The Denisovans occupied — we think — a range that extended across the central and eastern regions of Asia, from the Altai Mountains southward toward what is now Southeast Asia.

In the middle, in the crossroads territory of the Altai Mountains, these two worlds overlapped.

How often they overlapped, how much contact the two groups had, whether their encounters were typically peaceful or hostile, whether interbreeding was common or rare — all of these remain uncertain.

Denny tells us only that it happened once, at least, with sufficient intimacy to produce a child.

And that child lived long enough to leave bones in a cave that would, 90,000 years later, be excavated by archaeologists who had no idea what they were finding.