Now, 25 years later, Otzi has given scientists a new insight into early human life: The bacteria in his gut help confirm an ancient, intimate connection between humans and a particular kind of microbe. This connection is so strong that the bacterium Helicobacter pylori can be used to trace ancient human migrations, telling scientists where and when humans from different parts of the world became intimately involved.
Researchers have known for some time that H. pylori and humans have a long and storied history, probably stretching back at least 100,000 years. The bacterium only infects humans, and in modern times, it does so prolifically: Strains of it are found in the guts of around half the people alive today.
H. pylori strains are known to mix and recombine into hybrids when they come into close contact for a significant period of time: When couples pair up, when children play together, and so on. The H. pylori strains found today are all mixtures of ancestral strains, created as humans came together from disparate parts of the globe.
And that means we can use these bacteria to trace migration in much the same way that we can use genomic analysis to see when different groups of people interbred. In fact, for several years H. pylori analysis could paint a much better picture of human migration than genetic analysis could. Even today, scientists say, bacteria can often provide a closer look than human genes. The quickly evolving, mutation-prone microbes diverge from one another so quickly that the differences between individual strains are many and minute, allowing for a high-resolution look at human transit.
The new study doesn't provide any earth-shattering insight – no hitherto unknown human migrations have been revealed – but it does represent a major technological feat. Many bacteria can be found in well-preserved bodily tissues like bone, but H. pylori lives only in the gut. Otzi may have been incredibly well mummified in his icy grave, but his delicate stomach lining is long gone.
So the group of researchers took the long way round: They sequenced the DNA of the entire stomach, then weeded out everything but the H. pylori.
"It’s a really huge amount of data, in our case it was originally hundreds of gigabytes," study author Thomas Rattei of the University of Vienna said during a press conference held on Wednesday. "We had to separate the Heliobactor bacteria from other bacteria, and this was like searching for a needle in a haystack."
Sebastian Suerbaum, a microbiologist at Hannover Medical School who wasn't involved in the most recent study on H. pylori, told The Post that the technological accomplishment was impressive. "I did not think it was possible to do this from Otzi or even from younger mummies, because they’ve been dead so long and it’s so fragile, the bacteria," Suerbaum said. "I think this may be a very unique opportunity."
Or, in the words of study author Yoshan Moodley of the University of Venda, "This will, like, never happen again."
In examining the 5,300-year-old H. pylori DNA, the researchers noted strong similarities to the bacterial strains seen in modern day Central and South Asia, as opposed to those found in Europe, where Otzi's body turned up. This doesn't mean Otzi trekked all the way from Asia to the Alps, the researchers explained: Modern day Europeans tend to have strains of H. pylori that are the result of the mixing and recombining of ancient Asian and African strains, and it seems likely that this mixture occurred after Otzi's lifetime.
If H. pylori came out of Africa with humans when we first emerged some 60,000 years ago, that strain isn't the one that took hold in Europe. That's not surprising, because human migration was a complex affair. There were most likely humans moving from Africa to Eurasia around the time that Otzi lived, and there was a migration back into Africa not long after his time as well. Humanity's first trip out of Africa was far from the only opportunity for H. pylori to hitch a ride across the globe.
Suerbaum, who did some of the earliest work using modern H. pylori to infer human migration patterns, said it was nice to see confirmation of previous research using actual ancient bacteria.
"It's a study of one, of course," Suerbaum said. As useful as Otzi is as a glimpse into the past, any work done on him is cursed with irreproducibility. There simply aren't enough perfectly mummified humans from such an early period lying around waiting to be studied for researchers to confirm their conclusions. "But I think it provides a nice, solid data point. We have this person found in a precise location at this precise time with this precise strain," Suerbaum said.
The researchers found one other point of interest: Otzi's gut seems to have held a virulent strain of the bacteria – one that could potentially cause stomach upset or even ulcers – and he has protein markers associated with an immune response to the bug. Because Otzi's stomach is long gone, the researchers can't say for certain whether or not he was experiencing symptoms. But considering the fact that he died with an arrowhead in his shoulder, a possible tummy ache wouldn't have been high on Otzi's list of concerns.
This post was originally published on Jan. 7. It has been updated.
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