An article published in the journal “Science Advances” reports the traces of an interbreeding between the ancestors of Neanderthals and Denisovans with a population belonging to another species of hominins called superarchaics because they probably separated from other humans about 2 million years ago. A team of researchers led by anthropologist Alan Rogers studied the ways in which mutations are shared between various populations of Homo sapiens, Neanderthals and Denisovans, concluding that certain sharing patterns indicate that there were five episodes of interbreeding between species including the one occurred over 700,000 years ago between superarchaic hominins and ancestors of Neanderthals and Denisovans.
In recent years, advances in genetic techniques made it possible to obtain DNA from well-preserved Neanderthal and Denisovan bones, offering the possibility of conducting genetic comparisons between these species of hominins and Homo sapiens. The consequence has been the progressive reconstruction of migrations and interbreedings between different species that keep on offering new surprises because some mysteries still remain. Professor Alan Rogers of the University of Utah previously directed a study published in September 2017 in the journal “PNAS” concerning the initial part of Neanderthal and Denisovan history but two other anthropologists, Fabrizio Mafessoni and Kay Prüfer, obtained different results from similar studies. The new study led by Alan Rogers could resolve the controversy.
The researchers studied the ways in which mutations are shared among various populations of Homo sapiens, Neanderthal and Denisovans. They got a sharing pattern which implies that there were five episodes of interbreedings including one that was previously unknown. According to the reconstruction, this new discovered interbreeding occurred over 700,000 years ago between a hominin population that was called superarchaic that separated from other humans about two million years ago and the ancestors of Neanderthals and Denisovans.
So far, evidence of interbreedings concerned species that separated relatively recently, for example Homo sapiens and Neanderthal separated since about 750,000 years when they interbred. The relationship with the superarchaic hominins is more distant since at the time of their interbreeding they had separated from the ancestors of Neanderthal and Denisovans for well over a million years.
The image (Courtesy Alan Rogers et al. All rights reserved) shows an evolutionary tree that includes four episodes of genetic flow between species. The interbreeding that wasn’t known is the one indicated in orange dating back to a time estimated at 744,372 years ago.
Using also the traces of the various interbreedings, the researchers proposed three waves of migrations to Eurasia from Africa. The first wave occurred two million years ago by the superarchaics. 700,000 years ago the ancestors of Neanderthal and Denisovans migrated and interbred with the superarchaics. Homo sapiens migrated to Eurasia about 50,000 years ago and interbred with other hominins.
This type of study must be analyzed to verify compatibility with other estimates and possibly try to understand the reasons for inconsistencies with other datings. For example, another article recently published in the journal “Science Advances” reports a genetic research that offers evidence that some West African populations inherited a portion of their genes from an unknown species of hominins. Are those the superarchaics or yet another species?
If it were possible to obtain DNA from bones of Homo erectus and Homo heidelbergensis, two more ancient species that could have interbred with other hominins, the research could make a leap forward. For now, genetic studies of modern humans, Neanderthal and Denisovans increasingly show the complex genetic history of Homo sapiens.