As these GEITP pages have often described, modern human (Homo sapiens) migrated out of southeast Africa during the past 1-2 million years. Neanderthals (Homo neanderthalensis), Denisovans (Homo denisova), modern humans, and one other (still a mystery) hominin subline most likely have evolved from Homo erectus, an ancestor that left Africa ~1.8 million years ago (MYA). Increasing data have suggested that interbreeding between various hominin species had occurred (i.e. there were no “clean” “splits” of one subline from another). Numerous “molecular clock” genetic studies place divergence time of the Neanderthal and Denisovan lineages between 800,000 and 400,000 years ago, with modern human diverging from the Neanderthal/Denisovan ancester before those two sublines had become distinct. The genome of modern humans is known to contain bits and pieces (2% to 6%) of both the Neanderthal and Denisovan genomes.
The exciting publication that has just appeared [see attached] describes a female (who lived “only” ~90,000 years ago) who was half-Neanderthal and half-Denisovan, according to genome analysis of a single bone fragment recovered from Denisova Cave in the Altai Mountains of Russia. This is the first time that scientists have identified an ancient individual who was clearly “a hybrid” (i.e. parents belonged to two distinct human sublines)!! The Denisova Cave lends its name to the “Denisovans”, where DNA sequence of a bone in 2oo8 first identified that hominin subline. The Altai region, and the cave specifically, were also home to Neanderthals.
Given the patterns of genetic variation in ancient and modern humans, scientists already knew that Denisovans and Neanderthals must have bred with each other — and with Homo sapiens (See ‘Tangled tree’ p 418 of attached editorial). Until now, however, no one had previously found a first-generation offspring from such pairings –– although one study [Nature 2015; 524: 216] found the DNA of a Homo sapiens specimen who had a Neanderthal ancestor within the previous four to six generations.
Authors [see attached] show that the father’s genome bears traces of Neanderthal ancestry, derived from a population related to a later Denisovan found in the cave. The mother came from a population more closely related to Neanderthals who lived later in Europe –– than to an earlier Neanderthal found in Denisova Cave. These findings suggest that migrations of Neanderthals between eastern and western Eurasia had occurred sometime more recent than 120,000 years ago. Neanderthals and Denisovans inhabited Eurasia until they were replaced by modern humans ~30,000 years ago. Neanderthal remains have been found in western Eurasia, whereas, thus far, physical remains of Denisovans have been found only in Denisova Cave, where Neanderthal remains have also been recovered.
Although little is known about the morphology of Denisovans, their molar teeth lack the derived traits typical of Neanderthals. It has also been shown that Neanderthals mixed with ancestors of present-day non-Africans ~60,000 years ago, and possibly with earlier ancestors of modern humans. Furthermore, it is known that Denisovans interbred with the ancestors of present-day Oceanians and Asians. [In conclusion, back in those days, there seemed to have been a lot of ‘messing-around’ going on.] Finally, Denisovans appear to have received genes from at least one additional archaic hominin (i.e. one other subline that remains a mystery) –– which diverged more than a million years ago from the modern human, Denisovan, and Neanderthal sublines.
Nature 23 Aug 2o18; 560: https://doi.org/10.1038/s41586-018-0455-x and Editorial pp 417–418