The Science Behind Eye Color Variation

All humans initially had brown eyes. A genetic mutation affecting the OCA2 gene, which occurred near the Black Sea 6,000-10,000 years ago, resulted in the creation of the blue eye color.

Eye color is polygenic. Multiple genes influence the melanin levels in the iris, including HERC2 and OCA2. Variations in these genes determine the spectrum of eye colors from brown to green.

Melanin concentration in iris stroma adjusts the light absorption, affecting eye color. Lower melanin levels result in blue eyes, whereas higher concentrations create brown eyes. Green and hazel eyes have mid-range melanin levels.

Amber eyes are rarer than green, with a strong golden or coppery tint. Even rarer are violet eyes, sometimes found in albinism, and heterochromia, where two different colors appear in one's eyes.

Darker eyes offer more protection from the sun's UV rays, reducing the risk of cataracts. Lighter eyes may confer an advantage in lower-light environments by allowing more light into the eye.

Brown eyes are globally predominant. Blue eyes are primarily found in Europe, especially in Scandinavia. Green eyes are most common in Northern and Central Europe, but still quite rare worldwide.

As populations become more interconnected, the incidence of intermarriage increases, potentially leading to a wider variety of eye colors in future generations through new genetic combinations.

Blue-eyed parents can have brown-eyed children due to complex gene interactions, defying the simple Mendelian inheritance model.