The evolution of modern homo sapiens may be even more complicated than originally thought. During recent studies of our genome, scientists have come across what they call “Ghost DNA”, or evidence that what we consider to be modern humans mated with a yet-to-be-identified offshoot of our species.
While the moniker of Ghost DNA sounds spooky - it’s actually just a benign placeholder. When studying the genome, the scientists employed a statistical model (dust off your TI-83 graphing calculator) to pull out portions of DNA that were thought to come from populations other than the modern human. They discovered that these chunks were not from the usual culprits - Neanderthals and Denisovans - but from an unidentified species. This isn’t super shocking in the scientific community - experts have known for a while that our ancestors got freaky with Neanderthals and Denisovans. The evidence of both can be found in traces of our DNA today. In fact, all humans carry some trace of Neanderthal DNA to varying degrees.
The group responsible for our ‘ghost DNA’ does not appear to be closely related to the sequencing found in Neanderthals and Denisovans, but rather an archaic branch of hominin that likely split from us roughly 800,000 to 1,000,000 years ago, according to the study published by geneticists Sriram Sankararaman and Arun Durvasula,
So what does this all mean? Well, there is still work to be done to accurately piece together the full picture of our evolution. The hypothesis is based on results of a statistical model, and more studies will need to be done to prove its validity. One way to do this requires obtaining and extracting DNA from fossils, but time, weather and erosion means the material has likely deteriorated by now.
Image by Joannes Plenio