The science and beauty behind eye color diversity

Eyes are one of the first and most lasting features that catch our attention when we meet someone. Human eyes come in a wide palette of colors, with brown being the most common shade, blue more frequent especially in Northern and Eastern Europe, and green—the rarest color—found in only about 2% of the world's population.

SO, WHAT LIES BEHIND THESE COLOR DIFFERENCES?

The answer is hidden in the iris, the colored ring of tissue surrounding the pupil. Here, a pigment called melanin does most of the work. Brown eyes contain a high amount of melanin that absorbs light, creating their dark appearance. Blue eyes have very little melanin; their color comes not from pigment but from a physical effect called the Tyndall effect, the same phenomenon that makes the sky appear blue, where light is scattered within the iris.

In blue eyes, short-wavelength light (blue) scatters more effectively than longer wavelengths (like red or yellow). Because melanin concentration is low, less light is absorbed, allowing scattered blue light to dominate. This blue tone results from how light interacts with the eye's structure, not from pigment.

Green eyes result from a balance of moderate melanin pigment and light scattering. Hazel eyes are even more complex; an irregular melanin distribution in the iris creates a mosaic of colors that can shift depending on the ambient light.

WHAT ABOUT GENETICS?

The genetics of eye color is equally fascinating. For a long time, scientists believed a simple model where one gene controlled eye color with "brown beating blue." But research shows the reality is much more complex. Multiple genes contribute to determining eye color. This explains why siblings in the same family can have dramatically different eye colors and why two blue-eyed parents can sometimes have a green- or even light brown-eyed child.

Eye color can also change over time. Many babies of European descent are born with blue or gray eyes due to low melanin levels. As pigment gradually accumulates during the first years of life, those blue eyes may turn green or brown.

In adulthood, eye color tends to be more stable, although small changes in appearance are common depending on lighting, clothing, or pupil size.

THE TRULY INTERESTING CASES

There are also rare conditions like heterochromia, where one eye is a different color from the other or where a single iris contains two colors. The different eye colors of David Bowie were actually an illusion caused by permanent dilation of one pupil following an injury, mimicking heterochromia.

In conclusion, eye color is more than just a genetic and physical curiosity. It's a reminder of how biology and beauty intertwine. Each iris is like a tiny universe with pigment rings, golden flecks, or deep brown pools that catch light differently depending on your perspective.