LMore than a decade ago, American anthropologist James C. Scott described infectious diseases as “the loudest silence” in the prehistoric archaeological record. The pandemic must have devastated human society and changed the course of history in the distant past, but Scott laments that the artifacts left behind reveal nothing about them.
In the past few years, groundbreaking research analyzing microbial DNA extracted from very ancient human bones has broken the silence. The latest example is groundbreaking research that discovered three viruses in Neanderthal bones from 50,000 years ago. These pathogens still plague modern humans: Adenoviruses, herpesviruses, and papillomaviruses cause the common cold, cold sores, genital warts, and cancer, respectively. The discovery may help us unravel one of the greatest mysteries of the Paleolithic: what caused the Neanderthals to go extinct.
Recent advances in techniques for extracting and analyzing ancient DNA have given us incredible insights into the ancient world. Time travel aside, it’s hard to think of a technology that could so profoundly change our understanding of prehistory.
The first major advance in the ancient DNA revolution came with human genetic material. A study analyzing DNA from cemeteries across Britain has revealed that Stonehenge was built by dark-haired, olive-skinned farmers from modern-day Turkey, whose descendants became extinct centuries after the stone was built.
When a team led by Nobel Prize winner Svante Pääbo sequenced the Neanderthal genome, they realized that modern humans with European, Asian or Native American ancestry inherited about 2% of their genes from Neanderthals. Then, during the pandemic, it was discovered that several Neanderthal genetic variants that are particularly common in South Asians affected the immune response to the novel coronavirus, making carriers more likely to suffer severe illness and death. It’s crazy to think that an interspecies tryst that happened tens of thousands of years ago could affect the health of humans today.
When scientists extracted human DNA from human bones, they also extracted traces of microbes in the blood at the time of death. Some of the most interesting research in this area focuses on Yersinia pestis, the bacterium that causes plague. Not so long ago, the oldest evidence of Yersinia pestis came from the mid-14th century, when the Black Death killed about 60 percent of Europe’s population.
We now know that plagues date back much further. Between 4,000 and 5,000 years ago it was widespread across Europe and Asia, including Somerset and Cumbria, a recent study suggests. Around this time, the population of northwestern Europe declined by as much as 60%. The “Neolithic Black Death” likely led to a population collapse, at the same time as the farmers who built Stonehenge disappeared from Britain and the arrival of another group that contributed most to the DNA of modern Britain.
Ancient microbial DNA also provides tantalizing insights into the private lives of our distant ancestors.
Scientists have discovered Methanobrevibacter oralis, a bacteria-like organism associated with gum disease in modern humans, in the calcified plaque of 50,000-year-old Neanderthal teeth. By comparing prehistoric strains with contemporary strains, the researchers calculated that their last common ancestor lived about 120,000 years ago. Since this was hundreds of years after the divergence of Neanderthals and Homo sapiens, the bacteria must have spread between species. The most likely way this happens is through interspecies kissing.
Extracting and analyzing viral DNA from ancient bones is technically challenging. Because viruses are much smaller than bacteria, they contain less genetic material, and because they are less stable, they degrade faster. That’s what makes the recent news that scientists have sequenced the DNA of a 50,000-year-old virus so exciting.
While the discovery that Neanderthals were infected with adenoviruses, herpesviruses, and papillomaviruses will not in itself change our understanding of the distant past, it hints at solutions to the great paleolithic mysteries.
Until about 70,000 years ago, Homo sapiens lived in Africa, while Neanderthals lived in western Eurasia. Then everything changed. Our ancestors migrated north, quickly spreading throughout much of the world. Soon after, the Neanderthals disappeared.
At the end of the 19th century, when the German zoologist Ernst Haeckel proposed calling Neanderthals “Homo sapiens” to distinguish them from “Homo sapiens”, there has been a lot of interest in Neanderthals. The leading explanation for this shift is that our ancestors used their superior cognitive abilities to outcompete other human species. However, this argument is becoming increasingly clear as evidence mounts that Neanderthals were capable of a variety of complex behaviors, including burying their dead, painting cave walls, using medicinal plants, and sailing between Mediterranean islands. It is becoming increasingly untenable.
The discovery of viruses from 50,000 years ago provides another explanation for the demise of Neanderthals: deadly infectious diseases carried by Homo sapiens. After more than half a million years of separation, the two species have evolved immunity to different infectious diseases. When Homo sapiens encountered each other during their migrations from Africa, pathogens that caused harmless symptoms in one species could be lethal to another, and vice versa.
The reason why Homo sapiens survived and Neanderthals disappeared is simple. Our ancestors lived close to the equator. As more solar energy reaches Earth, plant life becomes more abundant there. This provides habitat for more dense and diverse animal life, which in turn supports more microorganisms capable of crossing species barriers and infecting humans. As a result, Paleolithic Homo sapiens harbored more deadly pathogens than Neanderthals.
The ancient DNA revolution not only transformed our understanding of prehistory, but also has important consequences for the present. If infectious diseases played such a key role in the demise of Neanderthals and the domination of the world by Homo sapiens, then the pathogens were far more powerful than we thought. Our ancestors had bacteria on them 50,000 years ago, but we may not be so lucky in the future.
