Hazel eyes appear to shift in color from brown to green. This eye color results from a combination of Rayleigh scattering and a moderate amount of melanin in the iris. The amount of melanin determines whether a person’s eyes are blue, green, hazel, amber, or brown. Hazel eyes have a fascinating history and genetics behind them.
Hazel eyes are considered to be a light brown eye color. They are characterized by appearing to shift in shade from light brown to light green. While hazel eyes may contain flecks of green, amber, gold, or red, they are genetically categorized as a brown eye color. The appearance of green comes from Rayleigh scattering of light in the stroma.
From a genetic perspective, hazel eyes are considered a shade of brown. Eye color is determined by the amount of melanin in the iris. Melanin is a pigment that absorbs light and produces brown coloring.
People with hazel eyes have a moderate amount of melanin in their irises. This results in an eye color that is not completely brown, but also not light enough to be green or blue. The brown melanin pigment is responsible for the shifting brown aspect in hazel eyes.
The main gene that codes for brown eyes is the OCA2 gene. The HERC2 gene regulates OCA2, determining how much melanin is produced. Most people with hazel eyes have a variant of the HERC2 gene that leads to reduced melanin production compared to fully brown eyes. However, they still carry the genetic coding for brown eyes.
Green Rayleigh Scattering
While hazel eyes are genetically brown, the green color comes from a physics process called Rayleigh scattering. This is the same process that makes the sky appear blue during the day.
Rayleigh scattering occurs when shorter wavelengths of light are diffused by particles that are smaller than the light’s wavelength. The stroma of the iris contains collagen fibers and other components that can diffuse blue light.
When brown irises contain less melanin pigment, the scattered blue light can pass through and mix with the brown melanin color. The combination is perceived as shades of light brown and green – the hallmarks of hazel eyes.
Melanin Amount Determines Color
The shift between brown and green hues in hazel eyes depends on the amount and distribution of melanin. Here are some of the possible eye colors from low to high melanin content:
– Blue – Very low melanin allows Rayleigh scattering to dominate.
– Green – Low melanin allows more light scattering with some brown.
– Hazel – Moderate melanin produces shifting brown-green color.
– Amber – Slightly more melanin than hazel eyes.
– Brown – High melanin content blocks most light scattering.
While hazel eyes appear multicolored, the brown melanin means they are categorized with other shades of brown genetically. The melanin amount can vary in distribution which gives rise to the many colors seen.
Distribution of Melanin
In addition to amount, the distribution of melanin also impacts eye color.
– Uniform melanin = solid brown eye color
– Low/moderate melanin with uneven distribution = hazel eyes
– Areas with less melanin = green Rayleigh scattering
– Areas with more melanin = golden-brown regions
This pattern and ratio of melanin distribution is what produces the trademark hazel eye appearance. The ratio of lighter and darker regions of the iris give rise to the multicolored hazel look.
While hazel eyes appear to shift between shades of brown and green, they are classified as brown eyes genetically. The brown color comes from melanin, while the green results from Rayleigh scattering of light. Hazel eyes have moderate melanin compared to other eye colors. The specific distribution of melanin also contributes to the hazel pattern and hue. So in summary, hazel eyes are considered a unique form of light brown eyes.
|Eye Color||Melanin Content|
|Amber||Slightly more than hazel|
Prevalence of Hazel Eyes
Hazel eyes are relatively uncommon globally, with an estimated prevalence of 5-10% worldwide. They are most common among Caucasian populations of European descent, especially in countries around the Baltic Sea. An estimated 10-20% of people in countries such as Lithuania, Estonia, and Latvia have hazel eyes.
Across Europe, hazel eyes are found at an average frequency of 5-10%. Populations along the Mediterranean sea generally have lower rates at 1-5%. Hazel eyes are particularly rare among Asian, African, and Native American peoples.
Famous People with Hazel Eyes
While rare overall, hazel eyes are seen among many noteworthy public figures throughout history. Some famous people with hazel eyes include:
– Leonardo da Vinci – Italian Renaissance polymath
– Marie Curie – Polish-French physicist and chemist
– Kristen Stewart – American actress
– Marilyn Monroe – American actress and model
– Elvis Presley – American singer
– Bob Dylan – American singer-songwriter
– Paul Newman – American actor
– Madonna – American singer-songwriter
– Prince Harry – British royal
Hazel Eyes in Art and Culture
The multicolored and shifting appearance of hazel eyes has captured the imagination of artists and poets for centuries. Some examples include:
– Ancient Greek poets used the term “kalos” to praise the beauty of hazel eyes.
– In Persian literature, hazel eyes were compared to almonds or amber using metaphors.
– Shakespeare referenced hazel eyes in works like Romeo and Juliet, comparing them to “morning dew” and “blessing”.
– Impressionist painters used brush techniques trying to recreate the dual brown-green hues.
– Fauvism and abstract art movements embraced the chromatic nature of hazel irises.
– Hazel eyes are found in many memorable film characters, like the replicants in Blade Runner.
Causes of Hazel Eyes
The genetic and environmental factors that contribute to hazel eye color include:
– Parents with Mixed Eye Colors – Having one parent with brown eyes and one with green/blue eyes makes hazel more likely.
– Moderate Melanin Production – The HERC2 gene regulates melanin amounts at intermediate levels.
– European Ancestry – Hazel eyes are most prevalent in European populations.
– Rayleigh Scattering Properties – The stroma in lighter irises permits blue light scattering.
– Random Melanin Distribution – The patchy melanin patterns create the hazel effect.
– Lack of Dark Iris Pigments – Low levels of eumelanin pigment result in light brown hues.
– Not Linked to Latitude or Climate – Hazel eyes can occur regardless of environmental conditions.
Eye Color Changes with Age
While genetics determine the baseline eye color, there can be some natural shifts with aging. As children grow into adulthood, these changes may occur:
– Increased Melanin – More melanin develops during early childhood, darkening light eyes. Hazel eyes may become more brown.
– Decreased Rayleigh Scattering – The thinning stroma scatters less light, reducing green hues.
– Fuchs Heterochromic Iridocyclitis – This condition commonly affects hazel eyes, increasing brown patches.
– Pigment Dispersion Syndrome – Shed iris pigment can be deposited on hazel eyes, darkening color.
– Cataracts or Glaucoma – These diseases can lighten iris color as melanin degrades.
However, hazel eyes are unlikely to shift fully to blue or green later in life due to the underlying brown genetics. The natural aging effects are usually subtle.
Statistics on Hazel Eyes
Some interesting statistics on the prevalence and genetics of hazel eyes:
– Global rate: Approximately 5-10% of people worldwide
– Northern Europe: Up to 20% in Baltic Sea countries
– Central heterochromia: Around 12% of hazel eyes exhibit central banding
– Sex difference: No significant difference between males and females
– Genetic influence: Up to 75% determined by HERC2 gene variants
– Rayleigh scattering: Accounts for up to 50% of hazel eye color
– Dark skin tones: 1-5% prevalence of hazel eyes
– Sensitivity to sunlight: Moderately high due to lower melanin
– Future trends: Projected to remain relatively stable based on genetics
– Hazel eyes are classified as brown eyes, with green color from Rayleigh scattering of light.
– The amount and distribution of melanin determines the various colors seen.
– Hazel eyes result from moderate melanin levels compared to other eye colors.
– They are most common in northern European populations at 5-20% prevalence.
– The genetics are linked to variants in the HERC2 and OCA2 genes that regulate melanin.
– Hazel eyes are praised in art and culture for their shifting, multicolored beauty.