Not all babies are born with gray eyes, despite a common belief. Eye color is a complex trait primarily determined by genetics and the amount of melanin in the iris, the colored part of the eye. This color can also change significantly over time as a baby develops and is exposed to light.
The Science Behind Eye Color
Eye color originates from melanin, a pigment also responsible for skin and hair color. The amount and type of melanin within the iris dictate its hue. Two primary forms of melanin influence eye color: eumelanin, which produces brown tones, and pheomelanin, contributing to amber, green, and hazel shades. Brown eyes, for example, contain a large amount of eumelanin, making them the most prevalent eye color globally.
The genetics of eye color are more intricate than once thought, involving multiple genes rather than a single dominant or recessive one. Genes like OCA2 and HERC2 play significant roles in melanin production and distribution within the iris. The interaction of these genes means that while parents’ eye colors offer clues, they do not guarantee a child’s eventual eye color. Light also interacts with the melanin and the iris’s structure. For example, blue eyes have very little melanin; their color results from light scattering in the iris’s front layers, a phenomenon similar to how the sky appears blue.
Why Many Newborn Eyes Appear Light
Many newborns are born with eyes that appear blue or gray due to an initial lack of melanin in their irises. During development in the womb, the eyes are not exposed to light, which minimizes melanin production by specialized cells called melanocytes. This low melanin content, coupled with the way light scatters within the iris’s stroma, often results in lighter shades.
For many babies, this light eye color is not permanent. Newborns with darker skin tones are often born with brown eyes, which are rich in melanin from birth and less likely to change. The appearance of light eyes in Caucasian babies is common because their melanocytes have not yet begun to produce much pigment.
The Evolution of Eye Color
A baby’s eye color often begins to change within the first few months after birth, with most noticeable shifts occurring between three and nine months of age. This transformation happens as the melanocytes in the iris, stimulated by light exposure, start producing and depositing more melanin. The gradual increase in melanin causes the eyes to darken, potentially changing from blue or gray to green, hazel, or brown.
While significant changes occur within the first year, subtle shifts can continue for several years. The final eye color is primarily determined by the genetic blueprint inherited from parents, which dictates the maximum amount of melanin the eyes will eventually produce. Light exposure plays a role in stimulating this melanin production, guiding the eyes towards their genetically predetermined shade.