Evolutionary theory meant not expecting absolute boundary lines between thinking and seeing, or between memory and hallucination. (...) in an essay on "The Dream as Revelation" later cited by Freud in The Interpretation of Dreams (1900), [James] Sully described how in sleep, evolution is reversed and adults go back to the groudwork of their life, in a primitive animal immersion in bodily sensation. Philip Davis, The Victorians , p. 189.