There were lots of different ways I could pose this question, but I think I’ll try it this way:
Why is black hair and brown eyes the majority heretical combination for the population of the Earth?
Think about it: Asians, Middle East, Indians(both types),Hispanic, even Africans (a bit different type of hair follicle, but still it fits the criteria)
When you think about it only a small percentage of people have different color eyes or hair differing from the above description and I’d like to know why.
I always learned that certain facial features changed (generationally)to accomodate the person for- ex. longer noses in arrid regions. So for what reason would so many people from so many different parts/climates of the world have black hair and brown eyes?
Mind you, in any population, there will be individual variation. There are even (very rare) natural redheaded Japanese, for instance.
But as to explaining the Caucasian coloring with blond/red hair and blue/green eyes (keeping in mind plenty of Caucasians have black or brown hair and eyes) – I’ve heard a few different theories. One theory is that the lighter coloring is a trait that was sex-selected – in other words, some people just happened to be born like that, and others found them sexually appealing, mated with them and thus perpetuated the genes. Another theory suggests that perhaps the light coloring was just a byproduct of the ‘bleaching’ Caucasians underwent when they migrated to colder climates – as their skin lightened, the hair and eyes just followed suit. There doesn’t seem to be any evident evolutionary neccesity for possessing light-colored hair and eyes, since the Inuit, for instance, live in very cold climates and still have dark hair and eyes.
Most likely the original humans were dark-skinned and dark-eyed. At least part of the group who migrated to Europe carried genes for lighter coloration. Since it was not a handicap there, or might have carried a slight advantage, they survived. I’ve heard this described as the “founder effect.” They would probably have done just as well if they were darker (as some people inhabiting even more northerly places were), but there was no selection against it, and the area obviously had some survival advantages. See “Guns, Germs and Steel.”
You have to remember that many traits are propagated for no particular reason except that they don’t create a disadvantage.
The genes for lighter hair and different color eyes only developed in a subset of the populations around the world. Most likely the ancestral population* from whch all human derive had dark hair and dark eyes. And although the genetics is more complicated than the simple recessive/dominant situation we all learned about in Jr. High, generally speaking you will only get the lighter phenotype when both of those alleles are present in the DNA of an individual.
Phenotype = the observable physical characteristic of an organism
Allele = One member of a pair or series of genes that occupy a specific position on a specific chromosome.
*The most commonly accepted hypothesis is that all humans alive today are descended from a small population (just a few thousand individuals) in Africa about 50 or 60 thousand years ago.
