The World Atlas ranks blue eyes as the second most common eye color worldwide, with an estimated eight to 10% of the population. But in the US, the proportion is higher at about 27%.
Scientists say that despite this, it is still relatively uncommon, and even more impressive is that all people who have blue eyes today have a single ancestor that spontaneously developed a mutation in a gene for this eye color. Since then, the mutation spread from that ancestor to the rest of the people across the globe for 6,000 to 10,000 years.
Blue-Eyed People Share One Ancestor That Developed the Mutation 6,000 to 10,000 Years Ago
Genetic Mutation From A Single Source Created Blue Eyes
Professor Hans Eiberg from the University of Copenhagen's (UoC) Department of Cellular and Molecular Medicine said that people have brown eyes initially before a genetic mutation that affected the OCA2 gene in the chromosome resulted in a "switch" that turned off the melanin production of the eyes.
According to ZME Science, Professor Eiberg and his team examined the genetic material from 100 families with blue eyes. They analyzed the DNA and mitochondrial DNA of participants to determine the mutation that is most likely responsible for the blue eye color and found that it affects an allele called the OCA2 gene.
The allele encodes the synthesis of the P-protein involved in the production of melanin in the body. The pigment gives color to the skin, hair, and irises in the eyes.
The mutation in people with blue eyes does not entirely switch off the production of melanin. Once it is switched off, it creates different hues of brown and blue eye colors. However, if the OCA2 gene is completely inhibited in the person, the team said that the lack of pigmentation results in a cognition known as albinism.
In terms of evolutionary advantage, Science Daily reported that the mutation that resulted in blue eyes presented no evolutionary advantage or disadvantage and did not affect the survival rate of a person with blue eyes. It is similar to the mutations that affect hair color, baldness, and freckles that do no good or harm to one's survival.
But it shows that nature is constantly shuffling the human genome to create a genetic cocktail of the human chromosomes and try out different changes.
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Health Problems Visible in Eye Color
According to Healthline, there are some medical conditions that are known to affect a person's eye color. One of them is albinism, which develops when the eyes do not produce melanin because a mutation has completely switched it off. Some people with mild albinism have light blue or violet eyes, but those who suffer from the severe form have pink or red because of blood vessels in the eye show.
Meanwhile, other conditions that can be seen by the change of eye color usually affect the whites or cornea of the eye. These include the following:
- Anisocoria - a condition when one of the pupils is larger than the other.
- Arcus senilis- happens when cholesterol builds up and forms a hazy white or blue ring in the eye.
- Hepatitis or Liver Disease- Since livers are damaged, they cannot remove bilirubin and build up in the blood, turning the white part to yellow.
- Hyphema- This happens when the blood is inside the eye due to an injury or surgery.
- Uveitis- An inflammation inside the eye caused by an infection, injury, or exposure to toxins.
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