Dark brown eyes, while intensely pigmented, are not rare when viewed on a global scale. They are exceptionally common, being the world’s most widespread eye color. This rich, dark hue represents the upper end of the spectrum for the color that dominates the iris of the vast majority of the human population.
Global Prevalence of Brown Eyes
Brown eyes are the most common eye color worldwide. Approximately 70% to 79% of the global population possesses brown eyes, a figure that highlights their statistical dominance.
This high prevalence is concentrated in specific geographic regions. Brown eyes are nearly universal across entire continents, including Africa, Asia, and South America. For instance, in East Asia, Southeast Asia, and sub-Saharan Africa, almost all inhabitants have brown eyes, often appearing in the darker shades. The sheer number of people in these highly populated regions contributes significantly to the overwhelming global percentage of brown eyes.
How Melanin Determines Eye Color
Eye color is determined by the amount of a pigment called melanin present in the iris’s front layer, or stroma. Melanin functions to absorb light, and the more of it an individual has, the darker their eyes appear.
Dark brown eyes result from a very high concentration of this melanin, effectively absorbing most incoming light. This high pigmentation is a protective trait, offering greater natural defense against intense sunlight and ultraviolet (UV) radiation. The genetic mechanisms governing eye color involve multiple genes that regulate the production and storage of melanin.
Genes like OCA2 and HERC2 play a primary role in controlling the melanin levels in the iris. The presence of high melanin concentrations, which leads to dark brown eyes, is genetically dominant compared to the lower concentrations that result in lighter colors. This biological mechanism explains why brown became the foundational and most widespread eye color for humanity over time.
Defining Rarity: The Least Common Eye Colors
Eye colors with significantly less pigmentation are statistically the least frequent globally.
The rarest eye colors include:
- Green eyes, accounting for only about 2% of the world’s population.
- Hazel eyes, present in approximately 5% of the global population.
- Amber eyes, also present in approximately 5% of the global population.
- Gray eyes, present in an estimated 3% or less of people worldwide.
These lighter colors are geographically concentrated, mostly found among people of European descent, contrasting sharply with the near-global distribution of dark brown eyes.