![[the-columbian-exchange.jpg]] Historians call the transfer of plants and animals that began with the encounter between Europe and the Americas after 1492 the Columbian Exchange. It's hard to overemphasize how much these biological transfers and their effects on the environments and people of Europe and the Americas shaped the modern world we live in. American maize, potatoes, and cassava fed growing European, African, and Asian populations, allowing the building of new cities and industries. European animals such as pigs, sheep, chickens, and cattle thrived in the Americas, enabling both Native Americans and Europeans there to add and maintain animal protein to their diets and eventually expand their populations. But before most indigenous peoples had a chance to benefit from the new food sources introduced by Europeans, they were struck down by the largely accidental transfer of viruses and bacteria from Europe to America, which caused the deaths of at least 90% of the native American population. When prehistoric Eurasians began living in close contact with the species they domesticated, the people were affected almost as much as the animals they kept. Most of humanity’s major diseases originated in animals and crossed from domesticated species to their human keepers. Whooping cough and influenza came from pigs; measles and smallpox from cattle; malaria and avian flu from chickens. The people who domesticated these species and lived with the animals for generations co-evolved with them. Animal diseases became survivable when people developed antibodies and immunity. Without the inherited protection enjoyed by most Eurasians and Africans, even a routine childhood disease such as chickenpox would be deadly. ![[Aztec_smallpox_victims.jpg]] The introduction of a disease into an area without inherited immunity is called a [virgin soil epidemic](https://en.wikipedia.org/wiki/Virgin_soil_epidemic). Such epidemics had happened in Eurasia, when the Romans spread [smallpox](https://en.wikipedia.org/wiki/History_of_smallpox) into the populations they conquered, and in Europe when the expanding Mongols introduced [bubonic plague](https://en.wikipedia.org/wiki/Bubonic_plague), the Black Death that killed probably half the population of Europe in the fourteenth century, reducing world population by about a hundred million. Virgin soil epidemics spread across the Americas when explorers and colonists introduced Eurasian diseases to the Native Americans. The Eurasian diseases that attacked native populations included smallpox, measles, chickenpox, influenza, typhus, cholera, typhoid, diphtheria, bubonic plague, scarlet fever, whooping cough, and malaria. ----- Next: [[4.15 - American Depopulation]] Back: [[4.13 - Dividing the World]]