Oxygen content increases to 31%

What would be the consequences for Earth and life on it if oxygen content in the atmosphere increased to 31% between 1 mln and 900,000 years ago, i.e. over a span of 100,000 years?

Hoow would Earth and life on it look like today, i.e. 900,000 years after the oxygen content stabilized at 31%?

Just initial thoughts:
1. Fires would be more common and more devastating. Fire resistant plants would be more common
2. Insects and other arthropods would grow significantly larger.
3. Oxygen is a greenhouse gas so temperatures would be at least slightly higher
4. More oxygen in the air means more oxygdn dissolved in ocean water, which might mean richer marine life
5. As for humans, several things:
a. More oxygen might mean more endurance (longer running) so possibly, earlier dispersal of humans around the world
b. More oxygen in the atmosphere means more oxygen available for the brain which in turn might accelerate the trend of higher brain volumes.

Any ideas?vAt least for hominids, 900,000 years ago is the time of late Homo erectus so there is plenty of room for evolutionary divergence.