世界人口增长趋势
专家告诉我们人口统计的4个时期。
HINTS:
Dr Ann Pawliczko
UNFPA
主持：lsy34
校对：z_i_y_u_n
翻译&注解：cherryxyr
答疑：阿焰
口语点评：fancyfrances
口语节目地址：http://bulo.hujiang.com/menu/2120/item/680244/http://t1.g.hjfile.cn/listen/201210/201210190916273894245.mp3That's Dr Ann Pawliczko, from the UNFPA. She says we can be pretty confident about the numbers.
"We can be very certain about the numbers for 2050 because persons who will be at age 60 in 2050 are already born. So this is not speculation."
Fair enough, but in the longer term, the figures aren't going to be dominated by the likes of you and me. It's the birth of new people that will have the largest effect on future statistics. And here's where it gets interesting. For a long time statisticians have observed something which they call the "demographic transition".
"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. You have several stages. Typically we speak of four stages. We have the first stage as high birth and high death rates, where there's slow population growth. Then we have the second stage. We have high birth rate and falling death rates, because of improvements in food supply, sanitation, technology, basic healthcare, education, etc. And that's we have high growth rates. Then stage three, declining birth rates and relatively low death rates, and this is characterised by 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."联合国人口基金会的安·波利兹克(Ann Pawliczko)博士表示对得出的数据很有信心。
“因为到2050年满60岁的人已经出生，所以我们对2050年的数据十分肯定。这并不是猜测。”
很好，但从更长远的角度来看，未来的数据并不是由我们这些已经出生的人决定的，而是由新生儿决定的。这一点十分有意思。长期之来，统计学家一直在研究“人口过渡”这一概念。
“人口过渡是指人口的出生率和死亡率由高往低转变。这种转变通常由经济和社会发展导致，一般要经历四个阶段。在第一阶段，人口增长缓慢，出生率和死亡率均很高。到了第二阶段，由于食物供给增加，公共卫生条件改善，科技日渐发达，基本医疗得到保障，教育日趋完善，出生率随之增高，死亡率降低，人口也因此急剧增长。到了第三个阶段，出生率下降，死亡率比出生率低，表现为人口增长缓慢，开始呈现平稳态势。在第四个阶段，出生率和死亡率都很低，人口缓慢增长。”
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