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Eye color is a defining attribute of physical appearance. Learn more about what makes blues so blue with Groupon’s study of eye color.

Eye Color: More Than Just a Window to Your Soul

Though they are often mesmerizing and regularly the subject of poetry, the pools of color surrounding the pupil are simply a matter of genetics. Eye color was once thought to be determined by what combination of recessive and dominant genes—blue being recessive and brown being dominant—that an embryo received from each parent’s gamete. However, this has proven to be incorrect, and a total of at least 16 genes are now considered to affect the shade of the iris. Complicating matters even more, the scattering of light waves by the iris stroma—its fibers and cells—adds variation and nuance to color, leading to what are considered blue-green and hazel eyes.

Changes to eye color throughout different phases of life have also been documented, the most common being a change from blue to brown before an infant reaches one year of age. The cause for this is attributed to the onset of melanin production, which is directly proportional to the depth of skin, hair, and eye color. Furthermore, eye color can change later in life, such as during pregnancy or adolescence, likely because of hormonal changes in the body.