Why Edinburgh residents are likely to be blue-eyed

Geneticist Katie Barnes. Picture: Ian Georgeson

We all inherit lots of physical traits in our DNA from our parents.

Babies are cooed over: “My, is he/she like his dad/mum?” There was a time I witnessed in Leith Walk when a proud dad was stopped by an alleged friend as he pushed a buggy. The old lady bent down and peered at the baby. “He looks like his mother, thank God.”

One of the most striking inherited traits is massively present in Edinburgh and the south-east where a staggering 57 per cent of all people have blue eyes. That is the highest in Britain where the average is 48 per cent.

The only place that comes close is Connaught in the west of Ireland with 53 per cent. Amongst the Princes Street crowds the vast majority will have baby blues while 29 per cent will have green eyes and 14 per cent brown eyes. Poor souls.

These statistics are remarkable – in Glasgow and the south-west, the average is a paltry 49 per cent – because outside of Europe and people of European descent, almost everyone else has brown eyes: Asians, Africans and Native Americans. Brown is the ancestral eye colour of our species, Homo sapiens, and the genetic variant that caused blue eyes arose in Europe about 10,000 years ago. Scientists at  ScotlandsDNA believe that this new colour first appeared in a single individual who probably lived on the shores of the Baltic Sea and it spread from there. But why?

There appears to be no evolutionary advantage in having blue eyes. You cannot see better through blue irises. One aspect of ScotlandsDNA’s Blue Eyes Project is to discover why blue eyes arose and multiplied across Europe so quickly, flipping the ancestral colour of brown to blue. Green eyes are also a result of this change since they arose because of the mixture of the blue variant with brown.

Why has 100 per cent brown dropped to 22 per cent in Britain and as low as 14 per cent in Edinburgh? Here is a simple but as yet unproven hypothesis.

Apart from the obvious, what do George Clooney, Cameron Diaz, Brad Pitt, Cate Blanchett, Angelina Jolie, Colin Firth, Nicole Kidman, Hugh Grant, Kate Winslet, Kiefer Sutherland, Charlize Theron, Matt Damon, Jennifer Aniston and Pierce Brosnan all have in common? Blue eyes. All of them have inherited their eye colour from their parents through their DNA. And because of the way that blue eyes deal with light, they also appear to have inherited a natural sparkle.

Dark coloured eyes are able to absorb both longer and shorter wavelengths of light and therefore they appear not to reflect it. They don’t seem to sparkle. But blue eyes absorb only longer wavelengths and reflect shorter ones. This gives George Clooney, Cameron Diaz and, memorably, Paul Newman, what seem to be sparkling blue eyes – and the rest, as they almost say, is movie history.

So it may be that blue eyes are like the peacock’s tail. It doesn’t confer any evolutionary advantage for the peacock except that it gets him more mates. And because people with blue eyes are more successful at attracting mates, a snowball effect follows.

The same might be true for the other dominant trait in Edinburgh and the south-east. Red hair. Nobody needs a DNA test to tell if they have red hair, just a mirror. But what is hidden is what causes children to inherit the glorious spectrum of tints from strawberry blonde to deep auburn. And that is the recessive gene variant, what both parents must carry if they are to have children with red hair.

In Edinburgh, the Lothians and the Borders, 40 per cent of all people carry it. It is the highest proportion in Britain, which itself has the highest number of carriers in the world per capita.

Why do we have so many carriers and redheads? One hypothesis is linked to vitamin D. Red hair, lighter skin tone and freckles are related and in an archipelago where the sun shines less than in continental Europe, we can absorb more D because of that. But if that were true then the cloudier parts of Britain and Ireland, in the west, places that directly face the Atlantic would have the highest percentages. But they don’t.

Perhaps migration provides an answer. The Northern Isles, the Hebrides and the Atlantic  coastlands saw significant Viking incursions and settlement after circa 800AD, and in the south-east of Britain, the Anglo-Saxons settled in numbers after circa 400AD. These in-migrations may have significantly diluted the red-hair variants present in the indigenous populations before those dates. And if that’s correct, then one of the most persistent bits of folk DNA about Vikings being redheaded will turn out to be wrong. And it may be significant that south-east Scotland appears to have had little Viking in-migration with comparatively few Norse place names and comparatively little ancestral DNA from Scandinavia.

Perhaps sexual selection is a potential reason – that having red hair, although not helping survival, was considered sexually attractive in the past, and thus redheads had more children than non-redheads, leading to an increase in frequency. Again, like the peacock’s tail.

So that’s why Edinburgh and the south-east can claim to be home to the best lookers and the best evolved. One of the city’s most famous sons, Rory Bremner, has been tested by ScotlandsDNA and not only does he have baby blues, he is also carrier of the red hair gene variant. The full set. Characteristics he shares with an awful lot of his compatriots.

• Alistair Moffat is managing director of ScotlandsDNA. He previously ran the Festival Fringe from 1976 to 1981 when it grew into the largest arts festival in the world, went on to become an award-winning documentary filmmaker, director of programmes at STV and is the author of many books about Scotland’s history.

‘Calculator’ to predict baby’s likely eye hue

Geneticist Katie Barnes was one of the first to try out the “blue eyes test” she created.

The 24-year-old, above, from Melrose, took a sample of her own DNA, and that of family members, to see if it worked.

She ran a sample of DNA, taken from a swab in the mouth, over a gene chip which looks at the DNA at the point of the gene mutation linked to blue eyes.

The gene controls the level of the pigment melanin in the iris – people with brown eyes have a lot of melanin in their irises, whilst people who have blue eyes have very little melanin.

“There are a number of genes that contribute to eye colour however, this gene allows a prediction of your future eye colour,” she said. “If you have one copy of the mutation, you’re more likely to have blue eyes and if you have two copies of the mutation, you’re very likely to have blue eyes. If you don’t have the mutation at all, you’re most likely to have brown eyes.”

Using this gene as the key, the University of Stirling graduate created the test before using relatives to check the theory.

Ms Barnes said: “My family all have blue eyes. They were the first people I tried the test on and thankfully it came back that they have blue eyes which meant it worked.”

It worked so well, geneticists are even able to include an eye colour “calculator” to predict children’s eye colour from their parent’s results.

“If we were to test both parents’ DNA, we could now give a percentage of what colour eyes their children are likely to have.”