A pair of Temple University researchers have found evidence to suggest that Neanderthals have mated and produced offspring with anatomically modern humans several times – not just once, as suggested by previous research. In his article published in the journal Ecology and Evolution of Nature, Fernando Villanea and Joshua Schraiber describe their genetic analysis of the people of East Asia and Europe and how they compare to people from other places. Fabrizio Mafessoni, from the Max Planck Institute for Evolutionary Anthropology, offers an article on News and Visions about the work done by the duo in the same issue of the magazine.
In recent years, scientists have discovered that the first humans leaving Africa found Neanderthals living in parts of what is now Europe and East Asia. When comparing Neanderthal DNA with modern humans, the researchers found that there was at least one pair that led to offspring, which is reflected in the DNA of humans – approximately 2% of the DNA in non-African humans today is Neanderthal. In this new effort, researchers have found evidence to suggest that there have been more than one such encounter.
Their findings make logical sense, considering that anatomically modern humans and Neanderthals coexisted for approximately 30,000 years. Recent research from other groups has suggested that a number of descendant-producing unions had taken place – some people in East Asia, for example, had up to 20% more Neanderthal DNA than people of strictly European descent. In this new effort, the researchers took a closer look to find out once and for all whether there were multiple pairs or just one. They collected and analyzed data from the 1000 Genome Project, measuring the amount of Neanderthal DNA in the genetic material of volunteers. The first step was to separate the data between people of European and Asian descent. This suggested that the two groups had evidence of several initial mating events. The researchers then studied the rates of the two groups, creating simulations showing results of different numbers of mating events between the two groups. Simulation data were then introduced into a machine learning algorithm that showed percentage DNA patterns based on the number of crossover events that occurred.
The researchers concluded that the most likely scenario was that there were multiple instances of crossing between the first humans in East Asia and Europe with the Neanderthals.
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Fabrizio Mafessoni. Encounters with archaic hominins, Nature Ecology and Evolution (2018) DOI: 10.1038 / s41559-018-0729-6
Fernando A. Villanea et al. Multiple episodes of crosses between Neanderthals and modern humans Nature Ecology and Evolution (2018) DOI: 10.1038 / s41559-018-0735-8