A Unique Child: Cognitive development - Left-handed and right-handed

Scientists have long known that our brain's two hemispheres are asymmetrical, with the left hemisphere governing the right side of the body and vice versa. This is why, when our left hemisphere becomes increasingly specialised during childhood, most of us become right-handed.

For right-handers, the left hemisphere specialises in several language functions and fine detailed processing, whereas the right hemisphere deals predominantly with emotion and global types of processing. Ninety per cent of the world's population are right-handed, but this is not present at birth; it becomes consolidated over developmental time.

Although foetuses display some degree of handedness - visible using ultrasound to assess the hand they use to grasp the umbilical cord and the thumb they suck - the link between foetal preferences and handedness isn't strong. Indeed, infants/toddlers show a high degree of ambidexterity, and it isn't until the third/fourth year that parents can accurately determine whether their child is right- or left-handed. But even then, handedness continues to become fully consolidated between the ages of three and seven, indicating that it requires a substantial amount of experience.