A common belief suggests that all babies are born with blue eyes, but this is a misconception. While many infants, particularly those of Caucasian descent, may have blue or gray eyes at birth, this is not universal. A baby’s eye color is not permanently established at birth and can undergo significant changes during early development. This initial appearance is often a temporary stage in eye color development, involving biological and genetic factors.
Melanin and Eye Color
The primary determinant of eye color is melanin, a pigment also responsible for skin and hair color. Specialized cells called melanocytes produce and store melanin within the iris, the colored part of the eye. The amount and specific types of melanin present in the iris influence the visible hue.
Different types of melanin exist: eumelanin (providing brown and black tones) and pheomelanin (contributing to red and yellow hues). Eyes with high concentrations of eumelanin appear brown, while lower amounts can result in green, hazel, or blue eyes. Blue eyes, surprisingly, do not contain blue pigment. Instead, their color results from a phenomenon called Rayleigh scattering. This occurs when light enters the iris and scatters off the collagen fibers within its structure, causing shorter blue wavelengths to reflect back, similar to how the sky appears blue.
Why Eye Color Changes
Many babies are born with minimal melanin in their irises, a result of developing in the darkness of the womb. This low pigment level often leads to their eyes appearing blue or gray due to light scattering. After birth, as infants are exposed to light, their melanocytes begin producing and depositing more melanin into the iris, causing eye color to gradually darken or shift over time. For instance, eyes that were initially blue may transition to green, hazel, or brown as more pigment develops. While significant changes typically occur between 6 and 12 months, eye color can continue to subtly evolve up to three years old, and sometimes into adulthood.
The Genetics of Eye Color
While melanin dictates the visible eye color, the potential for its production and distribution is determined by an individual’s genetic inheritance. Eye color is a polygenic trait, influenced by multiple genes rather than a single dominant or recessive gene. This multi-gene involvement explains the wide spectrum of eye colors observed in the human population. Genes such as OCA2 and HERC2, located on chromosome 15, play roles in regulating melanin production and distribution within the iris. The combined effect of these genes dictates the amount and type of melanin that melanocytes produce. This genetic blueprint means that even parents with the same eye color can have children with different eye colors, particularly if they carry recessive gene combinations. For example, two brown-eyed parents can have a blue-eyed child if both carry the necessary recessive genes.