DNA contains the biological instructions that drive the existence of every living organism, shaping the world as we know it. With the help of advanced technologies, these complex molecules can also reveal the secrets of people and creatures that came long before us. Scientists have studied DNA preserved within an array of centuries-old relics, from human remains, to fossilized rodents’ nests, to the pages of medieval manuscripts. Here are eight objects that have undergone DNA testing and yielded fascinating revelations about the history of life on Earth.
1. Old Chewing Gum
Thousands of years ago, ancient peoples in Scandinavia chomped down on birch pitch, a gooey substance that is produced by heating the bark of birch trees. This gum was used as an adhesive for crafting and repairing tools and, possibly, as a treatment for dental maladies, since birch has antiseptic properties. Scientists were recently able to sequence a complete human genome from a piece of birch pitch that was chewed up and spat out in southern Denmark around 5700 years ago.
The chewer was female, with dark skin, dark hair, and blue eyes. Like Ötzi, she may have had trouble digesting dairy. Also trapped within the gum was genetic material from one of her recent meals—duck and hazelnuts—along with DNA from the bacteria and viruses she harbored in her mouth. The study showed just how valuable birch pitch can be to researchers, particularly when it comes to ancient eras from which few human bones survive; by extracting DNA from just one little lump of discarded gum, scientists were able to glean a wealth of information about the appearance, diet, and health of a female hunter-gatherer.
In 1996, an urban development project in Namur, Belgium, led to the discovery of an archaeological treasure: a series of latrines containing barrels filled with 700-year-old human poop. By sequencing the genomes of viruses inside the fossilized feces—or coprolites, if we’re being scientific about it—researchers were able to gain new insights into the gut health of medieval defecators. Their poop, in fact, had a greater diversity of genes that may protect gut bacteria from antibiotics and toxic compounds, suggesting that our guts have become less hardy with the advent of food and water sanitation.
Because feces are filled with microbes, they tend to decompose quickly. But when coprolites do crop up in the fossil record, they can tell fascinating stories about the people, animals, and other creatures that once populated the planet. This past summer, the oldest-known parasite DNA was documented in puma poop that had been deposited in the Andes 17,000 years ago. The big cat did its business several thousand years before humans arrived in the region, disproving the theory that Toxascaris leonina—a type of parasitic roundworm—first infiltrated the intestines of carnivores in the Americas through contact with humans and their domesticated dogs and cats.
3. Illuminated Manuscripts
Historians typically value centuries-old manuscripts for their words and beautiful illustrations—but recent research has shown that these precious texts can also be treasure troves of DNA. Scribes of yesteryear often wrote on parchment made from the skin of animals, and conservators will periodically clean manuscript parchment with rubber erasers. A team led by Matthew Collins of the University of Cambridge and the University of Copenhagen collected debris that had been rubbed off from the York Gospels, a religious text believed to have been written around 1000 years ago in England, and studied them using high-tech methods of genetic analysis.
The scientists found that the parchment had been made largely from the skin of female calves—a curious discovery, given that breeders would have wanted female calves to mature and give birth to more offspring. It is possible, the researchers suggest, that the calves died in an outbreak of cattle plague known to have hit the British Isles in the late 900s CE. And it was not just animals that left their mark on the York Gospels; pages containing oaths were especially rife with human microbial DNA, likely because they were frequently handled and kissed by clergymen.
4. Human Bones
Skeletal remains provide our most direct link to the planet’s past inhabitants. Experts can glean a wealth of information about an individual’s age, sex, and health condition just by looking at bones, but advances in the analysis of DNA preserved within skeletons are opening up important new pathways of discovery. It was, for example, a genetic study that helped resolve a long and bitter conflict over Kennewick Man, one of the oldest and most complete skeletons ever found in North America. After the discovery of the 9000-year-old remains, a coalition of Native American tribes and bands demanded that the bones be returned to them for a ritual burial; some scientists, however, argued that Kennewick Man could not be definitively linked to living tribes. In 2015, an analysis of DNA obtained from the skeleton’s hand bone proved that Kennewick Man was indeed genetically Native American. Two years later, his bones were retrieved by members of five tribes and laid to rest.
DNA also played a crucial role in helping experts identify the bones of Richard III, which were unearthed beneath a city parking lot in Leicester, England in 2012. The clincher in this archaeological case was mitochondrial DNA (mtDNA), which is passed down from mother to child. By painstakingly tracing an all-female line through Richard III’s family tree, researchers were able to match the mtDNA of two living descendants to the skeleton’s mtDNA—indicating that the remains did indeed belong to the notorious king.
5. Rodent Middens
Like their modern counterparts, rodents of millennia past were resourceful nest builders. They collected bits and pieces from their surroundings and sealed the hodgepodge together with their urine, which in turn acts as a binder that has preserved rodent abodes for tens of thousands of years. Packed with plants, insect parts, bones, feces, and other materials, these nests—or middens—offer a snapshot of the local environment at the time when a nest was built. Middens also contain DNA, which scientists have been able to analyze.
One discovery came from a cave in southwestern Argentina, where experts found “a unique dung deposit” inside a midden left behind by vizcacha, a type of rodent belonging to the Chinchillidae family. Mitochondrial DNA showed that the dung came from an extinct ground sloth that once roamed through the region. In a more recent and broader study, scientists randomly sequenced DNA fragments from 25 packrat midden samples, ranging in age from 300 to 48,000 years old. The researchers found genetic evidence of everything from bacteria to insects to roses, allowing them to gain new insights into ancient ecosystems.
6. and 7. Teeth and Dental Plaque
Because the enamel that coats our teeth is 97 percent mineral, human chompers are sturdier than bone and more likely to survive in the archaeological record. DNA sequences sourced from our ancient ancestors’ teeth have been critical to experts’ understanding of the human family tree. In 2010, for instance, genetic material from a wisdom tooth discovered in Siberia helped scientists identify the Denisovans, a little-known group that shared a common ancestor with both Neanderthals and Homo sapiens.
If a tooth is coated in plaque, all the better (though a dentist might disagree). When it isn’t cleaned away by diligent brushing, plaque hardens into a substance known as calculus, which starts to fossilize while we’re still alive. The gunk traps food, bacteria, and DNA—about 25 times more DNA than bone or teeth themselves. In 2017, scientists announced that they had sequenced the genome of a microbe stuck in Neanderthal plaque. That microbe, Methanobrevibacter oralis, seems to have been swapped between Neanderthals and anatomically modern humans, suggesting that the two were prone to smooching.
Ancient Egyptians took great care to preserve the bodies of their dead, yet scientists once struggled to extract DNA from mummified remains. It was believed that Egypt’s scorching climate, and possibly the embalming process, destroyed genetic material—but the application of new sequencing techniques has shown that DNA does in fact survive in the bones and teeth of ancient mummies. For instance, genetic material sourced from the molars of two mummies that were entombed side by side suggested that the deceased were half-brothers; they shared the same mother, but likely had different dads.
Hailing from a much colder part of the globe is one of the world’s most famous mummies: Ötzi the Iceman, who was murdered and died in the Italian Alps some 5300 years ago. Ötzi’s body was naturally mummified by the frigid climate, and genetic material from his pelvic bone helped scientists create a near-complete sequence of his DNA, revealing that the “Iceman” may have had brown eyes, lactose intolerance, and a genetic predisposition to heart disease. Researchers have also tracked down some of Ötzi’s very distant, living relatives; 19 people in Austria were found to share a unique genetic mutation with the ancient mummy.
9. Edible Plants
Certain fruit, vegetables, and grains have made long journeys from their wild origins to modern plates, and DNA analysis can help scientists trace convoluted paths of crop domestication. The evolution of corn, for instance, began about 9000 years ago in Mexico, when farmers began selecting for favorable traits of a small, tough plant called teosinte. But by looking at the DNA of 11 ancient plants, along with the genomes of 100 varieties of modern maize, researchers discovered that "proto-corn" was carried to South America before the domestication process was complete, with the final stages occurring independently in multiple locations.
Watermelon leaves discovered in a 3500-year-old Egyptian tomb had a similarly fascinating story to tell. In contrast to their domesticated cousins, wild watermelons are not particularly palatable; their flesh is white and bitter. But a partial genome sequence of the ancient leaves showed that a gene dictating this bitter flavor had been disabled, as had a gene that sees the red pigment lycopene converted to another substance. In other words, watermelons were domesticated by at least 3500 years ago—and ancient Egyptians were snacking on sweet, red fruits very like the ones we know today.