Eye color showcases a wide spectrum of hues across individuals. While some eye colors are common globally, others, like green, stand out due to their comparative rarity. Eye color often sparks curiosity about its origins and distribution.
The Global Rarity of Green Eyes
Green eyes are one of the rarest eye colors worldwide, found in only about 2% of the global population. This makes them less common than brown eyes, which account for 70-80% of people globally, or blue eyes, 8-10% of the world’s population. Even hazel eyes are more prevalent, appearing in around 5% of individuals worldwide.
The Genetics and Pigmentation of Green Eyes
Green eyes result from genetics, pigmentation, and light scattering. The color is not due to a green pigment within the iris, as human eyes do not contain blue or green pigments. Instead, eye color is determined by the amount and type of melanin present in the iris, specifically eumelanin and pheomelanin. Green eyes have low concentrations of eumelanin (a dark brown pigment) combined with a presence of pheomelanin (a yellowish pigment).
This pigment composition interacts with light through Rayleigh scattering. Similar to how the sky appears blue, shorter wavelengths of light are scattered by the turbid medium in the iris stroma. This scattered blue light, when combined with the yellowish hue from the pheomelanin and a light brown underlying pigmentation, creates the perception of green. The inheritance of eye color is polygenic, meaning multiple genes influence the final hue, with genes like OCA2 and HERC2 playing roles in melanin production and distribution.
Geographic Concentration of Green Eyes
Green eyes are not evenly distributed across the globe, showing a higher concentration in geographic regions, particularly within Europe. They are most common in Northern, Western, and Central Europe. Countries like Ireland and Scotland have the highest percentages of green-eyed individuals. Other European countries, including Iceland and the Netherlands, also have prevalences of green eyes.
For instance, in Iceland, 8-10% of men and 18-21% of women have green eyes. This geographical pattern suggests a link to ancestral populations and historical migrations, contributing to the higher frequency of the genes responsible for green eyes in these areas. While less common, green eyes can also be found in other populations globally, sometimes attributed to historical intermarriage or specific genetic pockets.