I think that oxygen reduction is a positive factor for humans. Oxygen is toxic and destructive and leads to aging and cancer. Mountain air with a low oxygen content is considered healthier, and people live there longer, athletes train there.
It is also likely that an excess of the ozone layer leads to a lack of solar energy.

Smoking could be an evolutionary maneuver in the fight against excess oxygen. If it weren't for the benefit, natural selection would not have gone down the path when inhaling smoke is enjoyable and satisfying. The qualities that lead to survival evolve.

2 hours ago, altaylar2000 said:

athletes train there

And then they go back to sea level and perform better- because the increased oxygen is good for them.

As with many things, there is a balance, too much, or too little is a bad thing.

 

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Moderator Note

Don't hijack threads to bring up your pet theories. (smoking as an evolutionary maneuver, for example)