In this paper Devereux, a Hungarian ethno-psychoanalyst, naturalised French, reports some of his studies made among various populations among which he worked. These included Hawaiians, Indigenous American Indians, and some ethnic groups of the Aleutian Islands, Canada, and countries in Africa. It shows how among mothers and fathers there exists a diffuse cannibalistic instinct to which the baby may respond with a counter cannibalistic position. These impulses assume a universality and can be considered the unconscious universal origin of aggressiveness towards the other. Cannibalistic impulses represent a primitive matrix of parental aggressiveness, in which other causes of aggressiveness towards newborns and children may fit: jealousy, envy, perversions, and oedipal elements. Forensic psychotherapy may benefit from this knowledge indicating the psychic levels and capacities of the patients and evaluating the strength of these impulses in their psychopathology which may correlate to their inner time and their search for narcissistic power.