You may have already noticed that brown eyes are by far the most common color around you, and on a global scale. This color, far from being ordinary, actually tells a fascinating story about our genetics and evolution. The fact that nearly 70 to 80% of humans have brown eyes is neither a coincidence nor simply a matter of aesthetics.
It all starts with melanin
The color of your eyes depends primarily on a natural pigment: melanin. More precisely, it is the amount and distribution of this melanin in the iris that determines the shade. Brown eyes contain a high concentration of melanin. This high density absorbs more light, giving the iris its dark and deep appearance.
Conversely, blue, green, or gray eyes contain less melanin. There is no blue or green pigment in the eye: these colors appear thanks to a phenomenon of light scattering, much like the one that makes the sky blue.
Melanin is not just for aesthetics. It plays a vital protective role. It helps shield eye tissues from ultraviolet radiation. In very sunny environments, this protection represents a significant biological advantage.
Early humans had brown eyes
Researchers believe that the first humans all had brown eyes. This color corresponds to the earliest genetic state of our species. Variations toward lighter eyes are thought to have appeared much later in evolution. According to genetic studies, notably those published in the scientific journal Human Genetics , the mutation responsible for blue eyes appeared approximately 6,000 to 10,000 years ago. It is believed to be linked to a variation in the OCA2 gene and in a regulatory region of the HERC2 gene, two genes involved in melanin production.
Before this mutation, high melanin production was the norm. In regions heavily exposed to the sun—in Africa, the Middle East, or South Asia—this characteristic was an adaptive advantage. Darker pigmentation protected not only the skin but also the eyes. Brown eyes are therefore not "more common" by chance: they reflect our ancestral heritage.
A logical geographical distribution
Even today, brown eyes are the most common in Africa, Asia, Latin America, and Southern Europe. Light-colored eyes are more concentrated in Northern and Eastern Europe. This distribution is explained by the history of human migrations and the spread of certain genetic mutations within specific populations.
In regions with less sun exposure, a low concentration of melanin did not pose a major disadvantage. The mutations responsible for light-colored eyes were therefore able to be passed on and spread. It is essential to remember that there is no biological hierarchy among eye colors. These are simply natural variations resulting from adaptation and genetic mixing.
Genetics is far more complex than we imagine.
It was long taught that eye color depended on a simple mechanism: brown dominant, blue recessive. In reality, the situation is much more nuanced. Several genes are involved in determining iris color. The OCA2 and HERC2 genes play a central role, but other regions of the genome also influence the shades. This is why two brown-eyed parents can have a light-eyed child, and vice versa. Eye color results from a complex interaction between several hereditary factors.
In short, if approximately 80% of humans have brown eyes, it's the combined result of our ancestral genetic heritage, the protective role of melanin, and major human migrations. The color of your eyes, whether dark, light, or somewhere in between, reflects the richness of humanity. Your eyes are more than just a color: they carry within them thousands of years of history.
