in just four decades.

7.6 billion of us now live on the planet.

And it's likely there will be a billion more by 2030.

But population growth varies from continent to continent.

The fastest population rises are in Africa

and Asia which will have eight of the 10

most populous countries by 2050.

India is set to overtake China as

the country with the largest population.

Nigeria has one of the fastest growing

populations in the world.

It's set to become the world's third most populous country.

In many African countries, women have

on average five children each.

In Niger, it's seven.

That's well above the global average

of 2.4 children per woman.

Populations are also rising because they're aging.

Fewer people are dying than are being born.

In the last century, life expectancy has

almost double in some countries.

In India, it's almost tripled.

However, in some parts of the world,

populations are decreasing.

Japan's population of 127 million is forecast

to shrink by about one third in the next 50 years.

But the top 10 countries with the fastest

shrinking populations are all in Eastern Europe.

These countries suffer from the combined effect

of low birth rate, a relatively high mortality rate,

and massive out migration.

As populations shift, the world as we know it will change.

Today's dominant developed economies will be increasingly

focused on supporting the elderly.

Whereas less developed countries will

be transformed by population booms.

In 2100, it's projected that one third

of all people will live in Africa.

A bigger population is a burden with more

people to house, educate, and feed.

But it's also an opportunity.

A large working age population can boost the economy as long

as there are enough jobs and a strong infrastructure.