在发达国家，现在出生的人预期寿命约为80岁。这个数字在过去的1个世纪里几乎翻了一番。人在出生时的预期寿命衡量的是，现在出生的人，如果他们出生时整个社会的死亡率模式在他们一生中保持不变，那么他们的寿命是多久。但死亡率模式不会保持不变。

　　These patterns improve, so that most people born in the past century have lived far beyond their life expectancy at birth. Children born today can expect to live well beyond 80 years, even if the claim by Peter Thiel and Aubrey de Grey that the first 1,000-year man is already alive is optimistic.

　　死亡率模式在不断改善，因此，过去一个世纪中出生的大部分人活着的时间，已经远远超出了他们出生时的预期寿命。即便企业家彼得?蒂尔(Peter Thiel)和学者奥布里?德格雷(Aubrey de Grey)宣称第1个能活到1000岁的人已经出现的说法过于乐观，但可以预计，今天出生的儿童的寿命将远不止80岁。

　　死亡率模式保持不变 何必为长寿烦恼

　　Life expectancy was much lower a century ago because many children died in infancy and many adults failed to achieve a normal lifespan because they were killed by now-curable infectious diseases. Deaths from these sources are now so low that even dramatic further improvements will not have much effect on average lifespan. The most important factor today is increases in life expectancy after conventional ages of retirement. This measure has recently been improving at one to two months a year.

　　一个世纪以前，预期寿命比现在低得多，因为当时婴儿夭折率很高，许多现在我们已经能够治愈的传染性疾病又提前夺去了许多成年人的生命。现在因这些原因死亡的人数很少，以至于即使在这方面出现巨大的进步，也不会显著提高平均寿命。如今最重要的因素是，预期寿命减去通常退休年龄后所余时间的增长。近年来这项指标每年提高1到2个月。

　　Life-saving advances are the greatest benefit of technological change. And yet when pundits discuss the future, the excitement around driverless cars and nanotechnology gives way to long faces when the topic moves to human longevity. It may be nice to live longer, but what about the effect on the economy? The question is absurd. Economic growth is about giving people more choices, and no choice is more earnestly sought than the chance of a longer life. The hard economic evidence is the amount that people are willing to pay to extend their lives even for short periods.

　　技术变革带来的最大福祉就是生命救助方面的技术进步。然而同样是在展望未来，专家们谈论起无人驾驶汽车和纳米技术时一脸兴奋，话题转到人类长寿时他们却拉长了脸。长寿固然好，但是这对经济的影响该怎么办呢？这个问题是荒谬的。经济增长的目的是给人们更多选择，而没有什么选择能比有机会延年益寿更让人魂牵梦绕了。为了延长寿命，哪怕只是很短的时间，人们也愿意花很多钱，这就是经济上的铁证。

　　The demographic “crisis” has several components. There is the cost of pensions. Someone born today, retiring at 60 and living to 100, would have equal spells of work and retirement. Society is moving towards the obvious resolution – a concept of flexible retirement in which people can choose their preferred trade-off between work and leisure.

　　这个人口统计学上的“危机”有几个组成部分。养老金费用是其中之一。现在出生的人，如果60岁退休、活至100岁，那么退休后的时间就和工作的时间一样长了。社会正趋向显而易见的解决方式——弹性退休制，让人们可以在工作和退休间自由权衡。

　　Achieving these extended lifespans costs money. Not necessarily much, because healthy lifestyle is a more important contributor to longevity than medical treatment. But we all die, either from the remaining diseases we have not yet learnt to cure, or the accumulated effects of old age itself. So medical and care costs will inevitably be an increasing fraction of national income. But this is money the public really wants to spend. It resists attempts to control the grotesque costs of private US healthcare. “More for the National Health Service” is always the British electorate’s top spending priority.

　　实现寿命的延长要花钱。并不一定需要很多钱，因为就长寿而言，健康的生活方式比医疗保健更重要。但人都不免一死，要么死于那些我们还不知道如何治愈的绝症，要么死于年老本身带来的累积效应。因此，医疗和护理费用在国民收入中的比重将不可避免地上升。然而这份钱是公众确实想花的。美国控制私人医疗保健极高费用的尝试遭到了公众的抵制。“多向国民医疗服务体系(NHS)投入”一直都是英国选民对政府支出的头号要求。

　　Then there is the burden of an ageing population on a younger workforce. Here we are caught in a squeeze between the growing numbers of the elderly and a lower birth rate. In Europe today, the median age at which women have their first child is over 30. But we do not know whether these women, pursuing careers before starting a family, will ultimately have fewer children or just later children: completed family size is the key variable.

　　其二是老龄化人口对青壮年劳动力造成的负担。我们面对老龄人口日益增长和出生率降低的两头夹击。在当今的欧洲，女性生育第1胎的年龄中值超过了30岁。但是我们不知道这些先立业后生育的女性，最终将生育更少的孩子，还是仅仅选择晚生孩子：最终家庭中人口的数量才是关键变量。

　　Prediction is hard, especially about the future. Gloomy prognostications, sometimes of population explosion, then of secular stagnation, have repeatedly been falsified. But one certainty is that all the issues of concern result from developments that give us more choices – the choice between higher material living standard and more leisure, the indulgence of spending more looking after ourselves, and the opportunity for women to have careers as well as, or along with, family lives.

　　预测本来就很难，预测未来就更难了。那些悲观的预言，一会儿是人口爆炸一会儿是长期经济停滞，已经一次又一次的被证伪了。但有一点是肯定的，那就是所有这些令人担心的问题都是由一些新动向带来的，这些新动向让我们拥有了更多选择——是要更高的物质生活水平还是要更多的闲暇时间，要不要尽情花更多钱用于健康护理，女性也有了兼顾事业和家庭（或是在家庭之外也拥有一份事业）的机会。

　　What is not to like about these developments? Why should we care about lower gross domestic product per capita, or higher public spending as a share of national income if it is the consequence of things that make us better off?

　　这些新动向哪一点不好？如果人均国内生产总值(GDP per capita)没那么高或者公共支出占国民收入比重上升只是因为我们的生活变得更好了，我们又何须忧虑呢？