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  3. Most people are right-handed and children usually have the same handedness as their parents. This suggests that genes are at wor

Most people are right-handed and children usually have the same handedness as their parents. This suggests that genes are at wor

admin2013-03-22  99
问题     Most people are right-handed and children usually have the same handedness as their parents. This suggests that genes are at work. But identical twins have identical genes, so genes cannot be the whole story. Cultural attitudes seem to have played an important part in the development of hand preferences. In the past, left-handers have suffered anything from teasing to flogging. Even today in some countries enforced right-handedness, particularly for writing and eating, is still common.
    To explain the observed patterns of handedness, researchers have devised what is known as a ’gene-culture coevolution’ model. The initial assumption of the model-drawn from observation of non-human primates and other mammals such as mice—is that early on in human evolution, the genetic make-up of individuals inclined them to prefer one hand or the other, but that the population was equally divided between right- and left-handed people. Over time, according to the model, the interaction of genes and culture has produced a state where everyone has identical genes for handedness. This would happen if, for whatever reason, right-handers were more likely to survive and reproduce. The idea may not be that farfetched. Many biologists believe that handedness is related to brain structure—say for example, early right-handers may have been better at language.
    The model predicts that today everyone has genes which confer a basic predisposition of 78% to be right-handed. How children actually turn out, however, can be influenced by whether their parents are dextral or sinistral. For example, children may mimic their par-ents. Or parents may influence the handedness of their children in the way that they hand them toys or food.
    The researchers reckon that a child with two right-handed parents has a 91% probability of being right-handed; a child with two left-handed parents has a probability of only 63% of being right-handed. But parental influence does not account for everything. Random events during a child’s development can also have a small effect on handedness. Even if identical twins have parents who are both dextral, factors such as their position in the womb may result in the twins not preferring the same hands.
    The model seems plausible. It accurately predicts the results of 13 studies of the handedness of twins as well as the proportion of left-handers found in the population at large (roughly 12%, a figure that seems to be quite stable). Asymmetries in early tools, and in the way in which prey were clubbed, suggest that hominids as early as the Australo-pithecines may have preferred their right hands. Whatever the origin of this dextrous preference, though, left-handers remain at large. Some people are just sinister.
According to the passage, all of the following may affect a person’s handedness EXCEPT
选项 A、personality
B、genes
C、culture
D、random events
答案A
解析
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