Why do we yawn? Science gives us the answer


Yawning is an involuntary mechanism, through which we introduce a greater amount of air into our lungs.. Throughout our lives we yawn around 250,000 times. There is still no clear and precise explanation for this phenomenon, it seems that the structures that control yawning are found in the brain stem, including the responsible neurotransmitters found in the nucleus of the hypothalamus. The hypothalamus is located in the brain from where we know that the nervous system is also controlled.

Yawning would then seem to be related to brain processes and structures, but in what way? In today’s article we will try to answer this question, explaining everything that is known about yawning and exposing the different existing theories that have tried to understand its function.

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What is yawning?

Although it is commonly thought that yawning is a reflex, yawning is what is known in etiology as a “fixed pattern of action”, this means that it is an instinctive response and not the response to a stimulus. Being a “fixed pattern of fixed action” you cannot yawn just a little, that is, it has a certain intensity. Although it is true that we can stop yawning if someone bothers us or interrupts us.

All yawns look alike, it is easy to recognize when a person is yawning, they open their mouth wide, tilting their head slightly backwards and squint their eyes that turn reddish (tears). In this process you salivate and “open your ears” (the Eustachian tubes actually open). There are also many more cardiovascular, respiratory and neuromuscular actions that we are not aware of..

Although all yawns are practically the same, they can have a different duration. Normally, they last between 8 and 10 seconds, but there can be yawns of three seconds or much more than 10. The intervals between yawns (non-pathological) are estimated to be 68 seconds on average and the frequency does not present any relationship with the duration.

Depending on the moment, we can associate yawning with different non-verbal messages. We yawn when we are tired, but also when we feel anxious, even sometimes when we are hungry or before starting something new. Yawning could serve as a psychological release after a period or moment of alertness or high stress. It can also express strong and not very acceptable emotions such as boredom, rejection or anger, which is why we often cover our mouths to hide yawning. This is common to different cultures.

Bears, crocodiles, monkeys, iguanas, birds, turtles, fish, etc., all animals that have a backbone can yawn. Apparently it could have to do with the degree of evolution of the species. Not all mammals yawn the same length.


What is the use of yawning?

We have seen that yawning is an instinctive act present in many species. They are very similar, but have small differences. From these data several studies have attempted to determine the precise function of yawning.

1. Oxygenate the blood

Popularly, it is thought that we yawn when there is a lack of oxygen in the blood. Yawning would be the way to bring more oxygen to the blood through breathing. The assumption seems quite reasonable, the more air, the more oxygen. Historically, this has also been the most accepted theory for the logic presented. The more cycles of breaths, the more oxygen in the blood and less CO₂.

Some studies have tried to associate the detection of shortness of breath by the hypothalamus with yawning, however, there are still no conclusive results. Moreover, no relationship between blood oxygen and the number of yawns performed in any of the animals studied has been obtained.


2. Cool our brain

In 2016, Oneonta University, New York, carried out a study that related the duration of yawns with the brain development of mammals. As we mentioned, yawns differ in duration, since apparently this has to do with the weight of the brain and the number of neurons, but why? Apparently yawning would be a process by which we cool the different brain structures, it would be like a ventilation system. When we yawn we draw cold air into our nose and mouth.this process is capable of cooling the blood by increasing blood flow to the brain.

Differences in yawn duration in animals with larger brains may be due to enhanced cognitive abilities and displaying a greater range of behaviors. According to Professor Andrew Gallup, leader of the American study, the duration of yawns has an undeniable relationship with the complexity and size of the brain, the parameter that most influences this being the number of neurons in the mammals studied.

Mice have about 4,500 neurons on average and their yawns last about two seconds. Humans have 2.2 times more neurons and our yawns last 3 times longer, 6 seconds per 10,000 neurons. The human brain is the most complex of structures, it processes all the information that comes from our senses, gives a coordinated response and at the same time maintains all our vital functions, therefore, it is better that it does not get hot. It is not yet known, but the consequences of yawning are thought to affect all regions and areas of the brain.

As a result of these conclusions, to deepen and confirm the theory of refrigeration, another study carried out at the University of Vienna, wanted to relate temperature and yawning, these results were compared with those of another study carried out in Arizona. The idea was simple, if yawning serves to cool the brain, there is little point in yawning when the outside temperature is very high.

The results showed differences by temperature, showing an increase in summer yawning in Vienna and a decrease in Arizona. Although they may seem opposite at first, Vienna and Arizona have very different summer temperatures. In Vienna, summer temperatures range between 26 and 15 degrees, in Arizona it can reach 40 degrees. All these results allowed to establish an optimal temperature at 20 degrees.

Comparing studies from two different cities and with different daylight hours also allowed these parameters to be removed from the causes of yawning. Also, it was concluded that at very low temperatures yawning also decreases, since there is no need for refrigeration. Therefore, these studies reinforced the previous ones and the theory of refrigeration. Starting today, look at the duration of your yawns, it could mean that you are smarter than average and you are wasting it. Now, jokes aside, stay yawn longer, brain bigger and above all more neurons.


3. Other theories

In this last section we show a diversity of theories that have been appearing over time, although most do not present any scientific evidence or have even been discarded due to lack of results. For example, another of the more credible explanations would be that yawning is a mechanism to relieve stress and anxietyIt is true that many times when yawning we feel a sensation of peace and well-being similar to that of stretching. However, there are no conclusive studies establishing a direct correlation between yawning and stress relief.

Other research suggests that yawning was an early communication system between primates and humans, before speech appeared. Although there are studies that show that bonobos and humans share some forms of communication and structures, they are far from proving that yawning was a form of primitive language.

Although we have already said that yawning is a “fixed pattern of action”, some researchers propose that it is a reflex that is preserved since we are in the womb, although this theory does not really explain its function either. Maybe I might not have.

This is suggested by some biologists and students of evolution, who yawning is a legacy of the gills of the first amphibians that left the sea to inhabit the land, this could explain why it is a “fixed pattern of action”, something that does not respond to any stimulus. For this theory, yawning is simply an inheritance and has no function.

There are also theories that try to establish the relationship between yawning and sexual function, more precisely with erections in men. To speculate, we can name numerous theories that explain the function of yawning, but it seems that today there is a winner. The refrigeration theory has been supported by different studies and presents solid results.

However, it presents only a partial explanation, it may be that yawning has more than one function, for example, we still don’t know why yawning is contagious. One of the hypotheses would be to make people more attentive and the whole group to respond as quickly as possible to an external threat. But researchers agree, we still don’t know for sure why we yawn.


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