Author: Hanni Yang
Editors: Emily Yu, Hwi-On Lee
Artist: Olivia Yuan
Yawning—that seemingly involuntary reflex—has intrigued scientists and casual observers alike for centuries. But what’s truly puzzling is the phenomenon of contagious yawning; when one person yawns, it often triggers a chain reaction prompting others to follow suit, regardless if they’re fatigued or not. Why does this happen? What drives this curious social behavior?
Yawning itself is widely observed in various species, from humans to primates and even certain animals like dogs and birds. An older theory states that yawning occurs when the brain lacks sufficient oxygen. The idea was that yawning helped bring in fresh oxygen to the brain whenever there was more carbon dioxide than oxygen in the blood. However, studies have shown that yawning does not increase when people breathe in more carbon dioxide, so this theory was thrown out. Instead, recent studies suggest that yawning might serve multiple purposes.
One theory suggests yawning acts as a mechanism to keep the brain alert, increasing heart rate, releasing wakefulness-promoting hormones, and altering brain activity, especially during daily or passive activities. Another compelling hypothesis proposes that yawning aids thermoregulation, promoting facial muscle movement and increasing facial blood flow to help dissipate heat in the brain—a hypothesis supported by research correlating yawning frequency with changes in ambient temperature. Furthermore, yawning has been intricately linked to empathy and social bonding. The tendency to yawn in response to others' yawns has been theorized to reflect an empathic connection and foster social bonds. Brain activity studies have suggested correlations between yawning and empathic responses. These theories highlight the multifaceted nature of yawning, with intertwined physiological, neurological and sociological aspects that continue to fascinate researchers.
Contagious yawning is a widely documented phenomenon, observed not only in humans but also in many social vertebrates. Studies within conspecific populations demonstrate this behavioral synchrony, while interspecific phenomena have also been reported in captive settings, revealing its cross-species potential. Among primates, great apes like chimpanzees and bonobos exhibit contagious yawning, indicating a shared trait among this closely related group. Moreover, domestic dogs have also displayed this behavior in response to human yawns, highlighting the interplay between domestic and social cues in triggering this response. Additionally, even non-mammalian species like birds, especially budgies, exhibit contagious yawning, suggesting it may be more widespread than initially thought, with potential prevalence beyond mammals.
Mirror neurons, a fascinating aspect of neuroscience, play a pivotal role in the human brain's ability to imitate actions observed in others, including contagious yawning. These neurons, associated with empathy and social cognition, facilitate the mirroring of observed behaviors and sensations, enabling individuals to resonate with and replicate the actions they witness. For instance, contagious yawning is thought to involve mirror neurons, where observing a yawn activates neural networks associated with the urge to yawn. Zhoufeng Chen, a director at Washington University’s Center, conducted experiments on rats that showed that after observing one rat scratching, other rats quickly imitated the behavior, demonstrating immediate recognition of its purpose. This spontaneous imitation demonstrates an instinctive response to useful behavior without the need for conscious thought—just like how Thomas Scammell, a neurologist at Harvard Medical School, said that “If someone flashes you a nice friendly smile, without even thinking about it, you’re likely to smile back … It is a form of social communication, and it appears that people who are more empathetic are more likely to have this social mirroring.”
Yawning, once thought to be simply an oxygenation response, has now moved beyond this simplistic explanation. Instead, its complexity spans across social, neurological, and evolutionary domains. The phenomenon of contagious yawning, observed in different species, is linked to empathy and social mirroring, illustrating its multifaceted nature. Mirror neurons provide a glimpse into this intriguing behavior, highlighting its social and cognitive underpinnings. Yawning, therefore, stands as a testament to the relationship between biology, social connection, and the workings of the brain—an enigma that continues to captivate scientific curiosity and warrant further exploration.
Citations:
Carey, Teresa. “Why are yawns contagious? We asked a scientist.” PBS, 17 July 2018,
https://www.pbs.org/newshour/science/why-are-yawns-contagious-we-asked-a-
scientist. Accessed 7 January 2024.
Gallup, Andrew C., and Sabina Wozny. “Interspecific Contagious Yawning in Humans -
PMC.” NCBI, 27 July 2022, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9332820/.
Accessed 7 January 2024.
Summer, Jay, and Anis Rehman. “Why Do We Yawn?” Sleep Foundation, 8 November 2023,
https://www.sleepfoundation.org/sleep-faqs/why-do-you-yawn. Accessed 7 January
2024.