Sunday, February 03, 2008

Where Did You Get Those Blue Eyes?

"It is not known why blue eyes spread among the population of northern Europe and southern Russia. Explanations include the suggestions that the blue eye colour either offered some advantage in the long hours of daylight in the summer, or short hours of daylight in winter, or that the trait was deemed attractive and therefore advantageous in terms of sexual selection."


How one ancestor helped turn our brown eyes blue

By Steve Connor, Science Editor Independent
Thursday, 31 January 2008

Everyone with blue eyes alive today – from Angelina Jolie to Wayne Rooney – can trace their ancestry back to one person who probably lived about 10,000 years ago in the Black Sea region, a study has found.

Scientists studying the genetics of eye colour have discovered that more than 99.5 per cent of blue-eyed people who volunteered to have their DNA analysed have the same tiny mutation in the gene that determines the colour of the iris.

This indicates that the mutation originated in just one person who became the ancestor of all subsequent people in the world with blue eyes, according to a study by Professor Hans Eiberg and colleagues at the University of Copenhagen.

The scientists are not sure when the mutation occurred but other evidence suggested it probably arose about 10,000 years ago when there was a rapid expansion of the human population in Europe as a result of the spread of agriculture from the Middle East.

"The mutations responsible for blue eye colour most likely originate from the north-west part of the Black Sea region, where the great agricultural migration of the northern part of Europe took place in the Neolithic periods about 6,000 to 10,000 years ago," the researchers report in the journal Human Genetics.

Professor Eiberg said that brown is the "default" colour for human eyes which results from a build-up of the dark skin pigment, melanin. However, in northern Europe a mutation arose in a gene known as OCA2 that disrupted melanin production in the iris and caused the eye colour to become blue.

"Originally, we all had brown eyes," said Professor Eiberg. "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."

Variations in the colour of people's eyes can be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes, he said.

"From this we can conclude that all blue-eyed individuals are linked to the same ancestor. They have all inherited the same switch at exactly the same spot in their DNA," said Professor Eiberg.

Men and women with blue eyes have almost exactly the same genetic sequence in the part of the DNA responsible for eye colour. However, brown-eyed people, by contrast, have a considerable amount of individual variation in that area of DNA.

Professor Eiberg said he has analysed the DNA of about 800 people with blue eyes, ranging from fair-skinned, blond-haired Scandinavians to dark-skinned, blue-eyed people living in Turkey and Jordan.

"All of them, apart from possibly one exception, had exactly the same DNA sequence in the region of the OCA2 gene. This to me indicates very strongly that there must have been a single, common ancestor of all these people," he said.

It is not known why blue eyes spread among the population of northern Europe and southern Russia. Explanations include the suggestions that the blue eye colour either offered some advantage in the long hours of daylight in the summer, or short hours of daylight in winter, or that the trait was deemed attractive and therefore advantageous in terms of sexual selection.


23 comments:

  1. And to think Crystal Gayle didn't want her brown eyes turned blue!

    I discard the sexual selection idea.('when you're pokin' the fire you're not lookin' at the mantle'--ed abby) Thinking as I do that the somewhat differing metabolism found in people with a propensity to alcoholism might have had a survival value in the cold north in the very very early days, I go with the survival advantage idea.

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  2. Meaning that blue eyes had some unknown survival advantage in that environment, like my hypothetical advantage of a differing metabolism might have had. Ah , you understand what I mean.

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  3. Was ist das
    "Sexual Selection?"

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  4. Das is ven you b particler bout eyes but we ain't.

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  5. Ven you bin drikin' de laager and you pokin' the fire you not playin' peepers,

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  6. Hey Trish,
    Just occurred to me how elitist it is of you to dismiss the effect of illegals on our students, public schools being what they are, always catering to the lowest common denominator w/their dumbed-down "bilingual" classes, and ever lower results.

    Meanwhile, you've had access to govt schools and homeschooling.

    Think about it: We're ahead only of Mexico and Turkey out of 44 countries!

    We're be on a path to Turd World Status after an Machillobama Administration.
    No Big Deal, tho, I guess.

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  7. I got thinking about this a little more. A blue eyed person has the double recessive Gene, which means the are "bb". The original eyes were all brown so they were "BB". All the children of the first blue eyed person would have to be "Bb" as there would have been the genes of the blue eyed parent and the brown eyed parent, and you get one gene from each.

    The only way to have blue eyes is to be a "bb" since one "B" is dominate and therefore dominates making the eye brown. A "Bb" and another "Bb" both have brown eyes, but if they have sex and produce a child, the child has the possibility of being either a "BB" "bB" "Bb" or a "bb". Therefore a one in four chance of being "bb" or having blue eyes. You had to have sex with a sibling or cousin to get it rolling.

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  8. Getting Kinky, are we, Father Mendel?

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  9. Very Interesting:
    REUTERSC-SPANZOGBY POLL: Obama slight lead in CA; tied NJ, MO; 20-point lead GA...

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  10. Always looked at 1 inch (not counting tail) geckos as helpless midgets that ended up squished somewhere arond the house.

    One just passed by on the desk feeding on the f...... pissants that are everywhere.

    ...his little 3/8 inch tongue is hard at work.
    Meanwhile Punxsutawney Phil's work is done for another year.

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  11. Maybe the lad had the tongue rolling trait?

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  12. In fairness the question of tongue-rolling isn't entirely resolved

    Solid as a Martin or Matlock study may seem today, tomorrow could bring contradictory findings equally convincing. This is how science staggers drunkenly toward the truth.
    The happy news is that although tongue-rolling researchers have failed to exonerate your biology teacher, they have produced some very high-grade, if useless, trivia: In Spain 67 percent of females can roll their tongues, compared to just 64 percent of men. But Spanish men are twice as likely to wiggle their ears (20 percent) as are women. And an Iranian researcher discovered a dearth of tongue-rollers in Northern England, which, he concludes mysteriously, "may be due to mixture with Scandinavians." And hand-clasping -- concerning which thumb ends up on top -- seems related to handedness.

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  13. I know my tone blind green-grey-blue-red eyes can instantly see things that others miss hidden in the camouflage. Whether it will prove advantageous in natural selection is yet to be seen.

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  14. Zeitgeist

    http://quicksilverscreen.com/watch?video=25678


    It's in 3 parts. Part 2 is garbage, but parts 1 and 3 are worth watching.

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  15. It's an underhanded way of calling us all inbred:) but are you right about this? I'm unclear about this. Where'd the first two Bb's come from? If a Bb arose in Fjord A and another Bb arose in Fjord B then some fine summer somebody crossed over the mountain you'd be on your way. I never did do well with those peas. I have a distinct feeling I'm not thinking clearly about all this. And how does a recessive trait end up taking over the population?

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  16. I've seen my brother go from looking Israeli to Australian to Indian to Brazilian to Italian to Cuban to Costa Rican to Canadian.

    So yeah, If you only look like an American you probably are an inbreed. :)

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  17. bobal said...
    It's an underhanded way of calling us all inbred:) but are you right about this? I'm unclear about this. Where'd the first two Bb's come from? If a Bb arose in Fjord A and another Bb arose in Fjord B then some fine summer somebody crossed over the mountain you'd be on your way. I never did do well with those peas. I have a distinct feeling I'm not thinking clearly about all this. And how does a recessive trait end up taking over the population?

    The simplest way is for the first two people being born be a girl and a boy. They would both be Bb. If they mated they have a 25% chance of having a bb, and so it goes.

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  18. "Becky"

    Wake up Becky I think I got something to say to you
    Its late september and I really should be back at school
    I know I keep you amused but I feel Im being used
    Oh Becky I couldnt have tried any more
    You lured me away from home just to save you from being alone
    You stole my heart and thats what really hurt

    The morning sun when its in your face really shows your age
    But that dont worry me none in my eyes youre everything
    I laughed at all of your jokes my love you didnt need to coax
    Oh, Becky I couldnt have tried any more
    You lured me away from home, just to save you from being alone
    You stole my soul and thats a pain I can do without...

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  19. The Wife reminded me of that, and also the "Asparagus Pee" genetic marker.
    Shall we poll the Bar?

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