Cetacean brain development is an example of parallel evolution, adapted to the ocean environment. The brains of orcas are roughly four times larger than ours, have a greater surface area relative to brain weight, have enhanced development in different areas, and some of their nerve transmission speeds greatly exceed ours. Naturally enough we humans don't much like the idea that another species might rival us in that which we feel sets us apart from the rest of the animal kingdom: our intelligence, and so we have come up with many ways to explain it all away. At first it seemed obvious to make the claim that bigger animals just needed bigger brains...except that animals like the stegosaurus, close in size to orcas, had a brain about the size of a walnut. Not that they were mental giants - but they got by.
The next idea to come along was "brain to body weight ratio", a comparison between the size of an animal and how large it's brain is, and by that measure an orca would clearly be smarter than a stegosaurus, but not as smart as we humans. Unfortunately for us, both hummingbirds and squirrel monkeys beat us in that measurement (we are about 2%, while hummingbirds are about 4%).
Presently we have come up with a way of comparing brain size called "Encephalization Quotient", or EQ, in which we compare how big an animal's brain is versus how big you would expect it to be relative to the overall size. Ah ha! At last we win, our brains are 7 times bigger than you would expect them to be for our size, while our closest rivals are dolphins and toothed whales, which come in at the 2 to 5 times range. Whew! Except...
Their brains have a greater surface to volume ratio than ours. What this means, basically, is that the part of the brain that integrates information is much greater. Although scientists at first dismissed this by assuming that the tissue was 'primitive' because it differs in structure from ours, current research disputes that. Research also overturns the notions that the types of cells are related to adapting to ocean temperatures, or that the large brains are dedicated to processing echolocation information.
The layout of their brains is different from ours - some regions (such as those associated with smell) are diminished or absent, while others, such as the vision center, are moved around, and the structures associated with hearing are enhanced - but it is every bit as capable of intelligent thought.
Fortunately now though, scientists are beginning to concentrate more on learning how the cetaceans use their massive brains, and less on coming up with ways to dismiss and diminish the evidence that we share this planet with other intelligent beings.
. The recent discovery that cetaceans have a special type of cell (called a spindle cell) previously found only in humans and the great apes implies that they aren’t just intelligent: those cells are associated with our deeper emotions and social bonds.