You’ve probably heard that all people with blue eyes are related, but is there any truth to that statement?

Or if there is, why?

It turns out the genetic history of blue eyes is pretty twisty and interesting.

More than 1 in 4 Americans have blue eyes, and across the pond, it’s every 3 out of 7.

In some places, like the Netherlands and Iceland, it’s almost everyone – or at least, it can seem that way.

That said, blue isn’t often a naturally occurring color in nature, at least on animals. Some insects and fish manipulate physics in order to appear blue, but there is no mammal has naturally blue fur or hair.

And, I hate to break it to you, but optometrist Gary Heiting says there aren’t actually blue eyes, either.

“Blue eye color is determined by melanin, and melanin is actually brown by nature. Brown melanin is the only pigment that exists in the eye; there is no pigment for hazel or green or blue. Eyes only appear to be these colors because of the way light strikes the layers of the iris and reflects back toward the viewer.”

So when you’re comparing an eye color to the sky or the ocean, your observations are more accurate than you might think.

Author George Britton explains.

“In the animal kingdom there are many examples in which the observed color is the result of optical phenomena such as light scattering, interference or diffraction by microscopic structures present in the tissues. The most familiar example of this effect is the blue of the sky.”

The sky appears blue to us because as the sun’s (white) light is filtered and refracted by our atmosphere, only the smaller blue wavelength makes its way to our eyeballs.

“Very small particles, smaller in diameter than the wavelength of red or yellow light, will reflect or scatter more of the short-wave than the long-wave components of white light. Colors produced in this way are known as structural colors.”

There are two different kinds of scattering involved in the sky’s color and eye color – Rayleigh scattering and Tyndall scattering – but the basic principle is exactly the same.

Green and hazel eyes are a result of the the same scattering effect on eyes with slightly more melanin present in the iris. This is also why eye color can seem to shift in different lighting.

“It’s an interaction between the amount of melanin and the architecture of the iris itself. It’s a very complex architecture.”

So, pretty as those blue eyes are, they’re just a neat trick of the light.

No one knows who the common ancestor was who began passing down the trait of less and less melanin in the iris, which would appear as blue eyes, says professor Hans Eiberg.

“Originally, we all had brown eyes. But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a ‘switch’ which literally ‘turned off’ the ability to produce brown eyes.”

And yes, they’re absolutely sure that all blue-eyed people are descended from a single common ancestor.

“Blue-eyed people have all inherited the same switch at exactly the same spot in their DNA. From this we can conclude that all blue-eyed individuals are linked to the same ancestor.”

What researchers do find strange is that there doesn’t seem to be any evolutionary advantage that encouraged the mutation in the first place.

“It simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”

Next time you’re on a date, remember the person across from you is just a bunch of chromosomes in nature’s cocktail shaker.

No matter how pretty their eyes are.

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