Why are there so many blue eyed people?

[Kuciwalker]

2) In general, it would be a lot more likely for a small tribe to, over thousands of years, expand to a big one than for a noncompetitive genotype to, through pure random mutation, end up in some large % of a large population.

sqrt(N1*N2) = sqrt(N1)*sqrt(N2)

No, because if the tribe that randomly gets blue eyes ALSO randomly gets the competitive traits, then the blue-eyed genotype is more likely to remain highly correlated with the competitive traits. If the genotype just shows up in mutations throughout the population, it wouldn't.

[FrostyBoy]

Can we get back to my green eyes? Since they're even rarer and thus more interesting than blue eyes.

[KrazyHorse]

No, because if the tribe that randomly gets blue eyes ALSO randomly gets the competitive traits, then the blue-eyed genotype is more likely to remain highly correlated with the competitive traits. If the genotype just shows up in mutations throughout the population, it wouldn't.

Err...now you're just introducing another probability factor, dude.

???

[KrazyHorse]

I think a useful exercise for you to do would be to write down every step (uncorrelated event) in the process you envision along with a probability factor (not numerical, just a symbol) and write out the overall probability. Then do the same with a much larger original tribe. Then write down why you think one product of probabilities is larger than the other.

[Dry]

[QUOTE=Heraclitus;5621027]

What exactly is this "small competetive advatage"?

I have no scientific evidence to backup the following, but it has been my personal observation that people with light color eyes are more easily blinded by bright light, have better vision in poor light conditions and better color vision.
I also vaguely remember having read somewhere that sailors in the crow's nest were usually chosen among those with blue eyes, for their better vision.

So it seems that light colored eyes people might have that "small competetive advatage"? in cloudy areas and maybe on seas ... and on snow/ice? (although here, I fail to understand why or how...)

According to the wikipedia article for brown eyes:

In humans brown eyes contain large amounts of melanin within the iris stroma, which serves to absorb light at both shorter and longer wavelengths.

As far as I understand this, it would mean that statistically, light colored eyes people can see in a broader color spectrum.

My 2 eurocents.

[Felch]

It's not necessarily a neutral adaptation. Blue eyes might be advantageous at certain latitudes. Maybe it provides better night vision during the long dark winters, or something like that. That would explain why people from extreme latitudes are more likely to have the mutation.

[Felch]

[Dinner]

Because people think blue eyes are sexy.

[MikeH]

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

You have one of each not plural of each?

[Jon Miller]

My eyes change color.

Unfortunately, not with my mood but with the color of clothes I am wearing (at least, that is what I am told).

JM

[molly bloom]

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.

The same could be asked of red hair. My mother had red hair, her brother had red hair, one of her sisters was, em, 'strawberry blond', but I inherited the redness only in part, my brother not at all. All our family are blue eyed, some are short, some like my brother, 6 foot plus. Mother Nature is a scatterbrain.

[Flubber]

I have blue eyes and dark hair (well it USED to be dark-- now I have a lot of silver in there)
My wife has green eyes

Our children were both born with blue eyes. The five year old still has blue eyes while the 8 year old has green

[loinburger]

My mom and I had black eyes when we were young, now hers are hazel and mine are green-gray. I checked around on google, and learned that either the condition is caused by some horrible illness that will kill you within a year or two (it's unlikely that my mom or I have this disease, considering that I've been losing eye pigment for 25 years and she's bee losing eye pigment for 50 years, and neither of us is dead), or the condition is just one of those weird things that happens. (An eye doctor checked to make sure that there aren't chunks of pigment floating around in my vitreous humor that would cloud my vision, but there isn't any - apparently the pigment just evaporated)

[Dinner]

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?

It spreads for the same reason male peacocks got their tail feathers; the opposite sex finds it attractive so it gives them a reproductive advantage (I.E. they actually get laid more often so the trait spreads faster than other traits which mates don't consider as attractive).

[Al B. Sure!]

Why did you bump a 2 year old thread on a topic that I brought up again more recently in the context of how blue eyes harm your ability to see in daylight conditions, as evidenced by lower batting averages for blue-eyed baseball players in daytime games?