Yawning is a habitual and daily act. We yawn or see someone yawn early in the morning, at the afternoon meeting, and so on.
So do our pets (dogs, cats and even reptiles!). However, despite the routine of this phenomenon, it is unknown why we yawn or what functions it has in our body.
What is yawning?
It is an involuntary act that we can not control by which we open our mouth widely, making a deep inspiration, followed by a slight expiration, which almost sighs. The yawn appears when we are deeply bored or tired, and is accompanied by movements of the upper body to have greater thoracic expansion.
Why is it contagious?
The reason is unknown, but not only in the human species, but also in a wide variety of animals. It is curious that only in humans and monkeys is yawning contagious, something that seems to be due to the fact that both share a more developed social complexity than the rest of the animals.
There is a wide variety of theories, although none by itself contributes to a complete answer.
The most defended at present are:
Lack of oxygenation
In situations of tiredness, boredom, etc., we breathe less intensely than usual, causing a lower oxygen exchange or an excess of carbon dioxide in our body, yawning like this, to take a deep breath and compensate for the lack of oxygen.
This hypothesis is flawed: studies have shown that fetuses of about 12 weeks were yawning, but they do not breathe through the lungs until they are born. The way to obtain oxygen and expel carbon dioxide occurs through the umbilical cord.
Some experts think that yawning acts as a kind of mechanism that modulates the feeling of anxiety. As an example, there has been an increase in the number of yawns in politicians or professionals of public speaking who waited their turn to speak, athletes before important competitions, or in patients while they waited their turn in the waiting room.
In this case, the yawn has some evolutionary origins, used to synchronize the body in different situations such as: on waking, sleeping, in dangerous conditions, etc. After a yawn, blood pressure and heart rate increase by more than 25%, keeping the body on alert.