The encephalization quotient seems to suggest that a certain amount of brain-power is required to process nerve signals subconsciously (pain/touch/etc.). Larger

The encephalization quotient seems to suggest that a certain amount of brain-power is required to process nerve signals subconsciously (pain/touch/etc.). Larger animals have more nerves, and therefore need larger brains to perform the same abstract thinking activies, i.e. IQ. We can further combine this with the diminishing return of further reducing the brain size for an animal that is already large/ consuming large amounts of resources.