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.