Final answer:
The cerebrum is the area of the human brain that is proportionally much larger than in a fish or amphibian, due to the enlarged neocortex that is associated with higher brain functions and intelligence.
Step-by-step explanation:
The area of the human brain that is proportionally much larger than in a fish or amphibian is the cerebrum. This is due to the process of encephalization where human brain mass, especially on the neocortex, increased significantly compared to body mass. The neocortex covers the surface of the cerebrum and is associated with higher-order brain functions. It is much larger in humans and allows for advanced mental abilities. In intelligent mammals such as primates, a larger cerebrum supports higher levels of intelligence and complex social interactions. In contrast, regions like the midbrain, cerebellum, and medulla (part of the brain stem) are not disproportionately larger in humans as they are more involved in basic, autonomic functions.