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Saturday, July 05, 2014
The Denisovan gene in Tibet
Now that politics is out of the way, let's get back to race...
A few years ago a small and ancient bone was found in Denisova, a cave in Siberia. This bone was thought to be Neanderthal at first; it contained a large cluster of DNA for testing - which proved it something(s) else again. We now know it as a mongrel of at least two human subspecies, none seen before; of which the greater portion was tagged "Denisovan". (It was later that the other contributions were distinguished. But I think that the truly distinct "Denisovan" DNA may be triangulated, for instance from this other hybrid.)
Denisovan DNA was quickly found in Polynesia. Later, trace amounts were seen elsewhere in East Asia. It now turns out the Tibetans have a Denisovan gene that means something.
It has to do with red blood cells, which are iron-based and carry oxygen (in the form of rust) from the lungs to elsewhere. Most modern humans, including other high-altitude peoples like Peruvians, have the obvious genetic "hack" to get around low-oxygen environs: we increase red blood cell production. I imagine it's helpful underwater. It's definitely helpful for getting up hills... assuming we'd be descending them again in the short term.
But if we were to LIVE on the Tibetan plateau, our red blood count would STAY that high. And if we've any arterial blockage at all, eventually those red blood cells will get into a logjam. Most likely we'd stroke out. I've read elsewhere that miscarriages are common at high altitude as well.
For whatever reason the Denisovans never developed that "hack", or else lost it (on this I hope the researchers're still researching). It would appear that a Denisovan relic population climbed up into Tibet - whither they were followed, by Asian relatives to the Chinese. There were vanishingly few crossovers between these two peoples, by comparison with other Asians like the proto-Austrasians. But at least one couple passed on the "Denisovan downshift" of this DNA chain which allowed their children to survive up there. And their children developed other mutations to handle the reduced oxygen in other ways (they're definitely researching this much).
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