Thursday, May 2, 2019

Denisovans Were In Tibet First

The partial jaw bone shown above (which on my laptop screen is close to its actual size) from 160,000 years ago in Tibet was identified initially as Denisovan because the shape of the teeth in it had features unique to the Denisovan teeth from a Siberian cave from which Denisovan DNA was detected. The identification was confirmed by comparing non-DNA proteins in the Tibetan sample which degrade less readily than DNA does. 

The jaw bone brings us much closer to figuring out what Denisovan's looked like since we only had teeth and DNA until now, although our sense of what they looked like is still very fuzzy. There are a number of instances of East Asian hominin remains with a mix of archaic and modern features that might be Denisovans or might be something else, but those haven't yielded DNA or other evidence necessary to confirm or rule out the possibility that the samples are from the same species.

We already knew that it was likely that Denisovans had lived in Tibet because the high altitude adaptation genes in humans there today were introgressed from Denisovan DNA and then grew ubiquitous because those genes had selective advantage. This also implies that there was a Denisovan presence in Tibet as recently as 40,000-50,000 years ago when modern humans first arrived there. 

Genetically, Denisovans share a genetic clade with Neanderthals and appear to have diverged from modern humans at about the same time, but the Denisovans have a much less successful population history than the Neanderthals did, in the Siberian individuals, at least, because there is are genome based indications of a continually small effective population size among Denisovans.

There is also lots of introgressed Denisovan DNA in Papuans, Australian Aboriginal people, Filipino Negritos, people from Oceania with Papuan ancestry. All of this started to be visible in people who live just past the Wallace line. There is a much smaller percentage of Denisovan DNA in mainland Southeast and East Asians. Recent data suggests that Denisovan DNA in mainland Asians and that Denisovan DNA in Papuans are from highly diverged Denisovan clades and hence that there were at least two distinct instances of Denisovan introgression in Southeast/East Asia, before even considering a third one in Tibet.

The paper is:

Fahu Chen, et al., "A late Middle Pleistocene Denisovan mandible from the Tibetan Plateau." Nature, 2019 DOI: 10.1038/s41586-019-1139-x

A blog report with lots of images and a Bigfoot angle is here.


neo said...

off topic, but

there's a transcript of an interview with Witten at Bee's blog.

one thing i found interesting,

EW [00:17:48] But you’ve never been tempted down the other route. The other options are not.

EW [00:17:52] I’m not even sure what you would mean by other routes.

GF [00:17:54] Loop quantum gravity?

EW [00:17:56] Those are just words. There aren’t any other routes.

wow. for someone as smart as Witten he's shown close to zero curiosity and interest in other non-string research into QG

there's NO doubt, in this interview, Witten only believes in strings and nothing, not the results from LHC, has shaken is faith.

gcochran said...

Denisovans probably had a considerably larger population size than Neanderthals, judging from the greater genetic diversity ( seen in the introgressions into Melanesians).