Close
today i learned (til)

The Science of Yawning

December 6, 2023

We’ve all experienced that urge to open our mouths wide, take a deep breath, and stretch our facial muscles. But why do we yawn, and what explains the phenomenon of contagious yawning?

Scientifically, yawning is the synchronized motion of the thoracic muscles in the chest, the diaphragm, the larynx in the throat, and the palate in the mouth. This act helps to distribute surfactant, a wetting agent, to cover the alveoli, which are tiny air sacs in the lungs [3]. The brain, particularly the hypothalamus, plays a central role in triggering and regulating yawning. This seemingly simple action, however, sets off a cascade of changes within the body. Yawning increases heart rate, facilitates blood flow, and enhances oxygen intake.

The precise reason for why we yawn is still researched and debated by doctors and scientists. However, the most common explanations revolve around yawning being used as a way to keep us as alert. Yawning is considered a brain cooling mechanism which leads to an increase in peripheral and cerebral blood flow. The rhythmic contraction and relaxation of facial muscles during a yawn enhance blood flow in the face, leading to the dissipation of heat through emissary veins connecting the surface of the head with the internal blood vessels. Furthermore, the act of gaping the mouth and inhaling cool air during a yawn influences the temperature of the blood traveling from the lungs to the brain through convection [2].

Another explanation is drowsiness being a common stimulant for yawning, with boredom leading to drowsiness as the primary source of stimulation diminishes. Studies  demonstrate a significant increase in physiological arousal after yawning, shown in increased heart rate and skin conductance levels. This arousal response is likened to the effects observed with caffeine intake, supporting the idea that yawning plays a role in the brain’s arousal reflex. Additionally, the frequency of yawning is noted to be associated with viewing uninteresting stimuli and activities requiring minimal interaction, reinforcing the idea that yawning subserves arousal and higher brain activation [2].

What is known is that yawning is undeniably contagious, with a single person’s yawn capable of inducing yawning in an entire group. People with higher empathy levels are believed to be more susceptible to yawning in response to others as brain imaging studies have revealed that observing someone yawn activates brain areas associated with social functions. Interestingly enough, this phenomenon extends beyond humans, as dogs also yawn when witnessing their owners or strangers yawn, and similar contagious yawning has been observed in various animals [4].

Moreover, when members of a group yawn together, it could help align their mental states, making them more synchronized. This synchronization is believed to serve as a form of collective alertness, helping the group become more aware of external threats more rapidly than if each individual were to respond independently. As a result, the spread of yawning in a group is thought to be a way for individuals to share a collective state of readiness and awareness [4].

Recent research has shed light on the influence of breathing methods and forehead temperature on the contagious nature of yawning. A study exploring these factors found that nasal breathing acted as an antagonist to contagious yawning, significantly reducing its incidence. Participants engaging in other breathing conditions, however, yawned approximately 48% of the time. Moreover, applying a cold pack to the forehead greatly diminishing contagious yawning, while warm and room temperature packs showed no such impact. The combined conditions thought to promote brain cooling, involving nasal breathing and forehead cooling, virtually eliminated contagious yawning, since only one out of 22 participants experienced yawning. These findings highlight the connection between physiological factors, particularly breathing patterns and thermoregulation, and the occurrence of contagious yawning [1].

As research on the science of yawning advances, we can continue to discover more about this seemingly simple act. So the next time you feel that familiar yawn coming on, remember that you’re engaging in a fascinating scientific phenomenon!

References:

  1. Gallup, A. C., & Gallup, G. G. (2007). Yawning as a brain cooling mechanism: Nasal breathing and forehead cooling diminish the incidence of contagious yawning. Evolutionary Psychology, 5(1), 147470490700500. https://doi.org/10.1177/147470490700500109
  2. Gupta, S., & Mittal, S. (2013). Yawning and its physiological significance. International Journal of Applied and Basic Medical Research, 3(1), 11–15. https://doi.org/10.4103/2229-516x.112230
  3. Science Reference Section, Library of Congress. (2019, November 19). Why do we yawn?. The Library of Congress. https://www.loc.gov/everyday-mysteries/biology-and-human-anatomy/item/why-do-we-yawn/#:~:text=A%20yawn%20is%20a%20coordinated,we%20cannot%20yawn%20on%20command.
  4. Rabin, R. C. (2019, February 22). Why do we yawn?. The New York Times. https://www.nytimes.com/2019/02/22/well/live/why-do-we-yawn.html
0Likes
About Author

You May Also Like

Articles, Funny Bone, today i learned (til), vintage science
Deep Philosophical Questions About the Universe
today i learned (til), vintage science
A Chemist, a Vegetable, and Iron Oxide Walk into a Bar
today i learned (til)
Social media is killing our environment
today i learned (til)
Dino Nuggets: The Evolution of Birds from Dinosaurs

Your journey starts here! Let’s talk!

ThemeRex © 2026. All rights reserved.
  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.