The researchers discovered that the blue hue of the iris is not due to pigment but rather to the scattering of light. This phenomenon is known as the Tyndall effect. We encounter it all the time when we look at the sky and the sea: they appear blue, but in reality, they are transparent.
Dr. Davinia Beaver, the lead author of the study, explained that the culprit is melanin—a substance in our bodies responsible for the color of our skin and .
“Brown eyes contain a high concentration of melanin, which absorbs light and makes them darker. In contrast, blue eyes have very little melanin,” the scientist noted.
According to her, blue eyes scatter shorter wavelengths of light, which are associated with blue shades, more effectively than longer wavelengths associated with red and yellow.
“Due to the low concentration of melanin, less light is absorbed, allowing the scattered blue light to dominate our perception. This blue tint is not caused by pigment but by the interaction of light with the structure of the eye,” Dr. Beaver pointed out.
What about green eyes, which are less common than others? Green eyes, as the expert explains, result from a genetic trait that lowers melanin levels, but not as drastically as in blue eyes.
Brown eyes are even more complex. An uneven distribution of melanin in their iris creates a “mosaic” of color that changes depending on the lighting.
Despite years of speculation among scientists that eye color is controlled by a single gene, experts have recently determined that this trait is influenced by multiple genes.
“This explains why children from the same family can have completely different eye colors, and why two blue-eyed parents can sometimes have a child with green or even light brown eyes,” Dr. Beaver said.
She also explained why many , especially those of European descent, are born with blue or gray eyes. At the initial stages of life, melanin levels are quite low. As pigment gradually accumulates over the first few years, blue eyes can change to green or brown.
In adults, eye color is generally stable. However, it can be influenced by light or even the color of the clothing we wear, according to the publication Daily Mail. Dramatic changes in eye color are rare; they can occur with age or in response to certain diseases.
Some celebrities, like Kate Bosworth and Mila Kunis, exhibit a rare condition called heterochromia, where their eyes differ in color. The expert notes that this condition can be explained by genetics, trauma, or certain diseases.
For instance, musician David Bowie’s eyes appeared to be different colors due to a permanently dilated pupil from an accident.
Statistics show that brown is the most common eye color in the world.
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