Yawning, a seemingly simple and universal behavior, has perplexed scientists for centuries, leaving them grappling with its elusive purpose.
This act is not exclusive to humans; it is a shared phenomenon across species, including mammals, birds, reptiles, and amphibians. The widespread occurrence of yawning in the animal kingdom implies a fundamental, yet undiscovered, purpose of yawning.
While yawning is synonymous with sleepiness in humans, it also occurs when we are awake. This association has led some scientists to postulate that yawning might play a role in regulating brain temperature. But the “brain-cooling hypothesis” remains unconfirmed, with subsequent studies yielding inconclusive results.
Interestingly, yawning seems to intensify during stressful situations, such as high-stakes athletic competitions, and postprandial (after eating). The reason behind this remains an enigma. Among primates, yawning is prevalent, especially among males, potentially serving as a subtle warning signal by displaying formidable canine teeth. However, research indicates that yawning occurs with equal frequency among both genders in humans.
The phenomenon of contagious yawning adds another layer to the mystery. The mere sight, thought, or reading about yawning can induce a cascade of yawns. It is particularly prevalent among individuals with high empathic abilities, leading to speculations about its potential social role in human bonding through mirroring behaviors. However, social yawning constitutes a mere 10% of yawning instances, suggesting that its primary function lies elsewhere.
That said, Dr. Christiaan Doelman, a renowned researcher in the Department of Head and Neck Surgical Oncology at University Medical Center Utrecht, has delved deep into the yawning conundrum. His 2022 study offers a fresh perspective, proposing that yawning serves to restore a complex muscle balance, essential for maintaining an open airway.
Doelman elucidates that the dynamic airway passage, formed by the mouth and throat, necessitates adaptability to facilitate various functions such as breathing, chewing, swallowing, and vocalization. The balance in muscle tone is crucial; excessive looseness can lead to airway collapse, while excessive tightness can restrict the airway. Yawning, according to Doelman and his colleagues, acts as a muscle reset mechanism, restoring optimal muscle tone and balance.
Supporting this hypothesis are previous studies illustrating that the pharyngeal lumen (the throat area behind the mouth and nasal cavities) experiences dilation post-yawning. This dilation and subsequent muscle repositioning could be pivotal after extensive use or overstimulation, explaining the increased frequency of yawning post-eating and during anxiety-induced muscle tension.
“Yawning is happening in many vertebrates, and what they all have in common is that the throat could collapse due to low muscle tone or muscle tightness due to stress,” Doelman said. “No other movement has been described to restore that muscle tone.”
So, yawning appears to be a universal solution to prevent throat collapse due to variations in muscle tone across diverse vertebrates. In essence, yawning emerges as a vital mechanism to recalibrate and harmonize the throat muscles, ensuring their proper functionality.