"Today we have one in nine persons aged 60 or over, " says the UNFPA's Dr Ann Pawliczko, "but by 2050 it'll be one in five, and by that time there will be more older persons than those under 15 years."
预测者期望世界人口在2050年前达到100亿-但是这个数字能再高一点吗？
The UN sees these statistics as a cause both for celebration because more people are living longer, and some concern because the change presents an economic and social challenge.
联合国人口活动基金会最近公布了描述世界人口老龄化的报告 现在我们9个人里至少有一个60岁或以上的”，联合国人口活动基金会的 Ann Pawliczko博士说，“但是到2050年会是5个人里有一个，到那时候将会有更多的老人，远远超过那些15岁以下的人数。”联合国一方面把这些统计数据看作是庆祝的理由，因为有更多的人活得更长了，一方面又开始担心，因为这个改变对社会和经济都是一个挑战。
Dr Pawliczko would like see more countries prepare for the coming demographic shift. After all, she says, there is no doubt it is happening.
Pawliczko博士想看到更多的国家为即将到来的人口巨变作准备。她说毕竟这是必然要发生的。
"We can be very certain about the numbers for 2050 because persons who will be aged 60 in 2050 are already born. This not speculation."
“我们可以非常确定2050年的数字，因为那时候60岁的人现在已经出生了，这不是推测。”
There is, however, another side to the equation: the birth rate. Predicting how that will change is more difficult - and more interesting. For a long time statisticians have seen in the numbers something which they call the "demographic transition", which happens when a society gets wealthier.
然而，也有使它平衡的的因素：出生率。预测出生率如何平衡并改变人口比例是很困难-但也很有趣。统计学家有一段时间已经在数字中看到了他们称之为“人口过渡”
"The demographic transition is a shift of birth and death rates from high levels to low levels in a population. And that usually is a result of economic and social development, " says Dr Pawliczko.
的东西，当社会变得富足的时候将会发生。
"Typically we speak of four stages. We have the first stage which is high birth rates and high death rates. Then we have the second stage of high birth rates and falling death rates.
“人口过渡是在人口上出生和死亡率从高到低的一个转变，通常是经济和社会发展的产物。Pawliczko博士说道。
"And then stage three, declining birth rates and relatively low death rates, and this is characterised by a slow growth rate of the population, the growth begins to level off. And then stage four is where you have low birth rates and low death rates, and consequently a low population growth."
“一般我们提到有四个阶段。第一个阶段是高出生率和高死亡率。第二个阶段是高出生率和死亡率降低，第三个阶段是d出生率降低和相对较低的死亡率, 这是以缓慢的的人口增长率为特征的，增长开始停滞。 最后第四个阶段是有着低出生率和低死亡率的，所以也有着低的人口增长率。”
So as countries get richer their fertility rates fall. But what happens next? Many statisticians assume that advanced nations will remain in periods of low population growth.
因此随着国家的不断富裕，他们的人口出生率也随之降低。但是接下来会发生什么呢？许多统计学家想当然的认为发达国家会保持很长一段时期的低人口增长率。但是最近的很多证据表明他们设想的很可能是错的。
"Historically, fertility has been falling across Europe, " says Professor Jane Falkingham, director of the ESRC Centre for Population Change at Southampton University. "But actually if we look at the most recent period, the last 10 years or so, we see rises in fertility in the most advanced countries."
“在历史上，欧洲的人口出生率一直在降低，”Jane Falkingham教授说，在 南安普顿大学欧洲科学研究理事会研究人口变化的理事。“但是实际上如果我们从最近的时期来看的话，上一个十年，我们看到在大多发达国家出生率都有所上升。”
Oxford University's Professor Francesco Billari, a leading demographer, says this increase in fertility in highly-developed countries cannot be attributed solely to immigration, as some had assumed.
牛津大学教授Francesco Billari—主要的人口学家,说在高度发达国家出生率的这个增长不能仅仅归功于一些人推测的移民这个因素。
"Demographers used to be the lucky ones because we thought it was easy to forecast population change. I think that's no longer true. It's no longer true at the global level because recent fertility trends are showing that the future is much more uncertain than we thought. There may be a complete change in the ranking of fertility levels in the world."
他说“我们做了一些计算，从根本上说，这个新变化不仅仅因为移民，当地的人口也在变化。人口学家过去是幸运的，因为我们认为预测人口变化是容易的，但我想现在从全球层面上看这不再是正确的，因为最近的出生率趋势显示将来会有比我们所想的更多不确定因素。在世界上出生率水平高低排名也许会有一个彻底的改变。”
Evolutionary biologists might not be surprised by this. The idea that as we get richer we have fewer children is, from their perspective, very odd. Normally natural selection produces individuals who are good at converting their resources into lots of fertile descendants.
进化论生物学家也许不会对此感到惊讶。我们越富裕，小孩越少这个观点在他们看来是非常奇怪的。通常自然选择会产生擅长把他们的资源转换成能生育的后代的个人。
It's a demographic paradox that in the past few centuries, developing societies haven't been filled by families who raise as many kids as they can possibly afford.
在过去几百年里，尽可能多的抚养小孩的那些家庭并没有把这个发展中的社会填满。
But putting Darwin to one side, the question is: how much difference might the recently-observed increase in fertility in some developed countries actually make to global population projections?
但是暂且把达尔文的理论放一边，问题是：最近注意到的在一些发达国家出生率上的增长对全球人口预测实际上会有多大影响？
Dr Pawlizcko at the UNFPA says she doesn't expect it to be very significant. She may well be right. But, then again, neither she nor anyone else can be too sure. Statisticians have a long track record of failing to predict important demographic changes.
在联合国人口活动基金会Pawliczko博士说并不期望有显著的影响，她很有可能是正确的。但是任何人包括她都不能太确信。统计学家有一个失败预测重要人口变化追踪记录。
"We've actually got population projections wrong consistently over the last 50 years, " says Professor Falkingham, "and this is partly because we've underestimated the improvements in mortality, particularly older age mortality, but also we've not been very good at spotting the trends in fertility."
“我们人口预测上失误已经持续了过去的50年了，”教授Falkingham说，“在一定程度上是因为我们低估了在死亡率上的增长，尤其是老年人的死亡率，但我们也不是很擅长发现出生率的的趋势变化。”
One day we will know whether our population projections beyond 2050 are accurate, whether the so-called "demographic transition" enters a fifth and unexpected stage of higher fertility, or whether huge leaps in life expectancy change the picture completely, as they have in the past.
将来的某一天我们会知道我们现在对2050年的人口预测是不是正确的，所谓的“人口过渡”会不会进入较高出生率的第五或者意想不到的阶段，或者生命预期会向前迈一大步，彻底改变我们过去的格局。
But forecasting population will always be a highly uncertain science.
但是预测人口总是一门高不确定性的科学。
In 2004 the UN's department of economic and social affairs tried to guess what the global population could be in 2300.
2004年联合国经济和社会事务部试着去猜想2300全球人口会是怎样。
It said the population would stabilise at around nine billion by 2050 and then remain at that level for the rest of the period. But that was just its medium estimate. Its high estimate was 36.4bn, and its low estimate just 2.3bn.
它说在2050年前人口会稳定在90亿左右，接下的时期来的时期也依然保持在那个水平。但是那只是保守估计，高估计的话会在364亿，低的话就只有23亿。
In other words, when you look beyond existing generations, anything could happen.
换句话说，当你从我们现有的一代再往后看的话，任何事都有可能会发生。
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