Blue eyes result from a mutation in a gene that codes for the body's production of melanin. The mutation inhibits the production of melanin in the iris of the eye, preventing it from becoming brown. The earliest known person with blue eyes was a hunter-gatherer who lived in Spain 7,000 years ago. No one knows how blue eyes became so widespread, but one theory is that people simply found them attractive.
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Key Facts In This Video
Approximately 8% of the world's population has blue eyes. 00:19
In people with blue eyes, the stroma of the iris is full of nearly colorless cells that scatter blue wavelengths of light. 01:47
Blue eyes come from a recessive allele, which is why they are relatively rare. 02:42