Unless you’ve been sleeping under a rock, you may have seen a new paper, A late Middle Pleistocene Denisovan mandible from the Tibetan Plateau. The reason it is a big deal is that except for a fragment of a skull reported on at a conference, this is the first remains outside of Denisova cave identified as “Denisovan.” Part of the identification was morphological. Both this find and those in Denisova cave, are characterized by very large teeth.
But the really interesting aspect is that they used analysis of proteins to place this sample phylogenetically. You can see the results above. Proteins don’t degrade as fast as DNA, from what I know, so this isn’t surprising. This individual, from high altitude Tibet, dated to at least 160,000 years ago, is in the same clade as the Denisovan that has been sequenced in the broader context of hominin evolution. This is not a rock-solid inference…there wasn’t that much informative variation (I believe Janet Kelso said on Twitter that one particular position where the Denisovan were derived compared to all other hominins in particular matched this paleo-Tibetan sample). But, if you had to guess, it does seem likely that this was an individual related to the Denisovans that we’ve come to know and love.
Finally, there is an important twist that the high altitude adaptation in Tibetans due to EPAS1 seems to have arrived from an introgressed haplotype from Denisovans. Perhaps then the introgression occurred 40 to 50 thousand years ago, as modern humans replaced Denisovans. The majority of the ancestry of Tibetans though seems to share rather recent Holocene origins with groups such as the Han Chinese. Therefore, rather than absorption of an old substrate in Tibet, it could be that you are looking at a variant widely found in the northern Denisovans.
I’ve been talking a lot about Denisovans recently. Why? It seems that the investigations prompted by the original surprise sequencing of 2010 are finally yielding results. But one thing that is clear is that our understanding of the origin of our lineage, and how various hominins interacted with each other, and who they were, is much sketchier than we might like to think. Though the Tibetan and Denisova cave Denisovans were both robust, if the lineage began to diversify ~400,000 years ago, that’s certainly enough time for various morphological types to have emerged in different parts of Asia.
It could simply be we’ll never be able to specifically understand a lot of the detailed processes that occurred in terms of how different hominin groups related to each other. But, we will probably be able to get a better general picture in the near future. As Spencer mentioned in our podcast last week, the Neanderthals in some ways may have been atypical for ancient hominins, and not a good guide to the long term trajectory of the Denisovans.