The Science of Eye Color

Human eyes display a spectrum of colors, ranging from the darkest browns to the lightest blues. Melanin concentration in the iris's stroma and epithelium primarily determines these colors.

Eye color is polygenic, meaning it's determined by multiple genes. Previously, it was oversimplified as a single-gene trait, with brown being dominant over blue. The truth is much more complex.

All blue-eyed individuals share a common ancestor from around 6,000 to 10,000 years ago. This single ancestor experienced a genetic mutation affecting OCA2, a gene involved in melanin production.

Green is the rarest eye color, found in only about 2% of the world's population. It's a result of low melanin levels and a yellowish stroma, which together create the green hue.

Amber eyes are often confused with brown, but they have a solid golden or coppery tint without flecks and veins. They are an uncommon genetic variant with a similar melanin concentration to brown eyes.

Heterochromia refers to a difference in coloration of the iris. This can be complete, with each eye a different color, or sectoral, with multiple colors in one iris. It's usually genetic but can also be acquired.

Albinism affects melanin production, leading to a lack of pigment in the skin, hair, and eyes. Eyes may appear red or violet due to the visible blood vessels in the absence of sufficient melanin.