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Why We Yawn (Psychology Today)

Psychology Today title: Why We Yawn
PT subtitle: A large study about yawning reveals a surprising insight.
By: Sebastian Ocklenburg, Ph.D.
Date: 17 May 2021

“KEY POINTS

  • Why we yawn is still largely a scientific mystery.
  • The world’s largest study on yawning analyzed yawns from 101 species.
  • The results show the animals with bigger brains yawn longer.
  • This finding supports the hypothesis that people yawn to cool their brains.

Some people yawn a lot while others almost never seem to yawn. Unfortunately, yawning frequently can lead to uncomfortable situations, for example in social situations. For example, if someone tells a story that is important to them and the listener constantly yawns, the speaker may get the impression that the listener is bored and does not really care about the conversation. Thus, understanding why we yawn is important from a psychological perspective.

The Brain Cooling Hypothesis of Yawning

A new study, just published in the scientific journal Communications Biology (Massen et al., 2021), now was aimed at testing a fascinating hypothesis on why we yawn: The brain cooling hypothesis. This hypothesis suggests that the reason why we yawn is to cool the brain. According to the brain cooling hypothesis, the purpose of the muscular contractions and the deep inhalation during yawing is to flush away hotter blood from the head and replacing it with cooler blood. Cooling the brain is important as too much heat from the activity of the nerve cells and the surrounding temperature may impair brain function due to overheating.

The World’s Largest Study on Yawning

The brain cooling hypothesis of yawning suggests that animals with bigger brains and more nerve cells would yawn more often and longer, as bigger brains need more effort to cool down than smaller brains. To test this prediction, the scientists that performed the study conducted the largest analysis of yawning ever. The scientists analyzed videos of 1291 different yawns that were made by humans and non-human animals from 101 different species (55 mammal species and 46 bird species) and determined the length of each yawn. The study included data from a wide range of different animal species such as chimpanzees, rats, cats, hyenas, owls, ravens, and parrots. The videos were recorded in zoos or during scientific observations or obtained from internet pages. In addition, the researchers extracted data on the brain size and number of the yawning species from previous studies.

What Were the Main Results of the Study?

The scientist found a large, statistically significant association between yawning duration and both brain size and the number of nerve cells in the brain. Animals with bigger brains and more nerve cells yawned longer than those with smaller brains and fewer nerve cells. This association was found for both mammals and birds.

These findings provide strong support for the brain cooling hypothesis of yawning. The results of the study suggest that yawning is an evolutionary old mechanism to prevent the brain from overheating that is present across all animal species that yawn.

What Do the Results of the Study Mean for Chronic Yawners?

First and foremost, the study shows that it is not negative to yawn a lot. It is a normal function of the body that ensures the proper functioning of the brain. The stereotype that people that yawn during a conversation are bored or not interested in the conversation is false. In contrast, the study suggests that people yawn to keep their brains in working order, which is quite important during a conversation.

References
Massen, J.J.M., Hartlieb, M., Martin, J.S. et al. Brain size and neuron numbers drive differences in yawn duration across mammals and birds. Commun Biol 4, 503 (2021).”

Sources:
https://www.psychologytoday.com/us/blog/the-asymmetric-brain/202105/why-we-yawn
and
Nature: Brain size and neuron numbers drive differences in yawn duration across mammals and birds

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