By Crosby, Alfred W.

For tens of millions of years the dominant pattern of biological evolution on this planet has been one of geographical divergence dictated by the simple fact of the separateness of the continents. However, in the last few thousand years there has been a countervailing force. Homo sapiens have gone everywhere, taking with us, intentionally, our crops and domesticated animals and, unintentionally, our weeds, varmints, disease organisms, and such free-loaders as house sparrows, reversing the ancient trend of geographical biodiversification. Many of the most influential examples of this are in the category of the exchange of organisms between the Eastern and Western Hemispheres. This began when the Amerindians (or proto-Amerindians) first entered the New World a few millennia ago, bringing with them a number of other Old World species and subspecies, and was followed by later humans in the Americas, such as the Vikings around 1,000 CE, and possibly Japanese fishermen. But the tsunami of biological exchange did not begin until 1492, when the Europeans initiated contacts across the Atlantic (and, soon after, across the Pacific) which have never ceased.

Subjects

History / Environment and Nature / Indigenous Peoples of the Americas / Migration / Agriculture / Animals / Diseases / Colonialism /