Blue eyes are distinct, powerful and
undeniably beautiful. But have you ever wondered why some people are gifted
with blue eyes while the majority of us are born with brown eyes.
A study from the University of Copenhagen
reveals that every single person on the earth had brown eyes until a genetic
mutation occurred around 10,000 years ago.
Researchers interpret that all people with
blue eyes share a common ancestor.
The study examined the DNA of around 800
people with blue eyes from various parts of the world.
Out of all of the participants, 99.5% had the
same mutation in the gene that decides the color of our eyes. In other words,
they shared common DNA and were genetically related to one another.
The result also reveals that a single person
is responsible for this mutation.
About the Genetic Mutation
Researchers report that a
genetic mutation in our OCA2 (ocular cutaneous albinism
form 2) gene resulted in the formation of a 'switch,' which literally turned on
our ability to develop blue eyes or turned off our
ability to develop brown eyes.
Melanin is a pigment that
gives color to our hair, eyes and skin. The OCA2 gene codes for the so-called P
transporter protein or pink-eyed dilution protein homolog)
which is involved in the production of the pigment. However, the 'switch,'
which is seen in the gene adjacent to OCA2, cannot completely stop the gene
from functioning. Actually, it regulates the action of the gene to reduce the
generation of melanin in the iris - effectively 'diluting' brown eyes to blue.
The switch's influence on OCA2
is very specific therefore. A complete destruction of the OCA2 gene can lead to
albinism, which is a genetic condition characterized by the partial or complete
absence of pigment in the skin, hair and eyes.
"From this we can
conclude that all blue-eyed individuals are linked to the same
. They have all inherited the same switch at exactly the same
spot in their DNA" says Professor Hans Eiberg from the Department of
Cellular and Molecular Medicine, who is also the lead author of this study.
Difference in the color of the
eyes from brown to green can all be scientifically explained by the amount of
melanin in the iris, but people with blue eyes only have a small degree
of variation in the amount of melanin.
Study on Mitochondrial DNA
Professor Eiberg and his
research team studied mitochondrial DNA and also did a comparison of eye color
of blue-eyed people in countries as diverse as Jordan, Denmark and Turkey.
Eiberg's study is reportedly the most current findings in a decade of genetic
research, which started in 1996 when he first implicated the OCA2 gene as being
responsible for eye color.
The genetic mutation of brown
eyes to blue colored eyes represents neither a positive nor a negative
mutation. It is one of several mutations such as hair color, baldness, freckles
and beauty spots and such mutations have absolutely nothing to do with
increasing or decreasing chances of human survival. Eiberg says, "It
simply shows that nature is constantly shuffling the human genome, creating a
genetic cocktail of human chromosomes and trying out different changes as it
1. Hans Eiberg, Jesper Troelsen, Mette
Nielsen, Annemette Mikkelsen, Jonas Mengel-From, Klaus W. Kjaer, Lars Hansen.
Blue eye color in humans may be caused by a perfectly associated founder
mutation in a regulatory element located within the HERC2 gene inhibiting OCA2
2. Human Genetics
: 177 DOI: 10.1007/s00439-007-0460-x