Blue eyes

Blue eyes are eyes whose irises appear blue because they contain little melanin and scatter incoming light. They do not contain blue pigment.

Iris: The colored muscular ring around the pupil that regulates how much light enters the eye. Its tissue and pigment determine how much light is absorbed or scattered.
OCA2: A gene that helps regulate melanin production and contributes to variation in human eye color. Variants in OCA2 influence iris pigmentation associated with blue eyes.
Ancient DNA: Genetic material recovered from archaeological remains and other ancient biological samples. It allows researchers to estimate when eye-color-associated variants appeared in past populations.
Iris recognition: A biometric identification method that compares distinctive patterns in the iris. Blue iris color is distinct from the detailed iris patterns used for identification.
Eye color in human populations: The geographic and demographic variation of iris colors among human populations. Blue eyes are unevenly distributed across populations, without defining ancestry or identity.
Melanin: A group of pigments that absorb light and contribute to coloration in skin, hair, and eyes. Low melanin in the iris leaves more incoming light available for scattering.
HERC2: A gene containing regulatory DNA that affects expression of the nearby OCA2 gene. A well-studied regulatory variant in HERC2 can reduce OCA2 expression and iris melanin.
Mesolithic Europe: The European period between the end of the last Ice Age and the spread of farming. Ancient remains from this period provide evidence about early combinations of pigmentation traits.
Forensic phenotyping: The use of genetic data to estimate visible traits of an unknown person for investigative purposes. DNA variants can support probabilistic estimates of eye color, including blue eyes.
Beauty standards: Social ideals that shape judgments about physical appearance. The valuation of blue eyes varies across societies and historical periods.

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