Denisovans Settled The Tibetan Plateau First
Denisovans occupied the Tibetan Plateau 120,000 years before humans and passed on a gene to survive high altitude life
A new paper in Trends in Ecology & Evolution synthesizes current evidence and concludes definitively that Denisovans occupied the Tibetan Plateau 160,000 years ago. Furthermore, they contributed to many physiologic adaptations we have to high altitudes. The authors were able to integrate archaeological and genetic lines of evidence to make their claim.
Again, both of these claims are not new, a mandible discovered by a monk in 2019 was confirmed to be Denisovan and 160,000 years old last year. A couple of other studies have also addressed the genetic adaptations introgressed by Denisovans to populations in Tibet, which I outline below. The significance of this paper is the synthesis of evidence of what is currently known of human occupation and settlement of the Tibetan Plateau. Prior to this, there was a lack of cohesiveness in the literature.
In this current publication, the archaeological record demonstrates there were four periods of occupation in the Tibetan Plateau. The first began with Denisovans, about 160,00 years ago. And humans followed at first 40,000 years ago. Two subsequent waves of human populations came 16,000 and 8,000 years ago. Based upon this, the authors summarize two models of human occupation of the Tibetan Plateau. One involves sporadic visits up until 9,000 years ago, or around the time of the end of the last Ice Age. This is supported by the current evidence as there appear to be waves. Another model suggests humans continuously occupied the area beginning around 40,000 years ago and the gaps in the archaeological are thus due to incomplete sampling.
The first Denisovan identified in 2010 from the Altai Mountains in Siberia carried a haplotype similar to the modern EPAS1 gene. This gene encodes for proteins that improve oxygen transportation in blood. Humans living in high altitudes like Tibetans nowadays have a high allelic frequency of this EPAS1 gene.
Just who did this gene introgress from?
Calculating the variance, the Denisovan haplotype of the EPAS1 gene passed to modern humans between 46,000 to 48,000 years ago. It is represented in Tibetans. This indicates that interbreeding occurred among ancestral Asians on the Plateau; Denisovan and humans. Then another allele is subdivided into local populations since a unique variant to East Asians occurred somewhere in the lowland instead of the plateau. I think the authors provide a pretty convincing synopsis that the EPAS1 gene did come from Densiovans, who were adapting to the high country 120,000 years earlier than any other human. What do you think?
Zhang, P., Zhang, X., Zhang, X., Gao, X., Huerta-Sanchez, E., & Zwyns, N. (2021). Denisovans and Homo sapiens on the Tibetan Plateau: dispersals and adaptations. Trends in Ecology & Evolution. https://doi.org/10.1016/j.tree.2021.11.004
Zhang, D., Xia, H., Chen, F., Li, B., Slon, V., Cheng, T., Yang, R., Jacobs, Z., Dai, Q., Massilani, D., Shen, X., Wang, J., Feng, X., Cao, P., Yang, M. A., Yao, J., Yang, J., Madsen, D. B., Han, Y., … Fu, Q. (2020). Denisovan DNA in Late Pleistocene sediments from Baishiya Karst Cave on the Tibetan Plateau. Science (New York, N.Y.), 370(6516), 584–587. https://doi.org/10.1126/science.abb6320
Huerta-Sánchez, E., Jin, X., Asan et al. Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA. Nature 512, 194–197 (2014). https://doi.org/10.1038/nature13408
Jeong, C., Alkorta-Aranburu, G., Basnyat, B. et al. Admixture facilitates genetic adaptations to high altitude in Tibet. Nat Commun 5, 3281 (2014). https://doi.org/10.1038/ncomms4281