In detective series and films, where criminologists play the main role of the engine of the plot, you can often find how the person who left these traces was successfully determined by a cigarette butt or chewing gum stuck to the table. In real life, from chewing gum that has been in a personβs mouth, you can also learn a lot about him. Today we will look at a study in which scientists from the University of Copenhagen discovered during excavations a "chewing gum", which is approximately 5700 years old. What information about a person could scientists get from their find, who else could the ancient chewing gum tell about, and how this study can affect the fight against various diseases in the future? Answers to these questions await us in the report of scientists. Go.
Research basis
The protagonist of this study is birch tar or birch tar. This brownish-black substance is obtained by boiling the top layer of birch bark (birch bark) in a closed container. Under such conditions, heating occurs without access to oxygen, i.e. dry distillation. In the process of heating, the birch bark is converted into tar.
In ancient times, this process was carried out in clay containers on a fire. In those days, tar was usually used for processing stone products as a universal glue. The first archaeological finds of tar used by man date back to the Paleolithic period.
It is logical that tar was used in the "industry", so to speak. However, on many pieces of birch resin, archaeologists found traces of teeth. Why did our ancestors chew tar? There are several theories to explain this. Firstly, tar quickly hardens when cooled, so chewing it could be associated with a desire to warm it up and make it softer for work. There is a theory that tar was chewed to reduce pain caused by diseases of the oral cavity, since tar is considered an antiseptic, albeit a very weak one. Also, some researchers believe that these were the beginnings of dental hygiene, and tar acted as an ancient toothbrush. And the funniest theory, but not without meaning, is pleasure. Ancient people could chew resin just like that, i.e. without any good reason.
Production of birch resin in practice.
There are quite a lot of speculations on the topic of resin chewing by ancient people, but no one has conducted studies that give concrete results. Therefore, scientists from the University of Copenhagen decided to analyze a piece of chewed resin found during excavations in southern Denmark (1a). The study of the sample showed that it contains not only human DNA, but also microbial DNA, which can tell more about the microbiome of the oral cavity. Plant DNA has also been found that appears to have been eaten by early man before chewing the resin.
The DNA is so well preserved, scientists rejoice, that they have been able to isolate the complete human genome. This seemingly insignificant fact is actually a breakthrough in archeology and genetics. The fact is that the complete genome of an ancient person could previously be obtained exclusively from his remains (usually bones).
Results of the study
Having received "material evidence", archaeologists began its phased analysis to obtain the most complete information about our "suspect", who chewed birch tar.
Image #1
Radiocarbon dating, which is performed by changing the content in the sample of the radioactive isotope 14C in relation to stable carbon isotopes, said that the age of the gum is from 5858 to 5661 years (1b). This suggests that the specimen belongs to the Early Neolithic period. This period is also referred to as the "New Stone Age", as stone products became more complex, the technology of grinding and drilling holes appeared.
Chemical analysis using Fourier Transform Infrared (FTIR) spectroscopy yielded a spectrum very similar to modern birch tar. GC/MS (gas chromatography/mass spectrometry) revealed the presence of the triterpenes betulin and lupeol, which is quite common for samples taken from birch (1c). Additional confirmation that the sample was birch was the traces of dicarboxylic acids and saturated fatty acids detected by the same GC/MS.
Thus, scientists found out that the sample is birch resin aged from 5858 to 5661 years (early Neolithic).
At the next stage, DNA sequencing was performed, during which about 360 million base paired DNA sequences were generated, almost a third of which can be unambiguously compared with the reference human genome (hg19).
The sequences of paired bases of human DNA showed all the features inherent in the DNA of ancient people: rather short average lengths of fragments, frequent presence purines* before thread breakage and increased frequency of visible replacements cytosine* (C) on thymine* (T) at the 5' ends of the DNA fragments.
Purine* (C5N4H4) is the simplest representative of imidazo[4,5-d]pyrimidines.
Cytosine* (C4H5N3O) - organic compound, nitrogenous base, pyrimidine derivative.
Timin* (C5H6N2O2) is a pyrimidine derivative, one of the five nitrogenous bases.
Also, about 7.3 GB of data was generated regarding sequences that are not related to human.
The sample contained approximately 30% endogenous human DNA. This is comparable to the well-preserved teeth and bones of ancient people.
Based on the ratio between the sequences of paired bases corresponding to the X and Y chromosomes, scientists were able to determine the gender of the ancient chewing gum lover - female.
In order to predict the color of hair, eyes and skin, genotypes were bred for forty-one SNP*that are included in the system .
SNP* (single nucleotide polymorphism) - differences in the DNA sequence of one nucleotide in the genome of representatives of the same species or between homologous regions of homologous chromosomes.
This analysis showed that the woman was dark-skinned with dark brown hair and blue eyes.
Image #2
The scientists found 593102 SNPs in the study genome that had previously been genotyped in a database of >1000 modern humans and >100 previously published ancient genomes.
On the image 2a the results of the principal components method are shown. This method of data dimensionality reduction made it possible to determine that the ancient woman whose genome is being studied is most likely a Western hunter-gatherer (W.H.G.). Comparison alleles* modern people and an ancient woman confirmed her belonging to an established group (2b).
Alleles* - different types of the same gene located in the same regions of homologous chromosomes. Alleles determine the direction of development of a particular trait.
These results are also confirmed by qpAdm analysis. This analysis shows that a simple linear model, which assumes 100% origin of an ancient woman from the WHG group, cannot be discarded in favor of a more complex model (2s).
In order to broadly characterize the taxonomic composition of non-human sequences in a sample, MetaPhlan2, a tool specifically designed for taxonomic profiling of short sequences obtained from shotgun method*.
Shotgun Method* β a method of sequencing long DNA segments, when obtaining a random massive sample of cloned DNA fragments allows you to restore the original DNA sequence.
Image #3
On "origami" 3a shows the results of the principal component analysis, which compared the microbial composition of the studied sample and 689 microbiome profiles from the Human Microbiome Project (HMP). Clustering was found between the data from the sample and the HMP data, that is, they were similar in many ways. This is also visible on 3b, which shows the microbial composition of the resin in comparison with the same of two soil samples (sampled in the same place) and in comparison with the microbial composition of modern humans.
A more detailed analysis of the microbial composition showed the presence of bacteria neisseria subflava ΠΈ Rothia mucilaginosaand Porphyromonas gingivalis, Tannerella forsythia ΠΈ Treponema denticola. In addition, traces of the Epstein-Barr virus were detected.
Several species of streptococci belonging to the group mild, including Streptococcus viridans ΠΈ Streptococcus pneumoniae.
Table #1: A list of all non-human taxa found in a birch resin sample.
The consensus genome was reconstructed from the sequences of paired bases S. pneumoniae and an estimate of the number of heterozygous sites. The results showed the presence of several strains (image #4).
Image #4
To assess the virulence of strains S. pneumoniaeextracted from ancient resin, scientists matched contigs (a set of overlapping DNA segments) with a complete virulence factor database, allowing the identification of known genes virulence* S. pneumoniae.
Virulence* - the degree of ability of the strain to infect the organism under study.
Twenty-six S. pneumoniae virulence factors were identified in the ancient specimen, including capsular polysaccharides (CPS), streptococcal enolase (Eno), and pneumococcal surface antigen A (PsaA).
Analysis of the ancient resin sample also showed traces of two plant species: birch (Betula pendula) and hazelnut (Corylus avellana). In addition, about 50000 sequences were found that related to the mallard (Anas platyrhynchos, a species of duck).
For a more detailed acquaintance with the nuances of the study, I recommend looking at ΠΈ to him.
Finale
This study can rightly be called unique, given the amount of information received. Previously, the complete genome of an ancient person could be restored exclusively from his remains (bones and teeth), but in this work, scientists managed to get it from chewed birch resin.
They found that the 5700-year-old gum was chewed by a dark-skinned woman with dark brown hair and blue eyes. Such a description of the appearance once again confirms that lighter skin pigmentation among the inhabitants of the western part of Eurasia began to appear later. In addition, such external characteristics are comparable to those of Western hunter-gatherers, which, presumably, included the woman whose genome was obtained from the sample.
The advantage of studying chewed resin is that it provides information regarding the microbial composition of the oral cavity of an ancient person. This analysis showed the presence of several types of bacteria (neisseria subflava, Rothia mucilaginosa, Porphyromonas gingivalis, Tannerella forsythia ΠΈ Treponema denticola). In addition, traces of the Epstein-Barr virus were found, which is not surprising, given the high prevalence of this virus among modern people (90-95% of the adult population are its carriers).
Several species of streptococci from the group were also found. mild, including Streptococcus viridans ΠΈ Streptococcus pneumoniae.
As for the gastronomic preferences of the ancient woman, according to the assessment of non-human DNA sequences, which also did not belong to viruses or bacteria, traces of birch, hazelnuts and mallard ducks were found. It can be assumed that these plants and animals were the basis of the food of the ancient people of that period. However, there is a strong possibility that the DNA of these plants and animals got into the resin, as the ancient woman consumed them shortly before chewing the resin. In other words, it could be an isolated case.
Why is resin an excellent source of ancient human DNA? The thing is that in the process of chewing, DNA is βsealedβ with resin and stored in it, due to aseptic and hydrophobic properties.
In the future, scientists plan to analyze other samples found, which will help to better understand the life of ancient people. In addition, the microbial composition of ancient specimens provides insight into the evolution of oral-specific microbes and some pathogens.
Be that as it may, to collect so much information about a person from a piece of chewed resin that he spat out 5700 years ago is an incredible achievement. For some, information from the past, especially such a distant one, is not important. However, in fact, the more we know about our ancestors, the more we understand our true selves.
Friday off-top:
A video about how chewing gum is produced in the modern world.
Off-top 2.0:
A bit of nostalgia π
Thanks for watching, stay curious and have a great weekend everyone! π
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Source: habr.com