Every person with blue eyes shares a single common ancestor who lived between 6,000 and 10,000 years ago.

A landmark study published in 2008 by researchers at the University of Copenhagen identified the specific genetic mutation responsible for blue eyes. Led by Professor Hans Eiberg from the Department of Cellular and Molecular Medicine, the team analyzed the DNA of blue-eyed individuals from diverse regions including Denmark, Jordan, and Turkey. They discovered that 99.5 percent of blue-eyed people share the exact same mutation in the OCA2 gene.The OCA2 gene codes for the P protein, which is involved in the production of melanin, the pigment that gives color to our hair, skin, and eyes. The mutation does not fully 'turn off' the gene but rather limits its action to the iris, effectively diluting brown eyes to blue. If the OCA2 gene were completely destroyed or turned off, a person would have albinism rather than blue eyes.This genetic shift occurred approximately 6,000 to 10,000 years ago during the Neolithic expansion into Europe. Before this time, every human on Earth is believed to have possessed brown eyes. The consistency of the genetic 'switch' across different populations suggests that every blue-eyed individual inherited this specific trait from a single ancestor who lived near the Black Sea region.This discovery is significant because it allows scientists to trace human migration patterns and understand how specific traits spread through the gene pool. While blue eyes are a recessive trait, the mutation's survival suggests it may have offered some evolutionary advantage or was favored through sexual selection. Today, this single ancestral link connects roughly 8 percent to 10 percent of the global population.