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Populations With Blue Eyes

Blue eyes are one of the most unique features of the original European peoples. The trait has been in existence for thousands of years and thus has spread to many parts of the world.

A team at the University of Copenhagen did a study in 2008 which concluded that people with blue eyes have a common ancestor. They found that a genetic mutation sometime between 4,000 and 8,000 BC is the cause of blue eyes and the reason all people with blue eyes have this physical trait today.

The study of blue-eyed individuals showed they only have a small degree of 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," says Professor Eiberg. "They have all inherited the same switch at exactly the same spot in their DNA." Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production.

This genetic variation first developed in a group of people living just north of the Baltic Sea. These people are referred to as Proto-Indo-Europeans. Around 5,500 BC, they began to migrate out of this area and into western Europe, Iran, and India. This is why blue eyed people have been present in locations outside of Europe for thousands of years.

These original blue eyed ancestors appear to have rapidly spread throughout Europe. These people were Neolithic farmers and thus had an advantage over the few nomadic inhabitants of western Europe who had brown eyes. Genetic research also tells us that these people favored having children with others who shared this unique trait.

Current Prevalence of Blue Eyes in Europe

Between 8 and 10 percent of people worldwide currently have blue eyes. These people are primarily located in Europe, North America, and Australia. About 2 percent of people worldwide have green eyes. About 16% of people with green eyes are from Celtic and Germanic ancestry.

America

Europeans began settling in North America in the 1500s AD. By the year 1900, about half of those born in the United States had blue eyes. By the year 2015, only 16.6% of Americans had blue eyes. Over the same time period, the US population grew by 420%, meaning that the total number of people with blue eyes has increased by 40%. The reduced overall prevalence of this unique trait is due to immigration from populations with an extremely low occurrence of it.

Furthermore, since there are genes for blue eyes in the United States, even if there is no one that has blue eyes, children will still be born who will grow up to have blue eyes. The probability is such that two people with the recessive gene necessary for blue eyes will have children together, creating new people with blue eyes.

It is indeed true that the dominance of blue eyes in America no longer exists. But there will always be a substantial number of people there who will have blue eyes.

The Future

Europe is somewhat behind the United States with respect to demographic change, but is on a very similar path. In many European cities, the original Indo-European peoples who settled the continent over 7,000 years ago are currently a minority. Given that most of the new immigrants who have moved into Europe are from brown eyed populations and typically move into cities, it is safe to say that blue eyes are rare in European cities at this point in history. Blue eyes are, however, still a common trait for Europeans as a whole.

Immigration into Europe currently shows no signs of slowing down. So it would seem logical to assume that in the future, fewer than 10% of the population would have blue eyes. But we should not forget that this unique trait originated from one ancestor just north of the Baltic Sea many thousands of years ago. There was something that caused these people to rapidly multiply and spread. It is entirely likely that this could happen again over the course of time. Immigration into Europe could also be reduced for some reason in the future, preserving the dominance of this unique trait.

Originally published September 10, 2020

Sources:
  University of Copenhagen
  University of Copenhagen
  Blue Eye Color in Humans by Eiberg, H., Troelsen, J., Nielsen, M. et al
  UCLA
  European Hair and Eye Color by Peter Frost

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