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  3. A boy or a girl? That is usually the first question asked when a woman gives birth. Remarkably, the answer varies with where the

A boy or a girl? That is usually the first question asked when a woman gives birth. Remarkably, the answer varies with where the

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问题     A boy or a girl? That is usually the first question asked when a woman gives birth. Remarkably, the answer varies with where the mother lives. In rich countries, the chances of its being a boy are about 5 ％ higher than in poor ones. Equally remarkably, that figure has been felling recently. Several theories have been put forward to explain these observations. Some argue that smoking plays a role; others hold that diet may be important. Neither of these ideas has been supported by evidence from large studies. But new research points to a different factor: stress.
    Early studies revealed a shift in women who became pregnant during floods and earthquakes and in time of war. Moreover, a study carried out eight years ago by researchers at the University of Aarhus, in Denmark, revealed that women who suffered the death of a child or spouse from some catastrophic illness around the time they conceived were much more likely to give birth to girls than to boys.
    Taken together, these results suggest that acute stress to a woman at the time of conception shifts the sex ratio towards girls. However, Carsten Obel, a researcher at Aarhus who was not involved in the earlier study, wondered if the same might be true of chronic stress too. In a paper just published in Human Development, he shows that it is.
    Dr. Obel used a set of data collected between 2012 and 2015. During that period 8,719 expectant mothers were asked to fill in questionnaires that inquired, among other things, about their level of stress. Dr. Obel found that the more stressed a mother had been, the less chance she had of having given birth to a boy. Only 47％ of children born to women in the top quartile of stress were males. That compared with 52％ for women in the bottom quartile. Dr. Obel suspects the immediate cause is that male pregnancies are more likely to miscarry in response to stress than female pregnancies are, especially during the first three months. However, that is difficult to prove. More intriguing, though, is the ultimate cause, for he thinks it might be adaptive, rather than pathological.
    That is because the chances are that a daughter who reaches adulthood will find a mate and thus produce grandchildren. A son is a different matter. Healthy, strapping sons are likely to produce lots of grandchildren, by several women—or would have done in the hunter-gatherer societies in which most human evolution took place. Weak ones would be marginalized and maybe even killed in the cut and thrust of male competition. If a mother’s stress adversely affects the development of her fetus then selectively aborting boys, rather than wasting time and resources on bringing them to term, would make evolutionary sense.
    That, in turn, would explain why women in rich countries, who are less likely to suffer from hunger and disease, are more likely to give birth to sons. That this likelihood is, nevertheless, falling suggests that rich women’s lives may be more stressful than they used to be.
Which of the following can explain Dr. Obel’s opinion that the ultimate cause is adaptive rather than pathological?
选项 A、47％ of children born to women in the top quartile of stress were males while 52％ in the bottom quartile.
B、Women in rich countries are more likely to give birth to boys.
C、Women selectively abort boys rather than waste time and resources on bringing them to term for fear of male competition.
D、Women who suffer from calamity in conception are more likely to give birth to girls.
答案C
解析 本题关键词是Dr. Obel’s opinion和the ultimate cause，问题是：哪个选项可解释奥贝尔博士的观点：最根本的原因是适应性的而非病理性的?可以定位到原文第四、五段。根据第四段，奥贝尔博士发现女性承受的压力越大，她生男孩的概率就越小，他认为其根本原因可能是适应性而不是病理性。面临压力时，女性如果怀的是男孩，那么就更容易流产。紧接着第五段给出了解释，那就是在资源紧缺的男性竞争社会中，弱小的男性更容易被边缘化、被淘汰，而女性则不存在这个问题，所以如果压力对胎儿生长有负面影响，那么女性会选择将男婴流产，这是一种适应环境的做法，选项C是对原文的全面概括，为正确答案。选项A、B、D属于就事论事，只是一些表象，而不是对奥贝尔观点的深层次解释。
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