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The origins of left-handednessStone age implements discovered seem equally divided between left and right. Study of cave drawings indicates a preference for the left hand. When tools became more sophisticated, a clear hand preference emerged (practicality of making two versions of a tool) The right hand preference may have originated in sun worship. In the Northern hemisphere you have to face south to follow the sun and move from left to right until the suns sets in the west. This gave moving to the right and the right hand side a great significance. Another theory says that as the heart is on the left hand side, a shield would be in his hand to defend it. Any weapon therefore had to be held in the right, which became the dominant hand. Recent theories have included one that right is the normality and left-handedness, is a deficiency which result from a traumatic birth.
Brain wiringThe brain is cross-wired the left hemisphere controls the right
handed side of the body and vice-versa . GeneticsWhether there is a genetic reason for handedness is a contentious subject. It certainly seems to be true that left-handedness runs in families, although not in any predictable way. Various researchers have looked at groups of families and tried to work out the probabilities of left and right-handed parent combinations having left-handed children, but they all come up with different figures. The Left-handers Club have undertaken a survey that asks for child and parent handedness and we have analysed that as well as modelling the overall population under various assumptions to see if population numbers and levels of left-handedness should stay constant over time. Surprise, surprise, we have come up with more different numbers! We will be doing more research and analysis on this soon and will publish an article setting out our findings. In the meantime, the figures below should give a general guide... About 1 in 10 people are left-handed. Approximately 26% of children from two left-handed parents will
be left-handed. Where the parents have mixed handedness, the mother's handedness will have most influence on that of the children, so a left-handed mother and right-handed father should have more left-handed children than the other way round. Based on these same figures, nearly 75% of children of two left-handed parents will still be RIGHT-handed. To put it another way, only 2% of left-handed children will have TWO LEFT-handed parents. We hope that's all clear now! BirthAccording to the New England Journal of Medicine, mothers giving birth later on in life are more likely to produce a left-handed child. Mothers between the ages of 30 and 35 have a 25% higher chance of producing a lefty |
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