Why do humans, virtually alone among all animal species, display a distinct left or right-handedness? Not even our closest relatives among the apes posses such decided lateral asymmetry, as psychologists call it. Yet about 90 percent of every humanpolulation that has ever lived appears to have been right-handed. Professor Bryan Turner at Deakin University has studied the research literature on left-handedness and found that handedness goes with sidedness. So nine out of ten people are right-handed and eight are right-footed. He noted that this distinctive asymmetry in the human population is itself asymmetric.

Research has shown that there is a genetic or inherited element to headedness. But while left-handedness does not tend to run in families, left nor right hander will automatically producer off-spring with the same handedness; in fact about 6 percent of children with two right-handed parents will be left-handed. However among two left-handed parents, perhaps 40 percent of the children will also be left-handed. With one right and one left-handed parent, 15 to 20 percent of the offspring will be left-handed. Even among identical twins that have exactly the same genes, one in six pairs will differ in their handedness.

What then makes people left-handed if it is not simply genetic? Other factors must be at work and researchers have turn to the brain for clues. In the 1860s the French surgeon and anthropologist, Dr. Paul Broca, made the remarkable findings that patients who had lost their power of speech as a result of stroke( a blood clot in the brain vessel) had paralysis of the right half of their body. He noted that since the left hemisphere of the brain controls the right half of the body, and vice versa, the brain damage must have been in the brain’s left hemisphere. Psychologists now believe that among right-handed people, probably 95 percent have their language centre in the left hemisphere. Some 30 percent have right hemisphere language.

Dr.Brinkman, a brain researcher at the Australian National University in Canberra, has suggested that evolution of speech went with right-handed preference. According to Brinkman, as the brain evolved, one side become specialized for the fine control of movement (necessary for producing movement) and along with this evolution came right-hand preference. According to Brinkman, most left-handers Have left hemisphere dominance but also some capacity in the right hemisphere. He has observed that if a left-handed person brain-damaged in the left hemisphere, the recovery of speech is quite often better and this is explained by the fact that left-hander have a more bilateral speech function.

The results of this research may be some consolation to left-hander who has for centuries lived in a designed to suit right-handed people. However as more research is undertaken on the causes of left-handedness, attitude towards left-handed people are gradually changing for the better. Indeed when the champion tennis player Ivan Lendl was asked what the single thing was that he would choose in order to improve his game, he said he would like to become left-hander.