Emotion in animals teeth in aggressive action. A domestic dog's simple tail wag may be used in subtly different ways to convey many meanings as illustrated in Darwin's "The Expression of the Emotions in Man and Animals" published in 1872. Evidence for emotions in animals has been primarily anecdotal, from individuals who interact with pets or captive animals on a regular basis. However, critics of animals having emotions often suggest that anthropomorphism is a motivating factor in the interpretation of the observed behaviours. Much of the debate is caused by the difficulty in defining emotions and the cognitive requirements thought necessary for animals
The Expression of the Emotions in Man and Animals with "ill-temper", sulkiness and determination), Chapter 10 on hatred and anger, Chapter 11 on "disdain, contempt, disgust, guilt, pride, helplessness, patience and affirmation" and Chapter 12 on "surprise, astonishment, fear and horror". In his discussion of the emotion of disgust, Darwin notes its close links with the sense of smell, and conjectures an association with excretory products. In Chapter 13, Darwin discusses complex emotional states including self-attention, shame, shyness, modesty and blushing. Darwin describes blushing as "the most peculiar and most human of the expressions". Darwin closes the book with Chapter 14 in which he recapitulates his main argument: he