Why do we yawn? It’s almost certainly not for the reason you think

Given that we've literally grown up with them, we often know surprisingly little about how our bodies work. This new series aims to fill the gaps

All vertebrates yawn, or indulge in a behaviour that's at least recognisable as yawn-adjacent. Sociable baboons yawn, but so do semi-solitary orangutans. Parakeets, penguins and crocodiles yawn - and so, probably, did the first ever jawed fish. Until relatively recently, the purpose of yawning wasn't clear, and it's still contested by researchers and scientists. But this commonality provides a clue to what it's really all about - and it's probably not what you're expecting.

When I poll audiences and ask: Why do you think we yawn?', most people suggest that it has to do with breathing or respiration and might somehow increase oxygen in the blood," says Andrew Gallup, a professor in behavioural biology at Johns Hopkins University. And that's intuitive because most yawns do have this clear respiratory component, this deep inhalation of air. However, what most people don't realise is that that hypothesis has been explicitly tested and shown to be false."