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Demographic transition | Society and Culture | MCAT | Khan Academy - YouTube
Channel: khanacademymedicine
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Voiceover: Demographic
transition is a model that
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changes in a country's population.
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It states that the population
will eventually stop
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growing when the country
transitions from high
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birth rates and high death
rates to low birth rates
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and death rates,
stabilizing the population.
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This stabilization often
occurs in industrialized
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countries, because less
developed countries tend
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to rely on and follow the
more developed countries
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for their advancements.
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Right now, most countries
have a positive growth
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rate, which means their
population keeps getting
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bigger.
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First, let's pin down
what the growth rate is.
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Growth rate measures
how much the population
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of a country grows or shrinks
over some time period.
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For example, let's take
a look at this country.
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I'm going to call it "Zed".
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Zed, here, had one million
people at the beginning
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of the year.
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If we want to know the
growth rate of the population
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of Zed for the year, we
count how many people were
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added to the population
and how many people were
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removed.
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The number of people
added includes the number
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of births and the number
of people who immigrated
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into the country during that year.
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Let's say 20,000 babies
were born this year and
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50,000 people moved to
Zed from other countries.
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Then you have to subtract
from this number how
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many people were removed
from the population,
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so the number of deaths
and the number of people
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who emigrated from the
country during that year.
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Let's say, during the year,
15,000 people died and
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5000 people moved out of Zed.
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From here, it's pretty
easy to figure out the
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population of Zed at the end of the year.
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Started with one million,
add 20,000 births and
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50,000 immigrants and
subtract 15,000 deaths and
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5000 emigrants, which
gives us 1,050,000 people
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at the end of the year.
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If we want the growth rate
over this year, all you
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need to do is take that
total current population,
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subtract the total number
of people in the country
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at the beginning of the
year, and then divide by that
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number again.
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Multiply it by 100 and you
turn it into a percentage.
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Now you have your growth rate.
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So now you can see why,
when we say there's a
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positive growth rate, that
means that the population
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is now bigger than the
population in the past.
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But why do most countries currently have a
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positive growth rate?
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There are economic benefits,
because children can
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work to help support the family.
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Sometimes, the government
even provides incentives
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to families for each child,
like in Japan, where birth
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rates are very low.
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Religion also influences
population growth, because
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it often promotes large
families, which increase the
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number of people in their
faith and encourages
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stronger community.
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Some religions will even forbid the use of
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contraceptives by their
followers, pretty much
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ensuring large families.
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And there are cultural
influences that promote
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large families, too.
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Having children means
that a person is passing
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down their own family's traits and values.
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There's a kind of prestige
that goes along with
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having children.
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Okay, now let's dive into
the demographic transition
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model.
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There are five stages to the demographic
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transition model.
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In Stage 1, a country has
high birth rates, often due
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to limited birth control
and the economic benefit
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of having more people to work.
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They also have high
death rates, due to poor
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nutrition or high rates of disease.
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It is believed that most
countries were at Stage 1
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until the 18th Century,
when death rates in western
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Europe began to fall.
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You can see this type of
population modeled by a
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high stationary population
pyramid, with a high
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birth rate.
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This pyramid shows the
number of people alive in a
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population, depending on age and gender.
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As you can see, the Stage
1 stationary population has
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many births, creating a
large young population, as
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well as many deaths,
creating a small older
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population and keeping
the over all population
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fairly stable.
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The second stage is seen
in the beginnings of the
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developing country.
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The population begins to
rise as death rates drop,
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because of improvements
in health and sanitation
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and the availability of food.
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This trend can be seen
in western Europe in the
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19th Century, after the
Industrial Revolution.
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The birth rates are about
the same as they were in
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Stage 1, though, so the
over all population begins
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to grow.
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This is an early expanding
population pyramid.
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You have high birth rates still,
see, lots of young people,
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but the death rate is
declining, so you have more
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older people, making
this nice pyramid shape.
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In Stage 3, the death
rates continue to drop, but
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at the same time, birth
rates also begin to fall
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because of access to
contraception and a changing
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social trend toward smaller families.
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The society has better
health care and is becoming
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more industrialized by this
point, meaning there are
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fewer childhood deaths and
also the kids don't need
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to work, or aren't allowed
to work by law any more.
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Having lots of children
isn't economically beneficial
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any more, as the kids are
sent to school, rather than
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working to support the family.
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Many countries in South
America and the Middle East
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have such declining birth rates.
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This population is still
expanding, but at a slower
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rate.
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You can see in this late
expanding population pyramid,
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that, as birth rates decline,
there are fewer young
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people and, with the
already-declining death rates,
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people are living longer lives.
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The population finally
stabilizes in Stage 4 of
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the demographic transition
model, where both
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birth rates and death rates
are low and balance each
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other out.
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By this point, the population
is rather large, because
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it had been growing up until this point.
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The low birth rates are
due to a combination of
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improvements in contraception
as well as the high
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percentage of women in
the workforce and the fact
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that many couples choose
to focus on careers over
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having children.
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Countries like the United
States or Australia are in
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Stage 4 right now.
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The population can be
modeled by a low stationary
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pyramid, with low birth
rates and low death rates,
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as well as a longer life expectancy.
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The fifth and final stage
is only a speculation.
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There are few theories
as to what happens next.
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Some believe that the
world population will be
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forced to stabilize as
the Malthusian Theorem
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suggests.
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Perhaps we will run out of
resources, and there will
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be a global food shortage.
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Already, of the more than
seven billion people on our
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planet, there are about
one billion world-wide who
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suffer from hunger and malnutrition.
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The world population
continues to increase but,
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perhaps, we won't be able
to maintain the natural
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resources at the rate we
are going for how many
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people live on this planet,
which Malthusians believe
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will lead to a major
public health disaster and
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force the population to remain stable.
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Or, perhaps, the population
will begin to decrease
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after it stabilizes, continuing
the trend of decreasing
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birth rates until it drops
below the death rate.
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With more people dying
than being born, there
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would be a negative growth rate.
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This results in a constrictive
population pyramid,
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where there are fewer
young people than old.
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Perhaps this will be because
of a rise in individualism
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or, perhaps, as the
anti-Malthusian Theorem states,
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this will be because couples
only want to have one
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child or they have children later in life.
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Some evidence shows that
a better standard of
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living promotes smaller
families, as children become
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an economic burden,
rather than a source of
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financial support.
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Industrialized nations
often have better education
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and access to health care,
which contribute to more
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reproductive choices.
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Some governments, like in
China, are even adopting
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policies that encourage
small families to slow their
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population growth and save resources.
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Or, on the other hand,
perhaps the population will
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begin to grow again after
the stabilization of the
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fourth stage.
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Some evidence shows that
high standards of living
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actually promote fertility
and a higher birth rate.
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There's only one real way
for us to find out what
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will happen next and
we'll have to wait it out
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and see where the world
is in a century or two.
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So, I'll see you there, right?
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To sum it up, demographic
transition is a shift from
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high birth and death rates
to low birth and death
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rates as a country becomes
industrialized, but what
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will happen after that
is impossible to tell.
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Will the population stabilize?
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Will it decrease, will increase?
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Will we move off-planet
and colonize a world
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around a distant star?
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We could only guess for now.
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