In Jurassic Park, researchers famously extract dinosaur DNA from a mosquito preserved in amber for millions of years. In a new study published yesterday (December 28) in Molecular Biology and Evolution, scientists report a similar discovery in real life, albeit with considerably younger genetic material: human DNA preserved in the glue-like cement affixing lice eggs to the heads of mummies.
The cement is a sticky substance head lice make to anchor their eggs to the hair of host animals, making them difficult to remove. In this study, a team of researchers from the UK, Argentina, and Denmark found that lice cement on eight Argentinian mummies between 1,500-2,000 years old contained skin cells from humans’ scalps, thereby preserving the mummies’ DNA. Through DNA sequencing, the team was able to determine the mummies’ sex, as well as genetic evidence indicating that the population the mummies belonged to migrated from west Amazonia—likely the southern rainforests of present day Venezuela and Colombia—to the Andes in Argentina.
The team also analyzed mitochondrial DNA from the lice eggs, called nits, to confirm the migration pattern seen in the human DNA studies, and found that they too appeared to have originated from the Amazon rainforests. Furthermore, the nits location—close to the mummies’ scalps—indicated the hosts were likely subject to extremely cold temperatures around their time of death. Study coauthor Alejandra Perotti, an invertebrate biologist at the University of Reading, tells Smithsonian Magazine, “The beauty of gathering info from nits is that they are preserved for thousands of years, attached to hair or clothing.”
The lice cement from the mummy heads also preserved environmental DNA that belonged to neither humans nor lice, including traces of several strains of bacteria and Merkel cell polyomavirus, which causes aggressive skin cancer. The authors write in their study that this is “the earliest direct evidence for this human viral pathogen,” and that the work opens the possibility that lice are a vector for the virus’s spread.
“This study shows for the first time that ancient nit sheaths provide a reliable source of host and nonhost genomic DNA,” the team writes in the study. The researchers suggest the sheaths could be an alternative to analyzing DNA extracted from ancient teeth and bones, as these conventional methods often damage human remains that have significant cultural value. Using lice cement, which is commonly found on ancient human remains and clothing, would avoid such damage.
“By genetically characterising a human host using just a handful of nits, we prevent the destructive sampling of bones and teeth that deteriorate or destroy unique ancient specimens. This also prevents conflicts with indigenous related people as the mummies or skeleton are left intact, only a few hairs containing nits are sufficient,” Perotti explains to The Guardian.
In a statement about the research, Mikkel Pedersen, a researcher on ancient environmental DNA from the University of Copenhagen and coauthor of the research, calls the amount of human DNA found in the parasite’s glue surprising. He tells The Guardian that DNA within the nit glue seemed better-protected from chemical damage than that within teeth or bone. Nevertheless, Pedersen maintains that more studies are needed to assess the potential of nit cement as an alternative source of ancient human DNA.
David Reed, a Florida Museum of Natural History biologist who was not involved with the study, calls the work “remarkable” in comments to Smithsonian. “First, the authors were able to sequence the genome from such a small and seemingly insignificant starting material, and second the lice upon these heads contributed to our understanding of human migrations.” He adds, “It seems that lice still have more to say about our history.”