Some researchers have suggested that the size and complexity of the brain at birth is a better measure of intelligence. If that research holds up, however, once more the dolphin comes out on top. The bottle-nose dolphin has a brain mass at birth that is 42.5% of that of an adult humans brain mass. Humans at birth have 25% of their adult counterparts. At 18 months, the brain mass of the bottle-nose dolphin is 80% of the adult human, who doesn't usually achieve this level until the age of three or four.

While the research that has been obtained certainly makes it look like the dolphin may be the closest to our own level of intelligence, it may be quite some time before it's actually prove. Until then, they're true capabilities will remain a mystery.