Early farming village in China (Wikicommons – Xinyang City Museum, Gary Todd)
Respiratory viruses began to propagate more easily when hunting and gathering gave way to farming and as settlements grew larger. Humans may have then evolved to use coronaviruses as a natural vaccine against deadlier respiratory diseases, like tuberculosis and pneumonia.
A new genomic study has found that East Asians had to adapt to epidemics of coronaviruses some 25,000 years ago. The authors looked at gene variants for proteins that interact with coronaviruses in five East Asian populations: Han Chinese (Beijing); Han Chinese (South China); Dai (Yunnan, China); Japanese; and Vietnamese. There were three main findings:
· Ancestral East Asians had to adapt to coronavirus epidemics around 25,000 years ago
· They adapted by acquiring mutations that are close to genes that regulate the development of lung tissue and other tissues affected by COVID-19
· Those mutations either promote or block infection by coronaviruses (Souilmi et al. 2021, p. 3505).
The last finding is puzzling. Did those ancestral East Asians become more vulnerable or less vulnerable to coronaviruses? The authors simply say that half of those mutations from 25,000 years ago have “anti- or proviral effects” versus 29% of all proteins that interact with coronaviruses (Souilmi et al. 2021, p. 3509). Fine. But how many of those mutations were antiviral and how many proviral?
It might seem strange that natural selection would actually make people more susceptible to coronavirus infections. Yet such susceptibility could be beneficial. A viral infection can boost immunity to other viruses, including deadly viruses that cause tuberculosis, pneumonia, or pneumonic plague. Until recently, coronaviruses were typically mild in their effects, producing what we call the “common cold.” They may thus act as a natural vaccine against deadlier respiratory viruses (Frost 2020).
Respiratory viruses are believed to have become serious for humans when hunting and gathering gave way to farming. People became sedentary and their settlements grew larger with time, thus providing respiratory viruses with better conditions for propagation (Comas et al. 2013). This theoretical model is in conflict, however, with the above finding that ancestral East Asians began adapting to coronaviruses some 25,000 years ago, long before they adopted farming and became sedentary. We’re thus left with the unlikely conclusion that coronavirus epidemics began among scattered bands of hunter-gatherers.
The estimate of 25,000 years ago is probably wrong. The authors arrived at that figure by calculating the latest date when the ancestors of the four East Asian groups were still a single population. But East Asians are not descended from a single population. Their origins are best described by the "Two-Layer" (TL) hypothesis:
· Modern humans spread into East Asia through a northern route and a southern route.
· The southerners were then replaced to varying degrees by northerners who spread out of northeast Asia and successively occupied northern China, southern China, and Southeast Asia (Oxenham and Buckley 2016; Xu et al. 2006).
· Thus, as you go farther south in East Asia, the population has a greater admixture from the earlier southern “layer”—from hunter-gatherers who closely resemble the relic groups that still exist in parts of Southeast Asia, i.e., the Andaman Islanders, the Aeta of the Philippines and the Maniq and Semang of the Malayan Peninsula.
Admixture from that older southern substrate pushes back in time the latest common ancestors, who never existed. Adaptation to coronaviruses therefore happened at a later date, probably when the “northerners” pushed into what is now northern China and adopted farming. They then grew in population, pushed farther south, and intermixed with the hunter-gatherers who lived there.
References
Comas, I., M. Coscolla, T. Luo, et al. (2013). Out-of-Africa migration and Neolithic coexpansion of Mycobacterium tuberculosis with modern humans. Nature Genetics 45: 1176–1182. https://doi.org/10.1038/ng.2744
Frost, P. (2020). Does a commensal relationship exist between coronaviruses and some human populations? Journal of Molecular Genetics 3(2): 1-2. https://researchopenworld.com/does-a-commensal-relationship-exist-between-coronaviruses-and-some-human-populations/
Frost, P. (2022). A natural vaccine. Evo and Proud, February 21 http://evoandproud.blogspot.com/2022/02/a-natural-vaccine.html
Oxenham, M., and H.R. Buckley. (2016). The population history of mainland and island Southeast Asia, in M. Oxenham and H.R. Buckley (eds) The Routledge Handbook of Bioarchaeology in Southeast Asia and the Pacific Islands. Routledge.
Souilmi, Y., M.E. Lauterbur, R. Tobler, C.D. Huber, A.S. Johar, S.V. Moradi, W.A. Johnston, N.J. Krogan, K. Alexandrov, and D. Enard. (2021). An ancient viral epidemic involving host coronavirus interacting genes more than 20,000 years ago in East Asia. Current Biology31(16), 3504–3514.e9. https://doi.org/10.1016/j.cub.2021.05.067
Xue, Y., T. Zerjal, W. Bao, S. Zhu, Q. Shu, J. Xu, R. Du, S. Fu., P. Li, M.E. Hurles, H. Yang, C. Tyler-Smith. (2006). Male demography in East Asia: A north-south contrast in human population expansion times. Genetics 172: 2431-2439, https://doi.org/10.1534/genetics.105.054270