Real and fake smiles, 1872.

Plate from 'Expresion of the Emotions in Man and Animals' by Charles Darwin (1809-1882) published in 1872. The photograph (top) of a man smiling naturally was recognised instantly by everyone to whom it was shown as true to nature. Another photograph of the same man, with the corners of his mouth strongly retracted by the galvanisation of the great zygomatic muscles, was also shown to demonstrate the unnatural expresion created.