blue eyes are relatively new.

Originally, everyone was believed to have had brown eyes.

It wasn't until about 10,000 years ago

that blue eyed people started popping up everywhere.

It was probably creepy as (beep).

Today it's estimated that somewhere between

20 and 40% of Europeans have blue eyes.

So what the heck happened?

Where'd all these blue eyed people come from?

Short answer, genetic mutation.

(scary music)

Here's a quick breakdown:

Eye color is determined by the amount of pigment

you have in your irises.

If you have a lot of pigment, you have brown eyes.

Less pigment, green or hazel.

And when there's little or no pigment,

you get blue eyes.

So what causes your body to produce

little or no pigments?

Genetics.

There are up to 16 genes involved

in determining eye color,

but the two main genes are HERC2 and OCA2.

Wow, those sound fun, and cool.

The HERC2 works as a switch to activate your OCA2 gene,

and the OCA2 gene activates proteins that produce pigments.

If either of those genes are mutated,

it stops the chain and pigments wont be produced.

I know what you're thinking,

how do you explain when two normal brown eyed parents

have a blue eyed kid?

See that's where it gets a little more complicated.

Everyone has two of each gene in their body.

One from their mama bear, and one from their pop.

So if you're daddy has one mutated OCA2 gene

and one working one,

but neither of your mom''s OCA2 genes are mutated,

then you'd still have brown eyes

because you'd inherit the working OCA2 from your mom.

But what if both parents have a mutated OCA2?

Then there's a 25% chance that you would come out

with those lurid baby blues.

A hidden mutated OCA2 gene could theoretically

be passed down through a family tree for generations

without anyone knowing.

Making mama and papa bear wonder whether

they brought home the right cub from the hospital.

A study at the University of Copenhagen

looked at the DNA of blue eyed individuals

and found that 99.9% of them

had a mutation in their OCA2 gene

that rendered it useless.

This led scientists to believe that all blue eyed people

may have come from one single common

mutant European ancestor.

So next time you lock eyes with another blue eyed babe,

be nice, because odds are, you're distant relatives.

Go up and hug them.

They wont be scared.