Well, at low concentrations of oxygen, we basically want to make sure that all the oxygen ends up in our tissues of the body. So that means we do not want our hemoglobin to actually bind that oxygen very strongly. And that's exactly why, at low concentrations of oxygen, that two, three BPG binds to the allosteric side of hemoglobin. And that basically makes sure that it doesn't take that oxygen and it gives that oxygen off to with the tissues of our body. So this cooperative behavior is known as negative cooperativity. So we have positive and negative cooperativity.