The old image of Neanderthals as dim, stooped brutes shuffling through a dimly lit past has been replaced, through decades of research, with a more complex picture: a capable, culturally active human group that occupied a wide range for a very long time, adapted to challenging environments, and—as DNA evidence has since established—interbred with other human groups, including our own ancestors.
Modern humans outside of Africa carry approximately 1 to 2 percent Neanderthal DNA as a result of interbreeding that occurred after modern humans began dispersing out of Africa. This proportion is the residue of real reproductive encounters between real individuals—encounters that happened repeatedly enough to leave a measurable genetic signature that persists in the genomes of billions of people today.
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## Who the Denisovans Were
The Denisovans are harder to describe, for the simple reason that almost no physical evidence survives. What is known about them comes primarily from their DNA—their own ancient genome and the genetic traces they left in the populations they interbred with.
Genetically, Denisovans were more closely related to Neanderthals than to modern humans. The two groups shared a common ancestor that split from the lineage leading to modern humans somewhere between 550,000 and 750,000 years ago. Neanderthals and Denisovans then diverged from each other sometime between 400,000 and 500,000 years ago.
This divergence was geographic as well as evolutionary. The current understanding, based on genetic evidence, is that a population ancestral to both groups left Africa and then split: the western branch became Neanderthals, spreading through Europe and western Asia; the eastern branch became Denisovans, spreading through Central Asia and into Southeast Asia and beyond.