They turned out to be genetically very different from both the ancient farmers who replaced them and the modern Europeans who eventually descended from the mixture of the two.

Their existence was not predicted by the modern genetic landscape.

The Denisovans — a sister group to Neanderthals, known primarily from a single finger bone and a few teeth found in Denisova Cave in the Altai region of Siberia — have contributed genetic material to modern humans in Southeast Asia and the Pacific.

Their existence was entirely unknown before ancient DNA sequencing of those small fragments.

The Ancient North Eurasians, represented by the Mal’ta Boy from Lake Baikal, contributed a significant component of ancestry to both modern Europeans and Native Americans — a connection that was entirely unexpected and that required substantial revision of models of both European and American population history.