Every blue-eyed person on the planet is descended from a single European who lived around 6,000 to 10,000 years ago, and who first developed a specific mutation that accounts for the now widespread iris coloration.
Originally, all humans had brown eyes, although genetic variation relating to a gene called OCA2 resulted in changes to the amount of pigment produced by different individuals, resulting in the emergence of different shades of brown. Armed with this information, scientists had for many years searched for the source of blue eyes on the OCA2 gene, but without success.
More recently, a mutation to a separate, nearby gene called HERC2 has been identified as the cause of blue eyes. This alteration switches off OCA2, the gene that determines the amount of the brown pigment melanin that we make. It is thought to have first occurred when humans began to migrate from Africa to Europe, meaning that every person with blue eyes is a descendent of a single early European.
The fact that every blue-eyed person alive today has this same mutation is pretty compelling evidence for this theory, although the identity of the initial mutant remains something of a mystery. To date, the earliest set of sapphire-colored peepers ever found belong to a 7,000-year-old skeleton that was discovered in northern Spain. Naturally, the eyes had long since decayed, however genetic analysis revealed that they would have appeared blue in color.
- A Distinctive Haplotype Window
Geneticists have pinpointed a stretch of DNA roughly 100 kilobases around the HERC2/OCA2 region that is virtually identical in all blue-eyed individuals. The remarkable uniformity of this “haplotype” indicates a strong founder effect—in other words, virtually everyone with blue eyes today carries the same ancestral chromosome segment inherited from that one early carrier. - Geographic Frequency Gradients
- Highest prevalence (over 80 %) occurs around the Baltic Sea (Estonia, Finland, Sweden).
- Frequencies taper off through Western Europe (France, UK) to around 20–30 %, and are very rare (<1 %) in East Asia, Sub-Saharan Africa, and indigenous populations of the Americas.
- In parts of the Middle East and South Asia, low levels (~5 %) of the blue-eye haplotype likely reflect ancient north–south migrations.
- Timeframe Refined by Ancient DNA
- Beyond the 7,000-year-old Spanish skeleton, blue-eye–associated HERC2 variants have been detected in human remains from Sweden (circa 5,000 BCE) and Luxembourg (around 4,500 BCE), corroborating a rapid spread through early Neolithic farming communities.
- Neutral Mutation with Possible Drift
- Unlike skin-pigment genes under strong selection, the blue-eye mutation appears to have been selectively neutral—no clear survival advantage—so its prevalence today is attributed largely to genetic drift and population bottlenecks among early European farmers.
- Recessive Inheritance Pattern
- Blue eyes follow a classic recessive trait: an individual needs two copies of the HERC2 “switch-off” variant to express the phenotype. Carriers with only one copy still produce enough melanin to have brown or hazel eyes, which helped conceal the allele as it quietly spread.
- No Link to Other HERC2 Functions
- Though HERC2 is involved in cellular transport processes, no detrimental health effects have been linked to its blue-eye–associated mutation—underscoring its likely neutrality.
- Blue Eyes in Other Species—Convergent Evolution
- Dogs, horses, and certain primates also exhibit blue irises, but in each case it’s due to entirely different genetic changes. This highlights how the appearance of blue eyes in humans is a unique evolutionary event, not a recurrence of an ancient mammalian trait.