"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."
Yawning appears across all vertebrates, from parakeets and crocodiles to baboons, orangutans and ancient jawed fish. Common yawning behavior suggests a shared underlying function rather than random occurrence. The long-standing hypothesis that yawns increase oxygen or expel carbon dioxide has been directly tested and shown false by experiments manipulating inhaled gas concentrations and by observing no yawning differences in respiratory illnesses. The motor pattern of yawning includes an extended gaping and deep inhalation, which explains the intuitive respiratory appearance despite the lack of causal respiratory function. The consensus remains contested but points away from simple respiratory explanations.
Read at www.theguardian.com
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