What they did not expect — what no one expected — was that the cave had been home to not one ancient human species but two, and that those two species had apparently been present in the same location at periods that overlapped.

That discovery would take decades to fully emerge.

And it would begin, improbably, with a finger.

The Finger That Started Everything

In 2008, excavators at Denisova Cave recovered a tiny bone fragment from the cave’s sediments.

It came from the pinky finger of a small individual — just the tip of the bone, small enough to fit on a thumbnail.

Russian scientists working on the Denisova project sent the fragment to the laboratory of Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology in Leipzig.

Pääbo’s team had been working at the frontier of ancient DNA research for years, pioneering the methods that allowed scientists to extract and sequence genetic material from ancient, degraded bone.