Final answer:
The oral stage of human development occurs from birth to 1 year of age, focusing on pleasure derived from the mouth. Fixation at this stage can result in behaviors like smoking and overeating.
Step-by-step explanation:
The oral stage of human development, according to Sigmund Freud's psychosexual theory, occurs from birth to 1 year of age. During this stage, pleasure is focused on the mouth, and activities such as eating and sucking provide pleasure to the infant. The successful completion of this stage is important for the development of a healthy personality.
Freud believed that fixation at the oral stage could manifest in adulthood as behaviors such as smoking, overeating, or biting nails. This fixation may occur if a person was weaned too early or too late, leading to anxiety that is alleviated through these behaviors.