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  • The pyramid is a traditional way of visualising and explaining the age structure of a society.

  • If you draw a chart with each age group represented by a bar, and each bar ranged one above the

  • otheryoungest at the bottom, oldest at the top, and with the sexes separatedyou

  • get a simple shape.

  • In 1970 that shape was a pyramid because the largest segment of the global population was

  • the youngest (0-5 years old, comprising 14% of the total), followed by the next-youngest

  • (6-10, with 13%), and so on in regular increments until, above 85 years, there were so few people

  • that the shape vanished into a point.

  • The pyramid was characteristic of human populations pretty much since the day organised societies emerged.

  • With lifespans short and mortality rates high, children were always the most numerous group,

  • and old people the least. A population chart of England in 1700 looks likes a pyramid.

  • But now look at the chart of the global population in 2015. It looks more like the dome of the

  • Capitol building in Washington, DC, than something along the Nile.

  • Young children are still the largest group, but now make up only 10% of the population

  • and those above them are almost as big, with 9.5%

  • The angle of the slope changes most markedly after about age 40.

  • In 1970 the youngest had not only been the largest but also the fastest-growing section

  • of the population. But between 1970 and 2015, the population aged 0-19 grew by only 42%,

  • whereas the population aged 20-39 rose by 128%.

  • This group added almost twice as many people to the overall numbers than the group aged

  • below 20.

  • There are now also over 50m people above 85, so the dome of 2015 has a spike.

  • In 1970-2015 the dominating influence upon the global population was the fertility ratethe

  • number of children a women could expect to bear during her lifetime. It fell dramatically

  • over the period, meaning that the world shifted from having larger to smaller families.

  • But in 2015-60, the biggest influence upon the population will be ageing. Small families

  • are already becoming the norm, the fall in fertility is slowing down and now everyone

  • is living longer than their parentsdramatically so in developing countries.

  • So, by 2060, the dome will have come and gone and now the shape of the population looks

  • more like a column (or perhaps an old-fashioned beehive). It is a little fatter near the bottom

  • and curves in at the top.

  • But up to the age of about 50, the generations are of almost equal size and the shape has

  • vertical sides.

  • The size of the Earth’s population is still rising, from 7.2 billion in 2015 to 9.5 billion

  • in 2060. But, according to calculations by Emi Suzuki and Wolfgang Fengler of the World

  • Bank, two- thirds of the extra 2.2 billion people will come from the older age groups,

  • those aged 40 to 59 and those between 60 and 79, not from the younger.

  • The increase in the last, oldest segment is especially marked. Between 2015 and 2060,

  • the number of 60- to 79-year-olds will double to 850m.

  • That is more than four times the increase in the number of children and teenagers, which

  • will rise by only 200m, or 8%.

  • The numbers of the oldest people of all (those above 85, here lumped together in one bar)

  • will rise at the fastest rate of all (by 281% in 2015-60), but from a much lower base, so

  • they do not add as many people to the total.

  • For all of history, humans have lived in societies dominated (in numbers at least) by children.

  • By 2060 children will be no more numerous than any other age group. The year 2015 is,

  • roughly, the half-way point in this astounding transformation.

The pyramid is a traditional way of visualising and explaining the age structure of a society.

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B1 UK population pyramid youngest aged shape age

The World in 2015: Global population and the changing shape of world demographics

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    吳方瑀 posted on 2016/10/12
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