Why do we yawn?
The American magazine Forbes published a report based on an analysis by a specialized biologist, which debunks the common hypothesis linking yawning to a lack of oxygen or an excess of carbon dioxide in the blood. It reveals that this universal phenomenon, which we have practiced since we were fetuses in our mothers’ wombs, is governed by a deeper and more complex neurobiological logic than previously believed for decades.
The report clarified that Professor Scott Travers, an evolutionary biologist, confirmed that the prevailing idea that yawning increases oxygen levels in the blood was conclusively disproven scientifically as far back as the 1960s. This was demonstrated when experiments showed that breathing air enriched with oxygen or carbon dioxide did not alter the yawning rates of volunteers.
The report noted that the most accepted theory in scientific circles today is the “brain temperature regulation” hypothesis, which views yawning as an evolved biological cooling system for the body’s most energy-intensive neural center.
In this context, the biologist explained that although the human brain accounts for only 2 percent of body weight, it consumes about 20 percent of the body’s energy, making it susceptible to overheating. Yawning acts as a cooler by drawing cold air into the sinuses, which are located near the major arteries supplying the brain, thereby lowering its temperature and returning it to optimal performance levels.
The report detailed the evidence supporting this theory, noting that researchers have observed measurable changes in yawning frequency related to ambient temperature, as follows:
• Studies have shown that humans yawn more frequently during the mild seasons of winter and autumn, when external air temperatures are lower than body temperature, allowing for effective brain cooling. Conversely, the phenomenon decreases significantly on hot summer days when air temperature equals or exceeds body temperature.
• In a notable experiment, placing cold compresses on participants’ foreheads significantly reduced their urge to yawn while watching videos of people yawning, whereas warm compresses increased yawning rates, confirming the direct link between the brain’s need for cooling and the triggering of this mechanism.
The report also addressed the social dimension of the phenomenon, noting that “contagious yawning,” which occurs when seeing another person yawn, remains a subject of scientific debate. The biologist emphasized that the most likely explanation is not simple emotional mimicry or empathy, but rather a collective mechanism for cooling brains. In ancient human groups, one individual’s yawn may have signaled that the herd’s brains needed cooling in preparation for collective activity or to face an imminent threat, making a collective yawning response an evolutionary survival advantage.
This explanation reframes our understanding of one of the most common human behaviors, transforming it from a mere primitive reaction associated with boredom or drowsiness into a sophisticated neurothermal regulatory system. The question remains open regarding the precise reasons why certain medical conditions, such as migraines or epilepsy, are accompanied by episodes of excessive yawning. The conclusion remains that science, as often is the case, reveals that the simplest explanation is not necessarily the correct one, and that behind every simple human action lies a complex evolutionary story worth discovering.
