creepy old creatures who just hung onto the ring for too long, only about 8% of the world's

human population has blue eyes. Here in the U.S. it's about twice that, but that's still

a lot less than it was at the turn of the twentieth century when nearly half of all

Americans had the trait. So what happened? Are blue-eyed humans going the way of the

dodo?

Well, no. We cleared up that rumor about redheads going extinct; the same goes for blue eyes.

While the trait is becoming more rare, it's unlikely it will disappear all together. Which

is crazy when you consider that 10,000 years ago blue eyes didn't even exist. In fact,

there's a good chance that blue-eyed people may all share one common ancestor. Studies

over the past decade have actually traced the trait to a mutation that most likely arose

among brown-eyed people in a single human in the Black Sea region of southeastern Europe

between 6,000 and 10,000 years ago.

The mutation affected what's known as the OCA2 gene, which helps our bodies produce

melanin, the brownish pigment that gives color to our hair and eyes and skin. The mutation

created kind of a dimmer switch for the pigmentation, but it didn't affect the entire gene. Instead,

it only affected the production of melanin in the iris, the ring structure around the

eye that regulates how much light gets in.

The bulk of the iris is a thick layer of melanin-producing cells called the stroma. And the OCA2 mutation

turns the production of melanin in the stroma way down, but the pigmentation still shows

up elsewhere, like in the hair and skin and other parts of the iris. Basically, the mutation

keeps the stroma from being brown.

So why blue then? Well, strictly speaking, blue eyes aren't actually blue. Instead, in

people with this mutation, the stroma is full of nearly colorless cells. And when the light

strikes them, they scatter the wavelengths back out, in a process similar to what makes

smoke or fog look blue when light passes through them.

If there is some yellowish pigment in the stroma, then the blue light will combine with

that to make green. Throw in a little bit of brown, and you have hazel.

So how did we go from having no blue-eyed people, to hundreds of millions of them in

less than 10 millennia? No one's entirely sure why the trait spread so quickly through

Europe. Some scientists think the mutation could have helped prevent certain eye disorders

related to long, dark northern winters.

But another factors appears to be that, for whatever reason, lots of blue-eyed people

simply mated with other blue-eyed people in the past, which kept the trait in circulation.

Because for each of your genes, you have two different versions, called alleles, one from

your father and one from your mother. If you have at least one dominant allele for a gene,

that's the trait you have.

The blue eyes come from a recessive allele, which means if you inherit one allele for

blue eyes and another for brown, you're going to have brown eyes. But you still carry the

recessive blue allele, which can be passed on. Which means that that first person that

had that blue-eyed mutation didn't have blue eyes. They had to pass that onto their children,

and their children had to pass it onto their children, until eventually they came back

together to make someone with two blue-eyed alleles.

When both parents have blue eyes, they both have two recessive blue-eyed genes, which

means their children will also have blue eyes since there's no dominant gene to mask the

recessive one. This is how you end up with Scandinavian countries that are 95% blue-eyed,

and it also explains why the percentage of blue eye-ers is dropping in much of the western

world.

Human populations are a lot more evenly spread throughout the world than they were 10,000

years ago, so more blue eyes are pairing up with brown eyes and producing brown-eyed offspring.

I wouldn't go so far as to call them endangered, but safe to say those blue-eyed singers and

spies and Gollums will always be in the minority.

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