SYSK Selects: What Makes us Yawn?

Episode Summary

Executive Summary: The episode is a Stuff You Should Know Selects replay about yawning: what it is, why it happens, and why science still lacks a definitive answer. Hosts Josh and Chuck review competing theories—oxygen deprivation, boredom, social signaling, and brain cooling—while highlighting research on contagious yawning, empathy, autism, and fetal yawning. The episode closes with listener mail about Rodriguez and a personal encounter with him.

Main Topics: Defining yawning and pandiculation (Priority: 5/5): The hosts explain yawning as an involuntary action involving mouth opening, inhalation, brief eye closure, diaphragm movement, and often stretching (pandiculation). They emphasize how universal and familiar the behavior is. Competing theories for why we yawn (Priority: 5/5): They review and largely reject older explanations such as oxygen/CO2 regulation and boredom, while noting newer ideas like brain cooling and changes in arousal state as more plausible but still unproven. Contagious yawning and empathy (Priority: 5/5): The conversation explores why seeing or hearing about yawning triggers yawns in many adults and how mirror neurons, empathy, and social cognition may be involved. Yawning in development and animals (Priority: 4/5): The episode notes that fetuses yawn in utero and that yawning appears across vertebrates, suggesting an evolutionary significance that is still unclear. Autism and yawning research (Priority: 4/5): The hosts discuss studies suggesting people with autism may be less susceptible to contagious yawning, while also questioning whether eye-gaze differences or other factors may explain the findings. Listener mail about Rodriguez (Priority: 2/5): A listener shares a vivid story of meeting Rodriguez in Detroit and hearing him play a song three times, reinforcing the show’s appreciation for firsthand cultural stories and documentary connections.

Key Arguments: Yawning is involuntary and includes more than just opening the mouth; it often involves stretching (pandiculation) and eye closure. The oxygen/carbon dioxide theory does not hold up because adding oxygen or increasing CO2 did not reduce yawning in experiments. Boredom is not a sufficient explanation, since yawning occurs in many states of arousal, including before competition or during nervousness. Brain cooling is presented as the most current and plausible theory, though it remains unproven. Contagious yawning appears linked to social/emotional processing, possibly involving empathy and mirror neurons. Studies on autism and contagious yawning are suggestive but not conclusive; differences in gaze patterns may affect whether yawning cues are noticed. Fetal yawning and yawning across vertebrates suggest an evolutionary basis, but the exact function remains unknown.

Data Points: Adults susceptible to contagious yawning: 41% to 55% - The hosts cite a statistic for how many human adults yawn in response to seeing, hearing about, or reading about yawning. Fetal yawning observed: 11 to 20 weeks - They mention fetal yawning has been observed in utero during this range of development. Heart rate increase during yawning: up to 30 beats per minute - They cite research indicating yawning can temporarily raise heart rate during inhalation. Age when contagious yawning begins: around 4 years old - The discussion notes children are typically not susceptible to contagious yawning until about age four. Documented time span for paralysis/yawn phenomenon: about 150 years - They mention rare cases where a paralyzed limb moves during yawning have been documented over the last century and a half.

Pivotal Quotes: "we still can't explain what yawning is" — Josh Clark: Introductory framing of the episode’s central mystery. "yawns and orgasms share a neurobehavioral heritage" — Robert Provine (quoted by the hosts): Used to illustrate Provine’s view that yawning may be tied to broader arousal-related behaviors. "the more you empathize with other people, the more susceptible you are to contagious yawning" — Hosts summarizing research: Explains the empathy-based theory of contagious yawning.

Implications: Listeners learn that yawning is a real scientific mystery with no settled explanation, despite many studies. The discussion shows how basic behaviors can reveal links between arousal, social cognition, development, and evolution.