Blue eyes, like all eye colors, are determined by genetics. The appearance of blue eyes in humans likely emerged through a combination of genetic mutations and natural selection over thousands of years.  The exact timeline of when blue eyes "came into existence" is difficult to determine precisely. 

However, genetic studies suggest that the mutation responsible for blue eye color likely occurred between 6,000 to 10,000 years ago in the vicinity of the Black Sea region.  This mutation likely arose as a result of a genetic change in the OCA2 gene, which affects the production of melanin, the pigment that gives color to the eyes, skin, and hair. 

Blue eyes are a recessive trait, meaning both parents must carry the gene for blue eyes for their child to have blue eyes.  As humans migrated and populations mixed over time, the gene for blue eyes spread to various parts of the world. Today, blue eyes are most commonly found in populations of European descent, particularly those from northern and eastern Europe, although they can also occur in other populations due to genetic mixing.