Bass found that in fish, the part of the brain--the hindbrain--that controls the pectoral muscles also controls the muscles required for producing sound. And in many fish, that sound actually comes from the pectoral movement. Some fish species vibrate their pectoral fins rapidly to communicate, and some vibrate a muscle in a swim bladder, acting similar to our own vocal chords. "That's the historical linkage or coupling between what humans do: speech and hand movement," says Bass, who is presenting his research to the Society for Experimental Biology. "I'm not saying it's exactly the same in humans as it is in fish, but it shows this historical evolution over time."