A study with about 29 species has concluded that the size of the brain is related with the yawning and supports the hypothesis that we yawn to fill the brain with oxygen and "refresh" it.
Have you just yawned? Don't worry I know its a very contagious behaviour. Yet, the scientists don't manage to agree why or where does this gesture come from. Charles Darwin himself said in 1838 that "While seeing the yawn of the dog, the horse and the man I feel like all the animals are made on a same structure.
Well a team of scientist of the State University of New York in Oneonta decided to observe the yawns of 29 different mammals on youtube videos: mouses, cats, hedgehogs, sea lions, foxes ad human beings and they found a pattern. The animals with a small brain, with less neurons in the cortex yawned for a shorter period of time than animals with a bigger brain and more neurons. And so, animals with bigger and more complex brains have deeper and more complicated yawn.
From big to small the humans (with about 12m neurons in the cortex) had the longest yawn with an average of a bit more than 6 seconds; The apes are the mammals that yawn the longest time; the elephants -that have a similar number of cortical neurons as the humans yawned also with an average of 6 seconds.
What about the mammals with minuscule brain? In the case of the mouses the yawns barely last 1.5s.
In conclusion, the researchers note that *the yawn has a key physiological effect and it helps cooling down our thinking organ.
The study was published by the Science magazine.