Historically, humans were the only animals thought to have handedness. But in the last decade, researchers have shown that other animals' brain hemispheres may be specialized for particular tasks.

Bill Hopkins, PhD, an Agnes Scott College primate researcher and biopsychologist, was one of the first to establish that, like humans, chimps tend to be right-handed, though not quite as ubiquitously as humans—about 70 percent. A series of experiments in the '90s by Hopkins and others showed that movements requiring skilled coordination—the original research had chimps fishing peanut butter out of the end of a plastic pipe—were often done using the right hand, while the chimps were less preferential for unskilled movements such as simple reaching.

In 1998, Hopkins and his colleagues established that when making one-handed gestures, like pointing to something, chimps almost exclusively use their right hands. In 2004, he designed an experiment to determine which hand chimps throw with. "Chimps usually throw at new people—they'll often throw their [excrement] at them," Hopkins explains. So he and his colleagues introduced themselves to a variety of chimpanzees and recorded which hand each chimp used to throw feces at them. It turned out that chimps were extremely right-handed for this behavior (Journal of Comparative Psychology, Vol. 119, No. 4).

When Hopkins looked at MRI scans of these chimps' brains, he found that there were asymmetries between the hemispheres, especially in two motor cortex areas, the precentral gyrus and the inferior frontal gyrus. These chimps had somewhat lateralized brains (Behavioral Neuroscience, Vol. 118, No. 6) that corresponded with their handedness. What's more, these asymmetries mirror those found in motor areas of humans, which suggests a common evolutionary origin, Hopkins says.