Sigmund Freud's psychosexual theory focusses on the influence of unconscious conflicts and the role of sexual and aggressive drives in shaping personality development. Erik Erikson's psychosocial theory, on the other hand, emphasises the impact of social and cultural factors on the development of identity and the resolution of psychosocial conflicts. In terms of applicability to understanding human development, Erikson's psychosocial theory may be more relevant as it considers a broader range of psychosocial challenges throughout the lifespan, while Freud's theory primarily focusses on early childhood experiences and the unconscious mind.