Last week the journal Nature reported additional data supporting the astonishing idea that a previously unidentified hominid lived among us up until at least 30,000 years ago. The data were recovered from Denisova Cave, in the Altai Mountains of Siberia. The new data include DNA analysis of a finger bone reported earlier, mtDNA analysis on a tooth from a different individual, and a search of modern gene data for descendant remnants.
Exterior view, Denisova Cave
Photo Credit: Bence Viola
You may remember that in March 2010, Svante Pääbo and associates described the initial mtDNA analysis of a small finger bone. The finger bone was from a child, and it dated to approximately 30-45,000 years ago. Most astonishingly, the bone's mtDNA profile did not match either Early Modern Human (EMH--that's our direct ancestor) or Neanderthals, the two hominids that, up until March, we believed were the two dominant hominids on the planet at the time.
The latest information comes from regular DNA (not mitochondrial) and the team has identified that the Denisovans (as scholars have decided to name them) and Neanderthals come from a common lineage. Data suggests that a small percentage of the modern genes of present-day Melanesians show some commonalities to the Denisovans, leading scholars to believe that the Denisovans may have been widespread over Asia.
Further, a tooth found at Denisova in 2000 from a young adult was analyzed, and its mtDNA also reflects the Denisovan pattern. The tooth is a large molar, and it is outside the normal size range for most members of the Homo family, and closest to Australopithecus in size. It is most definitely not a Neanderthal tooth. Scholars believe the young adult was part of the same hominid population as the child.
Morphology of the Denisova Molar. Image courtesy David Reich, Nature
All of the Denisovan remains are from Layer 11 at Denisova, and that's a bit of a problem. Radiocarbon dates from this layer suggest that there are at least two and perhaps more occupations in the same layer, one older than 50,000 (the upper limit of C14 dating) and one between 23,000-30,000 years ago. The phalanx and molar both appear to be from the earlier occupation.
Why didn't we know about them?
It may surprise you that there could have been a completely unrecognized species of human running around the planet as recently as 30,000 years ago that scientists were unaware of: but the truth of the matter is that there are inconsistencies which have been noted in the fossil record that simply never fit into the "neanderthal" or "early Homo sapiens" categories, inconsistencies that are potentially solvable with new genetic techniques.
So, welcome, Denisovans! (Are you really there?)
Reich D, Green RE, Kircher M, Krause J, Patterson N, Durand EY, Bence V, Briggs AW, Stenzel U, Johnson PLF et al. 2010. Genetic history of an archaic hominin group from Denisova Cave in Siberia. Nature 468:1053-1060.
Best of the News Stories
- The old man of the mountain, The Economist
- Bone May Reveal a New Human Group, Nicholas Wade in the NYT
- Siberian Fossils Were Neanderthals' Eastern Cousins, DNA Reveals, Carl Zimmer, NYT
- New Type of Ancient Human Found--Descendants Live Today? , Ker Than, National Geographic
- Ancient humans, dubbed 'Denisovans', interbred with us, BBC News
- Chris Stringer: The tip of the iceberg in understanding of human history, The Independent
- The Denisova Genome FAQ, John Hawks