Your DNA is haunted.
According to a new study published in Science, all modern humans carry ancient genetic sequences from so-called “ghost ancestors”—lineages of hominins that died out tens and hundreds of thousands of years ago.
A team of computational biologists and geneticists discovered the archaic sequences using a new technique that’s able to suss out the old from the new by analyzing only modern genomes. In tests, the new method correctly identified sequences from both Neanderthals and Denisovans—two ancient hominins humans interbred with and whose DNA has been preserved in fossil specimens. In this latest research, the team has turned its attention to far older sequences from archaic hominins whose DNA is lost to the ravages of time, but still lives on in us.
One of the ancient hominin species interbred with Homo sapiens prior to a major wave of our species leaving Africa, more than 50,000 years ago. This ghost ancestor contributed a decent chunk of DNA to the modern human genome, up to 1 percent of our genetic material (similar to the average amount of Neanderthal DNA we carry). And this genetic contribution is present in all of us.
The team also discovered a contribution in people from Oceania from what they term a “super-archaic” ancestor. This ancestor diverged from modern humans over 1.8 million years ago. “The super-archaic finding is particularly exciting because it reveals genetic contributions from a human lineage that lived over a million years ago, despite the absence of any sequenced DNA from that population,” study co-author Arjun Biddanda of Johns Hopkins University said in a statement.
Read more: “How Neanderthals Kept Our Ancestors Warm”
Who were these mysterious ghost ancestors?
The team says the more recent (and prevalent) contribution may be from Homo heidelbergensis. This mysterious hominin lived in Europe and Africa between 700,000 to 200,000 years ago, and might have been the last common ancestor of modern humans, Neanderthals, and Denisovans.
The “super-archaic” ancestor is likely Homo erectus, according to the team. The stretches of super-archaic DNA were found contained within Denisovan sequences, and a study of tooth enamel published earlier this year suggests the two hominins interbred. Basically, we may have Homo erectus DNA which found its way into Denisovans and then into modern humans living in Oceania.
Taken together, the findings paint a portrait of human evolution that was shaped more by interbreeding with our human ancestors than previously thought. “We often think of human evolution as a branching tree, but new genomic data and analytical methods reveal a much more interconnected history—more like a complex web of populations connected by repeated episodes of migration and mixing,” explained study co-author Priya Moorjani of the University of California, Berkeley.
As for what exactly these archaic genes are doing, they’re found in regions associated with the immune system and our metabolic functions, which the researchers say makes sense. “Adaptation to new pathogens and food sources has been one of the strongest selective pressures in human evolution,” Moorjani added. “Interbreeding with other human groups introduced new genetic variation, providing additional raw material for natural selection. Beneficial variants could then be retained and spread over many generations.”
And so, the next time you dodge a cold, maybe thank the ghosts of our ancestors.
Lead image: AntonKhrupinArt / Adobe Stock