Just a guess, but CO2 levels in our body are much lower which would mean small changes are easier to detect. Also just a guess, when we were all just fish mak

Just a guess, but CO2 levels in our body are much lower which would mean small changes are easier to detect. Also just a guess, when we were all just fish making a first few steps into land, atmosphere O2 concentration was lower, CO2 higher, so maybe we evolved to detect what was more abundant then.