§ 8. Emotional Gestures. — Darwin, in his great work Expression of the Emotions, has attempted to account for the distinctive gestures accompanying the various specific forms of emotional consciousness. The principle of explanation on which he lays most stress is that of Serviceable Associated Habits. Many expressive movements are partial survivals of actions which have proved useful to the subject himself or to his ancestors in situations exciting analogous emotions. "So slight a symptom as the snarl or sneer, the onesided uncovering of the upper teeth, is accounted for by Darwin as a survival from the time when our ancestors had large canines, and unfleshed them (as dogs do now) for attack. Similarly the raising of the eyebrows in outward attention, the opening of the mouth in astonishment, come, according to the same author, from the utility of these movements in extreme cases. The raising of the eyebrows goes with the opening of the eye for better vision; the opening of the mouth with the intensest listening, and with the rapid catching of the breath which precedes muscular effort."+ A fainter form of the act of ejecting an unsavory morsel constitutes the facial gesture expressive of all forms of disgust. A smile calls into play the same muscles as those employed in sucking the breast, and in a similar manner.
* Naturalist in Nicaragua, p. 79.
+James, Principles of Psychology, vol. ii., p. 479.