Secrets From a Prehistoric Mummy's Gut Bacteria

The Iceman cometh, and he’s raising some questions about ancient migration patterns.

STR New / Reuters

Here are some of the things scientists know so far about Otzi, the frozen Copper Age mummy who was discovered in 1991 in the Otzal Alps: He suffered from parasitic worms, Lyme disease, tooth decay, joint problems, and other ailments. He died in his mid-40s, likely sometime between 3239 and 3105 BCE and likely from a blow to the head. He has at least 19 living relatives somewhere in Austria. His nickname, the Iceman, is a perfectly badass moniker for someone who wore leather leggings and had 60-plus tattoos.

Otzi, who now resides at the South Tyrol Museum of Archaeology in Bolzano, Italy, was well-preserved enough that the people studying him have even been able to determine his last few meals: grains, goat, and deer (including a few animal hairs—Otzi may not have been the best cook, or the cleanest). Food isn’t the only thing of interest in his stomach, though: In a paper published today in the journal Science, researchers from across Europe and the U.S. reported that a microbe taken from his gut reveals new information about human migration patterns during and after Otzi’s lifetime.

The bacterium, Helicobacter pylori, is found in roughly half of all people alive today. It’s been infecting humans for an estimated 100,000 years, causing ulcers and other gastrointestinal issues in 10 percent of them. The bug is a pain for a lot of people, but a handy tool for scientists, who use its evolution to map the paths of ancient populations as they moved across the globe. Modern strains of H. pylori can be classified into seven different groups based on where in the world they originated: one in Australia, one in Europe, two in Asia, and three in Africa.

The modern European strain is thought to be a hybrid of two older Asian and African strains. But when the authors of the Science paper reconstructed the genome of Otzi’s microbe, they found it to be nearly identical to the Asian variety—meaning it shared less ancestry with the African strain than the bug carried by modern Europeans.

With a sample size of just one, it’s hard to draw any firm conclusions about what this means, but the authors offer one possibility: that a mass migration from Africa to Europe took place sometime in the millennia between Otzi’s death and the present day.

“Until now, it was believed that this mixed strain was already present during the Neolithic [period], so the [first] farmers brought this mixed strain to Europe. And now we saw in the Iceman that it was not like this,” Frank Maixner, the lead author and a researcher at the Institute for Mummies and the Iceman at Italy’s European Research Academy, said in a video accompanying the paper. “He carried a more pure strain, an unmixed strain, and we can say that the history of Helicobacter population genetics in Europe is different than previously thought.”

Richard Green, a professor of evolutionary genetics at the University of California, Santa Cruz, who was unaffiliated with the paper, said that a previously unknown wave of African migration is a feasible explanation, even if it’s far from a certain one. “It's definitely suggestive of that,” he said. “Something needs to account for the large turnover in the prevalent haplotypes of H. pylori.”

The findings may also offer clues as to how the bacteria evolves over time: “We don't really have a great evolutionary model for how these strains are evolving and how they come to be recombinated, what kinds of interactions must occur to make different strains,” Green said. “It's likely that we will learn more about that as time goes on, and this is a great data point to have."

Scientists can only plumb so much from Otzi’s shriveled body, though, and a greater understanding of who moved where in prehistoric times will likely require more Icemen, with their own gut bacteria and other clues. “We don't know if Otzi was representative of all the folks in Europe at that time, or if he was a lone member of an isolated band of people that was genetically distinct," Green said. “It'd be great if we had a hundred Otzis all over Europe, but all we have is the one.”

But these hypothetical yet-to-be-discovered Icemen may be in short supply, as the field of archaeology begins feeling the effects of climate change more acutely. As Adrienne LaFrance reported for The Atlantic in July, the high level of carbon dioxide in the atmosphere is quickly making carbon dating inaccurate; meanwhile, melting glaciers are yielding bodies they’ve contained for millennia, leaving ancient specimens to decay before they can be found.

“It’s a race against time,” Albert Hafner, an archaeologist at the University of Bern in Switzerland, told Scientific American in July. Otzi’s stomach contains a piece of human history, but it remains to be seen how many more of them can be fit together before they disappear.