Final answer:
Phrenology, a pseudoscience, is associated with the belief that physical traits are related to intelligence level.
Step-by-step explanation:
The belief that one's physical traits, such as head circumference, are related to their intelligence level is associated with the pseudoscience of phrenology. This idea was proposed by Franz Joseph Gall, a German physician, in 1780. However, phrenology was later discredited for lack of empirical support and is no longer considered a valid scientific theory.