At the Yerkes Regional Primate Research Center in Atlanta, a large chimpanzee named Winston is taking part in an unusually pleasant experiment. Using his left hand, he reaches over and grabs a length of PVC pipe from primatologist Bill Hopkins, then he uses his right to scoop out some peanut butter smeared inside. "Winston's a righty," Hopkins says, offering another piece of pipe to a smaller chimp hovering nearby. This one grabs the pipe with his right hand and digs out the peanut butter with his left. "That's Winston's younger brother," Hopkins says.
Over the past 10 years, Hopkins's research has offered the first definitive proof that apes, like humans, have hand preferences: A third of the Yerkes chimpanzees are lefties and the rest are righties. But Winston and his brother point to an even more intriguing pattern: The younger the sibling, the more likely he or she is to be a lefty. And if handedness is clearly tied to birth order in chimps, it could throw a monkey wrench into theories of handedness in humans as well.
