system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I would put a family under a dome and every generation I would decrease the oxygen by 1%, in the end could they live without oxygen?
gpt
No, they would die in about 6 generations.  

Humans need 15% oxygen in the air (technically partial pressure of O*_2_* of 0.15 atm) in order to breathe, and a few generations of evolution won't change that.

If you reduced it by 1% every million years, you might squeeze out a few more percent.  Oxygen is so fundamental to animal metabolism, you are probably looking at tens, if not hundreds of millions of years to evolve a new anaerobic breathing mechanism.  At that point, you'd be looking at a new kingdom of life, far removed from anything you'd call human.