The “Columbian exchange” is a term popularized by Alfred Crosby in his 1973 book of the same name. Crosby formalized a concept that had been observed for several centuries, the two-way travel of plants, animals, and people between the Old World and the New World, primarily from the 1490s on, following Columbus’ arrival in the Caribbean. The exchange occurred because people in both hemispheres found new resources valuable.
In its simplest iteration, scholars understand that because of particular geographic, social, and cultural conditions, a wider variety of plants useful to human beings developed in the New World, while more useful animals had been domesticated in the Old World. Some species existed in both hemispheres, often distinct varieties but closely related, such as sugar and cotton, but particular selections adapted well to new conditions. People and animals also carried diseases and their sources; those unique to old area devastated people who had no resistance. Particularly lethal in this regard was smallpox, which was taken from the Old World. The origins of syphilis are still debated; it may have been a new disease generated from combinations of others existing in both areas.
The New World food crops that Europeans took to Europe included maize (often called corn), potatoes, tomatoes, and chocolate, as well as non-food crops, especially tobacco. Along with the legendary spices, dyestuff were valued, especially cochineal, grown on cactus, for red. While large domesticated animals were found throughout western South America, camelids were food and fiber sources and pack animals, but cannot support adult riders or be used as draft animals; tapirs and pigs were food sources only. No mammals suitable for surplus milk production were found.
The Old World animals that were especially significant were horses, suitable for riding and draft; cows and oxen, for draft, meat, and dairy; and sheep, for meat and wool. Silk fiber was transported primarily from Asia; efforts to grow mulberry and raise silk worms in the Americas were largely unsuccessful. Among the valuable plants taken to the Western Hemisphere were wheat and the related grains barley and rye; rice; and olives. Grapes well suited for wine were also important as the indigenous American varieties had very small fruit.