The Genetic Makeup of Hazel Eyes
Unlike the simplistic Punnett square genetics often taught in school, eye color inheritance is polygenic, meaning it is influenced by multiple genes interacting with each other. Hazel eyes result from a moderate concentration of melanin, the pigment responsible for coloring our skin, hair, and eyes. In hazel irises, this melanin is moderately present, somewhere between the low levels found in blue eyes and the high levels in brown eyes.
The unique and shifting appearance of hazel eyes is also caused by a phenomenon called Rayleigh scattering. This is the same optical effect that makes the sky appear blue. In hazel eyes, the stroma—the outermost layer of the iris—scatters light in a way that, combined with the moderate melanin levels, creates a multi-tonal effect of brown, green, and gold. The distribution of melanin is often uneven, with a moderate amount creating the brown tone near the pupil and less melanin allowing for more light scattering in the outer regions, which creates the greenish hue.
Global Distribution of Hazel Eyes
While no single ethnicity can claim ownership of hazel eyes, specific regional patterns of prevalence do exist, driven by historical population mixing and migration.
European and European-Derived Populations
Hazel eyes are relatively common among people of European descent. In the United States, for example, which has a large population of diverse European ancestry, approximately 18% of the population has hazel eyes, a significantly higher percentage than the global average. Countries in Western Europe like the United Kingdom and the Netherlands also show higher frequencies, likely due to the blend of genetic traits from northern (traditionally blue-eyed) and southern (traditionally brown-eyed) populations. A study of Spanish individuals also found a high percentage of hazel-toned eyes, reflecting the historic overlap of these populations.
Middle Eastern and North African Populations
Hazel eyes are also notably common in the Middle East and North Africa. Regions with a history of migration and intermarriage among Arab, Persian, and Mediterranean populations, such as Lebanon, Iran, Turkey, and Morocco, show a significant prevalence. This genetic mixing contributes to a wider range of eye color phenotypes, including hazel.
Latin American Populations
Thanks to extensive European ancestry admixture from Portugal, Spain, and Italy, hazel eyes are also observed in Latin American countries like Brazil and Argentina. These populations have diverse genetic backgrounds that contribute to the presence of hazel eyes.
Hazel Eyes vs. Other Eye Colors
| Feature | Hazel Eyes | Green Eyes | Brown Eyes |
|---|---|---|---|
| Melanin Level | Moderate and uneven distribution | Low to moderate | High concentration |
| Appearance | Multi-toned, typically a blend of brown, green, and gold; can appear to change color with light | More uniform green hue; fewer flecks | Solid brown; can range from light to dark |
| Rarity | Relatively uncommon (approx. 5–8% globally) | Very rare (approx. 2% globally) | Most common eye color (approx. 70–80% globally) |
| Genetic Complexity | Polygenic trait, complex inheritance with multiple genes | Polygenic trait, involves multiple genes | Predominantly determined by a few genes, historically viewed as dominant |
Health Considerations for Lighter Eyes
People with lighter eye colors, including hazel, have less protective melanin in their iris. This can increase their sensitivity to light, a condition known as photophobia. Additionally, research has suggested a potential link between lighter irises and a higher risk of certain sun-related eye and skin conditions, such as cataracts, macular degeneration, and even some forms of skin cancer. For these reasons, all individuals, especially those with lighter eyes, should take precautions like wearing UV-protective sunglasses when outdoors.
Conclusion: A Beautiful Expression of Diversity
Ultimately, what ethnicity has hazel eyes is not a simple question with a single answer. This captivating eye color is a product of complex genetic inheritance, reflecting the rich history of human migration and intermixing across continents. Rather than being a marker for a single group, hazel eyes are a testament to our global genetic diversity. They serve as a beautiful reminder of the fascinating and intricate story of human heritage, with roots spanning Europe, the Middle East, Latin America, and beyond.
For more in-depth information on eye color genetics, you can consult the National Library of Medicine.
