It seems that from the time of the Ancient Greeks onward, educated people knew that the earth was a sphere. There is genetic evidence that Polynesian chickens (from the Eastern Hemisphere) were living in South America before Columbus' famous voyage. And Leif Ericson was a Viking or Norse explorer who traveled from Norway to Greenland and the east coast of Canada, maybe even to New England. So Columbus was apparently not even the first European to find North America. In fact, his route, from Spain to the Caribbean, was really the long way. It's much shorter to hop between the continents at the poles.

None-the-less, Columbus' multiple voyages across the Atlantic led to an era of European exploration and colonization. His voyages set off what historian Alfred W. Crosby, in 1972, termed "the Columbian Exchange." Although it truly started before Columbus and his ships (the Niña, the Pinta, and the Santa Maria), the process by which organisms (genes, germs, weeds, crops, animals, bugs, people) from one hemisphere are exchanged with another continues still.

(New World)
Corn (Maize)
Bred by Aztecs
White potatoes
Bred by Incas
Beans (kidney, Lima)
Squash and pumpkins
Sweet potato
(came from Brazil, raised in European greenhouses, wound up in Hawaii.)
Peppers, chili, Bell
Tomatoes, incl. cherry
(source of chocolate)
Chicle(source of chewing gum)

(Old World)

Peas, String beans
Sugar cane
Cantaloupe, watermelon
Citrus (oranges, lemons, etc.)

A closer look at where familiar foods and items originated reveals some interesting details. For instance, sweet potatoes are often on the list of crops introduced to Europe from the Americas. But Polynesians were raising sweet potatoes from South America, Teosinte, hybrid and zea mays showncarbon-dated to well before 1492. Aztecs were, contrary to popular belief, actually breeding corn. It has proven by DNA analysis that the progenitor of corn (or maize) was a grassy plant called Teosinte, which still exists in Mexico.

some common Old World introductions
Accidental and not-so-much: earthworms, dandelions (food for the deliberately introduced honey bees), crabgrass (a weed in all of North and South America and elsewhere), smallpox (both accidental and deliberate), measles, mumps, diptheria, Plague, influenza, common cold, leprosy, scarlet fever, whooping cough and cholera and more! Interestingly, the Eastern Hemisphere did NOT have syphilis before 1492.

(click here) for one theory
Latest research indicates that the population of the Western Hemisphere at its height might have even surpassed that of the Europe. What Columbus or the Pilgrims met might have been the decimated remains of a once-huge empire. This theory has the Amazon being a managed collection of fruit trees, and the Great Plains being subject to periodic deliberate burns so as to create grasslands for the buffalo to graze upon. Rather than living lightly on the land, the pre-Columbian American may have been a skilled land manager, adapting and landscapes crops for his use.

As it says on Wikipedia, "Before the Columbian Exchange, there were no oranges in Florida, no bananas in Ecuador, no paprika in Hungary, no tomatoes in Italy, no potatoes in Germany, no coffee in Colombia, no pineapples in Hawaii, no rubber trees in Africa, no cattle in Texas, no donkeys in Mexico, no chili peppers in Thailand or India, and no chocolate in Switzerland." Thinking about Mexican food without rice or cheese or the Irish without potatoes is the obvious example, but clearly the modern world economy depends on crops like wheat (Old World), corn (New World) soybeans (Old World) and rice (Old World).

But why? Why were the Western Hemisphere and the Eastern Hemisphere so different? Why weren't the Amerindians better able to defend themselves against the Europeans, whom they clearly outnumbered? They weren't dumber or more naïve. What was the essential difference between the two populations? Current thinking says that Europeans were used to a diet heavy in meat, dairy and wheat, and consequently were used to living in close quarters with animals and sharing their diseases. (For instance, smallpox lives in cattle as cowpox, which jumps back to humans as the more lethal smallpox. Bubonic plague was carried by rats and humans; malaria by mosquitos; brucellosis (undulant fever) in cows, goats and buffalo and then becomes tuberculosis in humans.) Inhabitants of the Americas relied more heavily on a plant-based diet than Europeans did, and were not accustomed to living in such close quarters with animals. Contagious diseases jumped back and forth from human to animal, or from animal to human. Europeans were also already familiar with quarantine procedures, whereas Amerindians gathered around sick tribe members in community. Was it simply that many Europeans were already recovered from smallpox, and no Amerindians had yet been exposed to it?

Imagine "America's breadbasket" (the "amber waves of grain") without wheat, or Wisconsin without cheese. The Old World dandelions are a scourge on the Old World Kentucky Bluegrass lawns of the New World, but the flavors of Northern European cheese and sour cream, Asian rice, Aztec beans, tomatoes and chilis go together well as our beloved Mexican food. Old World sugar (from Arabia) and Northern European milk combined with New World cacao and vanilla make chocolate!

Christopher Columbus did make the existence of the American continents widely known to a lot of Europeans. Even though we've named a lot of things after him (Washington, District of Columbia; Columbus, Ohio; British Columbia; Colombia, South America; ad infinitum), by the time of his death, it seemed more appropriate to name the continents after Amerigo Vespucci, another Italian explorer. (Columbus insisted, until his death, that he had landed on the far-eastern edge of Asia.) Whether or not you believe Christopher Columbus "discovered" the Americas, you have to agree that after Europeans were traveling to the Western Hemisphere regularly with their diseases and weeds, and bringing seeds and samples back to Europe, things changed. The exchange of organisms and ideas began in the early parts of the modern age, around 1000 AD, with Polynesians traveling to South America and back and Vikings traveling to Canada or New England and back.

The continents are believed to have begun as one big land mass (Pangaea) about 300 million years ago. Many plants (and animals) evolved extremely similarly although separated by oceans; consider the yam from Africa and the South American sweet potato, for instance, which many grocery stores cannot tell apart. Cotton evolved simultaneously in Arizona and in India. Although events following Columbus' stumbling into the Caribbean have been civilization-shattering, we cannot imagine our modern world a different way.

For further reading, see 1491.

The portrait of Christopher Columbus is by Alejo Fernández (1475-1535). Picture of teosinte, maize and the cross between them is available via Creative Commons and provided by John Doebley.