Primatologist Signe Preuschoft traces the smile back over 30 million years of evolution to a “fear grin” stemming from monkeys and apes, who often used barely clenched teeth to portray to predators that they were harmless or to signal submission to more dominant group members.
Human smiling likely evolved from similar appeasement gestures, gradually expanding to signal cooperation and trustworthiness. In social species, reducing aggression is essential. A smile can say “I come in peace” – without words. Over time, this signal broadened to include friendliness and bonding.
A genuine smile – known as a Duchenne smile, named after 19th-century neurologist Guillaume Duchenne – involves two key muscle groups: the zygomatic major (which pulls the corners of the mouth upward) and the orbicularis oculi (which crinkles the outer corners of the eyes). That eye involvement, which is very hard to control voluntarily, is what makes a smile look “real”.
Fake smiles typically activate only the mouth. Hilariously, this fake smile is also sometimes referred to as the “Pan Am smile”, named after the now-defunct airline Pan American World Airways, whose flight attendants would flash each and every passenger the same perfunctory smile.
A more recent nick name is the “Botox smile”. Chronic use of Botox injections to deal with eye wrinkles can result in paralysis of the small muscles around the eyes, preventing the appearance of a Duchenne smile.
Smiling is wired into the brain’s emotional circuitry. The limbic system, especially the amygdala and basal ganglia, helps generate spontaneous smiles, while the motor cortex can produce voluntary ones. This dual control system explains why some smiles burst out uncontrollably, while others are socially deployed by the individual according to the situation.
Neurochemically, smiling can trigger the release of dopamine, endorphins and serotonin – feel-good neurotransmitters associated with pleasure, stress reduction and mood regulation. Even forcing a smile can sometimes create a feedback loop: facial muscles send signals back to the brain that nudge emotions in a more positive direction. Moreover, studies show people who smile are perceived as more approachable, competent, and likeable – traits that carry clear evolutionary advantages.
Smiling is also linked to lower heart rate during stress and may contribute to longer life expectancy, though causation is tricky to prove. Still, the combination of stress buffering, social bonding and positive emotional feedback makes smiling a low-effort, high-return behaviour.
And smiling, not unlike yawning [RR3:90] and laughing [RR6:43], is deeply contagious. Seeing a smile activates mirror neurons in the observer’s brain, subtly encouraging them to mimic the expression and, in turn, feel a bit of the associated emotion. This is emotional synchrony in action – one reason shared laughter and smiling strengthen group cohesion.
But smiling isn’t always about happiness. People smile when they’re embarrassed, anxious or grieving – a psychological mechanism that helps smooth social tension. In difficult moments, a small smile can signal resilience or reassurance, i.e. I’m OK [RR7:63], and you don’t need to worry.
REMORANDOM Chapter
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