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
History of beliefs about the human body as imbalances of the 4 fluids of the body. Aristotle was unable to dissect humans but did so to many animals and was a early founder of comparative anatomy. Aristotle did contend quasi spiritual manifestations of the body principally through sexual distinctions. He wrote that the sex of humans: “is determined by the male principle already contained in the semen. If this is not strong enough, then the opposite must necessarily come into existence, and the opposite of man is woman.” Aristotle clearly superimposed man as the more important figure in men and women but presents an almost Qi like