Why are there so many blue eyed people?

[Docfeelgood]

Is bloodshot an eye color?

[Heraclitus]

-For all you know, blue might have been the old "default" and was "invaded" by brown, until it stabilized.
-It could have started as an "invisible" mutation at the start (no effect on phenotype as a recessive trait), spread a bit in a small population by luck and had a small competitive advantage in that region which then helped it to spread.

1. Brown is default at least that is what is currently tought
2. That is precisly my question. What exactly is this "small competetive advatage"?

[KrazyHorse]

http://en.wikipedia.org/wiki/Vitamin_D

[KrazyHorse]

Also, I have no idea what blue eyes being a recessive trait has to do with anything. The question is why the genotype is so widely spread. Since blue eyes are not well-mixed across the population of the world, they will manifest a large fraction of the time among those who receive the genotype. As time goes on, of course, this becomes less and less true.

This effect is not necessarily as dramatic as you might think, however; my wife's father is a Yemeni Jew, but she has green eyes.

[KrazyHorse]

And Dan: green eyes are less common than blue.

[Heraclitus]

http://en.wikipedia.org/wiki/Vitamin_D

That is a weak explanation. Please correct me but as far as I know Vitamin D is produced in the skin. Now you may argue people with blue eyes tend to have fair skin too, but I don't think the correlation is strong enough, there are many people with very fair skin who have brown and sometimes even dark brown eyes.

[Heraclitus]

And Dan: green eyes are less common than blue.

I think Green is the rarest (with the exception of much rarer occurences of violet and perhaps red) I would however point out that distingusihing blue and green can be tricky sometimes.

[rah]

Colored contact lenses. That's the ticket.

[KrazyHorse]

Hera, I'm afraid that you have even less understanding of genetics than I do.

The approximation of traits as single-gene differences is, as I understand it, ONLY AN APPROXIMATION. In actuality, there could be a number of different ways to, say, get fair skin. Some of them may be strongly correlated with blue eyes. And there may be many different ways to get blue eyes. And the same goes with the correlations.

Melanin production in the eyes is not going to be independent of melanin production in the rest of the body. And both skin color and eye color are polygenic. So blue eye color is an indicator of an underlying advantage (vitamin D production).

In fact, you may not be aware of this, but there are significant numbers of cases of vitamin D deficiencies among dark-skinned people who move to northern climates. And it doesn't take much of an advantage to add up over time.

[Heraclitus]

I've read the wiki article, I've found an explanation there that sort of makes sense.


"Mate preference
Some studies have suggested that blue eyed men prefer blue eyed women due to the trait's recessive inheritance.[29] Under this theory, because blue eyed couples are likely to produce blue eyed offspring, males are more confident in the child's paternity."


I've just tought about this, anecdotal evidence from my own life seem to support this. Every gf I've ever had had blue eyes and most (60% or 70%) of the celebs I find very attractive have blue eyes.

I haven't read the source though, so I'm not sure how belivable this explanation is.


Also isn't it sort of bad for a male to be this picky? (genes that don't ensure survival but just help ensure paternity) Sure blue eyed women are better off (they are more attractive to blue eyed males and the rest don't care either way) but isn't a very picky male less likley to mate?


However this entirely depends on the society. I find it quite possible that early cultures weren't that promiscuous (we've all heard the old primitive promiscuity hype). As a stone age man living in the ice age, even if I am the cheif of my tribe I can't imagine supporting (for the sake of argument lets say supprot only extends to providing meat and everything during pregnancy, also perhaps teaching the sons how to hunt, I hope we all agree this is the bare minimum) more than 2 wives and perhaps having a mistress or two on the side. So perhaps being picky is a good thing for a long enough period to explain the 200 million people with blue eyes and the uncounted hundreds of millions who carry the gene.

[KrazyHorse]

Hera, are you deliberately being obtuse?

A same-color eye preference among males would NOT lead to a spread of a small mutation. It would merely make the mutation self reinforcing among a small population.

[Heraclitus]

Hera, I'm afraid that you have even less understanding of genetics than I do.

The approximation of traits as single-gene differences is, as I understand it, ONLY AN APPROXIMATION. In actuality, there could be a number of different ways to, say, get fair skin. Some of them may be strongly correlated with blue eyes. And there may be many different ways to get blue eyes. And the same goes with the correlations.

Melanin production in the eyes is not going to be independent of melanin production in the rest of the body. And both skin color and eye color are polygenic. So blue eye color is an indicator of an underlying advantage (vitamin D production).

In fact, you may not be aware of this, but there are significant numbers of cases of vitamin D deficiencies among dark-skinned people who move to northern climates. And it doesn't take much of an advantage to add up over time.

Yes I know there are many ways to get fair skin, I mean the blatant difference is the difference between the fair skin of East Asians and Euros. I'm not questioning that even within the caucasian race (and I do use the term loosely) there may be many ways to get fair skin. I'm just saying that people who get fair skin some other way (I'm taking your assumption into account here, I'd like to see citations to prove the link is not only present which is common sense but is also significant enough) still have brown eyes. Isn't it common sense that when modestly diverse people mate brown eyes dominate the phenotype very quickly?

http://www.usatoday.com/news/health/...lue-eyes_N.htm

6k to 10k ago, that puts it in the 4 to 8 thousand BCE range. I am quite certain that there where fair skinned people living in Eurasia by that time.
How did the gene even take off? Was it a "better way" to ensure fair skin?

[Heraclitus]

"In Estonia, 99% of people have blue eyes, Eiberg says. In Denmark 30 years ago, only 8% of the population had brown eyes, though through immigration, today that number is about 11%. In Germany, about 75% have blue eyes."

WTF the numbers for Germany can't be right... from what I remember to my trip to Berlin and Strasborug (know not in Germany). Germans are very far away from the "aryan" ideal they have become asociated with since the rise of the Nazis.

[Heraclitus]

Hera, are you deliberately being obtuse?

A same-color eye preference among males would NOT lead to a spread of a small mutation. It would merely make the mutation self reinforcing among a small population.

KH the argument isn't just about the spread. Its also about how such large populations of blue eyed people have survived for so long. To spell it out what this thread is about:

"I'm suprised so many people have blue eyes today."

See not nesecarily about how the large pop got there in the first place... in fact if it was about this alone I would probably be content with waving a hand and saying it was probably founder effect.

If you didn't notice I responded to a guy who said that perhaps blue eyes where the default and have since eroded.

[BeBMan]

"In Estonia, 99% of people have blue eyes, Eiberg says. In Denmark 30 years ago, only 8% of the population had brown eyes, though through immigration, today that number is about 11%. In Germany, about 75% have blue eyes."

WTF the numbers for Germany can't be right... from what I remember to my trip to Berlin and Strasborug (know not in Germany). Germans are very far away from the "aryan" ideal they have become asociated with since the rise of the Nazis.

75 % sounds too much indeed.