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Health

Our symbionts are death!

Gene ExpressionBy Razib KhanJanuary 2, 2012 11:55 AM

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Several readers have expressed skepticism of the high mortality numbers Charles C. Mann reports in his twobooks in relation to the Columbian Exchange. In case you are not aware, the thesis that Mann outlines is that the primary necessary condition whereby Europeans managed to eliminate indigenous populations from much of the New World was that they brought with them diseases which the native people did not have an immunity to. This model often argues that mortality rates were on the order of 90 percent. Such a scenario has broad plausibility because the situation in the New World has an inverse counterpoint: Africa. Before quinine the European dominion on the continent was limited to outposts and fringes (e.g., the Cape region of South Africa, which was free of many of the diseases deadly to Europeans). Overall I find Mann's argument qualitatively reasonable, even if one may qualify it on the margins quantitatively. But I stumbled upon more evidence recently: it still holds for those Amerindians which have not been exposed to Eurasian diseases. From a National Geographic story, Into the Amazon:

But violent clashes account for only a fraction of the deaths suffered by native communities at the hands of outsiders. Most died from epidemic diseases, including the common cold, for which they had no biological defenses. Ivan Arapa, one of our scouts, is from the Matis tribe, who were first contacted by the outside world about 25 years ago. Ivan still remembers the wholesale death that accompanied these very first visits of Brazilian government officials to his village. "Everyone was coughing, everyone was dying," he recalls. "Many, many Matis died. We didn't know why." More than half of the 350 Matis living along the Ituí River inside the Javari reserve perished in the months following contact, officials say. It's a dismal story that's become all too familiar to Possuelo during his 40-year career as a sertanista, a uniquely Brazilian profession that folds all the skills and passions of a frontiersman, ethnographer, adventurer, and Indian rights activist into a single, eclectic vocation. That's why our mission is not to make contact with the Flecheiros but rather to gather information on the extent of their territory's boundaries, information Possuelo will use to bolster his efforts to protect their lands. In other respects, the Flecheiros are to remain, in large measure, a mystery.

Over thousands of years Eurasians, and to a large extent most inhabitants of the "World Island" (Eurasia + Africa), have become habituated to a range of endemic ailments which may make us miserable, but do not kill us. Our bodies are hosts to an order of magnitude more bacteria than our own tissue cells. Most are innocuous or beneficial, but some are potentially deadly. Many of us carry pathogens which do not result in any illness over our lifetimes. There are geneticists who argue that a small minority of people exhibit genetic susceptibilities to pathogens which are normally benign. What if these people are the ancestral type? I think about this in particular when considering the case of the Sentinel Islanders. This tribe has been left alone by the Indian government, and remains out of contact with the rest of humanity. Some of this is a function that other Andaman Island tribes which have had extensive contact with people from the mainland have not done so well due to the combined effects of Indian disease and diet. But is it right and proper that modern humans be isolated from the rest of the population for their own good? What does the reality of a whole people who are viewed as "Bubble Boys" tell us about the range of the human condition?

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