Harry Jerison, famous researcher of brain sizes across classes and orders of animals, commented on the relation of “encephalization” to the intelligence of animals by considering the problem one of multidimensional optimization
The insight is that comparable amounts of intelligence in different species may not (and normally would not) reflect comparable kinds of intelligence. Many and various intelligences (in the plural) must have evolved in conjunction with evolving environments and with brains and behaviours adapted to those environments.
That intelligences would be of various kinds is almost an axiom of evolutionary analysis, since adaptations evolve in the contexts of the environments in which they are effective, and species never occupy identical niches. The evolution of neural and sensorimotor adaptations provides many fine examples of uniqueness of species. The visual systems of deer and wolf, for example, may be similar in many ways, for example, in the structure of the sensory cells, neural networks of the retina, and the central nervous pathways and centres. Yet these systems are significantly different: the deer, like most ungulate 'prey' species, probably has panoramic vision whereas the wolf's visual field is more nearly like the primate's proscenium stage. The visual system encumbers significant amounts of nervous tissues and, thus, contributes to brain size and measured encephalization. Neural machinery associated with the sensory systems and motor control systems as a group determines a large fraction of the mass of the whole brain. Equality of encephalization of deer and wolf, thus, implies that the neural control systems for the specialized adaptations, though different in the two species, sum to approximately equal amounts relative to body size.