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
The Expression of the Emotions in Man and Animals and a "geologizing expedition" – but actually spent some of his time re-exploring the old haunts of his undergraduate days. On the day of the coronation, 28 June 1838, Darwin was in Edinburgh. A few weeks later, he opened a private notebook with philosophical and psychological speculation – the "M Notebook" – and, over the next three months, filled it with his thoughts about possible interactions of hereditary factors with the mental and behavioural aspects of life.It should also be noted that Darwin made his first attempt at autobiography in August 1838. The critical importance of the "M Notebook" has