|Ancient DNA (aDNA) is DNA isolated from ancient clinical, natural history, and archeological specimens collected for DNA analysis / Photo by: microgen via 123RF|
Ancient DNA (aDNA) is DNA isolated from ancient clinical, natural history, and archeological specimens collected for DNA analysis. It is a powerful research tool that can help address diverse questions about the susceptibility, origin, distribution, or evolutionary changes of a pathogen, but samples are usually temporally and geographically sparse.
This is why it made headlines when scientists from the University of Copenhagen Faculty of Health and Medical Sciences extracted a complete human genome from 5,700-year-old chewing gum found in the archeological site of Syltholm, southern Denmark.
In their study, which appeared in the journal Nature Communications, Theis Z. T. Jensen and colleagues wrote that ancient genomics have revolutionized people’s understanding of human prehistory. Yet, its work still depends on the availability of samples. For their study, they used ancient chewing gum excavated by archeologists. They said that the gum was made from a birch pitch.
What Is a Birch Pitch?
The team explained that a birch pitch is a black-brown substance derived by heating the bark of a birch tree. Since the early Middle Paleolithic period, the second subdivision of the Old Stone Age, the birch pitch has been widely used as a hafting agent and an adhesive. The researchers found small lumps of the said organic material in the archeological sites and it showed tooth imprints. This led the scientists to believe that the birch pitch was chewed. Aside from using it as a hafting agent, the organic material may also have been used as a type of medicine because it contains antiseptic properties that can help treat dental ailments.
University of Copenhagen Globe Institute’s Associate Professor Hannes Schroeder said via science research platform Science Daily that it is “amazing” to find a complete ancient human genome from a gum instead of a bone. What’s even more interesting, Schroeder added, is that they have also collected ancient DNA from the oral microbes as well as significant human pathogens.
|The team explained that a birch pitch is a black-brown substance derived by heating the bark of a birch tree / Photo by: schan via 123RF|
Significance of Their Findings
The team believes that the aDNA they found in the material will provide clues about the periods that have no human remains to study. Based on their analysis, the birch pitch was chewed by a female who was connected to the hunter-gatherers in mainland Europe. They also theorized that the woman must have lived in central Scandinavia at that time and probably had blue eyes, dark hair, and dark skin.
Sex Determination From aDNA
The team determined the sex of the chewer by mapping the X and Y chromosomes found in the aDNA. As to predicting her skin, eye, and hair color, they imputed the genotypes as part of their HIrisPlex-S system. In forensic DNA, the HIrisPlex-S system is used to predict visible characteristics of the DNA by using the specific DNA variants responsible for skin, hair, and eye color.
As part of their DNA extraction and sample preparation, the team said that they washed the sample in a 5% bleach solution to remove surface contamination and then rinsed it in molecular biology grade water. When it was already dry, they used different extraction methods using only 20 to 50 mg of the material.
|The team determined the sex of the chewer by mapping the X and Y chromosomes found in the aDNA. As to predicting her skin, eye, and hair color, they imputed the genotypes as part of their HIrisPlex-S system / Photo by: Sergey Nivens via 123RF|
Information About the Oral Microbiome
Animal and plant DNA tapped in the ancient gum also suggests that the woman might have eaten duck or hazelnuts as part of her diet. Since the gum served as a time capsule by studying the oral microbiome that lived in the woman’s mouth, the researchers shared more evidence about their findings. For instance, the Epstein-Barr virus was detected in the traces of DNA. The said virus is one of the common viruses that can be a gateway to glandular fever (mononucleosis). Signatures of pneumonia were also detected in the aDNA. Researchers added that the woman was lactose-tolerant.
For now, the researchers have referred to the woman as Lola because the gum was found in Lolland, an island in Denmark.
Artistic Reconstruction of the 5,700-Year-Old Chewer
The University of Copenhagen has also published an artistic reconstruction of the 5,700-year-old chewer as illustrated by Tom Björklund. The group said that they found the birch pitch sealed in mud, which makes their discovery “absolutely phenomenal” because the organic remains were preserved.
Schroeder went on to say that their discovery can help them learn how pathogens spread and evolve and what made them severe (virulent) in the past. It may even help scientists predict how a pathogen may behave in the future or how it can be eradicated and contained.
The group acknowledged the help provided by the Museum Lolland-Falster for allowing them to access the ancient sample as well as the people at the Danish National High-Throughput Sequencing Center for their technical assistance.
The aDNA extracted by the University of Copenhagen from the thousands-year-old birch pitch is important not just for the study of our history but also the understanding of our nature as human beings. A piece of ancient chewing gum now serves as proof of our physical connection to our past.