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  3. Right and Left-handedness in Humans Why do humans, quite different from the other animal species, display a distinct left or

Right and Left-handedness in Humans Why do humans, quite different from the other animal species, display a distinct left or

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问题                     Right and Left-handedness in Humans
    Why do humans, quite different from the other animal species, display a distinct left or right handedness? Not even our closest relatives among the apes(猿) possess such decided lateral(横向的，侧面的) asymmetry(不对称), as psychologists call it. Yet about 90 per cent of every human population 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 systematic. "Humans are able to think about things in categories: black and white, up and down, left and right, It’s a system of signs that enables us to categorize phenomena that are essentially ambiguous."
    The Relationship of Handedness to Gene and Inheritance
    Research has shown that there is genetic or inherited(遗传的) element to bandedness. But while left-handedness tends to appear in families, neither left nor right handers will automatically produce children with the same handedness; in fact about 6 per cent of children with two right-handed parents will be left-handed. However, among two left-handed parents, perhaps 40 per cent of the children will also be left-handed. With one right and one left-handed parent, 15 to 20 per cent of the children will be left-handed. Even among identical twins who have exactly the same genes, one in six pairs will differ in their handedness.
    Researchers Turned to the Brain for Reasons
while anything on the left is dangerous or even evil. We speak of left-handed advantages, and on the other hand according to Moore, "it is certain that left-handers often develop a stammer(口吃) as they are robbed of their freedom of speech." However, as more research is undertaken on the causes of left handedness, attitudes towards left-handed people are gradually changing for the better. Indeed when the champion tennis player Ivan Lend was asked what the only factor had improved his game, he said he would like to become a left-hander.
Geoff Maslen (Adapted)
About ______ per cent of children with two right-handed parents will be left-handed.
选项
答案6
解析 见第二段“in fact about 6 percent of children with two right-handed parents will be left-handed”。
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