An article published in the journal “Nature Ecology & Evolution” describes a research on the number of interbreedings between Homo sapiens and Neanderthals. Fernando A. Villanea and Joshua G. Schraiber of the Temple University offered evidence to support the thesis of multiple interbreedings. Fabrizio Mafessoni of the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) in Leipzig, Germany, published in the same journal a commentary on that research, pointing out that this thesis is in agreement with the increasing evidence of interbreedings between different hominids.
The reconstruction of the origins and evolution of Homo sapiens but also of other hominins has been made more complex after advances in genetic research showed that modern humans possess a certain amount of genes inherited from other species. In particular, non-African humans have about 2% or more genes inherited from Neanderthals. Some ethnic groups possess genes inherited from another species, the Denisovans, and other genetic traces suggest other ancient interbreedings.
Neanderthal genes are definitely the most abundant and widespread among modern humans and their discovery stimulated new research on the possible interbreedings between the two species. This also means reconstructing the migrations of the various populations to understand when and how many times they may have met. Neanderthals had lived in Europe and Eastern Asia for a long time when groups of Homo sapiens started migrating from Africa and meeting them.
To try to better understand the interbreedings between the two species, Fernando A. Villanea and Joshua G. Schraiber analyzed data collected during the 1000 Genomes Project which, launched in 2008, was an international study with the aim of creating the most complete catalog of human genetic variants. Asian individuals have on average more Neanderthal genes than Europeans, a result that confirms previous research.
The study of those genomes also used simulations to try to understand how DNA could have been shared following that kind of interbreedings. The models obtained, also thanks to the use of machine learning software to analyze the data, indicate that there were several interbreedings between modern humans and Neanderthals. Probably in different periods some populations of the two species met and interbred.
One problem with this reconstruction is that the models are based on a neutrality of the genes inherited from the Neanderthals. Actually part of those genes were likely deleterious and an article published in November 2016 in the journal “PLOS Genetics” described a research on genes in non-African modern humans inherited from Neanderthals, concluding that only a small amount of them remained in the DNA of modern humans.
Another problem is that it’s possible that some genes that were attributed to Neanderthals were inherited from Denisovans, another species of hominins with which both Homo sapiens and Neanderthals have in turn interbred. This complexity of interbreedings was emphasized by Fabrizio Mafessoni in his article. In essence, this research offers new details on a part of the complex history of the human species, made of migrations with many meetings between populations of different species whose progeny left in our DNA traces that we are slowly reconstructing.