For the first time, scientists have extracted ancient human DNA from the sticky glue used by head lice to attach their eggs to their hosts’ hair. The new technique was tested on mummified remains, and the DNA revealed information about how people died and population movements thousands of years ago.
Scientists have discovered that human DNA can be extracted from the ‘cement’ used by head lice to glue their eggs to hairs thousands of years ago, which could provide an important new window into the past.
In a new study, scientists recovered DNA from cement on hairs taken from mummified remains dating back 1,500-2,000 years for the first time. This is due to the fact that skin cells from the scalp become encased in the cement produced by female lice as they attach eggs, known as nits, to the hair.
Analysis of this newly recovered ancient DNA, which was of higher quality than that recovered by other methods, revealed information about pre-Columbian human migration patterns in South America. This method could allow for the study of many more unique samples from human remains where bone and tooth samples are unavailable.
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 on our hair.
Dr. Alejandra Perotti
The University of Reading led the study, which was conducted in collaboration with the National University of San Juan in Argentina, Bangor University in Wales, the Oxford University Museum of Natural History, and the University of Copenhagen in Denmark. It appears in the journal Molecular Biology and Evolution.
“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 on our hair,” said Dr. Alejandra Perotti, Associate Professor in Invertebrate Biology at the University of Reading, who led the research. Aside from genetics, lice biology can reveal important information about how people lived and died thousands of years ago.
“As we seek to understand migration and diversity in ancient human populations, there has been an increase in demand for DNA samples from ancient human remains in recent years. Because headlice have been with humans since the beginning of time, this new method could unlock a treasure trove of information about our forefathers while also preserving unique specimens.”
Until now, ancient DNA has been extracted primarily from dense bone in the skull or inside teeth, as these provide the highest quality samples. However, skull and tooth remains are not always available because it is unethical or against cultural beliefs to take samples from indigenous early remains, and because destructive sampling causes severe damage to the specimens, jeopardizing future scientific analysis.
Recovering DNA from the cement delivered by lice is thus a solution to the problem, especially given that nits are frequently found on the hair and clothes of well preserved and mummified humans.
The DNA was extracted from nit cement of specimens collected from a number of mummified remains in Argentina by the research team. The mummies belonged to people who lived in the San Juan province of Central West Argentina 1,500-2,000 years ago. The researchers also looked at ancient nits on human hair used in a Chilean textile and nits from a shrunken head from the ancient Jivaroan people of Amazonian Ecuador.
The DNA concentration in nit cement samples was found to be the same as that of a tooth, double that of bone remains, and four times that recovered from the blood inside far more recent lice specimens.
“The high amount of DNA yield from these nit cements really surprised 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,” said first author Dr. Mikkel Winther Pedersen of the GLOBE institute at the University of Copenhagen.
“There is a search for alternative sources of ancient human DNA, and nit cement may be one of them. I believe that more research is required before we can fully understand this potential.”
In addition to DNA analysis, scientists can deduce information about a person and their living conditions based on the position of the nits on their hair and the length of the cement tubes. The interpretation of the biology of the nits can indicate their health and even the cause of death.
Analysis of the recovered DNA from nit-cement revealed and confirmed:
- The gender of each of the human hosts.
- A genetic link between three of the mummies and humans in Amazonia 2,000 years ago. This demonstrates, for the first time, that the San Juan province’s original population migrated from the Amazon’s land and rainforests in the continent’s north (south of current Venezuela and Colombia).
- All of the ancient human remains studied are from the founding mitochondrial lineages of South America.
- The first direct evidence of Merkel cell Polymavirus was discovered 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, enter the body and cause skin cancer. The discovery opens up the possibility that head lice could spread the virus.
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)
Morphological analysis of the nits informed that:
- All of the mummies were most likely exposed to extremely cold temperatures when they died, which could have contributed to their deaths. The very small gap between the nits and the scalp on the hair shaft indicated this. In cold environments, lice rely on the host’s head heat to keep their eggs warm, so they lay them closer to the scalp.
- Because cement degrades over time, shorter cement tubes on the hair correlated with older and/or less preserved specimens.
