I believe red hair is caused my a certain protien that developes in humans who are in cold climates. It is often said that Neanderthals had red hair, however, why doesn't the Mongols or the Eskimos have red hair? Surely they have lived in their climates as long as Europeans who have red hair, so why don't they have red hair?

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The mutation modifies the MC1 receptor and leads to red hair and pale skin. There is speculation that the gene was favoured in Northern Europe because the associated pale skin allowed better Vitamin D production in weaker sunlight. There is also speculation that the gene is selected against at low latitudes because of the risk of sunburn in strong sunlight.
Mongols don't live at high latitudes. Inuit do, but (until recently) they get a good dietary intake of Vitamin D.

Grant Hutchison

There are at least two different versions of melanin. One's redder and one's yellower. Small adjustments in the ratio of one kind of melanin to the other are what make some people's hair or skin look slightly redder or yellower even at the same overall level of darkness (including the trends for some races to be redder or yellower than others, which is one of the ways that native African races that aren't the black race are distinguished from it).

One mutation does have a bigger effect than most, particularly greatly reducing or eliminating the yellower melanin so the redder one dominates... but it's not related to cold weather. For that matter, an equivalent mutation exists in some members of the black African race. In them, given the overall higher level of melanin of both kinds to start with, the result is still generally dark brown, but lighter and redder than others of the same race.

You must understand that there is not a unique gene, allele, or mutation responsible for light skin. Being a redhead is just one possible path to having light skin.

The apperance of blond and red hair in northern Europe is a bit of an anomaly. While skin tone gets lighter and lighter, on average, the farther away you get from the equator all around the globe, blond and redheaded people are especially light-skinned, to a degree not found in the indigenous populations of the rest of the world. I suppose those traits must have originated in relatively recent genetic changes.*

Here's a map.

* I don't think the notion that Neanderthal men had red hair as well contradicts this, since according to most paleontologists interbreeding between Neanderthals and modern humans is unlikely to have happened to any substantial degree.

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The protein causing red in hair is not exclusive to redheads. It is also found in the hair of a fair percentage of those with dark brown hair and a high percentage of those with extremely dark brown hair. Many women know this because the browns bleach out first leaving any red and yellow colors behind (orange!). This even goes for Blacks who, if albino, may still have red hair. It is not true of those with truly black hair like the Japanese.

It follows then that red hair is more of a lack of brown pigment than the addition of red.

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I read somewhere that Neanderthals actually had an extra chromosome, so interbreeding would be impossible... any idea if this is at all true?

Even if true, why would that make interbreeding impossible? I'm thinking of people with Down's syndrome, who have an extra chromosome...

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The extra chromosome is a single chromosome, which is very different than an extra chromosome pair.

And then their fertility is extremely low. Only 3 recorded cases of people with Downs Syndrome parent children have been recorded, as far as I know.

And, because chromosomes aren't just something that can be forced into a genetic code. Things with different numbers of chromosomes aren't compatible.

It's like trying to plug a 110volt appliance into a 220volt electrical outlet. It's a no-go.

Interesting thread, I learned some biochemistry, and a bit of genetics. My friend Ed once asked me, "Do you know why, when a family has five kids, the youngest is usually a redhead???"
"No, why?".....rust, ......he says..........pete

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Horses and donkeys interbreed, and the horses have an "extra" chromosome pair compared to the donkeys. Likewise with horses and zebras, in which the mismatch is even greater. The offspring are generally sterile, however, since the formation of sex cells is messed up by the mismatched chromosomes.

Grant Hutchison

Horse = 64
Donkey = 62
Zebra = 46
(I think all of that is correct)


Thanks grant, I hadn't realized that.

Either way, Neanderthals genetic code wouldn't have been interbred into humans (Or whatever our ancestors at that point were...) due to the difference in chromosomes would make the offspring sterile, correct? Which means that all offspring would be childless....


Unless I'm mistaken on an individual point? And that was more the point of my original post (even if I was incorrect on some of the particulars).

Actually, there are 3 species of zebras and each has a different number of chromosomes.

There's one factor that you're not considering in the presence of redheads and blondes -- the cultural factor. For instance, the Aesir (gods of the north) were redhaired and blondhaired. There may have been a preference for lighter haired/redhaired people as mates.

In addition, if the blondes/redheads are higher status males, they could well have afforded many mistresses (and sired more illigitimate children) than poorer people.

Chimpanzees' number of chromosome pairs is different from ours by one. Presuming we couldn't interbreed, it's not because of chromosome number mismatch (which, if it did prevent interfertility, would also make it impossible for any species to ever undergo an evolutionary change in its chromosome pair number!), but because there are just too many biological differences. For pairs of species that can at least sometimes interbreed despite chromosome number differences, the way it works is that there are two (or more) chromosome pairs in one species that exactly correspond to one chromosome pair in the other, if they just line up end-to-end. To use a metaphor, if you have two strings of letters in alphabetical order, one A-F and the other G-Z, then you have what it takes to pair up each of your letters with someone else's letters if that other person has the entire alphabet in one string.

Neanderthals' chromosome pair number is not known because we've only had fragments of their DNA so far. The genetic basis for the belief that they didn't interbreed with "us" is that the bits of their DNA that we have collected and studied aren't similar enough to their counterparts in the human genome for either to have been included in the other's gene pool. That doesn't specify that interbreeding was biologically impossible; it just means that it didn't happen, for whatever reason.

* * *

Light hair and blue eyes are simply continuations of the general lightening process that's taken place in Eurasians. Hair, irises, and skin all get their dark-brownness/blackness from the same stuff: melanin. So low melanin level makes any of them lighter, which is why they generally tend to all be light or all be dark in the same person in most cases, depending on the person's general overall melanin level. Some people have speculated that coloring in general or in one of its three specific incarnations, along with other visible racial differences, got selected for because of sex appeal or because some quirky cultural factors favored people with one visible trait or another, but that idea depends too much on those things being essentially universal over a wide geographic area but suddenly switching around in another one and remaining that way for a very long time. That just doesn't make sense. That story is really just a manifestation of claims of unfairness in present society, massively overextended and projected into an unfair quasi-universality. Skin color is already known to affect health depending on level of UV light exposure (and dietary vitamin D supply), and light eyes & hair just come along for the ride when overall melanin gets low enough, so no explanation for the eyes & hair is needed.

Well someone made up a story about how males were in short supply in ice age Europe and so women who had blond hair or red were able to get mates because of their impressive distinctiveness. Personally I think this trend would be swamped by the evolution of men willing to have sex with more than one woman. (Maybe we should conduct a scientific study to see if we can find evidence of men willing to have sex with more than one woman in the modern European population?) Of course, if women were regarded as property and ones with blonde or red hair regared as more valuable than dark haired ones for cultural reasons, then you could definitely see differences in rates of survival of blonde and red haired women without positing a strong desire for monogamy among cavemen.

But how would a story spread among isolated nomadic tribes who rarely saw strangers and who mostly killed or drove off any competing groups they encountered?

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Someone made up the story today.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Any evidence that that was the case prior to the 19th century? It seems to me you're getting a little carried away with speculation.

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Where did anti-redhead prejudice come from? That's got to be the stupidest form of bigotry ever invented. It's almost like someone ran out of people to hate, so decided to target read headed people.

http://www.youtube.com/watch?v=bUhLIjlTNSk

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