ANDRZEJ KRAUZEFor decades, psychologists and biologists have puzzled over the physiological roots of two human traits—handedness and the asymmetrical nature of language in the brain. A peculiar behavioral distribution has spurred them on: the world over, 95 percent of right-handed people do the bulk of language processing in the left hemisphere of their cerebral cortex, while only 75 percent of left-handers show the same pattern. (The other 5 percent of right-handers and 25 percent of left-handers display what is called “atypical lateralization,” meaning their language processing happens bilaterally or mostly in their right hemispheres.)
It’s a quandary that keeps Metten Somers, a psychiatrist at University Medical Center Utrecht in the Netherlands, very busy. “It’s actually a weird thing that your [brain] organization can be so different between two subjects, but your function is essentially the same,” he says. “As neuroscientists we are very puzzled that there is this weird link between left-handedness and cerebral organization.”
For decades, a monogenic theory of handedness—that is, that there is a single gene, albeit unidentified, responsible for the trait in humans—has ruled among geneticists in the field. And many researchers felt that the handedness gene must be overlapping in some functional way with the genetic background of language lateralization in the brain. This would explain the correlation between what hand a person predominantly ...
