Neanderthals appear to carry the same derived variants of FOXP2 as modern humans, suggesting that they shared some of the genetic prerequisites for speech.

But the genetic and anatomical evidence for speech capability does not prove the existence of complex language.

The question of whether Neanderthals and Denisovans had language in the modern human sense — with the full combinatorial grammar, the open-ended productivity, the referential semantics that characterize modern languages — remains open.

What Denny adds to this question, indirectly, is evidence of social contact sufficient for interbreeding.

If Neanderthals and Denisovans produced children together, their encounters involved some form of mutual recognition and social negotiation.