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 to experience emotions in a similar way to humans. The problem is made more problematic by the difficulties in testing for emotions in animals. What is known about human emotion is almost all related or in relation to human communication. In recent years, the scientific community has become increasingly supportive of the idea of emotions in animals. Scientific research has provided insight into similarities of physiological changes between humans and animals when experiencing emotion. Much support for animal emotion and its expression results from the notion that feeling emotions doesn't require significant cognitive processes, rather, they could be motivated by