Live high/train low is a training method in which athletes live at high altitude and train at low altitude, usually with the goal of improving performance at sea level. The main idea is to reap the benefits of high altitude acclimatization while maintaining the intensity of low altitude training.
https://www.nsca.com/education/articles/nsca-coach/is-live-h...
Having exclusive use of an ecological niche is pretty advantageous.
> There really weren't that many people around so finding land with available food and water doesn't seem like it would be that much of an issue.
While density was (likely) quite low, so was "productivity", and people were no less territorial, just because you didn't need all that space didn't mean you'd allow other groups to exploit it.
One possible argument is that such people would transit high altitudes going between hunting grounds (for example) but is this really enough pressure to produce a genetic advantage like this?
Now nature does tend to want to find niches because having food only you can eat tends to be of more value than having abundant food other people can also eat (eg pandas and bamboo).
But it's not easy for humans to live at 14,000 feet elevation. Animals are scarce. Vegetation is limited (eg trees likely to be conifers).
This is different to just, say, living in Arctic regions as those do have much more available food options (eg fish, migrating game, plants that can grow in the summer) than high altitudes.
Has anyone put much thought into this?