Explaining Eye Color: Genetics and Melanin

Eye color is determined by melanin in the iris and how light scatters. Davinia Beaver from the Clem Jones Centre for Regenerative Medicine at Bond University explains that brown is the most common color worldwide, while blue is more frequent in northern and eastern Europe, and green is the rarest (about 2%).

Brown eyes have a high concentration of melanin, while blue eyes have minimal melanin, and their color results from light scattering (Tyndall effect). Green eyes are due to a combination of moderate melanin and scattering, and hazel eyes result from uneven distribution of melanin.

The genetics of eye color are multifactorial. Many infants of European descent are born with blue or gray eyes due to low levels of melanin, and the color often darkens in the early years of life. Heterochromia (different color between the two eyes or dichromia in the same iris) is rare but striking.