Why Do We Yawn? Exploring the Science Behind This Common Human Experience

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Yawning is something we all do. And it’s something we do daily. But why? And what exactly is a yawn?

Yawning is a complex physiological process that involves various muscular movements and brain regions and occurs with specific duration and frequency.

What does yawning accomplish for the human body, and what does it mean?

Muscular Movements Involved In Yawning

Yawning is a common action that requires the coordinated activity of multiple muscle groups. It begins with a long inspiratory phase (inhalation), where the diaphragm and intercostal muscles contract. This then causes the mouth to open. The jaw lowers, and the tongue retracts and moves downward. Simultaneously, the larynx and hyoid bone descend due to the contraction of the infrahyoidal muscles.

As the yawn progresses, air intake increases, and the soft palate and pharynx elevate. This action can produce a turbulent inhaling sound and clicking noises from the opening eustachian tubes. At the peak of inspiration, the pharynx diameter increases by 3-4 times.

Brain regions activated

The neural (brain) control of yawning is primarily orchestrated in the brainstem. This is near centers responsible for essential functions like breathing, swallowing, and coughing. There are several neuroactive agents that contribute to yawning. These include nitric oxide, dopamine, acetylcholine, glutamate, serotonin, and oxytocin. The neurons fire in a unique rhythmical pattern, which results in complex muscular contractions — the yawn.

Duration and frequency

The duration of a yawn varies across species and is closely related to brain size and complexity. In most animals, a typical yawn lasts between 4 to 7 seconds. Interestingly, research has shown that average yawn duration is a great predictor of brain size in mammals.

Human fetuses yawn approximately 25 times per day and the frequency decreases with age. Adults yawn about 9 times per day on average. Overall, the average amount is between 0 to 28 yawns a day. Yawning often occurs in fits of two or three, each one with increasing intensity.

Theories on Why We Yawn

Scientists have proposed several theories to explain why we yawn. Let’s explore some of the most intriguing ideas behind this common behavior.

Cooling the brain

One theory suggests that yawning helps to cool down the brain. According to this idea, yawning acts as a natural air conditioning system for our brains. When we yawn, we take in a deep breath of cool air, which may help lower brain temperature. This theory is supported by studies done on rats. The rats had increased brain temperatures just before yawning, and the temperature decreased immediately afterward.

Increasing alertness

Another interesting theory proposes that yawning serves to boost alertness. When we yawn, our body releases certain hormones that briefly increase heart rate and alertness. This might explain why we often yawn when we’re tired or bored – it’s our body’s way of trying to keep us awake and alert, even if only for a short time.

Equalizing ear pressure

Yawning also plays a role in equalizing pressure in our ears. This is particularly noticeable during rapid changes in altitude, such as when flying in an airplane or riding in an elevator. Yawning opens the Eustachian tubes, allowing air to flow into or out of the middle ear. This helps balance the pressure on both sides of the eardrum and relieves discomfort and potential hearing problems.

The Evolution of Yawning

Yawning in different species

Yawning is a behavior observed across quite a few species in the animal kingdom. It is not limited to humans but extends to almost all vertebrates. From birds to mammals, yawning appears to be a phylogenetically ancient phenomenon that has persisted throughout evolution. However, while yawning is common, its expression can vary among different animals. For instance, birds yawn, but their yawning differs from that of humans and other animals.

Theories on evolutionary purpose

Scientists have proposed several theories to explain the evolutionary purpose of yawning. One intriguing idea suggests that yawning evolved as a means for animals to subtly notify others in their group about their reduced alertness. This communication could prompt other group members to take over the responsibility of watching for potential threats. Another theory proposes that yawning serves to cool the brain. This cooling then improves cognitive function. The cooling effect might have been particularly advantageous for our ancestors and helped them maintain alertness during critical survival moments.

Changes in yawning behavior over time

As species evolved, so did their yawning behavior. Contagious yawning, for example, is a relatively recent development in evolutionary terms. While physiologically triggered yawns are widespread in vertebrates, the tendency to yawn contagiously varies significantly across species. Contagious yawning is common among great apes like chimpanzees, bonobos, and orangutans but not in gorillas. Some studies have even found evidence of contagious yawning in other mammals, such as wolves, domesticated pigs, and African lions. This suggests that yawning may have taken on additional social functions as species became more complex and socially oriented.

Psychological Factors in Yawning

Boredom and yawning

Yawning often occurs when people feel bored or tired. It’s a natural response to monotony and fatigue. Think of being in a lecture or waiting a long time for something with nothing to do but sit. When the primary source of stimulation in the environment can’t hold a person’s attention, it triggers drowsiness by activating the body’s sleep-signaling system. This explains why yawning is common late in the day or during uninteresting activities.

Stress and anxiety-related yawning

Yawning isn’t just linked to boredom. It’s also associated with stress and anxiety. Nervous individuals tend to yawn more frequently. Some scientists believe that yawning helps cool down the brain, which may be particularly useful during stressful situations. Studies have shown that yawning often follows a rise in blood cortisol levels, a hormone produced during stress.

Yawning as a communication tool

Yawning serves as a unique form of non-verbal communication. The contagious nature of yawning is thought to be related to empathy. People who are more empathetic are more likely to “catch” a yawn from others. Interestingly, individuals with autism spectrum disorder, who may have difficulty with social interactions, are less susceptible to contagious yawning. This phenomenon is stronger among close friends and family members. This further supports its connection to empathy and social bonding.

Yawning Through Life

Fetal yawning

Yawning begins even before birth. Fetuses start yawning in the uterus about 12 weeks after conception. This early yawning demonstrates the development of both the brainstem and peripheral neuromuscular function. Interestingly, fetuses yawn around 25 times per day, with the frequency decreasing as they grow older.

Yawning in infancy and childhood

As babies grow, their yawning patterns change. In a study of three-month-old infants, researchers found that yawning increased during stressful situations, such as when parents stopped interacting with them. It also showed that girls were more likely to yawn than boys in these situations. There might be possible differences in how boys and girls cope with stress.

Changes in yawning patterns with age

Yawning frequency continues to change throughout childhood and into adulthood. Research suggests that there’s a U-shaped pattern in yawning frequency: premature infants yawn more often than full-term babies, and primary school children yawn more frequently than kindergarten children. As people age, the frequency of yawning tends to decrease even more.

The Science of Contagious Yawning

Mirror neurons and yawning

Contagious yawning is a phenomenon linked to mirror neurons in the brain. These special neurons activate when we observe someone else yawning, simulating the action mentally as if it were happening to us. Studies have shown that the human mirror neuron system, specifically the Brodmann’s area 9 in the right inferior frontal gyrus, is activated when perceiving yawns. This activation suggests that contagious yawning is based on empathy, connecting the mirror neuron system to higher cognitive empathic functions.

Factors affecting contagious yawning

Several factors influence contagious yawning. Research indicates that empathy and familiarity play a role, with individuals more likely to catch yawns from those they know well. Age also affects susceptibility, with older people less likely to experience contagious yawning. Interestingly, contagious yawning isn’t limited to humans; it has been observed in various social vertebrates, including chimpanzees, dogs, and even birds.

Evolutionary advantages of contagious yawning

Contagious yawning may have evolved as a means of group communication. It could signal to others that the one yawning is less alert. This, in turn, prompts the other group members to increase their vigilance. This behavior might help maintain group alertness and synchronization, potentially enhancing overall safety and coordination within social groups. The widespread occurrence of contagious yawning across species suggests its importance in social dynamics and group behavior.

Cultural and Social Aspects of Yawning

Yawning etiquette across cultures

Yawning etiquette varies widely across cultures. In Islam, yawning is seen as a sign of Satan entering the body, and people are encouraged to cover their mouths when yawning. In India, it’s believed that spirits can enter the body through an open mouth during a yawn. In Western cultures, covering the mouth while yawning is considered polite, stemming from historical beliefs about preventing illness.

Yawning in social situations

Yawning in social situations can be tricky. Studies show that both implied and actual social pressure significantly reduce contagious yawns. This suggests that people actively inhibit yawns in social settings due to perceived stigma. Interestingly, contagious yawning is higher between strongly bonded individuals, such as friends and family members.

Misinterpretations of yawning

Yawning is often misinterpreted across cultures. In some societies, it’s seen as a sign of disrespect or boredom, especially during speeches or important conversations. However, it’s important to remember that yawning serves a physiological purpose and isn’t always a reflection of one’s interest or respect for others.

FAQs

What is the primary cause of yawning?

Yawning is a common yet somewhat mysterious behavior in humans. There are multiple theories about why people yawn, including triggers such as fatigue, boredom, waking up, and experiencing stress. Observing another person yawn can also provoke yawning.

Does yawning indicate a lack of oxygen?

It was once thought that yawning could signify an oxygen deficiency. However, recent studies have shown that yawning is not a mechanism to increase oxygen intake in the body.

Why do we yawn when we see someone else yawn?

Yawning in response to seeing someone else yawn may be due to a phenomenon known as echopraxia. This is where an observed behavior is involuntarily mimicked. This behavior is facilitated by mirror neurons in the brain, which play a role in this mimicry.

What is the purpose of yawning?

Yawning may serve a physiological function by releasing certain hormones that momentarily increase heart rate and alertness. This suggests that yawning could be the body’s way of maintaining alertness and wakefulness, especially when tired or bored.