Green eyes are one of the rarest eye colors in the world, yet they fascinate people and are often seen as mysterious or alluring. But what causes green eyes, and what makes them special biologically and genetically compared to other eye colors like brown and blue eyes? Here we’ll explore some interesting facts and insights about green eyes.
The genetics behind green eyes
Eye color is determined by the amount of melanin pigment in the iris of the eye. Brown eyes have a lot of melanin, blue eyes have very little, and green eyes fall somewhere in between. But it’s not quite as simple as the amount of melanin alone.
The main gene that controls eye color is OCA2 (also known as HERC2), which turns on a gene called P gene that produces melanin. The specific variations (alleles) of OCA2 determine whether you’ll have more melanin (brown eyes) or less melanin (blue eyes). Green eyes are a result of a different allele of OCA2.
So genetically speaking, green eyes have a distinct combination of melanin concentration and OCA2 alleles compared to other eye colors. The OCA2 allele that leads to green eyes seems to produce a small to medium amount of melanin in the iris, giving it that unique greenish hue.
The geographic distribution of green eyes
Only about 2% of the world’s population has green eyes. But they are much more prevalent in certain ethnic and geographic groups, concentrated mostly in and around Europe:
| Country/Region | Percentage of population with green eyes |
|---|---|
| Iceland | 89% |
| Ireland | 30% |
| Scotland | 30% |
| Wales | 27% |
| Sweden | 20% |
| Finland | 18% |
| Norway | 17% |
| Northern Germany | 15% |
Green eyes are rare in most other parts of the world, including Asia, Africa, and the Americas. This geographical pattern reflects the role genetics and ancestry play in determining eye color.
The evolutionary origins of green eyes
The predominance of green eyes in European populations points to it being a relatively new evolutionary trait that originated sometime after humans migrated out of Africa. One theory is that green eyes were a chance mutation that became concentrated in and spread throughout northern Europe.
One potential evolutionary advantage green eyes offered was helping people absorb more sunlight and vitamin D in cloudier northern climates. The medium melanin levels may have reduced glare and light scattering compared to blue eyes. This would have improved visual acuity and hunting ability, thus improving chances of survival and passing on green eye genes.
How the shade of green is determined
There are many possible shades of green eyes, from light mint green to deep emerald green. The exact shade is influenced by a couple factors:
- Amount of melanin – More melanin produces darker, olive green eyes.
- Amount of lipochrome – This yellow pigment combines with melanin to produce variation in green color.
- Size of melanin granules – Finer granules scatter light and produce lighter greens.
The combination and variation in these factors gives rise to the many different hues and patterns seen in green eyes.
Green eyes change over time
Green eyes, along with hazel eyes, are unique because they can appear to shift in color and lightness over time. A child may be born with light blue or gray eyes that darken into green eyes over the first couple years of life as melanin concentration increases. Then the eyes may get flecks of brown as a person ages due to increased melanin with age.
The changes are more apparent in green/hazel eyes compared to solid brown or blue eyes. Lighting conditions also cause more noticeable shifts in green eye color compared to other shades.
Sensitivity to sunlight
The moderate melanin levels in green eyes make them more sensitive to sunlight than darker eyes. The natural light blocking and glare reduction effects of melanin are reduced compared to brown eyes. Hence many people with green eyes are more easily blinded by bright sunlight.
Wearing sunglasses on sunny days can help avoid eye pain and damage. Green-eyed people may also be at higher risk for melanoma of the eye due to sun damage. But on the plus side, they often need less winter sun exposure to get adequate vitamin D levels compared to darker-eyed individuals.
Higher prevalence of visual issues
Green-eyed people are at greater risk for certain eye/vision conditions compared to the general population:
- Myopia – Green-eyed people have a 58% higher risk of needing glasses for nearsightedness.
- LASIK complications – Higher photosensitivity may increase side effects.
- Color blindness – 8% of green-eyed people have some level of color vision deficiency.
- Ptosis – Drooping upper eyelid affects over 5% of green-eyed individuals.
The moderate melanin levels are thought to contribute to these higher risks. But regular eye exams and proper vision correction can effectively manage most of these conditions.
Green eyes and personality
There are several alleged personality traits associated with people who have green eyes in astrology, literature, and popular culture. However, there is no scientific proof that eye color genetically determines personality or character.
Some stereotypical traits green-eyed individuals are associated with include:
- Curiosity and intelligence
- Passion and emotional depth
- Creativity and artistic flair
- Jealousy and envy
- Spontaneity and impulsiveness
But many psychologists believe these are not innate characteristics and more influenced by social perceptions and self-fulfilling prophecies. The only proven personality correlation is that people with lighter eyes tend to be more agreeable and trusting compared to those with darker eyes.
Conclusion
Green eye color is the result of moderate amounts of melanin combined with specific OCA2 gene variations mostly found in European populations. The rarity, visual appeal, and shifting hues of green eyes have endowed them with an air of mystery throughout history. But medically and genetically speaking, they do come with higher risks for certain eye issues.
While green eyes are undoubtedly special and unique, personality associations are unproven. The only real drawback of green eyes is increased sunlight sensitivity requiring more eye protection. But the distinctive appearance and lucky genetics of green make them a truly rare treasure.
