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 Formation of Vegetable Mould through the Action of Worms went the less controversial direction of the lowly worm. His network of correspondents and fans responded to his interest and "earthworm anecdotes began surfacing in his mountain of mail". He had been interested in earthworms "since his first fishing days at The Mount and flirting days at Maer". Still, other work constrained him. Broken off from "Descent", he had to finish his next work "The Expression of the Emotions in Man and Animals". By 1876, with his first grandson on the way, he felt his writing life was nearly over, with so much unfinished. He wanted to write on earthworms