How Blue eyes Originated
Everyone with blue eyes alive today – from Angelina Jolie to Wayne Rooney – can trace their ancestry back to one person who probably lived about 10,000 years ago in the [url=http://maps.google.com/maps?ll=41.0,36.0&spn=1.0,1.0&q=41.0,36.0 (Black Sea Region)&t=h]Black Sea region[/url], a study has found. Scientists studying the genetics of eye colour have discovered that more than 99.5 per cent of blue-eyed people who volunteered to have their DNA analysed have the same tiny mutation in the gene that determines the colour of the iris.
This indicates that the mutation originated in just one person who
became the ancestor of all subsequent people in the world with blue
eyes, according to a study by Professor Hans Eiberg and colleagues at the [url=http://maps.google.com/maps?ll=55.6797222222,12.5725&spn=0.01,0.01&q=55.6797222222,12.5725 (University of Copenhagen)&t=h]University of Copenhagen[/url].
The scientists are not sure when the mutation occurred but other
evidence suggested it probably arose about 10,000 years ago when there
was a rapid expansion of the human population in Europe as a result of the spread of agriculture from the Middle East .
“The mutations responsible for blue eye colour most likely originate
from the north-west part of the Black Sea region, where the great
agricultural migration of the northern part of Europe took place in the
Neolithic periods about 6,000 to 10,000 years ago,” the researchers
report in the journal Human Genetics.
Professor Eiberg said that brown is the “default” colour for human
eyes which results from a build-up of the dark skin pigment, melanin.
However, in northern Europe a mutation arose in a gene known as OCA2
that disrupted melanin production in the iris and caused the eye colour
to become blue.
“Originally, we all had brown eyes,” said Professor Eiberg. “But a genetic mutation
affecting the OCA2 gene in our chromosomes resulted in the creation of a
‘switch’ which literally turned off the ability to produce brown eyes.”
Variations in the colour of people’s eyes can be explained by the
amount of melanin in the iris, but blue-eyed individuals only have a
small degree of variation in the amount of melanin in their eyes, he
“From this we can conclude that all blue-eyed individuals are linked
to the same ancestor. They have all inherited the same switch at exactly
the same spot in their DNA,” said Professor Eiberg.
Men and women with blue eyes have almost exactly the same genetic
sequence in the part of the DNA responsible for eye colour. However,
brown-eyed people, by contrast, have a considerable amount of individual
variation in that area of DNA.
Professor Eiberg said he has analysed the DNA of about 800 people
with blue eyes, ranging from fair-skinned, blond-haired Scandinavians to
dark-skinned, blue-eyed people living in Turkey and Jordan.
“All of them, apart from possibly one exception, had exactly the same
DNA sequence in the region of the OCA2 gene. This to me indicates very
strongly that there must have been a single, common ancestor of all
these people,” he said.
It is not known why blue eyes spread among the population of northern
Europe and southern Russia. Explanations include the suggestions that
the blue eye colour either offered some advantage in the long hours of
daylight in the summer, or short hours of daylight in winter, or that
the trait was deemed attractive and therefore advantageous in terms of
Source The Independent
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