Origin of Red Hair

In the UK red hair is generally associated with people of Celtic descent, i.e Scotland and Ireland. It is believed the people of Scotland came from 5 different ethnic groups who occupied or invaded northern Britain in the dark ages. 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. Here is 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 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. 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.