It’s common knowledge that babies are often born with blue eyes, regardless of their ethnicity. But why is this? The answer has to do with melanin, the pigment that gives color to our hair, skin and eyes.
Melanin and eye color
Melanin comes in two forms – eumelanin which gives brown/black color, and pheomelanin which gives red/yellow color. The amount and type of melanin in our body is determined by our genes. More eumelanin leads to brown/black eyes, while more pheomelanin leads to blue/green eyes.
Melanin is produced by special cells called melanocytes. After melanin is produced by melanocytes, it gets packaged into tiny sacs called melanosomes. These melanosomes are then sent to different parts of the body, including the iris of the eyes, where they deposit melanin and give color.
Melanin production in infants
Melanocytes are present in the iris right from birth. However, in Caucasian infants, they don’t start producing large quantities of melanin until 3-6 months after birth. Very little melanin in the iris leads to the blue eye color that most Caucasian babies are born with.
On the other hand, the melanocytes of African and Asian infants start pumping out melanin right from birth. This leads to brown/black eye color in these babies.
So in summary, Caucasian babies have blue eyes mainly because their melanocytes don’t produce much melanin in the first few months. Once melanin production kicks in, their eye color starts to change.
When does eye color become permanent?
As melanin production increases in Caucasian infants, their eye color transitions from blue to hazel or green. By age 1, only 10% of Caucasian infants still retain blue eye color.
Eye color is usually stable by age 3. At this point, the concentrations of melanin in the iris determine the final eye color of the child. The melanocytes adjust the production of melanin based on complex genetic instructions inherited from the parents.
Common age for eye color changes
- 0-6 months: Mostly blue
- 6-12 months: Blue changing to green/hazel
- 12-18 months: Green/hazel/brown
- 18-24 months: Mostly final color
While most changes happen by 24 months, subtle shifts can occur till age 3. After age 3, very little change in eye color is seen barring any trauma or medical condition affecting melanin production.
What determines the final eye color?
As mentioned before, the final eye color is determined by the amounts and types of melanin present in the iris. Here are some key factors that control melanin production and eye color:
Genetics
Our genes encode instructions for producing melanin. The major genes involved are:
- HERC2 – Determines total melanin content
- OCA2 – Controls balance between eumelanin and pheomelanin
- SLC24A4 – Influences melanosomes and calcium levels
The specific genetic variants inherited for these genes significantly influence total melanin content and type, and hence eye color.
Ethnicity
Certain genetic mutations for eye color arose in specific ethnic populations. For instance, a mutation in HERC2 that reduced melanin production became very common in Europeans. This is why lighter eye colors like blue and green are far more common in Caucasians compared to other ethnicities.
Exposure to sunlight
Increased sun exposure ramps up melanin production. Babies who live in tropical regions generally have higher melanin and darker eyes compared to babies in temperate regions with less sun.
Medical conditions
Certain medical problems like ocular albinism, which affect melanin production, can alter normal developmental patterns of eye color in infants.
Can eye color change later in life?
For most people, eye color remains stable through adulthood. However, in some cases, eye color can change slightly.
Here are some reasons for eye color change in adults:
Oxidative stress
Oxidative stress in the eye can degrade melanin pigment over time. This can cause a slight lightening of eye color in older adults.
Diseases
Certain medical conditions like pigmentary glaucoma can lead to increased melanin deposition and browner eyes.
Medications
Some medications like rifabutin (antibiotic) and chloroquine (antimalarial) can bind to melanin in the eye and cause lightening of eye color.
Injuries
Physical trauma to the eye can damage the iris and alter melanin content, leading to change in eye color.
However, such changes later in life are typically subtle and not as pronounced as the changes seen in infancy and early childhood.
Summary
Here is a quick summary answering why babies are born with blue eyes:
- Melanocytes in the iris produce melanin pigment
- Caucasian infants don’t produce much melanin initially
- Lack of melanin makes the iris appear blue
- Melanin production ramps up within first year of life
- Final eye color gets fixed around age 3 years
- Genetics and ethnicity determine how much melanin is produced
So in conclusion, transient low melanin levels in Caucasian infants leads to the common occurrence of blue eyes at birth, which then undergo changes as melanin production kicks in during development.
Frequently Asked Questions
Why are some babies born with brown eyes?
In African, Asian and Hispanic populations, melanin production starts right from birth leading to brown/black eyes. The melanocytes inherit a genetic program to produce high levels of melanin from birth.
Can blue eyes turn green later?
Yes, as melanin production increases in infancy, blue eyes can transition to green, hazel or brown. The specific color depends on the genetically determined levels of melanin synthesized.
Is eye color determined by genetics?
Yes, genetics plays a major role in determining eye color. The genes HERC2, OCA2 and SLC24A4 have a significant influence on the total melanin content and type of melanin produced, and hence final eye color.
Does eye color indicate ancestry?
To some extent yes. Certain genetic mutations for eye color originated in specific populations. For instance, blue/green eyes are far more common in Europeans. However, intermixing of populations has led to more overlapping of eye colors across ancestries.
Conclusion
The common occurrence of blue eyes in Caucasian infants is due to low melanin levels in the first months after birth. As melanin production ramps up, eye color progresses to its final stable state by age 3. Genetics plays an important role in determining how much and which type of melanin is made, and hence the final eye color of the individual.