Denny is what she is.

And what she is proves, beyond any remaining doubt, that Neanderthals and Denisovans could mate and produce offspring — offspring that were, at minimum, viable enough to survive to adolescence.

The biological barrier between these two ancient human groups, whatever form it took, was not absolute.

They were not separated by the kind of profound reproductive incompatibility that characterizes species like horses and rhinos.

They were different enough to be called different species by the working conventions of paleoanthropology, but not different enough to prevent their children from existing.