Theories on Handedness

Because it develops so early, this brain asymmetry appears to be largely innate. It is possible, however, that environmental factors begin operating even before birth. One hypothesis is that the right hand becomes more skillfull because it has greater freedom to move in the womb. About three-quarters of all fetuses spend the last several weeks of gestation with their right arm facing out—toward the mother's abdominal wall. This arm has more space in which to move than does the left arm, whi...