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How all blue-eyed people share one common ancestor

Between 6,000 and 10,000 years ago, the first blue-eyed member of the human race came to be.

This person was, in the truest sense of the word, a mutant; their gene sequence was altered in a way that changed the colour of their eyes from brown to blue.

This original individual obviously got to work producing offspring and succeeded in creating and proliferating what has become a highly coveted physical trait in today’s human population.

Now, evidence of the mutation that codes those pretty baby blues is most common around the Baltic sea, but it can be found in almost every human population on earth.

According to a study by the University of Copenhagen, the mutation affects the OCA2 gene in human chromosomes, creating a kind of “switch” to turn off the production of melanin, preventing the eyes from turning brown.

Melanin refers to the dark pigments that determine the colour of human skin and hair and, it seems, the colour of our eyes, in many organisms.

“Originally, we all had brown eyes,” said Professor Hans Eiberg from the Department of Cellular and Molecular Medicine, in conversation with Science Daily.

“But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a switch.”

This “switch” prevents the normal melanin production in the iris that was responsible for our ancestors’ brown eyes.

The more melanin in your iris, the darker it is. From dark brown to hazel to green eyes, the amount of melanin decreases, with the smallest amount found in blue eyes. When the OCA2 gene is turned off and melanin production is cut completely, it results in albinism.

According to Professor Eiberg, “all blue-eyed individuals are linked to the same ancestor”. The original blue-eyed mutation was passed on through genes to every blue-eyed human on Earth today.

“They have all inherited the same switch at exactly the same spot in their DNA,” he said.

So, while eye colour is genetic, it’s not the simple matter of recessive and dominant genes that you learnt with those punnet squares in high school biology.

Like hair colour, baldness and freckles, this mutation isn’t strongly positive or negative. However, melanin is believed to afford protection from harmful UV light, meaning light-skinned people are more susceptible to solar skin damage, and people with blue eyes should probably invest in some proper sunglasses.

A study even suggests blue-eyed people might be more susceptible to alcohol dependency, though I’m unconvinced that’s more than coincidental.

Whether or not the aesthetic benefits of blue eyes outweigh the sun sensitivity is yet to be determined, but I encourage further investigation.

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Comment (2)


    Friday 30 November 2018

    I am a pisspot – can I blame that on my sexy blue eyes?



      Sunday 20 January 2019