Find yourself transfixed when you come across green eyes? It's no surprise that you might do a doubletake as green eyes are an unusual ocular gem.
The topic recently sparked discussion in a viral clip on TikTok shared by @cheggbiology that noted "having green eyes is actually really rare." The clip has had three million views since it was posted on January 2.
Timothy Sexton, who has a PhD in population genetics and over 18 years of experience with genetic analysis, told Newsweek: "The development and rarity of green eyes are influenced by intricate genetic interactions and the mixing of human populations."
The complexity of these genetic factors as well as geographical and population-specific variations "underscores why green eyes are among the rarest eye colors," he said.
Dr. Jovi Boparai, an ophthalmologist and ophthalmic surgeon, told Newsweek eye color is determined by the amount and type of pigments in the front part of the iris (the colored portion of the eye) as well as by "the scattering of light by the turbid medium in the stroma [a fibrous layer of tissue] of the iris."
"Green eyes are typically a result of a combination of a moderate amount of melanin [the substance that produces eye, skin and hair pigmentation] and the scattering of light in the iris," he added.
How Rare Are Green Eyes?
According to a study published in late January this year in Scientific Reports, "the most common iris color in the world is brown, accounting for about 79 percent."
Sexton, the founder of DNA Romance, an online dating platform providing connections based on a DNA test analysis, said green eyes are estimated at 2 percent of the population worldwide. This prevalence is much higher in certain European countries, such as Ireland, Scotland, the U.K., France and Germany, he added.
Boparai, founder/CEO of CorneaCare, which provides personalized eye treatment plans, said that the rarity of green eyes varies across the globe. In Europe, they're found in around 8 percent of the population. However, "in other parts of the world, like Africa and East Asia, they're much less frequent, occurring in less than 1 percent of people," he added.
Why Are Green Eyes So Rare?
The chance of being born with green eyes hinges on a "complex interplay" of multiple genes and single nucleotide polymorphisms (SNPs), "making precise prediction challenging," Sexton noted.
"The likelihood increases in populations with more frequent relevant genetic variations, particularly in some European groups," he said.
Can Eye Color Change With Age?
Eye color often changes in early life due to melanin development. However, significant changes in adulthood, such as transitioning from dark to light colors, such as from brown to green, are rare and any changes that do occur are "typically not due to natural genetic variation," Sexton noted.
Boparai further explained that many babies are born with lighter eye colors, such as blue or gray, because melanin production in the iris is "still ramping up."
But as they grow older, typically between six months and three years of age, the iris produces more melanin, "potentially causing the eyes to darken to hazel, brown, or even a deeper shade of green," he said.
Even beyond infancy, eye color can undergo subtle changes depending on lighting, mood, and even clothing choices. Boparai said: "This is primarily due to the way light interacts with the melanin and other pigments in the iris." For example, green eyes might appear more blue in certain lighting conditions or slightly hazel in direct sunlight, he said.
The doctor also noted: "In rare cases, certain medical conditions can affect eye color. Iridoschisis, for example, is a condition where the layers of the iris separate, sometimes leading to a change in color, including a lightening of greens."
Another example is heterochromia, where each eye has a different color, which can be present from birth or develop later in life, Boparai said.
Got a health-related question or dilemma? Let us know via life@newsweek.com. We can ask experts for advice, and your story could be featured on Newsweek.
Uncommon Knowledge
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Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.
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Soo Kim is a Newsweek reporter based in London, U.K. She covers various lifestyle stories, specializing in travel and health.
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