Freud's study of human sexuality brought about a Copernican revolution in the temporal conception of the experiences of childhood in relation to adult life. These first experiences produce mnemic material that will only constitute a definite place and function for the subject après coup (nachträglich) : the unconscious mind. In this sense, the postulate that psychic causality organizes mental processes implies, among other things, calling into question the classical model of time in the Western world. Freud's relation to these crucial questions was already present in his first scientific study at the University of Vienna, where he was confronted with problems linked to sexual differentiation and to heterochrony between living beings.