Test yourself: "What emotions are written all over their faces?"
IN 1868, while working on his latest book on evolution, Charles Darwin liked to show visitors to his house a series of ghoulish photographs of people's faces.
The pictures, taken by French physiologist Guillaume-Benjamin Duchenne, showed people whose facial muscles were being zapped by electric shocks, contorting them into strange and often eerie arrangements. Darwin was fascinated by how a twitch of the mouth here or furrow of the brow there could conjure up the impression of an emotion - fear, say, or surprise. He wanted to know whether his guests perceived the same emotions in the pictures. They usually did.
Darwin came to the conclusion that emotional facial expressions were universal: people all over the world made the same ones, and could easily and automatically recognise them in others. He didn't claim to know what the expressions were ...
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