MadSci Network: Evolution

Re: Where and why did red hair originate

Date: Wed Sep 15 15:29:45 1999
Posted By: Marc Greener, Grad student, Division of Medical and Molecular Genetics, Division of Medical and Molecular Genetics
Area of science: Evolution
ID: 935765902.Ev

Here in the UK red hair is generally associated with people of Celtic
descent, i.e Scotland and Ireland.  I believe the people of Scotland came
from 5 different ethnic groups who occupied or invaded northern Britain in
the dark ages.  I remember reading somewhere that in all of recorded
history, red-haired people have never been mentioned as a group except by
the Romans.  The 'Picts' where foes who the Romans fought and were
described as having red-hair and 'large limbs' by Roman historian Tacitus. 
Modern historians with the help of anthropologists have placed red-hair as
a unique characteristic belonging to the Picts, who were characteristic to
what is now regarded as Scottish.
As far as the world-wide distribution of red-hair is concerned, it would be
fair to say that the majority may well have descended from this
North-Western European region, although as with all variations between
people, mutations in genes can occur and be maintained in any population
provided there is no detrimentus effect to the populations growth.

As for the reasons for red-hair, it's not easy to see any immediate
selective advantage in terms of evolution.  I haven't come across any
theories that might explain this, but I have been able to piece together
some information of the genetics behind red-hair and this seems to provide
a clue....

Variation in both skin and hair pigmentation is due to varied amounts of
the chemicals eumelanin (brown/black melanins) and phaeomelanin (red/yellow
melanins) produced by melanocytes ("colour-cells").  The melanocortin-1
receptor (MC1R) is a regulator of eu- and phaeomelanin production in the
melanocytes and mutations in this gene are known to cause coat colour
changes in many mammals.  Studies on Irish and Dutch populations have
significantly linked variations in the MC1R gene to red-hair.  Also, so
called 'loss-of-function' mutations in the human MC1R gene are known to be
common and have recently been shown to be associated with red-hair.  One
other interesting point is that recent work has shown that some variants on
the MC1R gene may be preferentially associated with hair colour rather than
skin type.  Because the primary function of melanins is thought to be for
both 'photoprotection' and 'photosensitising` (eu- and phaeomelanins
respectively), this offers reason to suggest that MC1R variants (most
red-heads) are a risk factor, possibly independant of skin type, for
melanoma susceptibility.

Why would mutations occur?  Who knows?!  If such variations in MC1R
originally arose in areas of northern-Europe, maybe it was because there
was NO selection AGAINST such mutations occuring in that region of the
world.  i.e., due to the poor quality of weather in this area of the world,
any mutations in MC1R would hold no relevance as the UV-levels would be
significantly low enough to cause no damage despite decreased melatonin
protection. Unfortunately this assumes that MC1R mutations occuring in
'hot-climates' would result in high mortality rates occuring before age of
parenthood which is probably unlikely.  Other than that, I can't think of
any other reason to suggest why red-hair originated in north-west Europe
other than by random chance!

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