan to the American Indian Movement to the National Council of Churches.

The Italian navigator tends to provoke strong reactions throughout the Western Hemisphere, and every year we renew our debates about whether he was a bold and brave explorer or a cruel and genocidal colonist (or, as in my view, a mix of both).

While we may downplay the individual achievements of Columbus, weshould acknowledge he launched one of most significant events in the history of the world: the Columbian Exchange.

The term “Columbian exchange” was coined in 1972 when historian Alfred W. Crosby published his book, The Columbian Exchange. The exchange refers to the ecological ramifications Columbus’s landing in 1492 had on both the Old World and the New.

We may mock the use of labels like “Old World” and “New World” but the two hemispheres were indeed almost two separate and environmentally distinct worlds. As Crosby says in his book,

The two worlds, which God had cast asunder, were reunited, and the two worlds, which were so very different, began on that day to e alike. That trend toward biological homogeneity is one of the most important aspects of the history of life on the planet since the retreat of the continental glaciers. (p. 3)

Because we live on this side of the divide, it’s difficult for modern people to imagine the world (or worlds) that existed before the Columbian exchange. But the widespread transfer of animals, culture, ideas, plants, populations, and technology between the areas has forever changed the planet.

Consider, for example, just two of the hundreds of plants that were involved in the exchange: potatoes and maize.

The potato didn’t arrive in Europe until 1570. But wherever the potato was introduced—particularly in Europe, the US and the British Empire—the population grew rapidly. As Jeff Chapman notes, before the widespread adoption of the potato, France managed to produce just enough grain to feed itself each year. The adoption of the potato made it possible for countries in Europe to increase their food security. The Irish population, for instance, doubled to eight million between 1780 and 1841, by which time almost one-half of the Ireland had e entirely dependent upon the crop.

Maize also had a similar impact on Europe, Africa, and Asia, leading to rapid population growth.“If suddenly American Indian crops would not grow in all of the world, it would be an ecological tragedy,” says Crosby. “It would be the slaughter of a very large portion of the human race.”

While the New World was giving the eastern hemisphere plants that would increase their populations, the Old World was sending over infectious diseases that would devastate entire people. Some of the diseases that were introduced included bubonic plague, chickenpox, cholera, diphtheria, influenza, leprosy, malaria, measles, scarlet fever, smallpox, typhoid fever, typhus, and yellow fever.

The profound effects of the Columbian exchange, both positive and negative, are nearly incalculable, and plicate our reaction to Columbus’s influence. For example, we can and should both lament the extraordinary loss of life that resulted from the exchange and be grateful for the lives that it created (including, most likely, both yours and mine).

But whether we love him or hate him, we should be aware that Columbus set in motion a series of interchanges that will affect us more than we’ll ever know.