Sandra Upson in Scientific American:
Ask why most people are right-handed, and the answer might fall along the same lines as why fish school. Two neuroscientists suggest that social pressures drive individuals to coordinate their behaviors so that everyone in the group gets an evolutionary edge.
Approximately 85 percent of people prefer their right hand, which is controlled by the left hemisphere of the brain. One theorized benefit of locating a particular function in one hemisphere is that it frees the other to deal with different tasks. But that idea does not explain why population-wide trends for handedness exist in the first place. Moreover, evidence gleaned in recent years has overturned the long-held belief that human handedness is a unique by-product of brain specialization attributable to language. A suite of studies has revealed brain lateralization in species from fish to primates. Last August, for instance, scientists discovered that in the wild, chimpanzees show hand preferences.
The presence of lateralization throughout the animal kingdom suggests some benefit from it, contend neuroscientists Giorgio Vallortigara of the University of Trieste and Lesley Rogers of the University of New England in Australia. Also, last August, in the journal Behavioral and Brain Sciences, the two presented evidence to support their idea that social constraints force individuals toward asymmetry in the same direction. They noted, for example, that baby chickens attack more readily when a threat appears on their left. And Rogers has found that chicks with more asymmetrical brains form more stable social groups: perhaps by approaching each other on the right, she hypothesizes, the chicks fight one another less and are more likely to notice predators.