It is a common belief that all babies are born with grey or blue eyes. This is a misconception. While many infants may indeed have blue or grey eyes at birth, it is not true for all. Many babies, especially those of darker heritage, are born with brown eyes. For those born with lighter eyes, the initial color may change significantly during their first year of life.
The Science Behind Baby Eye Color
The color of a baby’s eyes is determined by melanin, a pigment produced by specialized cells called melanocytes in the iris. At birth, melanocytes have not been fully activated by light exposure, resulting in minimal melanin production, which often leads to eyes appearing blue or grey as these colors are essentially the result of light scattering within the iris. The amount of melanin in the front layers of the iris determines the visible eye color. Blue eyes contain very little melanin, allowing more blue light to reflect; green or hazel eyes have moderate levels, while brown eyes contain a high amount of melanin.
How Eye Color Changes Over Time
After birth, as a baby is exposed to light, the melanocytes in their irises become more active and produce more melanin, which can cause eye color to darken or change. The most significant changes typically occur within the first six to twelve months of life, though subtle shifts can continue up to three years of age. Common transitions include blue eyes changing to green, hazel, or brown as melanin accumulates; conversely, if a baby is born with dark eyes, they are less likely to lighten. The developmental timeline and the extent of eye color change vary among individuals, influenced by genetic factors that determine the potential for melanin production.
What Determines a Child’s Permanent Eye Color
A child’s final, permanent eye color is primarily determined by genetics. Multiple genes inherited from both parents influence the amount and type of melanin produced in the iris. While early theories suggested eye color was controlled by a single gene, it is now understood to be a complex polygenic trait involving many genes. Two major genes, OCA2 and HERC2, located on chromosome 15, play significant roles in determining eye color by affecting melanin production and distribution, leading to different levels of melanin and a spectrum of eye colors. Although the inheritance pattern is complex, parental eye colors provide clues, as traits like brown eyes are generally more common and often dominant.