Why are there so many blue eyed people?

[Heraclitus]

Perhaps they botched the quote? Maybe 75% carry the gene?

[KrazyHorse]

Isn't it common that when people mate brown eyes will dominate the fenotype very quickly?

Why would this be true? Even in the simplified recessive-Dominant model and assuming that the choice of mates is independent eye color (either genotype or phenotype). Then:

given prevalence of blue genotype b and prevalence of brown genotype B (note that b+B = 2; a bb individual counts twice for b under this scheme) we have that the prevalence of blue phenotype is b^2/4. If b is small then the blue phenotype becomes very rare. But if b is relatively large then the blue phenotype can easily remain dominant (or at least relatively common).

[KrazyHorse]

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.

WTF are you on about here? How much mixing do you think was going on among iron age populations and so forth until the last 50 years?

It seems to me as though you're pretty terribly confused about this whole issue. There weren't boatloads of Italians voyaging north to inseminate Norwegians.

To a large extent people lived and died within a few miles of their birthplace until the last century. And social mores against marrying outsiders was unbelievably strong.

The blue eye genotype is STRONGLY GEOGRAPHICALLY CONCENTRATED. This is because blue eyes provide an obvious competitive advantage in northern latitudes AND because genetic mixing was VERY slow until recently.

[Heraclitus]

Isn't it common that when people mate brown eyes will dominate the fenotype very quickly?

Why would this be true? Even in the simplified recessive-Dominant model and assuming that the choice of mates is independent eye color (either genotype or phenotype). Then:

given prevalence of blue genotype b and prevalence of brown genotype B (note that b+B = 2; a bb individual counts twice for b under this scheme) we have that the prevalence of blue phenotype is b^2/4. If b is small then the blue phenotype becomes very rare. But if b is relatively large then the blue phenotype can easily remain dominant (or at least relatively common).

You are right on that. This disscusion is now only about how the pop of blue eyed people got that large in the first place.



The founder effect can't really explain it since othervise half of Europe should be as genetically close knit as the Finns are.

[Heraclitus]

WTF are you on about here? How much mixing do you think was going on among iron age populations and so forth until the last 50 years?

It seems to me as though you're pretty terribly confused about this whole issue. There weren't boatloads of Italians voyaging north to inseminate Norwegians.

To a large extent people lived and died within a few miles of their birthplace until the last century. And social mores against marrying outsiders was unbelievably strong.

The blue eye genotype is STRONGLY GEOGRAPHICALLY CONCENTRATED. This is because blue eyes provide an obvious competitive advantage in northern latitudes AND because genetic mixing was VERY slow until recently.

WTF is up with the 50 years number? Are you completley ignorant about the effects of railroads and urbanization of the 19th century? "Mestni zrak osvobaja" people in the cities where more than willing to marry someone who's origins where in a village a dozens or hundreds of km from their own.

Also free movement in the Roman empire (which I admit is not a major factor for blue eyed populations, but there are many blue eyed people in modern France and northern Italy as well as the balcans) had a detectable effect on genetics.

And finally you are also grosly underestimating the many many recorded migrations of entire tribes. Especially in eastern Europe (Scandinavia probably was more isolated). Many of these tribes where CE or even Asian in origin.

I mean just wiki up the homelands of the Germanic tribes, the full extent of Celtic expansion, Slavic migrations. The Huns the Bolgars and a dozen other Aziats, the Mongols even! And this is just the recorded history of the region! (talking about central and eastern Europe)

Any major raid or war almost nesecarily entailed quite a bit of rape.

[KrazyHorse]

Dude, WTF are you talking about? There is some genetic mixing. But:

a) It was EXTREMELY slow. Some pops mixed more than others.
b) It's a diffusion process, village by village. Not country by country. I can't remember what the source is, but paraphrasing a history of England in the dark ages "it's a commonplace that the men of northern England enjoy to this day a 2 inch height advantage over their cousins to the south". That's the effect of the ****ing Viking invasions a THOUSAND YEARS LATER. So in a country which was basically politically united for 900 years, the populations of places separated by a couple of hundred kilometers had not yet mixed thoroughly.

[Heraclitus]

Dude we have fricking Germanic tribes in North Africa and the mass raids (which include rapes) of every single village in the path of major hordes. The movement of peoples at the very least was a major reshuffle.


Tell me do the city dwellers (those who can trace their roots as city dwellers at least 200 years back) enjoy the 2 inch advantage? You completley ignored my comment on urbanization! In the 19th century a large % was already dwelling in cities. And metropolises like Paris had attracted immigrants on a country even empire wide scale.

[KrazyHorse]

WTF is up with the 50 years number? Are you completley ignorant about the effects of railroads and urbanization of the 19th century?

Given your posts so far in this thread I find it pretty funny that you would question my knowledge.

When people moved from the countryside to the cities, which city did they move to? The one nearest their village or the one on the other side of the country?

Ethnic mixing is DIFFUSION. Populations are very badly mixed. Even when separated by relatively small distances and when there are no strong social mores against intermarriage, the geographic mobility of individuals was DRASTICALLY lower even a few decades ago than it is today.

****, look at the ****ing Ashkenazi. While there was some obvious mixing between them and the majority populations of the areas in which they lived, there are still genetic markers which remain prevalent in their population. And they lived AMONG the gentiles for a thousand years.

Populations mixed SLOWLY. Only in exceptional circumstances was there large mixing.

Seriously, the fact that you're having trouble wrapping your head around this is pretty sad.

[KrazyHorse]

Dude we have fricking Germanic tribes in North Africa and the mass raids (which include rapes) of every single village in the path of major hordes. The movement of peoples at the very least was a major reshuffle.

You do realize that a single sexual encounter (or even multiple encounters in a short timeframe) are unlikely to lead to a pregnancy, right? And that it does not stretch the imagination to think that the child of an invader might be ostracized?

You're reading FAR too much into history as a series of mass movements and mixings of peoples. Populations are much more stationary than you're giving them credit for.

Seriously, dude: give it up. You thought you were asking an interesting question, but the answer is straightforward.

Brown eyes are at a competitive disadvantage in northern latitudes. Brown eyes are a "dominant" trait, but even with a significant prevalence of the brown eye genotype blue eyes can easily remain dominant. Populations did not mix quickly until VERY recently. And even nowadays there is marked preference for mating within your own ethnicity/skin tone. By the way, much of this is to be placed at the feet of women. Men are far less prejudiced against the attractiveness of women of other races than vice versa.

[Supr49er]

How rare is the combination of dark brown hair and blue eyes?

[Heraclitus]

****, look at the ****ing Ashkenazi. While there was some obvious mixing between them and the majority populations of the areas in which they lived, there are still genetic markers which remain prevalent in their population. And they lived AMONG the gentiles for a thousand years.

Yes the ****ing Ashkenazi are a perfect example. I mean they truly are a representative population to ilustrate your point. I mean there really where no special circumstances made it more difficult for a Jew to marry a gentile in medieval Europe.


I'm not denying mixing was slow. I'm just saying it was not as low as you think and that it was not constantly slowly growing or stagnant untill some miracle occured 50 years ago. Sometimes it spiked sometimes it dropped.

[Heraclitus]

Fair skinnned tribe somewhere in Eurasia. A kid is born, he has brown eyes just like all the rest but he is carrying a gene for blue eyes. A few generations later we have a blue eyed kid pops up in the tribe.


Your explanation hinges on positive selection because of skin tone. I'm not convinced.

How did you go from that one kid to 200 million people considering that the people in question already had a good mechanism for fair skin? Selection for fair skin takes a time scale of just a few thousand years (pretty fast 5k/6K or something like that if I remember a study I read right) but selection between a "good" and a "decent" genetic way to ensure fair skin is probably weaker.

And we are perhaps dealing with a time frame as short as 6000 years?

[KrazyHorse]

Yeah, and there were no barriers to somebody who spoke a totally different language from waltzing into a feudal town and marrying whomever he chose.

Some mixing happened. But the quadratic function doesn't drop THAT quick. You have to thoroughly mix in a brown genotype in 30% of the available available alleles in order to drop the proportion of blue-eyed people to 50%.

That's ****ing huge, man. Like, hundreds of thousands or millions of people per country (even based on middle ages populations). Movements like that happened EXTREMELY rarely.

[KrazyHorse]

Fair skinnned tribe somewhere in Eurasia. A kid is born, he has brown eyes just like all the rest but he is carrying a gene for blue eyes. A few generations later we a blue eyed kid pops up in the tribe.

No. POLYGENIC TRAITS.

A kid is born with somewhat lighter skin than average. He still has brown eyes. Maybe a bit lighter. He absorbs sunlight better. He has a better chance of avoiding rickets, cognitive disorders etc. Him and others like him reproduce better. As time goes on, more and more of the light-skinned/blue-eyed genes get turned on in more and more of the population through continuing mutations and natural selection. Eventually blue eyed kids start showing up instead of just light brown eyed kids. The process continues. Pretty soon it's hard to find brown eyes anywhere.

[Heraclitus]

Yeah, and there were no barriers to somebody who spoke a totally different language from waltzing into a feudal town and marrying whomever he chose.

cultural identity/language =/= genetic diversity


France is genetically diverse, the Roman empire was genetically diverse, Slavic people are genetically diverse (and their languages didn't significantly fragment untill the end of the first millenium).


Also "whomever he choose"? Are you saying genetic mixing is somehow not happening if I don't marry a well to do instead of a low class woman?

WTF Waltzing? How about living in a city for a decade?



You are just trying to make my argument seem absurd, by saying its as easy as today or that today people don't mix more than they did... Ok I need to calm down. Perhaps this is a cultural thing, NA probably has higher mobility for a longer time than European countries. Maybe that is why an effect that has barley taken off in my country seems to be "the last 50 years" in Canada. And I due to inertia see the change of post WW2 as significant but not so much as to eclipse previous movement in the first half of the 20th century, the 19th century and what came before.