Despite being one of the rarer pigments, some countries have high populations of blue-eyed people, particularly in Europe. Studies in 2019 found 89% of people in Estonia and Finland were blue-eyed, with just over half of people in Ireland (57%) and half the population of Scotland sporting blue eyes. By contrast, only about 16.6% of people in the United States have blue eyes and 16.3% in Spain. The numbers are even starker on an international scale: worldwide only about 8-10% of people have blue eyes, with the majority (about 79%) having brown eyes.
Where do blue eyes come from?
The color is derived from melanin, a brown pigment found in the iris, and blue eyes are believed to be the result of a genetic mutation of the HERC2 gene that originated with a single ancestor about 10,000 years ago, which causes less melanin to be produced in the eyes. Melanin absorbs light, and the more light it absorbs the darker the iris becomes, while light that is not absorbed is reflected. The light reflected from eyes that do not have high levels of melanin comes from the blue side of the spectrum, delivering the more rare shades of eye color.
Some scientists believe all of humanity began with brown eyes prior to the gene mutation, which some believe occurred once people began emigrating to the north, away from regions of prolonged exposure to intense sunlight like the Middle East and other countries in the southern hemisphere. These claims assert the melanin in brown eyes protected people from the amount of light they took in regularly, which was not necessary in northern countries where people were not prone to the same level of sun exposure, particularly in darker winter months.
Where are blue eyes more common?
Estonians are known for their fair-haired, blue-eyed appearance with the percentage of people with blue eyes estimated at nearly 90%, though some observational studies have concluded many of these may be more toward blue-grey in color meaning they contain even less melanin than their pure-blue cousins.
In the Land of the Midnight Sun, about 89% of Finnish people have blue eyes. Also known for their fair skin and blond hair, their love of sauna and penchant for coffee, the people of Finland have a distinct Nordic look that scientists have been studying for years.
Ireland and Scotland
More than 57% of the approximately 4.9 million people who call Ireland home have blue eyes, narrowing the divide between those with brown or blue eyes to nearly even. About half of Scots are blue-eyed, with DNA studies from a sampling of 12,000 people conducted by ScotlandsDNA determining the highest number of gene mutations were found in Edinburgh, the Lothians, and Borders. Some researchers believe the prevalence of blue eyes in the country could stem from them being seen as more attractive with a natural sparkle, which is likely caused by the reflection of light not typically seen in brown eyes, which absorb melanin—meaning blue-eyed people are more likely to procreate and pass on their genes.
There is a risk to having blue eyes
A study completed in 2011 found some diseases, such as eye cancer and macular degeneration, are less common in brown-eyed people than others, leading to assertions that melanin is a form of protection. Research has shown blue eyes can be more susceptible to ultraviolet and blue light, and those with lighter-colored eyes are often more sensitive to sunlight exposure. It is recommended people with blue eyes are diligent about wearing sunglasses for protection while outdoors and eyeglasses when using computers or other devices that put out blue light.