https://advances.sciencemag.org/cont...ay5483/tab-pdf

Neanderthal-Denisovan ancestors interbred with a distantly related hominin
Alan R. Rogers*, Nathan S. Harris and Alan A. Achenbach

Science Advances 20 Feb 2020: Vol. 6, no. 8, eaay5483 DOI: 10.1126/sciadv.aay5483

Previous research has shown that modern Eurasians interbred with their Neanderthal and Denisovan predecessors. We show here that hundreds of thousands of years earlier, the ancestors of Neanderthals and Denisovans interbred with their own Eurasian predecessors—members of a “superarchaic” population that separated from other humans about 2 million years ago. The superarchaic population was large, with an effective size between 20 and 50 thousand individuals. We confirm previous findings that (i) Denisovans also interbred with superarchaics, (ii) Neanderthals and Denisovans separated early in the middle Pleistocene, (iii) their ancestors endured a bottleneck of population size, and (iv) the Neanderthal population was large at first but then declined in size. We provide qualified support for the view that (v) Neanderthals interbred with the ancestors of modern humans.