Rivets on ancient mummies shed light on South American descent

A mummified adult male from the Ansilta culture, from the Andes in San Juan, Argentina, walking approx. 2,000 years back. Credit: Universidad Nacional de San Juan

Human DNA can be extracted from “cement” head lice that were used to glue their eggs to hair thousands of years ago, scientists have found, which can provide an important new window into the past.

In a new study, scientists for the first time rediscovered DNA from cement on hair taken from mummified remains dating back 1,500-2,000 years. This is possible because skin cells from the scalp are encapsulated in the cement produced by female lice when they attach eggs, known as nits, to the hair.

Analysis of this newly recovered ancient DNA – which was of better quality than that recovered through other methods – has revealed traces of pre-Columbian human migration patterns in South America. This method could make it possible to study many more unique samples from human remains, where bone and tooth samples are not available.

The research was led by the University of Reading, working in collaboration with the National University of San Juan, Argentina; Bangor University, Wales; Oxford University Museum of Natural History; and the University of Copenhagen, Denmark. It is published in the journal Molecular biology and evolution.

Dr. Alejandra Perotti, associate professor of invertebrate biology at the University of Reading, who led the research, said: “Like the fictional story of mosquitoes encased in amber in the film Jurassic Park, which carries the DNA of the dinosaur host, we have shown that our genetic information can be preserved by the sticky substance produced by head lice on our hair. In addition to genetics, lice biology can provide valuable clues about how humans lived and died thousands of years ago.

“The demand for DNA samples from ancient human remains has grown in recent years as we seek to understand migration and diversity in ancient human populations. Head lice have followed humans throughout their existence, so this new method could open the door to a goldmine of information. about our ancestors, while preserving unique specimens. “

Rivets on ancient mummies shed light on South American descent

Nit of human lice showing the cement covering the eggshell and hair shaft, including a human cell (nucleus, willow). Fluorescence micrograph in UV light, sample prepared with a fluorescence dye that binds to DNA (DAPI). Cell and bacterial nuclei, Riesia-primary symbiotic lice bacterium, show signal (arrows). Credit: University of Reading

Until now, ancient DNA has preferably been extracted from dense bones from the skull or from internal teeth, as these provide samples of the best quality. However, skull and tooth remains are not always available as it may be unethical or against cultural belief to take samples from original remains, and due to the severe damage, causes destructive sampling on the samples, which compromises future scientific analysis.

Recovery of DNA from cement supplied by lice is therefore a solution to the problem, especially as nits are often found in the hair and clothing of well-preserved and mummified humans.

The research team extracted DNA from nit cement from samples collected from a number of mummified residues from Argentina. The mummies were of humans who reached the Andes Mountains in the province of San Juan in central western Argentina 1,500-2,000 years ago. The team also examined old nits on human hair used in a textile from Chile and nits from a shrunken head that originated from the ancient Jivaro people of Amazonas Ecuador.

The samples used for DNA tests of nit-cement were found to contain the same concentration of DNA as a tooth, double that of bone remains and four times that recovered from blood inside much more recent lice samples.

Dr. Mikkel Winther Pedersen from the GLOBE Institute at the University of Copenhagen, and first author, said: “The high DNA yield from these nit cements really came as a surprise to us, and it was striking to me that such small amounts could still give us all these information about who these people were and how the lice related to other lice species, but also gives us hints about possible viral diseases.

“There is a hunt for alternative sources of ancient human DNA, and nitrous cement may be one of those alternatives. I believe that future studies are needed before we can seriously uncover this potential.”

Rivets on ancient mummies shed light on South American descent

A human hair with a rivet attached to with ‘cement’. Credit: University of Reading

In addition to the DNA analysis, the researchers are also able to draw conclusions about a person and the conditions they lived under, based on the location of the nits on their hair and based on the length of the cement pipes. Their health and even cause of death can be indicated by the interpretation of the biology of the rivets.

Analysis of the recovered DNA from nit-cement revealed and confirmed:

    • Each of the sexes of the human hosts
    • A genetic link between three of the mummies and humans in the Amazon 2,000 years ago. This shows for the first time that the indigenous people of the province of San Juan migrated from the land of the Amazon and rainforests in the northern part of the continent (south of present-day Venezuela and Colombia).
    • All studied ancient human remains belong to the basic mitochondrial genera in South America.
    • The earliest direct evidence of Merkel cell Polymavirus was found in the DNA trapped in nitrous cement from one of the mummies. The virus, which was discovered in 2008, is secreted by healthy human skin and can in rare cases penetrate the body and cause skin cancer. The discovery opens up the possibility that head lice can spread the virus.

Analysis of the rivets’ DNA confirmed the same migration pattern for human lice, from the northern Amazon planes to central western Argentina (San Juan Andes)

Morphological analysis of nits informed that:

    • The mummies were probably all exposed to extremely cold temperatures when they died, which could have been a factor in their death. This was indicated by the very small space between the nits and the scalp on the hair shaft. Lice rely on the host’s main heat to keep their eggs warm and therefore lay them closer to the scalp in cold environments.
    • Shorter cement pipes on the hair correlated with older and / or less preserved samples due to the degradation of the cement over time.

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More information:

OUP accepted manuscript, Molecular biology and evolution (2021). DOI: 10.1093 / molbev / msab351

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