Ever since Tacitus, the Roman historian, noted with awe the flame-headed natives of Caledonia, observers have wondered at the prevalence of ginger hair among the Scots.
Now a genetics research student has stumbled on an explanation based on another remarkable feature of Scottish life — the weather.
Emily Pritchard, 26, revealed her insights in an article about her sister’s red hair for a University of Edinburgh magazine.
Her formula — genetic mutation + bad weather = red heads — “was speculation rather than scientific study, but it is plausible”, she said.
It is certainly plausible enough to explain an over-population of fiery red-headed Scottish footballers — Billy Bremner, Alex McLeish and Gordon Strachan — or to account for the red-headed singer Shirley Manson and the television presenters Jackie Bird and Ann McKevitt. Nor are these famous names exceptional, for while redheads amount to 1-2 per cent of the European population, an estimated 8 per cent of Scots and Irish are ginger.
Although human beings probably evolved in Africa 1 million to 2 million years ago,red hair appeared only once they had settled in Europe, possibly as recently as 20,000 years ago.
Ms Pritchard’s explanation of this trait is based on well-established scientific theory. Its foundation is the premise that ginger hair is genetically less advantageous because redheads have fair skin and are more prone to sunburn and skin cancer — unhelpful characteristics in hunter-gatherer societies. In large populations in sunny climates, the ginger strain would tend to die out. In Ancient Europe, however, small tribes broke away from bigger societies, and moved north and westwards, into areas where summers were shorter and winters longer. These smaller groups effectively formed genetic bottlenecks, small gene pools in which chance mutations such as red hair were able to come to the fore.
The genetics of red and blond hair are complex. For example, one of the main genes for hair colour has 40 variants — but only about six cause red hair. People must inherit two of these six genes — one from each parent — to have red hair.
The chances of this are always small, which is why there are so few redheads. The best chance occurs in stable rural communities with a common ancestry — where people carrying the genes are likely to meet and have children.
“The smaller your sample the more likely something rare is going to happen,” said Ms Pritchard, 26, a student at the MRC Human Genetics Unit at the Western General Hospital.
“The Celts, by chance, had a high frequency of the ginger mutation, which was able to persist over time.”
Ms Pritchard is researching Cornelia de Lange syndrome, a rare genetic disorder that causes abnormal arms and faces, behavioural problems, autistic-like learning difficulties and slow growth in sufferers. In her spare time she writes accessible scientific studies for the general public and said her next work will focus on shampoo.