Why do yawns start a chain reaction of other yawns?
In: Biology
So there’s no definite answer out there to this, it’s still a mystery, but one I’ve thought about for a decade now, so I’ll share my personal theory. Disclaimer: This is purely my speculation, there’s no study that I know of which confirms or denies this. The first interesting thing is this occurs *across species*. This is profound, and suggests we’re talking about some very *ancient* behavior. It had to have a compelling survival adaptation for this trick to work *between* species. Most social species also have a social hierarchy. Social hierarchies are violent in the animal world. Likewise, interspecies struggles are violent.
Now consider what a yawn does, biologically. A large supply of Oxygen is let in first, and then a slow, gradual, exhalation of C02 follows. What does this do? It eases heart rate, causing you to relax. We know this reduces stress and calms you down. This is invaluable in the meat grinder that is nature. Now imagine two animals meet. Hostility begins. Maybe some growls, some posturing. This could get ugly… but suddenly, through what is ultimately the sheer dicerolls of DNA and the weathering of natural selection, one yawns. Eyes close, signaling less hostility. The other’s mirror neurons also yawn. Reciprocation. Heart rates drop. Anxiety decreases. Things de-escalate, and while both animals are still very tense, this minor tipping of the scales causes both animals to not get injured or killed. The genes thrive.
Likewise, within a tribe of pre-human ancestors, any violent conflict could work the same way. Even if there is **no conflict**, this has the identical effect: De-escalation of even the **potential** of violence, a win win. Those who do not express the phenotype of yawn-mirroring, don’t receive this benefit, and get killed off with the passage of evolutionary time.
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