Monday, 19 December 2016

Africans are more likely to have sickle cell because SC trait is protective against malaria, which still ravages Africa.

BiologyIn a scenario where human life is exposed to long term (millions of years) reduction of oxygen (like in mountain tops), would the human body adapt do this change? 
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[–]baloo_the_bearInternal Medicine | Tissue Engineering | Hematology/Oncology 27 points  
Actually, yes; and it wouldn't even take that long. In some groups of people who have lived at high altitude for generations, there are specific and discernible biochemical changes in the blood that make it more efficient at transporting oxygen. The molecule in question is 2,3-DPG. It helps stabilize the low oxygen tension state (T state) of hemoglobin and causes a shift of the oxygen-hemoglobin dissociation curve to right. This helps the blood offload more oxygen to respiring tissues, thus reducing potential tissue hypoxia in situations where this may occur.
Some of these changes are inducible, meaning a person who normally lives at sea level can spend some time in high altitude and acclimate to the new environment. However, the rapidity and degree to which this happens is thought to be determined genetically. This is why before climbing some of the tallest peaks in the world, climbers have to spend time at base camp to allow their bodies to undergo some of the physiologic changes to try to avoid altitude sickness, which can be fatal.
There have been studies to look at these phenomena. They can be seen here, here, here, and here. The last link probably directly answers your specific question. It's an old paper and they don't gave a great explanation for the exact mechanism, but it's worth the read. Feel free to message me or reply if you have further questions.
[–][deleted] 3 points  
Thanxs for the reply! Truly helped me, gonna take a look at those links.
Edit: Further questioning, if you don't mind, what if those effects were constant, meaning they would keep lowering and lowering, reaching levels of oxygen that we cannot live in rn, but in very a long time frame where the body would be able to adapt through 'evolution'? I assume there's no concrete answer for that, but you seem well versed in the subject and I'd love to hear (if there is no real answer) some speculation on what you think would happen.
[–]baloo_the_bearInternal Medicine | Tissue Engineering | Hematology/Oncology 3 points  
Honestly, I'm not too sure. There are microorganisms (extremophiles) which have evolved to thrive in extreme environments such as low oxygen, or high/low temperature. There is a fungus in Chernobyl that was discovered to use radiation for energy. But to extrapolate that sort of adaptation to complex, multicellular organisms seems too much of a stretch. I think at a certain point the viability of the organism would be reduced, either in growth, or intelligence, or both, leading to an evolutionary dead end rather than a flourishing species. Most organisms in such a situation would try find a new niche to inhabit rather than face mounting environmental pressure. Done artificially, I'd think it would go more in the growth restriction direction.

[–]gladeyes 2 points  
Also the tribes that live north of the arctic circle have developed better blood flow to their extremities and the ability to withstand freezing temperatures. Genetic selection is powerful.
[–]baloo_the_bearInternal Medicine | Tissue Engineering | Hematology/Oncology 2 points  
Yep there are many such cases, the most well known are that Caucasians are more likely to have cystic fibrosis because it is protective against cholera, which ravaged Europe; and Africans are more likely to have sickle cell because SC trait is protective against malaria, which still ravages Africa.

https://www.reddit.com/r/askscience/comments/51uxo7/in_a_scenario_where_human_life_is_exposed_to_long/
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