Why Do Some People Have Blue Eyes?

Early humans all had brown eyes. Then, a mutation occurred in one person's genetic code, probably someone living in the northwestern part of the Black Sea region about 10,000 years ago. A 2008 study by researchers at the University of Copenhagen determined that the same tiny mutation in the gene that determines eye color is present today in about 99.5 percent of blue-eyed people, indicating the link back to a single ancestor.

Why you may have baby blues:

• The scientists theorized that the mutation occurred during a time of rapid population expansion in Europe, as a result of the spread of agricultural activities from the Middle East.
• Brown is, essentially, the "default" color of human eyes, linked to the build-up of the dark skin pigment called melanin. The mutation OCA2 disrupted melanin production in the iris, turning brown eyes blue.
• It’s not known why blue eyes spread among the population of northern Europe and southern Russia. It could be that the trait was deemed particularly attractive, and played a role in sexual preference. Or there could be other evolutionary causes.