All hail the powerful smile. The right smile, at the right time, wins friends and calms enemies. The smile held for too long, not long enough, flashed too intensively or too dimly, arouses suspicion, fear or anger.
Far from being a straightforward show of joy, the language of smiles is filled with subtlety: a meld of our inner state, surroundings, social training, conscious and unconscious.
In the late 1800s Charles Darwin published his famous book The Expression of Emotions in Man and Animals. He devoted some time to smiling, but was more interested in other facial expressions. His colleague across the channel, Guillaume-Benjamin Duchenne, was doing experiments where he would zap single muscles on the face with electricity and then look at the changes. His primary distinction was between smiles that came from the soul, non-deliberate smiles, and the ones put there consciously. That’s why people who study smiles call the spontaneous smile the Duchenne smile.
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Guillaume-Benjamin-Amand Duchenne (de Boulogne) (born September 17, 1806 in Boulogne-sur-Mer; died September 15, 1875 in Paris) was a French neurologist who revived Galvani's research and greatly advanced the science of electrophysiology.