An article published in the journal “PLOS Genetics” reports a genetic study showing the traces of various interbreedings between different species of hominins. Melissa Hubisz and Amy Williams of Cornell University and Adam Siepel of Cold Spring Harbor Laboratory developed a genetic analysis software that can recognize relations and applied it to a group of genomes that includes two Neanderthals, a Denisovan, and two African modern humans. The result is evidence that 3% of Neanderthal DNA came from ancient humans in an interbreeding between 200,000 and 300,000 years ago, 1% of Denisovan DNA came from an older species, maybe Homo erectus, and 15% of that “superarchaic” DNA may have been passed on to modern humans.
Paleogenetics, the application of genetic techniques to extinct species, is offering information on the history of humanity that reveals its complexity. Each new success in the sequencing, even partial, of a Neanderthal or a Denisovan DNA and their comparison with the genomes of modern humans brings new evidence of the interbreedings that occurred between the various species. These hominins are considered separate species, but genetic analyzes show beyond doubt that they were genetically compatible, so much so that modern humans are largely the result of such interbreedings.
This research shows the genetic traces of some of these interbreedings between species, including one with an unknown species. It could be Homo erectus, but we don’t have any bones of individuals of this species preserved to the point that we still have DNA to sequence, so geneticists have no way of verifying it. It could be the same species identified in another genetic research whose results were published in February 2020 in the journal “Science Advances”.
The researchers developed an algorithm called ARGweaver-D to analyze the genomes of individuals belonging to different hominin species. They applied it to a group of genomes that includes two Neanderthals, a Denisovan, and two African modern humans with really interesting results because they indicate genetic traces of unknown migrations.
The image (Courtesy Hubisz et al. Https://doi.org/10.1371/journal.pgen.1008895.g003) illustrates the population model used in the research. Population sizes are estimated in the parentheses. At the base, there are chimpanzees as a reference, superarchaics, Denisovans, Neanderthals, and modern humans. The graph shows ancient humans and generic hominin populations.
Neanderthal genes are widespread among modern humans, particularly Europeans, but this research showed that Neanderthals also inherited genes from ancient humans between 200,000 and 300,000 years ago. This suggests that there was already a migration of a population of early Homo sapiens of which only this genetic trace remains.
What is perhaps the most intriguing discovery is the presence in the DNA of the Denisovans of genes from another species of hominins defined as superarchaic. The divergence between those two species may have occurred about a million years ago, but it’s a rough estimate. 1% of Denisovan DNA consists of genes inherited from this species, which remains unknown even though Homo erectus is the main suspect. A further interbreeding, between Denisovans and Homo sapiens, resulted in the passage of some superarchaic genes into modern humans.
The limited amount of Denisovan genomes available makes it difficult to estimate with a good approximation the amount of genes that they inherited from the superarchaics and that they subsequently passed on to Homo sapiens. According to the researchers, it may be possible to identify other genes of that species by applying ARGweaver-D to a group of 161 genomes of native Oceanian, modern humans who inherited genes from the Denisovans.
Waiting for new details, the complex history of humanity is confirmed yet again. It’s a history made up of migrations and interbreedings between various populations that increasingly shows that the concept of human being is broader than we thought just a few decades ago.
