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  3. Twins to Impaired Fertility of Women A woman with a twin brother has fewer children. Twin brothers can leave quite an impres

Twins to Impaired Fertility of Women A woman with a twin brother has fewer children. Twin brothers can leave quite an impres

admin2013-06-05  92
问题                     Twins to Impaired Fertility of Women
    A woman with a twin brother has fewer children. Twin brothers can leave quite an impression. The mere presence of a boy in the same womb as his sister causes her to develop bigger teeth than she otherwise would. Girls with twin brothers perform better on spatial ability tests. They have better ball skills than most females and are more likely to be short-sighted. Now it seems that sharing the womb also has a harmful effect on the sexual reproduction of women with a twin brother.
    Virpi Lummaa of the University of Sheffield, in Britain, and her colleagues made the claim after studying detailed data from several generations of church records from many parishes in Finland. They report that women with a twin brother were 15% less likely to get married than were women with a twin sister. Those with a male twin also had a 25% lower chance of giving birth even though they lived just as long as those with a female twin. When the researchers considered only married women, those with a twin brother on average had two fewer children during their lifetimes than did women with a twin sister.
    And finally—to rule out any influence of sharing a house as well as a womb—Dr. Lu-mmaa checked the results were the same for women whose twin brothers died before they were three months old. The researchers reported their findings in this week’s Proceedings of the National Academy of Sciences.
    As with the teeth, the supposed cause of untypical female biology is early exposure to testosterone. This hormone is made by a male fetus’s developing testes from about seven weeks after conception and is thought to diffuse, thus influencing his sister’s growth. But the exact mechanism by which a twin brother lowers his sister’s chances of reproductive success is unclear.
    Dr. Lummaa’s results also suggest that, if a woman wishes to maximize the chances of passing on her genes, she would do better to avoid producing pairs of twins consisting of one boy and one girl and go for a single-sex combination instead. Mothers included in the study who produced opposite-sex twins had 19% fewer grandchildren than did mothers who gave birth to same-sex twins.
    Evolutionary theory thus predicts that there should be fewer pairs of girl-and-boy non-identical twins than single-sex pairs of non-identical twins. Whether that is so requires another set of figures. Finnish church records, helpful as they are, do not distinguish non-identical same-sex twins from identical ones. In the eyes of God, unlike those of natural selection, twin girls are created equal.
The word "conception" (Line 5, Para. 3) here has a meaning closest to______.
选项 A、childbirth
B、pregnancy
C、teeth-forming
D、labour
答案B
解析 语义理解题。定位在第三段。首句提到了可以用解释牙齿情况的理论来解释龙风胎中女性生理方面的情况。而非具体讨论长牙齿的问题，故C项错误；该段强调了原因可能与龙凤胎中的女性过早接触到了激素有关。而激素是由“conception七周后a male fetus’s developing testes”产生的，虽然很多考生对fetus和testes这两个单词不熟悉，但是developing一词传递出“正在形成中”的意思，结合前面提到的“过早接触”，可以推得pregnancy(受孕)最为恰当，故选B项。A项与D项同义(分娩)，故可排除。
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