Pompeii DNA sequenced from 2000 year old remains

In 79 AD, a huge eruption of Mount Vesuvius destroyed the ancient city of Pompeii. It covered everything in a layer of ash, and, in the process, preserved some of the bodies of the people who lived there. Visitors can see plaster casts made in the late 1800s of some of these remains. And, incredibly, when those casts were recently taken for restoration, a team of scientists were able to extract DNA from the remains of the 2000 year old victims encased within some of them. But while the bodies are certainly authentic Vesuvius victims, the genetic analysis has also pulled the rug from under some of the more romantic narratives that historians have woven previously about the bodies. Alissa Mittnik at the Max Planck Institute for Evolutionary Anthropology is one of the team behind the work…

Alissa - Notoriously, DNA preservation is not very good over long-term in warm climates such as the Mediterranean. Then of course the extreme heat of the Vesuvius eruption might have also contributed to the destruction of DNA. So first of all, we just wanted to see, would we be able to retrieve authentic ancient DNA, and then we really wanted to test some of these popular narratives that had been projected onto some of the individuals from which casts had been made in the past.

Chris - I think I've seen those casts, because I've been to both Pompeii and Herculaneum. It's a very striking place isn't it? But these are the plaster casts of the victims. They were made decades ago, weren't they, some of those plaster casts?

Alissa - Yes, so the method was first developed in the 19th century and since then over a hundred casts have been made. They would find some kind of cavity in this compacted ash sediment and then pour plaster in and then excavate that, and see what it actually was. A human that died there, an animal perhaps? That's quite interesting to think about what actually happened to the bones inside that cavity. So the soft tissue was decaying and the skeletal elements remained and they kind of followed gravity and fell down in this cavity. Then the actual pouring of the plaster would have moved around the bone some more. So what we were working with was, 86 of the plaster cast were undergoing reconstruction at that time, a restoration because they had been damaged in the past during the second World War. So at some of the points in the plaster, we could actually see inside the cast and we could see the bones that were embedded in the plaster. That's where we could take samples for our DNA study.

Chris - Do you get good quality DNA out of that, even nearly 2000 years later?

Alissa - It was difficult. So we sampled a total of 14 individuals, and in the end we only got usable analysable data for five of them. Then we also have to make sure that this is not any modern contamination that was introduced by any of the researchers, the archaeologists or anthropologists, that had been working with these casts in the past.

Chris - Some of them were probing the site even several hundred years ago, weren't they? People became interested in the Pompeian site. So how do you know this really is authentic Roman or Roman era DNA?

Alissa - There are some in silico methods, so by analysing the genetic sequencing data that we get, we can check for certain characteristics that are typical for old DNA. We do have somewhat a picture of what we could expect perhaps for general patterns of ancestry during the Roman era. There has been a big study done on the city of Rome during that time period, and what we found was that, what we see in Pompeii is quite similar.

Chris - Can this begin to give us some insights into the kinds of people who were in Pompeii?

Alissa - Yes, that was part of the analysis we did. So, we looked at different parts of the genome, the nuclear genome that is inherited both from the mother and the father, and then the mitochondrial genome that is inherited only from the mother's side. We compare that to populations around the world, both modern day populations as well as contemporaneous populations, where there has already been ancient DNA published. We related the individuals from Pompeii to see who they were most close to. That gave us some information about who their most recent ancestors could have been, and from which region of the world they originated.

Chris - What emerged then, because Pompei was an interesting place, wasn't it? It was a very rich Roman town. There were a lot of what we in the modern era would call posh people living there, very well moneyed, educated. They also had a large number of people working for them who would've been less so. Does that get reflected potentially in what you see in the DNA?

Alissa - During the Roman imperial era there's a real explosion of genetic diversity, and there's also a greater influence from the Eastern Mediterranean regions like Aegean, Anatolia, the Levant. Although Pompeii is a much smaller town, we do see the same pattern. So there is a large genetic diversity and we see this more Eastern Mediterranean genetic influence. Of course, this could be because these people were indeed themselves migrants from that region or their parents or grandparents were. The surprising thing was that in some of the cases that we studied, the DNA infected did not agree with some of these narratives that had been popularly spread. For example, we were looking at this group of four individuals from the house of the golden bracelet. These were two adults and two small children, and one of the adults was cradling one of the children on their lap. They were traditionally interpreted as being a mother and her child, and the other adult was the father of this group, and there was a second child, so a nuclear family.

Alissa - What we found is that, in fact, all four of these individuals were males. They were also genetically distinct from each other. When we look at their ancestry, although we can't create any definitive new story for these people, we don't know exactly who they were, and how they were related to each other. But it just shows us that maybe the first idea that comes to mind, the most intuitive or the most dramatic, is not the accurate one. We have to keep open mind. I was quite happy to be able to contribute to these people's story and maybe bring their truth a bit closer to us.