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  • Russia, with the largest territory in the world,

  • has roughly the same total population as Nigeria,

  • a country 1/16 its size.

  • But this similarity won't last long.

  • One of the populations is rapidly growing,

  • while the other is slowly declining.

  • What can this tell us about the two countries?

  • Population statistics are some of the most important data

  • social scientists and policy experts have to work with.

  • But understanding a country's situation

  • and making accurate predictions

  • requires knowing not just the total size of the population

  • but its internal characteristics,

  • such as age and gender distribution.

  • So, how can we keep track of all that data

  • in a way that makes it easy to comprehend?

  • Complex data is more easily interpreted

  • through visualization,

  • and one of the ways that demographers represent

  • the internal distribution of a population

  • is the population pyramid.

  • Here, the data is divided by gender

  • with females on one side and males on the other.

  • The population numbers are shown

  • for each five-year age interval,

  • starting from 0-4

  • and continuing up to 100 and up.

  • These intervals are grouped together

  • into pre-reproductive (0-14),

  • reproductive (15-44),

  • and post-reproductive years (45 and up).

  • Such a population pyramid can be a powerful predictor

  • of future population trends.

  • For example,

  • Rwanda's population pyramid shows it to be a fast-growing country,

  • with most of the population

  • being in the youngest age groups at the bottom of the pyramid.

  • The number will grow rapidly in the coming years.

  • As today's children reach their reproductive years

  • and have children of their own,

  • the total population is almost certain to double

  • within the next few decades.

  • For our second example,

  • let's look at Canada,

  • where most of the population is clustered

  • around the middle of the graph.

  • Because there are less people

  • in the pre-reproductive age groups

  • than there are in the reproductive ones,

  • the population will grow more slowly,

  • as the number of people reaching their reproductive years decreases.

  • Finally, let's look at Japan.

  • Because the majority of its population

  • is in its post-reproductive years

  • and the number of people is smaller

  • at each younger interval,

  • this means that at current rates of reproduction

  • the population will begin to decline

  • as fewer and fewer people reach reproductive age.

  • Comparing these three population pyramids

  • side by side

  • shows us three different stages

  • in a demographic transition,

  • as a country moves from a pre-industrial society

  • to one with an industrial

  • or post-industrial economy.

  • Countries that have only recently begun

  • the process of industrialization

  • typically see an increase in life expectancy

  • and a fall in child mortality rates

  • as a result of improvements

  • in medicine, sanitation, and food supply.

  • While birth rates remain constant,

  • leading to a population boom.

  • Developing countries that are farther along

  • in the industrialization process

  • begin to see a fall in birth rates,

  • due to factors such as

  • increased education and opportunities for women outside of child-rearing

  • and a move from rural to urban living

  • that makes having large families

  • less economically advantageous.

  • Finally, countries in advanced stages of industrialization

  • reach a point

  • where both birth and death rates are low,

  • and the population remains stable

  • or even begins to decline.

  • Now, let's take a look at the projected population pyramids

  • for the same three countries in 2050.

  • What do these tell us

  • about the expected changes

  • in each country's population,

  • and what kinds of factors

  • can alter the shape of these future pyramids?

  • A population pyramid can be useful

  • not only as a predictor of a country's future

  • but as a record of its past.

  • Russia's population pyramid

  • still bears the scars of World War II,

  • which explains both the fewer numbers of elderly men

  • compared to elderly women

  • and the relatively sudden population increase

  • as soldiers returned from the war

  • and normal life resumed.

  • China's population pyramid

  • reflects the establishment of the one child policy

  • 35 years before,

  • which prevented a population boom

  • such as that of Rwanda

  • but also led to sex-selective abortions,

  • resulting in more male children than female children.

  • Finally, the pyramid for the United States

  • shows the baby boom that followed World War II.

  • As you can see,

  • population pyramids tell us far more

  • about a country

  • than just a set of numbers,

  • by showing both where it's been

  • and where it's headed

  • within a single image.

  • And in today's increasingly interconnected world,

  • facing issues such as food shortages,

  • ecological threats, and economic disparities,

  • it is increasingly important

  • for both scientists and policy makers

  • to have a rich and complex understanding

  • of populations and the factors affecting them.

Russia, with the largest territory in the world,

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B1 中級

TED-ED】人口ピラミッド。未来を予測する強力な予言者 - キム・プレスホフ (【TED-Ed】Population pyramids: Powerful predictors of the future - Kim Preshoff)

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