The color of a person’s eyes depends on the amount and type of pigment in the iris. Usually, the more melanin (pigment) in the iris, the darker the eye color. But it’s not quite that simple – eye color is determined by variations in many genes and the interactions between them. So while brown and amber may appear similar, there are some key differences.
The Genetics Behind Eye Color
Three main genes influence eye color:
- HERC2 – This gene activates expression of the OCA2 gene, which controls melanin production.
- OCA2 – Also called the “P” gene, this gene codes for an enzyme involved in melanin production in the iris.
- SLC24A5 – This gene codes for a protein that influences pigment deposition in the iris.
The specific variations (alleles) of these genes that a person inherits impact how much and what type of melanin is produced. The two main types of melanin are:
- Eumelanin – A brown/black pigment that produces darker eyes (brown and black).
- Pheomelanin – A red/yellow pigment that produces lighter eyes (green, amber, yellow).
Most eye colors are a combination of both types of melanin. More eumelanin produces brown or black eyes. More pheomelanin produces green or amber eyes. So the amount and type of melanin in the iris is the key difference between brown and amber eyes.
What Makes Brown Eyes Brown?
Brown eyes have a large amount of eumelanin in the iris, which gives them their darker brown color. The OCA2 gene plays a major role in producing brown eyes. The allele of the OCA2 genes most associated with brown eyes is HERC2-OCA2(brown).
Nearly 80% of the world’s population has brown eyes. They are the most common eye color worldwide. Within brown eyes, there is some variation in shade from light golden brown to very dark brown.
What Makes Amber Eyes Amber?
Amber eyes have a moderate amount of lipochrome (a yellow pheomelanin pigment) in the iris, giving them their distinctive golden/honey color. Unlike brown eyes, they have very little eumelanin pigment.
Amber eyes are quite rare globally, occurring in less than 1% of the population. They are however more common in certain parts of the world, like the Middle East and Asia. The SLC24A5 gene is thought to play a role in producing amber eyes.
Amber eyes can range from a bright honey gold color through to a light brown shade. The more yellow/golden the eyes appear, the less eumelanin pigment is present.
Key Differences Between Brown and Amber Eyes
While brown and amber eyes may sometimes appear similar, there are some key differences:
| Brown Eyes | Amber Eyes |
|---|---|
| Rich brown color | Golden yellow/honey color |
| High amounts of eumelanin | Low amounts of eumelanin |
| Low amounts of pheomelanin | High amounts of pheomelanin |
| Very common (most people) | Rare (less than 1% of people) |
| OCA2 gene major influence | SLC24A5 gene influence |
While shades can overlap, in general amber eyes have a distinct golden, yellowish hue from the pheomelanin pigment. Brown eyes lack this golden color and are a deeper, darker brown.
Amber Eyes with Central Heterochromia
Some people with amber eyes have central heterochromia, where their eyes are amber/light brown on the outside with an inner ring of brown, green or blue around the pupil. This is caused by differences in melanin content between the outer and inner iris.
Central heterochromia is more common in amber eyes than solid brown eyes, as amber irises tend to have less melanin overall. The melanin concentration is often lower in the central part of the iris, allowing the underlying pigment to show through.
Difference in Rarity
One of the biggest differences between brown and amber eyes is their frequency in the population:
- Brown eyes – Most common eye color worldwide, with 70-80% of people having brown eyes.
- Amber eyes – Quite rare globally, occurring in less than 1% of the population.
Brown is by far the most common eye shade, while amber is one of the rarest colors. Certain ethnic groups have higher rates of amber eyes, like Asians and Hispanics, but they are still very uncommon compared to brown.
Geographic Differences in Brown and Amber Eyes
Geographic and ethnic origins also influence whether brown or amber eyes are more common:
- Brown eyes are the most common eye color worldwide, particularly in parts of Africa, Asia and the Americas.
- Amber eyes occur at higher frequency in some Asian countries like Afghanistan and some parts of the Middle East.
So amber eyes are more likely to occur in certain ethnicities, like Middle Eastern and Central Asian groups, while brown eyes are ubiquitous across all population groups.
Can Brown Eyes Change to Amber?
No, the melanin content and genetics that determine eye color are set from infancy and remain constant throughout life. Brown eyes cannot turn into amber eyes later in life.
However, some brown-eyed people may appear to have hints of amber in their eyes. This can happen for a few reasons:
- Their eyes may naturally have both eumelanin and pheomelanin pigments present.
- Decreased melanin with age causes lighter eye color.
- Reflective effects from clothing and lighting conditions.
But while the shade of brown eyes can vary under different conditions, the underlying genetics remain unchanged. So amber hints in brown eyes are an optical effect, not an actual color change.
Can Contacts Change Brown Eyes to Amber?
Colored contact lenses that mimic amber eyes are available. But these cannot permanently change the natural color of brown eyes.
Contact lenses cover the iris with a uniform artificial color, masking the natural eye shade underneath. clears away the artificial color, returning eyes to their original brown hue.
However, colored contacts can temporarily transform brown eyes into amber eyes for aesthetic/cosmetic purposes. But it is important to have them properly fitted by an optometrist.
Causes of Amber Eyes Appearing Brown
In some cases, eyes that are genetically amber may appear more brownish. Reasons for this include:
- Increase of eumelanin pigment with age.
- Decreased lipochrome pigment density.
- Oxidation of lipochrome over time.
- Eye conditions like pigmentary glaucoma.
- Lighting conditions and reflections.
While these factors can cause amber eyes to seem brownish, the underlying genetic makeup remains amber. Proper examination by an optometrist can confirm the true color.
Conclusion
While amber and brown eyes may sometimes look similar, they arise from different combinations of melanin pigments in the iris. Brown eyes have high eumelanin, while amber eyes have high pheomelanin. This results in key differences in their genetics, prevalence, geographic distribution and stability over a person’s lifetime.
So in summary: brown and amber eyes are quite distinct genetically, despite occasional overlaps in shade. Understanding the precise melanin content is needed to differentiate between true amber eyes versus brown.
