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  3. One of the paradoxes of human biology is that the rich world has fewer children than the poor world. In most species, improved c

One of the paradoxes of human biology is that the rich world has fewer children than the poor world. In most species, improved c

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问题     One of the paradoxes of human biology is that the rich world has fewer children than the poor world. In most species, improved circumstances are expected to increase reproductive effort, not reduce it, yet as economic development gets going, country after country has experienced what is known as the demographic transition; fertility(defined as the number of children borne by a woman over her lifetime)drops from around eight to near one and a half. That number is so small that even with the reduced child mortality which usually accompanies development it cannot possibly sustain the population.
    This reproductive collapse is particularly worrying because it comes in combination with an increase in life expectancy which suggests that, by the middle of the century, not only will populations in the most developed countries have shrunk(unless they are propped up by historically huge levels of immigration)but also that the number of retired individuals supported by each person of working age will increase significantly. If Mikko Myrskyla of the University of Pennsylvania and his colleagues are correct, though, things might not be quite as bad as that. A study they have just published in Nature suggests that as development continues, the demographic transition goes into reverse.
    Dr. Myrskyla compared two things. One was the total fertility rate(the number of children that would be born to a woman in a particular country over the course of her life if she experienced the age-specific fertility rates observed in that country during the calendar year in question). The other was the human development index for that country. The HDI, a measure used by the United Nations, has three components: life expectancy; average income per person; and level of education. Its maximum possible value is one.
    Back in the 1970s, no country got anywhere near one. Of the 107 places the researchers looked at, the best was Canada, with an HDI of 0.89. By 2005, however, things had improved markedly. Two dozen of what were now 240 countries had HDIs above nine—and something else remarkable had happened. Back in 1975, a graph plotting fertility rate against the HDI fell as the HDI rose. By 2005, though, the line had a kink in it. Above an HDI of 0. 9 or so, it turned up, producing what is known in the jargon as a "J-shaped" curve(even though it is the mirror image of a letter J). In many countries with really high levels of development(around 0.95)fertility rates are now approaching two children per woman. There are exceptions, notably Canada and Japan, but the trend is clear.
    Why this change has come about, and why the demographic transition happens in the first place, are matters of debate. There are lots of social explanations of why fertility rates fall as countries become richer. The increasing ability of women in the developed world to control their own reproductive output is one, as is the related phenomenon of women entering the workplace in large numbers. The increasing cost of raising children in a society with more material abundance plays a part. So does the substitution of nationalised social-security systems for the support of offspring in old age. Falling rates of child mortality are also significant. Conversely, Dr. Myrskyla speculates that the introduction of female-friendly employment policies in the most developed countries allows women to have the best of both worlds, and that this may contribute to the uptick.
    No doubt all these social explanations are true as far as they go, but they do not address the deeper question of why people’s psychology should have evolved in a way that makes them want fewer children when they can afford more. There is a possible biological explanation, though.
What is the role of the 4th paragraph in the development of the topic?
选项 A、To illustrate that fertility rates in some highly developed countries began to rise.
B、To show that countries like Canada and Japan remain low fertility rates.
C、To explain how demographic transition occurred from 1975 to 2005.
D、To indicate that the trend of HDI is unrelated to the rise or fall of fertility rates.
答案A
解析 篇章题。第四段承上启下，通过对相关数据的比较分析，证明了迈斯基拉博士等人的观点，即随着经济的发展，人口转变趋势会发生逆转，也为下文解释这种逆转进行了铺垫。因此选[A]。此段的意图并不是为了解释第一段提到的“人口转变”，因为根据此段的分析，当人口转变发展到一定程度时还会发生逆转，所以[C]不正确，故排除；日本和加拿大没有出现逆转，文中将其作为一种例外，但并未作为解释的重点，因此排除[B]；尽管生育率和HDI两个指标之间并不是严格的同向或逆向变化，但并不等于二者彼此无关，事实是二者在HDI达到0．9的转折点之前是逆向变化，达到转折点之后则是同向变化，因此[D]不正确，故排除。
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