In a scene from the director’s film Jurassic Park Steven SpielbergMillionaire philanthropist John Hammond explains to a group of scientists how his team found a fossilized mosquito in amber. The discovery allowed them to extract DNA from dinosaurs, and they preserved them for more than 65 million years.
Of course this is because it is a science fiction movie. Maria Alejandra Perotti, Professor of Invertebrate Biology at the University of Reading in England.
But this does not mean that the technology itself is not viable. This is exactly what Beiruti accomplished. Like Hammond, she was able to extract DNA, not from dinosaurs and mosquitoes, but from ancient humans and lice.
Perotti, Argentinian works in England For nearly 20 years, he has been studying the scientific and historical significance between invertebrates (more specifically lice) and humans to answer one of the questions everyone asks: Where did we come from?
But it takes the question to a more regional level: How was South America inhabited?
A group of scientists from five universities, coordinated by them, discovered that the “cement” that lice use to stick their eggs (eggs) into people’s hair turned out to be a source of “very good” genetic information from mummies until they were found and preserved 2,000 years ago in San Juan, Argentinanear the Andes Mountains.
Mummy louse: The ‘cement’ that lice use to stick their eggs into people’s hair has become a source of genetic information for 2,000-year-old mummies found in San Juan, Argentina – Photo: g1
Unlike modern humans, our ancestors did not have effective methods of getting rid of lice, which can infect the scalp and clothing.
The female laid eggs and stuck with extraordinary efficiency to her host, in such a way that, in some cases, they would remain there for thousands of years.
Lice may be annoying to their former hosts, but for scientists like Perotti, the fact that they’ve been around for so long is good news.
Knowing that it was possible to study the evolutionary history of humans through lice, I set out to search for samples of human remains that contained hair.
Due to its properties, nits can remain intact for thousands of years, surrounded by their own “glue”. And within this material can be found human cells.
“Yes, it’s a bit like Jurassic Park,” Perotti told BBC Mundo. “The film is fiction, of course, but we make the comparison because the goal is the same: to distinguish the host through a parasite with a substance produced by the parasite itself.”
The human DNA in these samples proved to be of very good quality, as can be extracted from the teeth and from the petrous bone behind the ear.
Thanks to this, scientists are discovering more details about the ancient inhabitants of South America and these mummies, such as migration routes on the continent, gender and even possible causes of death.
“It’s very interesting,” Perotti told BBC Mundo. “Lice have always caught my attention because they live near the host and act like a mirror. I started using it to explain what happened to the host.”
“Thanks to them we can study thousands of years of history. They are a mirror of evolutionary history.”
Reflection of ancient humans
There are two subspecies of lice that infect humans, namely louse: the the body (from the body) and Head (from the head).
Thousands of years ago, a file the body It adapts to life, in addition to the skin, in clothes, too. That’s when ancient humans began covering themselves with fur and fabric.
This in itself is evidence of how the human louse evolves with its hosts.
Perotti was aware of this relationship and began researching ancient collections in natural history museums to study the history of our ancestors of parasites.
The project includes the University of Reading (England), and the Oxford University Museum of Natural History (England), Bangor University (Walesand San Juan National UniversityArgentina). In 2016, they hired scientists from the University of Copenhagen (Denmark) for the analysis of human DNA.
The results were published in the journal Molecular Biology and Evolution.
“I’ve been searching for samples from the indigenous people of South America for a long time. I did more research until I had access to collections of human remains that contain hair.”
These samples were from the mummies preserved in Argentina, as well as other human remains, with a different date, between 1300 and 2000 years ago, were found in the Calingasta Caves, in San Juan County. For this analysis, the team extracted no more than six lice per mummy.
Extracting DNA from samples of this age is not easy and is sometimes considered controversial, especially in samples that are in good condition.
The genetic material is usually extracted from the tooth or petrous bone, which means its destruction.
The sample must also meet certain requirements and be in good condition. This is not always possible, and sometimes the material is destroyed or partially damaged.
By studying the lice, the scientists realized that they avoided many of these inconveniences and also saved the samples for further study.
The original idea was to extract human DNA from the same preserved lice.
But they were surprised to discover that the “shell” that covered the nits held human DNA, not only “of the highest quality,” but also well-protected thanks to the chemical properties of the glue, explains Mikkel Winter Pedersen of the University of Copenhagen.
“Once the egg is stuck in the hair, it immediately absorbs the skin cells, possibly from the scalp,” he says.
“The interesting thing here is that (the material) was protected from degradation. Everything is decomposing, including me. We disappear over time. And we still have these samples here,” he asserts.
Migration routes and diseases
What did the scientists discover?
It was one of the 2,000-year-old mummies of a person from the northern Amazon. They know this because the extracted DNA matches that of other aborigines previously analyzed from the southern regions of the Colombia and yes Venezuela.
The other species, in turn newer (between 1300 and 1500 years old), do not have the same genetic characteristics, so they are of different origin: from Patagonia, from the south.
All this reveals that there was a large migration movement in the region thousands of years ago. Those from the north may have taken an eastern route, likely driven by climate change such as drought. Beiruti admits: “But we did not know that they had reached the far south.”
These pathways were suggested years ago by anthropological studies that did not include genetics. But the DNA results may provide more clues about how humans were distributed across the continent thousands of years ago.
They know this because in environments with lower temperatures, nits are closer to the scalp, where there is more heat.
Because gum nits carry everything around it, not just human DNA, the scientists also found genetic material that was neither from the louse nor from the host. This is the oldest evidence of Merkel cell polyomavirus.
Discovered in the United States in 2008, this virus is suspected to cause the majority of cases of Merkel cell carcinoma, a rare but aggressive form of skin cancer. Experts now suspect that lice may have something to do with the spread of this virus.
To support the findings, the team also analyzed the DNA of the lice themselves, and what they found was that they had the same migration pattern as their hosts.
“There is a great deal of interest on the part of Europe, the United States and even Asia in learning about the history of South America,” Perotti adds. “South America received the last migrations of anatomically modern humans. Humans have been studied all over the world, but there is a lack of focus and more rigorous studies to find out what happened in South America.”
He concludes, “For me, being from Latin America, I am proud to have conducted this research.”
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