Blue Eyes / Blue Eyed People: All Descended From A Single Common Ancestor?

[EnolaGaia]

Newly published research has identified the genetic mutation that makes brown eyes blue. Certain features of this genetic configuration are claimed to indicate all blue-eyed people may be descended from a single common ancestor who first expressed this genetic innovation.

Blue-eyed humans have a single, common ancestor

New research shows that people with blue eyes have a single, common ancestor. A team at the University of Copenhagen have tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye colour of all blue-eyed humans alive on the planet today.

What is the genetic mutation

"Originally, we all had brown eyes," said Professor Hans Eiberg from the Department of Cellular and Molecular Medicine. "But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a "switch," which literally "turned off" the ability to produce brown eyes." The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives colour to our hair, eyes and skin. The "switch," which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris -- effectively "diluting" brown eyes to blue. The switch's effect on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin colour -- a condition known as albinism.

Limited genetic variation

Variation in the colour of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. "From this we can conclude that all blue-eyed individuals are linked to the same ancestor," says Professor Eiberg. "They have all inherited the same switch at exactly the same spot in their DNA." Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production. ...

FULL STORY: https://www.sciencedaily.com/releases/2008/01/080130170343.htm

PUBLISHED RESEARCH REPORT:
Hans Eiberg, Jesper Troelsen, Mette Nielsen, Annemette Mikkelsen, Jonas Mengel-From, Klaus W. Kjaer, Lars Hansen.
Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression.
Human Genetics, 2008; 123 (2): 177
DOI: 10.1007/s00439-007-0460-x

 

[Cochise]

Wouldn't that be the way evolution works? A single beneficial mutation that makes its way through the population? Be it of humans or moths.

 

[EnolaGaia]

Wouldn't that be the way evolution works? A single beneficial mutation that makes its way through the population? Be it of humans or moths.

Natural selection isn't as much a matter of "what affords an advantage" as "what you can get away with."

Mutation needn't occur on a "once and done" basis. It's conveniently simplistic to assume all new mutations / traits originated with a single point source and then propagated throughout the given species.

The thing in this (Eiberg's) explanation that gives me pause is the claim the blue-eyed trait originated as recently as 6,000 - 10,000 years ago. This would be after humans had spread all around the planet.

I'm still uneasy accepting both the single-source and historically recent factors at face value.

 

[ChasFink]

Hard to say where I stand on this. I'm not a geneticist, but I would think that if this mutation can happen once, there's at least a chance it could happen again. And even though blue eyes occur almost exclusively in Europeans, I do know that eye color is determined by more than one gene, so this might cast doubt on at least the timing of this. It could just be that more people with the blue eye "switch" wound up in Europe, and the factor died out in other areas. And of course, we can speculate that ALL Homo Sapiens came from a single ancestor.

Interesting idea, but I think the evidence is far from conclusive.

 

[Victory]

Any excuse for this

 

[charliebrown]

Two of my grandkids have red hair and blue which is really rare.

They have 25% of my genes which makes me wonder about my genetic makeup.

My genetic test I sent away for is ambiguous, mostly European with a dash of Siberian and a dash of Scandinavia ?

 

[hunck]

There may be a better place for this:​

All blue-eyed people on Earth share the same ancestor​

Every blue-eyed person on Earth can trace their ancestry back to a single individual who lived between 6,000 and 10,000 years ago.

Scientists have worked out that, long long ago, all humans had brown eyes. Until a specific gene mutation caused them to change.

The mutation comes from a gene called HERC2. Scientists say it switches off OCA2, another gene that regulates the amount of brown pigment that develops in the eye.

It’s believed the first person to have blue eyes lived in Europe up to 10,00 years ago. And every blue-eyed person alive today has that same mutation present in their body.

But it’s a very specific kind of gene mutation, which has meant that while eyes turned blue, hair and skin colour still retained the same levels of pigment.

A full switch off would result in albinism.

In Britain, the majority of people – 48% – have blue eyes, while 30% of us are green eyed and just 22% have brown ones.

Whereas there’s a pretty big variation in iris shades between green and brown, blue eyes have a tiny variation in the amount of melanin present.

And it’s this fact that has led Professor Eiberg, from the University of Copenhagen to suggest that blue-eyed individuals are all linked to the same ancestor.

‘They have an inherited the same switch at exactly the same spot in their DNA,’ he said.

Basically, it’s a wheel of genetic fortune what colour eyes you develop. Although brown is usually thought of as the more dominant gene, two brown-eyed parents won’t necessarily create a brown-eyed child.

It’s actually entirely possible for two brown-eyed parent to have a blue-eyed child, and vise versa.

 

[Erinaceus]

That's interesting. I wonder whether the same applies in other animals? Most birds in the garden have brown eyes but jackdaws have pale bluish-grey eyes.

 

[Cochise]

All blue-eyed people on Earth share the same ancestor​

I'm very surprised by the percentages in your quote. I'd have said the vast majority of people have brown eyes, and while I've met a couple of people with grey eyes, I've never met anyone with green eyes. And the variation in blue eyes goes from violet to almost scarily pale. Are you sure those figures aren't for Scandinavia, not the UK?

 

[hunck]

I'm very surprised by the percentages in your quote. I'd have said the vast majority of people have brown eyes, and while I've met a couple of people with grey eyes, I've never met anyone with green eyes. And the variation in blue eyes goes from violet to almost scarily pale. Are you sure those figures aren't for Scandinavia, not the UK?

I have no idea. It’s from the Metro so I wouldn’t rely on it for factual accuracy..

Might have to look for the story on a more scientific site.

 

[Xanatic*]

I have green eyes. Hello Cochise.
Even if it's the same mutation, rather than common ancestry might it not be that it's simply easy for that specific mutation to arise?

 

[Cochise]

I have green eyes. Hello Cochise.
Even if it's the same mutation, rather than common ancestry might it not be that it's simply easy for that specific mutation to arise?

I started out with one brown and one blue. Don't know how that fits!

 

[Xanatic*]

There is a mutation which causes blue eyes, but at the same time tends to cause deafness. If you see a cat with one blue eye for example, it's probably deaf in one ear.

 

[Cochise]

There is a mutation which causes blue eyes, but at the same time tends to cause deafness. If you see a cat with one blue eye for example, it's probably deaf in one ear.

We're getting way off topic now but curiously my ear on the formerly blue side (I lost the eye when I was 12, long story) has always been weaker.

 

[Endlessly Amazed]

We're getting way off topic now but curiously my ear on the formerly blue side (I lost the eye when I was 12, long story) has always been weaker.

So, are you part cat?

 

[EnolaGaia]

... Might have to look for the story on a more scientific site.

The currently prevalent scientific interpretation is that blue eyes emerged no earlier than circa 10,000 years ago in the Black Sea area. This interpretation derives from a 2008 research report:

Eiberg, H., Troelsen, J., Nielsen, M. et al.
Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression.
Hum Genet 123, 177–187 (2008).
https://doi.org/10.1007/s00439-007-0460-x

The effect of this report has been massive ...

Pale skin and eyes are believed to have originated in Europe; the origin of one mutation in HERC2 has been dated to 6000–10,000 years ago in Romania (Eiberg et al., 2008). Green eyes are first known in Bronze Age Siberia, and are the least common eye color, although interestingly they have been found to be more common in women than men. The frequency of paler eye colors has increased dramatically in Europe, and has remained stable. It has been suggested that sexual selection could have been acting to select and maintain this variety of paler eye colors at such high frequencies, but this can only be achieved because climatic conditions were favorable. The signature of positive selection detected on pigmentation genes in Europeans in between 5000 and 10,000 years ago (Eiberg et al., 2008; Wilde et al., 2014) might also suggest multiple and additive factors (selective and demographic). The fact that blue eye color has arisen only once during the past 10,000 years, as a founder mutation shared among different European populations (Eiberg et al., 2008) might suggest that a strong positive selection, other than—or in addition to—sexual selection, could also be responsible for its significant diffusion in northern Europe ...

https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/herc2

More recent research suggests there may have been a secondary mutation in the Nordic / Scandinavian area once the blue-eyes mutation had migrated there.

Evidences from haplotype analysis comparing Dutch and Mediterranean population samples suggest that blue eye color has only arisen once during the Neolithic period, past 6–10,000 years ago, as a founder mutation shared by diverse European populations17. During the great agriculture migration to the northern part of Europe, the mutations spread out from the Black Sea region. Newer studies have also indicated that some OCA2 missense mutations give rise to blue eye color, when the genotype rs12913832 C/T predicts brown eye color and that these are only found in the Scandinavian population and not in individuals of Southern-European descent ...

Suarez, P., Baumer, K. & Hall, D.
Further insight into the global variability of the OCA2-HERC2 locus for human pigmentation from multiallelic markers.
Sci Rep 11, 22530 (2021).
https://doi.org/10.1038/s41598-021-01940-w

https://www.nature.com/articles/s41598-021-01940-w