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  3. Being a man has always been dangerous.There are about 105 males born for every 100 females, but this ratio drops to near balance

Being a man has always been dangerous.There are about 105 males born for every 100 females, but this ratio drops to near balance

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问题     Being a man has always been dangerous.There are about 105 males born for every 100 females, but this ratio drops to near balance at the age of maturity, and among 70-year-olds there are twice as many women as men.But the great universal of male mortality is being changed now, by babies survive almost as well as girls do.This means that, for the first time, there will be an excess of boys in those crucial years when they are searching for a mate.More important, another chance for natural selection has been removed.Fifty years ago, the chance of a baby (particularly a boy baby) surviving depended on its weight.A kilogram too light or too heavy meant almost certain death.Today it makes almost no difference.Since much of the variation is due to genes one more agent of evolution has gone.
    There is another way to commit evolutionary suicide: stay alive, but have fewer children.Few people are as fertile as in the past.Except in some religious communities, very few women has 15 children.Nowadays, the number of births, like the age of death, has become average.Most of us have roughly the same number of offspring.Again, differences between people and the opportunity for natural selection to take advantage of it have diminished India shows what is happening.The country offers wealth for a few in the great cities and poverty for the remaining tribal peoples.The grand mediocrity of today everyone being the same in survival and number of offspring means that natural selection has lost 80% of its power in upper-middle-class India compared to the tribes.
    For us, this means that evolution is over; the biological Utopia has arrived.Strangely, it has involved little physical change.No other species fills so many places in nature.But in the pass 100,000 years-even the pass 100 year our lives have been transformed but our bodies have not.We did not evolve, because machines and society did it for us.Darwin had a phrase to describe those ignorant of evolution: they "look at an organic being as average looks at a ship, as at something wholly beyond his comprehension." No doubt we will remember a 20th century way of life beyond comprehension for its ugliness.But however amazed our descendants may be at how far from Utopia we were, they will look just like us.
What does the example of India illustrate?
选项 A、Wealthy people tend to have fewer children than poor people.
B、Natural selection hardly works among the rich and the poor.
C、The middle class population is 80% smaller than that of the tribes.
D、India is one of the countries with a very high birth rate.
答案B
解析 本题可参照文章的第2段。从中可知，如今很少人像从前那样能生育了。除了在一些宗教群体，很少有妇女生15个孩子。今天所生孩子的数目就像死亡年龄一样，人人都差不多。我们大多数人家的子女数量几乎都一样多。人与人之间的差异和利用差异进行自然选择的机会再次减小。印度的情况就是这样。该国为大城市的一部分人提供财富，而其余那些仍保持群居的部落民族依然贫困。今天最大的相同点——每个人的生存机会和子女数量都一样——意味着，与部落比较，自然选择在印度中上阶层已失去80％的作用。据此可知，印度的例子说明——在印度，自然选择在穷人
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