The belief that all babies are born with blue eyes is inaccurate. While many newborns, particularly those of European descent, initially have blue or slate-gray eyes, this is not universal. The initial color is often temporary and changes as the child develops. This change is a natural biological process driven by pigment production and depends on the child’s genetic blueprint.
The Direct Answer: Eye Color at Birth
The color of a newborn’s eyes is determined by the amount of melanin present in the iris. At birth, the specialized cells that produce this pigment, called melanocytes, have not yet fully begun their work. Due to this initial lack of pigment, most babies of Caucasian ancestry are born with eyes that appear blue or a pale gray.
In contrast, babies of African, Hispanic, or Asian descent are commonly born with eyes that are already brown or black. These infants have melanocytes that are more active from birth, resulting in a higher concentration of melanin immediately. In these cases, the eye color is usually close to its final, darker adult shade and is less likely to undergo a significant change.
The Science Behind Eye Color Change
The temporary blue or gray color seen in many newborns is a structural effect, not a true pigment color. Blue eyes do not contain blue pigment; the iris only produces shades of brown melanin. The blue appearance is caused by Rayleigh scattering, the same principle that makes the sky appear blue.
When there is little melanin in the iris’s stroma (front layer), light entering the eye is scattered. The shorter, blue wavelengths scatter back out, making the eye appear blue or gray. As the infant is exposed to light, the melanocytes activate and begin producing melanin.
This accumulation of brown pigment absorbs light instead of scattering it, causing the eye color to darken from blue to green, hazel, or brown. The amount of melanin produced determines the final eye color. A small amount of accumulated melanin will result in blue or green eyes, while a large amount leads to brown eyes. This process of pigment accumulation is a one-way path, meaning that eyes can darken over time but will not naturally become lighter.
The Genetic Factors That Determine Final Color
The ultimate eye color a child develops is determined by a complex interplay of multiple genes inherited from both parents, a trait known as polygenic inheritance. Scientists have identified as many as 16 different genes that contribute to eye color, though two specific genes, OCA2 and HERC2, play the most significant roles. Both of these genes are located on chromosome 15.
The OCA2 gene regulates the amount of melanin within the iris. The nearby HERC2 gene controls the expression of OCA2, acting like an on/off switch. A specific variation within the HERC2 gene can reduce OCA2 expression, which leads to less melanin and ultimately results in blue eyes.
The old model of simple dominant (brown) and recessive (blue) genes is an oversimplification that does not account for the spectrum of colors like hazel or green. Because multiple genes are involved, two parents with brown eyes can still have a child with blue eyes if both carry the genetic variants for lighter eyes. Conversely, two blue-eyed parents have a very high probability of having a blue-eyed child, but the possibility of another color, while small, is not impossible due to the complexity of the genetic interaction.
When Eye Color Becomes Permanent
The transition from newborn color to the permanent adult color is a gradual process that unfolds over the first few years of life. The most significant changes typically occur between six and nine months of age, marking the most active phase of melanin production within the iris.
For most children, the eye color becomes relatively stable and close to its final shade by their first birthday. Subtle shifts in hue can continue until a child is about three years old. Once the melanocytes reach their genetically determined level of pigment production, the eye color is considered fixed for life.