In 2010, the human story became a bit more complicated when researchers reported that they had extracted the genome sequence from a finger bone found in Denisova Cave in southern Siberia. The bone belonged to an enigmatic new hominin group designated the Denisovans.
Sequencing showed that Denisovans were close cousins to Neanderthals: the two species are both known to have lived in the environs of Denisova, and even interbred. And, just as many modern Eurasian genomes have a sprinkling of Neanderthal genomes, the Denisovan legacy lives on as a light dusting in the genomes of several modern human populations in southeast Asia and Australasia.
But the origins and appearance of Denisovans remains a pressing mystery in human evolution. Until now, this species was known only from teeth, the finger bone and assorted nondescript fragments, all found in the Siberian cave.
Nature this week reveals the first Denisovan remains found in a different part of the world — a partial jawbone from a cave on the Tibetan Plateau (F. Chen et al. Nature https://doi.org/10.1038/s41586-019-1139-x; 2019). Although discovered in 1980, the jawbone remained in limbo until further work at the site, along with radiometric dating and proteomics studies, could shed light on the life and times of its owner. The dating places it at around 160,000 years old; the proteomics allies it with the Denisovans.
One of the most notable contributions of the Denisovan genome to humanity is an allele of a gene involved in adaptation to low oxygen that allows today’s Tibetans and the Sherpa people to live at high altitude more comfortably than many other people. When discovered, this seemed odd, because modern humans did not penetrate the region until 40,000 years ago at the earliest, and the same allele is found in modern populations living much farther down. Denisova Cave itself is a relatively modest 700 metres above sea level.
The newly described jaw, however, was found at the more challenging altitude of 3,280 metres, and has a robust build and large size — bigger than the jawbones of modern humans — to go with its extreme habitat. This makes it likely that Denisovans evolved from a common ancestor with Neanderthals that made its home on the Roof of the World and adapted to life at high altitude, before coming down again.
The find is also important because it’s the first physical remnant of this species larger than a single tooth or bone. This could allow comparison with a number of hominin skulls from China, whose place in the general sweep of the human story has been unclear. In China, the skulls are generally regarded as representing very early forms of Homo sapiens, a view increasingly at odds with evidence of migration and admixture from other parts of the world.
On hearing the news of a burly, robust hominin specialized for a cold, high-altitude life, one might just be forgiven for wondering whether the find is the first credible evidence of the yeti or Abominable Snowman (given that all other evidence has proved illusory: B. C. Sykes et al. Proc. R. Soc. B 281, 20140161; 2014). And last month, Nature published the discovery of a short-statured hominin species whose remains were found in a Philippine cave, reminiscent of the diminutive ‘Hobbit’ from Flores.
Some might be tempted to wonder whether the next revelations will include creatures reminiscent of giants, mermaids, centaurs or other mythological beings. But that is fancy. All we can say with certainty is that our understanding of the diversity of human form in the very recent past has increased once again, and that the mysterious Denisovans have at last come in from the cold.