It is still not known exactly why yawning is contagious. By the way, this is a great mystery for scholars. “There are some theories to try to explain this phenomenon, but there are no conclusive answers”, says biologist Débora Hipólide, from the Department of Psychobiology at the Federal University of São Paulo (Unifesp). According to her, evidence suggests that yawning is a primitive form of communication between individuals of the same species, to signal changes in the environment. Contagion would be the way to confirm receipt of the message, while passing it on. These clues are taken into account in one of the main theories of yawning, known as the «Evolutionary Theory». According to this thesis, yawning was a very important behavior for some vertebrate ancestor – it is not known which one. At that time, the open mouth would alert the group and synchronize the action, passing messages such as “attention, predator in the area”, “here comes rain” or “hey, it’s time to sleep”. With evolution, threats have decreased and communication has improved, but we keep this primitive remnant, today without any special meaning. We are not the only vertebrates that yawn: dogs, cats and lions are some examples of animals that have the same mania. Another theory about the phenomenon proposes that the open mouth may have the function of showing changes in the internal conditions of our body. That is, yawning would have a physiological character, used by the body as a warning system, when the person is bored, sleepy or tired. “As in these situations you breathe more slowly, as the level of carbon dioxide increases in the blood, a message is sent to the brain, asking for more oxygen. Yawning would be a response to the need for deep breathing to wake up the body,” says Débora.
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I want air! Physiological theory points to yawning as a tactic by the body to gain more oxygen
1. When oxygenation in the pulmonary alveoli decreases, a message is sent to a region of the brain called the paraventricular nucleus, which is located in the hypothalamus. From there, several chemical messengers are released — the neutrotransmitters — that induce yawning and simultaneous reactions throughout the body.
2. The mouth opens and the person inhales a large amount of air, which is sent to the lungs. At the same time, the muscles stretch to improve circulation and the heart rate increases. Thus, the feeling of tiredness decreases and the body returns to a state of alert.
3. Yawning is characterized by being an involuntary reflex. It’s almost impossible to interrupt it, even if you want to – that’s why the «contamination» is so big. Studies at the State University of New York show that between 40% and 60% of people feel infected by other people’s yawning