When a person is left-handed, all it means is that they can do certain things better with the left side of their body than with the right. You may have noticed that some people write with their left hand instead of their right, and that they hold their knife in their left hand, and other similar things. This is not ‘wrong’, and in fact attempts to force someone to become right-handed can often do more harm than good. But what causes left-handedness? Nobody can really say. It is not something with a single explanation. One theory is that the human body is not the same on both sides – that is, it is not symmertrical. One side dominates the other, and it is believed that the two halves of the brain control this, the left side of the brain controlling the right side of the body, the right side of the brain controlling the left side of the body. In most people, the right side of the body (the left side of the brain) dominates, but in left-handed people the opposite is the case. But nobody knows why this should be so, and in any case, not all scientists accept this theory.