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HEAD LICE on ancient South American mummies contain more human DNA than a tooth

Head lice found on ancient mummies contain more DNA than a tooth, according to scientists, who say it could help shed light on ancient people and migration.

A team were able to extract the DNA from the ‘cement’ head lice used to glue their eggs to hairs on mummified bodies in South America, thousands of years ago. 

The DNA extracted from the cement was of better quality than that recovered through other methods, according to the team led by the University of Reading.

It revealed clues about pre-Columbian human migration patterns throughout South America, including that  the original population of the San Juan province migrated from the land and rainforests of the Amazon in the North of the continent.

‘There is a hunt out for alternative sources of ancient human DNA and nit cement might be one of those alternatives,’ said study first author Dr Mikkel Winther Pederson, from the University of Copenhagen in Denmark. 

Head lice found on ancient mummies contain more DNA than a tooth, according to scientists, who say it could help shed light on ancient people and migration

KEY FINDINGS OF NIT CEMENT ANALYSIS

GENETIC LINK: A genetic link between three of the mummies and humans in Amazonia 2,000 years ago. 

This shows for the first time that the original population of the San Juan province migrated from the land and rainforests of the Amazon in the North of the continent (south of current Venezuela and Colombia).

FOUNDING DNA: All ancient human remains studied belong to the founding mitochondrial lineages in South America.

MERKEL CELL VIRUS: The earliest direct evidence of Merkel cell Polymavirus was found in the DNA trapped in nit cement from one of the mummies. 

The virus, discovered in 2008, is shed by healthy human skin and can on rare occasions get into the body and cause skin cancer. 

The discovery opens up the possibility that head lice could spread the virus.

MIGRATION: Analysis of the DNA of the nits, confirmed the same migration pattern for the human lice, from the North Amazonian planes towards Central West Argentina (San Juan Andes) 

They recovered the DNA from head lice eggs, or nits, found in the hair of mummified bodies dating back 1,500 to 2,000 years, and were found in Argentina.  

‘This was possible because skin cells from the scalp become encased in the cement produced by female lice as they attach eggs to the hair,’ researchers explained.

The findings include clues into the migration of pre-Columbian South American people that haven’t been available through other methods.

They believe this method could allow for more unique samples to be studied from human remains – even when no bone or tooth samples are available.   

Dr Alejandra Perotti, Associate Professor in Invertebrate Biology at the University of Reading, led the research.

He said: ‘Like the fictional story of mosquitos encased in amber in the film Jurassic Park, carrying the DNA of the dinosaur host, we have shown that our genetic information can be preserved by the sticky substance produced by headlice.’

‘In addition to genetics, lice biology can provide valuable clues about how people lived and died thousands of years ago,’ Dr Perotti added.

‘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.

‘Headlice have accompanied humans throughout their entire existence, so this new method could open the door to a goldmine of information about our ancestors, while preserving unique specimens.’

Until now, ancient DNA has been extracted from dense bone from the skull or from inside teeth, as these provide the best quality samples. 

However, skull and teeth remains are not always available, as it can be unethical or against cultural beliefs to take samples from indigenous early remains.

Severe damage destructive sampling causes to the specimens also make these extractions taboo, as well as compromising future scientific analysis.

Recovering DNA from the cement delivered by lice is therefore a solution to the problem, especially as nits are commonly found on the hair and clothes of well preserved and mummified humans.

The DNA taken from the  mummies in Argentina revealed they reached the Andes mountains of the San Juan province, Central West Argentina. 

A team were able to extract the DNA from the 'cement' head lice used to glue their eggs to hairs on mummified bodies in South America, thousands of years ago

A team were able to extract the DNA from the ‘cement’ head lice used to glue their eggs to hairs on mummified bodies in South America, thousands of years ago

FINDINGS OF  MORPHOLOGICAL ANALYSIS OF NITS 

VERY COLD: The mummies were all likely exposed to extremely cold temperatures when they died, which could have been a factor in their deaths. 

This was indicated by the very small gap between the nits and scalp on the hairs shaft. 

Lice rely on the host’s head heat to keep their eggs warm and so lay them closer to the scalp in cold environments.

OLDER AGE: Shorter cement tubes on the hair correlated with older and/or less preserved specimens, due to the cement degrading over time.

The team also studied ancient nits on human hair used in a textile from Chile and nits from a shrunken head originating from the ancient Jivaroan people of Amazonian Ecuador.

The samples used for DNA studies 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 far more recent lice specimens.

Dr Winther Pedersen said: ‘The high amount of 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 this information about who these people were, and how the lice related to other lice species but also giving us hints to possible viral diseases.

‘There is a hunt out for alternative sources of ancient human DNA and nit cement might be one of those alternatives. I believe that future studies are needed before we really unravel this potential.’

As well as the DNA analysis, scientists were also able to draw conclusions about a person and the conditions in which they lived from the position of the nits on their hair and from the length of the cement tubes.  

They were able to determine the sex of the human hosts, how the populations migrated throughout south America, and evidence of viruses. 

The DNA extracted from the cement was of better quality than that recovered through other methods, according to the team led by the University of Reading

The DNA extracted from the cement was of better quality than that recovered through other methods, according to the team led by the University of Reading

The team revealed a genetic link between three of the mummies and other humans known to be living in Amazonia 2,000 years ago. 

‘This shows for the first time that the original population of the San Juan province migrated from the land and rainforests of the Amazon in the North of the continent, in the area south of current Venezuela and Colombia,’ the authors found.

They also discovered that all ancient human remains studied belonged to the founding mitochondrial lineages in South America.  

The mummies were all likely exposed to extremely cold temperatures when they died, which could have been a factor in their deaths. 

This was indicated by the very small gap between the nits and scalp on the hairs shaft. Lice rely on the host’s head heat to keep their eggs warm and so lay them closer to the scalp in cold environments.

Shorter cement tubes on the hair correlated with older and less preserved specimens, due to the cement degrading over time.

As well as the University of Reading, researchers from National University of San Juan, Argentina; Bangor University, Wales; the Oxford University Museum of Natural History; and the University of Copenhagen, Denmark were involved. 

The findings were published in the journal Molecular Biology and Evolution. 

DNA: A COMPLEX CHEMICAL THAT CARRIES GENETIC INFORMATION IN ALMOST ALL ORGANISMS

DNA, or deoxyribonucleic acid, is a complex chemical in almost all organisms that carries genetic information.

It is located in chromosomes the cell nucleus and almost every cell in a person’s body has the same DNA. 

It is composed of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

The structure of the double-helix DNA comes from adenine binding with thymine and cytosine binding with guanine. 

Human DNA consists of three billion bases and more than 99 per cent of those are the same in all people.

The order of the bases determines what information is available for maintaining an organism (similar to the way in which letters of the alphabet form sentences).

The DNA bases pair up with each other and also attach to a sugar molecule and phosphate molecule, combining to form a nucleotide.

These nucleotides are arranged in two long strands that form a spiral called a double helix.

The double helix looks like a ladder with the base pairs forming the rungs and the sugar and phosphate molecules forming vertical sidepieces.

A new form of DNA was recently discovered inside living human cells for the first time.

Named i-motif, the form looks like a twisted ‘knot’ of DNA rather than the well-known double helix. 

It is unclear what the function of the i-motif is, but experts believe it could be for ‘reading’ DNA sequences and converting them into useful substances.

Source: US National Library of Medicine

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