Grey eyes are a rare and stunning eye color that some people are born with. Unlike blue eyes that have a lot of melanin or brown eyes that have a high concentration of melanin, grey eyes contain less melanin and have a darker grey-blue, grey-green, or light brown appearance. The amount of melanin present in the iris determines the eye color. So what causes grey eyes and where did this unique eye color originate from?
What Causes Grey Eyes?
Eye color is determined by genetics and is linked to two factors – the pigmentation of the eye’s iris which can be brown or blue, and the way light scatters around the iris fibers. Grey eyes are a result of having less melanin in the anterior border layer of the iris. This causes the light scattering effect to make grey eyes appear more blue/green.
The amount of melanin present in your body is determined by multiple genes. For brown or blue eyes, a single gene controls the production of melanin pigment. The OCA2 gene located on chromosome 15 determines how much brown melanin is produced, while the HERC2 gene activates expression of OCA2. Variations in these genes account for the difference between brown and blue eyes.
Grey eyes are thought to be influenced by genes controlling melanin as well as other genetic factors that aren’t fully understood yet. Researchers have proposed multiple genes on chromosomes 15 and 19 that control melanin production and contribute to grey eye color, but more studies are needed.
The Genetic Origins of Grey Eyes
When it comes to eye evolution, some scientists believe grey eyes may have developed from blue eyes. Originally, the human ancestor population that migrated to Europe from Africa had brown eyes. But a genetic mutation affecting the OCA2 gene reduced melanin production and resulted in blue eyes spreading through the European population.
Further reductions in melanin led to the light scattering effect that causes grey, green, and hazel eyes. The exact evolutionary timeline is debated, but grey eyes are likely related to blue eyes and arose in European populations.
Geographic data supports the idea of grey eyes originating in European ancestry. While grey eyes are globally rare, they occur at higher frequencies in northern and eastern European countries like Estonia, Denmark, Finland, Russia, and Lithuania. This points to grey eyes arising as part of genetic adaptations in European populations.
The Geographic Origins and Prevalence of Grey Eyes
Studies looking at eye color distribution show grey eyes appear at the highest frequency in northern European countries:
| Country | Grey Eyes Percentage |
|---|---|
| Estonia | 18.2% |
| Denmark | 14.5% |
| Finland | 11.4% |
| Russia | 3% |
| Iceland | 8.9% |
| Lithuania | 7.3% |
In comparison, grey eyes only occur in around 1-2% of the global population. The highest frequencies point to Eastern Baltic regions as the potential origin of this rare eye color before spreading through Northern Europe.
While grey eyes likely arose in European ancestry, they can occur in any ethnicity. The scattering of light that makes eyes appear grey or blue can happen in people of all backgrounds if they inherit alleles that reduce melanin production. But the highest occurrences trace back population movements in Northern Europe.
The Appearance of Grey Eyes
While grey eyes may look similar to blue at first glance, they have some distinct characteristics:
- More muted and darker in color compared to blue eyes
- Grey, silver, light brown tone rather than vivid blue
- Often contain yellow/brown central heterochromia around the pupil
- Reflect light less intensely than blue eyes due to more melanin
The color can shift between cool grey-blue to warm green-browns depending on lighting conditions. Unlike vivid blue eyes, the darker pigmentation in grey eyes absorbs more light which gives them a darker, muted tone.
How Melanin Levels Produce Grey Eyes
Melanin is a pigment that colors your hair, skin, and eyes. Eyes with high concentrations of melanin appear darker, while low levels make eyes look lighter.
Here’s an overview of melanin amounts in different eye colors:
| Eye Color | Melanin Level |
|---|---|
| Brown | High |
| Hazel | Moderate |
| Green | Low to moderate |
| Grey | Low |
| Blue | Very low |
Grey eyes have low levels of melanin, but slightly more than blue eyes. This small increase in melanin gives grey eyes a darker appearance compared to light blue eyes.
Eye Color Changes in Infants
Melanin levels also explain why many babies are born with blue or grey eyes that darken over time. Infants often have lower melanin levels at birth. For Caucasian babies, eye color can change dramatically in the first three years of life as melanin concentrations increase.
Initial eye colors at birth:
- Blue – 80% of Caucasian infants
- Grey – Most of the remaining 20%
- Brown – 15% of Caucasian babies
By age 3, only about 10% of Caucasian children retain blue or grey eyes due to increasing melanin levels that change eye color to green, hazel, or brown.
Conclusion
In summary, grey eyes are a rare and unique eye color caused by having low amounts of melanin in the iris. They likely originated as a variation of blue eyes in northern European ancestry where they occur at the highest frequencies.
While the exact genes behind grey eyes are still being researched, they arise from similar genetic factors that reduce melanin production in both blue and grey eyes. The slightly higher melanin levels are what give grey eyes their darker grey-blue, green, brown, or hazel appearance compared to light blue eyes.
Grey eyes stand out for their beautiful, muted coloration and remain one of the rarest and most attractive eye colors around the world.