When archaic hominids lived for a long time in special environments, they naturally developed genetic adaptations to those environments, and since such adaptive alleles are easily transmitted, requiring only a smidgen of gene flow, it’s not surprising to see some of the beneficial archaic alleles in modern humans living in such environments. So archaic altitude-adaptation alleles were likely in modern Tibetans, and have apparently been found. They likely exist in Ethiopians, particularly since their altitude adaptations work so well, as do those of Tibetans.

It looks as if there is a specific suite of changes that is favored when living in dense tropical jungles – being some kind of Pygmy. We know that this has happened repeatedly (Pygmies, various Negritos). Perhaps archaic humans lived in and adapted to that niche – they certainly had plenty of time to do so. If so, we may expect to find archaic-origin adaptive alleles in those groups. There are already indications of of gene flow into Pygmies (and Bushmen) from an unknown but highly divergent archaic lineage. Perhaps there were Pygmy versions of Denisovans or advanced erectus in Sundaland, which could then have contributed alleles to modern Negrito groups.