The adult bottlenose dolphin has a brain weighing 1700 grams. An adult human has a brain weighing 1450 grams. Ape's brains are limited in size, three hundred to four hundred fifty grams. When humans are born and become adults with brains restricted to these sizes, they are unable to use spoken language adequately to function in our society. To master speech as we know it, humans apparently require a brain size of at least seven hundred to eight hundred grams. The bottle-nosed dolphin's brain as an adult is much larger than this, comparable to that of larger-than-average human brains.
Size of Brains in Selected Mammals
There seems to be a critical size for the associational cortex to furnish an adequate integration between the other areas of the cortex, the sensory and the motor, to form language. One other characteristic of a larger associational cortex would be a much larger memory space available for the storage of the programming necessary for language.
Comparitive Weights of Dolphin and Human Brains