That's as many humans as in the next 20 most populous countries combined, or in the whole

other 170 countries in the world.

Over the last 300 years, India and China each added more than a billion people to their

populations, way more than any other country, but they have actually been growing at about

the same rate as the rest of the world.

They have a lot more people today because they had a lot more people a few hundred years

ago, when the world began its period of modern, and rapid, population growth.

It's like comparing a big bank account and a small one.

If they both grow at about the same rate over many years, the big one gains a lot more money,

simply because it started with more.

So the billion-dollar, er, billion-person question, is why did India and China have

so many people when they started their rapid growth?

We can’t know for sure, since so many variables factor into long-term population dynamics,

but the two most plausible explanations are food and area.

Having lots of fertile land and good access to fresh water makes it possible to grow lots

of food, which in turn makes it possible to nourish a lot of people.

Even today, the 10 most populated countries in the world all have a relatively large amount

of farmland.

And Asia - and in particular south and east Asia - has tons of farmland, lots of river

valleys, and the ability to grow food year-round.

Plus, domestication of plants and animals essentially started in Asia, giving populations

an early leg - or wing - up.

As such, Asia’s been the most densely populated region of the world for a really long time.

Area matters too; countries like Pakistan and Bangladesh may be filled with farms and

densely-populated, but because they’re smaller in area than India and China, they simply

cannot contain as many people.

Of course, a few other things happened in India and China in the last few thousand years,

and some of them helped the populations grow, and some of them shrank the populations, but

through it all, the large and fertile lands of India and China were able to sustain lots

of people, such that when the era of modern population growth came around, they had a

head start.

Or rather, a hundred-million-head start.

This video was sponsored by the University of Minnesota, where students, faculty and

staff across all fields of study are working to solve the Grand Challenges facing society.

The Minnesota Population Center is helping demographic researchers explore past and current

trends in world population, the Global Landscapes Initiative is working to figure out how to

keep feeding the world's growing population without harming the planet, and the IPUMS

Terra project integrates global population data with data on the environment to better

understand how humans transform ecosystems, and how ecosystems transform humans.

Thanks, University of Minnesota!