The Expression of the Emotions in Man and Animals usually been viewed in its relationship to Darwin's conception of "natural selection" as the central mechanism of evolutionary development, which he probably grasped some time around September 1838. These notes have a tentative and fragmented quality, especially in Darwin's descriptions of conversation with his father (a successful doctor with a special interest in psychiatric problems) about recurring patterns of behaviour in successive generations of his patients' families. Darwin was anxious about the materialistic drift in his thinking – and of the disrepute which this could attract in early Victorian England – at the time, he was mentally preparing for marriage
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