Dolphin brains are pretty comparable to human brains; dolphins in many species have brains that are larger than ours. Humans only come out on top when you correct for differences in body weight. Even then, dolphins are typically second to us in terms of relative mass. Magnetic resonance imaging (MRI) scans have shown that dolphin brains -- in relation to their body size -- are about four to five times larger than any other animal of similar size [source: Viegas].
Brain size is not the real measure of how these sea mammals compare to humans, though. What really matters is how their brains function. That's true of humans, of course. It's all of the unique ways our brains are wired that help us use them like supercomputers. Imaging also shows that the area of the brain known for higher-ordered thinking -- namely the neocortex -- is proportionally larger in the dolphin. That makes them different from great white sharks. In the shark, the largest brain component is the olfactory bulb, which detects scents. And domestic dogs get a little of both: A dog has a neocortex, but it's proportionally smaller than the one in a human brain. Canines have four times the odor processors of humans in their brains, though [source: American Museum of Natural History].
Scientists have long studied and learned from how dolphins use sonar to navigate the seas and objects in them. Dolphin brains also have many features correlated with higher brain functions similar to human brains. Research has shown that they comprehend language, at least certain whistled commands. Captive dolphins also have been taught to answer yes or no when asked simple questions with about 75 percent accuracy. They're using an artificial language, though, and tests of their intelligence and communication abilities continue [source: Dolphin Research Institute]. Dolphins also can be social, understand some abstract concepts and recognize themselves in mirrors.