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
Man of the Hole Man of the Hole Man of the Hole () is a nickname used by officials and the media to describe a man who is indigenous to Brazil and lives alone in the Amazon rainforest. He is believed to be the last surviving member of his tribe. It is unknown what language he speaks or what his tribe was called. The Man of the Hole's nickname derives from the deep hole found in each home that he has abandoned. It was originally believed that these holes were used to trap animals or for him to hide in, but some observers have