Height data tends to be split by gender.

So, we'll look at women for now.

Okay, we're ready.

We'll chart heights by country.

Let's look at where my dad's family is from: South Korea.

The average woman born near the beginning of the 1900s like my great grandmother was just 142 centimeters or 4'7".

For comparison, the average American woman was 159 centimeters or 5'2".

If we chart every country...

we can see that people a century ago were pretty short for today's standards.

But over the next hundred years, humans grew.

Let's just look at those blue bars:

How much each country grew.

We need to adjust the vertical axis so we can see this chart better.

Ah, that's better.

Many of the countries that saw the most growth were European, North American countries.

For example, here's France and here's the US.

The countries that grew the least were in Africa.

And Asian countries were mostly in the middle.

But all the way on the right is an outlier.

A country where women grew nearly 8 inches in the last century.

South Korea.

And South Korean boys grew nearly 6 inches in that time period.

So why did humans grow so much in such a short amount of time?

And why did this happen in South Korea?

For most of the last 2000 years, human height didn't change much.

This chart shows the height of European men, but this stagnation pretty much was happening everywhere.

But in the last 200 years, we started to see some growth.

Here's some better data of 1800s.

You can see people in wealthier European countries starting to get taller.

We know a lot about why.

And it all starts with our genes.

One study from 2006 looked at thousands of siblings and analyzed how much of their DNA was shared, and compared that to how different their height was.

They found that about 80% of the difference in sibling height is genetic.

But that other 20% are external forces that affect our height.

Because even if our DNA says we can grow to a certain height during puberty, that growth is often interrupted.

There's a great study that tracks English and Welsh boys born in the 1890s.

Many of these boys eventually enlisted in WWI, which created a record of their adult height.

Researchers compared that to their childhood living conditions using the 1901 census.

They found that, if a person grew up in a white-collar household, which probably had better access to nutrition, they were on average about a half inch taller than everyone else.

If they grew up in a crowded home where they were more likely to spread disease or infection, they were nearly a third of an inch shorter.

And if they grew up in an industrial area, exposed to pollution and disease, they were nearly an inch shorter.

Even within the same country, the environment had a noticeable effect on people's height.

That's what changed drastically in the last 200 years.

Over the last century, we made massive advancements in nutrition, sanitation medicine and overall quality of life.

And humans got way taller.

But now let's put South Korea on this chart.

100 years ago, South Korea was poor and the people were shorter than the global average.

But by the 1960s, they had mostly caught up.

Then something drastic happened.

A military-led government focused on economic growth.

Eventually, the country shifted from producing things like textiles to consumer electronics and cars.

And South Korean wealth skyrocketed.

In the 60s, many South Koreans didn't have enough to eat.

The food supply was basically in line with other low-income countries.

But the food supply rapidly improved and soon it exceeded the world average.

And then it caught up to affluent countries in Europe.

As for childhood health, in the 1950s, more than 20% of South Korean kids died before age one.

Worse than most low income countries.

Then, South Korea's infant mortality plummeted.

And as a result of these improved conditions, especially for children, South Koreans kept growing and growing.

I want to show you one more chart.

This is the height of South Koreans and North Koreans in the 1930s.

Back then, they were one country so naturally they were about the same height.

The North is where my maternal grandparents and their siblings grew up.

Then in 1945 the North and South were split up.

In 1950, the Korean War began.

The war ended in a stalemate and North Korea shut its borders walling itself off from the rest of the world.

In the 1990s, millions of North Koreans starved to death.

We only have data on North Korean height today because of the thousands of people who escaped to the South during that period.

And in the generations since the division, the height gap between the two Koreas has continuously widened.

My grandparents were lucky.

Early in the war, they fled their home in North Korea, and escaped to the southern tip of South Korea.

And a few years later, my mother was born.

My mom is a bit taller than her mother, and my generation is taller than hers.

Height is inherited, written into our very genetic code.

But height is also something history gives to us.