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What would humans look like if they lived 50-100,000 years 20,000-30,000 feet / 6 to 9 km above sea level? Or 500,000 years?

Would we have bigger lungs / chests? Bigger wider noses? Thicker skin and fattier bodies (to insulate from cold)? Thicker hair? Taller or thinner bodies?

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  • $\begingroup$ It goes without saying that these changes will only happen if humans without those changes don't breed as much or at all (because of death, health issues, lack of dominance, etc.). $\endgroup$ – BrettFromLA Oct 12 '16 at 23:48
  • $\begingroup$ What do you mean? That we were suddenly and forcibly moved to those levels or that we evolved there? $\endgroup$ – MichaelK Oct 14 '16 at 12:25
  • $\begingroup$ I like the question Noob (and welcome to the site) as it stands the question is a little broad/unclear. Could you clarify on the scenario a bit? What technology level are we dealing with. Did humans evolve on an earth-like world and then move up or did a human ancestor exist way up high and humans always lived there? $\endgroup$ – James Oct 14 '16 at 18:43
  • $\begingroup$ I think most of your question can probably be answered by this wikipedia article: en.wikipedia.org/wiki/High-altitude_adaptation_in_humans The only thing I would add is that above 8 km is called the "death zone" so it may be impossible for humans to survive prolonged periods above that altitude. $\endgroup$ – Mike Nichols Oct 15 '16 at 3:56
  • $\begingroup$ The Tibetan plateau is a 2 million square kilometers region with an average elevation of about 4500 meters (15,000 feet). It has been inhabited since 30,000 years ago. Have you tried to look at pictures of Tibetans to see how a population inhabiting a high-elevation area looks like? Hint: they look pretty much like any other Central Asian humans. $\endgroup$ – AlexP May 25 at 13:04
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Like Tibetans and Sherpas and Peruvian highlanders.

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If we look at existing high altitude adaptations in humans we can probably get a clue as to what they might be like, should they survive long enough to reproduce.

Adaptations for low oxygen

By far the biggest selective pressure on your people will be hypoxia during pregnancy, which is a big problem. On the positive side, issues affecting fertility tend to get selected out very quickly.

Tibetans show the most adaptation to high altitude of all the high altitude populations. They breathe more rapidly than lowlanders, inhale more air with each breath (larger lungs), and have increased levels of nitric oxide in the blood (allows for greater dilation of blood vessels). Interestingly, they don't show elevated haemoglobin levels (a common adaptation). Their normal haemoglobin levels is thought to protect them from chronic mountain sickness.

Andeans and Ethiopians display other adaptations, notably increased oxygen-carrying capacity of their haemoglobin.

I suspect that your high-altitude people will need to use all of these adaptations, and increased in efficiency where possible. They may well have reduced capacity for exercise in their homeland, although it would be far greater than a visiting lowlander.

Another interesting adaptation they may use is a sort of blood-doping used by horses. Horses store fully one third of their red blood cells in their spleens at rest. When they need rapid bursts of speed, this blood is shunted into the rest of their system and produces a burst of oxygen in excess of what their lungs can supply. If your highlanders develop a similar adaptation then they may still be capable of bursts of speed and strength when they're otherwise sluggish.

These are all relatively easy adaptations as far as things go. They're tweaks to existing systems, rather than whole new ones.

Adaptations to cold

Luckily, this one is pretty straight forwards. Stockier build, thicker fat layers and more hirsute are easy adaptations. I'd expect them to have larger noses as well (the nose acts as a heat exchanger to warm incoming air before it reaches the lungs).

I'm not certain if the timeframe is long enough, but if they can develop translucent hair and dark skin like polar bears then that would help retain heat from the sun as well.

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Not sure about the sea level issues.

longevity wise this would depend on what changed that allowed for increased life span. As humans are now the smallest changes to allow for vastly increased life spans would be if our cells replicated error free and the mechanisms in our bodies that trigger our progression toward death simply didn't flip. In that case we would physically remain fairly similar.

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  • $\begingroup$ are you saying that. we evolved from our cousin apes because the environment was so destructive and hard to live that made us the way we are? and that we live simple safe lives now so we won't change? $\endgroup$ – NoobCreator Oct 13 '16 at 2:38
  • $\begingroup$ Ah i think I misunderstood the question. I took it to mean an individuals lifespan would be 50-100k years. $\endgroup$ – Tathel Oct 13 '16 at 11:54
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If we would live under such conditions without technology and if we would find enough food to survive , we would definitely develop bigger lungs, more body fat, and body hair.

We would very likely have smaller noses and ears, since we don't need good hearing or smelling in such an windy and open area, while they are weak spots against the cold but our vision would improve, it wouldn't be far to assume that we would start to use our hands for moving around as well, resulting in stronger arms and thicker skin on our hands. On that point our feet would probably also regain the ability to at least grab a little, for better climbing.

At good last we would very likely start to shrink, since size doesn't bring advantages against such terrain and predators won't be a worse problem until about half our size today.

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