Demographic transition | Society and Culture | MCAT | Khan Academy

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

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