Why Europeans are so colourful
2007-10-22 14:41
Washington - A few dozen genetic
changes can help explain why people of European descent have so
many different shades of hair, eye and skin colour - but it is
still impossible to tell the colour of someone's eyes or hair
based on DNA alone, researchers said on Sunday.
The team at Decode Genetics said their scans of 7 000
Icelandic and Dutch people found 60 separate genetic mutations
linked with hair, eye and skin colour.
As with earlier gene surveys, no single mutation or cluster
of mutations can tell whether a person has brown, blue or green
eyes; brown, blonde or red hair or whether his or her skin is
fair or freckled.
But, writing in the journal Nature Genetics, Kari
Stefansson of Decode Genetics and colleagues said their new
suite of genes help narrow down the possibilities and might be
used to study certain diseases that are more common in people
with certain colouring.
Dark skinned originally
"It has long been thought that before the migrations that
first brought our species out of Africa some 60 000 years ago,
ancestral human populations had characteristically dark skin,
eyes and hair," the researchers wrote.
In Europe, humans evolved big variations in skin, eye and
hair colour. But skin and hair tends to be darker in populations
originating from near the equator, which supports the idea that
pigmentation helps protect from the sun's radiation.
It is unclear why people living in the North - including
not only Europeans but many Asians - have lighter skin.
"The most obvious functional advantage of lighter skin
pigmentation in northerly latitudes is that it facilitates the
synthesis of vitamin D3 in spite of low levels of ultraviolet
radiation exposure," the researchers wrote.
And the big variations in eye and hair colour among
Europeans are even more mysterious.
Stefansson's team found evidence that these variations are heavily selected for, however - meaning people who have them
were more likely to reproduce and pass them along to offspring.
This could be because they provide a survival advantage, or
merely because people liked such traits and tended to choose
mates who have them.