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
Animals' Rights: Considered in Relation to Social Progress Salt is undoubtedly ahead of his age by many years." A new edition of the book was published in 1980 with a preface by the Australian philosopher Peter Singer, who is well known for his work on the ethics of treatment towards animals (specifically in the book "Animal Liberation"). The 1980 reissue prompted a review from Stephen Clark who praised Salt's book with some provisos. He states that Salt's attempt to blame the treatment of non-human animals on the theological doctrine of man having "dominion" over the natural world was mistaken. Animals' Rights: Considered in Relation to Social Progress Animals'