HEALTH × ENVIRONMENT

Two Worlds Collide

1492 CE

History · Middle Ages · Holocene · Meghalayan

After 1492, the hemispheres traded everything: maize, potatoes and cassava eastward, wheat, horses, cattle, and above all diseases westward. Old World epidemics killed on the order of ninety percent of Indigenous Americans within a century, tens of millions of people; so much farmland returned to forest that atmospheric carbon dioxide measurably dropped, a human catastrophe legible in Antarctic ice.

Why it matters

This is the sharpest demographic catastrophe in our species' record, and the origin of the modern world's food map: no Italian tomato, Indian chilli or Irish potato precedes it. The reunion of populations separated since the ice age was, epidemiologically, a one-way massacre, immunity written by ten thousand years of livestock. Its signature in the planet's atmosphere is a candidate marker for the Anthropocene's beginning.

Dating & uncertainty

The date is a calendar one; the consequences unrolled over centuries. The scale of the American die-off rests on contested pre-contact population estimates, around 60 million in a recent synthesis with wide error bars, and regional studies show losses arriving decades to a century after first contact rather than at once.

Sources

1. Koch et al. (2019), Quaternary Science Reviews · Earth system impacts of the European arrival and Great Dying in the Americas after 1492doi:10.1016/j.quascirev.2018.12.004
2. Nunn & Qian (2010), Journal of Economic Perspectives · The Columbian Exchange: a history of disease, food, and ideasdoi:10.1257/jep.24.2.163
3. Liebmann et al. (2016), PNAS · Native American depopulation, reforestation, and fire regimes in the Southwest United States, 1492-1900 CEdoi:10.1073/pnas.1521744113

Our species’ history as one day

23:57:332 min 26 s before midnight

if the 315,000 years of Homo sapiens were compressed into a single day