Colored eyes, including shades of blue, green, hazel, and gray, evolved primarily due to genetic changes affecting the production and distribution of melanin, the pigment responsible for eye, skin, and hair color.
The Role of Melanin in Eye Color
Melanin is the key player in determining eye color.
- Brown Eyes: People with brown eyes have a high concentration of melanin in the iris. This pigment absorbs most light entering the eye, resulting in the appearance of brown.
- Lighter Eyes: Individuals with blue, green, gray, or hazel eyes have less melanin in the front layers of their iris. Instead of absorbing light, the structure of the iris scatters light, making these lighter colors visible.
The Evolutionary Change
Researchers believe the emergence of the wide spectrum of eye colors, beyond brown, was a direct result of a specific genetic mutation. As stated in the reference, scientists surmise that the addition of new colors, such as grays, blues, greens, and hazels, was caused by a change in the gene that produces melanin. This mutation likely altered the amount of melanin produced or how it was deposited in the iris, leading to the diverse range of non-brown eye colors we see today.
This single genetic alteration is thought to be the common ancestor for individuals with blue eyes, suggesting it was a relatively recent evolutionary event. Subsequent genetic variations likely led to the development of green, hazel, and gray eyes.
Key Takeaway
The evolution of colored eyes is fundamentally linked to genetic changes that influenced the amount of melanin pigment in the iris. Less melanin allows for light scattering, creating the appearance of lighter colors.
