Why don’t chimpanzees have language the way humans do? Researchers are confident that it has something to do with differences in their brains that arose sometime in the past 5 million to 7 million years, when the chimp and human lines went their evolutionary ways. But exactly what differences account for human language are not entirely clear. Size might have something to do with it, because the modern human brain is about 3.6 times as big as that of a chimp. And yet chimp brains appear to share many features with their human counterparts, including a frontal lobe region called Broca’s area (purple in image) that in humans is closely associated with speech and language.
Most studies of Broca’s area in human brains have concluded that it is larger on the left side than the right, which seems to correlate with the finding that 94% of right-handers do most of their speech and language processing on the left sides of their brains. Scientists had long assumed that this asymmetrical enlargement of Broca’s area in humans was key to language abilities. But in 2001, researchers led by William Hopkins, a primate neuroanatomist at Emory University in Atlanta, began reporting that the brains of many apes also had asymmetrical Broca’s areas. The first such report, in the 29 November 2001 issue of Nature, found enlarged left-side Broca’s areas in the brains of chimpanzees, bonobos, and gorillas. And in a 2008 paper in Current Biology, Hopkins and his colleagues reported that Broca’s area is activated in chimp brains when they communicate with gestures or vocalizations. Hopkins and his co-workers concluded that the enlargement of Broca’s area, and its role in communication, began before the chimp-human split and was not unique to humans.
Yet a new paper, published online last week in Cerebral Cortex, challenges some of these findings and argues once again that the language centers of human brains are special.