Imagine an Earth-like world with oceans, some complex vegetative and animal life, but with an extreme low amount of oxygen in the atmosphere, let's say one third of what we are accustomed to, like the death zone of Everest, but on the sea level.

Imagine a ship with colonists from Earth arrives on this world. The atmosphere is breathable but not survivable without taking to the oxygen bottle from time to time (like on Everest). How long would it take their descendants to adopt? People in Himalaya or Peru feel good at 5000 meters, and they likely came there from lower areas. Would their grandgrandchildren be able to live there without an extra oxygen supply? Will they feel ok?


4 Answers 4


For humans there is a physical (chemical) limit on O2, CO2 partial pressures and their difference. If these conditions are not met our lungs start to extract oxygen from blood into the air, which leads to fast suffocation.

And these are fundamental physical limits (based on gases' solubility in water) - you could not overcome it without changing the breath method. This would hardly happen, because it would lead to total "redesign" of all body systems (including nervous, i.e. brain).

This limit is about 8% - that is about 8 km above sealevel, about 1 km below Everest. On Everest you don't need "oxygen bottle time-to-time" - you need it constantly. And if you open you mask you need to keep your breath or you would loose oxygen you have in your body.

As for altitudes less than 8km (5-7) humans can and do adopt by starting producing more blood cells, increasing their lung volume, reducing body mass/volume ratio. But it has its drawbacks (greater risk of thrombus, bleeding is far more dangerous etc.).

And 5km (10%) is an actual limit for quite an interesting reason: this percentage is a difference between CO2 and O2. But indoors, some people can easily have their concentration of CO2 rise up to 1-2% (especially if some open fireplace is there). If it happens near the limit at more than 5km height - people will start to suffocate.

So a stable breathable atmosphere is about 5 km (0.1 atm of oxygen partial pressure) and some people already adopted to those heights. But they are small, thin and weak, compared to "lowlanders".

  • $\begingroup$ Interesting bit that I found out while googling this-- if you produce more read blood cells, it can lead to an increased risk of blood clots. That means headaches, nausea, heart attack, and stroke risk all spike at higher elevations. We see this even among people who have spent their entire lives in high altitude environments, which I didn't expect. $\endgroup$ Jan 24, 2020 at 13:04
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    $\begingroup$ True although some humans have climbed Everest without oxygen so the effects aren't instant or at least not in every case. $\endgroup$
    – Slarty
    Jan 24, 2020 at 13:10
  • $\begingroup$ @Slarty, that is quite a speculative (I've heard that that ascention was about 1 hundreds of meters with bottle but without mask), + there are other factors, like air and body temperature (lower temperature - more moles of gas for same pressure, greater gas solubility) and many more $\endgroup$
    – ksbes
    Jan 24, 2020 at 13:27
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    $\begingroup$ @ksbes there was a number of Everest accents without supplemental oxygen. The fastest record right now is 16 hours and 45 minutes from the base camp. So this definitely can be done, just "don't try this at home". $\endgroup$
    – Alexander
    Jan 24, 2020 at 18:04
  • $\begingroup$ @Alexander So... as long as I don't live on Mt. Everest, I can feel free to try it? :P $\endgroup$ Jan 24, 2020 at 20:33

Air at sea level is roughly 20% oxygen. When we hit 16% or lower, our cells physically stop working as well with physical activity. 14% to 10% and we start losing cognitive functionality (source). If the oxygen concentration is only a third of what we're used to, that's (roughly) 7% oxygen at sea level-- well below what any human would need to function. There are two ways we can get around this issue in terms of better humans.

1) Random Mutation

Do like our ancestors did-- randomly mutate until we have better offspring. Get rid of the idea of monogamy. It's critical that everyone reproduce to the limits of what the colony can sustain! If someone seems to be able to function better with less oxygen, they need to be reproducing more! It's pretty much impossible to know how quickly this will work (or how it would even work) since we obviously don't have any humans that we know of that can survive in such an environment.

Genetically Modify our new humans

We can probably do this a bit quicker, though it will depend on some (hand wavey) science to produce new humans. Obviously, the tech to make a human who breathes 1/3 of the oxygen we're used to doesn't exist at this point in history. But we could wave our hands a bit and speculate about it. What traits do we want?

A smaller human will certainly need less to survive. Less food, less water, less oxygen, less everything, really. So that's probably a good start. Then let's study just what makes those humans who live at high altitudes function so well. We've actually already identified some potential genes that would make humans survive better at higher altitudes. Those can be injected into anyone who wasn't already from those mountainous regions to ensure that they could survive on the planet better.

Past that.... it's kinda guess-and-check. We can only come up with so many ideas for how to build a better human before we have to test them. How long it takes in that instance is now up to you.

  • $\begingroup$ Can we raise the bar to half instead of 1/3? $\endgroup$
    – petera1289
    Jan 24, 2020 at 11:49
  • $\begingroup$ yes :) I've been myself at 5200 elevation and I felt sleepy and nauseaous. Moving was hard. But I bet I could stay there longer and function. The bar here is basically a bit worse than what I experienced. That it's really that bad that you need that oxygen bottle.. $\endgroup$ Jan 24, 2020 at 12:09

At half or lower, it might as well be zero like Mars because no one is going to survive any negative event. Artificial support will be the norm so adaptation won't take place.

Above half normal and there are biochemical rather than mechanical interventions (red blood cell membrane, drugs) to prevent a negative event from being immediately fatal allowing adaptation to occur that naturally incorporate the interventions.

Other adaptations beside smaller size and larger chest/lungs that will occur are loss of muscle mass (assuming gravity permits) and reduced brain mass as these affect resting oxygen demand.

A hibernation reaction might develop where the body basically shuts down to below resting state allowing survival of extended exposure below the new normal. This would probably be a repurposing of the current "keep the core warm by sacrificing the extremities" reaction to hyperthermia


Assume that the colonists are drawn from high altitude populations, as making use of an existing trait will take much less time than depending on a random mutation randomly showing up just in time.

Even with pre-existing traits, it is not guaranteed that humans would ever be able to exist without supplemental O2. If the traits from these three populations did combine in a beneficial manner, it may still only result in just needing much less additional O2 rather than removing the need for an emergency bottle.

For your story, assume that these traits did optimally combine into humans that could breath unaided. It will take quite a few generations for the individual traits to be spread among the entire population, even if breeding was deliberately controlled. Perhaps between 100 and 200 years after initial colonization?

Here is a bit of background on high altitude populations.

O2 availability similar to that at 5,000 meters would still require supplemental O2, but traits existing in the Tibetan, Andean, and/or Ethiopian populations should give your population a jump start on evolutionany processes to reduce the need for O2 bottles.

Andeans have higher hemoglobin concentrations which allows for more O2 to be carried (though it does thicken the blood a bit).

Tibetans increase their O2 intake with quicker breathing, along with expansion of the blood vessels to allow increased flow.

Ethiopian highlanders also successfully deal with high altitudes with minimal hypoxia, but do not have any of the adaptations shown by the Andeans or the Tibetans. So what adaptations have the Ethiopeans evolved to do this?

To quote Cynthia Beall, a physical anthropologist, "Right now we have no clue how they do it."

Three High-Altitude Peoples; Three Adaptations to Thin Air


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