The secrets of human handedness

日期:2019-03-02 02:01:05 作者:长孙峁铬 阅读:

By David Wolman ARE you right or left-handed? Chances are you know which camp you belong to, and the chances are also good that, like 90 per cent of the human population, you consider yourself to be right-handed. But while our “handedness” is one of the few things about ourselves we feel we can be sure of, the issue is anything but clear-cut, scientifically speaking. In fact, despite an almost 200-year search for clear biological or psychological differences between left and right-handers, the one thing that most studies have in common is their inconclusiveness. Psychologist Stephen Christman at the University of Toledo in Ohio thinks he knows why: we have been looking at handedness in the wrong way. He says it is not being left-handed or right-handed that matters, but the strength of your preference for one hand over the other. According to his controversial idea, people are not either left-handed or right-handed, but “strong-handed” or “mixed-handed”. When you classify people in this way, he insists, measurable differences between the two groups start to emerge. Even more controversially, Christman believes that those differences can be explained by variations in the size of a particular part of the brain and are linked to other tangible differences in cognition and behaviour. There is no doubt, of course, that almost everyone has some preference for one hand or the other. How this handedness arises remains uncertain, but the most popular theory is that its origin is genetic. Humans are not alone in having some degree of handedness: most other animals have an equivalent pawedness, hoofedness or clawedness. Strangely though,