A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Why did so many Native Americans die of European diseases but not vice versa?

July 29, 1994

Dear Cecil:

Why is it that native Americans died from Europeans brought by the Europeans but Europeans didn't die in great numbers from native American diseases?

Cecil replies:

There may have been at least one native American bug that wiped out a few boatloads of Europeans; see below. But in general you're right: percentagewise, and probably absolute numberswise, a lot more native Americans died of European diseases than did Europeans of American diseases. The natives had no resistance to smallpox, influenza, or plague or even to mild (to us) diseases like measles. Entire populations were virtually wiped out, with some Atlantic coast tribes losing 90 percent of their adult members. Some historians go so far as to say European diseases reduced the pre-contact population of the New World as a whole by 90 percent or more. One says the population of central Mexico was reduced from 25 million in 1519 to 3 million by 1568 and only 750,000 by the early 1600s, 3 percent of the pre-conquest total.

Granted, some of these horrifying numbers may be arrived at by exaggerating the size of the original population. One researcher says there were 18 million people living north of Mexico before Columbus, but a more conservative estimate puts it at four million and some say only 1 million. Maybe there were only 12.5 million precolumbian Mexicans, not 25 million. Even so we're talking 94 percent mortality for central Mexico, maybe 87 percent for the Americas overall, reducing the population from 80 million in 1500 to 10 million 50 years later. One can make a good case that it was European germs rather than European military prowess that conquered the New World. One can also argue that disease led to the African slave trade. The conquistadors would have been happy to enslave local labor except that it was dead.

Why were the natives so vulnerable? The best guess is that Europe had been a crossroads for war and commerce for millennia and so had encountered an extraordinary number of pestilences, while the Americas were isolated and had not. Europeans had also spent a long time around domestic animals, which were the source of many of the most virulent diseases to afflict humans in the Old World. In contrast, native Americans had few domestic animals. As a consequence Europeans had developed some resistance to disease but native Americans hadn't.

That's not to say Europeans were immune. While millions of native Americans died of European diseases, millions of Europeans died of European diseases, too. In fact, one reason the natives suffered such catastrophic mortality was that Europeans arriving in the New World were walking petri dishes for germs. In some years 25 percent of European immigrants died at sea, often of diseases such as typhus that they had picked up in the ports they had just left. Epidemics were common in Europe. It was not uncommon for a town to lose a third of its population to some new outbreak. Armies invariably lost more soldiers to disease than to combat. (Judging from U.S. figures, this remained true up until World War II.)

By comparison to Europeans, historian Thomas Berger says, native Americans were remarkably healthy. Most lived not in unsanitary cities but "in small, isolated bands and were therefore less likely to spread diseases over large geographical areas." Berger even claims the few germs they carried with them during the original migration across the Bering land bridge didn't survive the Arctic "cold screen" — a little hard to believe, since the humans made it through OK.

However edenic the New World may have been, it may have harbored one bug that did kill a lot of Europeans: syphilis. The question remains controversial. The first known cases of syphilis showed up in Italy in 1494, and we know what happened in 1492. Many believe the Spanish contracted syphilis in Hispaniola (Haiti and the Dominican Republic) and gave it to the Italians and French at the siege of Naples. Bone damage characteristic of syphilis found at preColumbian New World archaeological sites supports this view. But others say syphilis was merely an old European disease that prior to 1500 had been improperly diagnosed. Even if it did originate in the Americas, syphilis was little enough payback for the disaster visited on the original inhabitants of the Americas by the subsequent ones.

Why they died

Dear Cecil:

Upon reading your column on the demise of the Native Americans following European contact, I immediately recognized myself as an expert and am forwarding the enclosed articles, making your story far more complex. My question for you is from an old Firesign Theatre album: "Why does the porridge bird lay its eggs in the air?"

Cecil replies:

Who knows? Maybe she's waiting for the electrician or someone like him. Your enclosures raise an interesting point but one that, far from complicating matters, is in line with the view I presented and had I not taken that second coffee break would surely have thought of myself. The point is this: recent research suggests that Native Americans lacked "genetic diversity" — bluntly put, that they were inbred, virtually the entire indigenous population of the Americas having descended from just four (4) women — or at least four groups of closely related women.

We also know that a virus you contract from a family member is far more likely to be fatal than one you get from a total stranger. That's because the family-bred virus has already figured out your clan's genetic code and thus can evade your natural defenses. Since Native Americans were all close cousins (at least compared to Europeans), a virus that killed one would pretty much kill them all.

In short, American Indians were more vulnerable not simply because they had been exposed to fewer diseases, as I argued, but also because they had been exposed to fewer humans. They were exposed to plenty of both once European settlers arrived.

On a somewhat different subject …

Dear Cecil:

I've enjoyed your column for many years and was delighted to see a Firesign Theatre reference. For your information, the famous Zen question or virus which breaks the computer in our record I Think We're All Bozos on This Bus actually comes from a lovely woman named Angel I dated back in the '60s. She's from Texas, and claims that when she was a little girl a leprechaun appeared in her backyard one day while she was playing, asked her that exact question, and then laughed and ran away! I've always interpreted the query as referring to the ecological challenge that faces the planet: to wit, the steady loss of trees in which many birds are wont to nest. But it's obviously open to many interpretations, as is much of our work.

Cecil replies:

Well, that clears that up. Now if we can figure out why there was hamburger all over the road in Mystic, Connecticut, we'll really start making some progress.

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