Extensive fossil and DNA evidence from around the world has shown that extinct human species occasionally interbred when they encountered one another. Modern humans interbred with at least two other species — — which have left traces in our DNA to this day.
In contrast to the well-studied Neanderthals, the Denisovans are a poorly understood species known from only a handful of 50,000 to 160,000 year old fossils from . But have shown that Denisovans interbred with modern humans in Island Southeast Asia (ISEA), thousands of miles from where all known fossils were found.
There are plenty of fossils in ISEA, belonging to three distinct species: the well-traveled , and two endemic "super-archaic" species. The last of these species have a deep history in the region but around 50,000 years ago. This combination of super-archaic fossils and Denisovan DNA has complicated our understanding of the history of this region. To disentangle the genetic relationships among human species in ISEA, an international team of scientists of over 400 people from across the world, searching for segments that corresponded to both super-archaic and Denisovan DNA.
Surprisingly, they found no evidence that any of these super-archaic species interbred with modern humans, despite the wealth of fossils from the area. On the contrary, people with ancestry from ISEA, Papua New Guinea, and Australia had the largest amounts of Denisovan ancestry of all populations studied.
Finding genetic traces of Denisovans in an area of the world where they have yet to be found shows how little we know about the history of this region. While Denisovans appear anatomically distinct from the three super-archaic species of ISEA, it’s possible that they’ve been hiding in plain sight all along. There may also be Denisovan fossils still hidden across ISEA, waiting to be found. Either possibility will have major impacts on how we understand our own evolutionary history.