阅读理解 New research asks whether psychopaths are born that way, or are made so by their upbringings. That, of course, is rather a crude way of putting it. After decades of debate, biologists have come to understand what was blindingly obvious to most laymen—which is that rather than being shaped by nature or nurture, most behavioural traits are the result of an interaction between the two. Nevertheless, one or the other can still be the dominant factor. And the study in question suggests that in the case of psychopathy, the genetic side is very important indeed.
Researchers have drawn their conclusion from a study of twins. The twins in question are on the books of a long-term project known as the Twins Early Development Study(TEDS), which has been following several thousand twins since their births in 1994 and 1995. Among other things, many of the twins in TEDS have been assessed both for a tendency to bad behaviour("conduct disorder", in the argot of the field)and for the display of what are referred to as callous-unemotional traits, such as a lack of feelings of guilt after doing something wrong, or not having at least one good friend. In adults, callous and unemotional traits are symptoms of psychopathy, and those who display such traits in childhood frequently keep them into adult life. The assessments were done by the children's teachers, whom years of experience have shown are more objective and accurate than a child's parents.
Based on the teachers' assessments, the researchers identified the naughtiest 10% of the individuals in their sample—in other words those with severe conduct disorder. They then subdivided these children into those with psychopathic traits and those without and asked, in each case, whether an individual's twin showed bad behaviour, psychopathy, or both. Their analysis showed that bad behaviour without psychopathy has relatively little genetic component—less than a third. By contrast, four-fifths of the difference in behaviour between the general population and children with psychopathic traits seems to lie in the genes.
Though the genes in question have yet to be identified, this result suggests they are too abundant to be there by chance—in other words they are being kept in the population by natural selection because psychopathic behaviour confers a selective advantage. If it does, such an advantage probably pertains only when psychopaths are in the minority(a state of affairs known to biologists as a balanced polymorphism). But it does mean that far from being an aberrant behaviour, psychopathy may be disturbingly normal.

【正确答案】 C

【答案解析】属推断题。原文首段第三句指出：几十年的争论之后，生物学家们渐渐明白了以前大部分门外汉都盲目接受的明显事实：人的大部分行为特征都是先天因素和后天因素相互作用的结果，而不是由先天因素或后天因素决定的。由此推知，以前人们的观点是行为特征是由先天因素或后天因素决定的，所以答案为C。同时否定A、B。D项接近人们现在的研究成果，但属答非所问。