Why Do We Yawn?
We are not entirely sure why we yawn. Leading theories include brain cooling (bringing cool air to regulate brain temperature), increasing alertness (stretching facial muscles and boosting heart rate), and social signaling. The old theory that yawning increases oxygen intake has been largely disproven. Yawns are contagious likely due to social empathy mechanisms.
Key Takeaways
- The brain cooling theory is currently most supported by research.
- You may have yawned just reading about yawning - this is normal.
- Fetuses yawn in the womb, suggesting a developmental function beyond social signaling.
Explanation
The brain cooling theory is currently most supported by research. Yawning brings a large influx of air and stretches the jaw, potentially cooling blood flowing to the brain. Studies show yawning increases when brain temperature rises and decreases in cold environments. A cooler brain may function more alertly.
Yawning also appears related to state changes - transitioning from rest to alertness or vice versa. Stretching facial muscles, opening airways, and the brief heart rate increase from yawning may help reset our arousal state. This explains why we yawn when tired, bored, or just waking up.
Contagious yawning - yawning after seeing or even thinking about yawning - seems linked to social empathy. People who score higher on empathy tests are more susceptible. Children develop contagious yawning around age 4-5 when empathy develops. Some evidence shows dogs 'catch' yawns from humans, suggesting social bonding involvement.
The oxygen theory was once the most popular explanation but has been largely debunked. Researcher Robert Provine tested this in the 1980s by having subjects breathe air with different oxygen and CO2 concentrations. Breathing pure oxygen did not reduce yawning, and breathing high-CO2 air did not increase it. If yawning were about oxygen intake, these results would have been opposite. The brain cooling theory gained traction partly because it better explains the observed data.
A typical yawn lasts about 6 seconds, during which heart rate can increase by up to 25%. The jaw opens wide, stretching muscles in the face, neck, and upper body. Brain scans show that yawning activates the precuneus region of the brain, which is involved in self-awareness and consciousness. Nearly all vertebrates yawn, from fish to birds to mammals, suggesting the behavior has deep evolutionary roots predating the development of empathy or complex social behavior.
Things to Know
- You may have yawned just reading about yawning - this is normal.
- Fetuses yawn in the womb, suggesting a developmental function beyond social signaling.
- Excessive yawning can occasionally indicate medical conditions like sleep disorders or medication side effects.
- People with autism spectrum disorder tend to be less susceptible to contagious yawning, which aligns with the empathy-connection theory, though this does not mean they lack empathy in other areas.