Insights into the movement of ancient human populations come from a variety of sources, although possibly none as unusual as a mummy’s stomach ache. Bacteria samples gleaned from the frozen skin of Ötzi the Iceman, a European natural mummy who dates back to around 3,300 B.C, has given scientists new theories about how and when our ancestors populated the continent.
The bacterium in question is a strain of Helicobacter pylori (H. pylori), which currently infects about half of any given population and can on occasion cause stomach ulcers. Due to the bacteria’s prevalence and the fact that it requires close contact to be transmitted, H. pylori levels around the world closely mirror human population distributions. It is this factor that allows the bacteria’s various genetic strains to be used to help track migration patterns.
The H. pylori strain that is prevalent in modern-day Europe is a hybrid of a Eurasia and African strain and narrowing down when this hybridization occurred would also identify when humans began to fill European soil. Ötzi’s stomach bug is a pure Eurasian variety, meaning that humans carrying the African strain could not have arrived at the time he had lived. This means the hybridization would have had to have occurred some time within the past 5,000 years. It is a large window to be sure, but much smaller than one of the prior theories which placed the hybridization happening roughly 20,000 years ago.
The tricky part is that this new theory requires Ötzi’s sample to be representative of how bacteria was distributed at the time. It is possible, for instance, that hybridization had already occurred and that Ötzi’s bacteria simply hadn’t joined in before he died. It is one of the limitations of having only a single mummy from the time period to work off of.
If it can be assumed that hybridization had truly not occurred by the time Ötzi died, then the most likely candidates for bringing over the African H. pylori strain would be some of humanity’s first farmers, dating back around 8,000 years ago in the Middle East. Prior theories also suggested that migrants from the Middle East brought the African strain into Europe, but this event was placed some 20,000 years ago when populations began to move north to recolonize Europe following the last ice age.
The ability to track pathogens across thousands of years is a relatively new field of science that exists thanks to the ability to decode DNA molecules. In addition to tracking populations, these methods have been used to analyze the evolutionary history of modern-day afflictions to better understand them. For example, researchers from the University of Copenhagen reported in 2015 that they had tracked the plague as far back as the Bronze Age and showed how it was initially too lethal to spread properly and that it took until 1,000 B.C for the bacteria to be able to survive inside a flea.
Sources for Today’s Article:
“Iceman Mummy Reveals New Clues about Stomach Bacteria,” Reuters web site, January 12, 2016; http://in.reuters.com/article/us-italy-iceman-idINKCN0UP2JD20160112.
Wade, N., “Ötzi the Iceman’s Stomach Bacteria Offers Clues on Human Migration,” The New York Times web site, January 7, 2016; http://www.nytimes.com/2016/01/08/science/otzi-the-iceman-stomach-bacteria-europe-migration.html.