Before Denny, the evidence for Neanderthal-Denisovan interbreeding was inferential.

The genetic analysis of Denisova 5 — the Altai Neanderthal — had found a small but statistically significant signal of Denisovan ancestry, suggesting that there had been gene flow from Denisovans into Neanderthals at some point.

And analyses of the Denisovan genome had found evidence of some gene flow in the other direction — from Neanderthals into Denisovans.

But these were statistical signals in genomes that were primarily one thing or the other, with a small component attributable to ancient mixing.

Denny was something entirely different.