Final answer:
Freud's psychosexual theory of development posits that personality develops through a series of early childhood stages, each associated with a specific erogenous zone. If properly nurtured, individuals move through the stages healthily; otherwise, they may get fixated and develop unhealthy traits.
Step-by-step explanation:
Sigmund Freud's theoretical contributions to psychology include the psychosexual theory of development, wherein he posits that personality develops through early childhood via a series of stages. These stages include oral, phallic, latency, and genital, each associated with a specific erogenous zone. Proper nurturing and parenting during each stage are essential, as inadequacies may lead to fixation and unhealthy personality traits in adulthood. Freud's theory is characterized by its emphasis on the sexual nature of early development, distinguishing it from theories such as Erikson's psychosocial development theory, which focuses on social interactions and continues throughout the lifespan.