Green Eyes Exist in 2% of People

Evolutionary biologist Mark Lucock and others are studying why only about 2% of humans have green eyes. For most of human history, people had dark eyes, with lighter pigmentation appearing roughly 3,000 years ago.

Researchers propose that lighter irises may have evolved to allow more light in during long periods of darkness in Northern Europe. This could have helped regulate melatonin and improve reproductive success, though this connection isn't definitively proven.

Another theory suggests that people simply found light eyes attractive, driving their prevalence through sexual selection. Green eyes require a precise combination of melanin, lipochrome, and light scattering—making them biologically difficult to create. The genetic variant responsible for eye color, rs12913832, shows evidence of positive selection, but the exact mechanism favoring lighter eyes remains unclear.

The alleles for green eyes concentrated in Celtic and Nordic lineages and did not spread widely.