It’s also unlikely to be about oxygen because oxygen levels that reach the brain in a healthy person depend almost entirely on the amount of saturated haemoglobin, which is 95-100% of Hb in someone without serious lung heart or haemoglobin defects. This means that variability in O2 availability is more dependent on one’s iron level than breathing/air effects. (I disclaim that I haven’t yet looked into literature about O2 chemistry and supply to the brain so may be wrong)
The CO2 hypothesis at least makes some sense because bloodstream CO2 levels vary a bit.
Gwern’s evolutionary argument seems weak because we did not develop in ancestral environments where we could properly trap CO2 (our CO2 sensors mightn’t need to be very sensitive), and for our ancestord it was at least somewhat more important to conserve energy from breathing and somewhat less important to be be so intelligent.
It’s also unlikely to be about oxygen because oxygen levels that reach the brain in a healthy person depend almost entirely on the amount of saturated haemoglobin, which is 95-100% of Hb in someone without serious lung heart or haemoglobin defects. This means that variability in O2 availability is more dependent on one’s iron level than breathing/air effects. (I disclaim that I haven’t yet looked into literature about O2 chemistry and supply to the brain so may be wrong)
The CO2 hypothesis at least makes some sense because bloodstream CO2 levels vary a bit.
Gwern’s evolutionary argument seems weak because we did not develop in ancestral environments where we could properly trap CO2 (our CO2 sensors mightn’t need to be very sensitive), and for our ancestord it was at least somewhat more important to conserve energy from breathing and somewhat less important to be be so intelligent.