In his pioneering work on child behavior, the American developmental psychologist Arnold Gesell claimed that infants as young as four weeks display signs of handedness and that right-handedness is clearly established by age one.
Broca suggested that people's handedness was the opposite of their language-specialized hemisphere, so that a person with left-hemisphere language specialization would be right-handed.
However, when an individual has two copies of the recessive form of the gene-one copy from the mother and one copy from the father-the gene does not determine handedness.
Others believe that ambidexterity-the equal use of both hands-is a third type of handedness, and some think that there are two types of ambidexterity.
If handedness is not apparent by the time a child enters school, the teacher must determine which hand the child should learn to write with.
Children of left-handed parents have a 50 percent chance of being right-handed and 18 percent of identical twins differ in their handedness.
There is some doubt on the point; but a contemporary and intimate friend, Luca Pacioli, speaks of his "ineffable left hand"; all the best of his drawings are shaded downward from left to right, which would be the readiest way for a left-handed man; and his habitual eccentric practice of writing from right to left is much more likely to have been due to natural left-handedness than to any desire of mystery or concealment.
Yet in spite of this savagery the Fijians have always been remarkable for their hospitality, open-handedness and courtesy.
But at times in history, left-handedness was thought to be a malady in need of curing (and in some parts of the world still is).
Having been recalled and ordered to appoint a dictator, he gave another instance of his high-handedness by nominating a subordinate official, M.