What is making the world so much older? There are two long-term causes and a temporary blip that will continue to show up in the

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问题     What is making the world so much older? There are two long-term causes and a temporary blip that will continue to show up in the figures for the next few decades.【F1】The first of the big causes is that people everywhere are living far longer than they used to, and this trend started with the industrial revolution and has been slowly gathering pace. In 1900 average life expectancy at birth for the world as a whole was only around 30 years, and in rich countries under 50. The figures now are 67 and 78 respectively, and still rising. For all the talk about the coming old-age crisis, that is surely something to be grateful for-especially since older people these days also seem to remain healthy, fit and active for much longer.
    【F2】A second, and bigger, cause of the ageing of societies is that people everywhere are having far fewer children, so the younger age groups are much too small to counterbalance the growing number of older people. This trend emerged later than the one for longer lives, first in developed countries and now in poor countries too. In the early 1970s women across the world were still, on average, having 4.3 children each. The current global average is 2.6, and in rich countries only 1.6.【F3】The UN predicts that by 2050 the global figure will have dropped to just two, so by mid-century the world’s population will begin to level out. The numbers in some developed countries have already started shrinking. Depending on your point of view, that may or may not be a good thing, but it will certainly turn the world into a different place.
    The temporary blip that has magnified the effects of lower fertility and greater longevity is the baby-boom that arrived in most rich countries after the Second World War.【F4】The timing varied slightly from place to place, but in America—where the effect was strongest—it covered roughly the 20 years from 1945, a period when nearly 80 million Americans were born. The first of them are now coming up to retirement. For the next 20 years those baby-boomers will be swelling the ranks of pensioners, which will lead to a rapid drop in the working population all over the rich world.
    As always, the averages mask considerable diversity.【F5】Most developing countries do not have to worry about ageing—yet, in the longer term, however, the same factors as in the rich world—fewer births, longer lives—will cause poorer countries to age too.
【F3】

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答案联合国预计,到2050年,全球妇女的人均生育率将降至2,因此,到本世纪中叶,世界人口总数将开始呈现平稳状态。

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