To test the idea that we yawn to bring in more oxygen or expel excess carbon dioxide, studies published in the 1980s manipulated the levels of both gases in air inhaled by volunteers – and they found that while changes did significantly affect other respiratory processes, they didn’t influence the regularity of yawns. There also doesn’t seem to be any systematically measurable difference in the yawning behaviour of people suffering from illnesses associated with breathing and lung function – which is what you would expect if yawns were respiration-related.