Analysis of hundreds of recordings of yawns in different species of mammals and birds showed that the longer the brain, the larger the animal's brain and the more neurons, the longer it lasts.
Why yawn is needed and why it is "contagious" - probably one of the oldest mysteries that still remain without a final answer. However, in 2007, Andrew Gallup and his colleagues put forward a hypothesis that is now widely accepted: it links yawning with the need to cool the brain.
The jaw muscles are stretched, the mouth and nasal cavities are filled with fresh air, reducing the temperature of the blood entering the brain. From this it is easy to conclude that the larger the brain, the more intense yawning is required to cool it down. Indeed, in 2016, Gallup's team compared yawning times in 24 mammalian species, showing that it correlated with their brain size. So, for mice to cool the organ, an average of 0.8 seconds was enough, and for humans - 6.5 seconds.
In a new paper published in the journal Communications Biology, Gallup and his co-authors present the results of such work on an already wider scale. In various zoos around the world, scientists were able to collect almost 1,300 records of yawning from representatives of 55 species of mammals and 46 species of birds, confirming a reliable positive correlation between its duration, the number of neurons in the brain and its mass.
“Despite the fact that the behavioral pattern of yawning is strictly fixed, its duration changes with changes in the brain,” summarize the authors of the article. In their opinion, the curious exception in the face of giraffes indicates the same. They are the only mammals that do not appear to yawn. This feature may be associated with their incredibly long neck, which forced these animals to develop their own unique mechanisms of blood supply and regulation of the brain.