This is what all blue-eyed people have in common.

Most interestingly, all blue-eyed people have one thing in common, which has surprised many. Somebody writes, “I had no idea!” Fascinating…” Another joke goes, “Spoiler alert: all of their eyes are blue.” However, it turns out to be far more intriguing than that (quite obvious) reaction. Blue eyes are caused by a gene called HERC2. This gene suppresses OCA2, which creates different shades of brown eyes, and it controls the amount of brown pigment melanin generated.

Professor Hans Eiberg of the University of Copenhagen’s Department of Cellular and Molecular Medicine explains: “At first, we all had brown eyes. However, a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the construction of a’switch’ that literally ‘turned off’ the potential to produce brown eyes.” According to The Independent, it began when people first migrated from Africa to Europe.

According to research conducted at the University of Copenhagen, all blue-eyed people are descended from the same person.Although it is uncertain who first developed this initial mutant gene, the fact that every blue-eyed person possesses it is rather compelling evidence. According to Professor Eiberg, research on the genetic mutation of people with blue eyes “simply indicates that nature is constantly mixing the human genome, building a genetic cocktail of human chromosomes and testing out new alterations as it does so.”