It is a common belief that all babies are born with blue eyes, but this is not consistently accurate. While many infants may present with lighter eye shades at birth, studies indicate that a significant number are born with brown eyes. The development of eye color is a more intricate process than it might initially appear, involving several biological factors.
Why Newborns Often Have Blue-Tinted Eyes
Many newborns appear to have blue or bluish-gray eyes primarily because of the limited amount of melanin present in their irises at birth. Melanin is the pigment responsible for coloring eyes, skin, and hair. Specialized cells called melanocytes, which produce melanin, are not fully active in newborns.
The blue appearance is not due to blue pigment within the eye. Instead, it results from a phenomenon known as the Tyndall effect. Light entering the iris is scattered by collagen fibers within its translucent layers. Shorter blue wavelengths scatter more readily, causing the eyes to reflect blue light, similar to how the sky appears blue. This initial blue or gray hue is often temporary, reflecting the developing state of the infant’s eyes, not their permanent color.
How Eye Color Develops Over Time
After birth, the melanocytes in a baby’s iris continue to mature and increase their production and storage of melanin. This ongoing melanin production causes a baby’s eye color to change over the first few months and years of life. As more melanin accumulates, eyes tend to darken.
The most noticeable shifts in eye color typically occur within the first 6 to 12 months, though the process can continue more subtly for up to two or three years. Eyes that are born brown generally remain brown and may even darken further, while lighter eyes are more prone to changing to darker shades like green, hazel, or brown as melanin levels increase.
The Genetic Blueprint of Eye Color
A baby’s eventual eye color is primarily determined by their genetic inheritance, making it a complex trait influenced by multiple genes. Eye color is not controlled by a single gene but rather by the interaction of several genes, such as OCA2 and HERC2, which play significant roles in melanin production.
While parental eye colors offer clues, the polygenic nature of eye color makes predicting a child’s exact eye color challenging, as various gene combinations can lead to unexpected outcomes. The amount and type of melanin produced, influenced by these genetic factors, determine the wide spectrum of human eye colors, ranging from blue and green to hazel and brown.