A very cool series of three studies were published several days ago in Science and Nature that I just have to share. The punchline is ultimately how ancient DNA helps us understand how the horsemen Huns & Mongols of Eurasia supplanted sedentary Indo-European with Hepatitis B and other communicable diseases. Books like the Horse, Wheel and Language have done a wonderful job painting this process. But we haven’t had the ancient DNA and even much resolution to communicable diseases amongst ancient populations, like hepatitis B.
Hepatitis B is caused by a blood born virus which infects approximately 250 million people. This disease causes chronic inflammation to the liver, sometimes leading to cirrhosis and liver cancer. It does so through a reverse transcriptase activity similar to retroviruses which incorporates its viral genome into human DNA.
Despite its almost ubiquitous presence throughout the entire world, we know little about the roots about this virus. To figure this out, researchers extracted ancient DNA from over 300 ancient remains that spanned a range of more than 6,000 years, with the oldest specimen being 7,000 years old.
Peter de Barros Damgaard who co-authored two of the studies attributed this phenomenal accomplishment due to advances in genetic techniques and decades of painstaking work by archaeologists who excavated the burial mounds. Barbara Mühlemann found that 25 individuals showed signs of a hepatitis B infection. That makes a 8% representative prevalence of hepatitis in ancient people.
Half of those individuals dated between 800 and 4,500 years old had genomes intact enough for further analysis. This makes them the oldest hepatitis viruses identified in ancient human remains to date. Actually, a 4,500-year-old sample from the group is the oldest exogenous viral DNA ever recovered so far, which beating out a 450-year-old hepatitis B sample found in an earlier study.
What was interesting is that nine of the samples had viral genomes that would fit into a modern-day genotype, but three didn’t. That means those three were of a Hepatitis B virus strain that is now extinct. Additionally curious, some of the ancient viral sequences came from regions not typically associated with their specific genotypes today. For example, Hepatitis B genotype strain A is thought to have emerged slave trade between the 16th and 19th centuries. But since it is present in these ancient samples, in fact two 4,000-year-old Eurasian samples and in one Hungarian Scythian sample that was around 2,600 years old had strain A. That changes things! The fact that we have this ancient genomes we can study virus evolution that was we haven’t before.
Some other interesting findings have been plucked out of these studies. Using linguistic evidence, specifically the Indo-European linguistic group is thought to have given rise to modern-day tongues such as English, French, German, Russian, Hindi, and Persian, while Turkish is part of the Turkic language group thought to have originated in east Asia, including Mongolia. From about 800 to 200 BC, the Eurasian steppe was dominated by the Scythians, a group of Iranian-speaking mounted warriors who are thought to have originated from Bronze Age farmers of western “European” ancestry.
But we now know that Scythians were “absorbed and replaced” by Huns, a group of horsemen spreading westward out of Mongolia, “killing all the people they met but also mixing with them”. Eske Willerslev of the University of Copenhagen eluded that horse herding and riding changed the face of Eurasia,
“You can say that the vast majority of the genetic makeup of contemporary people in this 8,000 kilometre-long (4,971 mile) stretch across Europe and Asia has really mainly been formed within the last approximately 1,000 years.”
Lastly, the Justinian plague pandemic, which sparked off in Constantinople in 541 around killed 25 million Europeans afterwards, and was thought to have originated from Greece had really come with the east Asian conquerers… the pandemic reached Europe from regions in China via the Silk Road along the southern fringe of the steppes.
- 137 ancient human genomes from across the Eurasian steppe, Nature (2018). nature.com/articles/doi:10.1038/s41586-018-0094-2
- Ancient Hepatitis B viruses from the Bronze Age to the Medieval period, Nature (2018). nature.com/articles/doi:10.1038/s41586-018-0097-z P. de
- Barros Damgaard el al., “The first horse herders and the impact of Early Bronze Age steppe expansions into Asia,” Science (2018). science.sciencemag.org/lookup/ … 1126/science.aar7711