American Psychological Association the one percent preferring to use one hand is in part genetic American Psychological Association preferring to use one hand is in part genetic American Psychological Association write with both hands write with both hands According to the American Physiological Association http://www.apa.org/monitor/2009/01/brain.aspx According to the American Physiological Association According to the American Physiological Association "The left brain knows what the right hand is doing" "The left brain knows what the right hand is doing" 1 percent the one percent The left brain knows what the right hand is doing