Islands in the sky

There are three major high-altitude regions inhabited by humans: highland Ethiopia, Tibet, and the Andean altiplano. In each of these three cases, the locals have adapted in various ways to high altitude – physiological adaptations, as well as cultural. To make it even clearer, those physiological changes are, to a large extent,  a consequence of natural selection,  rather than individual acclimatization.

There are several recent papers on the genetic basis of human adaptation to high altitude-, and they clearly show that natural selection has taken a different path in each of these populations. This was obvious even before the sequencing started: Andean Amerindians are barrel-chested and have high levels of hemoglobin, while Tibetans pant at the drop of a hat but don’t have particularly high levels of hemoglobin.  Moreover, the Tibetan adaptive response works better.  Very few Tibetans get chronic mountain sickness, but a significant fraction of Andean highlanders do, especially with increasing age.  Tibetan babies are significantly plumper than Andean babies.  There are hints that the Ethiopian pattern may also be more effective than the Andean, but that hasn’t been studied as much.

Overall, as Cynthia Beall has pointed out, the  Tibetan pattern is closer to that seen in animal species that have lived at high altitude for long periods of time.

Rasmus Nielsen concluded the changes in Tibetans happened over about 3,000 years. I  doubt that.  People have probably been in the altiplano longer than that, and yet their adaptations are substantially less effective.

Hominids have lived in or near Ethiopia and Tibet for much, much longer than anyone has lived in the New World – something like 100 times longer.  It is possible that the populations of modern humans living in those areas picked up some altitude-friendly alleles from archaic humans that had lived at high altitude for a very long time – and naturally had more effective adaptations. It only takes a tiny bit of admixture to transmit  beneficial alleles.  We now have some probable examples of such transmission: it looks as if some archaic HLA alleles (Neanderthal and Denisovan) have reached high frequency in Eurasians, while a very divergent Denisovan version of OAS1, a innate immune gene, is common in Melanesians.

We can be sure that the Andean Indians did not have this opportunity, since humans have only been in the New World for 15,000 years or so.  No llama jokes, please.

 

 

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19 Responses to Islands in the sky

  1. dearieme says:

    Race is a social construct.

  2. Pincher Martin says:

    At what altitude would you guess these adaptations start to become necessary?

    • billswift says:

      I would assume that any group constantly living above the area where altitude sickness starts to be a noticeable problem (from memory of my rock climbing days, I think it’s about 10,000 feet) would begin to adapt significantly.

      • Pincher Martin says:

        The reason I ask is because many Tibetans and related groups in the Himalayas aren’t constantly above 10,000 feet. In Tibet as it is defined today, even though most cities are above 10,000 feet in elevation, you still have some places below that level. Nyingchi, for example, is located in a green and verdant valley below 10,000 feet, and it looks very different from the dry and desolate population centers of Lhasa and Shigatse, both of which are well above 10,000 feet in elevation. I can’t say how much of Tibet’s population lives in places that are more like Nyingchi and less like Shigatse, but I wonder if it’s substantial.

        I spent a week traveling through Bhutan, and I would say that most of that country’s small cities and towns are well below 10,000 feet. Some might even be lower than 5,000 feet, and I’m not including the places in the south which border India. (Those southern population centers are not geographically and ethnographically contiguous to Tibet, anyway, so they shouldn’t be part of the discussion.) Many of the Bhutanese in these mountainous areas are closely related to Tibetans, both culturally and racially, and there is a small group of Tibetan migrants who traveled to Bhutan to live after the PRC took control of their country.

        I also traveled to the northern mountains of Sichuan, which has a large Tibetan population, and I would say that many of these populated areas in that Chinese province are similar to Bhutan in their geographical features and elevation. Most Tibetans appear to live in green valleys between 5,000 and 10,000 feet high. I’ve never been to Qinghai or Gansu province, but I wonder if they are similar to what I saw in Sichuan. They too have significant Tibetan populations that are demographic relicts of when the Tibetan empire spread throughout what is today known as western China.

        As a person who has lived near sea level my entire life, I wasn’t inconvenienced by altitude sickness during my trips to Sichuan and Bhutan, but I did suffer greatly when I went to Lhasa. Of course, I was visiting as a tourist. The physical needs for a woman giving birth are likely to be quite different. But the variability of elevation where you can find significant groups of Tibetans still living in their historical homelands must be over ten thousand feet, and I imagine there must be a significant physiological difference between these Tibetan subgroups as it relates to this question.

    • dave chamberlin says:

      From what I have read the primary reason these adaptions have become nessecary is women without these adaptions have a very difficult time bringing a baby to full term. Hence the recolonization of Tibet by the Chinese isn’t going as well as planned and the Andean Amerinds living at high elevations are exceptionally pure Amerinds as compared to their lower elevation neighbors.

      • Ortu Kan says:

        Re- only if a Manchu amban, a garrison or two (Mongol and Manchu as well as Han), and at most a few thousand Han civilians (many of the merchant families extensively admixed with locals) qualified as Chinese colonization.

        Most of the long-term Han civilian migrants to Tibet seem to be of Sichuanese origin (I’ve heard estimates as high as 80% for the present-day share), and I wonder if there’s something more than geographic proximity going on here…

  3. Leo Szilard says:

    Next week on Cryptozoology TV: Hunt for the wild Lla-man.

  4. TGGP says:

    I’ve heard about different Andean blood content and Tibetan breathing patterns, but haven’t yet heard what the nature of the Ethiopian adaptation is, just that they differ from the aforementioned two. Do we know what it is yet?

    • gcochran9 says:

      The most recent report I’ve seen on the Ethiopian adaptive pattern (Beall 2011) says that they have elevated pulmonary artery pressure, without the elevated pulmonary vascular resistance you see in Andeans and Europeans, where the pulmonary arteries constrict to raise pressure in response to hypoxia. Tibetans have yet another response, involving panting easily.

      Looks as if the Ethiopians manage using high pulmonary blood flow.

  5. steve says:

    I thought the Tibetan adaptation was found in at least a few percent (5 percent?) of Han Chinese. If so, wouldn’t this just be a case of selection at altitude pushing it to fixation?

    • anon1000 says:

      Also, during the 4th quarter of the Nets game the announcer kept saying that Jeremy looked exhausted. What he doesn’t know is that Jeremy always looks like that. He would appear to be dead tired after 5 minutes of warm ups. No one really knew why, but no one really cared because he would always come out and put in work for 40 minutes.

      :-O

      http://www.quora.com/Jeremy-Lin-1/Whats-it-like-to-play-on-the-same-basketball-team-as-Jeremy-Lin

      And what about the high-altitude pops of the Rocky Mountains? Too few, too admixed for there to be any interest? Sounds like they’re comparable to Andeans (not as well-adapted as Tibetans iow) but then again they’re likely to have been there longer than the S. American highlanders (right?) and it’d be cool to see how much convergence in mechanism there’s been.

  6. j says:

    Andean Amerindians are barrel chested as are all the peoples descended from Artic peoples. It seems to be an adaptation to cold and not to altitude.

    Interesingly, there is a large movement in these days toward upward colonization – La Frontera Agricola. It is based on irrigated alfalfa and dairy. A personal observation: Many “indios” of the high Andes seem to carry African genes.

  7. j says:

    It’s rewarding corresponding with you because you force me to be more precise. I imagined that Mongol wrestlers were barrel-chested, with large chest circumferences relative to their height. But Mayo Clinic says that the term “barrel chest” describes a rounded, bulging chest that may indicate an underlying condition such as chronic obstructive pulmonary disease (COPD). It occurs because the lungs are chronically overinflated with air, so the rib cage stays partially expanded all the time. This makes breathing less efficient and aggravates any existing shortness of breath. Trying to make better sense leaves me more confused than before.

  8. Mrs. M. says:

    Dear geocran9. I am very interested in this subject and need the references please on “There are several recent papers on the genetic basis of human adaptation to high altitude-, and they clearly show that natural selection has taken a different path in each of these populations.” Thanks so much if you can supply.
    Mrs. M.

  9. Pingback: Tibet | West Hunter

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