Tracking Human Migration on a Micro Scale

By Drs. David Niesel and Norbert Herzog

We have featured several episodes about the Iceman, Ötzi who lived 5300 years ago, but whose remains were found by hikers in the Italian Alps in 1991. Studies of his mummified remains have revealed much about his life during the Copper Age, between 3500 and 2300 BCE. Now we report not on Ötzi himself, but on his stomach bacteria, which tells us about his life and the history of human geography.

Heliobacter pylori or H. pylori found in Ötzi’s stomach infects two thirds of the world’s population. This bacterium is thought to have become associated with humans at least 100,000 years ago. As humans spread to different locations around the world, and often formed isolated communities, different strains of H. pylori arose. By analyzing the genetic information of these bacteria in different human populations, scientists gain insight into how these ancient humans might have traveled and intermingled. These bacteria are only passed between people through intimate contact therefore its distribution is limited to the isolated population. So looking at the genome of Ötzi’s H. Pylori, we can get an idea of the people he had interacted with.

It was a difficult task to separate out the genetic information from a single type of bacteria among all the genetic information in the Iceman’s body. Scientists managed to pull out his H. pylori DNA bit by bit and compared its sequences to those of modern strains. The modern European H. pylori strain is actually a combination of an Asian and an African strain meaning that sometime in the past, those two populations came together but where and when is unknown. So Ötzi’s H. pylori could tell us which strains existed in Europeans during the Copper Age.

The DNA sequence of Ötzi’s H. pylori revealed that it was almost purely Asia in origin despite his never having left Southern Europe. Only 6.5% of its genetic information was of African origin suggesting it was likely in Europe for quite some time. This data suggests that there were not waves of migration from Africa but it is unclear who brought the bacteria from Africa into Europe. It is theorized that the mixing to create the modern stain of H. pylori had to have occurred after the Copper Age which is much later than previously estimated. The speculation is that the African strain came to Europe via the Middle East but earlier than 9,000 years ago. It may have been the first farmers who brought the agricultural revolution from the Middle East to Europe and brought their strain of H. pylori as well.

Of course, these are conclusions based on the sequence of H. pylori obtained from a single individual. Scientists will need sequences from many more ancient peoples to understand how they moved around and intermingled. Our ability to isolate and sequence the DNA of ancient mummies and their microbiomes from around the world will provide much more insight into the human populations and how they migrated. Who would have thought that we could use a bacterium to further our understanding of ancient human migration.

Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professor emeritus, Norbert Herzog, and professor, David Niesel, biomedical scientists at the University of Texas Medical Branch at Galveston. Learn more at www.medicaldiscoverynews.com.