Van Morrison may have sung about his ‘brown-eyed girl’ but Elton John soulfully let us know that his ‘baby’s got blue eyes’. This lyrical dichotomy could never have occurred if blue eyes had not, at some point, blue eyes evolved. In fact according to a study from the University of Copenhagen we know exactly what genetic change allowed old blue eyes to make an appearance.
In the study researchers examined mitochondrial DNA and compared the eye colour of blue-eyed individuals from countries as diverse as Jordan, Denmark, and Turkey. The findings fit in the lineage of work on this topic that dates back to 1996 when the OCA2 gene was first identified as being responsible for blue eye colour.
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The results of this study showed that a genetic mutation in the OCA2 gene in the human chromosome resulted in the creation of a switch that turned off the ability to produce brown eyes. Specifically the OCA2 gene codes for the P protein that is involved in the production of melanin, the pigment that gives colour to our hair, skin, and eyes. The biological switch is located next to the OCA2 gene and does not turn it off completely but reduces its capacity to produce melanin in the iris thereby diluting brown eyes into blue. So the switches effect is very precise because if it turned off the OCA2 gene altogether, you would have a condition known as albinism.
Essentially this means that all people with blue or green eyes come from the same ancestor as they have inherited the switch at exactly the same spot in their DNA. We know that this genetic mutation first occurred sometime between 7,000 and 10,000 years ago probably from around the Black Sea and spreading from there across Europe. It is not clear why blue eyes spread among ancient Europeans although one theory is that the gene could have helped to prevent eye disorders due to low light levels found in European winters, while another theory is that the trait spread because it was deemed sexually attractive.
It is all a reminder that our evolution is still in progress and that a fundamental thing like blue eyes only came about 10,000 years ago. No doubt it was the OCA2 gene that Crystal Gale was singing about in the 1970s when she warbled, ‘don’t it make my brown eyes blue’.
