Monday, July 23, 2007

Knitting together the seams of Pangaea

Just over five hundred years ago, before the European colonization of the Americas, tomatoes, potatoes and chilies, the widely used vegetables of today (the first two at least), were unknown to Africa, Europe and Asia. It seems unimaginable now, but before the 15th century, the cuisines of Thailand and the Indian subcontinent were actually bereft of chilies! Similarly, the Americas did not have wheat or rice, just as the rest of the world had no knowledge of maize (corn).

Charles Mann in his book 1491: New Revelations of the Americas before Columbus provides an intriguing take on the topic:
“Until about 200 million years ago Eurasia and the Americas” [as indeed the rest of the world] “were lashed together in a single landmass that geologists call Pangaea. Pangaea broke into pieces, sending the continents drifting like barges across the ocean floor. For millions of years, the separate fragments of Pangaea had almost no communication. Evolution set their species spinning of on separate trajectories, and the flora and fauna of each land diverged…”
But with Columbus’s discovery of the Americas, the pieces of Pangaea that had drifted apart for countless millennia were now brought together: not literally but through a massive exchange of people, plants, crops and animals from the different continents. The historian and professor Alfred Crosby who first proposed the idea in his books (Mann borrows heavily from Crosby’s writings) refers to this exchange as the Columbian Exchange: a “knitting together of the seams of Pangaea”.

In this colorful description below, Mann summarizes how agriculture was radically transformed in many parts of the world :
“Ever since 1492 the hemispheres have become more and more alike, as people mix the world’s organisms into a global stew. Thus bananas and coffee, two African crops, become the principal agricultural exports of Central America; maize and manioc, domesticated in Mesoamerica [today Mexico and Central America] and Amazonia respectively, return the favor by becoming the staples in tropical Africa. Meanwhile, plantations of rubber trees, an Amazonian native, undulate across Malaysian hillsides; peppers and tomatoes from Mesoamerica form the culinary backbones of Thailand and Italy; Andean potatoes lead Ireland to feast and famine; and apples, native to the Middle East, appear in markets from Manaus to Manila to Manhattan.”
But there were some very unpleasant and tragic consequences as well. Smallpox, typhus, influenza, diphtheria, measles, all diseases from Europe swept through the American continent. Native Americans, who had no immunity to these diseases, died in inordinately large numbers. Nearly a fifth of humanity perished.

Even more startling is Crosby’s assessment of the impact of all this on Africa. When the Native American crops of maize, manioc and peanuts reached Africa after the 15th century, they transformed African agriculture and led to a population boom. As Native Americans vanished in large numbers, the colonizing Europeans faced a labor shortage. They now looked towards Africa for slaves. In Crosby’s view, “the maize-fed population boom [in Africa]” allowed “the awful [slave] trade [to] continue without pumping the well dry.”

These interpretations show just how oddly interconnected and cruel the twists of history can be.
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Finally, here’s Crosby again stating in these superbly composed paragraphs (link to complete essay here) how the migration of people in the last few thousand years has altered the dominant pattern of biological evolution:
“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. Even where climates have been similar, as in the Amazon and Congo basins, organisms have tended to get more different rather than more alike because they had little or no contact with each other. The Amazon has jaguars, the Congo leopards.

However, very, very recently—that is to say, in the last few thousand years—there has been a countervailing force, us, or, if you want to be scientific about it, Homo sapiens. We are world-travelers, trekkers of deserts and crossers of oceans. We have gone to and lived or at least spent some time everywhere, taking with us, intentionally, our crops and domesticated animals and, unintentionally, our weeds, varmints, disease organisms, and such free-loaders as house sparrows. Humans have in the very last tick of time reversed the ancient trend of geographical biodiversification.”

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