By Bruce Bower
Ancestors of Neandertals and Denisovans left Africa for Eurasia around 700,000 years ago and then interbred with a Homo population that had exited Africa long before, according to a new genetic study. The finding reveals the oldest known case of interbreeding among members of the genus that includes people today, Homo sapiens.
Evidence of genetic exchanges between distinct hominid populations roughly 400,000 years before H. sapiens evolved highlights a role for interbreeding in Homo evolution long before ancient people occasionally mated with Neandertals and Denisovans.
The scenario begins with an early Homo species making its way into Eurasia roughly 1.9 million years ago, in what was probably the first Homo migration out of Africa, scientists report February 20 in Science Advances. Those now-extinct travelers may have been members of Homo erectus, a species that includes Eurasian fossils dating to about 1.8 million years ago (SN: 10/17/13), or Homo antecessor, a controversial species designation based on 1.2-million- to 1.1-million-year-old fossils found in Spain (SN: 3/26/08). Or they could have been part of another Homo population unknown from any fossils.
Then ancestors of Neandertals and Denisovans trekked out of Africa about 700,000 years ago, say the researchers, led by anthropologist and population geneticist Alan Rogers of the University of Utah in Salt Lake City. That timing would also have allowed for the evolution of Neandertals or their direct ancestors in what’s now northern Spain around 430,000 years ago (SN: 3/14/16). Some previous research had suggested that Neandertals originated roughly 300,000 years ago, raising questions about the evolutionary identity of older, Neandertal-like fossils in Spain.