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  3. More boys than girls are born all over the world, but a new study has found that the closer people live to the equator(赤道), the

More boys than girls are born all over the world, but a new study has found that the closer people live to the equator(赤道), the

admin2017-06-11  66
问题     More boys than girls are born all over the world, but a new study has found that the closer people live to the equator(赤道), the smaller the difference becomes. No one knows why.
    The imbalanced sex ratio at birth has been known for more than a hundred years, and researchers have found a large variety of social, economic and biological factors that relate to the sex ratio at birth-war, economic stress, age, diet, selective abortion and more. But latitude(纬度)is a natural phenomenon, unaffected by cultural or economic factors.
    To look at the effect of latitude, Kristen J. Navara of the University of Georgia used the latitude of the capital city in 202 countries, as well as 10 years of data on sex ratio at birth and annual variations in day length and temperature. Dr. Navara performed a statistical analysis which showed that there was a significant relation between sex ratios in favor of boys and latitude. African countries produced the lowest sex ratios—50. 7 percent boys—and European and Asian countries had the highest with 51. 4 percent.
    There are some possible explanations, but none entirely satisfactory. It could be that there is some survival value in producing more girls in warmer regions, but it is unclear what this might be. There may be genetic or racial differences that could explain it, but the connection persists over so many varied populations that this seems unlikely. Mice also produce more male offspring during shorter days or colder weather, but the reasons in these animals are just as mysterious as they are in humans.
    " There’s a possibility that humans might be responding to factors they were programmed to respond to a long time ago-not cultural or socioeconomic, but climate and things like latitude," Dr. Navara said. " What’s interesting is that we may be seeing something that connects us with our animal ancestry. "
According to Navara, which of the following probably explains the imbalanced sex ratio?
选项 A、There is cultural preference for boys.
B、Humans are designed that way by nature.
C、Different races have different birth ratios.
D、Humans are different from animals in birth ratio.
答案C
解析 细节理解题。文章没有提到文化差异对性别比例的影响，由此排除A。人类性别由天生决定的，也不符合原文，故B也被排除。在第四段提到：There may be genetic orracial differences that could explain it，but the connection persists over so many varied populationsthat this seems unlikely，种族不同，其出生率也不同，选项C符合原文这一说法，是正确答案。在第四段的最后提到老鼠的例子，其目的想证明：…but the reasons in these animals arejust as mysterious as they are in humans，所以D也被排除。
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