In the 25 years since two German tourists discovered the startlingly well-preserved corpse of a Copper-Age man in the eastern Italian Alps, scientists have learned an incredible amount about the life and death of Ötzi, or the “Iceman,” as he is known. They know how he died (he was shot by an arrow and bled to death), they know what he was wearing when he died (a loincloth, bearskin hat and goat-hide leggings) and they’ve even mapped the 61 tattoos he sported on his body. Now, analysis of a common stomach bacteria found inside the Iceman’s gut has shed new light not only on Ötzi himself but also on the patterns of human migration that occurred before and after him.

In a study published last week in the journal Science, researchers from the Institute for Mummies and the Iceman at the European Academy of Bozen/Bolzano (EURAC) in Italy reported their discovery and analysis of the Helicobacter pylori, or H. pylori, microbes found inside the stomach of the 5,300-year-old mummy known as Ötzi the Iceman. The scientists determined that the microbes found in Ötzi’s stomach were a virulent strain of H. pylori that may have caused him stomach upset or even ulcers. (Add this to the list of health woes scientists have determined the Iceman suffered—including gum disease, heart disease, gallbladder stones, lyme disease and parasites—and it’s clear he had his share of discomforts even before meeting his violent end.)

It is estimated that more than half the world’s population harbors various strains of H. pylori; in about 10 percent, the pathogen causes diseases such as gastritis, gastric ulcers or even stomach carcinoma. These gut microbes are so common among humans—and so ancient—that tracking their evolution into different strains can help scientists reconstruct human migration patterns as far back as 100,000 years ago.

Different strains of H. pylori are associated with different places in the world. For example, the microbes harbored by modern Europeans represent a mixture of Asian and African ancestral strains. But when the EURAC researchers analyzed the DNA of the 5,300-year-old H. pylori found in Ötzi’s gut, they found it to be a surprisingly pure strain that is similar to that found in modern Asian populations. This means that the waves of ancient human migration that brought the African strain to Europe had not occurred, at least not in earnest, before the Iceman’s time. Instead, the African strains of H. pylori had arrived only within the past few thousand years.

A 2003 study led by Daniel Falush of Swansea University had suggested that European H. pylori was a hybrid of African and Asian strains, but guessed that the migration that produced the mixture occurred during the Neolithic Age, some 9,000 years ago. But as reported in Smithsonian Magazine, study co-author Yoshan Moodley of the University of South Africa explained at a press briefing that the pure stomach bacteria he and his colleagues found in Ötzi’s stomach was “in line with recent archaeological and ancient DNA studies that suggest dramatic demographic changes shortly after the Iceman’s time, including massive migration waves and significant demographic growth.”

Scientists in separate studies have previously found that global patterns of H. pylori variance match other existing evidence of human migration. In 2009, Colin Renfrew tracked genetic data from H. pylori bacteria alongside language distribution to reconstruct the waves of human migration that spread across the Pacific region beginning some 5,000 years ago. More broadly, Falush’s 2003 study used genetic analysis of H. pylori to trace several major migrations known from the historical record, including the European colonization of the Americas and the transatlantic slave trade. Along these lines, the researchers studying Ötzi’s H. pylori bacteria now hope to compare it with other pathogens found in mummies from different regions—including South America and Asia—in order to get more information on the evolution and onset of the pathogen.