It seems that people who live at very high altitudes have demonstrably "thicker" blood, highly concentrated with red blood cells to overcome the low concentration of oxygen in the air. Moving between extremes of altitude apparently needs to be done gradually for the same reason.

Assuming a biology largely similar to humans:

Two (or more) humanoid species, in many ways biologically similar/compatible. One species lives almost exclusively in an isolated location at a very high altitude. One or more other species live in a variety of environments.

Is it plausible for species A to survive as such a height that members of species B were guaranteed not to survive in? Phrased differently, is it possible for a species to live in a habitat so extreme as to be radically socially isolating?

  • $\begingroup$ People who live in higher altitudes also tend to have more lung capacity $\endgroup$ – David Wilkins Nov 6 '14 at 14:34
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    $\begingroup$ Out of curiosity, when you say "in many ways biologically ... compatible", what do you mean by that? For example, if they are able to interbreed and that results in fertile offspring, that is commonly the definition of a single species. $\endgroup$ – a CVn Nov 6 '14 at 14:51
  • $\begingroup$ That's specifically why I said similar and not just compatible. I mean, for example, they'd be able to eat much of the same food, have similar internal organs, similar proportions etc. In terms of speciation, plausibly closely related species. $\endgroup$ – lea Nov 7 '14 at 9:27
  • $\begingroup$ You may need to redefine that. We eat the same food and have similar organs to nearly every mammal. We are similarly proportioned to almost all the land mammals. $\endgroup$ – Nick2253 Jan 21 '15 at 0:17
  • $\begingroup$ Interestingly, only some people who live at altitude have thicker blood. Check out the adaptations Tibetans, Andeans and Ethiopians have (thinner blood, higher oxygen holding capacity, faster breathing). They're quite interesting :) there's a good wiki page for it: en.m.wikipedia.org/wiki/High-altitude_adaptation_in_humans $\endgroup$ – Ynneadwraith Mar 22 at 8:16

The simple answer is yes, however the more complicated answer is no.

The yes:

If a species is adapted to one extreme environment then that often renders them unable to function effectively at another.

Sky Islands for example have isolated species that only survive on them.

If this hypothetical species were adapted to an altitude where humans cannot survive then that species would also find lower altitudes hard for them to live in. There would be little or no contact between the two species.

But the No:

Many animals, and humans in particular, are very adaptable. We can adjust our clothing, use tools, fire, buildings, etc to survive in a vast range of conditions.

Conditions so extreme that they are absolutely impossible for the non-adapted to survive in would be unlikely to support much life in the first place. What would be far more likely is that the high altitude dwellers have a strong advantage there, but visitors from below can survive for at least a while.

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    $\begingroup$ Case in point, the Antarctic? $\endgroup$ – a CVn Nov 6 '14 at 14:50
  • $\begingroup$ Technically sort of possible, but not meaningfully plausible. That's about what I expected. $\endgroup$ – lea Nov 8 '14 at 8:54

Yes but not separated by altitude

I agree with Tim B that mammal in general and humans in particular are very versatile.

But one exception would be water.

In an appropriate environment it probably wouldn't take long for human to evolve as marine animal.Not to the same level as Dolphin, of course, but to the same level than sea otter, why not.

To help the process, you could make this specie specific to the Caspian sea. With a water salinity merely matching human biology.

To give you an idea, the polar bear (Ursus maritimus)"diverged" from brown bear about 150 000 years ago (quote/unquote "diverged" because they can interbreed. They don't do it much because they are socially isolated)

Now, it wouldn't be really socially isolating. Normal human can not live this way, but they can ride a boat and Homo Maritimus can walk on firm ground.

EDIT2: polar and brown bear diverged about 150 000 years ago


I could imagine it happening.

Suppose we have a mutation: It improves the ability to function with low levels of oxygen but the flip side of this is that the system becomes very vulnerable to too much oxygen--for much lower levels of "too much".

When you get one copy of the gene you don't function quite as well at any altitude but you can function at a higher altitude than those who don't have it at all.

If you get two copies you can function at even higher altitudes but the lowlands become lethal with prolonged exposure. (Think of humans--we can function between about 2 and 10 psi of oxygen, with prolonged exposure to pressure outside this range causing serious problems or death.)

Those who get two copies have a niche they can live in that starts out without competition and since everyone up there has two copies it now breeds true. You have your separated population and thus they will in time diverge.


Around the world, many high altitude populations adapt by having higher concentrations of red blood cells, which allows them to better make use of the limited oxygen at those altitudes. While some populations may be more prone to do this, it is mostly a process of acclimation. Spending several weeks at heights will let your body adapt and produce extra red blood cells.

It Tibet, however, they have a genetic mutation related to genes that appear to better balance anaerobic and aerobic metabolism processes. It appears to do this in a way that is more optimal for the low-oxygen environment of high altitude. Recent immigrants from lower altitudes get headaches, tire easily, and have lower birthrates and higher child mortality than the native population.

To directly relate this to your question, it would not be too much of a stretch to have a low altitude population have a mutation that exacerbates oxygen deprevation (perhaps they can no longer adapt by producing the extra red blood cells). The high altitude population might have another mutation that they cannot long survive higher concentrations of oxygen.


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