Thursday, February 07, 2008

Scientist: All Blue-Eyed People Are Related

.. from My commentary follows.

If you've got blue eyes, shake the hand of the nearest person who shares your azure irises: He or she may be a distant cousin.

Danish researchers have concluded that all blue-eyed people share a common ancestor, presumably someone who lived 6,000 to 10,000 years ago.

"Originally, we all had brown eyes," Professor Hans Eiberg of the University of Copenhagen said in a press release. "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."

That "switch" — a simple change from "A," or adenine, to "G," or guanine, in the DNA — actually sits next to the OCA2 gene, which regulates the pigmentation of our eyes, hair and skin, and hence has only a limiting effect on it.

If the mutation had completely deactivated OCA2, all blue-eyed people would be albinos.

Eiberg and his team analyzed 155 individuals in a large Danish family, plus several blue-eyed people born in Turkey and Jordan.

All blue-eyed subjects had the mutation, and there was very little variation on the genes neighboring it on the chromosome, indicating that the mutation first arose relatively recently.

In contrast, most mammals share the "normal" form of the gene. The six-letter sequence is exactly the same among mice, horses, cows, rats, dogs, cats, monkeys, chimpanzees and humans with brown eyes. (No word on what gives Siberian huskies and Siamese cats blue eyes.)

Eiberg figures the mutation took place on the northern of the Black Sea, but that's an educated guess, assuming the first blue-eyed humans were among the proto-Indo-Europeans who subsequently spread agriculture into western Europe and later rode horses into Iran and India.

Ironically, neither the first person to have the mutation, nor his or her children, would have had blue eyes themselves.

Blue eyes are a recessive trait, and the gene must be inherited from both parents. (Green eyes involve a related but different gene, one that is recessive to brown but dominant to blue.)

It wasn't until the original mutant's grandchildren or great-grandchildren hooked up — cousin marriage is the norm through most of human history — that the first blue-eyed person appeared. He or she must have looked pretty odd for the Neolithic era.

Eiberg stresses that the genetic variation, as the press release puts it, is "neither a positive nor a negative mutation."

That's a bit disingenuous, as the mutation also produces greater instance of blond hair (sexually selected for even today) and fair skin, which confers a survival advantage by stimulating greater production of vitamin D in sun-starved northern European countries — exactly where blue eyes are still most prevalent.

• Click here for the full journal article.


If the author stressed that the blue eyed mutation is "neither a positive nor a negative mutation," then why did the journalist then contradict the scientist?

Grr. If I had been the editor I would have corrected the author. The mutation does NOT produce blonde hair and pale skin. Correlation is not causation. It just so happens that those traits co-occur.

What else is interesting about blue eyes is that they arouse suspicion in some parts of the world — Turkey and Jordan included. Cultures across the Mid East and North Africa believe blue eyes are the source of the evil eye. They have the power to dry up a mother's milk. When I was in Tunisia I saw one blue-eyed person the entire time. He was so remarkably different that I actually blurted out loud to him "Vous avez les yeux bleu!" He responded "Yes! Yes! Blue eyes" and pointed out mine. It was cool, and memorable.

I could imagine that blue eyes are indeed a sexually selected trait like some evolutionary scientists think blonde hair is. Perhaps there is some truth to the "What is exotic is erotic" idea. Who knows.

But, I definitely want to read the original article!


Jessica Doyle said...

Hi - just met you on Etsy.

I have blue/green eyes. Even less common. My mom has green, dad blue and my brother blue.

I have a ring of yellow... this is true around my pupil giving the appearance of blue green.

Nice article. :)

ky*ko said...

i also found you through the etsy forum - this is a very interesting article! in reponse to the previous comment i too have blue/green eyes with a ring of yellow - maybe we are related ;)

Field Notes said...

The thing I find a little ironic about all this genetic relatedness stuff is that all forms of life on this planet are related — to some degree. Humans are 99.9999% alike when it comes to shared DNA. With chimps and other apes, we share 95% of our genetic code. BUT we also share something like 50% with worms and 30% with bananas! So, ky*ko, we are definitely relatives :D

glasfaden said...

Interesting. I don't have blue eyes, but I love looking at them :)

KieutiePie said...

Whoa!!! I'm one of those ancient brown eyed types. =}

Ophelia Miller Boutique said...

Very interesting article. I'm one of the ancients too!

XUE said...

I don't have blue eyes either...but my husband has. And we hv one kid with brown eyes & the other with black (like mine). Nice to know that you like Tokyo. Japan is quite a spectacular country to live in. Very exotic!