Why are there so many blue eyed people?

[Heraclitus]

How did the male peacock get its tail? It serves no selective advantage except that femal peacocks dig it. Maybe blonde hair and blue eyes got selected because young people with those traits stood out amongst their brown hair brown eyed sexual competitors and got shagged more.

The other thing to consider is that blue eyes go along with a pale complexion. A blue eye is blue simpy because it has less melanin pigment in the iris than a brown eye. Presumably the factors which selected for light skin made the likelihood of some people having blue eyes more likely. In areas of the world where there is less sunlight having less pigment in the skin is thought to increse the amount of 1,25 vitamin D produced because one of the final steps of 1,25 vitamin D synthesis requires sunlight. As Nordic, Scythian and Celtic peoples evolved lighter complexions the amount of pigment (melanin) in their irises also decreased. In some it decreased to the point that when combined with red light reflected from the highly vascular retina the very light golden-brown iris actually came to look blue.

Well, I understand the origin. I'm just at a loss why so many people would have it if it dosen't provide any advantage be just a very rare random recesive trait with very few blue eyed people in the Caucasian population.


Your theory of sexual selection makes sense. Maybe this is the peackock factor, but does this still play a role when about 50% of people in a population have the gene? Perhaps this has to do with the fact that young caucasian children/babies have blue or at least light eyes (hence the expression baby blue). Young = fertile in evolutionary psych, so perhaps blue eyed women seemed more sexy?

[BeBMan]

Lotsa blue eyed people were given to the US as post WWII reparations, FACT

[Dis]

my eyes are blue-ish. or at least that's the closest color to what they are. It's what's on my driver's license.

My hair is blonde-ish. So blonde hair and blue eyes just go together, don't they?

[Dis]

Off course blue eye's aren't common, but far more people have them that they should. And in the US blue eyes are being bread out. So my question is since even the most blue eyed countries don't go over 60% is why there are so many blue eyed people in absence of a founder effect.

From wikipedia:

A 2002 study found the prevalence of blue eye color among Caucasians in the United States to be 33.8 percent for those born from 1936 through 1951 compared with 57.4 percent for those born from 1899 through 1905.

they are mainly being bred out due to contamination from other races. I'm not saying this is a bad thing. I'm not some aryan. And of course immigration will cause the numbers to appear to go down with respect to the entire population.

[C0ckney]

my eyes are pale green but in photos they look bright blue, which is a little strange.

[Dis]

now if I could get some tang becaues of my blue eyes. Chicks do like my eyes. It was a big factor in me getting laser surgery. A couple women lately said they liked my eyes. They are probably my best feature, so I want to show them off.

[Lul Thyme]

My question is considering that blue eyes are a recesive trait, how come there are so many? Also how exactly does such a gene spread if it has no selective advantage from a common ancestor?

Being recessive has nothing to do with allele frequency. Assuming no selective advantage, a recessive gene's frequency will stay constant (as will dominant), on average.

Take the blue eyes examples. If a BlBl-girl mates with a BrBr-boy. All they kids will have brown eyes. At first sight, it may appear blue-ness was a victim of recessiveness. But this is confusing phenotype and genotype! Blue will still have exactly 50% Allele frequency! (all the kids are BlBr). If the kids mate together, on average you will get 25% of the population have blue eyes (which again seems like a drop from the initial 50%, but again this is confusing phenotype and genotype) but 50% of the genotype. It's quite possible for a gene to have allele frequency over 99% in a population (and stable) and yet be recessive.

If you are wondering about the INITIAL spread, then things are a bit more complicated but not necessarily mysterious. Some possible explanations:
-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.

Those are simple scenarios but there are also more complicated ways to explain this that have to do with more biology (some alleles can be "linked" together, etc..) of which I am less familiar.

[Japher]

My eyes are green, my wife's are blue. Both kids have blue eyes, though I swear Josie's are turning green.

I have O+ blood and my wife A-... Josie is O-... She's grabbed a recessive gene to buy her beer in college

[KrazyHorse]

I have blue eyes. I also have green eyes and brown eyes.

[Lorizael]

In a jar on your desk?

[KrazyHorse]

No.

[DanS]

From wikipedia:

Blue eyes have become increasingly rare among American children with only 1 out of every 6 – 16.6 percent

Hmmm... Learn something new every day. I have blue eyes, but it sure seems a rarer trait nowadays.

[KrazyHorse]

You live in an East Coast city, Dan. The number of people with British/Irish/German/Scandinavian ancestry is far lower there than it is in flyover country.

[Sprayber]

We Fremen are hardy people.

[DanS]

You live in an East Coast city, Dan. The number of people with British/Irish/German/Scandinavian ancestry is far lower there than it is in flyover country.

Yeh, but I grew up in the heart of flyover country. In my family, green eyes is more common than blue, IIRC.