Q&A For History of Mankind (21)
Native American Vs Himalayan Genetic Adaptations, Thinking About the Roman Empire
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This is the twenty-first Q&A for History of Mankind. Paying subscribers received an email asking for questions; and those are right below the paywall.
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One other reminder: as you may have noticed, the monthly Q&A session is behind the paywall, but that doesn’t mean I don’t welcome questions, comments, suggestions and corrections from non-paid readers. Quite the contrary: I know quite a few of you are history professionals and all are history aficionados, and I’m not infallible, so if you think I got something wrong or my interpretation of whatever is dubious, please let me know. If I have to correct something, I will and I will make it public in these monthly notes so that readers are aware.
Today we’re going to be looking at pre-print paper, still not published in any academic magazine, “Convergent evolution of complex adaptive traits enabled human life at high altitudes,” by Giulia Ferraretti et al. This paper is an important contribution to the study of comparative human adaptations to life in high altitude. Some of you may remember that, a long time ago (I didn’t have as many followers back then, not by a long shot) , in Chinese Kings & Alcohol-Filled Pools, I discussed the development of the earliest attested Tibetan populations in the highlands of modern Sichuan, China:
The Hengduan Mountains, an impressive range just to the west of the Sichuan plateau, was another key geographic marker – then as now – as it represented the eastern-most point where ethnic Tibetans with specific genetic adaptations for high-altitude-living accounted for a majority of the population; it may have also been the place through which cold-tolerant barley agriculture, based on Yellow River strains, expanded to Tibet proper around 1600 BC, together with millet farming techniques, making a huge impact on demographic expansion in Tibet.
Like I explained then, David Epstein, in “The Sports Gene: Inside the Science of Extraordinary Athletic Performance” (2013), notes that high-altitudes adaptations across continents have been surprisingly different:
From the 20th century AD, Kenya and Ethiopia’s long-distance runners thrived on their altitude-adapted genes, but people living in the different Andean and Himalayan climates – both not fostering a narrow body type – had different genetic adaptations. Native Andeans have profuse portions of red blood cells and, within them, oxygen-carrying hemoglobin; they in fact have so much hemoglobin that their blood can become viscous and unable to circulate well, and some Andeans develop chronic mountain sickness. Tibetans, however, have normal, sea-level hemoglobin values, and low oxygen saturation, lower than people at sea level. Most Tibetans have a special version of a gene, EPAS1, that acts as a gauge, sensing the available oxygen and regulating the production of red blood cells so that the blood does not become dangerously thick. But it also means Tibetans don’t have the increase in oxygen-carrying hemoglobin that Andeans do; they survive by having extremely high levels of nitric oxide in their blood. Nitric oxide cues blood vessels in the lungs to relax and widen for blood flow: 240 times as much nitric oxide in the blood as White Europeans, so they adapted to having very high blood flow in their lungs, and to breathe deeper and faster than native lowlanders, as if they’re in a constant state of hyperventilation. Ethiopians, and specifically the Amhara ethnic group living along the Rift Valley, have normal, sea-level allotments of hemoglobin and normal, sea-level oxygen saturation: their own trick is moving oxygen unusually rapidly from the tiny air sacs in their lungs into their blood.
The new paper by Ferraretti et al argues that high-altitude Andean human groups experienced pervasive selective events driving the formation of extra blood vessels, which resemble those previously attested for Himalayan populations, although they were concentrated on much shorter time spans.
This helps to explain what the authors describe as “less effective genetically regulated physiological adjustments, especially to counteract long-term detrimental effects of hypobaric hypoxia, than populations of Tibetan/Sherpa ancestry.” Which, of course, is consistent with Epstein’s explanation.
Is this the reason why Andean populations took longer to settle high-altitude regions like those around Lake Titicaca, and they still need products like coca leaves to avoid high-altitude sickness? Probably, although, as scientists like to say, more research is needed. I personally spent some time (my honeymoon!) in Tibet, and my non-Tibetan wife needed bottled oxygen while in Lhasa, but I noticed that Tibetans seem to be remarkably relaxed about the whole altitude thing.
Tibetans don’t appear to require any extra products or precautions when traveling across their land: they are truly remarkable people, in the that sense, and many others. The time to discuss the rise of the Tibetan Empire will come, although we’re still like a 1,000 years away from that yet…
Now, for the questions by paying subscribers…
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