If You Have Blue Eyes, You Share an Ancestor With Jake Gyllenhaal, Scientists Claim
Blue-eyed people inherited same "genetic switch."
Here's a shocking family secret you might not mind learning: If you have blue eyes, you are distantly related to the actor Jake Gyllenhaal through a common ancestor, scientists say. It all comes down to how a certain gene expresses pigment. Read on to find out how that can be, how researchers made the finding, and if you should add Jake to your holiday card list this year.
According to scientists, every blue-eyed person on Earth can trace their ancestry back to a single person who lived in Europe between 6,000 and 10,000 years ago. At one point, every human had brown eyes—until a mutation developed on the gene HERC2. Scientists say it switches off OCA2, another gene that regulates the amount of brown pigment that develops in the eye. The result: The first set of blue eyes.
OCA2 is a very specific gene mutation, affecting eye color but not changing the pigment of hair or skin color. A fully switched-off gene HERC2 would cause albinism, scientists say. About 8% to 10% of people worldwide have blue eyes. In the U.S., that number is higher, at 27%. About 45% of Americans have brown eyes, and 18% have hazel eyes (shades of brown and green).
In brown eyes and green eyes, the amount of melanin in the iris can vary widely. But blue-eyed people only have a small variation in the amount of melanin in their eyes. "From this we can conclude that all blue-eyed individuals are linked to the same ancestor," said Professor Hans Eiberg of the University of Copenhagen. "They have all inherited the same switch at exactly the same spot in their DNA. Nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so."
Because blue eyes are a recessive trait, even two brown-eyed parents can produce a blue-eyed child. The reverse is also true: Two blue-eyed parents can have a brown-eyed child. And blue eyes can change over time. At birth, the human eye doesn't have its full adult amount of pigment. As children grow, the color of their eyes can shift from blue to brown as more melanin is produced in the eye.
At the beginning of the twentieth century, about half of American children were born with blue eyes. By mid-century, that number had declined to about one-third. Today, only about 1 in 6 children are born with blue eyes. Researchers say that's because a century ago, 80 percent of people married within their ethnic group. Blue eyes, a genetically recessive trait, were regularly passed down to ancestors. But by the 1950s, ethnicity became less of a priority in mate selection, and as intermarriage between different ethnic groups became more frequent, blue eyes began to disappear, replaced by brown.