Medical students and residents
Asymmetrical Information: More on medical residents ... residents driving home from work were being pulled over by the police for driving poorly. The cops found, that despite not being intoxicated, the exhausted residents could barely drive. Some later research stated that a relatively small amount of sleep-deprivation was equivalent to an illegal blood-alcohol level ...
UCI (University of California, Irvine) at the time I was in school there was known for relatively high acceptance rates of graduates into medical school. There were a lot of pre-med students.
The defining characteristic of pre-med students was an overriding interest in maintaining a high GPA. If you could be assured of a high grade from intense study and rote-learning, the class tended to attract pre-med students. Outside the mass-required classes I saw very few pre-med students, as the Physics classes were too hard, and the other interesting classes were too risky. The few pre-med students that strayed into Physics dropped out very quickly.
Selecting for high GPA is simply a means of limiting the supply of new doctors, and has very little to do selecting for intelligence.