During the second half of the 20th century, the global population explosion was the big demographic bogey. Robert McNamara, president of the World Bank in the 1970s, compared the threat of unmanageable population pressures with the danger of nuclear war. Now that worry has evaporated, and this century is spooking itself with the opposite fear: the onset of demographic decline.
　　The shrinkage of Russia and eastern Europe is familiar, though not perhaps the scale of it: Russia's population is expected to fall by 22% between 2005 and 2050, Ukraine's by a staggering 43%. Now the phenomenon is creeping into the rich world: Japan has started to shrink and others, such as Italy and Germany, will soon follow. Even China's population will be declining by the early 2030s, according to the UN, which projects that by 2050 populations will be lower than they are today in 50 countries.
　　Demographic decline worries people because it is believed to go hand in hand with economic decline. At the extremes it may well be the result of economic factors: pessimism may depress the birth rate and push up rates of suicide and alcoholism. But, in the main, demographic decline is the consequence of the low fertility that generally goes with growing prosperity. In Japan, for instance, birth rates fell below the replacement rate of 2.1 children per woman in the mid1970s and have been particularly low in the past 15 years.
　　But if demographic decline is not generally a consequence of economic decline, surely it must be a cause? In a crude sense, yes. As populations shrink, GDP growth will slow. Some economies may even start to shrink, too. The result will be a loss of economic influence.
　　Governments hate the idea of a shrinking population because the absolute size of GDP matters for greatpower status. The bigger the economy, the bigger the military, the greater the geopolitical clout: annual GDP estimates were first introduced in America in the 1940s as part of its war effort. Companies worry, too: they do not like the idea of their domestic markets shrinking. People should not mind, though. What matters for economic welfare is GDP per person.
　　The crucial question is therefore what the effect of demographic decline is on the growth of GDP per person. The bad news is that this looks likely to slow because workingage populations will decline more rapidly than overall populations. Yet this need not happen. Productivity growth may keep up growth in GDP per person: as labour becomes scarcer, and pressure to introduce new technologies to boost workers' efficiency increases, so the productivity of labour may rise faster. Anyway, retirement ages can be lifted to increase the supply of labour even when the population is declining.
　　People love to worry-maybe it's a symptom of ageing populations-but the gloom surrounding population declines misses the main point. The new demographics that are causing populations to age and to shrink are something to celebrate. Humanity was once caught in the trap of high fertility and high mortality. Now it has escaped into the freedom of low fertility and low mortality. Women's control over the number of children they have is an unqualified good-as is the average person's enjoyment, in rich countries, of ten more years of life than they had in 1960. Politicians may fear the decline of their nations' economic prowess, but people should celebrate the new demographics as heralding a golden age.

　　在二十世纪后半叶，全球人口大爆炸还是令人担忧的人口问题。70年代，世界银行行长Robert McNamara甚至还把人口压力所带来的威胁与核战相提并论，然而在今天看来，这种忧虑已经不复存在了。这个世纪悄悄过去了，带给人们的却是一个恰恰相反的忧虑：人口衰退开始初露端倪。
　　尽管俄罗斯和东欧各国人口递减的具体比例可能不被知晓，但对这一事实人们已经有所了解。实际上，从2005年到2050年，俄罗斯的人口预计会减少22%，而乌克兰竟然有43%之多。今天这一现象在发达国家也悄然出现：日本人口已经开始递减，而其他的一些国家，如：意大利和德国，也将步日本的后尘。联合国有关报告指出，即便是中国，到2030年初期人口也将开始递减。这份报告同时还指出，到2050年，将有50个国家的人口低于今天的水平。
　　人口的衰退之所以让人们担心，是因为人们相信与之相伴随的是经济的衰退。进一步来说，我们有理由认为人口的衰退是经济因素导致的。因为悲观会降低出生率却会提高自杀和酒精中毒的比率。但是，大体上人口降低是由人口出生率过低导致的。而低的人口出生率通常与不断增进的繁荣相联系。比如在日本七十年代中期，出生率降至相当于平均每个妇女生2.1个孩子以下，而且在过去的15年里一直明显的偏低。
　　但是如果人口衰退不是一般意义上的经济衰退所导致的后果，那么它确切地说一定是它的一个原因吗？在某种不确定的意义上，答案是肯定的。随着人口的衰退，GDP的增长也将缓慢。一些经济体甚至也开始衰退。其结果将是经济影响力的丧失。
　　政府不愿意看到人口的收缩，因为GDP的绝对大小关乎强国的地位。经济越繁荣，军队越强大，地缘政治的影响也就越大。比如在四十年代，美国首次把年GDP评估的引入作为其战争成就的一部分。公司也不愿看到人口衰退。因为他们不想自己的国内市场有所收缩。但普通人对此却并不关心，因为关系他们经济福利的是人均GDP。
　　因此，至关重要的问题是人口衰退对人均GDP增长的影响是怎样的。不利的一面是它将减缓人均GDP的增长，因为适宜工作的人口将比总人口下降的更快一些。然而这也并不一定会发生。生长率的增长将维持人均GDP的增长。由于劳动者的不足和引进增加工人效率的新技术的压力的增大，劳动者的生产率可能会增长得更快。无论怎样，即使当人口正在衰退的时候，我们仍然可以通过提高退休年限的方式来增加劳动力的供给。
　　人们喜欢担忧--这可能是上年纪的人的症状--但围绕着人口衰退的忧愁却没有抓住要害。引发人口老龄化和衰退的新人口问题也有值得庆幸的地方。人类过去掉入高出生率和高死亡率的陷阱，而现在逃到了低出生率和低死亡率的自由之地。女人拥有一种绝对的优势，那就是对自己生孩子的数量的掌控。在发达国家，对普通人而言，能比六十年代的人多享受十年的生活也同样是种绝对优势。政治家可能会担心他们国家的经济实力下降。而我们普通人应该为新人口问题所预兆的黄金时代而欢呼。