When Christopher Columbus landed in the Caribbean in October 1492, the two halves of the globe — Eurasia/Africa on one side, the Americas on the other — had been biologically separated for about thirteen thousand years. They had developed distinct flora, fauna, microbiota, and crops. Within fifty years of contact, the separation was over. The Columbian Exchange — the historian Alfred Crosby's 1972 term — names the biological reunification of the two hemispheres, and its consequences were more profound than the political and economic ones with which they are usually grouped.
The plant exchange alone reshaped global cuisine and demography. From the Americas to the Old World: potatoes, tomatoes, maize, cassava, sweet potatoes, peanuts, chilies, cacao, tobacco, rubber, vanilla, pumpkins, beans, sunflowers. The potato alone enabled European population to roughly double in the 18th and 19th centuries; maize transformed African farming; chilies became inseparable from Indian, Thai, and Sichuan cooking; tomatoes anchored Italian cuisine. From the Old World to the Americas: wheat, rice, sugarcane, coffee, bananas, citrus, livestock (cattle, pigs, horses, sheep, chickens), the honeybee. The animal exchange revolutionized American agriculture and warfare (the horse, in particular, transformed Plains Indian societies before nearly destroying them). The microbial exchange was catastrophic for the Americas: smallpox, measles, influenza, typhus, and yellow fever entered populations with no historical exposure, killing perhaps 90% of indigenous Americans across the next century — one of the largest demographic collapses in recorded history. The Old World imported syphilis (the case is contested but most historians now accept American origin) and little else of comparable consequence, partly because the Americas had relatively few domesticated animals to act as disease reservoirs.
Every modern cuisine contains Columbian Exchange artifacts. The Anthropocene biogeography — invasive species, monoculture commodity agriculture, pandemic-prone livestock-microbe interfaces — is, in a long view, a continuation of the same homogenizing process. Contemporary debates about biodiversity loss, agricultural concentration, and zoonotic disease risk (COVID-19, avian influenza) all sit on top of the post-1492 reorganization of global biology. The demographic and ecological reunification of the hemispheres was one of the largest events in the planet's biological history; we are still living inside it.