Emotion in animals specialised form of Occam's razor used in ethology, in which he stated: Charles Darwin initially planned to include a chapter on emotion in "The Descent of Man" but as his ideas progressed they expanded into a book, "The Expression of the Emotions in Man and Animals". Darwin proposed that emotions are adaptive and serve a communicative and motivational function, and he stated three principles that are useful in understanding emotional expression: First, "The Principle of Serviceable Habits" takes a Lamarckian stance by suggesting that emotional expressions that are useful will be passed on to the offspring. Second, "The Principle of
The Variation of Animals and Plants under Domestication grown too long, & I think I shall publish separately a very small volume, 'an essay on the origin of mankind'". This "essay" would become two books: "The Descent of Man, and Selection in Relation to Sex" (1871) and "The Expression of Emotions in Man and Animals" (1872). The book had been advertised as early as 1865 with the unwieldy title "Domesticated Animals and Cultivated Plants, or the Principles of Variation, Inheritance, Reversion, Crossing, Interbreeding, and Selection under Domestication" but Darwin agreed to the shorter "The Variation of Animals and Plants Under Domestication" suggested by the compositors. By May he