Human uses of mammals that "one is well advised to study the behaviour rather than attempting to get at any underlying emotion". Charles Darwin however had accepted the idea of emotion in animals, writing his 1872 book "The Expression of the Emotions in Man and Animals" on the subject. Darwin believed that mammals had social, mental and moral lives. In "The Descent of Man" (1871), he wrote: "There is no fundamental difference between man and the higher mammals in their mental faculties." Biologists remained wary of the idea, even for the great apes, but this led to serious difficulties, as Donald O. Hebb explained
Emotion in animals animals being able to experience emotions in his book "The Emotional Lives of Animals". The following is an excerpt from his book: Bystander affiliation is believed to represent an expression of empathy in which the bystander tries to console a conflict victim and alleviate their distress. There is evidence for bystander affiliation in ravens (e.g. contact sitting, preening, or beak-to-beak or beak-to-body touching) and also for solicited bystander affiliation, in which there is post-conflict affiliation from the victim to the bystander. This indicates that ravens may be sensitive to the emotions of others, however, relationship value plays an important role